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  1. ISDN Instructor: Sam Nanavaty

  2. ISDN • The Original Digital Service • Technology was defined in the mid-80s • Uses circuit switched technology to support • D (Delta) channels are used for signaling • Data is transported over 64 Kbps B (Bearer) channels • Channels may carry voice, packet data, video, and fax Instructor: Sam Nanavaty

  3. ISDN basics • BRI (Basic Rate Interface) • – Targeted at home and small business users • – Provides 2 B channels over a single twisted pair • • PRI (Primary Rate Interface) • – Targeted at larger corporate customers • – Provides 23 B channels over T1 in North America • – Provides 30 B channels over E1 in Europe Instructor: Sam Nanavaty

  4. Instructor: Sam Nanavaty

  5. Advantages • ISDN provides more bandwidth than a traditional 56 kbps dialup connection. • ISDN uses bearer channels, also called B channels, as clear data paths. • Each B channel provides 64 kbps of bandwidth. • An ISDN connection with two B channels would provide a total usable bandwidth of 128 kbps. • ISDN can be used for backup connections or for implementing Bandwidth on demand. • Each ISDN B channel can make a separate serial connection to any other site in the ISDN network. Instructor: Sam Nanavaty

  6. Disadvantages • BRI is slower than DSL and cable • More expensive than DSL and cable • PRI is still used as a backup mechanism or for load balancing. Instructor: Sam Nanavaty

  7. ISDN Protocol Stack Instructor: Sam Nanavaty

  8. ISDN applications Dial-on-demand routing (DDR) is triggered when traffic that matches a predefined set of criteria is queued to be sent out a DDR-enabled interface. • The traffic that causes a DDR call to be placed is referred to as interesting traffic. • Once the router has transmitted the interesting traffic, the call is terminated. Instructor: Sam Nanavaty

  9. ISDN applications • ISDN is also used for the following purposes: • Backup for the network and the access links • Load balancing Instructor: Sam Nanavaty

  10. Homework 2 • What are the different types of ISDN Interfaces? • What is V.120? • What Protocols are supported over B channels? Instructor: Sam Nanavaty

  11. Frame Relay Instructor: Sam Nanavaty

  12. Frame Relay • Modern telecommunications networks are characterized by relatively error-free digital transmission and highly reliable fiber infrastructures. • Frame Relay relies on upper-layer protocols to detect and recover from errors. • Frame Relay does not have the sequencing, windowing, and retransmission mechanisms that are used by X.25. • The network providing the Frame Relay service can be either a carrier-provided public network or a privately owned network. Instructor: Sam Nanavaty

  13. Most popular service today that replaces existing leased line and X.25 infrastructures. • Why – Better control of bandwidth, scalability, low latency, congestion control and efficiency • Used in private and public networks Instructor: Sam Nanavaty

  14. Frame Relay Network Instructor: Sam Nanavaty

  15. FRAME RELAY PROTOCOL FORMAT Instructor: Sam Nanavaty

  16. Field definitions • Flag: Beginning or end of frame • Address/ control – 2 bytes • DLCI is a 10 bit address field • Congestion control – 3 bits [FECN,BECN, DE] • Information field – variable length • FCS – Frame Check sequence for error control • Flag: End of frame Instructor: Sam Nanavaty

  17. Data Link Connection Identifier • Identifies a logical circuit between a router and a frame relay switch • DLCI s normally have local significance (exception global DLCIs) • Think of DLCI as the equivalent of MAC address in LAN domain. • The FR switch maps DLCIs between each pair of routers to build a Permanent Virtual Connection (PVC). Instructor: Sam Nanavaty

  18. Instructor: Sam Nanavaty

  19. CIR, Bc, Be • Committed Information Rate (CIR) is a guaranteed rate, in bits per second that a service provider commits to providing • Committed Burst (Bc) is the maximum number of bits that the switch agrees to transfer during any Committed rate measurement interval • Excess Burst (Be) is the maximum number of uncommitted bits that a FR switch attempts to transfer beyond CIR. (Be) is limited to the port speed of the Local Access. Network treats (Be) data as discard eligible. Be Bc CIR Instructor: Sam Nanavaty time

  20. Forward Explicit Congestion Notification/ Backward Explicit Congestion Notification • FECN – Upon encountering congestion in the network, a FR switch sends FECN to the destination device indicating that the congestion has occurred • BECN – Upon encountering congestion in the network, a FR switch sends BECN to the source device instructing it to reduce the rate at which it is sending the packets. Instructor: Sam Nanavaty

  21. Discard Eligibility (DE) • DE bit is set by the switch at the ingress for all the Frame Relay traffic that exceeds the Committed Information Rate • Upon detecting heavy congestion, the Switch is authorized to drop the traffic marked DE Instructor: Sam Nanavaty

  22. ATM Asynchronous Transfer Mode Instructor: Sam Nanavaty

  23. ATM Facts • Worldwide ATM switch market for 2004 was about $5.23 Billion • Roughly 80% of Service Providers use ATM in their core networks Instructor: Sam Nanavaty

  24. Where is ATM deployed? • ATM workgroup in campus networks • ATM in Core Network • Content Delivery Networks (CDNs) • Internet backbones • Carrier infrastructures Instructor: Sam Nanavaty

  25. ATM switches Instructor: Sam Nanavaty

  26. ATM – Cell switching • •ATM breaks up streams of data, video, and voice into fixed size units called “cells” • •A fixed size cell allows switching decisions to be done at the hardware level • •Hardware Level switching implies high speed! • •ATM networks switch and multiplex all information using these fixed length cells Instructor: Sam Nanavaty

  27. ATM over SONET • ATM cells are transported over long distances via SONET • Please note that SONET does not “switch” the ATM cells. The switching is accomplished by ATM switches. Instructor: Sam Nanavaty

  28. Voice Video Data Adaptation module ATM Physical Layer Instructor: Sam Nanavaty

  29. ATM User to Network Interface (UNI) header PT: Indicates the type of information in the Payload field CLP: Cell Loss Priority: when set to 1, the cell is discard eligible GFC- Generic Flow Control: Control traffic flow at the User network Interface VCI – Virtual Channel Identifier: Have same QOS requirements as the VPI and multiple VC’s are multiplexed within a single VP. VPI – Virtual Path Identifier: bundle of virtual channels switched transparently across the ATM network on the basis of the common VPI Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  30. Relationship between the TP, VP and VC Virtual Path Transmission Path Virtual Channels Instructor: Sam Nanavaty

  31. Service Types supported by ATM CBR Constant Bit Rate service provides constant bandwidth with a fixed timing relationship, which requires clocking synchronization. Because CBR traffic reserves a fixed amount of bandwidth, some trunk bandwidth might go unused. CBR is typically used for circuit emulation services to carry real-time voice and video. VBR-RT Variable Bit rate – Real Time service provides only a partial bandwidth guarantee. Cell delay is controlled in this case due to real time requirements. Typical applications include packetized voice and video, and interactive multimedia. Supports statistical multiplexing VBR-NRTVariable Bit rate – Non Real Time service provides a partial bandwidth guarantee, but with a higher cell delay than VBR-RT. This service category is suitable for bursty applications (i.e. applications with unpredictable traffic patterns). Supports statistical multiplexing. E.g., Web browsing Instructor: Sam Nanavaty

  32. Service Types supported by ATM • ABR provides a best effort service, in which feedback flow control within the network is used to increase bandwidth when no congestion is present, maximizing the use of the network. ABR does guarantee a minimum cell rate (MCR). Applications include Database Archival, File Transfers etc. • UBR service provides no bandwidth guarantee, but attempts to fill bandwidth gaps with bursty data. Used for low bandwidth applications or the applications where end user experience is not impacted by latency variations. Instructor: Sam Nanavaty