L20 - Logic Link control (802.2) The ETHERNET protocol...

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Logic Link control (802.2) The ETHERNET protocol provides for collisions, retries, but not for retransmission in case of errors in collision-free packets. Retransmission, sequence numbering is provided for in a separate Logic Link Control (LLC) sublayer. An error detection field (32 bits) is already built into the Ethernet frame. But without LLC, can only discard a packet with detected errors. An LLC header - part of the payload of the standard Ethernet frame - is added to complete the link error control task.
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LLC is like HDLC, except the FCS is already part of the Ethernet MAC frame. Access point addresses allow multiplexing of frames between two points. LLC control frames are like HDLC frames - unnumbered frames can be used, acknowledged or unacknowledged. Connection mode uses Balanced Mode of HDLC, sequence nos, acknowledgments. If the Internet Transport Protocol TCP/IP is used, acks are not needed at link layer level.
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When Ethernet was strictly CSMA/CD, it was sometimes desired to use repeaters (to combat attenuation) or to tie two Ethernet LANs to appear as one. In CSMA/CD operation, anything sent on one of the Ethernet cables would be repeated on the other, possibly causing a collision. Rules same as if a single LAN.
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Data link layer switching - Bridges (Text 4.8) - back to wireless LANs later. A bridge connects two or more LANS. Let’s consider first connection between two LANs. Often most of the traffic is local to LAN 1 or LAN 2, with lesser interchange. If a message is between two members
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L20 - Logic Link control (802.2) The ETHERNET protocol...

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