rivier college cs575: advanced lans atm technology: atm layer

CS575 ATM: ATM Layer 1

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Rivier College

CS575: Advanced LANs

ATM Technology: ATM Layer


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Overview

0 ATM Layer Functions0 UNI ATM Cell Header Format0 NNI ATM Cell Header Format0 VP/VC/Transmission Path Concept0 Virtual Channel and Virtual Path0 ATM Switch Routing/Switching0 ATM Virtual Path Switching0 ATM Virtual Channel/Virtual Path Switching0 Impact of Random Bit Errors on HEC Performance0 Payload Type Indicator Encoding0 Management Information Flows

Jain


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ATM Layer Functions

0 Support Virtual Paths and Virtual Channels0 Multiplexing/demultiplexing cell streams onto transmission path 0 Cell header generation/extraction0 Provides cell routing functions (in ATM switch)0 Performs VPI/VCI translation at switching nodes0 Generic flow control0 Traffic control and congestion control0 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) Virtual Channel (VC) Virtual Path (VP)

Physical Layer (PL)Transmission Convergence Sublayer (TC)

Physical Medium Sublayer (PM)


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UNI ATM Cell Header Format

Generic Flow Control (GFC) Virtual Path Identifier (VPI)

Virtual Channel Identifier (VCI)

Header Error Control (HEC)

8 7 6 5 4 3 2 1

Payload Type (PT) Cell LossPriority (CLP)

Bit

Octet 1

2

3

4

5

Virtual Path Identifier (VPI)




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NNI ATM Cell Header Format


Header Error Control (HEC)

8 7 6 5 4 3 2 1

Payload Type (PT) Cell LossPriority (CLP)





Bit

Octet 1

2

3

4

5


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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



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ATM Virtual Channel/Virtual Path Switching



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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 Interpretation

000

001

010

011

100

101

110

111

User data cell, congestion not experienced, SDU-type = 0

User data cell, congestion not experienced, SDU-type = 1

User data cell, congestion experienced, SDU-type = 0User data cell, congestion experienced, SDU-type = 1Segment OAM F5 flow related cellEnd-to-end OAM F5 flow related cellReserved for future traffic control and resource managementReserved for future functions


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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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W. Stalling, Local and Metropolitan Area Networks, 6th edition, Prentice Hall, 2000, Chapter 11

References

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.

rivier college cs575: advanced lans atm technology: atm layer

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