DCN386 - Frame Relay

DCN386 - Frame Relay - Bit 7 [DE] Discard Elegibility If...

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Frame Relay is developed by ITU. It is based on X-25 and it can handle large bursts of data. It is designed to be very fast. Frame Relay discards error handling and flow control to achieve higher speeds. Frame only contains [flag][address][DATA][CRC][Flag]. No control information is included Addressing o 2-4 bytes long (typically only 2) o Byte 1 Bits 1-6 – Data Link Connection ID [DLCI] Bit 7 – command/response [C/R] (not used) Bit 8 – extended address bit [EA] Set to 1 to indicate the next byte is part of the address header o Byte 2 Bits 1-4 – An extension of the [DLCI] Bit 5 – [BECN] Backward Explicit Congestion Notification Suppose to signal network congestion No one has found a way to use this bit Bit is ignored Bit 6 – [FECN] Forward Explicit Congestion Notification Suppose to signal network congestion No one has found a way to use this bit Bit is ignored
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Unformatted text preview: Bit 7 [DE] Discard Elegibility If the frame size is too big, the FRAD will set the bit to 1 When the network gets congested, the first frames to be dumped will be the ones with DE bit set to 1 Bit 8 extended address bit [EA] If the address header extends to a third byte, this bit is turned on FRAD - Frame Relay Assembler/Disassembler. It is used to connect LANs to the Frame Relay network. Frame Relay has no flow control. FRAD provides flow control. No flow control beyond the FRAD in the FR network. Bell assigns a Committed Information Rate (CIR) to each network connected to a FRAD. FRAD will check frame sizes and set the DEs to 1 if the frames are too big. In error checking, Frame Relay switch will verify the DLCI and perform CRC error checking. If an error is found, the frame is discarded, but the host is not notified....
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This note was uploaded on 04/18/2011 for the course DCN 386 taught by Professor Allison during the Spring '10 term at Seneca.

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