Ethernet basics

contains whatever payload the frame carries. 

these are bytes which make up the remaining 64 bytes of information within a frame if that frame does not contain actual data.

the minimum ethernet frame is 64 bytes, but not all of it has to be actual data. if the frame is less than 64 bytes, the sending NIC will add extra data - a pad- to fill in the remaining bytes.

allows nodes to recognize when bad things happen to data. a mathematical operation is conducted and attached to the frame. the same operation is performed at the receiving end. If the results don't match, it asks to retransmit.

media access control

it's a binary address

it contains 48 bits or 6 bytes

other names: 48-bit binary address or 6 byte binary address

carrier sense multiple access/ collision detection

it is a network access method which deconflicts which machine should send data at which time on a shared cable.

carrier sense means that each node on the network examines the cable before transmitting

a computer detects traffic on the segment, waits, rechecks. if there is no traffic (or the cable is free) it sends the frame.

it maps to the 802.3 standard for ethernet

all machines have equal access to the wire

this occurs when two machines determine a shared cable is free from traffic and send information simultaneously.

when this occurs transmissions are lost

a collision domain is a group of nodes that have the capability of sending frames at the same time as each other, resulting in a collision. A segment is a collision domain.

NICs are able to easily detect collisions. both immediately stop transmitting after the hub sends out the overlapping signals.

10 base 2

this had wires which connected to a NIC into a T connector

a version of ethernet created in 1990 to modernize the ethernet generation. Over 99% of all networks use 10BaseT or a newer version. The classic 10BaseT network has two or more computers connected to a central hub. 

if I run into a situation on a 10BaseT network or later network in which none of the computers can get on the network, always check the hub first.

500m

185m

CAT 3 or greater

2 pairs of wires; 1 and 2 send, 3 and 6 recieve

UTP officially

a 10 base T device connected to a hub cannot send and receive simultaneously, however.

the color coding standards are 568a and 568b

100m

1,024

10Mbps

star-bus (physical star, logical bus)

CAT 3 or better UTP with RJ-45

this is a fiber optic version of 10 base T.

faster, immune to EMI, more difficult to tap into

10Mbps

baseband

2,000m

1,024

star bus: (physical star, logical bus)

MMF with ST or SC connector

this is a port on a switch that enables you to connect two switches or hubs using a straight-throug cable

use a straight-through cable to connect to a second hub. You connect one to the uplink and the other end goes into a regular port. You cannot connect multiple hubs to a single hub, like a physical star topology. 

Media Dependent Interface is a regular port on a hub or switch.

Media Dependent Interface Crossover is the uplink.

a UTP cable to connect routers to switches, or NICs without a switch. (they reverse the sending and receiving wire pairs from the one end to the other -one end is 568a and the other is 568b)

-cannot connect two hubs with a standard straight-through (both will want to send on 3/6 and receive on 1/2)

-use crossover to connect two computers using 10 base T without a hub!

straight through; uses the same standard at both ends

crossover; uses 568a on one end and 568b on the other

rollover; uses RJ-45 on one end and RS 232 serial port on the other (makes it possible to connect a comoputer directly into a cisco switch or router

these are layer 2 devices which connect two networks and passes traffic between them bsed only on the MAC address, so traffic between nodes on one network don't appear on the other.

these help preserve precious bandwidth and makes larger ethernet networks possible

to stop traffic from crossing from one network to another

to pass traffic originating on one side of the bridge to the other

layer 2/data-link layer and link/network interface of the TCP/IP model.

it monitors and records the traffic until it can filter and forward after just a few seconds.

A table stored by a switch, listing the MAC addresses and port of each connected device.

exam tip; a big difference btw a hub and switch is the repeating of frames during normal use. Although they initially forward all frames, they filter by MAC address in regular use. Hubs never learn and always forward frames

half duplex switches; CSMA/CD dictates the collisions. they only occur btw the switch and node, not btw two nodes

with full duplex, developers made NICs and switches to send/receive simultaneously. in this case CSMA/CA is disabled, no collisions occur and each node gets its full bandwidth

broadcast domain vs collision domain (hub)

there was no difference btw them: in pre-switched ethernet times.  All broadcast traffic went to all nodes; all nodes connected to the same bus and thus collisions occurred. switches eliminated collisions among the nodes attached to the switches within a broadcast domain.