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Rivier College
CS575: Advanced LANs
ATM Technology: ATM Layer
CS575
ATM: ATM Layer
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Overview
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ATM Layer Functions
UNI ATM Cell Header Format
NNI ATM Cell Header Format
VP/VC/Transmission Path Concept
Virtual Channel and Virtual Path
Jain
ATM Switch Routing/Switching
ATM Virtual Path Switching
ATM Virtual Channel/Virtual Path Switching
Impact of Random Bit Errors on HEC Performance
Payload Type Indicator Encoding
Management Information Flows
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ATM Layer Functions
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Support Virtual Paths and Virtual Channels
Multiplexing/demultiplexing cell streams onto transmission path
Cell header generation/extraction
Provides cell routing functions (in ATM switch)
Performs VPI/VCI translation at switching nodes
Generic flow control
Traffic control and congestion control
Support a set of ATM layer Quality of Service (QoS) classes
Higher Layers
ATM Adaptation Layer (AAL)
Convergence Sublayer (CS)
Segmentation and Reassembly Sublayer (SAR)
ATM Layer (ATM)
Physical Layer (PL)
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Virtual Channel (VC)
Virtual Path (VP)
Transmission Convergence Sublayer (TC)
Physical Medium Sublayer (PM)
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UNI ATM Cell Header Format
Bit
Octet
8
7
6
5
1
Generic Flow Control (GFC)
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Virtual Path Identifier (VPI)
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4
5
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Virtual Path Identifier (VPI)
Virtual Channel Identifier (VCI)
Virtual Channel Identifier (VCI)
Virtual Channel Identifier (VCI)
Payload Type (PT)
Cell
Loss
Priority
(CLP)
Header Error Control (HEC)
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NNI ATM Cell Header Format
Bit
8
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6
5
4
3
2
1
Octet
1
2
3
4
5
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Virtual Path Identifier (VPI)
Virtual Path Identifier (VPI)
Virtual Channel Identifier (VCI)
Virtual Channel Identifier (VCI)
Virtual Channel Identifier (VCI)
Payload Type (PT)
Cell
Loss
Priority
(CLP)
Header Error Control (HEC)
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VP/VC/Transmission Path Concept
Source: Stallings: Data and Computer Communications
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Virtual Channel and Virtual Path
0 A virtual channel (VC) is a concept used to describe unidirectional transport
of ATM cells associated by a common unique identifier value
0 This identifier is called the virtual channel identifier (VCI) and is part of the
cell header
0 A virtual channel link is a means of unidirectional transport of ATM cells
between a point where a VCI value is assigned and the point where that
value is translated or removed
0 A concatenation of VC links is called a virtual channel connection (VCC)
0 VCCs are provided for the purpose of user-user (workstation-workstation),
user-network (workstation-switch), or network-network (switch-switch)
information transfer
0 ATM cells are transported across the ATM network on VCCs
0 Cell sequence integrity is preserved for the cells belonging to the same VCC
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Virtual Channel and Virtual Path (Continued)
0 A virtual path (VP) is a concept used to describe unidirectional transport of
ATM cells belonging to virtual channels that are associated by a common
identifier value
0 This identifier is called the virtual path identifier (VPI) and is also part of
the cell header
0 A virtual path link is terminated by the points where a VPI value is assigned
and translated or removed
0 A concatenation of VP links is called a virtual path connection (VPC)
0 VPCs are provided for the purpose of user-user (workstation-workstation),
user-network (workstation-switch), or network-network (switch-switch)
information transfer
0 A VPC is a labeled path which can be used to transport a bundle of VCCs
that have the same end points and to manage the resources used by these
connections
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Virtual Channel and Virtual Path (Concluded)
0 If the VPCs are permanent or semi-permanent and have reserved
capacity, establishing new VCCs requires simple connection
admission decisions at the VPC terminators of existing VPCs
0 This would enable faster connection establishment since transit
nodes are not involved in the connection set up
0 The virtual path concept also allows the possibility of segregating
traffic types according to Quality of Service (QoS) requirements
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ATM Switch Routing/Switching
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ATM Virtual Path Switching
Source: Stallings: Data and Computer Communications
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ATM Virtual Channel/Virtual Path Switching
Source: Stallings: Data and Computer Communications
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Impact of Random Bit Errors on HEC
Performance
Stallings: Data and Computer Communications
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Payload Type Indicator Encoding
PTI
Coding
000
001
010
User data cell, congestion not experienced, SDU-type
=0
User data cell, congestion not experienced, SDU-type = 1
100
User data cell, congestion experienced, SDU-type
=0
User data cell, congestion experienced, SDU-type =
1
Segment OAM F5 flow related cell
101
End-to-end OAM F5 flow related cell
110
Reserved for future traffic control and resource
management
Reserved for future functions
011
111
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Interpretation
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Management Information Flows
0 The ATM Layer management information is carried via F4 - F5
OAM cells
0 The OAM cell flow used for end-to-end management functions
may be carried through the private ATM switch and made
available to the users
0 The F4 flow is used for segment (link between ATM nodes) or VP
end-to-end management at the VP level using VCIs 3 and 4
0 The F5 flow is used for segment (link between ATM nodes) or VC
end-to-end management at the VC level using PTI code points 4
and 5
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References
W. Stalling, Local and Metropolitan Area Networks, 6th edition,
Prentice Hall, 2000, Chapter 11
W. Stalling, Data and Computer Communications, 6th edition,
Prentice Hall, 2002, Chapters 11-12
A. Wu, Advanced Local Area Networks, Lectures & Slides, Rivier
College, 2001.
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