28. Protocol Frame Relay (fr).

Frame Relay is a protocol standard for LAN internetworking which provides a fast and efficient method of transmitting information from a user device to LAN bridges and routers. The Frame Relay frame is transmitted to its destination by way of virtual circuits to a destination point. 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 to a Frame Relay node .Frame Relay offers an attractive alternative to both dedicated lines and networks for connecting LANs to bridges and routers.

Advantages of Frame Relay:

The success of the Frame Relay protocol is based on the following two underlying factors:

• Because virtual circuits consume bandwidth only when they transport data, many virtual circuits can exist simultaneously across a given transmission line. In addition, each device can use more of the bandwidth as necessary, and thus operate at higher speeds.

• The improved reliability of communication lines and increased error-handling sophistication at end stations allows the Frame Relay protocol to discard erroneous frames and thus eliminate time-consuming error-handling processing.

These two factors make Frame Relay a desirable choice for data transmission; however, they also necessitate testing to determine that the system works properly and that data is not lost.

29. The main functions of tcp. Protocol udp.

A protocol is a collection of rules and procedures for two computers to exchange information. Protocol also defines the format of data that is being exchanged. Typical protocols:

• TCP – Transmission Control Protocol

Provide further the functions such as reordering and data resend. The protocol corresponds to the transport layer of TCP/IP suite. TCP provides a communication service at an intermediate level between an application program and the Internet Protocol (IP). TCP is a connection-oriented protocol. Does not mean it has a physical connection between sender and receiver. TCP provides the function to allow a connection virtually exists – also called virtual circuit.

TCP provides the functions:

• Dividing a chunk of data into segments

• Reassembly segments into the original chunk

• Provide further the functions such as reordering and data resend

Offering a reliable byte-stream delivery service.

• (((Connection Establishment, Management and Termination: TCP provides a set of procedures that devices follow to negotiate and establish a TCP connection over which data can travel. Once opened, TCP includes logic for managing connections and handling problems that may result with them. When a device is done with a TCP connection, a special process is followed to terminate it.

• Data Handling and Packaging: TCP defines a mechanism by which applications are able to send data to it from higher layers. This data is then packaged into messages to be sent to the destination TCP software. The destination software unpackages the data and gives it to the application on the destination machine.

• Data Transfer: Conceptually, the TCP implementation on a transmitting device is responsible for the transfer of packaged data to the TCP process on the other device. Following the principle of layering, this is done by having the TCP software on the sending machine pass the data packets to the underlying network-layer protocol, which again normally means IP.

• Providing Reliability and Transmission Quality Services: TCP includes a set of services and features that allow an application to consider the sending of data using the protocol to be “reliable”. This means that normally, a TCP application doesn't have to worry about data being sent and never showing up, or arriving in the wrong order. It also means other common problems that might arise if IP were used directly are avoided.

• Providing Flow Control and Congestion Avoidance Features: TCP allows the flow of data between two devices to be controlled and managed. It also includes features to deal with congestion that may be experienced during communication between devices.)))

• UDP – User Datagram Service

The UDP is a transport layer protocol defined for use with the IP network layer protocol. UDP provides a minimal, unreliable, best-effort, message-passing transport to applications and upper-layer protocols. UDP communication consequently does not incur connection establishment and teardown overheads and there is minimal associated end system state. Because of these characteristics, UDP can offer a very efficient communication transport to some applications, but has no inherent congestion control or reliability. UDP does not provide any communications security. Use when the message to be sent fit exactly into a datagram, use also when a more simplified data format is required.

The main difference between the two protocols is that TCP uses a connection-oriented transport, while UDP uses a connectionless type of communication.