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Hello, I am a Newbie in Networking and Wanted to Learn Networking , Yesterday i was Reading an article in Newspaper educational Section about the Frame relay and X.25 Protocol and Tried hard to understand it but cannot get it. so can you guys please provide me some information about frame relay and x.25 protocol and what is the diffrence between the both ? thanks in advance
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Frame relay is a synchronous HDLC protocol based network. Data is sent in HDLC packets, referred to as "frames". The diagram below of an HDLC frame may be familiar, since without adding specific definitions of how the Address, Control and CRC is used, the diagram is applicable to IBM's SDLC, to X.25, to HDLC, to Frame Relay, as well as other protocols.
The protocol is similar to that of an X.25 network, except all circuits are permanently assigned. What is a circuit? A circuit is a link between user end points. In frame relay and X.25 networks, circuits are known as "permanent virtual circuits", or PVC's. The circuits are known as virtual because they are not electrical ciruits where there is a direct electrical connection from end to end. Rather, there is a "logical" connection, or virtual connection, where the user data moves from end to end, but without a direct electrical circuit.
X.25 circuits can be initiated and ended from the users terminals. Frame relay circuits are set up at the time of installation and are maintained 24 hours per day, 7 days per week. Frame relay circuits are not created and ended by user at their terminals or PC's. However, the user may have an application running over a frame relay circuit where computer to terminal sessions are initiated and ended by the user. These sessions are related to the application, not to the underlying frame relay network.
Frame relay relies on the customer equipment to perform end to end error correction. Each switch inside a frame relay network just relays the data (frame) to the next switch. X.25, in contrast, performs error correction from switch to switch. The networks of today are sufficiently error free to move the burden of error correction to the end points. Most modern protocols do error correction anyway, protocols such as SDLC, HDLC, TCP/IP, stat mux protocols, etc.
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Frame relay is a telecommunication service designed 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 a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continous, 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. An enterprise can select a level of service quality - prioritizing some frames and making others less important. Frame relay is offered by a number of service providers, including AT&T. Frame relay is provided on fractional T-1 or full T-carrier system carriers. Frame relay complements and provides a mid-range service between ISDN, which offers bandwidth at 128 Kbps, and Asynchronous Transfer Mode (ATM), which operates in somewhat similar fashion to frame relay but at speeds from 155.520 Mbps or 622.080 Mbps.
Frame relay is based on the older X.25 packet-switching technology which was designed for transmitting analog data such as voice conversations. Unlike X.25 which was designed for analog signals, frame relay is a fast packet technology, which means that the protocol does not attempt to correct errors. When an error is detected in a frame, it is simply "dropped." (thrown away). The end points are responsible for detecting and retransmitting dropped frames. (However, the incidence of error in digital networks is extraordinarily small relative to analog networks.)
Frame relay is often used to connect local area networks with major backbones as well as on public wide area networks and also in private network environments with leased lines over T-1 lines. It requires a dedicated connection during the transmission period. It's not ideally suited for voice or video transmission, which requires a steady flow of transmissions. However, under certain circumstances, it is used for voice and video transmission.
Frame relay relays packets at the data link layer of the Open Systems Interconnection (OSI) model rather than at the Network layer. A frame can incorporate packets from different protocols such as Ethernet and X.25. It is variable in size and can be as large as a thousand bytes or more.
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Frame Relay vs. X.25
There are various differences between X.25 and Frame Relay. The most significant are:
- Call Control
X.25 connection establishment and release (call control) use in-band signaling within the same virtual channel used for user data transmission causing additional overhead. Frame Relay call control uses separate virtual channels identified by reserved DLCI using the LMI (Local Management Interface) protocol.
- Routing vs. Switching
X.25 performs packet switching on OSI layer 3 (network layer); Frame Relay performs packet switching on OSI layer 2 (data-link). Frame Relay does not use any layer 3 protocol.
- Flow Control
Frame Relay (FR) doesn't perform flow control between frame handlers (FR routers). X.25 routers have to acknowledge each frame; in case of frame errors frames have to be retransmitted and acknowledged. Frame Relay relies on flow control performed by higher layer protocols.
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Frame relay
In the context of computer networking, frame relay consists of an efficient data transmission technique used to send digital information. It is a message forwarding "relay race" like system in which data packets, called frames, are passed from one or many start-points to one or many destinations via a series of intermediate node points.
Network providers commonly implement frame relay for voice and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line (or leased line) to a frame-relay node. The frame-relay network handles the transmission over a frequently-changing path transparent to all end-users.
With the advent of MPLS, VPN and dedicated broadband services such as cable modem and DSL, the end may loom for the frame relay protocol and encapsulation.[citation needed] However many rural areas remain lacking DSL and cable modem services. In such cases the least expensive type of "always-on" connection remains a 64-kbit/s frame-relay line. Thus a retail chain, for instance, may use frame relay for connecting rural stores into their corporate WAN.
X.25
X.25 is an ITU-T standard network layer protocol for packet switched wide area network (WAN) communication. An X.25 WAN consists of packet-switching exchange (PSE) nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links. X.25 is part of the OSI protocol suite, a family of protocols that was used especially during the 1980s by telecommunications companies and in financial transaction systems such as automated teller machines. X.25 is today to a large extent replaced by less complex protocols, especially the Internet protocol (IP) although some telephone operators offer X.25-based communication via the signalling (D) channel of ISDN lines.
Source-wikipedia
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Hello ,Lets get some historial perspective here. X.25 and Frame are switched packet delivery services. X.25 is generally for much slowly links and is extremely useful is very bad comm areas.. 3rd world countries and such where the infrastructure is mariginal at best. It has quite a bit of overhead for error checking *native* to the protocol unlike Frame which has very little error checking and relies on the upper level protocols in the stack to take care of the error correction. X.25 is still very popular in parts of Europe ( the old East Germany), parts of Russia, South America, Middle East and others which I'm forgetting. Many times those in America forget that the rest of the world is not quite as far as along as they are.
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Frame Relay Vs X.25
The biggest difference between Frame Relay and X.25 is that X.25 guarantees data integrity and network managed flow control at the cost of some network delays. Frame Relay switches packets end to end much faster, but there is no guarantee of data integrity at all. Frame Relay is cost effective, partly due to the fact that the network buffering requirements are carefully optimized. Compared to X.25, with its store and forward mechanism and full error correction, network buffering is minimal. Frame Relay is also much faster than X.25: the frames are switched to their destination with only a few byte time delay, as opposed to several hundred milliseconds delay on X.25.
An evolution beyond the X.25 protocol, Frame Relay is a network interface standard based on statistical multiplexing. By combining the flexibility of X.25 packet protocol with the performance of private lines, Frame Relay Service can move data much more efficiently than the packet protocol. In fact, Frame Relay Service streamlines the processing steps associated with X.25 error detection/correction and routing procedures.
Frame Relay technology takes advantage of highly accurate digital networks with their reduced line errors and intelligent network end point devices with their end-to-end error checking protocols. The reduced per packet processing time allows you to process more user data. Also, the upgrade to Frame Relay Service is simple and cost effective because Frame Relay Service is based on the HDLC protocol, which is popular among LAN bridges, routers and other communications devices.
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