Chapter 19 ATM

1. Chapter 19ATM • Design Goal • ATM Topology • ATM Architecture

2. ATM • ATM is a cell based, high-bandwidth, low-delay switching and multiplexing technology designed to deliver variety of high-speed digital communication services.

3. Design Goals • Optimize the use of high data rate transmission media (i.e fiber optic) • Interoperability with exiting technologies • Implementation at reasonable cost • Support for existing telecommunications hierarchies • Reliable and predictable • Hardware implementation of functions where possible • Suitable for real-time and non real-time services

4. Multiplexing with Different Packet Sizes

5. Multiplexing with Cells

6. ATM Characteristics • Packet switching network • Uses fixed-size cell of 53 bytes • High speed data transmission (155.52Mbps, 622.08 Mbps) • Primarily WAN technology, being used in LANs • Suitable for voice, data, real-time video • Coaxial, TP and fiber optics can be used • Max. data rates being used over fiber optic cable 1.062 Gbps. • Data rates of 2.13 and 4.26Gbps are under development • Supports variable rate data transmission

7. ATM Characteristics • Uses fixed-size cell of 53 bytes • Data: 48 bytes • Header: 5 bytes • ATM does not provide any error checking on user data (only on header information) • It is connection oriented and it uses virtual circuits: • Permanent VC • Switched VC • ATM prioritizes transmission based on the type of service.

8. ATM Layers

10. ATM Protocol Reference • ATM is implemented through three layers (Control plane, user plane , and Management plane) • Physical layer • ATM layer • ATM Adaptation layer (AAL) • Segmentation and reassembly (SAR) sublayer • Convergence sublayer

12. AAL3 and 5 are designed for connection-oriented service and AAL4 for datagrams. Like AAL2 for video, both data services require error checking (CRC), sequencing, and identification of the cells as part of the message. In addition, some sort of indication has to be given to the receiver about the total length of the message, so an appropriate buffer size can be reserved for the message.

14. ATM Adaptation Layer • AAL is a set of five standard protocols designed to deal with different types of data. • AAL1 • Supports applications that require constant bit rate (I.e. video, audio) • AAL2 • Supports variable bit-rate applications • AAL3/ALL4: • Provides support for connection oriented data services and connectionless data services • AAL5 • Provide support for higher layer protocols that are connection-oriented.

16. ATM Adaptation Layer • AAL5 • Provide support for higher layer protocols that are connection-oriented. • Reduce protocol-processing overhead • Reduce transmission overhead

17. ATM Virtual Connections • Connection between two end devices are established through: • Transmission path (TP): represent the physical connection (wire, satellite) Analogous to highways connecting two cities • Virtual channel (VC): A connection between two end users. • Virtual path (VP):A group of connections (virtual circuits) with the same endpoints. • All of the cells flowing over all of the VCs in a VP are switched together.

18. AAL5 does not bother to insert all this extraneous information into each cell. Instead, before the TCP or some • other data message is chopped into cells, a 'trailer' is appended to that message, containing a 'length' indicator • of two bytes (TCP segments can be 65,536 bytes long), a CRC error checking code for the whole message, and • some bits signaling user-to-user (end-to-end) what this message is about (this is still under study and is to be • used by each user equipment as it sees fit). Then this 'adapted' message is put through the chopper and the • cells are sent.

19. VPI and VCI VPI=8 (UNI)bits, a host can have 256 VP groups, each containing 65,536 VC VCI=16 bits VPI=12 (NNI)bits

20. Advantages of Virtual Path • Simplified network architecture • Transport and control signals can be: • Related to individual VC • Related to a group of VCs or VP • Increased network performance and reliability: • Fewer entities to deal with • Reduced processing and shorter connection setup time • Additional capacity is reserved when VP is set and new VCs can be set using simple control signals

21. Virtual Channels Usage • Between end users • Used to transfer control and data between end users. • Between end user and a network entity • Connection between a user and a network server • Between two network entities • Used for network management and routing decisions

22. ATM Service Classes ATM provides four different class of services: 1. Constant bit rate (CBR) • A constant predefined data rate must be provided by the circuit. • Used for voice and delay sensitive applications • (video conferencing, interactive audio) • Audio/video distribution (TV, pay-per view) • Video-on-demand, audio library • Variable bit rate (VBR) • Variable bit rate-real-time (VBR-RT) • The data are expected to be delivered in timely manner • Methods used for video compression produces a sequence of image frames of varying sizes • Variable bit rate non real time (VBR-NRT) • Variable speed and delays are expected (suitable for bursty traffic, error messages)

23. ATM Service Classes (continued) • Available bit Rate(ABR) • The circuit can tolerate wide variation of transmission speeds and delays (they receive the lowest amount of guarantee capacity) • Unspecified bit rate(UBR) • The circuit has no guaranteed rate, data are transported when capacity is available.

24. ATM LANs Compatibility issues: • Connectionless versus connection- oriented • Physical address Vs. VC identifiers • Multicasting and broadcasting delivery

25. ATM LANs Compatibility issues: • Interaction between an end system on an ATM network and an end system on a legacy LAN • Interaction between an end system on a legacy LAN and system on another legacy LAN of the same type • Interaction between an end system on a legacy LAN and system on another legacy LAN of a different type

26. ATM LAN Solutions • Using routers • Upgrading to ATM • Using ATM LAN emulation

27. LAN Emulation • Makes an ATM switch behave like a LAN switch. • It provides connectionless service • Stations can use their MAC address instead of VPI/VCI • Allows broadcast delivery

28. LAN Emulation Components • LECS (LAN Emulation Configuration server) • LEC (LAN Emulation client, interpreter) • LES (LAN Emulation server) • BUS (Broadcast and Unknown server)

29. LAN Emulation Configuration Server (LECS) • Assigns client to different emulated LANs (used in wireless LAN ATM LANs)

30. LAN Emulation Client (LEC) Functions • Establishing a connection to the LES • Establishing a connection to the BUS • Registering with LES • Generating and responding to address resolution requests. • Depending on the type of service requested from the higher layers, Services of BUS or LES are requested

31. LAN Emulation Components • LES (LAN Emulation server) • Sets up virtual circuit between the source and destination • Provides address resolution mechanism for resolving MAC addresses • BUS (Broadcast and Unknown server): Handles broadcast messages (simulates multicasting and broadcasting)

32. ATM Interfaces

33. Homework • The transmission efficiency in an ATM network cab be defined as: • N=number of information octets/(number of information octets + number of overhead octets) • Let: • L=data-field size of the cell in octets • H= header size of the cell in octets • X= number of information octets to be transmitted as a single message. • Drive an expression for N.

34. Homework (solution) • N=number of information octets/(number of information octets + number of overhead octets) • Let: • L=data-field size of the cell in octets • H= header size of the cell in octets • X= number of information octets to be transmitted as a single message.