Lecture 1(c):Networking Basics

CSMA/CD:

nCarrier Sense/Multiple Access with Collision Detection (CSMA/CD) When a protocol that uses CSMA/CD has data to transmit, it first senses if a signal is already on the wire (a carrier), indicating that someone is transmitting currently. That’s the “Carrier Sense” part.

nIf no one else is transmitting, it attempts a transmission and then listens to hear if someone else tried to transmit at the same time.

nIf someone else transmits at the exact same time, a collision occurs.

nJamming Signal is send to all Stations. Both senders “back off” and don’t transmit until some random period of time has passed. Then they both retry. That’s the “Collision Detection” part.

nThe final part (“Multiple Access”) just means that more than one station can be on the network at the same time.

nCSMA/CD is the access method used in Ethernet and wireless Ethernet networks. 

Collision domain and Broadcast Domain:

 

Collision Domain:

A collision domain is a logical area in a computer network where data packets can collide with one another. The term is used mainly with regard to Ethernet, which is by far the most commonly used type of local area network (LAN).

A collision occurs when two or more devices attempt to send a signal along the same transmission channel at the same time.

Collision domains can range in size from a single segment of cable to an entire network, at least a small one. They are extended by physical layer devices, such as repeaters and hubs, because such devices automatically forward all data that is sent on the cable or other media.

Means - HUB ( layer 1 Device ) can not break the collision it creates it.

But a Switch or Bridge (layer 2) Device can Break a collision. 

Broadcast domain:

 

A broadcast domain is the portion of a computer network that is reachable by a broadcast.

A broadcast is the transmission of a message to all hosts (i.e., computers) on the network or part thereof (i.e., network segment) simultaneously.

In contrast to a collision domain, which is determined at the data link layer (the second layer of the OSI reference model) and is typically confined to a network segment in a LAN (local area network), a broadcast can be initiated at any of several layers, and it thus can be either confined to a single segment or routed across multiple segments. 

Cisco Icons and Symbols:

Network Node:

 

The device connected to a network is called Node.

BRIDGES:

A Bridge consists of computer with two or more network interface cards. Connecting two different types of network. E.g. one interface card might connect to an Ethernet system, while a second card connects to a token Ring System. These two systems speak two entirely different data languages and require bridge to translate node address supplied by one network into node address that can be recognized by the other.  

Network Interface Card:

Network interface card (NIC) or also called as ‘LAN Card’ is a circuit board, plugged into one of the expansion slots of the computer (Workstation or Server). The transmission cable is attached to the connector on the NIC and handles transmission and reception of signals.  

Modem:

Its is used for Modulation and Demodulation of a signal.

 

Lecture 1 is End,Lecture 2 Will Start From OSI Layered Model But Before that a Quiz will be Taken.

Assignment will be Given at the end of Lecture 3.