asynchronous transfer mode - wpirek/grad_nets/spring2006/atm06.pdf · atm conceptual model four...
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ATM
Asynchronous Transfer Mode
Computer Networks: ATM 1
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Issues Driving LAN Changes• Traffic Integration
– Voice, video and data traffic– Multimedia became the ‘buzz word’
• One-way batch Web traffic• Two-way batch voice messages• One-way interactive Mbone broadcasts• Two-way interactive video conferencing
• Quality of Service guarantees (e.g. limited jitter, non-blocking streams)
• LAN Interoperability• Mobile and Wireless nodes
Computer Networks: ATM 2
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Computer Networks: ATM 3
Stallings “High-Speed Networks”
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Computer Networks: ATM 4
Stallings “High-Speed Networks”
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AATMTM AAdaptationdaptation LLayersayersVoice
AALA/Dcellss1 , s2 …
Digital voice samples
Video
Computer Networks: ATM 5
A/D … Compression AALcells
compressed frames
picture frames
cellsAALData
Bursty variable-length packets
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.3
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AAsynchronous synchronous TTransfer ransfer MModeode (ATM)(ATM)
MUX
Wasted bandwidth
TDM
4 3 2 1 4 3 2 1 4 3 2 1
Voice
Data packets
Images
`ATM4 3 1 3 2 2 1
Computer Networks: ATM 6
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 7.37
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ATM• ATM standard (defined by CCITT) is widely
accepted by common carriers as mode of operation for communication – particularly BISDN.
• ATM is a form of cell switching using small fixed-sized packets. [ to facilitate hardware switches]
Basic ATM Cell Format
48 Bytes5 Bytes
Header Payload
Computer Networks: ATM 7
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.1
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ATM Conceptual ModelFour Assumptions
1. ATM network will be organized as a hierarchy.User’s equipment connects to networks via a UNI (User-
Network Interface).Connections between provided networks are made through
NNI (Network-Network Interface).
2. ATM will be connection-oriented.A connection (an ATM channel) must be established before any cells are sent. [The connection setup phase is called signaling.]
Computer Networks: ATM 8
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Computer Networks: ATM 9
X
X
X
X
X
X
X
X
X
Private UNI
Public UNI
NNI
Private NNI
Private ATM network
Public UNI
B-ICI
Public UNIPublic ATM network A
Public ATM network B
Figure 9.5Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
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ATM Connections
• two levels of ATM connections:virtual path connectionsvirtual channel connections
• indicated by two fields in the cell header:virtual path identifier VPIvirtual channel identifier VCI
Computer Networks: ATM 10
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ATM Virtual Connections
Physical Link
Virtual Paths
Virtual Channels
Computer Networks: ATM 11
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 7.40
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ATM Conceptual ModelAssumptions (cont.)
3. Vast majority of ATM networks will run on optical fiber networks with extremely low error rates.
4. ATM must supports low cost attachments• This decision lead to a significant decision – to
prohibit cell reordering in ATM networks.ATM switch design is more difficult.
Computer Networks: ATM 12
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GFC HEC (CRC-8)
4 16 3 18
VPI VCI CLPType Payload
384 (48 bytes)8
Figure 3.16 ATM Cell Format at the UNI
Computer Networks: ATM 13
P&D slide
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UNI Cell Format
GFC (4 bits) VPI (4 bits)
VPI (4 bits) VCI (4 bits)
VCI (8 bits)
VCI (4 bits) PT (3 bits) CLP (1 bit)
HEC (8 bits)
ATM cell header
Payload (48 bytes)
Computer Networks: ATM 14
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.7
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ATM Cell Switching
2
3
N
1Switch
N
1…
5
6
video 25
video
voice
data
32
32 61
2532
3261
7567
3967
N1
32
video 75
voice 67
data 39
video 67
…
…
Computer Networks: ATM 15
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 7.38
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c ATMSw1
ATMSw4
ATMSw2
ATMSw3
ATMDCC
ab
de
VP3 VP5
VP2
VP1
a
bc
deSw = switch
Digital Cross ConnectOnly switches virtual paths
Computer Networks: ATM 16
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 7.39
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ATM Protocol Architecture• ATM Adaptation Layer (AAL) – the protocol
for packaging data into cells is collectively referred to as AAL.
• Must efficiently package higher level data such as voice samples, video frames and datagram packets into a series of cells.
Design Issue: How many adaptation layers should there be?
Computer Networks: ATM 17
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Management plane
Physical layer
ATM layer
ATM adaptation layer
Higher layers Higher layers
Plane managem
entControl plane User plane Layer m
anagement
Computer Networks: ATM 18
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.2
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AAL
ATM
User information
User information
AAL
ATM
PHYPHY
ATM
PHY
ATM
PHY
…
End system End systemNetwork
Computer Networks: ATM 19
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.4
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Original ATM Architecture
• CCITT envisioned four classes of applications (A-D) requiring four distinct adaptation layers (1-4) which would be optimized for an application class:
A. Constant bit-rate applications CBRB. Variable bit-rate applications VBRC. Connection-oriented data applicationsD. Connectionless data application
Computer Networks: ATM 20
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ATM ArchitectureAn AAL is further divided into:
Convergence Sublayer (CS)manages the flow of data to and from SAR sublayer.
Computer Networks: ATM 21
Segmentation and Reassembly Sublayer (SAR)breaks data into cells at the sender and reassembles
cells into larger data units at the receiver.
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■ ■ ■ ■ ■ ■
AAL
ATM
AAL
ATM
Figure 3.17 Segmentation and Reassembly in ATM
Computer Networks: ATM 22
P&D slide
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Computer Networks: ATM 23
Original ATM Architecture
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Transmission convergence
sublayer
Physical medium dependent sublayer
Physical medium
ATM layer
Physical layer
Computer Networks: ATM 24
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.6
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Original ATM Architecture
Computer Networks: ATM 25
• The AAL interface was initially defined as classes A-Dwith SAP (service access points) for AAL1-4.
• AAL3 and AAL4 were so similar that they were merged into AAL3/4.
• The data communications community concluded that AAL3/4 was not suitable for data communications applications. They pushed for standardization of AAL5 (also referred to as SEALSEAL – the SSimple and EEfficient AAdaptation LLayer).
• AAL2 was not initially deployed.
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Computer Networks: ATM 26
Revised ATM Architecture
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Revised ATM Service Categories
Computer Networks: ATM 27
Class Description Example
CBR Constant Bit Rate T1 circuit
RT-VBR Real Time Variable Bit Rate
Real-time videoconferencing
NRT-VBR Non-real-time Variable Bit Rate
Multimedia email
ABR Available Bit Rate Browsing the Web
UBR Unspecified Bit Rate Background file transfer
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QoS, PVC, and SVC
Computer Networks: ATM 28
• Quality of Service (QoS) requirements are handled at connection time and viewed as part of signaling.
• ATM provides permanent virtual connections and switched virtual connections.– Permanent Virtual Connections (PVC)
permanent connections set up manually by network manager.
– Switched Virtual Connections (SVC)set up and released on demand by the end user via signaling procedures.
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AAL 1 Payload
(b) CS PDU with pointer in structured data transfer
AAL 1 Pointer
1 Byte 46 Bytes
47 Bytes
optional
(a) SAR PDU header
CSI SNPSeq. Count
1 bit 3 bits 4 bits
Computer Networks: ATM 29
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.11
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AAL 1
User data streamHigher layer…b1 b2 b3
CS PDUsConvergence sublayer
474747
Computer Networks: ATM 30
SAR sublayer
ATM layer
SAR PDUs
1 47 1 471 47
ATM Cells
H H H
5 48
H
5 48
H
5 48
H
Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies Figure 9.10
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Convergent SublayerPDUs
(a) CPCS-PDU format
CPI Btag BASize CPCS - PDU Payload
1 1 2 1 - 65,535 0-3 1 1 2 (bytes) (bytes) (bytes)
AL Etag LengthPad
Header Trailer
CPI Btag BASize Pad 0 Etag Len
8 16 0─24 8 8 16< 64 KB8
User data
Figure 3.18 AAL 3/4Computer Networks: ATM 31
P&D slide
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Segmentation and AssemblyPDU
(b) SAR PDU formatTrailer (2 bytes)
Header (2 bytes)
ST SN MID SAR - PDU Payload
2 4 10 44 6 10 (bits) (bytes) (bits)
LI CRC
ATM header Length CRC-10
40 2 4
SEQ MIDType Payload
352 (44 bytes)10 6 10
Computer Networks: ATM 32
Figure 3.19 AAL 3/4 P&D slide
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CS-PDUheader
CS-PDUtrailerUser data
44 bytes 44 bytes 44 bytes ≤ 44 bytes
ATM headerAAL header
Cell payloadAAL trailer
Padding
Figure 3.20 Encapsulation and Segmentation for AAL3/4
Computer Networks: ATM 33
P&D slide
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AAL 3/4
Higher layerInformation User message
TPAD
Service specific convergence
sublayerAssume null
Common part convergence
sublayer
Pad message to multiple of 4 bytes. Add header and trailer.
H
44
2 44 2 2 44 2 2 44 2
Computer Networks: ATM 34
SAR sublayer
ATM layer
Each SAR-PDU consists of 2-byte header, 2-byte trailer, and 44-byte payload.
…
Information
…Figure 9.15Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks
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AAL 5 Convergent Sublayer Format
Information UU CPI Length CRCPad
0 - 65,535 0-47 1 1 2 4 (bytes) (bytes)
Figure 9.19Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
CRC-32
< 64 KB 0─47 bytes 16 16
ReservedPad Len
32
Data
Figure 3.21 ATM Adaptation Layer 5
Computer Networks: ATM 35
P&D slide
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AAL 5 SAR Format
48 bytes of DataATMHeader
1-bit end-of-datagram field (PTI)Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 9.19
Computer Networks: ATM 36
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Computer Networks: ATM 37
Higher layer
PTI = 0
Common part convergence
sublayer
SAR sublayer
ATM layer
Service specific convergence
sublayer Assume null
48 (1)
Information
TPAD
…
…
Information
48 (0)
48 (0)
AAL 5
Figure 9.18
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
PTI = 0PTI = 1
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User data
48 bytes 48 bytes 48 bytes
ATM header Cell payload
Padding
CS-PDUtrailer
Figure 3.22 Encapsulation and Segmentation for AAL5
Computer Networks: ATM 38
P&D slide
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Switchfabric
Controlprocessor
Outputport
Inputport
Figure 3.28 ATM Switch
Computer Networks: ATM 39
P&D slide
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Figure 3.30 4 x 4 Crossbar Switch
Computer Networks: ATM 40
P&D slide
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Computer Networks: ATM 41
�Switchfabric
�Outputport
�Inputport
Original packetheader
�Switchfabric
�Outputport
�Inputport
�Self-routingheader
Sw it �chfabric
�Outputport
�Inputport
(a)
(b)
(c)
Figure 3.31
Self-RoutingHeaders
P&D slide
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001
011
110
111
001
011
110
111
Figure 3.32 Banyan Switching
Computer Networks: ATM 42
P&D slide