Ethernet

Gigabit Ethernet is used between switches and for the links to the Servers. That really eats up a lot of bandwidth.

Some network layer protocols are IP (in case of TCP/IP), IPX (in case of some IPX protocol suite), and AppleTalk (in case of AppleTalk protocol suite). If we are using some protocol other than TCP/IP, then we need to have a logical link from Data Link layer up to the Network Layer, this LLC layer fields tells the device as it is passing the data to up the OSI model for de-capsulation, which network layer protocol should get it, most of time it would be IP, but it could be some other protocol as well.

 

Physical standards are the media over which Ethernet data can travel. Ethernet can drive over nearly any type of cable that’s out there.

The older technique used for data transmission over Ethernet media was Multiple Access,  but in this case collisions could occur between packets, so this technique was improved with the feature of sensing the carrier before sending the data over the carrier, this is called Carrie Sense Multiple Access.

 

This method later evolved into two methods. 
CSMA/CD (carrier sense multiple access/ collision detection)
CSMA/CA (carrier sense multiple access/ collision avoidance)

CSMC/CD: in this case if there is no collision, the station is finished, but if there is a collision the frames are sent again. Switches uses CSMA/CD (for each port, as each port has its own collision domain), while Hubs uses shared CSMA/CD (for all port of hubs). So in case of Hub, if there is a collision the whole traffic of the network will stop unless the collided frames are sent again. The reason behind it is that Hubs have 1 collision domain, and that collision domain is actually shared by all the system of the network. That is why we use the term shared CSMA/CD for Hubs. This method of shared CSMA/CD is also a drawback of Hubs.

Competing standard to Ethernet is Token Ring. Token Ring use CSMA/CA means that the stations try to avoid the collision. But they can avoid the collision up to speed of 33 Mbps. 

Multicast: one message to a group. Receiver must be a member of multicast group in order to receive this message. It helps to save bandwidth. 

In today’s networks, Ethernet Technology is implemented by using LAN switches. In older day it was implemented by Hubs.

Hubs just regenerate signals. There is not distinguishing in Broadcast, Multicast and Unicast in case of Hub. If Computer A sends a message to Computer B, it will go to everybody, that’s why we say that Hub has 1 collision domain. And 1 broadcast domain (1 broadcast will travel everywhere).

Collision Domain:  how many devices can send or receive at the same time.

Broadcast Domain: define how far a broadcast will travel before it stops. In case of hub it goes to each and every port.

So in case of a Hub, there is only 1 collision domain (means only one device at a time can send or receive) and 1 broadcast domain ( means a broadcast will go to each and every port )

Switches have a chip called ASIC (Application specific integrated chip) that has all the intelligence of a Bridge, that is to learn MAC addresses and to forward data according to it. So a switch can forward data as fast as a Hub can.