Ethan Banks On productivity.

OECG – Chapter 1 Definitions


The end of each chapter encourages you to do certain things to help you retain the information. One of those things is to define a set of words they provide, and check your answers on the CD glossary. (Note – the only thing I can’t find on the companion CD that came with the book is the glossary.) Here goes.

auto-negotiation – the process by which 2 ethernet devices determine the speed and duplex that they will run on a link. Uses FLP’s (fast link pulses).

half-duplex – one side of a link talks at a time. You can transmit OR receive, not both. Need to communicate this way if there’s the potential for collisions.
full-duplex – both sides can talk at the same time, sending on one pair, and receiving on the other. This should only be done where there is not possibility of a collision, i.e. a collision domain of 1.

cross-over cable – pinouts swap the send and receive pairs on each end of the cable. 568A on one side, 568B on the other. 1-2 are swapped with 3-6. Like devices (switch to switch) generally require a crossover cable to communicate. Auto-MDIX capable switches will auto-sense the needs of the link and perform this crossover for you despite the pinouts.

straight-through cable – pinouts match on either end.

unicast address – unique destination address send to one ethernet station.

multicast address – sent to multiple ethernet stations. 01.00.5E (24 bits) + 0 (25th bit) + last 23 bits of L3 multicast address.
broadcast address – sent to all ethernet stations in a broadcast domain, FF.FF.FF.FF.FF.FF.

loopback circuitry – what a half-duplex NIC uses to detect that a collision has occurred. When the NIC transmits, it loops the signal onto the receive pair. That way, the NIC will see the signals clobber each other and know a collision has occurred.
I/G bit – the individual/group bit (position 8 of byte 1), where 0 is a unicast and 1 is a multicast or broadcast.

U/L bit – the universal/local bit (position 7 byte 1?), where 0 is a universal/BIA address, and 1 means that the address was overwritten to be something with only local significance.

CSMA/CD – carrier sense multiple access with collision detection. This is the algorithm used to access an ethernet. Several stations can access the segment, and sense signal on the wire. If 2 stations transmit at once, a collision has occurred, the consequences of which are the electrical destruction of the frames that collided. During collisions, the colliding stations back of a random amount of time and then retransmit their frame.

By Ethan Banks
Ethan Banks On productivity.

You probably know Ethan Banks because he writes & podcasts about IT. For example, he co-authored "Computer Networks Problems & Solutions" with Russ White.

This site is Ethan on productivity--not tech so much.

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