1. CHAPTER #6  Introducti on to ATM

2. Contents  Introduction  ATM Cells  ATM Architecture  ATM Connections  Addressing and Signaling  IP over ATM

3. 6.1. Introduction  ATM-Asynchronous Transfer Mode  A transfer mode in which the information is organized into cells  It is asynchronous in the sense that the recurrence of cells containing information from a particular user is not necessarily periodic

4.  Asynchronous transfer mode (= Statistical multiplexing) – Sources packetize data. Packets are sent only if there is data – Sources packetize data. Packets are sent only if there is data

5.  ATM requires connections to be established before any communication takes place  A connection is called a virtual circuit (VC) which could be permanent or switched

6.  Information to be transmitted is divided into cells consisting of: 5 bytes header and 48 bytes user data.  Fixed sized cells enable HW switching  Typical speeds of ATM are 155 and 622 Mbps

7. 6.2.ATM’s Key Concepts  ATM uses Virtual-Circuit Packet Switching(VCPS)  ATM can reserve capacity for a VC  This is useful for voice and video, which require a minimum level of service  Overhead for setting up a connection is expensive if data transmission is short (e.g., web browsing) (e.g., web browsing)

8. 6.2. (Follow)  ATM packets are small and have a fixed size – Packets in ATM are called cells – Small packets are good for voice and video transmissions

9. 6.3.ATM Cells  Why 53 Bytes?  Advantages  Disadvantages

10. 6.3.1.Why 53 Bytes?  A 48 byte payload was the result of a compromise between a 32 byte payload and a 64 byte payload

11. 6.3.2.Advantages – Low packetization delay for continuous bit rate applic- ations (video, audio) – Processing at switches is easier

12. 6.3.3.Disadvantages – High overhead (5 Bytes per 48) – Poor utilization at lower line rates links

13. 6.3.4. UNI Cells

14. 6.3.5. NNI Cells

15. 6.4.ATM Architecture  The ATM Reference Model: ATM technology has its own protocol architecture ATM technology has its own protocol architecture

17. 6.5.ATM Reference Model

18. 6.6.ATM Layers and Planes  ATM is a three dimensional model consisting of layers and planes  Physical layer deals with physical media issues,further divided into: (1) PMD and (1) PMD and (2) TC sub layers (2) TC sub layers

19.  ATM layer defines cell format and connection setup

20. 6.6.(Follow)  ATM Adaptation Layer (AAL) segments and reassembles upper layer into and from cells,divided into : 1.SAR and 2.CS sub layers

21.  User planes deals with data transport,flow and error control

22.  Control plane deals with connection management

23.  The Layer and Plane management deals with resource management and interlayer coordination

24. 6.7.ATM Adaptation Layer (AAL)  AAL encapsulates user- level data  Performs segmentation and reassembly of user- level messages

26. 6.8.Layers of ATM

27. 6.8.1..Functions of Layers

28. 6.9.ATM Layer  The ATM Layer is responsible for the transport of 53 byte cells across an ATM network

29.  Multiplex logical channels within a physical channel

30.  The ATM Layer can provide a variety of services for cells from an ATM virtual connection: -Constant Bit Rate (CBR) -Variable Bit Rate(VBR) - Available Bit Rate(ABR) -Unspecified Bit Rate(UBR) -Guarantees Frame Rate(GFR)

31. 6.10. Correspondence between ATM and OSI Reference Models

33. 6.11.ATM Connections  A Packet Switch

34. 6.12.Forwarding with VCs

35. 6.13.Addressing and Signaling ATM End system Addresses (AESA)  ALL ATM addresses are 20 bytes long

36.  Source and destination address are supplied when setting up a connection

37.  ATM endpoints use the NSAP (Network Service Access Point) format from ISO OSI

38.  Three different types of addresses : 1.NSAP encoding for E.164: ISDN telephone numbers (e.g., 001-434-9822200) -

39. 2.DCC format: for public networks, 3.ICD format: for private networks

40. 6.14.ATM End system Addresses (AESA)

41. 6.15.Formats of an ATM address

42. 6.16.ATM UNI Signaling  Significant Signaling Protocols

43.  ATM Forum: 1.UNI 3.0. UNI signaling protocol for point-to- point connections. -

44. 2.UNI 3.1. Supports point-to- multipoint connections.

45. 3.UNI 4.0. Supports Leaf initiated join multipoint connections

46.  4. -PNNI. for network node signaling

47. 6.17.Which Address Format To Use?  Currently each service provider makes its own choice – This introduces problems (SVC compatibility)

48.  Most ATM switches support multiple formats

49.  ATM Forum prepares standards to translate addresses at network boundaries (NNI interfaces) –

50.  Interworking of ATM Networks (IAN)

51. 6.18.IP over ATM  Issues with sending IP traffic over ATM

52.  Address resolution: – IP address  VPI/VCI – IP address  ATM address

53.  Emulation of broadcast operation on IP sub networks

54.  Routing