BISDN and ATM 1 ATM BISDN Broadband Integrated

B-ISDN and ATM 1

ATM / B-ISDN • Broadband Integrated Services Digital Network – In the 1970 s the telecommunications industry conceived that digital services would follow much the same pattern as voice services, and conceived a grandiose vision of end-to-end circuit switched services, known as the Broadband Integrated Services Digital Network (B-ISDN). – This was conceived as a logical extension of the end-to-end circuit switched data service, ISDN. – The technology for B-ISDN was going to be Asynchronous Transfer Mode (ATM), which was intended to carry both synchronous voice and asynchronous data services on the same transport. – The B-ISDN vision has been overtaken by the technology of the Internet. The ATM technology survives as a low-level layer in most DSL technologies. – Over fibre optic lines, the maximum Data bandwidth is 1. 5 Megabits and point-to-point protocol is typically used to carry data over the B channels.

ATM / B-ISDN • Asynchronous Transfer Mode (ATM) – cell relay network protocol which encodes data traffic into small fixed sized (53 byte; 48 bytes of data and 5 bytes of header information) cells instead of variable sized packets as in packet-switched networks (such as the Internet Protocol or Ethernet).

Characteristics of ATM • • • Uses small, fixed-sized cell Connection oriented Bandwidth allocation on demand Supports multiple service types Applicable to LAN and WAN 4

ATM Signaling • UNI : User to Network Interface • NNI : Network to Network Interface • Different protocol in the different domain 5

Virtual Path / Virtual Channel • • Connection Identifier : VPI/VCI Physical Link : Contains multiple VPs Virtual Path : Contains multiple VCs Virtual Channel : Logical path between ATM endpoint 6

VP and VC Switching 7

ATM Cell Header PTI Payload Type Identifier(3 Bits) - 1 bit : User/Control Data. - 2 bit : Congestion flag. - 3 bit : Last Cell flag CLP Cell Loss Priority Bit HEC Header Error Check(8 Bits) 8

Permanent Virtual Circuit • Manual updates of VPI/VCI tables in network equipment 9

Switched Virtual Curcuit • Setup connection using UNI/NNI signaling 10

ATM Reference Model Q. 2931, Q 2971 SAAL ATM PHY Signaling ATM Adaptation Layer 11

ATM Service Criteria • Traffic parameters – Peak Cell Rate(PCR), Sustainable Cell Rate(SCR) – Maximum Burst Size(MBS), Minimum Cell Rate(MCR) • Quality of Service – Maximum Cell Transfer Delay(MCTD) – Cell Delay Variation Tolerance(CDVT) – Cell Loss Ratio(CLR) 12

ATM Service Categories 13

Traffic Management - I • CAC(Connection Admission Control) • Determine whether a connection can be progressed or not - satisfy the traffic contract of the connection - not disturb traffic contracts of the other connections 14

Traffic Management - II • UPC(Usage Parameter Control) • Protect network resources from malicious as well as unintentional misbehavior - based on traffic contract of the connection - action : cell discard, cell tagging 15

Traffic Management - III • CLP(Cell Loss Priority) Control • In Congestion state - EFCI(Explicit Forward Congestion Control) - CLP(Cell Loss Priority) 16

Traffic Management – IV • • • CAC / Connection Management UPC (Policing) CLP / EFCI control Frame Discard Traffic Shaping ABR Congestion Feedback 17

ATM Signaling Protocol • Point-to-Point ATM Connection(Q. 2931) 18

Reserved VPI/VCI Q. 2971 Q. 2931 19

Message Structure Information Element Length Protocol discriminator Distinguish Message 1 Call reference Identify call at the local UNI 4 Message type Identify the function of message 2 AAL parameter 4 -21 ATM traffic descriptor 12 -20 Broadband bearer capability 6 -7 Qo. S parameter 6 … … … 20

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