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TRANSCRIPT
© Dr. Z. Sun
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ATM and B-ISDN
Dr. Zhili SUNUniversity of Surrey
GuildfordSurrey
GU2 7XHTel: 01483 68 9493Fax: 01483 68 6011
Email: [email protected]
Components of DATA and INTERNET NETWORKING MSc MODULE
(EEM.din, Linked EE4.din)
ATM and B-ISDN
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ATM and B-ISDN
Table of Contents
1. ATM technology2. Quality of Service (QoS) 3. Traffic Control and Management4. Traffic Policing and Shaping Algorithms5. Recommended Texts
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ATM and B-ISDN
Aims
This lecture component is developed as part of the course moduleto provide you with information on advanced topics in ATM and Broadband Communications Networks and Technology.
This component covers a range of topics that provides you with acomprehensive view of Asynchronous Transfer Mode (ATM) and Broadband Integrated Service Digital Networks (B-ISDN) technology. The topics include review of ATM, ATM Standard, ATM switches, Traffic control, ATM networks, and Broadband services and applications.
If you have any comment or suggestion on this component, you are welcome to send it to me.
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ATM and B-ISDN
1. ATM Technology
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ATM and B-ISDN
ATM and B-ISDN
■ ITU-T definition of Broadband: • A service or system requiring transmission channels capable
of supporting rates greater than the primary rate.
■ Relationship Between ATM and B-ISDN• ATM evolved from the standardization efforts for B-ISDN. • ATM is the technology upon which B-ISDN is based.
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ATM and B-ISDN
ATM Technology
■ Cell Switching • 53 bytes cells• 48 payload and 5 byte header
■ Negotiated Service Contract• Connection Oriented • end-to-end Quality of Services.
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Principle of ATM
■ cell-based transfer mode • this means that information from the source is transferred as
fixed-length cells
Head
5 Octets
Payload
48 Octets
Why 53 bytes?
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Why fixed size 53 bytes?
■ Switching efficiency■ Transmission Efficiency = Linfo/(Linfo + Loverhead)■ Process Delay Factor = Dinfo/(Doverhead + Dinfo)
■ Europe (32) and US (64) due to echo cancellors
Payload
Overhead%
9.43%
48 bytes0
Delay ms
4
64 bytesPayload0
8
32
@64kbit/s
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ATM and B-ISDN
ATM cell stream
No blank space between cells
ATM cell
ATM cell-stream
unassigned cell
source 1
source 2
source 3
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ATM and B-ISDN
Head Structure at UNI and NNI Interfaces
GFC
CLPPTVCI
VCI
VPI
VPI VCI
HEC
1 2 3 4 5 6 7 8
1
2
3
4
5
at the UNI
CLPPTVCI
VCI
VPI
VPI VCI
HEC
1 2 3 4 5 6 7 8
at the NNI
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ATM and B-ISDN
VPs and VCs
Physical LayerVirtual Path (VP)
Virtual Channel (VC)
Each VP within the Physical Layer has itsown distinct VPI; each VC within a VP has itsown distinct VCI
■ VCs and VPs are an important property of ATM
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ATM and B-ISDN
Hierarchy of the ATM transport Network
Transmission Path Level
Digital Section Level
Regenerator Section Level
Physical Layer
ATM Layer
Virtual Path Level
Virtual Channel
Higher Layer (AAL)
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VC & VP Switching
VC switch
Endpointof VPC
VP switch
VC and VP switching VP switching
VP switch
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ATM Routeing and Header Translation
14
22
32
43
in out
76
54
66
87
a
b
c
d
w
x
y
z
Switchingfabric
port in Headera 1a 4b 2c 3c 2d 4d 3
port out Headerx 5w 6y 6z 8x 4w 7z 7
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ATM and B-ISDN
B-ISDN ATM Adaptation Layer (AAL) Service Classification(362)
Timing relationBitrate
Connectionmode
Class A Class B Class C Class D
required not required
constant variable
connection-oriented connection-less
Examples: A - Circuit emulation, CBR VideoB - VBR video and audioC - CO data transferD - CL data transfer
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ATM and B-ISDN
B-ISDN ATM Adaptation Layer (AAL) Types (363)
■ AAL 1 for Class A■ AAL 2 for Class B■ AAL 3/4 for Class C & D■ AAL 5 for Class C & D
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ATM and B-ISDN
AAL1 for Class A
Header functions include:
• SN - Sequence Number (Lost cell detect: used by Adaptive Clock Method), CSI - Convergence sublayer indication (0=no pointer, 1=pointer), SNP - Sequence Number Protection by CRC
• Byte alignment: allows channelise circuit emulation, e.g.,channelised DS 1
• Time stamp: used for end-to-end clock synchronisation, e.g., Synchronous Residual Time Stamp method
Payload
4 bits 47 or 46 bytes
SNPCS
I
SN
1 3 bits
Pointer(optional)
8 bits
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AAL2 for Class B
SN - Sequence Number, IT - Information Type
LI - Length Indicator, CRC - Cyclic Redundancy Check
PayloadIT
48 bytes
SN CRCLI
1 byte 2 bytes
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ATM and B-ISDN
AAL3/4 for Class C&D
44 bytes of data per cellST - Segment Type (COM,BOM,EOM,SSM)LI - Length Indicator
Cyclic Redundancy Check (CRC) per cellMessage Identifier (MID) allows muitipleinterleaved packets on a virtual connection
ErrorChecking
2 4 10bits 6 10 bits
4
44 bytes
Data
ErrorChecking
4 or 8 bytes
0 - 65535 bytes
CRCUser DataMIDSNST LI
CRCUser DataSNST MID LI
CRCUser Data PADSNST MID LI
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ATM and B-ISDN
AAL5 for Class C&D
48 bytes of data per cellUse PTI bit to indicate last cellOnly one packet at a time on a virtual connection
0 User Data
48
Data
0 - 65535 bytes
0 User Data
48
148
PAD
Last cell flag
0-47
0 LEN
CRC
2 2 4 bytes
Error Detection Fields
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ATM and B-ISDN
Mapping ATM into STM-1
270 bytes
11
2
3
4
5
6
7
8
9
Section overhead
AU ptr
Section overhead
9 10 270
9 bytes
125 microseconds
STM-1 Payload
J1
B3
C2
G1
F2
H4
Z3
Z4
Z5
VC-4
POH
...... ......
ATM Cells
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Mapping ATM into Cell Based Transmission
......1 2 26 27 28
......1 2 26 27 28
29
OMA Cell
ATM layer: 149.760 Mbit/s
Physical Layer: 155.520 Mbit/s
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ATM and B-ISDN
ITU-T
■ ITU - International Telecommunication Union (Formally known as CCITT)• three main sectors: ITU-T, ITU-R and ITU-D• five classes of member: Administrative (PTT), Private operators (BT),
Regional telecom organisation (ETSI), Telecom vendors and scientific organisation, others
• Study group, work parties, expert teams, ad hoc groups,
■ ITU-T Responsible for Public ATM network Specifications
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The ATM Forum
■ International non-profit organization formed in 1991. With the objective of accelerating the use of ATM products and services through a rapid convergence of interoperability specifications.
■ Promotes industry cooperation and awareness.■ Consists of Technical Working Group, three
Marketing Working Groups for North America, Europe and Asia-Pacific as well as the Enterprise Network Roundtable, through which ATM end-users participate.
■ Responsible for Private ATM network Specifications
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ATM and B-ISDN
Summary of Physical Layer UNI Interface
(ATM Forum).(* Underdevelopment, SMF - Single Mode Fibre)
Frame Format Bit Rate (Mbit/s) Transmission MediaDS1 1.544 Twisted pairDS3 44.736 Coax pair
STS-3c, STM-1 155.520 SMFE1 2.048 Twisted pairE3 34.368 Coax pairJ2 6.312 Coax pair
N x T1 * N x 1.544 Twisted pairN x E1 * N x 2.048 Twisted pair
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ATM and B-ISDN
2. Quality of Service (QoS)
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ATM Service Categories
■ CBR: Constant Bit Rate• Continuous flow of data with tight bounds on delay and delay
variation
■ rt-VBR: Real Time Variable Bit Rate• Variable bandwidth with tight bound on delay and delay variation
■ nrt-VBR: Non-Real Time Variable Bit Rate• Variable bandwidth with tight bound on cell loss
■ UBR: Unspecified Bit Rate• No guarantees (i.e., best effort delivery)
■ ABR: Available Bit rate• Flow control on source with tight bound on cell loss
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ATM and B-ISDN
Traffic parameters and descriptors
■ PCR: Peak cell rate is the maximum rate at which the send is planning to send.
■ SCR: Sustained cell rate is the expected or required cell rate averaged over a long time interval.
■ MCR: Minimum cell rate is the minimum number of cells/second that the customer considers as acceptable.
■ CDVT: Cell delay variation tolerance tells how much variation will be presented in cell transmission times.
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ATM and B-ISDN
Cell transfer performance and QoS parameters
■ CTD: It is the extra delay added to an ATM network at an ATM switch, in addition to the normal delay through network elementsand lines.
■ CDV: The 1-point CDV describes variability in the pattern of cell arrival events observed at a single boundary with reference to the negotiated 1/T. The 2-point CDV describes variability in the pattern of cell arrival events observed at an output of a connection with the reference to the pattern of the corresponding events observer at the input to the connection.
■ CLR: lost cells divided by the total transmitted cells.
■ CER: errored-cells / (successful-transferred-cells + errored-cells).
■ SECBR: Total severely errored cell block / Total transmitted cell blocks.
■ CMR: misinserted cell / Time interval
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ATM and B-ISDN
3. Traffic Control and Management
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Traffic Control and Resource Management (371)
■ Protect network, provide QOS & optimise resource usage■ Connection admission control■ Usage parameter control (Policing function)■ Network parameter control (Policing function)■ Priority control■ Congestion control■ Traffic Parameter: type, peak, mean burst, peak duration ■ QOS: delay, delay variation & loss
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ATM and B-ISDN
Traffic Management
■ Problem: provide Quality of Services (QoS)• How should ATM network resources be allocated to ensure
good performance including preventing congestion control, e.g., how many virtual channels should be assigned to a particular transmission link?
■ Solution: Traffic Management• Specify the traffic “contract” on each virtual channel/path• Route (including rejecting setup request) each virtual
channel/path along a path with adequate resources (Connection Admission Control - CAC)
• Mark (via cell loss priority bit) for loss all cells that violate the contract (traffic policing)
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ATM and B-ISDN
Traffic contract between customer and Network
■ The traffic to be offered (traffic parameters and descriptors)
■ The service agreed upon (QoS)■ The compliance requirements
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Usage and Network Parameter Control
Network interface 1
0
NP0
P0 ?
P1 ?Output
NP1
+
A. No cell tagging.
Network interface 1
0
NP0
P0 ?
P1 ?Output
NP1
+
B. Cell tagging.
+
Tagging
P ? Control of parameter P
Cell discard
NP0: CLP=0 cell flowNP1: CLP=1 cell flow
Network Performance Objective:
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ATM and B-ISDN
4. Traffic Policing and Shaping Algorithms
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ATM and B-ISDN
Leaky Bucket
B u cke t S ize :L + I
1 to ken fo r e a ch
ce ll a rr iva l
1 to ke n le ak p e r
u n it o f tim e
A T MSw itch
A T M ce lls
T o ke nO ve rflo w
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ATM and B-ISDN
Leaky Bucket - Generic Cell Rate Algorithm (GCRA)
For a sequence of cell arrival time {ti} determine which cells conform to the traffic contract
Bucket Size: L+ I
1 token for each cell arrival
1 token leak per unit of time
A counter scheme based on two parameters denoted GCRA(I,L):
• I - Increment Parameter, affects cell rate
• L - Limit Parameter, affects cell burst
Leaky Bucket:
• Finite-capacity bucket
• Contents leak out 1 per unit time
• Contents are increased by 1 if L is not exceeded
A cell that would cause the bucket overflow in non-conforming
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Generic Cell Rate Algorithm (GCRA)
Arrival of a cell at time ta(k)
X’ = X - (ta(k) - LCT)
NonconformingCell
X’ < 0?
X’ > L?
X = X + ILCT = ta(k)
Conforming Cell
Yes
X = 0
Yes
No
No
TAT < t a(k)?
TAT > t a(k) + L?
TAT = TAT + I
Conforming Cell
Yes
TAT = t a(k)
Yes
No
NoNonconforming
Cell
VirtualSchedulingAlgorithm
Continuous-stateLeaky BucketAlgorithm
TAT: Theoretical Arrival Timeta(k): Time arrival of a cellX: Value of leaky bucket counterX’: Auxiliary variableLCT: Last compliance time
I: IncrementL: Limit
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ATM and B-ISDN
Leaky Bucket - GCRA(1.5, 0.5)
Time
Cell Cell Cell CellNo cell
GCRA(1.5, 0.5)
1
2
t- t+
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ATM and B-ISDN
Leaky Bucket - GCRA(4.5, 7)
Time
Cell Cell CellNo cell
GCRA(4.5, 7)
5
10
No cell
1
2
3
4
0
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Virtual Scheduling Algorithm
cell 1 cell 2
TimeI
L
cell 2cell 2 cell 2 cell 2
Nonconforming Conforming
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Maximum Burst Size
The maximum number of conforming cell back-to-back
N <= 1 + L/(T - d)Where T = 1/PCR, d is cell transmission time
units, and L is CDVT
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Traffic shaping: token bucket
Traffic shaping is used to smooth out a traffic flow and reduce cell clumping
Server
Token generator
Arrivalcells Departing
cellsCapacity K
Capacity β
Rate α
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ATM and B-ISDN
Recommended Text Books
■ Tanenbaum A. Computer Networks - 3rd edition. Prentice Hall 1996, 0-133-499456. £27.95
■ Uyless BLACK, “ATM: Foundation for Broadband Networks”, Prentice Hall Series in Advanced Communication Technologies, ISBN: 0-13-297178-X , 1995.
■ L. G. Cuthbert, “ATM: Broadband Telecommunications Solution”, IEE Telecommunication Series No.29, ISBN: 0852968159, 1993.