Frame relay
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  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2
  • Protocols and the TCP/IP Suite Chapter 2

Frame relay Presentation Transcript

  • 1. Frame Relay
    • To provide a telecommunication service for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN).
    • Frame Relay puts data in variable-size units called "frames" and leaves any necessary error-correction (such as re-transmission of data) up to the end-points.
    • This speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection
      • without having to pay for a full-time leased line ,
      • while the service-provider figures out the route each frame travels to its destination and can charge based on usage.
    NDSL, Chang Gung University
  • 2.
    • Frame Relay has its technical base in the older X.25 packet-switching technology, designed for transmitting data on analog voice lines.
    • Unlike X.25, whose designers expected analog signals , Frame Relay offers a fast packet technology , which means that the protocol does not attempt to correct errors.
    • When a Frame Relay network detects an error in a frame, it simply drops that frame.
    • The end points have the responsibility for detecting and retransmitting dropped frames.
    NDSL, Chang Gung University
  • 3. NDSL, Chang Gung University
  • 4. Introduction
    • Frame Relay (FR) is a high-performance WAN protocol that operates at the physical and data link layers of the OSI reference model.
    • FR originally was designed for use across Integrated Service Digital Network (ISDN) interfaces.
    • Today, it is used over a variety of other network interfaces as well.
    • FR is an example of a packet-switched technology.
  • 5. What is Frame Relay?
    • “ A packet-switching protocol for connecting devices on a Wide Area Network (WAN) ”
    • FR networks support data transfer rates at
      • T-1 (1.544 Mb/s)
      • T-3 (45 Mb/s) speeds.
    • In fact, you can think of Frame Relay as a way of utilizing existing T-1 and T-3 lines owned by a service provider.
    • Most telephone companies now provide FR service for customers who want connections at 56 Kb/s to T-1 speeds. (In Europe, FR’s speeds vary from 64 Kb/s to 2 Mb/s.
    • Frame Relay is quite popular because it is relatively inexpensive . However, it is being replaced in some areas by faster technologies, such as ATM.
  • 6. Frame Relay Devices (cont.)
  • 7. Frame Relay Devices
    • Devices attached to a Frame Relay WAN fall into the following two general categories:
      • Data terminal equipment (DTE)
        • DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer.
        • Example of DTE devices are terminals, personal computers, routers, and bridges.
      • Data circuit-terminating equipment (DCE)
        • DCEs are carrier-owned internetworking devices.
        • The purpose of DCE equipments is to provide clocking and switching services in a network, which are the devices that actually transmit data through the WAN.
  • 8. Frame Relay Devices (cont.)
    • The connection between a DTE device and a DCE device consists of both a physical layer component (L1) and a link layer component (L2) .
    • The physical component defines the mechanical, electrical, functional, and procedural specifications for the connection between the devices.
    • One of the commonly used physical layer interface specifications is the recommended standard (RS)-232 .
  • 9. Serial Point-to-Point Connection Network connections at the CSU/DSU EIA/TIA-232 EIA/TIA-449 EIA-530 V.35 X.21 End user device Service Provider DTE DCE Router connections
  • 10. Circuit-Switching
    • Long-haul telecom network designed for voice
    • Network resources dedicated to one call
    • Shortcomings when used for data:
      • Inefficient (high idle time)
      • Constant data rate
  • 11. Packet-Switching
    • Data transmitted in short blocks, or packets
    • Packet length < 1000 octets
    • Each packet contains user data plus control info (routing)
    • Store and forward
  • 12. The Use of Packets
  • 13. Advantages with compared to Circuit-Switching
    • Greater line efficiency (many packets can go over shared link)
    • Data rate conversions
    • Non-blocking under heavy traffic (but increased delays). When traffic becomes heavy on a circuit-switching network, some calls are blocked.
    • Priorities can be used.
  • 14. Disadvantages relative to Circuit-Switching
    • Packets incur additional delay with every node they pass through
    • Jitter : variation in packet delay
    • Data overhead in every packet for routing information, etc
    • Processing overhead for every packet at every node traversed
  • 15. Simple Switching Network
  • 16. Switching Technique
    • Large messages broken up into smaller packets
    • Datagram
      • Each packet sent independently of the others
      • No call setup
      • More reliable (can route around failed nodes or congestion)
    • Virtual circuit
      • Fixed route established before any packets sent
      • No need for routing decision for each packet at each node
  • 17. Packet Switching: Datagram Approach
  • 18. Packet Switching: Virtual-Circuit Approach
  • 19. Virtual Circuits and Frame Relay Virtual Connections
  • 20. Protocol Architecture
  • 21. Control Plane
    • Between subscriber and network
    • Separate logical channel used
      • Similar to common channel signaling for circuit switching services
    • Data link layer
      • LAPD (Q.921)
      • Reliable data link control
      • Error and flow control
      • Between user (TE) and network (NT)
      • Used for exchange of Q.933 control signal messages
  • 22. User Plane
    • End to end functionality
    • Transfer of info between ends
    • LAPF (Link Access Procedure for Frame Mode Bearer Services) Q.922
      • Frame delimiting, alignment and transparency
      • Frame mux and demux using addressing field
      • Ensure frame is integral number of octets (zero bit insertion/extraction)
      • Ensure frame is neither too long nor short
      • Detection of transmission errors
      • Congestion control functions
  • 23. LAPF Core Formats
  • 24. User Data Transfer
    • One frame type
      • User data
      • No control frame
    • No inband signaling
    • No sequence numbers
      • No flow nor error control
  • 25. FRAME RELAY CALL CONTROL
    • Call Control Alternatives
    • In frame relay operation, a user is not connected directly to another user, but rather to a frame handler in the network;
    • For X.25, a user is connected to a packet handler.
  • 26. Switched access
  • 27. Switched access
    • The local exchange does not provide the frame-handling capability.
    • Switched access must be provided from the user's terminal equipment (TE) to the frame handler
    • Connection will be a demand connection (set up at the time of the call) or a semi-permanent connection (always available).
  • 28. Integrated access
  • 29. Integrated access
    • The user is connected to a pure frame-relaying network or to a switched network
    • The local exchange provide the frame handling capability.
    • The user has direct logical access to the frame handler.
  • 30. Access Connection
    • The connection between the subscriber and the frame handler is access connection.
    • Once this connection exists, it is possible to multiplex multiple logical connections as frame relay connections,
    • They may be either on-demand or semipermanent.
  • 31. Frame Relay Connection
    • The subscriber must established an access connection to a frame handler
    • A frame relay connection, analogous to a packet-switching virtual circuit, must first be established between two users.
    • Each connection has unique data link connection identifier (DLCI).
  • 32. Data Transfer
    • 1. Establish a logical connection between two end points, and assign a unique DLCI to the connection.
    • 2. Exchange information in data frames. Each frame includes a DLCI field to identify the connection.
    • 3. Release the logical connection.
  • 33. Data Transfer
    • 1. Establish a logical connection between two end points, and assign a unique DLCI to the connection.
    • 2. Exchange information in data frames. Each frame includes a DLCI field to identify the connection.
    • 3. Release the logical connection.
  • 34. Frame relay Connection
    • The establishment and release of a logical connection will be carried out in a connection.
    • Exchange of messages over a logical connection is dedicated to call control
    • A frame with DLCI = 0 contains a call control message in the information field. At a minimum, four message types are needed:
  • 35. Messages
    • SETUP - request the establishment of a logical connection if it accepts the connection
    • CONNECT - assign the DLCI by choosing an unused value and including this value in the SETUP message; otherwise, the DLCI value is assigned by the accepting side in the CONNECT message.
    • RELEASE - to clear a logical connection
    • RELEASE COMPLETE - Not accept a connection
  • 36. Messages
  • 37. Connection
    • Exchanges involved for switched access to a frame handler
    • The calling user must establish a circuit-switched connection to a frame handler
    • Done with the usual SETUP, CONNECT and CONNECT ACK messages,
  • 38. Data Transfer