cisco sdh presentation
TRANSCRIPT
Network ArchitectureNetwork Architecture
Chapter 1Chapter 1
© 2001, Cisco Systems, Inc.
© 2001, Cisco Systems, Inc. Network Architecture-2
ObjectivesObjectives
Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main terms used to describe
network components
• Describe the link structure and network elements
• Describe the interface options and interface layers
© 2001, Cisco Systems, Inc. Network Architecture-3
AgendaAgenda
1.1 - Link Structure and Line Interfaces
1.2 - Network Elements
Summary, Information Resources
Link Structure and Line Interfaces
Link Structure and Line Interfaces
Section 1.1Section 1.1
© 2001, Cisco Systems, Inc.
© 2001, Cisco Systems, Inc. Network Architecture-5
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Describe the functionality and interaction of the
interface layers
• Define the three overhead layers
• Describe the topology concepts related to the overhead layers
• Describe the main features of electrical and optical interfaces
© 2001, Cisco Systems, Inc. Network Architecture-6
Overhead Layer ConceptsOverhead Layer Concepts
path
path termination
pathtermination
service (E1, E4..)mapping demapping
service (E1, E4..)mapping demapping
PTE PTE
multiplex section multiplex section
multipl. section termination
ADMor
DCS
regeneratorsection
regen. section termination
regen. sectiontermination
REG REG
PTE = path terminating elementMUX = terminal multiplexerREG = regeneratorADM = add/drop multiplexerDCS = digital cross-connect system
regen.section
regen.section
regeneratorsection
© 2001, Cisco Systems, Inc. Network Architecture-7
Regenerator SectionRegenerator Section
• Regeneration section layer is the lowest level of link components in a SDH network
• Deals with the transport of an STM-N frame across the physical medium
• Point-to-point connection between two regeneration section termination points with direct optical or electrical domain connectivity
• Terminated by Regenerator Section Terminating Equipment (RSTE)
• The Regeneration section is mainly designed to overcome physical limitations of the transport technology
© 2001, Cisco Systems, Inc. Network Architecture-8
Multiplex SectionMultiplex Section
• One or more consecutive regenerator sections might compose a multiplex section
– Main element to build different topologies (e.g. ring)
• Deals with the transport of path layer payloads across the physical medium
• Multiplex section is a point-to-point logical link that connects to ADM, MUX, or DCS devices
– These devices might not include a path termination
• Overhead is interpreted and modified by Multiplex Section Terminating Equipment (MSTE)
– Multiplex section (MS) overhead is accessed only after the section overhead has been first terminated
© 2001, Cisco Systems, Inc. Network Architecture-9
PathPath
• One or more connected multiplex sections may provide a transport service for a path
– Multiplex section may carry multiple paths by multiplexing
• Deals with the transport of various payloads between SDH terminal multiplexing equipment
• Path layer maps payloads into the format required by the MS Layer
• Communicates end-to-end via the Path Overhead (POH)
• POH is terminated and modified by Path Terminating Equipment (PTE)
– Regenerator and multiplex section overhead must be terminated to access the overhead
© 2001, Cisco Systems, Inc. Network Architecture-10
HO and LO PathsHO and LO Paths
• In SDH the PDH payload multiplexing is done at 2 different layers
• High-order (HO) path carries E3/E4 or similar payloads
– Organized into administrative units (AU) including higher order tributaries
• Low-order (LO) path carries E1/E2 or similar payloads
– Organized into tributary units (TU) including lower order tributaries
© 2001, Cisco Systems, Inc. Network Architecture-11
Topology ConceptsTopology Concepts
• SDH topologies are designed for providing a flexible and reliable transport for required paths
• Main issues:
– Capacity planning, bandwidth provisioning
– Redundancy, automatic fail-over
– Delay and jitter control
• Typical topology concepts:
– Point-to-point links (with protection) and DCS/MUX
• Arbitrary complex topology may be built
– Interconnected protected rings with ADM/DCS
• Minimum resource usage (physical media) for avoiding single point of failures
© 2001, Cisco Systems, Inc. Network Architecture-12
Physical Layer - I.Physical Layer - I.
Photonic
Path
Multiplex Section
Regen. Section
STM-N
Signal
Light
Pulse
VC and MS Overhead
Payload and Path Overhead
TerminalRegenerator
Optical Conversion
Terminal
Map internal signal and RS OH
into STM-N signal
Map Payload and Path OH into VC
Map VC and MS OH into internal
signal
Services (E1, E2, E3, E4, Video, etc.)
Regen. Section
Physical
Layers
© 2001, Cisco Systems, Inc. Network Architecture-13
Physical Layer - II.Physical Layer - II.
• Line coding applied:
– CMI for electrical interfaces
• Guarantees transmit-receive clock synchronization
– Binary NRZ for optical interfaces
• May change for very high speeds (STM-256 or higher) into RZ solitons
• Does not guarantee enough 1-0 or 0-1 changes, and thus clock transmit-receive synchronization
– Depends on the frame content
– Scrambling is needed for a guarantee
© 2001, Cisco Systems, Inc. Network Architecture-14
Electrical InterfacesElectrical Interfaces
• Defined to be as compatible as possible with existing PDH physical interfaces
–Same hardware should be used
• For intra-office applications only
–Maximum 150 m 75 Ohm coax for STM-1
• 155.520 Mbit/s, CMI line coding
© 2001, Cisco Systems, Inc. Network Architecture-15
Optical InterfacesOptical Interfaces
• Intra-office (application code: I-<n>)
– LED or MLM laser at 1310 nm or 1550 nm
– Up to 2 km, max. loss 7-12 dB
• Inter-office, short-haul (application code: S-<n.w>)
– Low power SLM or MLM laser at 1310 nm or 1550 nm
– Up to 15 km, max. loss 12 dB
• Inter-office, long-haul (application code: L-<n.w>)
– High power SLM or MLM laser at 1310 nm or 1550 nm (zero-dispersion or dispersion-shifted fiber)
– Up to 40-60 km, loss: 10-28 dB up to STM-1, 10-24 dB up to STM-16
© 2001, Cisco Systems, Inc. Network Architecture-16
SummarySummary
• Describe the functionality and interaction of the interface layers
• Define the three overhead layers
• Describe the topology concepts related to the overhead layers
• Describe the main features of electrical and optical interfaces
© 2001, Cisco Systems, Inc. Network Architecture-17
Review QuestionsReview Questions
• How many layers are used to build up a SDH network?
• What is the purpose of the Multiplex Section layer?
• What is the purpose of the HO Path overhead and the LO Path overhead ?
• Why do electrical and optical interfaces have different line coding?
• Is there a Regenerator Section termination in a Terminal Multiplexer?
• Is a usual add-drop multiplexer also a Path terminating equipment?
Network ElementsNetwork Elements
Section 1.2Section 1.2
© 2001, Cisco Systems, Inc.
© 2001, Cisco Systems, Inc. Network Architecture-19
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify main network concepts
• Describe the functions of typical network elements
© 2001, Cisco Systems, Inc. Network Architecture-20
Network ConceptsNetwork Concepts
• Networks should be designed by decomposition
–Service needs into layers
–Logical connectivity needs into subnetworks
• Devices might be categorized by functionality and role in the network layers and topology
• Multiple set of functionality may be integrated into a single device if it is economically feasible
© 2001, Cisco Systems, Inc. Network Architecture-21
Terminal MultiplexerTerminal Multiplexer
• Terminal multiplexer is at the edge of the SDH network
–Provides connectivity to the PDH network devices and certain end-user equipment
• It includes a regenerator section, multiplex section, and path termination in one link
© 2001, Cisco Systems, Inc. Network Architecture-22
RegeneratorRegenerator
• A regenerator simply extends the possible distance and quality of a line by decomposing it into multiple sections
–Replaces regenerator section overhead
–Multiplex section and path overhead is not altered
© 2001, Cisco Systems, Inc. Network Architecture-23
Add-drop Multiplexer - I.Add-drop Multiplexer - I.
• Add/drop multiplexer (ADM)
– Main element for configuring paths on top of line topologies (point-to-point or ring)
– Multiplexed channels may be dropped and added
– Special drop and repeat mode for broadcast and survivability
– An ADM has at least 3 logical ports: 2 core and 1 or more add-drop
• Ports have different roles
• No switching between the core ports
• Switching only between the add-drop and the core ports
© 2001, Cisco Systems, Inc. Network Architecture-24
Add-drop Multiplexer - II.Add-drop Multiplexer - II.
• ADM always includes regenerator and multiplex section termination. However paths might not be terminated, but only switched from one multiplex section’s channel to another multiplex section’s channel
• ADM may be integrated with terminal multiplexer functionality for direct interfacing to non-SDH network elements
• ADM always processes and replaces the multiplex section overhead
– ADM may not change the path overhead (POH)
• POH is changed only if terminal multiplexer function is included
© 2001, Cisco Systems, Inc. Network Architecture-25
SDH Cross-connectSDH Cross-connect
• ADM concept is extended to have many similar capacity ports with any-to-any channel connectivity: the resulting device is called a Digital Cross-connect (DCS)
– SDH DCS may have only 2 logical ports
• Pure SDH DCS may connect only STM-1 or higher channels with each other
– Cross-connects are named after historical patch panels interconnecting regenerator or multiplex section termination devices
• Pure SDH DCS may not include path termination, switching of channels is typically done at the multiplex section layer
© 2001, Cisco Systems, Inc. Network Architecture-26
Wideband Digital Cross-connect
Wideband Digital Cross-connect
• SDH wideband digital cross-connect (WDCS) is designed for interconnecting a large number of channels at the LO path (e.g. E1 basic PDH) level
• SDH WDCS has only SDH ports carrying a large number of LO path payloads
• Interconnection of LO paths may be done virtually, without a physical LO path termination
–Provides an economical alternative to legacy physical E1 cross-connects
© 2001, Cisco Systems, Inc. Network Architecture-27
Broadband Digital Cross-connect
Broadband Digital Cross-connect
• Broadband digital cross-connect (BDCS) uses a transparent switch matrix for HO path speeds to interconnect a large number of channels
• HO path BDCS has a similar architecture to a WDCS in an integrated device
• Many SDH ports carrying HO path payloads
– Interconnect without physical HO path termination
© 2001, Cisco Systems, Inc. Network Architecture-28
Subscriber Loop Access System
Subscriber Loop Access System
• Subscriber loop access system (SLAS) is a concentrator of low speed services
– Provides an efficient feed of subscribers into the central office by using multiplexing to create a higher speed trunk line
• By using SLASs at the edge of the network, the cross-connects and ADMs can be optimized by having ports with concentrated end-user services
• SLAS does not provide a local switching function between the input channels, only aggregation
© 2001, Cisco Systems, Inc. Network Architecture-29
SummarySummary
• Identify main network concepts
• Describe the functions of typical network elements
© 2001, Cisco Systems, Inc. Network Architecture-30
Review QuestionsReview Questions
• What is the purpose of a regenerator equipment?
• What is a Subscriber Loop Access System (SLAS)?
SummarySummary
Information ResourcesInformation Resources
© 2001, Cisco Systems, Inc.
© 2001, Cisco Systems, Inc. Network Architecture-32
QuestionsQuestions
?
© 2001, Cisco Systems, Inc. Network Architecture-33
Information ResourcesInformation Resources
• Books
–Mike Sexton, Andy Reid: “Broadband Networking: ATM, SDH, and SONET”
• Artech House, 1997. ISBN 0-89006-578-0
• Web
– ITU-T standards
• http://www.itu.int
–ETSI standards
• http://www.etsi.org
© 2001, Cisco Systems, Inc. Network Architecture-34
SummarySummary
After completing this chapter, you should be able to perform the following tasks:• Identify the main terms used to describe
network components
• Describe the link structure and network elements
• Describe the interface options and interface layers
Frame StructureFrame Structure
Chapter 2Chapter 2
© 2001, Cisco Systems, Inc. Network Architecture-36
ObjectivesObjectives
Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main frame concepts
• Describe the basic structure of frames at various hierarchy levels
• Make basic computations for bit rates at various hierarchy levels
• Describe the internal details of payloads and overheads
© 2001, Cisco Systems, Inc. Network Architecture-37
AgendaAgenda
2.1 - Frame Concept
2.2 - STM-1 Frames
2.3 - STM-n Frames
2.4 - Frames and Rates
2.5 - Payload Internals
2.6 - Overhead Internals
Summary, Information Resources
Frame ConceptFrame Concept
Section 2.1Section 2.1
© 2001, Cisco Systems, Inc. Network Architecture-39
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Describe the notation for electrical and optical
signals
• Describe the two-dimensional frame model
• Describe the main components of the frame
© 2001, Cisco Systems, Inc. Network Architecture-40
Electrical and Optical SignalsElectrical and Optical Signals
• STM-<N> is electrical, STM-<N>O is optical
• STM-<N>c means concatenated
–Not multiplexed signal
–Originates at that speed
–Administrative overhead optimized compared to real multiplexed signal
• Frame format is independent from electrical or optical signals
–For simplicity we will always refer to STM-<N> only
© 2001, Cisco Systems, Inc. Network Architecture-41
Two-dimensional Frame ModelTwo-dimensional Frame Model
• Fixed 125 microseconds frame time length
–To support 8 KHz sampled voice applications
• Bytes organized into rows and columns
–Administrative channels are rate decoupled for easier processing
• STM-1 frame is organized into 270 (3 x 90) columns by 9 rows
–Frame size is 2430 bytes
–9 x 270 bytes/frame x 8 bits/byte x 8000 frame/s = 155.52 Mbit/s
© 2001, Cisco Systems, Inc. Network Architecture-42
SONET CompatibilitySONET Compatibility
• STM-0 frame is defined to be compatible with STS-1 of SONET
– Originally it was only a virtual tool to show SONET compatibility (not part of ITU-T specifications in 1993)
– Recently it has become a valid real-life frame format for microwave links (proposed by ETSI, included into new merged ITU-T G.707 standard in 1996)
• STM-1 has a compatibly structure with STS-3 of SONET
• Although STM-0 is already defined, for historical reasons most SDH discussions are based on STM-1
– In many places specifications use a multiplication by the hierarchy level, so 0 cannot be used
© 2001, Cisco Systems, Inc. Network Architecture-43
Path Terminator Path TerminatorREG REGADM
or DCS
M-Section M-Section
Path
R-Section R-Section R-Section R-Section
OverheadsOverheads
• 3x3=9 columns section overhead (SOH) for STM-1
– Includes a complex set of OAM information
– 3 rows (27 bytes) for regenerator section (RS) overhead (RSOH)
– 1 row (9 bytes) for administrative unit (AU) pointer
– 5 rows (45 bytes) for multiplex section (MS) overhead (MSOH)
• Path overhead (POH)
– Provides framing for payload, not part of SOH
© 2001, Cisco Systems, Inc. Network Architecture-44
Payloads - I.Payloads - I.
• Two main types of payloads:
– Multiplexed voice channels originated in PDH based devices
– Transparent bit stream services
• May be used for data packet transport or ATM
• Payloads are organized into paths over the network
– Different path types based on the content
• STM path, HO or LO path etc.
• Payloads are managed by using the multiplex section overhead (MSOH) and the path overhead (POH)
© 2001, Cisco Systems, Inc. Network Architecture-45
Payloads - II.Payloads - II.
• Payloads are put into a so called payload or VC (virtual container) capacity
– Frames provide a higher bit rate than the payload
• Required to be able to compensate for frequency differences
– Similar concept to PDH stuffing
• Payloads may arrive with very different phases
– Varying line delays cannot be avoided in a WAN with long distances
• Light needs some time to reach from the transmitter to the receiver that is much bigger than the bit timing interval or the frame cycle time
© 2001, Cisco Systems, Inc. Network Architecture-46
PointersPointers
• Pointers were included into SDH design to provide tools to compensate for incoming payload phase differences
–Without extensive buffering
• So not too much delay and jitter
• Advantage over PDH network where this problem was solved by asynchronous multiplexing and a lot of bad consequences
• Pointers make it possible to create ring topologies (efficient fail-over redundancy) for SDH
© 2001, Cisco Systems, Inc. Network Architecture-47
SummarySummary
• Describe the notation for electrical and optical signals
• Describe the two-dimensional frame model
• Describe the main components of the frame
© 2001, Cisco Systems, Inc. Network Architecture-48
Review QuestionsReview Questions
• Why are SDH frames repeated every 125 micro-seconds?
• Why are overhead channels distributed evenly in the bit stream?
• Why are pointers needed to implement ring topologies?
STM-1 FramesSTM-1 Frames
Section 2.2Section 2.2
© 2001, Cisco Systems, Inc. Network Architecture-50
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Describe the overall structure of the frame
• Describe the payload pointer solution for timing differences
© 2001, Cisco Systems, Inc. Network Architecture-51
General StructureGeneral Structure
9 columns 261 columns
270 columns
VC Capacity(for AUG)
Sectionoverhead(SOH)
1st
2nd
Order of transmission
© 2001, Cisco Systems, Inc. Network Architecture-52
Synchronous Payload Envelope - I.
Synchronous Payload Envelope - I.
• SPE = Synchronous Payload Envelope is the common sense name (also used for SONET)
• AUG = Administrative Unit Group is the official ITU-T name for the SPE + 4. row of SOH (AU pointer)
– 261 columns x 9 rows
– POH is 1 column
– Fixed stuffing depends on internal structure of AUG
– 260 columns = 2340 bytes for AUG-4 payload capacity
• AUG may be composed by different type of administrative units (AU)
– 1 x AU-4 (specific to carry PDH E4, not compatible with SONET frame structure)
– Or 3 x AU-3 (compatible with SONET frame structure)
© 2001, Cisco Systems, Inc. Network Architecture-53
Synchronous Payload Envelope - II.
Synchronous Payload Envelope - II.
• Administrative unit is composed of a pointer and a virtual container (VC)
– Pointer for VC-4 inside an AU-4 is the full 4. row of SOH
– Pointer for VC-3 inside an AU-3 is determined by a 1:3 demultiplexing of the 4. row of SOH
• VC inside AU may begin anywhere in STM-1 VC capacity
• AU (payload) pointer in SOH designates the first byte of VC inside AU (SPE)
© 2001, Cisco Systems, Inc. Network Architecture-54
STM-1 VC-3 Capacity Structure
STM-1 VC-3 Capacity Structure
1 column
87 columns
30. column
Payload Capacity
59. column
Path overhead(POH)
Path overhead(POH)
Path overhead(POH)
Path overhead(POH)Fixed stuffFixed stuff
© 2001, Cisco Systems, Inc. Network Architecture-55
STM-1 VC-4 Capacity Structure
STM-1 VC-4 Capacity Structure
1 column
261 columns
Payload Capacity
Path overhead(POH)
Path overhead(POH)
© 2001, Cisco Systems, Inc. Network Architecture-56
Payload PointerPayload Pointer
Section Overhead
90 (VC-3) or 270 (VC-4) Columns
9 Rows
STM-1 Frame #1
9 Rows
STM-1 VC-3 or VC-4
125 μsec
250 μsec
STM-1 Frame #2
H1 H2 H3...
Payload Pointer marksstart of STM-1 VC-3 or
VC-4
Payload Pointer marksstart of STM-1 VC-3 or
VC-4
STM-1 VC-3 or VC-4POH column
STM-1 VC-3 or VC-4POH column
© 2001, Cisco Systems, Inc. Network Architecture-57
SummarySummary
• Describe the overall structure of the frame
• Describe the payload pointer solution for timing differences
© 2001, Cisco Systems, Inc. Network Architecture-58
Review QuestionsReview Questions
• What is the size of a basic STM-1 frame?
• Which type of frame has been defined to show compatibility with SONET ?
• What are the overheads carried by a STM-1 frame?
• What is the purpose of pointers in a SDH frame?
STM-n FramesSTM-n Frames
Section 2.3Section 2.3
© 2001, Cisco Systems, Inc. Network Architecture-60
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Describe the overall structure of multiplexing
frames
• Describe the main steps of the multiplexing process
• Identify the concept of concatenated payloads
• Determine the details of frame structures for a common hierarchy level
© 2001, Cisco Systems, Inc. Network Architecture-61
General StructureGeneral Structure
• STM-N structure
– Byte-interleaving STM-1 modules
• No extra overhead introduced
• Overhead of multiplexed signals taken over, but section overhead (SOH) should be replaced with new information for the STS-N multiplex section
• Overhead is growing in absolute number of bits, but relative size is the same
• New overhead is bigger than necessary for regenerator and multiplex section overheads, so some bytes are unused
– Section overhead (SOH) is frame aligned
– SPE (multiplexed VC-3 or VC-4 channels) is not frame aligned
© 2001, Cisco Systems, Inc. Network Architecture-62
125 μsec
9 Rows
Section Overhead
270 x N Columns
9xN Columns
STM-N VC capacity
STM-N frameSTM-N frame
© 2001, Cisco Systems, Inc. Network Architecture-63
Multiplexing ProcessesMultiplexing Processes
• Multiplexing is composed of various processes:
– Mapping
• Tributaries adapted into Virtual Containers (VC) by adding stuffing and POH
– Aligning
• Pointer is added to locate the VC inside an AU or TU
– Multiplexing
• Interleaving the bytes of multiple paths
– Stuffing
• Adding up the fixed stuff bits to compensate for frequency variances
© 2001, Cisco Systems, Inc. Network Architecture-64
Concatenated FramesConcatenated Frames
FixedStuff(9X-9bytes)
9 Rows
STMPOH
9 bytesSTS-Xc Payload Capacity
(AU-4-Xc)
X x 261 Columns
125 μsec
STM-4c = 599.040 Mbit/sSTM-16c = 2396.160 Mbit/s
X x 260 Columns
SDH terminology is using X instead of N (X = N)
X-1 ColumnsX-1 Columns
© 2001, Cisco Systems, Inc. Network Architecture-65
Frame Structures for Each Common Hierarchy Level
Frame Structures for Each Common Hierarchy Level
270 Columns
9 Rows
9 Rows
9 Rows
1,080 Columns
4,320 Columns
STM-1
155.52 Mbit/s
STM-4
STM-16
622.08 Mbit/s
2488.32 Mbit/s
STM-64 9 rows x 17280 columns, 9953.28 Mbit/s
© 2001, Cisco Systems, Inc. Network Architecture-66
SummarySummary
• Describe the overall structure of multiplexing frames
• Describe the main steps of the multiplexing process
• Identify the concept of concatenated payloads
• Determine the details of frame structures for a common hierarchy level
© 2001, Cisco Systems, Inc. Network Architecture-67
Review QuestionsReview Questions
• What is the big advantage of the SDH multiplexing concept over PDH in terms of overhead?
• Why is it important to have more fixed stuffing at higher line rates?
• What is the concept behind allocating the amount of fixed stuffing?
Frames and RatesFrames and Rates
Section 2.4Section 2.4
© 2001, Cisco Systems, Inc. Network Architecture-69
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the various bit rates used to
characterize TDM networks
• Describe how the multiplexing process affects the bit rates
• Make the computation to summarize the rate hierarchy
© 2001, Cisco Systems, Inc. Network Architecture-70
Line, SPE and Payload RatesLine, SPE and Payload Rates
• Line rate = SOH + SPE
• SPE rate = POH + payload capacity + fixed stuffing
• VC payload capacity rate = line rate - SOH - POH - fixed stuffing
• Transparent bit-stream capacity rate = line rate - SOH - POH
• Example for STM-1 frame line rate:
–270 columns x 9 rows = 2430 bytes
–8000 fps x 19440 bits = 155.52 Mbit/s
© 2001, Cisco Systems, Inc. Network Architecture-71
Multiplexing Effect on RatesMultiplexing Effect on Rates
• Because of synchronous TDM byte-multiplexing the line rate is simply multiplied
• Example for STM-4 frame line rate:
– 4 x STM-1 byte-multiplexing
– 4 x 155.52 Mbit/s = 622.08 Mbit/s
• With higher level concatenated frames the transparent bit-stream capacity rate increases slightly as a relative value
– Since the POH is a fixed absolute value in this case
– However, fixed stuff may use up this extra capacity
© 2001, Cisco Systems, Inc. Network Architecture-72
Rate HierarchyRate Hierarchy
SDH Level
Line Rate (Mbit/s)
SPE Rate (Mbit/s)
Optical Level
Electrical Level
STM-1 OC-3 STS-3 STM-4 OC-12 STS-12STM-16 OC-48 STS-48STM-64
155.52622.08
2488.329953.28 OC-192 STS-192
STM-256 39813.12
150.336601.344
9621.50438486.016 OC-768 STS-768
SONET
2405.376
© 2001, Cisco Systems, Inc. Network Architecture-73
SummarySummary
• Identify the various bit rates used to characterize TDM networks
• Describe how the multiplexing process affects the bit rates
• Make the computation to summarize the rate hierarchy
© 2001, Cisco Systems, Inc. Network Architecture-74
Review QuestionsReview Questions
• Is the SPE rate a good measure of the capacity available to a data transport client?
• What is the VC payload capacity rate of a concatenated 40 Gbit/s SDH signal? Demonstrate the computation steps!
• How much frequency variation is allowed by the fixed stuffing in a 10 Gbit/s SDH signal? Demonstrate the computation steps!
Payload InternalsPayload Internals
Section 2.5Section 2.5
© 2001, Cisco Systems, Inc. Network Architecture-76
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the need for special structures to
support a mixture of payloads
• Describe the grouping options of various payloads
• Describe the pointer processing associated with the individual payloads
© 2001, Cisco Systems, Inc. Network Architecture-77
Administrative and Tributary Units
Administrative and Tributary Units
• Multiplexing of PDH signals inside SDH is organized using administrative and tributary units
– One more multiplexing level than SONET
• Administrative unit (AU) is a special construct for SDH, which allows two alternative ways of multiplexing and thus supporting PDH E4 mapping and SONET compatibility at the same time
• Tributary unit is a construct which accommodates various PDH signals at the lower level
• AU and TU are both called units, because both are composed from a virtual container and a pointer
• Byte-multiplexed AUs and TUs are called an AU group (AUG) and a TU Group (TUG) respectively
© 2001, Cisco Systems, Inc. Network Architecture-78
Virtual Containers - I.Virtual Containers - I.
• Virtual containers (VC-x) encapsulate a PDH payload with a special framing and a POH
• In SDH terminology, the original PDH payload with special framing is called a container (C-x)
• Various container sizes with some space for stuffing are defined
– C-11 for DS1 (25 bytes = 1.600 Mbit/s)
– C-12 for E1 (34 bytes = 2.176 Mbit/s)
– C-2 for DS2 (106 bytes = 6.784 Mbit/s)
– C-3 for DS3 or E3 (84 columns = 48.384 Mbit/s)
– C-4 for E4 (260 columns = 149.760 Mbit/s)
© 2001, Cisco Systems, Inc. Network Architecture-79
Virtual Containers - II.Virtual Containers - II.
• Various VC sizes defined:
– With 1 byte allocated for POH
• VC-11 for DS1 (26 bytes = 1.664 Mbit/s)
• VC-12 for E1 (35 bytes = 2.240 Mbit/s)
• VC-2 for DS2 (107 bytes = 6.848 Mbit/s)
– With 1 column allocated for POH
• VC-3 for DS3 or E3 (85 columns = 48.960 Mbit/s)
• VC-4 for E4 (261 columns = 150.336 Mbit/s)
© 2001, Cisco Systems, Inc. Network Architecture-80
Tributary Unit StructureTributary Unit Structure
• TUs are defined to fit into a number of columns
– This requirement determines the size of virtual containers and containers
– TU-3 adds up 3-byte pointer plus stuffing to VC-3
– Lower TUs add up 1 byte for pointer storage
• Organized into 4 frames (500 μs multi-frame)
• This provides V1, V2, V3, V4 TU pointer bytes
• Lower TUs also organize POH along the multi-frame
– This provides V5, J2, N2, K4 POH bytes
© 2001, Cisco Systems, Inc. Network Architecture-81
AUAUAU
DS1 E1 DS1C DS2TUDS1 E1 DS1C DS2TUDS1 E1 DS1C DS2TU
Mapping Hierarchy - I.Mapping Hierarchy - I.
STM-N
STS-1 Frame
STS-1 Frame
STS-1 Frame
STM-1 Frame
AU
DS1 E1 DS2 DS3/E3 E4
SPE-Nc
IP/ATM/Video
DS1 E1 DS1C DS2TU
DS3/E3
DS1 E1 DS1C DS2TU
© 2001, Cisco Systems, Inc. Network Architecture-82
Mapping Hierarchy - II.Mapping Hierarchy - II.
C-4
C-3
C-2
C-12
C-11
VC-4
VC-3
VC-2
VC-12
VC-11
TU-3
TU-2
TU-12
TU-11
VC-3
STM-N AUG AU-4139 Mbit/sATM
AU-3
TUG-3
44 Mbit/s34 Mbit/s
TUG-26.3 Mbit/s
2 Mbit/s
1.5 Mbit/s
xN
x3
x1
x7
x7
x4
x3
x1
x3
STM-0
x1
VT-1.5VT-1.5
VT group
VT group
STS-1SPE
STS-1SPESTS-1STS-1
STS-3NSTS-3N
DS3 BULKDS3 BULK
STS-3c BULKSTS-3c BULK
AUG
Aligning
Mapping
xNMultiplexing
x1
© 2001, Cisco Systems, Inc. Network Architecture-83
Pointer Processing - I.Pointer Processing - I.
• Pointer processing compensates for phase differences and small frequency variations (lasting for a number of frames)
• 10-bit pointer offset is stored in the H1, H2 overhead bytes (normal range is 0-782)
– Specifies the byte position after the last H3 byte in the VC capacity
– For AU-4 the byte position is 3 x (pointer offset) + 1
• TU pointer processing has a similar concept but different implementation details
– TU-3 uses H1, H2, H3 bytes inside the TU payload capacity
– Lower TUs use V1, V2, V3, V4 bytes in 500 μs multi-frame
© 2001, Cisco Systems, Inc. Network Architecture-84
Pointer Processing - II.Pointer Processing - II.
• AU-4 positive frequency justification
– If the tributary has a lower speed than its nominal rate, then 3 stuffed bytes are inserted just after the last H3 overhead byte
– Indicated by an inversion of the I-bits in the H1, H2 overhead bytes
• AU-4 negative frequency justification
– If the tributary has a higher speed than its nominal rate, then H3 overhead bytes are used to carry extra payload bytes
– Indicated by an inversion of the D-bits in the H1, H2 overhead bytes
© 2001, Cisco Systems, Inc. Network Architecture-85
Low- and High-order PathsLow- and High-order Paths
• 2 mapping levels may be clearly identified in SDH:
– AU for high-order (HO) paths
• Direct termination of DS3, E3, E4, ATM
• May carry multiple LO paths by multiplexing
– TU for low-order (LO) paths
• Termination of DS1, DS2, DS3, E1, E3
• 2 special layered networks on top of STM-1 SDH network
– HO and LO networks
– Managed by HO-POH and LO-POH information
• DS3/E3 may be part of both the HO or the LO network
© 2001, Cisco Systems, Inc. Network Architecture-86
SummarySummary
• Identify the need for special structures to support a mixture of payloads
• Describe the grouping options of various payloads
• Describe the pointer processing associated with the individual payloads
© 2001, Cisco Systems, Inc. Network Architecture-87
Review QuestionsReview Questions
• What are the two pointer options used by an AUG?
• Does an E3 client signal belong to a High-order Path or to a Low-order Path?
• What is the main difference between positive and negative frequency justification?
Overhead InternalsOverhead Internals
Section 2.6Section 2.6
© 2001, Cisco Systems, Inc. Network Architecture-89
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Describe the multiplexing process of overhead
bytes
• Describe the meaning of overhead bytes at various hierarchy levels
© 2001, Cisco Systems, Inc. Network Architecture-90
STM-1 OverheadsSTM-1 Overheads
• STM-1 overheads were designed to be compatible with SONET overheads
–Thus STM-1 overhead looks very similar to STS-3 overhead
• Easiest to understand by drawing STM-0 section overhead first
• Then creating STM-1 section overhead by multiplexing STM-0 3 times, and leaving out unnecessary bytes
• POH is not changed by multiplexing
© 2001, Cisco Systems, Inc. Network Architecture-91
STM-0 OverheadsSTM-0 Overheads
Data ComD8
Data ComD4
Data ComD7
Data ComD10
Data ComD5
Data ComD11
Data ComD6
Data ComD9
Data ComD12
APSK2
APSK1
Data ComD1
Data ComD3
Data ComD2
Section Overhead
Path TraceJ1
BIP-8B3
Signal LabelC2
Path StatusG1
User ChannelF2
Multiframe Indicator
H4
User ChannelF3
APSK3
TandemN1
FramingA1
BIP-8B1
PointerH1
BIP-8B2
SyncS1
OrderwireE1
PointerH2
RS TraceJ0
User ChannelF1
(REI)(M1)
PointerH3
OrderwireE2
HO PathOverhead
R-SectionOverhead
M-SectionOverhead
FramingA2
AU pointer
© 2001, Cisco Systems, Inc. Network Architecture-92
STM-1 Section OverheadSTM-1 Section Overhead
A1 A1 A1 A2 A2 A2 J0
B1 E1 F1
D1 D2 D3
H1 H1* H2 H2* H3 H3 H3
B2 K1 K2
S1 M1 E2
B2 B2
D4
D7
D10
D5
D8
D11
D6
D9
D12
H1* = 10010011
H2* = 11111111
H2*H1*
R-SectionOverhead
M-SectionOverhead
AU pointer
Δ
Δ
Δ
Δ
Δ
Δ
Δ - media dependent
national use
© 2001, Cisco Systems, Inc. Network Architecture-93
STM-N Section OverheadSTM-N Section Overhead
• Created by multiplexing STM-1 section overheads
• Only a few bytes are extended into each position
–A1/A2, B2, national use
• Most bytes are not multiplied by multiplexing, only the first appearance is used in the higher level (bigger) frames
© 2001, Cisco Systems, Inc. Network Architecture-94
Regenerator Section Overhead Bytes
Regenerator Section Overhead Bytes
• Framing bytes (A1, A2)
– Identify the start of each STM-0 frame
• R-Section Trace (J0)
– Used to trace the origin of the STM-1 frame
• BIP-8 = Bit Interleaved Parity (B1)
– Checks even-parity on previous STM-N frame after scrambling
• Orderwire (E1)
– 64 Kbit/s voice path used for communication
• User (F1)
– Optional, vendor specific
• DCC = Data Communications Channel (D1-D3) D1 D3D2
A1
B1 E1
J0
F1
A2
R-Section OH
© 2001, Cisco Systems, Inc. Network Architecture-95
1 2 3 4 5 6 7 8 268 269 270
271 273
2430
H1 c c H2 c cSTM-1 SDHFrame
Section Overhead (SOH) Path
Overhead (POH)
SPE
D1 D2 D3
R-Section
M-SectionK1 K2
Data Communication Channel (DCC)
Data Communication Channel (DCC)
• Formed by the D1, D2 and D3 bites in the Section Overhead
• Creates a 192 Kbit/s link
• Used for monitoring, alarms, provisioning, and software download
• Protocol is point-to-point between ADMs
• Today protocol is proprietary
• Moving to IS-IS, CLNS and ES-IS
109
© 2001, Cisco Systems, Inc. Network Architecture-96
AU Pointers AU Pointers
• Pointer (H1, H2)
– Two bytes used to indicate the offset between the pointer bytes and the first byte of the SPE
– Also indicates concatenation
• Pointer Action (H3)
– Used to compensate for the SPE timing variations
• Positive/negative stuff bytes
– Pointer bytes tell when H3 is being usedK2K1
H1
B2
D7
D10
S1
H2
D8
D11
M1
H3
D9
D12
E2
D6D5D4
M-Section OH
© 2001, Cisco Systems, Inc. Network Architecture-97
10 268 269 2701 2 3 4 5 6 7 8 9
271 273
2430
H1 H1 H1 H2 H2 H2
87 89 90
810
1 2 3
H1 H2
Section Overhead (SOH)
SPE
STM-1
3 x AU-3's
Pointer Bytes (H1, H2) for AU-3 Based Frames
Pointer Bytes (H1, H2) for AU-3 Based Frames
• STM-1 pointer bytes usage:
– 3 x AU-3 bit streams should be located
Path Overhead (POH)
© 2001, Cisco Systems, Inc. Network Architecture-98
Multiplex Section Overhead Bytes - I.
Multiplex Section Overhead Bytes - I.
• BIP-24 (B2) interleaved parity
– Used for STM-N multiplex section error monitoring
• Parity check on MSOH and previous STM-N frame before scrambling
• Provided for each STM-1 inside STM-N
• APS = Automatic Protection Switching (K1, K2)
– APS commands and error conditions between line termination equipment
K2K1
H1
B2
D7
D10
S1
H2
D8
D11
M1
H3
D9
D12
E2
D6D5D4
M-Section OH
© 2001, Cisco Systems, Inc. Network Architecture-99
Multiplex Section Overhead Bytes - II.
Multiplex Section Overhead Bytes - II.
• DCC (D4-D12)
– Uses same protocols and procedures as the RS-DCC
– For OAM&P messages between OSS and SDH multiplex-section-level equipment
• Synchronization Status (S1)
– Allows the SDH equipment to choose the best clocking source from many candidates
• STM-N REI-L (M1)
– Multiplex Section Level Remote Error Indicator
• Orderwire (E2)
– 64 Kbit/s voice channel
• Defined only in the first STS-N signal
K2K1
H1
B2
D7
D10
S1
H2
D8
D11
M1
H3
D9
D12
E2
D6D5D4
M-Section OH
© 2001, Cisco Systems, Inc. Network Architecture-100
Path Overhead Bytes - I.Path Overhead Bytes - I.
• STS Path Trace (J1)
– Fixed length Access Point ID enabling the path terminator to verify connection
• 15-byte E.164 address plus 1 byte CRC-7
• A 64-byte version permitted for SONET compatibility
• Path BIP-8 (B3)
– Parity check of previous VC before scrambling
Path TraceJ1
BIP-8B3
Signal LabelC2
Path StatusG1
User ChannelF2
IndicatorH4
User ChannelF3
APSK3
TandemN1
Path OH
© 2001, Cisco Systems, Inc. Network Architecture-101
Path Overhead Bytes - II.Path Overhead Bytes - II.
• Path Signal Label (C2)
– VC content type (mapping)
• Path Status (G1)
– Allows the entire path to be monitored end to end
– Used to notify the originating end of the path
• Performance and status of the entire duplex path
• Carries the Remote Error Indicator (REI) and the path Remote Defect Indicator (RDI)
Path TraceJ1
BIP-8B3
Signal LabelC2
Path StatusG1
User ChannelF2
IndicatorH4
User ChannelF3
APSK3
TandemN1
Path OH
© 2001, Cisco Systems, Inc. Network Architecture-102
Path Overhead Bytes - III.Path Overhead Bytes - III.
• Path User Channel (F2)
– Used by the network provider for internal network communications
• Position and Sequence Indicator (H4)
– Used when the frame is organized into various mappings like Virtual Tributaries or ATM cells
• User Channel (F3)
• APS (K3)
• Network Operator Byte (N1)
Path TraceJ1
BIP-8B3
Signal LabelC2
Path StatusG1
User ChannelF2
IndicatorH4
User ChannelF3
APSK3
TandemN1
Path OH
© 2001, Cisco Systems, Inc. Network Architecture-103
SummarySummary
• Describe the multiplexing process of overhead bytes
• Describe the meaning of overhead bytes at various hierarchy levels
© 2001, Cisco Systems, Inc. Network Architecture-104
Review QuestionsReview Questions
• What are the H1 and H2 bytes in the Multplex Section overhead used for?
• What are the A1 and A2 bytes in the Regenerator Section overhead used for?
• Why is the parity computed before scrambling?
• Is there a difference between SDH frames in various countries?
SummarySummary
Information ResourcesInformation Resources
© 2001, Cisco Systems, Inc. Network Architecture-106
QuestionsQuestions
?
© 2001, Cisco Systems, Inc. Network Architecture-107
Information ResourcesInformation Resources
• Books
–Stamatios V. Kartalopoulos: “Understanding SONET/SDH and ATM”
• IEEE, 1999; ISBN 0780347455
© 2001, Cisco Systems, Inc. Network Architecture-108
SummarySummary
After completing this chapter, you should be able to perform the following tasks:• Identify the main frame concepts
• Describe the basic structure of frames at various hierarchy levels
• Make the basic computation for bit rates at various hierarchy levels
• Describe the internal details of payloads and overheads
Topology and Protection
Topology and Protection
Chapter 3Chapter 3
© 2001, Cisco Systems, Inc. Network Architecture-110
ObjectivesObjectives
Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main issues in topology design
• Define the main topologies
• Identify the main protection switching concepts
• Describe the operations of typical topology configurations
© 2001, Cisco Systems, Inc. Network Architecture-111
AgendaAgenda
3.1 - Topology Basics
3.2 - Protection Switching
3.3 - USHR Topology
3.4 - BSHR Topology
Summary, Information Resources
Topology BasicsTopology Basics
Section 3.1Section 3.1
© 2001, Cisco Systems, Inc. Network Architecture-113
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify main topology alternatives
• Describe routing and provisioning concepts
© 2001, Cisco Systems, Inc. Network Architecture-114
• Point-to-point
– Used for SDH island trunks in old asynchronous networks, or data services as POS or ATM links
• Linear point-to-multipoint
– Adds up ADM in the middle
– Max. 16 nodes
• Hub network
– A DCS interconnects ADMs
• Ring
– ADMs are put into a ring
– Redundant, multiple connected rings
• Automatic protection switching (APS)USHR
Topology AlternativesTopology Alternatives
© 2001, Cisco Systems, Inc. Network Architecture-115
Uni- and Bi-directional Routing
Uni- and Bi-directional Routing
• Only working traffic is shown
• Subnetwork (path) or multiplex section switching for protection
A
CE
BF
D
Uni-directional Ring(1 fiber)
C-A
A-CA
CE
BF
D
Bi-directional Ring(2 fibers)
C-A
A-C
© 2001, Cisco Systems, Inc. Network Architecture-116
Add-drop ProvisioningAdd-drop Provisioning
• Transport connections over a SDH infrastructure are created by add-drop provisioning
–A path is built up by specifying hop-by-hop which channels should be added to a ring and which channels should be dropped from the ring
• Add-drop provisioning is typically done by the network management system
–There is no signaling protocol
© 2001, Cisco Systems, Inc. Network Architecture-117
ADM2
ADM3
ADM1
ADM4
OC-12
Drop
Add 1-3
Add 3-4
Drop
Add 4-2
Drop
Add and Drop ExampleAdd and Drop Example
• STM-4 Ring
• 4 x STM-1 channels
• Uni-directional routing
• Provisioning:
– add 1-3 (drop 3-1)
– add 3-4 (drop 4-3)
– add 4-2 (drop 2-4)
• 2 channels occupied
© 2001, Cisco Systems, Inc. Network Architecture-118
Drop and Continue ExampleDrop and Continue Example
• STM-4 Ring
• 4 x STM-1 channels
• Uni-directional routing
• Provisioning:
– add 1-2,3
– add 2-4,1
• 2 channels occupied
ADM2
ADM3
ADM1
ADM4
OC-12
Add 1-2,3
Add 2-4,1
Drop
Drop
Drop & Continue
Drop & Continue
© 2001, Cisco Systems, Inc. Network Architecture-119
Uni- and Bi-directional Example
Uni- and Bi-directional Example
Provisioning:• add 1-3
• add 3-1
ADM2
ADM3
ADM1
ADM4
ADM2
ADM3
ADM1
ADM4
Uni-directional routing Bi-directional routing
© 2001, Cisco Systems, Inc. Network Architecture-120
SummarySummary
• Identify main topology alternatives
• Describe routing and provisioning concepts
© 2001, Cisco Systems, Inc. Network Architecture-121
Review QuestionsReview Questions
• Which types of topologies does the SDH network support?
• Is there a signaling protocol that allows the addressing of different SDH nodes within a network?
Protection SwitchingProtection Switching
Section 3.2Section 3.2
© 2001, Cisco Systems, Inc. Network Architecture-123
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the main alternatives in creating
protection switching solutions
• Describe the main features of various configuration options
• Describe the operational steps in the activation of protection switching
© 2001, Cisco Systems, Inc. Network Architecture-124
Multiplex Section Protection Switching
Multiplex Section Protection Switching
• Conditions resulting in a protection switch:
– Loss of signal, loss of frame
– Line AIS (all 1’s)
– Signal degrade
• Excessive BIP-24 errors in MS overhead
LOS AIS
OCNREIupstream
downstream
Payload
R-SectionOverhead
M-SectionOverhead
information controllingprotectionswitching
© 2001, Cisco Systems, Inc. Network Architecture-125
Path Protection SwitchingPath Protection Switching
• Conditions resulting in a protection switch:
– Loss of pointer, STM or VC AIS
– Excessive BIP errors for STM path, BIP errors for VC path
R-SectionOverhead
M-SectionOverhead
Info controllingprotectionswitching
Payload
STMPath
Overhead
VCPath
Overhead
VCPayload
© 2001, Cisco Systems, Inc. Network Architecture-126
STM -N Mux
K1K2Read/Sel
K1K2Write
WorkingSTM-N
ProtectSTM-N
STM-N Mux
K1K2Write
K1K2Read/Sel
TributaryChannels
TributaryChannels
MSTE
MSTE
Automatic Protection Switching - I.
Automatic Protection Switching - I.
• APS = Automatic Protection Switching
– Allows network to react to failed lines, interfaces, or poor signal quality
• Performed over the entire STM-N payload
• Uses K1 and K2 bytes of MS Overhead
© 2001, Cisco Systems, Inc. Network Architecture-127
Automatic Protection Switching - II.
Automatic Protection Switching - II.
• K1 byte:
– Type of request (bits 1-4)
– Channel requested (bits 5-8)
• K2 byte:
– Channel selected (bits 1-4)
– Architecture (bit 5)
– Mode of operation (bits 6-8)
• e.g. Alarm Indication Signal (AIS), Remote Defect Indicator (RDI)
STM -N Mux
K1K2Read/Sel
K1K2Write
WorkingSTM-N
ProtectSTM-N
STM-N Mux
K1K2Write
K1K2Read/Sel
TributaryChannels
TributaryChannels
MSTE
MSTE
© 2001, Cisco Systems, Inc. Network Architecture-128
Uni- and Bi-directional APSUni- and Bi-directional APS
• Uni-directional APS
–Only traffic on the affected fiber is switched to the protect line
• Bi-directional APS
–TX and RX are both switched when channel is affected
© 2001, Cisco Systems, Inc. Network Architecture-129
Revertive and Non-revertive APS
Revertive and Non-revertive APS
• Revertive switching
–Will restore to the working channel when WTR timer expires
• Non-revertive switching
–Will not move to working channel after failure unless requested
© 2001, Cisco Systems, Inc. Network Architecture-130
Working facility
Protection facility
ADM/Router ADM/Router
1+1 Protection1+1 Protection
• Bi- or unidirectional
• Non-revertive
• Transmits traffic on both channels
© 2001, Cisco Systems, Inc. Network Architecture-131
Protection facility
Working facility
ADM/Router ADM/Router
1:n Protection - I.1:n Protection - I.
• 1:1 protection (special case of 1:n)
– Bi- or unidirectional
– Revertive
– Typically dedicated protection
– May transmit traffic on both channels, or use protect for low priority traffic
© 2001, Cisco Systems, Inc. Network Architecture-132
Protection facility
Working facility
ADM/Router ADM/Router
1:n Protection - II.1:n Protection - II.
• 1:n protection
– Bi- or unidirectional
– Revertive
– Shared protection facility
© 2001, Cisco Systems, Inc. Network Architecture-133
APS OperationsAPS Operations
• 1:n Bi-directional switching:
– Switch when transmitted bits K1:5-8 equals received bits K2:1-4
• 1:n Unidirectional switching
– Same as 1:n
• 1+1 Switching
– Bi-directional - as above
– Unidirectional - each end operates independently
• Switch occurs immediately without capability to reset
© 2001, Cisco Systems, Inc. Network Architecture-134
SummarySummary
• Identify the main alternatives in creating protection switching solutions
• Describe the main features of various configuration options
• Describe the operational steps in the activation of protection switching
© 2001, Cisco Systems, Inc. Network Architecture-135
Review QuestionsReview Questions
• What is APS used for?
• What is the difference between a two-fiber uni- and bi-directional link?
• What is the difference between revertive and non-revertive protection switching?
• Which two bytes of the Multiplex Section overhead are used to initiate an APS?
USHR TopologyUSHR Topology
Section 3.3Section 3.3
© 2001, Cisco Systems, Inc. Network Architecture-137
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the main concepts in constructing
protected ring topologies
• Describe the main features and application areas
• Describe the typical operational scenarios
• Describe the standardization efforts for interoperability
© 2001, Cisco Systems, Inc. Network Architecture-138
USHR ConceptsUSHR Concepts
• USHR/P = Unidirectional Self-Healing Ring / Path Switched
• 2-fiber ring topology
– Head-end bridge, tail-end switch logical topology
• 1+1 protection with uni-directional routing on each fiber
• Traffic is sent in both directions on the ring on separate fibers
• The better signal is selected by the receiver
© 2001, Cisco Systems, Inc. Network Architecture-139
Application AreasApplication Areas
• Used in the access network or MAN
–All traffic homing into a central node
• e.g. CO
• Typical for STM-1, STM-4 rings
© 2001, Cisco Systems, Inc. Network Architecture-140
FeaturesFeatures
• Simplicity at the expense of capacity
–Bandwidth used, cannot be reused
• VC-1/2 and/or STM visibility
• Quick local fail-over independent from the rest of the network
–No signaling protocol needed
© 2001, Cisco Systems, Inc. Network Architecture-141
A
CE
BF
D
workingtraffic
protectiontraffic
Operations – Traffic FlowOperations – Traffic Flow
• One direction of duplex traffic between any two nodes goes through each ring link for both working and protection traffic
• Reverse direction of transmission is dedicated to protection
• Therefore, the maximum capacity of this ring equals the line rate, i.e. STM-4, STM-16 etc.
© 2001, Cisco Systems, Inc. Network Architecture-142
Operations – Fiber Cut - I.Operations – Fiber Cut - I.
• Protection dedicated - head end bridge
• Failure interrupts A-C working traffic
• Receiver at C detects failure
A
CE
BF
D
WorkingTraffic
ProtectionTraffic
Workingtraffic selected
© 2001, Cisco Systems, Inc. Network Architecture-143
A
CE
BF
D
WorkingTraffic
ProtectionTraffic
Protectiontraffic selected
Operations – Fiber Cut - II.Operations – Fiber Cut - II.
• Fiber cut recovery steps:
– Tail end (receiver) switches to protection traffic
– Only the receiving node knows about the protection switch
• No traffic lost
© 2001, Cisco Systems, Inc. Network Architecture-144
Operations – Node Failure - I.Operations – Node Failure - I.
• Protection bandwidth dedicated - head end bridge
• Failure interrupts A-C working traffic
• Receiver at C detects failure
A
CE
BF
D
WorkingTraffic
ProtectionTraffic
Workingtraffic selected
Node Failure
© 2001, Cisco Systems, Inc. Network Architecture-145
A
CE
BF
D
WorkingTraffic
ProtectionTraffic
Protectiontraffic selected
Node Failure
Operations – Node Failure - II.Operations – Node Failure - II.
• Node recovery steps:
– Tail end (receiver) switches to protection traffic
– Only receiving node knows about the protection switch
• Traffic to/from failed node is lost
© 2001, Cisco Systems, Inc. Network Architecture-146
StandardizationStandardization
• Basic APS operations are defined in ITU-T G.783
• USHR/P is originally not fully defined by ITU-T
• Later defined in ITU-T G.841 as general VC trail protection switching independent of the underlying topology
–USHR/P is called 1+1 unidirectional VC trail switching (ring topology is only a special case) with dedicated protection
• USHR/MS and other variants are more a theoretical possibility than real products
© 2001, Cisco Systems, Inc. Network Architecture-147
SummarySummary
• Identify the main concepts in constructing protected ring topologies
• Describe the main features and application areas
• Describe the typical operational scenarios
• Describe the standardization efforts for interoperability
© 2001, Cisco Systems, Inc. Network Architecture-148
Review QuestionsReview Questions
• Why is the USHR/P based APS very fast?
• Why is it natural to use only uni-directional APS in a USHR/P configuration?
• Why USHR/MS is not a practical idea?
BSHR TopologyBSHR Topology
Section 3.4Section 3.4
© 2001, Cisco Systems, Inc. Network Architecture-150
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the main concepts in constructing
protected ring topologies
• Describe the main features and application areas
• Describe the typical operational scenarios
• Describe the standardization efforts for interoperability
© 2001, Cisco Systems, Inc. Network Architecture-151
BSHR Concepts - I.BSHR Concepts - I.
• BSHR/MS = Bi-directional Self-Healing Ring / Multiplex Section Switched
• 1:1, or 1:N redundancy options
• 2 fibers with shared protection configuration
– Half the bandwidth in each direction in a link is reserved for the shared protection of all traffic in that reverse direction of the link
• An even number of STM-1s are required
• 4 fibers for dedicated protection configuration
– Bi-directional routing on 2 fibers (working line)
– Each direction has a working and a protect fiber
© 2001, Cisco Systems, Inc. Network Architecture-152
BSHR Concepts - II.BSHR Concepts - II.
• Multiple fail-over options for 4-fiber BSHR/MS
– In normal operation traffic is sent only in the required direction
– During fiber interruption, the traffic is routed around the break in opposite direction (long path)
• Ring switching
– Optionally if the other 2 fibers are still available, then traffic might be routed onto the parallel 2 fibers (short path)
• Span switching
© 2001, Cisco Systems, Inc. Network Architecture-153
Traffic to/from an NETraffic to/from an NE
NetworkElement
STM-1 #1-12 all pathsworking traffic
STM-1 #1-12 all paths dedicated protection traffic
STM-1 #1-12 all pathsworking traffic
STM-1 #1-12 all pathsdedicated protection traffic
NetworkElement
STM-1 #1-6 working trafficSTM-1 #7-12 shared protection traffic
STM-1 #1-6 working trafficSTM-1 #7-12 shared protection traffic
STM-1 #1-6 working trafficSTM-1 #7-12 shared protection traffic
STM-1 #1-6 working trafficSTM-1 #7-12 shared protection traffic
Both rings have an add/drop capability of up to 12 STM-1s at any node
shared protection
dedicated protection
© 2001, Cisco Systems, Inc. Network Architecture-154
Application AreasApplication Areas
• Used in the WAN backbone
–Neighboring traffic pattern is the best fit
• BSHR/MS rings are interconnected in a hierarchy
–Number of hops should be minimized
–Capacity of rings increasing as moving up in the ring hierarchy
• Rings might be classified into aggregation and core
© 2001, Cisco Systems, Inc. Network Architecture-155
FeaturesFeatures
• More complexity, but more flexible capacity
–Bandwidth used can be reused
–Requires signaling between ADMs
• STM visibility
• Might restore service in less than 50 milliseconds on a 1200 km or less ring
© 2001, Cisco Systems, Inc. Network Architecture-156
A
CE
BF
Donly workingtraffic shown
Operations – Traffic FlowOperations – Traffic Flow
• Duplex traffic between two nodes goes through a subset of ring links
• Minimum capacity equals line rate (same as USHR/P maximum)
• Line rate must be an even integer of STM-1 for 2-fiber configurations
– Automatically fulfilled with newer standards
© 2001, Cisco Systems, Inc. Network Architecture-157
A
CE
BF
D
Onlyworkingtrafficshown
B-C
A-B
C-DD-E
E-F
F-A
C-B
B-A
D-CE-D
F-E
A-F
Maximum Bandwidth CapacityMaximum Bandwidth Capacity
• Each link represents half of the line rate of STM-1s (i.e. 8 STM-1s for an STM-16)
• All traffic from a node goes to adjacent nodes
• Max. capacity = 0.5 (line rate) x number of nodes
© 2001, Cisco Systems, Inc. Network Architecture-158
A
CE
BF
D
Extra Trafficin Protectionbandwidth
WorkingTraffic
Extra TrafficExtra Traffic
• Extra traffic utilizes shared protection bandwidth
• Extra traffic is not protected when a failure occurs
• Extra traffic could be lost when a failure of working traffic occurs
• Extra traffic is ONLY available on a BSHR/MS
© 2001, Cisco Systems, Inc. Network Architecture-159
Operations – Fiber Cut - I.Operations – Fiber Cut - I.
• Failure interrupts A-C and C-A traffic
• A and B detect failureA
CE
BF
D
Fiber cut
WorkingTraffic
STM-1#4
STM-1#4
© 2001, Cisco Systems, Inc. Network Architecture-160
Operations – Fiber Cut - II.Operations – Fiber Cut - II.
• No dedicated protection bandwidth - only used when protection required
• Only nodes next to the failure know about the protection switch
• No traffic lost
A
CE
BF
DProtectionTraffic
Loops
Fiber cut
WorkingTraffic
STM-1#10 into STM-1#4
STM-1#4 into STM-1#10
STM-1#10 into STM-1#4
STM-1#4 into STM-1#10
© 2001, Cisco Systems, Inc. Network Architecture-161
Operations – Node Failure - I.Operations – Node Failure - I.
• Failure interrupts D-F and F-D traffic
• A and C detect failure A
CE
BF
D
Node Failure
WorkingTraffic
STM-1#4
STM-1#4
© 2001, Cisco Systems, Inc. Network Architecture-162
Operations – Node Failure - II.Operations – Node Failure - II.
• No dedicated protection bandwidth - only used when protection required
• Only nodes next to the failure know about the protection switch
• Traffic to/from failed node lost
A
CE
BF
DProtectionTraffic
Loops
Node Failure
LoopsWorkingTraffic
STM-1#10 into STM-1#4
STM-1#4 into STM-1#10
STM-1#10 into STM-1#4
STM-1#4 into STM-1#10
© 2001, Cisco Systems, Inc. Network Architecture-163
A
CE
BF
D
WorkingTraffic
Node Failure
STM-1#1STM-1#1
STM-1#1
STM-1#1
Squelching ProblemSquelching Problem
• Traffic terminating on nodes cut off by failures could be misconnected to other nodes on the ring in case ofusing a localfail-over decision
© 2001, Cisco Systems, Inc. Network Architecture-164
Squelching MisconnectionsSquelching Misconnections
• Node F now talking to Node E instead of Node B
• Misconnection would occur
STM-1#1
STM-1#7 STS-1#1
A
CE
BF
D
ProtectionTraffic
Node Failure
WorkingTraffic
© 2001, Cisco Systems, Inc. Network Architecture-165
Squelching - Path AIS Insertion
Squelching - Path AIS Insertion
• STM Path AIS is inserted instead of the looped STM-1#7
• No mis-connections
STM-1#1
STM-1#7 STS-1#1
A
CE
BF
D
ProtectionTraffic
Node Failure
WorkingTraffic
STM-1#1 Path AIS inserted by Node C
STM-1#1 PathAIS insertedby Node A
© 2001, Cisco Systems, Inc. Network Architecture-166
Squelching - SummarySquelching - Summary
• Squelching is required to assure that misconnections are not made
– Only required for bidirectional line switched rings since it is the only ring to provide a reuse capability of STM-1s around the ring
– Only required when nodes are cut off from the ring
– Only required for traffic terminating on the cut off nodes
• A ring map that includes all STM and VC Paths on the ring is available at every node on the ring
• Squelching is also required for extra traffic since the extra traffic may be dropped when a protection switch is required
© 2001, Cisco Systems, Inc. Network Architecture-167
StandardizationStandardization
• Basic APS operations are defined in ITU-T G.783
• BSHR/MS is first defined in ITU-T G.803 (1993), but exact details are referred to as for further study
• Later ITU-T G.841 (1995) defines BSHR/MS, but only for shared protection
– Dedicated protection is referred to as for further study (1998)
• Conflict with common sense terminology
• 4-fiber BSHR is called shared (!) protection since extra traffic might use the protection fibers
• BSHR/P and other variants are more a theoretical possibility than real products
© 2001, Cisco Systems, Inc. Network Architecture-168
SummarySummary
• Identify the main concepts in constructing protected ring topologies
• Describe the main features and application areas
• Describe the typical operational scenarios
• Describe the standardization efforts for interoperability
© 2001, Cisco Systems, Inc. Network Architecture-169
Review QuestionsReview Questions
• Why is signaling required to ensure proper fail-over in a BSHR/MS protection switching?
• What is the difference between shared protection in a 2-fiber and a 4-fiber ring?
• Is 1:n protection available in a 4-fiber ring?
• Why is there a potential misconnection problem at node failures?
SummarySummary
Information ResourcesInformation Resources
© 2001, Cisco Systems, Inc. Network Architecture-171
Remember...Remember...
• Unidirectional ring: all working traffic travels around the ring in the same direction for both A to B and B to A traffic; i.e. clockwise or counterclockwise
• Bidirectional ring: all working traffic between two nodes travels the two directions on the same set of fiber links between the two nodes; i.e. A to B clockwise and B to A counterclockwise
• MS switching: APS is based on received MS signal status and MS layer performance parameters
• Path switching: APS is based on received path layer signal status and path layer performance parameters
© 2001, Cisco Systems, Inc. Network Architecture-172
Remember...Remember...
• Ring switching: alternative path used is in the other direction on the ring
• Span switching: alternative path used is in parallel with the failed path
• Squelching: insertion of AIS for looped signals during protection switching to avoid misconnections
• Extra traffic: the utilization of the the protection bandwidth in a MS switched ring for traffic that can and may be disrupted when a protection switch is established
© 2001, Cisco Systems, Inc. Network Architecture-173
Remember...Remember...
• + BSHR/MS provides higher bandwidth capacity when internodal traffic exists between ring nodes
• ø BSHR/MS provides the same bandwidth capacity as USHR/P when all traffic homes on a single node, as in some access configurations
• + BSHR/MS evolves to support new service types like ATM easily, path switched rings require new paths to be defined for new services that don’t fit into STSs or VTs
• - USHR/P is perceived to be simpler since it can be thought of as diverse routing
• - BSHR/MS is perceived to be complex because of protection loops and squelching
• ø Both BSHR/MS and USHR/P require synchronization protection switching which in a line switched protection scheme is not needed
© 2001, Cisco Systems, Inc. Network Architecture-174
QuestionsQuestions
?
© 2001, Cisco Systems, Inc. Network Architecture-175
Information ResourcesInformation Resources
• Articles
–Dave Johnson, et al.: “The Evolution of a Reliable Transport Network”
• IEEE Communications Magazine, August 1999, pp.52-57.
© 2001, Cisco Systems, Inc. Network Architecture-176
SummarySummary
After completing this chapter, you should be able to perform the following tasks:• Identify the main issues in topology design
• Define the main topologies
• Identify the main protection switching concepts
• Describe the operations of typical topology configurations
Time SynchronizationTime Synchronization
Chapter 4Chapter 4
© 2001, Cisco Systems, Inc. Network Architecture-178
ObjectivesObjectives
Upon completion of this chapter, you will be able to perform the following tasks: • Identify the main requirements for time
synchronization
• Describe the main synchronization modes
• Describe the principles of network synchronization
• Describe the concept and operation of time synchronization protection
© 2001, Cisco Systems, Inc. Network Architecture-179
AgendaAgenda
4.1 - Time Synchronization Basics
4.2 - Synchronization Networks
4.3 - Synchronization Protection
Summary, Information Resources
Time Synchronization Basics
Time Synchronization Basics
Section 4.1Section 4.1
© 2001, Cisco Systems, Inc. Network Architecture-181
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Describe the historical evolution of time
synchronization
• List main synchronization requirements
• Describe the network element synchronization modes
© 2001, Cisco Systems, Inc. Network Architecture-182
History - I.History - I.
• Time synchronization might be needed for all digital voice communication networks
–On point-to-point links transmit and receive frequencies should be the same
– In synchronous multiplexing transmit and receive frequencies should be synchronized everywhere in the network, otherwise information might be lost
– In asynchronous multiplexing the multiplexers are independent from the timing of the multiplexed signals (PDH concept)
© 2001, Cisco Systems, Inc. Network Architecture-183
History - II.History - II.
• SDH is quite different from PDH, since it uses synchronous multiplexing
• Beginning of 1990s, SDH is used mainly as point-to-point island, no synchronization with E1, direct replacement for asynchronous transport
• Middle of 1990s, SDH becomes time synchronized, using complex topologies, making pointer adjustments
© 2001, Cisco Systems, Inc. Network Architecture-184
Network Clock(Stratum 1)
• Synchronous DS0/E1 switching network (Stratum 1)• Asynchronous transport network
DS0Switch
CB
E1
M14 M14LT CBLT LT
E4 prop. E4 E1E1 E4 prop. E4 E1
M14 M14
0.000001 ppm
LT
Switching Network
Transport Network
VF
Transport Network
Synchronization in Classical Voice Networks - I.
Synchronization in Classical Voice Networks - I.
© 2001, Cisco Systems, Inc. Network Architecture-185
Synchronization in Classical Voice Networks - II.
Synchronization in Classical Voice Networks - II.
Network Clock(Stratum 1)
• Asynchronous transport network uses pulse stuffing and is transparent to E1 timing
DS0Switch
CB
E1
M14 M14LT CBLT LT
E4 prop. E4 E1E1 E4 prop. E4 E1
M14 M14
0.000001 ppm
LT
f120ppm
f220ppm
f320ppm
f420ppm
f520ppm
f620ppm
© 2001, Cisco Systems, Inc. Network Architecture-186
• Timing distribution is done using embedded E1 facility• Asynchronous transport network is transparent to E1 timing
Synchronization DistributionSynchronization Distribution
Network Clock(Stratum 1)
DS0Switch
CB
E1
M14 M14
20ppm
LT CBLT LT
E4 prop. E4 E1E1 E4 prop. E4 E1
M14 M13
0.000001 ppm
20ppm
LT
Dedicated TimingE1
© 2001, Cisco Systems, Inc. Network Architecture-187
• SDH used in point-point configuration• Direct replacement for async transport• SDH terminals free-run at 20ppm. Not network synchronized. No pointer adjustments so no issues with E1/E4 mapping jitter !
f120ppm
f220ppm
f320ppm
f420ppm
f520ppm
f620ppm
Network Clock(Stratum 1)
DS0Switch
CB
E1
M14 M14 CBLT LT
E4 STM-16 E4 E1E1 E4 prop. E4 E1
M14 M14
0.000001 ppm
SDHNE
SDHNE
Initial SDH DeploymentsInitial SDH Deployments
© 2001, Cisco Systems, Inc. Network Architecture-188
Current SDH Deployments - I.Current SDH Deployments - I.
Questions:• How do I time the SDH network ?• Can I still just free run all my SDH NEs at 20ppm ?• What is the impact of pointer adjustments ?• How do I distribute timing to the CBs and DS0 switches ?
Network Clock(Stratum 1)
DS0Switch
CB
E1
CBSTM-1
E4 E1E1 E1
0.000001 ppm
STM-16
STM-1 STM-1 STM-1
STM-4
???
© 2001, Cisco Systems, Inc. Network Architecture-189
• All STM-N interfaces traceable to PRS to avoid excessive pointers• Excessive pointers cause jitter/wander in embedded E1/E4 payloads• Timing distributed to CB and DS0 switches directly via STM-N lines
Current SDH Deployments - II.Current SDH Deployments - II.
Network Clock(Stratum 1)
DS0Switch
CB CB
BITS
E1E1 E1
0.000001 ppm
STM-16
STM-1STM-1 STM-1
STM-4
STM-1
© 2001, Cisco Systems, Inc. Network Architecture-190
Synchronization Requirements
Synchronization Requirements
• Frequency variation of bits transmitted should be inside the limits determined by the next hop’s ability to transmit these bits further
– Stuffing allows for some limited tolerance
• Frequencies should be synchronized all over the network to guarantee a low level of BER
• Synchronization is done by recovering the embedded clock signal from the input signal
• Synchronization source should have a very precise clock (reference clock)
• Reference clock might be reached only by multiple hops
– Number of hops should be minimized
© 2001, Cisco Systems, Inc. Network Architecture-191
• Timing loops can be caused by either careless planning or fault conditions • Timing loops cause unpredictable sync performance• Elimination of timing loops was the driver for sync status messaging (SSM)
Synchronization and Timing Loops
Synchronization and Timing Loops
Network Clock(Stratum 1)
DS0Switch
CB CB
BITS
E1E1 E1
0.000001 ppm
STM-16
STM-1STM-1 STM-1
STM-4
STM-1
Timing Loop
Fiber Cut
© 2001, Cisco Systems, Inc. Network Architecture-192
Synchronization Modes for Network Elements
Synchronization Modes for Network Elements
• Each network element has to be configured for time synchronization
• Time reference distribution should minimize delay
• Various timing alternatives:
–External
–Line
–Loop
–Through
© 2001, Cisco Systems, Inc. Network Architecture-193
WEST
EAST
Network Element
BITS
External TimingExternal Timing
• All signals transmitted from a node are synchronized to an external source received by that node; i.e. BITS timing source
© 2001, Cisco Systems, Inc. Network Architecture-194
Line TimingLine Timing
• All transmitted signals from a node are synchronized to one received signal
WEST
EAST
Network Element
© 2001, Cisco Systems, Inc. Network Architecture-195
Loop TimingLoop Timing
• The transmit signal in a optical link, east or west, is synchronized to the received signal from the same optical link
WEST
EAST
Network Element
© 2001, Cisco Systems, Inc. Network Architecture-196
Through TimingThrough Timing
• The transmit signal in one direction of transmission around the ring is synchronized to the received signal from that same direction of transmission
WEST
EAST
Network Element
© 2001, Cisco Systems, Inc. Network Architecture-197
SummarySummary
• Describe the historical evolution of time synchronization
• List main synchronization requirements
• Describe the network element synchronization modes
© 2001, Cisco Systems, Inc. Network Architecture-198
Review QuestionsReview Questions
• In general, why is synchronization needed?
• How is synchronization achieved in PDH networks?
• How is synchronization achieved in SDH networks?
Synchronization Networks
Synchronization Networks
Section 4.2Section 4.2
© 2001, Cisco Systems, Inc. Network Architecture-200
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the reference clock concept
• Describe clock distribution methods
• Describe the concept of using alternative clock sources
• Provide the basic design considerations for synchronization network design
© 2001, Cisco Systems, Inc. Network Architecture-201
Reference Clocks - I.Reference Clocks - I.
• Precision of internal clock is classified into so called “Stratum” levels
– Accuracy is defined as the ratio of bit slip happening (causing a bit error)
• Stratum 1 => 1 x 10-11 (synchronization to atomic clock)
• Stratum 2 => 1.6 x 10-9
• Stratum 3E => 1 x 10-6
• Stratum 3 => 4.6 x 10-6
• Stratum 4 => 32 x 10-6 (typical for IP routers)
• Accuracy level might decrease at each hop in clock distribution
© 2001, Cisco Systems, Inc. Network Architecture-202
Reference Clocks - II.Reference Clocks - II.
• Originally providing Stratum 1 clocks for each network element was far from being economical, even providing this service at multiple locations was too much demanding
– So clock distribution methods were developed to minimize the number of high accuracy clocks needed in the network
• Global Positioning System (GPS) includes Stratum 1 atomic clocks on the satellites
• Recently cheap GPS receivers make it possible to have a Stratum 1 time source at almost any place
– Less need for time synchronization network (might even go away in the future…)
© 2001, Cisco Systems, Inc. Network Architecture-203
Clock Distribution Methods - I.Clock Distribution Methods - I.
• External clock input might be used in case when all equipment is at the same location
– BITS = Building Integrated Timing Signal
• Uses an empty T1 or E1 framing to embed clock signal
• Root of the clock distribution tree
• Might be provided as a dedicated bus reaching into each rack in a CO environment
– BITS should be generated from a Stratum 1 clock
• Typically with a hot spare alternative source for fail-over
© 2001, Cisco Systems, Inc. Network Architecture-204
Clock Distribution Methods - II.
Clock Distribution Methods - II.
• Network elements not close to a BITS source should recover clock from the line
• Clock distribution should not have loops, so a tree distribution topology should be configured
• Typical carrier network element has Stratum 3 accuracy when running free
– By synchronization to the reference clock, this clock is running at the same rate as the reference clock (that is Stratum 1)
• Minimum requirement for any network element is 20 ppm (that is between Stratum 3 and Stratum 4)
© 2001, Cisco Systems, Inc. Network Architecture-205
Alternative Clock Sources - I.Alternative Clock Sources - I.
• If the trail to the reference clock source is lost, the network element still continues normal operation
– However, alarm might be generated
• After some time the clock might drift away so much, that bit errors would occur
• Some time is left for switching over to an alternative clock source
– The network element gets into a holdover state
– Requirement is to have less than 255 errors in 24 hours
© 2001, Cisco Systems, Inc. Network Architecture-206
Alternative Clock Sources - II.Alternative Clock Sources - II.
• A hierarchy of potential clock sources should be configured at each network element to achieve a high-availability operation
– Typically a maximum 3 alternative time reference sources might be configured
– Meaningful only if there are different paths to the alternative time reference sources
• If only one natural path exists to a single time reference source, then the path must be protected by automatic protection switching
– Requires some extra signaling to do it properly
– Called SPS = Synchronization Protection Switching
© 2001, Cisco Systems, Inc. Network Architecture-207
SummarySummary
• Identify the reference clock concept
• Describe clock distribution methods
• Describe the concept of using alternative clock sources
• Provide the basic design considerations for synchronization network design
© 2001, Cisco Systems, Inc. Network Architecture-208
Review QuestionsReview Questions
• What is the maximum allowed shift in frequency in a SDH network?
• What are the different methods of providing the master clock?
• What is the alternative to embedded clock distribution?
Synchronization Protection
Synchronization Protection
Section 4.3Section 4.3
© 2001, Cisco Systems, Inc. Network Architecture-210
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the basic concepts of synchronization
protection
• Describe the operational steps in synchronization protection
© 2001, Cisco Systems, Inc. Network Architecture-211
A
CE
BF
D
BITS
Synchronization Protection Basics
Synchronization Protection Basics
• Normal synchronization around a ring:
– Nodes B-F are line timed
– Node A is timed to an external reference
• In case of failure a new time source should be selected in a reasonable amount of time
• BER is increasing through time if synchronization is not restored
© 2001, Cisco Systems, Inc. Network Architecture-212
SPS Timing LoopsSPS Timing Loops
• SPS = Synchronization Protection Switching
• During a ring failure, simple reference switching would result in timing loops
A
CE
BF
D
BITS
Fiber Cut
Timing Loop
© 2001, Cisco Systems, Inc. Network Architecture-213
Operations – Normal FlowOperations – Normal Flow
• Synchronization messaging in normal operation
– S1 = Stratum 1 Traceable
– DU = Don’t Use
– HO = Holdover
A
CE
BF
D
BITS
S1
Synch Msg = S1
S1
S1S1
S1
S1
DU
DUDU
DU
DU
© 2001, Cisco Systems, Inc. Network Architecture-214
Operations – Fiber Cut - I.Operations – Fiber Cut - I.
• Node C goes into short term holdover
A
CE
BF
D
BITS
Fiber Cut
Node C inHoldover
HO
S1
S1
HO
HO
S1
DU
DUDU
HO
DUHO
© 2001, Cisco Systems, Inc. Network Architecture-215
Operations – Fiber Cut - II.Operations – Fiber Cut - II.
• Node F switches to timing from Node A
A
CE
BF
D
BITS
Fiber Cut
Node C inHoldover
HO
S1
S1
HO
HO
S1DU
DUDU
HO
DU
S1
© 2001, Cisco Systems, Inc. Network Architecture-216
Operations – Fiber Cut - III.Operations – Fiber Cut - III.
• Ring is reconfigured and all nodes are again synchronized to BITS
A
CE
BF
D
BITS
Fiber Cut
Node Ccomes outof Holdover
DU
S1
S1
DU
DU
S1DU
S1S1
S1
DU
S1
© 2001, Cisco Systems, Inc. Network Architecture-217
SummarySummary
• Identify the basic concepts of synchronization protection
• Describe the operational steps in synchronization protection
© 2001, Cisco Systems, Inc. Network Architecture-218
Review QuestionsReview Questions
• What kind of signaling is used to prevent timing loops?
• Does SPS work properly in a complex meshed network?
• How long is the Hold-over period in SPS?
SummarySummary
Information ResourcesInformation Resources
© 2001, Cisco Systems, Inc.
© 2001, Cisco Systems, Inc. Network Architecture-220
Remember...Remember...
• External timing: all signals transmitted from a node are synchronized to an external source received by that node; i.e. BITS timing source
• Line timing: all signals transmitted from a node are synchronized to one receive signal
• Loop timing: the transmit signal in a optical link, east or west, is synchronized to the received signal from the same optical link
• Through timing: the transmit signal in one direction of transmission around the ring is synchronized to the received signal from that same direction of transmission
© 2001, Cisco Systems, Inc. Network Architecture-221
Remember...Remember...
• All network elements should be able to trace back clock synchronization to a single reference clock
• Synchronization messaging: messaging procedure that avoids timing loops when protection switching the synchronization source on a ring
• Messaging is based on bits in the S1 byte in the MS Overhead
© 2001, Cisco Systems, Inc. Network Architecture-222
Remember...Remember...
• Synchronization protection switching is controlled by synchronization messages in bits 5-8 of the S1 byte in the SDH MS overhead, and is considered a MS switching function
• Synchronization protection switching is required for both BSHR/MS rings and USHR/P rings
• Short term holdover is defined as holdover during synchronization reconfiguration on the ring
© 2001, Cisco Systems, Inc. Network Architecture-223
QuestionsQuestions
?
© 2001, Cisco Systems, Inc. Network Architecture-224
SummarySummary
After completing this chapter, you should be able to perform the following tasks:• Identify the main requirements for time
synchronization
• Describe the main synchronization modes
• Describe the principles of network synchronization
• Describe the concept and operation of time synchronization protection
SONET versus SDHSONET versus SDH
Chapter 5Chapter 5
© 2001, Cisco Systems, Inc. Network Architecture-226
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks: • Relate SONET and SDH concepts to each other
• Translate between SONET and SDH terminology
• Compare SONET and SDH terminology
• Describe the internetworking principles between SONET and SDH
© 2001, Cisco Systems, Inc. Network Architecture-227
Standardization - I.Standardization - I.
• First: many proprietary solutions
• In 1984 ECSA (Exchange Carriers Standards Association) started on SONET
• SONET became an ANSI standard
–Tuned to carry US PDH payloads
• Later CCITT created SDH as a superset
–Tuned to carry European and international PDH payloads including E4 (140 Mbit/s)
© 2001, Cisco Systems, Inc. Network Architecture-228
1984 1985 1986 1987 1988
SONET/SDHStandardsApproved
ANSI ApprovesSYNTRAN
Divestiture
Exchange CarriersStandards Associate (ECSA)T1 Committee Formed
ANSI T1X1Approves
Project
Bellcore ProposedSONET PrinciplesTo ANSI T1X1
CCITT ExpressesInterest in SONET
British and JapaneseParticipation in T1X1
CCITT XVIIIBegins StudyGroup
CEPT ProposesMerged ANSI/CCITT
Standard
US T1X1 AcceptsModifications
SONET Concept Developed by Bellcore
Standardization - II.Standardization - II.
• More than 400 technical proposals
• Rate discussions AT&T vs. Bellcore
• International changes for byte/bit interleaving, frames, data rates
• Phase I, II, III, separate APS etc.
© 2001, Cisco Systems, Inc. Network Architecture-229
Abbrev.Bit Rate Signal Signal speed(Mbit/s) DS1 DS3 E1 E4 (Gbit/s)51.84 STS-1 28 1 STM-0 21 0
155.52 STS-3 84 3 STM-1 63 1622.08 STS-12 336 12 STM-4 252 4
2488.32 STS-48 1344 48 STM-16 1008 16 2.59953.28 STS-192 5376 192 STM-64 4032 64 1039813.1 STS-768 21504 768 STM-256 16128 256 40
ChannelsSONET SDH
Channels
Synchronous TDM HierarchySynchronous TDM Hierarchy
• SONET Synchronous Transport Signal
– STS-<n> electrical, OC-<n> optical
• SDH Synchronous Transport Module
– STM-<n>E electrical, STM-<n>O optical
© 2001, Cisco Systems, Inc. Network Architecture-230
Comparison of TechnologyComparison of Technology
• Both SONET and SDH use the same technology components
• All the differences might be implemented in software
• Still US based companies tend to be late in SDH implementations
–Mostly because of other customer environment related standards
• Privately SONET or SDH might be used
• Interfacing to public networks requires configuring the proper selection
© 2001, Cisco Systems, Inc. Network Architecture-231
Comparison of Hierarchy Comparison of Hierarchy
• Hierarchies aligned at 155 Mbit/s
ETSI PDH
2 8 34 140 Mbit/s
US PDH
1.5 6 45
T3
Mbit/s
SONET
VT1.5 VT6 OC-1 OC-12 OC-48 OC-192
52 155 622 2488 9953Mbit/s
OC-3
SDH
TU-12 TUG-2 AU-3 AU-4
STM-1 STM-4 STM-16 STM-64
© 2001, Cisco Systems, Inc. Network Architecture-232
Comparison of FramingComparison of Framing
• Same framing concept of using 9 rows
• STM-1 frame can be subdivided into 3 virtual STM-0 frames
–STM-0 frame compatible with STS-1 frame
• Multiplexing of STM and STS is the same
• Overhead byte interpretation is slightly different
–Based on different needs for PDH multiplexing and protection
© 2001, Cisco Systems, Inc. Network Architecture-233
Comparison of PayloadsComparison of Payloads
• Similar concepts, but significant differences in details of payload multiplexing
VT 1.5 VT 6 STS-1
(4)
7(1)
28 DS1s
3 STS-3
84 DS1s
OC-3
DS1
1.5 Mb/s
SONET SONET
(3)
VC-37VC-12 (1)
21 E1s
TUG 3 AUG
63 E1sE1
STM-1
2 Mb/s
SDHSDH
© 2001, Cisco Systems, Inc. Network Architecture-234
Comparison of Network Architectures
Comparison of Network Architectures
• Similar layered architecture
• Slightly different terminology
–Regenerator section (SDH) = section (SONET)
–Multiplex section (SDH) = line (SONET)
• SDH defines high- and low-order paths, too
© 2001, Cisco Systems, Inc. Network Architecture-235
Comparison of ProtectionComparison of Protection
• SONET APS schemes are almost the same as SDH MPS and SNCP schemes
• Operations are practically the same
–APS protocol is equivalent
• Terminology is different
–UPSR (SONET) = USHR/P (SDH)
–BLSR (SONET) = BSHR/L (SDH)
© 2001, Cisco Systems, Inc. Network Architecture-236
InternetworkingInternetworking
• Voice internetworking still requires conversion between μ-law and a-law
• Voice trunks can be accessed with a single step of demultiplexing
• SONET and SDH might carry each others PDH load, so the voice conversion point might be located flexibly anywhere inside the SONET or the SDH network
• Repacking PDH between SONET and SDH might be done in a single step by a single device
• Data internetworking is easy at STM-1 (STS-3) or higher since the payloads are the same size and structure
© 2001, Cisco Systems, Inc. Network Architecture-237
SummarySummary
• Relate SONET and SDH concepts to each other
• Translate between SONET and SDH terminology
• Compare SONET and SDH terminology
• Describe the internetworking principles between SONET and SDH
© 2001, Cisco Systems, Inc. Network Architecture-238
Review QuestionsReview Questions
• What is the major difference between SONET and SDH?
• Why does SONET start at a signaling rate of 51,84 Mbit/sec?
• Why does SDH start at a signaling rate of 155,52 Mbit/sec?
• What is the purpose of an STM-0 frame?
© 2001, Cisco Systems, Inc. Network Architecture-239
QuestionsQuestions
?
Network ManagementNetwork Management
Chapter 6Chapter 6
© 2001, Cisco Systems, Inc. Network Architecture-242
ObjectivesObjectives
Upon completion of this chapter, you will be able to perform the following tasks: • Describe the basic network management
functions needed in TDM networks
• Describe the architecture and main components of implementing network management solutions
© 2001, Cisco Systems, Inc. Network Architecture-243
AgendaAgenda
5.1 - Network Management Basics
5.2 - Network Management Internals
Summary, Information Resources
Network Management Basics
Network Management Basics
Section 5.1Section 5.1
© 2001, Cisco Systems, Inc. Network Architecture-245
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify the main operational tasks
• Describe OAM functions and layers
• Describe the in-band network management channels
© 2001, Cisco Systems, Inc. Network Architecture-246
Operational Tasks - I.Operational Tasks - I.
• Basic operational tasks:
– Protection
• Circuit recovery in milliseconds (so failure should not be detected by voice customers)
– Restoration
• Circuit recovery in seconds or minutes (done by manual configuration)
– Provisioning
• Allocation of capacity to preferred routes (according to certain time schedules)
• Configuration time is separated from activation time
© 2001, Cisco Systems, Inc. Network Architecture-247
Operational Tasks - II.Operational Tasks - II.
– Consolidation
• Moving traffic from unfilled bearers onto fewer bearers to reduce waste trunk capacity
– Grooming
• Sorting of different traffic types from mixed payloads into separate destinations for each type of traffic
© 2001, Cisco Systems, Inc. Network Architecture-248
OAM Functions and LayersOAM Functions and Layers
• Level 3 - Path
–Assembly and disassembly, cell delineation control
• Level 2 - Multiplex Section
–Loss of frame synchronization, degraded error performance
• Level 1 - Regenerator Section
–Loss of synchronization, signal quality degradation
© 2001, Cisco Systems, Inc. Network Architecture-249
Data Communication Channel (DCC)
Data Communication Channel (DCC)
• DCC is a 192 kb/s in-band channel to facilitate communication between all Network Elements (NE) in a network
– Remote login, alarms reporting, software download, provisioning
DCN
SDHDCC
ManagementServer
OSS
Network Operations Center
ADM
ADM
ADM
GNEGNEGNEGNE
ADM
GNEGNEGNEGNEGNEGNEGNEGNE
ManagementClients
SDHDCC
SDHDCC
ManagementClient
Alarm and Event
Forwarding
TDM
TDM
TDM
TDM
TDM
© 2001, Cisco Systems, Inc. Network Architecture-250
SummarySummary
• Identify the main operational tasks
• Describe OAM functions and layers
• Describe the in-band network management channels
© 2001, Cisco Systems, Inc. Network Architecture-251
Review QuestionsReview Questions
• What are the operational tasks of a Network Management System?
• What are the OAM functions needed for?
• What is the DCC channel used for?
Network Management Internals
Network Management Internals
Section 5.2Section 5.2
© 2001, Cisco Systems, Inc. Network Architecture-253
ObjectivesObjectives
Upon completion of this section, you will be able to perform the following tasks:• Identify main requirements for network
element management support
• Describe the typical management interfaces used to access network elements
• List management functions and features typically supported by network elements
© 2001, Cisco Systems, Inc. Network Architecture-254
Network Element Requirements
Network Element Requirements
• All network elements should support various management interfaces
– Local (craft terminal using TL1)
– Remote (TMN DCN model)
• All network elements should support certain management function areas
– FCAPS (fault, configuration, accounting, performance, security)
• Since original payload is voice, a separate management network is needed for remote management operations
– Data Communications Network (DCN)
© 2001, Cisco Systems, Inc. Network Architecture-255
Management Interfaces - I.Management Interfaces - I.
OS
DCN
WS
TMN
NE QA
F
XQ3/X/F
Q3 Q3
TMN Model as of M.3010
Reference pointReference point
© 2001, Cisco Systems, Inc. Network Architecture-256
Management Interfaces - II.Management Interfaces - II.
• CMIP over OSI
– TMN Manager/Agent communication standard
Agent
Mgr.
Agent
Element ManagerLayer
Network Element Layer
CMIP/OSI
© 2001, Cisco Systems, Inc. Network Architecture-257
Configuration Management Support
Configuration Management Support
• Installation
–Setting up basic parameters (identification, management access and authorization, etc.)
–Activating and testing hardware
• Provisioning
– Implementing add-drop commands
• Status and control
–APS switching messages for manual control
© 2001, Cisco Systems, Inc. Network Architecture-258
Performance Monitoring Support
Performance Monitoring Support
• Separate handling of section, line, path termination
• Performance data collection
– Error counts: B1, B2, B3
– Historical data presentations
• Threshold settings
• Threshold crossing alerts (TCA)
– For B1, B2, B3
• Performance data reporting
• Accuracy and resolution should be considered
– Typically 15-minute interval is the basis
• Monitoring should be done even in trouble conditions
© 2001, Cisco Systems, Inc. Network Architecture-259
Fault Management SupportFault Management Support
• Alarms surveillance
– Reactive mechanisms
– Autonomous and requested alarms
• Testing
• Alarm configuration
Alarm Hierarchy
LOS |
LOF |
LAIS => LRDI | |
PAIS => PRDI |
LOP
© 2001, Cisco Systems, Inc. Network Architecture-260
Accounting SupportAccounting Support
• In voice networks accounting support is implemented in toll switches
• In data networks accounting is supported by data link layer or network layer traffic data collection
• In general, neither voice networks, nor data networks transport on top of SDH require accounting support
• Transport network billing is not based on traffic, since bandwidth is allocated in fixed amounts
– Billing records might be generated by the OSS controlling the provisioning of paths
• Typically no requirement for accounting support in SDH network elements
© 2001, Cisco Systems, Inc. Network Architecture-261
SummarySummary
• Identify main requirements for network element management support
• Describe the typical management interfaces used to access network elements
• List management functions and features typically supported by network elements
© 2001, Cisco Systems, Inc. Network Architecture-262
Review QuestionsReview Questions
• What network management protocol is mainly used in telecommunication?
• What three functions does Fault Management support?
SummarySummary
Information ResourcesInformation Resources
© 2001, Cisco Systems, Inc. Network Architecture-264
QuestionsQuestions
?
© 2001, Cisco Systems, Inc. Network Architecture-265
SummarySummary
After completing this chapter, you should be able to perform the following tasks:• Describe the basic network management
functions needed in TDM networks
• Describe the architecture and main components of implementing network management solutions
© 2001, Cisco Systems, Inc. Network Management-266