ASYNCHRONOUS TRANSFER MODE (ATM)

Basic concepts of ATM. ATM works on Data link layer. It provides switched networking between devices.

1. ATM ASYNCHRONOUS TRANSFER MODE BROADBAND DIGITAL NETWORK Group Members: SANIA DANISH SHUAIB ALI ZILLAY HUMA RAMSHA JAMAL ZAHID ALI DAWOOD UNIVERSITY OF ENGINEERING AND TECHNOLOGY

2. Main Objectives

3. INTRODUCTION OF ATM

4. The term broadband is used to describe a type of data transmission in which a single  medium  (wire) can carry several  channels  at once. Cable TV, for example, uses broadband transmission . and DSL modems (which use your existing phone line ). Relationship Between ATM and B-ISDN ATM evolved from the standardization efforts for B-ISDN. ATM is the technology upon which B-ISDN is based. BROADBAND

5. WHAT’S ATM? ATM is Asynchronous Transfer Mode . ATM is a connection-oriented, high-speed, low-delay switching and transmission technology that uses short and fixed-size packets, called cells, to transport information. ATM is originally the transfer mode for implementing Broadband ISDN (B-ISDN) but it is also implemented in non-ISDN environments where very high data rates are required

6. ATM Overview Used in both WAN and LAN settings Packets are called cells (53 bytes) 5-byte header + 48-byte payload Commonly transmitted over SONET other physical layers possible Connections can be switched (SVC), or permanent (PVC). ATM operates on a best effort basis. ATM guarantees that cells will not be disordered. 5 octets 48 octets 53 octets Header Information

7. Asynchronous TDM ATM uses asynchronous time-division multiplexing-that is why it is called Asynchronous Transfer Mode-to multiplex cells corning from different channels. It uses fixed-size slots (size of a cell). ATM multiplexers fill a slot with a cell from any input channel that has a cell; the slot is empty if none of the channels has a cell to send

8. WHY ATM ?

9. WHY ATM ??

10. Problems Frame Networks Before ATM, data communications at the data link layer had been based on frame switching and frame networks. Different protocols use frames of varying size and intricacy. As networks become more complex, the information that must be carried in the header becomes more extensive. The result is larger and larger headers relative to the size of the data unit.

11. Problems (cont.) Large Data Fields In response, some protocols have enlarged the size of the data unit to make header use more efficient (sending more data with the same size header). Unfortunately, large data fields create waste. If there is not much information to transmit, much of the field goes unused. To improve utilization, some protocols provide variable frame sizes to users.

12. Problems(cont.) Mixed Network Traffic As you can imagine, the variety of frame sizes makes traffic unpredictable . Internetworking among the different frame networks is slow and expensive at best, and impossible at worst. Another problem is that of providing consistent data rate delivery when frame sizes are unpredictable and can vary so dramatically

13. ATM provides the solution Cell Networks Many of the problems associated with frame internetworking are solved by adopting a concept called cell networking . A cell is a small data unit of fixed size. In a cell network, which uses the cell as the basic unit of data exchange, all data are loaded into identical cells that can be transmitted with complete predictability and uniformity . As frames of different sizes and formats reach the cell network from a tributary network, they are split into multiple small data units of equal length and are loaded into cells. The cells are then multiplexed with other cells and routed through the cell network. Because each cell is the same size and all are small, the problems associated with multiplexing different-sized frames are avoided.

14. ARCHITECTURE OF ATM

15. Consider a SWITCH..

16. For WAN, Lots of Switches

17. Lots of Switches leads to lots of Users

18. UN I UN I NNI NNI NNI NNI NNI UNI= USER to NETWORK INTERFACE NNI= NETWORK To NETWORK INTERFACE User 1 User 2 User 3 User 4 User 1 User 2 User 3 User 4 Transmission Path Transmission Path

19. Transmission path (TP) A transmission path (TP) is the physical connection (wire, cable, satellite, and so on) between an endpoint and a switch or between two switches. Think of two switches as two cities . A transmission path is divided into several virtual paths . A virtual path (VP) provides a connection or a set of connections between two switches. Cell networks are based on virtual circuits (VCs ). All cells belonging to a single message follow the same virtual circuit and remain in their original order until they reach their destination.

20. Identifiers In a virtual circuit network, to route data from one endpoint to another, the virtual connections need to be identified. Virtual path identifier (VPI) : defines the specific VP Virtual-circuit identifier ( VCl ): defines a particular VC inside the VP. The VPI is the same for all virtual connections that are bundled (logically) into one VP. VPI VCI VPI=Virtual path identifier VCI=Virtual Circuit Identifier

21. Length of Identifiers Length of VPI in User Network Interface: 8 bits Length of VPI in Network To Network Interface: 12 bits Length of VCI will remain same in UNI and NNI: 16 bits

22. ATM Cell Format ATM cell is only 53 bytes long with 5 bytes allocated to the header and 48 bytes carrying the payload. ATM header also contain different fields except VPI and VCI

23. GFC - the Generic Flow Control: field provides local functions such as identifying multiple stations that share a single ATM interface VPI - the Virtual Path Identifier: is used together with the Virtual Channel Identifier (VCI) to identify the virtual circuit. VCI - the Virtual Channel Identifier: is used together with the Virtual Path Identifier (VPI) to identify the virtual circuit along which the cell will be directed as it passes through an ATM network on the way to its destination (values of 0 to 31 are reserved). PT –Payload Type: If 1 st bit=1, then cell has Control data If 1 st bit=0, then cell contains User data If 2 nd bit=1, Congestion occurs If 2 nd bit=0, No Congestion If 3 rd bit=1, this cell is the last one CLP - the Cell Loss Priority: bit field indicates whether the cell should . be discarded if it encounters extreme congestion as it moves through the network. If set to 1, the cell should be discarded before cells that have the bit set to 0. HEC - the Header Error Control: field contains a checksum calculated on the first 4 bytes of the header. It can be used to correct a single bit error in these byte.

24. HOW ATM WORKS

25. ATM uses two types of connections: ATM provides permanent virtual connections and switched virtual connections. Permanent Virtual Connections ( PVC ) P ermanent connections set up manually by network manager. Switched Virtual Connections ( SVC ) S et up and released on demand by the end user via signaling procedures .

26. STEPS Of Establishing ATM Connection: Source PC uses Q.2931 procedures (VPI=0/VCI=5) to setup an ATM connection . The local ATM switch receives the signaling message and passes it to the Connection Manager. The Connection Manager the level of services for that machine calculates the bandwidth required to setup this connection for the forward and reverse paths. If the bandwidth on either the reverse channel or the forward channel is not available, alternate paths are examined . The setup message is then sent back to the Network Switch to allocate the necessary links.

27. The Network switch forwards the connection setup request to the destination machine. The Network switch receives the connection-accept message from the destination machine. Once the Network switch receives the connection-accept message from the called PC, it passes the information to the Connection Manager. The Connection Manager allocates the reverse channel capacity for the called party. Connection Manager informs the Local switch that the connection has been accepted. Connection Manager confirms the connection to the destination PC. Connection Manager informs the source PC and data transmission can begin. STEPS cont .

28. How ATM works to connect a setup:

29. The ATM routing protocol The Private Network Node Interface (PNNI) protocol provides both topology-discovery and call-establishment services. PNNI uses the same shortest-path-first algorithm (OSPF). A PNNI routing table within each switch maintains information about network routes and the bandwidth available on individual links. PNNI routing table to determine a path to the intended destination that meets the specified Quality of Service ( QoS ).

30. SERVICE CATEGORIES: Represents particular combination of traffic and QoS parameters: Constant Bit Rate (CBR): Supports real-time applications. Supports real-time applications requiring tightly constrained delay variation. Real-Time Variable Bit Rate (RT-VBR): Deals with real-time applications with bursty traffic. Non Real-Time Variable Bit Rate ( NRT- VBR ): Deals with non-real time applications wit bursty traffic. Unspecified Bit Rate (UBR): Represents “best effort service” for non real-time applications. Available Bit Rate (ABR): Similar to UBR but enhanced to handle applications of low bandwidth

31. Revised ATM Service Categories

32. ATM LAYERS

33. ATM Layers ATM works on three basic layers: ATM adaption Layer ATM Layer Physical Layer PMD Sublayer Transmission Convergence Sublayer

34. Physical Layer: The physical layer provides for the transmission and reception of ATM cells across a physical medium between two ATM devices. This can be a transmission between an ATM endpoint and an ATM switch, or it can be between two ATM switches . The physical layer is subdivided into a Physical Medium Dependent sublayer and Transmission Convergence sublayer. Physical PMD Transmission Convergence ATM ATM ADAPTION Data Transfer

35. PMD Sublayer The Physical Medium Dependent (PMD) sublayer is responsible for the transmission and reception of individual bits on a physical medium . These responsibilities encompass bit timing, signal encoding, interacting with the physical medium, and the cable or wire itself. PMD Transmission Convergence ATM ATM ADAPTION Data Transfer Physical

36. Transmission Convergence Sublayer The Transmission Convergence (TC) sublayer functions as a converter between the bit stream of ATM cells and the PMD sublayer. When transmitting, the TC sublayer maps ATM cells onto the format of the PMD sublayer PMD Transmission Convergence ATM ATM ADAPTION Data Transfer Physical

37. ATM Layer The ATM layer multiplexes and de-multiplexes and routes ATM cells, and ensures their sequence from end to end. If a cell is dropped by a switch due to congestion or corruption, it is not the responsibility of the ATM layer to correct the dropped cell by means of retransmission or to notify other layers of the dropped cell . Layers above the ATM layer must detect the lost cell and decide whether to correct it or disregard it. PMD Transmission Convergence ATM ATM ADAPTION Data Transfer Physical

38. ATM Adaptation Layer The ATM Adaptation Layer (AAL) creates and receives 48-byte payloads through the lower layers of ATM on behalf of different types of applications. There are five different types of AALs, each providing a distinct class of service. PMD Transmission Convergence ATM ATM ADAPTION Data Transfer Physical

39. ATM Adaptation Layer (AAL) Types In order for ATM to support a variety of services with different traffic characteristics and system requirements: • It is necessary to adapt the different classes of applications to the ATM layer. • This function is performed by the AAL, which is service-dependent. • Four types of AAL were proposed, but two of these (3 and 4) have now been merged into one, AAL 3/4: – AAL 1: Supports connection-oriented, constant bit rate, time-dependent services. – AAL 2: Supports connection-oriented services that do not require constant bit rates. – AAL 3/4: Intended for both connectionless and connection oriented variable bit rate services. – AAL 5: Supports connection-oriented variable bit rate data services. • More efficient compared with AAL 3/4 at the expense of error recovery and built in retransmission.

40.  Conclusion ATM has received a lot of attention recently because of its exciting promises. With ATM, the bottlenecks of the current networks will be solved, networked multimedia capabilities like video conferencing, home shopping, home education, video library, etc. will be brought to the desktops . Due to its high speed and the integration of traffic types (voice, data, and video can be transported on the same network). ATM can accommodate the upcoming new teleservices easily even the requirements for these services are unknown. It also improves the efficiency and simplifies the management of the network by using the same technology for all levels of the network. The ATM Forum has sponsored interoperability demonstrations to prove the technology and continues to meet to discuss the uncertain problems of ATM. At the moment, ATM coexists with current LAN/WAN Technology. Equipment, Services and Applications are available today and are being used in live networks. The telecommunications industry is converging on ATM!