ch02-error_cl

ch02-error_cl - CNAS Supcom Chapter II Error control...

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1 Chapter II Error control Engineering of Computer and telecommunication Engineering of Computer and telecommunication Networking Networking Master Master F 2006 F 2006 CNAS CNAS Supcom Supcom
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2 Summary Bit errors Packet and frame errors Packet insertion Packet detection Transmission control Control mechanisms
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3 1. Bit errors Bit errors are due to bit transmission over the network (noise) CRC mechanism can detect all single bit errors and almost all 2-bit errors any odd number of errors all bursts up to M, where generator length is M longer bursts with certain probability Software implementation of the CRC Software implementation of the CRC Pre-computes remainders for 16-bit words Pre-computes remainders for 16-bit words add remainders to a running sum add remainders to a running sum needs only one lookup per 16-bit block needs only one lookup per 16-bit block
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4 2. Packet and frame errors Different from bit errors Types: not just bit-based, but also duplication, insertion,etc. Correction: retransmission, instead of redundancy Loss Loss Due to uncorrectable bit errors Due to uncorrectable bit errors Buffer loss on overflow Buffer loss on overflow especially with bursty traffic especially with bursty traffic loss rate depends on burstiness, load, and buffer size loss rate depends on burstiness, load, and buffer size fragmented packets can lead to error multiplication fragmented packets can lead to error multiplication longer the packet, more the loss longer the packet, more the loss Burst collision (optical) Burst collision (optical)
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Types of packet errors Duplication same packet received twice: usually due to retransmission Insertion packet from some other conversation received: header corruption Reordering packets received in wrong order: usually due to retransmission, some routers also reorder Collision Collision : Optical bursts can get in collision : Optical bursts can get in collision Detection: Sequence numbers, Timeouts, etc. Detection: Sequence numbers, Timeouts, etc.
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ch02-error_cl - CNAS Supcom Chapter II Error control...

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