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ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks

ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks 1
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Dr.NeerajMittal,India,Teacher
Published Date:19-07-2017
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ISDN, B-ISDN, X.25, Frame-Relay, ATM Networks: A Telephony View of Convergence Architectures Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Switched Packet-Data Services  Integrated Services Vision and Concept Ingredients  History: X.25, ISDN, Frame Relay  ATM Networks: foundation for B-ISDN  ATM Key Concepts  ATM Signaling and PNNI Routing  ATM Traffic Management  IP over ATM: setting the stage for MPLS Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2A Telephony View of Convergence  Separate Voice network (PSTN) and Data Networks (Frame Relay, SMDS, etc.)  PSTN sometimes used as a data network backbone, but  PSTN is circuit switched (voice-optimized) and PSTN- based WAN not efficient  Delay sensitive traffic such as voice not possible on data networks since no guarantee of QoS  Initial attempts to converge data and voice network not too successful, i.e. ISDN  B-ISDN and ATM networks viewed as the convergence end-point leading world-wide domination of telephony driven standards Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Switched Packet-Data Services  After the success of T1, the telephone carriers saw the growth in packet switched networks  Evolved their own flavors of packet switching, notably X.25, ISDN, SMDS, Frame Relay, ATM etc  Key concept: Switched services  Switched services: (aka dial-up service)  Digital communications that is active only when the customer initiates a connection.  Subsumes both circuit switched and packet switched.  Customer to be billed only when the line is active.  Led to activity-based or average-load-based pricing models that did not necessarily have a distance-based component  Vs peak-rate and distance-sensitive T-carrier pricing Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Ingredients  Signaling and setup of a virtual circuit (I.e. nailing down a switched path) is a common feature  Signaling was heavyweight, and was coupled to heavyweight QoS routing  Contrast this to “connectionless, best-effort” Internet  Long 20-byte global addresses used only in signaling  Short 4-byte local labels (aka DLCI etc) used in packets (cells): “label-switching”  Large address space, low per-packet overhead  ISDN/B-ISDN vision of an end-to-end integrated digital network:  Rich QoS capabilities developed: support for voice, data, video traffic Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Ingredients (contd)  X.25 - Frame relay/ATM: reduction of hop-by-hop processing complexities  Led to the development of high-speed switches and networks  A serious attempt to inter-network with a variety of data-networking protocols (IP, Ethernet etc)  Integration (“coupling”) of too many features led to slow rollout, enormous overall complexity  Failure to attain the end-to-end market vision  Current trend is to “de-couple” building blocks of the architecture within the context of IP/MPLS, sacrificing strict performance guarantees. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6X.25 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7X.25  First packet switching interface in the telephony world  Issued in 1976 and revised in 1980, 1984, 1988, and 1992.  Data Terminal Equipment (DTE) to Data Communication Equipment (DCE) interface  User to network interface (UNI)  Slow speeds, used in point-of-sale apps (eg: credit-card validation) and several apps abroad Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8X.25 Virtual Circuits  Circuit: Pin a path, reserve resources, use TDM based transmission  Virtual Circuit = Virtual Call: pin a path, optionally reserve resources  Connection-oriented: Setup an end-to-end association (data- structure); path not pinned  Connectionless: stateless. No path, no end-to-end association  Two Types of Virtual Circuits:  Switched virtual circuit (SVC): Similar to phone call  Permanent virtual circuit (PVC): Similar to leased lines  Up to 4095 VCs on one X.25 interface Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9X.25 Protocol Layers  Note: the three modular layers were co-specified by the same standards body  Layers:  X.21 replaced by EIA-232 (RS-232C)  LAP-B = Link access procedure - Balanced  Packet layer = Connection-oriented transport over virtual circuits Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10X.25 Physical Layer  Electrical and mechanical specifications of the interface  X.21 = 15-pin digital recommendation  X.21bis = X.21 twice = X.21 second  Interim analog specification to allow existing equipment to be upgraded.  Now more common than X.21 = X.21 Rev 2  RS-232-C developed by Electronics Industries  Association of America (EIA) is most common  Uses 25-pin connector. Commonly used in PCs. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Link Layer Roots: HDLC Family  Original:  Synchronous Data Link Control (SDLC): IBM  Derivatives:  High-Level Data Link Control (HDLC): ISO  Link Access Procedure-Balanced (LAPB): X.25  Link Access Procedure for the D channel (LAPD): ISDN  Link Access Procedure for modems (LAPM): V.42  Point-to-Point Protocol (PPP): Internet  Logical Link Control (LLC): IEEE  Link Access Procedure for half-duplex links (LAPX): Teletex  Advanced Data Communications Control Procedures (ADCCP): ANSI  V.120 and Frame relay also use HDLC Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12HDLC (contd)  Primary station: Issue commands (master)  Secondary Station:Issue responses (slave)  Hybrids:  Combined Station: Both primary and secondary: a.k.a Asynchronous Balanced Mode (ABM) Balanced Configuration: Two combined stations  Unbalanced Configuration: One or more secondary  Normal Response Mode (NRM): Response from secondary  Asynchronous Response Mode (ARM): Secondary may respond before command Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13LAPB  Uses balanced mode subset of HDLC between DTE and DCE  Uses 01111110 as frame delimiter  Uses bit stuffing to avoid delimiters inside the frames  Uses HDLC frame format  Point-to-point: Only two stations - DTE (A), DCE (B)  Addresses: A=00000011, B=00000001  Address = Destination Addresses in Commands Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14HDLC frames  Information Frames: User data  Piggybacked Acks: Next frame expected  Poll/Final = Command/Response  Supervisory Frames: Flow and error control  Go back N and Selective Reject  Final No more data to send  Unnumbered Frames: Control  Mode setting commands and responses  Information transfer commands and responses  Recovery commands and responses  Miscellaneous commands and responses Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15HDLC Operation SABM: Set Asynchronous Balanced Mode UA: Unnumbered ACK DISC: disconnect RR: Receiver Ready RNR: Receiver Not Ready I: information frame Heavyweight Link-Setup and Per-Packet Acking Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16HDLC Operation (Contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17X.25 Packet Level: Layer 3  Packet Level = “End-to-end” for X.25 networks But really Layer 3 (network layer)  Packet level procedures: Establishment and clearing of virtual calls Management of PVCs Flow Control Recovery from error conditions Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18X.25 Packet Level (Layer 3) Signaling Operation Redundant signaling and reliability functions at L2 and L3 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19X.25 Packet Format  GFI = Packet formatting information  PTI = 20 possible packet types (for de-multiplexing)  Logical Channel Group and Channel Numbers:  Virtual circuit identifier Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20