Carrier Ethernet Synchronization
Technologies and Standards
DataEdge, Dublin, May 19, 2010
PAGE 2© COPYRIGHT SYMMETRICOM (2009)
Overview
What and Where of Synchronization
Synchronization Delivery Strategies
o Synchronous Ethernet
o IEEE 1588-2008
Selecting a Synchronization Method
Network Impairments
Deployment Guidelines
PAGE 3© COPYRIGHT SYMMETRICOM (2009)
Making It Happen, The Real World
Mobile broadband use will double every
year through 2013*.
► 10M new IP connections will be made
to base stations in the next 5 years,
► The mobile sector will drive the market
(products & practices).
Pure packet deployment has been slow
… driven by concerns for voice quality.
Synchronization challenges include:
► Selecting the strategy
► Knowing the goals
► Engineering for cost, performance &
simplicity
* Cisco® Visual Networking Index (VNI) Mobile Forecast
** Source. Infonetics
*** Source. Heavy Reading
0
1
2
3
4
5
6
CY'07 CY'08 CY'09 CY'10 CY'11 CY'12 CY'13
Mil
lio
ns
**BaseStation Backhaul Connections
Non-IP Connections IP Backhaul Connections
***Live Packet Backhaul Deployments
PAGE 4© COPYRIGHT SYMMETRICOM (2009)
MEF: Where is Sync Required?
►MEF 2 Requirements and Framework for Ethernet Service Protection
►MEF 3 Circuit Emulation Service Definitions, Framework and Requirements in MEN
►MEF 4 Metro Ethernet Network Architecture Framework Part 1: Generic Framework
►MEF 6.1* Metro Ethernet Services Definitions Phase 2
►MEF 7 EMS-NMS Information Model
►MEF 8 Implementation Agreement for the Emulation of PDH Circuits over MEN
►MEF 9 Abstract Test Suite for Ethernet Services at the UNI
►MEF 10.1* Ethernet Services Attributes Phase 2*
►MEF 11 User Network Interface (UNI) Requirements and Framework
►MEF 12 Metro Ethernet Network Architecture Framework Part 2: Ethernet Services Layer
►MEF 13 User Network Interface (UNI) Type 1 Implementation Agreement
►MEF 14 Abstract Test Suite for Traffic Management Phase 1
►MEF 15 Requirements for Management of Metro Ethernet Phase 1 Network Elements
►MEF 16 Ethernet Local Management Interface
►MEF 17 Service OAM Framework and Requirements
►MEF 18 Abstract Test Suite for Circuit Emulation Services
►MEF 19 Abstract Test Suite for UNI Type 1
►MEF 20 User Network Interface (UNI) Type 2 Implementation Agreement
►MEF 21 Abstract Test Suite for UNI Type 2 Part 1: Link OAM
►MEF 22 Mobile Backhaul Implementation Agreement
* MEF 10 .1 replaces and enhances MEF 10 Ethernet Services Definition Phase 1 and replaced MEF 1 and MEF 5. MEF 6.1 replaced MEF 6.
PAGE 5© COPYRIGHT SYMMETRICOM (2009)
MEF: Where is Sync Required?
►MEF 2 Requirements and Framework for Ethernet Service Protection
►MEF 3 Circuit Emulation Service Definitions, Framework and
Requirements in Metro Ethernet Networks►MEF 4 Metro Ethernet Network Architecture Framework Part 1: Generic Framework
►MEF 6.1 Metro Ethernet Services Definitions Phase 2
►MEF 7 EMS-NMS Information Model
►MEF 8 Implementation Agreement for the Emulation of PDH
Circuits over Metro Ethernet Networks ►MEF 9 Abstract Test Suite for Ethernet Services at the UNI
►MEF 10.1 Ethernet Services Attributes Phase 2*
►MEF 11 User Network Interface (UNI) Requirements and Framework
►MEF 12S Metro Ethernet Network Architecture Framework Part 2: Ethernet Services Layer
►MEF 13 User Network Interface (UNI) Type 1 Implementation Agreement
►MEF 14 Abstract Test Suite for Traffic Management Phase 1
►MEF 15 Requirements for Management of Metro Ethernet Phase 1 Network Elements
►MEF 16 Ethernet Local Management Interface
►MEF 17 Service OAM Framework and Requirements
►MEF 18 Abstract Test Suite for Circuit Emulation Services►MEF 19 Abstract Test Suite for UNI Type 1
►MEF 20 User Network Interface (UNI) Type 2 Implementation Agreement
►MEF 21 Abstract Test Suite for UNI Type 2 Part 1: Link OAM
►MEF 22 Mobile Backhaul Implementation Agreement
* MEF 10 .1 replaces and enhances MEF 10 Ethernet Services Definition Phase 1 and replaced MEF 1 and MEF 5. MEF 6.1 replaced MEF 6.
PAGE 6© COPYRIGHT SYMMETRICOM (2009)
Carrier Ethernet Use cases for MBH:
Packet Offload or Full Ethernet
Packet Offload / Carrier Ethernet – Use Case 1
Carrier Ethernet
Network
Legacy Network
Non-Ethernet I/F
UNI
Non-Ethernet I/F
UNIGIWFRAN BS RAN AggGIWF
Carrier Ethernet Network
U
N
I
U
N
I
RAN BS RAN Agg
Full Ethernet – Use Case 2
BOTH CASES NEED SYNCH
PAGE 7© COPYRIGHT SYMMETRICOM (2009)
MEF 8: Carrier Ethernet Private
Line (EPL)
Designed for TDM Replacement
Point-to-Point
EVC
Carrier Ethernet Network
CE
CE
CE
ISP
POP
Data Center Service
Internet
PAGE 8© COPYRIGHT SYMMETRICOM (2009)
MEF 8: E-Tree (EP-Tree or EVP-
Tree)
A
B
C
EVC1
Root
Leaves
Efficient use of ISP router port
One subnet to configure on ISP router
Simple configuration
A, B, C can’t see each other’s traffic
Some limits on routing protocols used
Designed for mobile backhaul
and triple-play infrastructure
PAGE 9© COPYRIGHT SYMMETRICOM (2009)
at the Wireless Air Interface …
Variations in the Radio frequency of
cellular base-stations affect the ability of
the system to hand-off calls without
interruption.
F1+ F
F1
T1 T2
+/- 50ppb
+/- 50ppb
Time
Mobile cannot lock to
BTS2
and call is dropped
BTS2 drifts outside 50ppb window
BTS 1
BTS 2
Mobility Standard Frequency Time/Phase
CDMA2000 50 ppb Range: <3µs to <10µs
GSM 50 ppb
WCDMA 50 ppb
TD-SCDMA 50 ppb 3µs inter-cell phase ∆
LTE (FDD) 50 ppb
LTE (TDD) 50 ppb *3µs inter-cell phase ∆
LTE MBMS 50 ppb *5µs inter-cell phase ∆
WiMAX (TDD) 50 ppb inter BTS Typically 1 - 1.5 µs
Backhaul 1 to 16 ppb
* Standards being consolidated 50 ppb or 5 x 10-8
MBH Sync Requirements
PAGE 10© COPYRIGHT SYMMETRICOM (2009)
Mobile Back-Haul (MBH)
► First phase :
► Synchronization is delivered
1 outside of the Ethernet transport network
2 using a packet based method
(IEEE1588 PTP standard, or proprietary solutions)
► Subsequent (future) phases:
► Other synchronization methods
► Synchronous Ethernet
MEF 22 Mobile Backhaul Implementation Agreement
Approved as an official MEF Specification in January 2009.
PAGE 11© COPYRIGHT SYMMETRICOM (2009)
NGN Synchronization Standards
ITU-T Frequency Time
Definitions-Terminology G.8260 G.8260
Basics G.8261 (G.pactiming) G.8271
Network Jitter-Wander G.8261
Network PDV G.8261.1 G.8271.1
Clock-SyncE G.8262
Clock-Packet G.8263 G.8272
Methods-SyncE G.8264
Methods-Packet G.8265 G.8275
PTP Telecom Profile G.8265.1 G.8275.1
PTP Telecom Profile 2 G.8265.2
IEEE 1588-2008IEEE Standard for a Precision Clock Synchronization Protocol
for networked measurement & control systems.
MEF MEF 3, MEF 8, MEF 18, MEF 22 MEF Standards that Refer to
or Require Synchronization.
PAGE 12© COPYRIGHT SYMMETRICOM (2009)
Overview
What and Where of Synchronization
Synchronization Delivery Strategies
o Synchronous Ethernet
o IEEE 1588-2008
Selecting a Synchronization Method
Network Impairments
Deployment Guidelines
PAGE 13© COPYRIGHT SYMMETRICOM (2009)
Sync Delivery Strategies
Synchronization Strategies
E1/SDH Hybrid
Shorter term strategy based on use of legacy systems (higher
OPEX). Bandwidth & 4G/LTE limit long term suitability.
Adaptive Clock Recovery
A vendor specific book-end solution used to support TDMoIP
services. ACR methods are being superseded by IEEE 1588.
GPS Radio at Base Stations
Good performance, supporting wide range of applications. Cost
and autonomy define deployment adoption.
Synchronous Ethernet
An end-to-end solution that depends on the uninterrupted
SyncE deployment.
IEEE 1588-2008
A standards based solution with the flexibility, lowest cost, and
high rate of adoption (driven by mobile sector).
E1/SDH
Packet
ACR
Packet
SyncE
Packet
1588-v2
Packet
PAGE 14© COPYRIGHT SYMMETRICOM (2009)
Synchronous Ethernet
► Proposed in September 2004 to use the physical layer to transport a
frequency reference in order to
o Provide G.811 traceability to applications
o Provide a timing quality independent of traffic payload
► It was decided to align SyncE on SDH
o to avoid defining a new synchronous hierarchy
o To allow a mix of SDH and SyncE NEs in the G.803 reference chain
► Defined by 3 ITU-T SG15 recommendations (consented in Feb 2008)
o G.8261 for architecture and network limits
o G.8262 for the definition of the clock
o G.8264 for the definition of the SSM
PAGE 15© COPYRIGHT SYMMETRICOM (2009)
Synchronous Ethernet
Architecture
► In order to provide interworking between SyncE and SDH
o A chain of 20 SDH NEs must be replaceable by 20 SyncE NEs
o A chain of 20 NEs can mix SDH and SYNCE NEs
o An NE can be equipped with both SDH and SyncE ports
► The SyncE NE
o Must have a clock compatible with SDH/SONET
o Recovers timing from a synchronous Ethernet signal, with an SSM
o Must be able to recover the data from an Ethernet signal
o Must be able to provide traceablity via SSM
PAGE 16© COPYRIGHT SYMMETRICOM (2009)
SyncE clock – G.8262
► Compliance with SDH implies that SyncE clocks are based on G.813
► Jitter is related with clock recovery
► Wander is due to noise accumulation in a chain of NE/clocks.
► Frequency pull-in range
o Must be 100 ppm on the port so that data of legacy Eth can be
processed
o Must be 4.6 ppm at clock input to comply with SDH clocks
100 ppm
TXTX
RXRX
4.6 ppm
TXTX
RXRX
TX
RX
TXTX
RXRX
Ext.Sync
Inaccurate
100 ppm
4.6 ppm
TX
RX
Accurate
SyncE Switch Asynchronous
Switch
Async Switch
SyncE Switch
PAGE 17© COPYRIGHT SYMMETRICOM (2009)
SSM Transport – G.8264
► The SSM is transported in the ESMC Ethernet Synchronization
Messaging Channel
► Two types of messages are transmitted
o An event message sent immediately in case of SSM change
o A heartbeat message
Sent at a rate of about 1 Hz
No message for 5 seconds means ESMC failure
► Quality Level data is mapped into a TLV format
o Future information might be mapped according to TLV format
PAGE 18© COPYRIGHT SYMMETRICOM (2009)
IEEE 1588 Overview
IEEE 1588-2008 …
► Is a protocol definition, not a product,
► is known as Precision Time Protocol (PTP)
► -2008 is also referred to as version 2
(with the Telecom Profile)
► is the second version of a mature IEEE
standard,
► defines how to transfer precise time over
networks. It does not define how to
recover frequency or high precision time of
day.
► The challenge is to convert packets to
traceable Time & Frequency, and cost
effectively.
PAGE 19© COPYRIGHT SYMMETRICOM (2009)
1588 – Precision Time Protocol
• Each “event message” flow (sync,
delay_req) is a packet timing signal
• Master frequency determined by comparison
of timestamps in the event message flows
• e.g. comparison of t1 to t2 over multiple sync
messages, or t3 to t4 in delay_req messages
• Time offset calculation requires all four
timestamps:
• Client time offset = (t1 – t2) + (t4 – t3)
• assumes symmetrical delays
(i.e. the forward path delay is equal to the
reverse path delay)
• Time offset error = fwd. delay – rev. delay
2
2
Master Clock Time Slave Clock Time
Data atSlave Clock
Follow_Up messagecontaining true value of t1
Delay_Resp message
containing value of t4
Sync message
Delay_Req message
timet1, t2, t3, t4
t1, t2
t2
t1, t2, t3
t2
t3
t1
t4
PAGE 21© COPYRIGHT SYMMETRICOM (2009)
The PTP Protocol – Main Features
21
Rate of Delay_req/Delay_resp Transactions can be adjusted to cope with
Target frequency/time accuracy
Network conditions
64 transactions/sec/client is a good, practical value
30 to 128 transactions/sec range
PTP supports Unicast and Multicast
Unicast: more flexible, supported by all networks
Multicast: required later with larger numbers of clients
e.g., Femtocells
When core/access networks support it
Boundary Clocks
BC serving a sub-network can be sync’d to a remote St1 server
No need for a local Stratum1 reference
PAGE 22© COPYRIGHT SYMMETRICOM (2009)
The PTP Protocol – Main Features
► Boundary Clocks
► Acts as a slave clock at the port that connects to the grand master, and as a
master to all other ports
► Therefore, it isolates the “down stream” clocks from any delays and jitter within the
switch
► Creates master-slave synchronization hierarchy
Grandmaster
S
Slave
Clock
Boundary
Clock
Transparent
Clock
Ordinary
Clock
S
M M
M
S
M
S
Ordinary
Clock
S
Ordinary
Clock
S
Slave
Clock
PAGE 23© COPYRIGHT SYMMETRICOM (2009)
The PTP Protocol – Main Features
► End-to-end transparent clock► Alternative (simpler & cheaper implementation) to boundary clocks
► Switch/Router modifies time stamps in packets to adjust for delays introduced by Switch/Router itself
► Residence time is accumulated in special field (correction field) of PTP message event or associated
Follow_Up message
► Peer-to-peer transparent clock► Similar to end-to-end transparent clock but computes link delay in addition of residence time
PHY PHY
MACMAC
PORT1 PORT2
Switch1
PHY PHY
MACMAC
PORT2
Switch2
PORT1
Link time correction
Residence time correction
Residence time correction
PAGE 24© COPYRIGHT SYMMETRICOM (2009)
Overview
What and Where of Synchronization
Synchronization Delivery Strategies
o Synchronous Ethernet
o IEEE 1588-2008
Selecting a Synchronization Method
Network Impairments
Deployment Guidelines
PAGE 25© COPYRIGHT SYMMETRICOM (2009)
Selecting The Sync Strategy
► TDM circuits are the most widely used
method today.
► Will still be used beyond 2012
► SyncE & IEEE 1588 are standards based
► Supports interoperability
► Addresses multiple applications
► Cost effective & reached viability
► Can be used together
► Adaptive Clock Recovery is proprietary &
a bookend offer.
► No inter-operability
► Multiple parallel systems
► High engineering, management &
maintenance effort
► GPS & other methods will be used on
limited scale.
Source. Heavy Reading
PAGE 26© COPYRIGHT SYMMETRICOM (2009)
Defining The Goals
Select the frequency goals:
► ITU-T G.823 sync mask
► Vodafone Lab Acceptance Mask
(G.823 sync mask + 1ppb)
► ITU-T G.823 traffic mask
► 1 - 15ppb (short & long term)
► Other proprietary masks
Define the Absolute Time/Phase goals:
► 3 µS absolute phase accuracy
► 5 µS absolute phase accuracy
► Other goals
What is the Time of Day interface?
FDD Objectives Time & Phase Objectives
0.1 1 10 100 1000 10000 100000
Observation Interval (sec)
100
1000
10000
MTIE
(nsec)
0.1 7.3 20 2000 100000
732732
20002000
5330
PAGE 27© COPYRIGHT SYMMETRICOM (2009)
SyncE or IEEE 1588-2008
IEEE1588 needed when:
► Applications need time/phase
► Applications with leased services (no end-end SyncE path assurance)
► Transport other than switched Ethernet
Attribute IEEE 1588 SyncE
Capability Frequency, Time Frequency
Layer UDP/IP or Layer 2 Physical
Distribution In-band 1588 Packets Physical layer
Schema Point to multi-point Point to point
Distribution In-band 1588 Packets Physical layer
Transport MediaNative Ethernet, xDSL, Microwave
Native Ethernet
Inter-Operability
Standards based Grandmaster & slave. Independent of intermediate nodes.
Standard based SyncE switches only
Relevant Standards IEEE 1588, ITU G.8264 ITU G.8261/2/4
PAGE 28© COPYRIGHT SYMMETRICOM (2009)
Overview
What and Where of Synchronization
Synchronization Delivery Strategies
o Synchronous Ethernet
o IEEE 1588-2008
Selecting a Synchronization Method
Network Impairments
Deployment Guidelines
PAGE 29© COPYRIGHT SYMMETRICOM (2009)29 19/05/2010
Packet Delay Variation
Packet
Environment
FIFO BuffersVoice
Video
Data
Voice
Video
Data
Main Delay Variation Causes
Waiting time jitter in network elements
Routers/switches congestion
Extended packet loss, Network outages/re-routing: may cause holdover from
lack of information
Note: absolute delay, even high, is not a problem for sync technologies
PAGE 30© COPYRIGHT SYMMETRICOM (2009)
Class of Service Traffic Separation
► MEF provides service mapping guidelines for the number of CoS classes to use
► Bundles traffic types into limited number of CoS classes
► Describes CoS class performance requirements
Service
Class Name
Example of Generic Traffic Classes mapping into CoS
4 CoS Model 3 CoS Model 2 CoS Model
Very High
(H+)
Synchronization - -
High (H) Conversational,
Signaling and
Control
Conversational and
Synchronization,
Signaling and Control
Conversational and
Synchronization,
Signaling and Control,
Streaming
Medium (M) Streaming Streaming -
Low (L) Interactive and
Background
Interactive and
Background
Interactive and
Background
PAGE 31© COPYRIGHT SYMMETRICOM (2009) 19/05/2010
CoS/QoS- Priorities
► Even with priority schemes packet delay variation can be significant
Large Low priority Packet 1000 Bytes+
High priority Packet
At 100 Mbit/s 1000 byte packet = 8 x 1000 / 100 x 106 = 80 s
At 10 Mbit/s 1000 byte packet = 8 x 1000 / 10 x 106 = 0.8ms
PAGE 32© COPYRIGHT SYMMETRICOM (2009)
Typical PDV Profile
32
Minimum Delay
Packets
PDV Tail
Distribution
PAGE 33© COPYRIGHT SYMMETRICOM (2009)
Packet Network Characterization
Key characteristics:
• variance of minimum delay
• frequency of packets with minimum delay
10 switches, 20% load
10 switches, 40% load 10 switches, 80% load
10 switches, 60% load
Packets experiencing minimum delay
PAGE 34© COPYRIGHT SYMMETRICOM (2009)
Sample Field Trial Result
Live deployed network in Europe
Sync was tested over MPLS-over-SDH, 2 weeks
Moderately loaded network ring (7 hops in one direction, 15 hops in the other)
TP500 Frequency ~0.1 ppb most of the time, worst case performance over
two weeks shown above, ~0.3 ppb
PAGE 35© COPYRIGHT SYMMETRICOM (2009)
Sample Field Trial – MTIE
35Symmetricom Confidential
G.823 traffic
15 ppb
G.823 1 ppb
TP500
Same live network
Meets G.823 Sync Mask + 1 ppb with margin
PAGE 36© COPYRIGHT SYMMETRICOM (2009)
SHDSL Field Trial: 0.26ppb
PAGE 37© COPYRIGHT SYMMETRICOM (2009)
G.8261 Test Case 12: Description
Test case 12 models the “Static” Packet load.
Test Case 12 must use the following network conditions:
•Network disturbance load with 80% for the forward direction
(Server to Client)
•20% in the reverse direction (Client to Server) for 1 hour
•The test measurements should start after the clock recovery
is in a stable condition.
PAGE 38© COPYRIGHT SYMMETRICOM (2009)
G.8261 Test Case 12: Phase
PAGE 39© COPYRIGHT SYMMETRICOM (2009)
Other Freq+Phase Performance
► 10 hops, G.8261 traffic type and load variation
► Using carrier grade routers/switches► Pass = pass G.823PDH (sync) mask and <=1us phase accuracy
G.8261 Test
Case
Description Duration Result Comments
Test Case 13 Large, sudden
changes in traffic
load
6 hours Pass 2nd hardest test
Test Case 14 Slow, steady
traffic ramp up
and down
24 hours Pass Hardest Test
Test Case 17 Network failures
causing routing
changes with
impairment
2 hours Pass
PAGE 40© COPYRIGHT SYMMETRICOM (2009)
Overview
What and Where of Synchronization
Synchronization Delivery Strategies
o Synchronous Ethernet
o IEEE 1588-2008
Selecting a Synchronization Method
Network Impairments
Deployment Guidelines
PAGE 41© COPYRIGHT SYMMETRICOM (2009) 41
Empirical Behaviour
Number of switches
2 4 6 8 10
Limit of operational area
Varies with:
Application requirements
Type of switches
Traffic loading patterns
Slave performance
Local oscillator stability
clock stability compliant with application
clock stability non-compliant with application
100%
80%
60%
40%
20%
0%
Tra
ffic
lo
ad
on
netw
ork
► Clock stability, showing dependence on network size and traffic load
► Green Zone expanding
► 5 nodes met under any conditions
► 10 nodes met under most network configurations
► Focussing on 20 nodes
PAGE 42© COPYRIGHT SYMMETRICOM (2009) 42
Packet Sync Planning Strategy
► Step 1: Identify PTP slave locations
► Step 2: Identify suitable locations for PTP Grand Masters► Masters should be distributed towards the edge of the network
► Rule of thumb: For minimum dependency on traffic load, the PTP Master should be no more than 8/10 switches from the PTP Slave
► Step 3: Check that► Grand Master capacity constraints are not exceeded
► The “8/10 switch distance rule” is not violated, or that the traffic load is appropriate to the network span
► Step 4: Field trial – measure performance on critical links► Monitor TIE, MTIE, TDEV of output timing signals
► Also monitor PDV of packet network to verify suitability for timing distribution
► Step 5: Ongoing monitoring of critical or selected links to ensure synchronization quality is maintained in operation
PAGE 43© COPYRIGHT SYMMETRICOM (2009) 43
Redundancy Strategy
► Redundancy Strategy
► Separate Grand Masters, or built-in redundancy?
► Best Master Clock Algorithm, or manual configuration?
► BMCA requires multicast message distribution
► BMCA may elect a grandmaster that is not close to the slave
► Unicast slaves are configured with the correct master address
► Unicast slaves can switch to an alternate master in the event of a master failure
► Symmetricom product redundancy features
► TP5000 has redundant power and redundant clock cards
► Multiple PackeTime blades can be placed in an SSU shelf to give redundancy
PAGE 44© COPYRIGHT SYMMETRICOM (2009) 44
Security
► A PTP slave needs to be able to trust that timing
messages:
► Come from the correct master
► Have not been tampered with in transmission
► IEEE1588-2008 defines an experimental security protocol
► This is not widely implemented at present
► Network-based security methods
► Use VLANs to prevent distribution of timing messages outside of the
defined VLAN
► In a Metro Ethernet network, use E-Line or E-LAN services
► Similar to VLANs, running over a public Metro Ethernet network
► In an MPLS network, use pseudo-wires
► Symmetricom recommend the use of network-based
security
PAGE 45© COPYRIGHT SYMMETRICOM (2009) 45
Multicast vs. Unicast
► Unicast facilitates the use of distributed masters
► Allows easier planning of the synchronization network
► Redundancy strategy can be carefully managed
► Unicast packets propagate uniformly through the network
► Multicast requires packet replication at each network element – may add
variable delay
► Upstream multicast often not supported in telecom networks
► Symmetricom recommend use of unicast transmission in telecom
synchronization networks
PAGE 46© COPYRIGHT SYMMETRICOM (2009) 46
Frequency of Timing Packets
► Frequency required is dependent on several factors
► Amount of noise in the network
► Local oscillator stability
► Efficiency of clock servo algorithm
► Doubling number of timing packets does not double the
performance of the system or the reach of the network
► Better to manage traffic load than increase timing message frequency
► PTP slave determines the message rate required
► Recommended settings for the TP500 PTP slave:
► 2 announce messages per second
► 64 sync messages per second
► 64 delay_request messages per second
PAGE 47© COPYRIGHT SYMMETRICOM (2009) 47
Quality of Service
► Use simplest QoS techniques, where available
► In general, switches/routers optimized for maximum throughput with
minimum intervention
► Example: rate metering for bandwidth consumption requires
computational effort, which causes delay
► Depends heavily on implementation technique
► Symmetricom recommended traffic classes:
► Diffserv Expedited Forwarding (EF) Class
► IEEE 802.1 p-bit marking of 5 or above
► UMTS conversational class
(3GPP TS23.107, normally mapped to p-bit = 5)
PAGE 48© COPYRIGHT SYMMETRICOM (2009) 48
Telecom Profile
► “Telecom Profile” for PTPv2 under development in ITU-T Synchronization Group► Set of options and parameters for telecom usage, to ensure
interoperability of PTP equipment
► Likely to consist of separate profiles for frequency and time synchronization
► De-facto understanding of telecom profile used in inter-operability trials► Unicast-only operation
► PTPv2 short messages, running over IPv4/UDP/Ethernet
► Two-way operation (includes delay_request/response)
► Manual configuration (no Best Master Clock Algorithm)
► No on-path support (boundary clocks/transparent clocks)
► No encryption or authentication support
► De-facto profile supported by Symmetricom products, as will future profiles to be defined by ITU-T
Thank You!