Rivier College CS575: Advanced LANs ATM Technology: ATM Layer

1. Rivier CollegeCS575: Advanced LANsATMTechnology:ATM Layer ATM: ATM Layer

2. Jain Overview • ATM Layer Functions • UNI ATM Cell Header Format • NNI ATM Cell Header Format • VP/VC/Transmission Path Concept • Virtual Channel and Virtual Path • 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 ATM: ATM Layer

3. Higher Layers Convergence Sublayer (CS) ATM Adaptation Layer (AAL) Segmentation and Reassembly Sublayer (SAR) Virtual Channel (VC) Virtual Path (VP) ATM Layer (ATM) Transmission Convergence Sublayer (TC) Physical Layer (PL) Physical Medium Sublayer (PM) ATM Layer Functions • 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 ATM: ATM Layer

4. UNI ATM Cell Header Format Bit 8 7 6 5 4 3 2 1 Octet Generic Flow Control (GFC) Virtual Path Identifier (VPI) 1 Virtual Path Identifier (VPI) 2 Virtual Channel Identifier (VCI) Virtual Channel Identifier (VCI) 3 Cell Loss Priority (CLP) Virtual Channel Identifier (VCI) Payload Type (PT) 4 Header Error Control (HEC) 5 ATM: ATM Layer

5. NNI ATM Cell Header Format Bit 8 7 6 5 4 3 2 1 Octet Virtual Path Identifier (VPI) 1 Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) 2 3 Virtual Channel Identifier (VCI) Cell Loss Priority (CLP) Virtual Channel Identifier (VCI) Payload Type (PT) 4 Header Error Control (HEC) 5 ATM: ATM Layer

6. VP/VC/Transmission Path Concept Source: Stallings: Data and Computer Communications ATM: ATM Layer

7. Virtual Channel and Virtual Path • A virtual channel (VC) is a concept used to describe unidirectional transport of ATM cells associated by a common unique identifier value • This identifier is called the virtual channel identifier (VCI) and is part of the cell header • 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 • A concatenation of VC links is called a virtual channel connection (VCC) • VCCs are provided for the purpose of user-user (workstation-workstation), user-network (workstation-switch), or network-network (switch-switch) information transfer • ATM cells are transported across the ATM network on VCCs • Cell sequence integrity is preserved for the cells belonging to the same VCC ATM: ATM Layer

8. Virtual Channel and Virtual Path (Continued) • 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 • This identifier is called the virtual path identifier (VPI) and is also part of the cell header • A virtual path link is terminated by the points where a VPI value is assigned and translated or removed • A concatenation of VP links is called a virtual path connection (VPC) • VPCs are provided for the purpose of user-user (workstation-workstation), user-network (workstation-switch), or network-network (switch-switch) information transfer • 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 ATM: ATM Layer

9. Virtual Channel and Virtual Path (Concluded) • 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 • This would enable faster connection establishment since transit nodes are not involved in the connection set up • The virtual path concept also allows the possibility of segregating traffic types according to Quality of Service (QoS) requirements ATM: ATM Layer

10. ATM Switch Routing/Switching ATM: ATM Layer

11. ATM Virtual Path Switching Source: Stallings: Data and Computer Communications ATM: ATM Layer

12. ATM Virtual Channel/Virtual Path Switching Source: Stallings: Data and Computer Communications ATM: ATM Layer

13. Impact of Random Bit Errors on HEC Performance Stallings: Data and Computer Communications ATM: ATM Layer

14. Payload Type Indicator Encoding PTI Interpretation Coding 000 User data cell, congestion not experienced, SDU-type = 0 001 User data cell, congestion not experienced, SDU-type = 1 010 User data cell, congestion experienced, SDU-type = 0 User data cell, congestion experienced, SDU-type = 1 011 Segment OAM F5 flow related cell 100 End-to-end OAM F5 flow related cell 101 Reserved for future traffic control and resource management 110 Reserved for future functions 111 ATM: ATM Layer

15. Management Information Flows • The ATM Layer management information is carried via F4 - F5 OAM cells • 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 • 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 • 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 ATM: ATM Layer

16. 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. ATM: ATM Layer