Ethernet

• While connecting computers through networks we need to have set of rules/standards for the data to travel from one computer to other computer.

• One such set of rules for the networking traffic to follow is IEEE 802 standards.

• Its developed by IEEE (Institute of Electrical and Electronics Engineers, Inc.)

• The IEEE 802 standards are further divided into many parts. They are, IEEE 802.2 Logical link control IEEE 802.3 Ethernet (CSMA/CD) IEEE 802.11 Wireless LAN & Mesh (Wi-Fi certification) IEEE 802.15.1 (Bluetooth certification)

Ethernet Cabling

Name Cable Max. Segment /wire Length

Maximum number of Nodes /Segment

Advantages

10Base5 Thick coax 500 m 100 Long cable length

10Base2 Thin coax 185 m 30 Low cost

10Base-T Twisted pair 100 m 1024 Easy to maintain

10Base-F Fiber optics 2000 m 1024 No noise interference

Repeaters

Making connections - Tools

Step 1 – Strip cable end

• Strip 1 – 1½” of insulating sheath• Avoid cutting into conductor insulation

Step 2 – Untwist wire ends

• Sort wires by insulation colors

Step 3 – Arrange wires

• TIA/EIA 568A: GW-G OW-Bl BlW-O BrW-Br• TIA/EIA 568B: OW-O GW-Bl BlW-G BrW-Br

Step 4 – Trim wires to size

• Trim all wires evenly• Leave about ½” of wires exposed

Step 5 – Attach connector

• Maintain wire order, left-to-right, with RJ45 tab facing downward

Step 6 - Check

• Do all wires extend to end?• Is sheath well inside connector?

Step 7 - Crimp

• Squeeze firmly to crimp connecter onto cable end (8P)

Step 8 – Test

• Does the cable work?

Linear topology

The linear topology is like a single cable running in all portions of building. The stations are connected to the cable through tapping

Spine topology

It looks like our back one spinal cord, where multiple numbers of horizontal cables are connected to a vertical line through special amplifiers or repeaters

Tree topology

This is most general topology because a network with two paths between some pairs of stations would suffer from interference between the signals

Segmented topology

Since each version of 802.3 has maximum cable length per segment, to allow larger networks, repeaters can connect multiple cables

Manchester Encoding

• The normal binary logics of one and zero are no more used to send data from one station to other station.

• The reason of not using plain binary signal is they cause ambiguities resulting in false interpretation of sent data.

• The major culprit is zero, where even no data is sent the receiver can assume it as zero.

• So to clear out the ambiguity or to ensure proper interpretation of data, a coding technique called Manchester coding is employed in IEEE802.3 standards

MAC Sublayer Protocol

The binary Exponential Backoff Algorithm

• Exponential backoff is an algorithm that uses feedback to multiplicatively decrease the rate of some process, in order to gradually find an acceptable rate.

• It is often used in network congestion avoidance to help determine the correct sending rate.

• For example, a sender might send a message, set a timer to wait 0.25 seconds for an acknowledgment, and if none arrives, retransmit the message and wait 0.5 seconds for an acknowledgment.

• It will continue to retry until it receives an acknowledgement and will wait, 1s, 2s, 4s, 8s, etc. each time before retrying.

• Time slots are defined to be 51.2µsec during contention period. After i collisions, backoff random number of intervals between 0 and 2i -1. i is bounded at 10. After 16 attempts, the sender quits