This article covers topics such as fast ethernet,10/100 ethernet,Gigabit ethernet,collosion dtection & recovery,ethernet hardware address.
Fast ethernet
- It is formally known as 100Base-T
- It uses category 5 twisted pair cable
- Data is transmitted or received at the rate of 100Mbps
- Although network supports 100Mbps, the computers connected to the network may not be able to provide such high data rates.
10/100 Ethernet
- It is also called dual speed ethernet.
- It can support either 10 or 100 Mbps connection.
- It is formally known as 100Base-T.
- It automatically detects the speed of the connection at other end and automatically adjusts to either 10 or 100 Mbps depending on the speed of the connection at other end.
Gigabit ethernet
- It is formally called 1000Base-T
- It operates at a speed of 1Gbps.
- Wiring scheme used in this ethernet is different as compared to that used in other types of ethernets.
- Packet size and format is same for all ethernets.
Properties of an ethernet
- The topology is called shared bus because all stations connect to a single,shared communication channel.
- It is called a broadcast technology because the packet is transmitted to all the stations in the network at the same time.
- Ethernet is called a best effort delivery mechanism because the hardware provide no information to the sender about whether the packet was delivered or not.
- The ethernet access scheme is called Carrier Sense Multiple Access with Collision Detect (CSMA/CD).
- CSMA/CD working:
- Since every station in the network can access the ethernet simultaneously.So there is a chance of collision.To avoid this we use CSMA/CD.
- When a host has to transmit a message,it listens to see if a message is being transmitted in the network by any other stations.
- If it can't sense any other signal it begins transmitting its signal.
- If it senses a signal it waits for a fixed amount of time without transmitting and then it checks the network again.
- Each transmission is limited in duration because there is a maximum packet size.
- Hardware must also observe minimum idle time between transmissions which means no two machines can access network without giving oppotunity for other machines to access.
Collision detection and recovery
- These signals does not reach each station simultaneously.It travels along copper wires at a approximately 70% of the speed of light.
- So there is every chance that two stations may sense network as idle and starts transmitting signal.
- In such cases when these two signals cross each other they become scrambled.Such incidents are called collisions.
- So technique used to monitor COLLISIONS is called collision detection (CD).
- When collision occurs the host interface aborts transmission and waits for certain time.
- But situation may arise in which all stations are busily attempting to transmit and every transmission produce collision which means each stations wait for certain time as a result of which transmission wont occur.
- To avoid above scenario we use binary exponential backoff policy.
- In binary exponential backoff policy sender delays a random time after first collision,doubles the range if second attempt results in collision and so on.Thus making probability of collision lower.
Ethernet Hardware Address
- It is a 48-bit addressing scheme.
- Each computer attached to an ethernet network is assigned a unique 48-bit number known as its ethernet address.
- Ethernet hardware manufacturers purchases blocks of ethernet addresses and assign them in sequence to their manufactured products,thus all of them will have unique addresses.
- Ethernet addresses are also called hardware addresses,physical addresses,media access(MAC) addresses, or layer 2 addresses and ethernet address would be in machine readable format.
- In ethernet if a sender sends a packet to a particular station the packet is received by all stations in the network,they accepts or rejects it by seeing the destination addrtess of the packet.
- There are three types of addresses they are:
- Physical address of one network interface or unicast address:It is assosciated with only one network interface hardware(station) in the network.
- Network broadcast address:This address is generally represented as all 1's and this address in the destination field of the packet indicates that it is to be received by all stations in the network.
- Multicast address:This address is maeant for a certain groups of computers in the network called the multicast group and this address in the destination field of the packet indicates that it is to be received by stations belonging to the multicast group in the network.
|
|
No comments:
Post a Comment