ATM. COMPSCI 726 Network Defence and Countermeasures. Shujie Cui

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1 ATM COMPSCI 726 Network Defence and Countermeasures Shujie Cui

2 Asynchronous Transfer Mode (ATM) Network Source:

3 ATM Overview IP protocol only provides best effort service. RSVP is a solution on the top of IP. IPv6 optimize IP layer. ATM is a good alternative of IP based network: ATM has low network latency for voice, video, and realtime applications. Bandwidth flexibility: The bandwidth can be dynamically assigned to users. Scalability: capacity may be increased on demand. The bandwidth up to 10Gbps bit rate

4 ATM Network Architecture ATM endpoint An ATM endpoint contains an ATM network interface adapter. ATM endpoints can be workstations, routers, digital service units (DSUs), LAN switches, and video coder-decoders (CODECs). ATM Switch ATM switches support two primary types of interfaces: UNI and NNI UNI NNI

5 User-Network Interface (UNI) Private UNI Connects an ATM end-point to a private ATM switch Public UNI Connects an ATM end-point or a private ATM switch to a public ATM switch

6 Network-Node Interface (NNI) Private NNI Connects two ATM switches within the same private organization Public NNI Connects two ATM switches within the same public organization

7 Asynchronous Transfer Mode ATM cell is small fixed-sized packet, can be switched very quickly. 5 Bytes 48 Bytes Header Payload ATM is a cell-switching that combines the benefits of circuit switching with those of packet switching.

8 Circuit switching VS Packet switching circuit switching guarantees reliable connection, capacity and can guarantee a specific QoS. packet switching guarantees flexibility and efficiency for intermittent traffic

9 ATM Virtual Channels ATM is connection-oriented. A virtual channel is set up between a pair of hosts connected to a network of switches. ATM switching is based on the idea of a virtual channel or VC.

10 ATM Virtual Connection Two levels of ATM connections: Virtual path connections Virtual channel connections Indicated by two fields in the cell header: Virtual Path Identifier (VPI) Virtual Channel Identifier(VCI)

11 ATM Switching The existence of a VC is based on entries in routing tables in each switch. ATM switch accepts the incoming cell from an ATM endpoint or another ATM switch. It then reads and updates the cell header information and quickly switches the cell to an output interface toward its destination. Source:

12 ATM Switching Routing can be on the basis of the value of VPI or VCI, or both VPI and VCI. The VPI can be used where multiple connections are set up between the same pair of hosts. The VCI field is used where connections are not between the same pair of hosts.

13 Cell Switching (Virtual Circuit ) Offering the advantage of circuit switching and packet switching.

14 ATM Multiplexing Technology Statistical Time Division Multiplexing (STDM): first-come first-served

15 ATM Virtual Connection Voice Data packets 1,b 1,a 2,a 2,a 1,a 1,b MUX In practice VPI,VCI 1,b 1,a 2,a 2,b 2,a 1,a 1,b Images 2,b In concept We can image the cells with the same VPI and VCI are transferred in the same channel. 1 2 b a b a 1,b 1,b ` 1,a ` 1,a 2,a 2,a 2,b 2,b

16 Create Virtual Connection Default connection: VPI=5, VCI=0 setup Call proceeding connect ACK setup Call proceeding connect ACK setup Call proceeding connect ACK Setup=(A s ATM address, B s ATM address, CBR, traffic parameters release release release Release complete Release complete Release complete

17 Virtual Circuit Permanent Virtual Circuit (PVC): Dedicated virtual circuit established for continuous use. No need for repeated call setup and clearing. Usually preconfigured by a service provider. PVC is similar to a leased line. Switched Virtual Circuit (SVC): Setup on a per-call basis and disconnected when the call is terminated. SVC is dynamically established on demand. SVC is torn down when transmission is finished. SVC is similar to a normal PSTN phone line.

18 ATM Traffic Control and QoS Constant Bit Rate (CBR) service A constant Cell Rate (PCR) is specified, e.g. 128Kbit/sec voice. For applications such as telephone, video conferencing, interactive Audio, TV. Variable Bit Rate (VBR) An average cell rate is specified, require a bounded delay for delivery. For bursty traffic, VoIP, interactive compressed voice/video. ABR - Available bit rate A minimum guaranteed rate is specified. Used for data traffic such as file transfer and . UBR Unspecified bit rate: traffic is allocated to all remaining transmission capacity. Delay and delay variations can be tolerated. For non-real time applications, most TCP/IP applications.

19 ATM Services Network Architecture Internet ATM ATM ATM ATM Service Model best effort CBR VBR ABR UBR Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no Congestion feedback no (inferred via loss) no congestion no congestion yes no Guarantees?

20 ATM Protocol Reference Model source

21 AAL (ATM Adaptation Layer) Segment data into cells for ATM layer. Resemble cells into data for upper layer. AAL exists only in end systems, not in switches.

22 AAL (ATM Adaptation Layer) The Convergence Sublayer (CS) The Segmentation and Reassembly Sublayer (SAR) 4 types of AALs: AAL1 AAL2, AAL3/4 AAL5

23 Source

24 AAL Layer AAL1 is used for CBR services, such as video and voice from upper layer. Require synchronisation of source and destination. AAL2 is used for VBR services such as compressed video, voice, and fax. AAL3/4, AAL5 support connection-oriented and connectionless data services. Many ATM products use AAL5 to support all the above classes of traffic.

25 ATM Layer It accepts 48 bytes segments from AAL layer, transforms them into 53 bytes by adding 5 bytes cell header. Establishment and release VC Switching Multiplexing Congestion control

26 ATM Cell Format The format of header has two different forms. One for use at UNI The other use at NNI 5 bytes

27 ATM Cell Format GFC, generic flow control, is designed to control the amount of traffic entering the network. CLP, cell loss priority, cells with low-priority can be discarded during period of congestion. HEC, header error check, used to reduce errors in header. 5 bytes

28 Physical Layer SONET/SDH(Synchronous Optical Network / Synchronous Digital Hierarchy) ATM Forum also proposed physical layer standards over twisted-pair wire, to accelerate the acceptance of ATM.

29 Advantages Fast switching of small cells Better utilisation than circuit switching No fragmentation problem Reduce jitter (variance in delays) Easier to allocate bandwidths and delays to VCs Easier to implement priorities to traffic Enables traffic management and congestion control Suitable for time-critical information such as voice or video

30 Disadvantages The cell header overhead is too heavy, 5/53. The applications that based on ATM are less. High cost. High speed Ethernet (HSE) is more competitive. Gigabit Ethernet (a much cheaper technology) has replaced ATM on many networks. Gigabit Ethernet is a natural upgrade path for Fast Ethernet.

31 Application

32 References e_switching#figure:_an_atm_network_comprises_atm_s witches_and_endpoints Siu K Y, Jain R. A brief overview of ATM: protocol layers, LAN emulation, and traffic management[j]. ACM SIGCOMM Computer Communication Review, 1995, 25(2): 6-20.

33 Thanks for your attention Any questions?

ATM. Asynchronous Transfer Mode. Networks: ATM 1

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