Data Communication & networking

This blog is for undergraduate/graduate students who require some basic information about their subjects or any other topic related to data communication.

Tuesday, 29 March 2011

Frame Relay Frame Format

Frame Relay Frame Format

Figure shows the standard frame relay frame format. Flag indicates the beginning and end of the frame. Three primary components make up the frame relay's frame, the header and the address area, the user-data portion, and the frame check sequence.

FLAGS: Delimits the beginning and end of the frame. The value of this field is always the same and is represented either as the hexadecimal number 7E or as the binary number 01111110.
ADDRESS: It contains the following information,
  • DLCI: The 10 bits DLCI is the essence of the frame relay header. This value represents the virtual connection between DTE devices and the switch.
  • Extende Address (EA): The EA is used to indicate whether the byte in which the EA value is 1 is the last addressing field. If the value is 1, then the current byte is determined to be the last DLCI octet. the eighth bit of each byte of the address field is used to indicate the EA.
  • C/R: The C/R is the bit that follows the most significant DLCI byte in the address field.
  • Congestion Control: this consist of 3 bits that control the frame relay congestion notification mechanisms. These are FECN, BECN, and DE bits, these are the last 3 bits in the address field.
DATA: It contains encapsulated upper layer data. Each frame in this variable length field includes a user data or payload field that varies in length up to 16,000 octets.

FRAME CHECK SEQUENCE: It ensures the integrity of transmitted data. This value is computed by the source device and verified by receiver to ensure integrity of transmission.

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