I was thinking maybe I went a bit overhead with the last
post. So I am going to be trimming it down from now on. Chapter two starts off
with looking at both typical Small Office Home Office Local Area Networks. A SOHO LAN usually consists of a Modem with
some sort of internet connection either DSL or CABLE. The modem in a SOHO LAN will incorporate a
switch and even a wireless access point into once simple device. In an
Enterprise LAN we use the same offerings but they are usually separated into
various devices. A Modem is replaced with a Router that acts as the gateway
between buildings, Dedicated switches
within buildings that connect everything together, and Dedicated access points
throughout the building to provide wireless access to users. One Major difference is that in a SOHO LAN one
device can take care of it since there are very few users. In an enterprise
network we need devices to take care of specific tasks because they are faster
and easier to manage.
Ethernet and Physical Layer Standards. There are many Physical layer standards,
which Ethernet can travel through. A quick comparison is the different type of
people that speak English, it doesn't matter what ethnicity, race, color if
they all speak English they are able to understand each other at different ends
of the communication medium. Same goes with Ethernet, instead of races,
ethnicity, colors we have different types of wires, connectors, signaling
methods, the good thing is that Ethernet runs through these physical standards
therefore it is able to talk across different physical places.
T is for Copper and X is for Fiber. 10BaseT (10Mbps)
100BaseT(100Mbps)1000BaseT(1000 Mbps) 10GBasteT(10 Gbps).
100 Meters
1000Base-LX (1000 Mbps) 5000 Meters Fibre
UTP Unshielded Twisted Pair.
10 Base T , 100Base T
Pair 1 (1,2)
Pair 2 (3,6)
Straight trough
Crossover crosses Pairs 1->2
1000 Base T
Pair 1 (1,2)
Pair 2 (3,6)
Pair 3 (4,5)
Pair 4 (7,8)
Straight trough
Crossover crosses Pairs
1->2
3->4
No matter what medium is used an Ethernet header will tell
the receiving end what to do with the packet.
Routers, PC’s, and WAP Transmit on Pins 1,2
Hubs and Switches Transmit on Pin 3,6
If you are connecting similar devices you need a Crossover cable.
A Data Link PDU or Ethernet Frame
Header[[[[[[7Byte Preamble, 1 Byte SFD, 6 Byte Destination,
6 Byte Source ,2 Byte Type,]]]]]] Data and Pad (46-1500) TRAILER [[[[[4 Byte
FCS]]]]]]]
MAC Addresses 3 Byte Organization 3 Byte Device
The Computer does a Math Calculation to the frame and adds
it to FCS.
Full Duplex, Half Duplex… Older hardware like hubs needs
Half Duplex because of CSMA/CD. Carrier Sense Multiple Access Collision
Detection. There is a potential for collisions
when using these devices and that is because some devices might transmit at the
same time. With a switch that is avoided.
Hubs send stuff out on all ports, like a repeater except the
one it came in on.
Switches send it out only on the correct port.
This was a bit more than notes , but this is merely what I
want them to be.
