Framing in Computer Networks | Computer Networks - Computer Science Engineering (CSE) PDF Download

FRAMING
The sream of bits are not advisible to mqaintain in networks. When an error occurs, then the entire stream have to retransmitted. To avoid this, the framing concept is used. In this, the stream of bits are divided into manageable bit units called frames. To achive, we are using several ways. They are,
1.     Byte Oriented Protocols
2.     Bit Oriented Protocols
3.     Clock Based Protocols

BYTE ORIENTED PROTOCOLS:
Each frame is considered as a collection of bytes rather than a collection of bits. There are two approaches. They are,

1. Sentinel approach
In this approach it uses special characters called sentinel characters to indicate where frames start and end. This approach is called character stuffing because extra characters are inserted in the data portion of the frame.
Ex:    1. Binary Synchronous Communication (BISYNC)
2. Point to Point Protocol

2. Byte Count Approach
In this approach no of bytes in frame are counted and entered in the header. The COUNT Field specifies how many bytes are contained in the frame‟s body. Ex:    1.Digital Data Communication Message Protocol

2. BIT ORIENTED PROTOCOLS:
It views the frames as a collection of bits. The Synchronous Data Link Control (SDLC) protocol developed by IBM is an example of a bit oriented protocol. It was later standardized by the ISO as the High Lever Data Link Control (HDLC)

HDLC – HIGH LEVEL DATA LINK CONTROL
It is a bit oriented data link protocol designed to support both half duplex and full duplex communication over point to point and multi point links.

FRAME FORMAT

Framing in Computer Networks | Computer Networks - Computer Science Engineering (CSE)

 

HDLC denotes both the beginning and the end of a frame with the distinguished bit sequence 01111110. To guarantee that a special sequence does not appear in advertently anywhere else in the frame, HDLC uses a process called bit stuffing.

On the sending side, any time five consecutive 1s have been transmitted from the body of the message, the sender inserts a 0 before transmitting the next bit. On the receiver side, should five consecutive 1s arrive, the receiver makes its decision based on the next bit it sees. If the next bit is a 1, then one of the two things is true. Either this is the end of the frame or an error has been introduced. By looking at the next bit, it can conclude. If it sees a 0, then it is the end of frame. It else, then there must have an error and the whole frame has been discarded.

3. Clocks Based Protocol:
The Synchronous Optical NETwork (SONET) is one of the protocols using the clock based framing approach.

SONET:
It was developed by the ANSI for digital transmission over optical network. It addresses both the framing and encoding problems. A SONET frame has some special information to distinguish where the frame starts and ends.

Framing in Computer Networks | Computer Networks - Computer Science Engineering (CSE)

Framing in Computer Networks | Computer Networks - Computer Science Engineering (CSE)

The document Framing in Computer Networks | Computer Networks - Computer Science Engineering (CSE) is a part of the Computer Science Engineering (CSE) Course Computer Networks.
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FAQs on Framing in Computer Networks - Computer Networks - Computer Science Engineering (CSE)

1. What is framing in computer networks?
Ans. Framing in computer networks refers to the process of dividing a stream of data into manageable and distinguishable units called frames. It adds frame synchronization information to the data, which helps in proper identification and extraction of the data at the receiving end.
2. Why is framing important in computer networks?
Ans. Framing is important in computer networks as it helps in the reliable transmission of data. By dividing the data into frames, it becomes easier to detect and correct errors that may occur during transmission. It also ensures that the receiver can properly identify the start and end of each frame, allowing for efficient extraction of the data.
3. What are the common framing techniques used in computer networks?
Ans. The common framing techniques used in computer networks are: - Character-Oriented Framing: In this technique, each character is framed individually, and special characters are used to indicate the start and end of frames. - Bit-Oriented Framing: This technique treats the data as a sequence of bits. A specific pattern of bits, called a flag, is used to mark the start and end of frames. - Byte-Oriented Framing: Similar to bit-oriented framing, but treats the data as a sequence of bytes. A specific byte pattern is used as the flag to indicate the start and end of frames.
4. How does framing help in error detection and correction?
Ans. Framing helps in error detection and correction by adding error-checking mechanisms to each frame. These mechanisms, such as checksums or cyclic redundancy checks (CRC), generate a unique value based on the data in the frame. At the receiving end, the same mechanism is used to calculate the value again. If the calculated value matches the one received, it indicates that the frame was transmitted without errors. If the values don't match, it indicates the presence of errors, and appropriate error correction techniques can be applied.
5. Can framing be used in wireless networks?
Ans. Yes, framing can be used in wireless networks. The concept of framing remains the same, regardless of the type of network. However, the specific techniques and protocols used for framing may vary depending on the characteristics of the wireless network. Wireless networks often face challenges like interference and variable signal strength, which need to be considered while designing the framing mechanism for such networks.
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