ATM uses fixed-size cells and virtual connections to transfer data between network entities. It defines several adaptation layers to map various protocols to ATM cells. AAL1 is for constant bitrate traffic. AAL3/4 supports both connectionless and connected services. AAL5 provides a streamlined transport for connection-oriented protocols and reduces overhead. Control signaling is used to establish and release virtual paths and channels in ATM networks.

1. Chapter 5
Asynchronous Transfer Mode
(ATM)
Chapter 2 Protocols and the TCP/IP Suite 1

2. Introduction
• ATM Protocol Architecture
• Logical connections
• ATM Cells
• Service categories
• ATM Adaptation Layer (AAL)
Chapter 2 Protocols and the TCP/IP Suite 2

3. ATM Protocol Architecture
• Fixed-size packets called cells
• Streamlined: minimal error and flow control
• 2 protocol layers relate to ATM functions:
– Common layer providing packet transfers
– Service dependent ATM adaptation layer (AAL)
• AAL maps other protocols to ATM
Chapter 2 Protocols and the TCP/IP Suite 3

4. Protocol Model has 3 planes
• User
• Control
• management
Chapter 2 Protocols and the TCP/IP Suite 4

5. Figure 5.1
Chapter 2 Protocols and the TCP/IP Suite 5

6. Logical Connections
• VCC (Virtual Channel Connection): a logical
connection analogous to virtual circuit in X.25
• VPC (Virtual Path Connection): a bundle of
VCCs with same endpoints
Chapter 2 Protocols and the TCP/IP Suite 6

7. Figure 5.2
Chapter 2 Protocols and the TCP/IP Suite 7

8. Advantages of Virtual Paths
• Simplified network architecture
• Increased network performance and reliability
• Reduced processing and short connection
setup time
• Enhanced network services
Chapter 2 Protocols and the TCP/IP Suite 8

9. Table 5.1
Chapter 2 Protocols and the TCP/IP Suite 9

10. VCC Uses
• Between end users
• Between an end user and a network entity
• Between 2 network entities
Chapter 2 Protocols and the TCP/IP Suite 10

11. Figure 5.3
Chapter 2 Protocols and the TCP/IP Suite 11

12. VPC/VCC Characteristics
• Quality of Service (QoS)
• Switched and semi-permanent virtual channel
connections
• Cell sequence integrity
• Traffic parameter negotiation and usage
monitoring
• (VPC only) virtual channel identifier restriction
within a VPC
Chapter 2 Protocols and the TCP/IP Suite 12

13. Control Signaling
• A mechanism to establish and release VPCs
and VCCs
• 4 methods for VCCs:
– Semi-permanent VCCs
– Meta-signaling channel
– User-to-network signaling virtual channel
– User-to-user signaling virtual channel
Chapter 2 Protocols and the TCP/IP Suite 13

14. Control Signaling
• 3 methods for VPCs
– Semi-permanent
– Customer controlled
– Network controlled
Chapter 2 Protocols and the TCP/IP Suite 14

15. ATM Cells
• Fixed size
• 5-octet header
• 48-octet information field
• Small cells reduce delay for high-priority cells
• Fixed size facilitate switching in hardware
Chapter 2 Protocols and the TCP/IP Suite 15

16. Header Format
• Generic flow control
• Virtual path identifier (VPI)
• Virtual channel identifier (VCI)
• Payload type
• Cell loss priority
• Header error control
Chapter 2 Protocols and the TCP/IP Suite 16

17. Figure 5.4
Chapter 2 Protocols and the TCP/IP Suite 17

18. Generic Flow Control
• Control traffic flow at user-network interface
(UNI) to alleviate short-term overload
conditions
• When GFC enabled at UNI, 2 procedures used:
– Uncontrolled transmission
– Controlled transmission
Chapter 2 Protocols and the TCP/IP Suite 18

19. Table 5.3
Chapter 2 Protocols and the TCP/IP Suite 19

20. Header Error Control
• 8-bit field calculated based on remaining 32
bits of header
• error detection
• in some cases, error correction of single-bit
errors in header
• 2 modes:
– error detection
– Error correction
Chapter 2 Protocols and the TCP/IP Suite 20

21. Figure 5.5
Chapter 2 Protocols and the TCP/IP Suite 21

22. Figure 5.6
Chapter 2 Protocols and the TCP/IP Suite 22

23. Figure 5.7
Chapter 2 Protocols and the TCP/IP Suite 23

24. Service Categories
• Real-time service
– Constant bit rate (CBR)
– Real-time variable bit rate (rt-VBR)
• Non-real-time service
– Non-real-time variable bit rate (nrt-VBR)
– Available bit rate (ABR)
– Unspecified bit rate (UBR)
– Guaranteed frame rate (GFR)
Chapter 2 Protocols and the TCP/IP Suite 24

25. Figure 5.8
Chapter 2 Protocols and the TCP/IP Suite 25

26. ATM Adaptation Layer (ATM)
• Support non-ATM protocols
– e.g., PCM voice, LAPF
• AAL Services
– Handle transmission errors
– Segmentation/reassembly (SAR)
– Handle lost and misinserted cell conditions
– Flow control and timing control
Chapter 2 Protocols and the TCP/IP Suite 26

27. Applications of AAL and ATM
• Circuit emulation (e.g., T-1 synchronous TDM
circuits)
• VBR voice and video
• General data services
• IP over ATM
• Multiprotocol encapsulation over ATM
(MPOA)
• LAN emulation (LANE)
Chapter 2 Protocols and the TCP/IP Suite 27

28. AAL Protocols
• AAL layer has 2 sublayers:
– Convergence Sublayer (CS)
• Supports specific applications using AAL
– Segmentation and Reassembly Layer (SAR)
• Packages data from CS into cells and unpacks at other
end
Chapter 2 Protocols and the TCP/IP Suite 28

29. Figure 5.9
Chapter 2 Protocols and the TCP/IP Suite 29

30. Figure 5.10
Chapter 2 Protocols and the TCP/IP Suite 30

31. AAL Type 1
• Constant-bit-rate source
• SAR simply packs bits into cells and unpacks
them at destination
• One-octet header contains 3-bit SC field to
provide an 8-cell frame structure
• No CS PDU since CS sublayer primarily for
clocking and synchronization
Chapter 2 Protocols and the TCP/IP Suite 31

32. AAL Type 3/4
• May be connectionless or connection oriented
• May be message mode or streaming mode
Chapter 2 Protocols and the TCP/IP Suite 32

33. Figure 5.11
Chapter 2 Protocols and the TCP/IP Suite 33

34. Figure 5.12
Chapter 2 Protocols and the TCP/IP Suite 34

35. AAL Type 5
• Streamlined transport for connection oriented
protocols
– Reduce protocol processing overhead
– Reduce transmission overhead
– Ensure adaptability to existing transport protocols
Chapter 2 Protocols and the TCP/IP Suite 35

36. Figure 5.13
Chapter 2 Protocols and the TCP/IP Suite 36