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

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

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