1. Network Communication Technology Chapter 20 Asynchronous Transfer Mode (ATM)

2. ATM Network ATM SWITCH UNINNI ATM EndUserATM EndUser ATM SWITCH NNI UNI Figure 20.1

3. ATM Cell Fixed size cell (53 Bytes) Telephony Standard – Intended as a universal, shared bandwidth service Typically 155 Mbit/sec (OC-3, STS-3) user interface with low latency Figure 20.2

4. ATM Connections Virtual Path Identifier (VPI) –High-level route identifier Virtual Channel Identifier (VCI) –Sub-route identifier Connections –PVC Permanent Virtual Connection –SVC (normal) Switched Virtual Connection Figure 20.3

5. A Railroad Model Figure 20.4 VCI 14VCI 10 VCI 11 VCI 15 VPI=2 VPI=1 VCI=3VCI=6 VCI=9VCI=2 ATM Switch VPI=4 VPI=3 Train Station or cell VCI=3

6. ATM Switch Fast –Simple HW –Fixed cell size Flexible BW sharing –Small cells –Low latency Figure 20.5 Input Output Port 1 VPI/VCI 1/26 1/45 Port 2 3 VPI/VCI 2/45 3/39 Table 20.1: Routing Table

7. ATM Switch Architecture Figure 20.6

8. ATM Connection Setup Figure 20.7

9. ATM Cell Formats User Network Interface (UNI) –Generic Flow Control: Not currently in use –VPI/VCI: Identify the next destination of the cell (which switch) –Payload Type: Data/control, congestion, terminating –Congestion Loss Priority: High/low, determines QoS –Header Error Control: Weak CRC on header only Network-to-Network Interface (NNI) Figure 20.9: UNI Cell Header Figure 20.10: NNI Cell Header

10. ATM Layered Architecture Figure 20.11

11. ATM Adaptation Layer 1 (AAL1) Constant bit rate traffic i.e. 64 Kb Telephony Figure 20.12

12. ATM Adaptation Layer 2 (AAL2) Variable bit rate traffic i.e. Compressed audio Figure 20.13 Information CS Sub-Layer HeaderPayloadTrailer 1 45 2 bytes SAR Sub-layer - - - - - - - CSISCIT 1 bit 3 bits 4 bits 6 bit 10 bits PayloadLIFEC Cell headerPayload ATM Layer Cell HeaderPayload

13. ATM Adaptation Layer 3/4 (AAL3/4) Variable Frame length Error control Variable delay Figure 20.14 Information < 65K Bytes PadBEtagALTypeBEtagBA CS Header Length CS Trailer CS-PDU Bytes 1 1 2 0-3 1 1 1 SAR HeaderCS Header40 bytes PayloadSAR Trailer 2440 2 bytes 2 44 2 SAR Header44 bytes PayloadSAR Trailer SAR-PDU STSNMID LIFCS 2 4 10 bits 6 10 bits

14. ATM Adaptation Layer 5 (AAL5) Efficient LAN emulation Control info in the last cell Figure 20.14 CS-PDU CS trailer SAR-PDU - - - - - ATM Layer <65535 Bytes Bytes PADUUCPILengthFCS 114 2 0-47 Information from upper layer 48 Bytes Payload 48 Bytes Payload 40 Bytes Payload 8 Bytes CS Trailer Cell Header 48 bytes Payload 48 Bytes Payload Cell Header 48 Bytes Payload

15. ATM vs. Gigabit Ethernet ATM –Supports real-time –Offers QoS support –Good as a WAN Gigabit Ethernet –QoS add-on (802.1Q) supports priority delivery –Low cost –Replaced ATM in LAN backbones, also used for short haul WAN connectivity