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Describe various IEEE standards for network topologies.
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Answer 1

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1. IEEE STANDARDS FOR LANs

2. Local Area Networks <ul><li>Local area networks (LANs) connect computers within a building or a enterprise network </li></ul><ul><li>Almost all LANs are broadcast networks </li></ul><ul><li>Typical topologies of LANs are bus or ring or star </li></ul><ul><li>We will work with Ethernet LANs. </li></ul><ul><li> </li></ul>

5. IEEE 802 Standards <ul><li>IEEE 802 is a family of standards </li></ul><ul><li>for LANs, which defines an </li></ul><ul><li>LLC and several MAC sub layers </li></ul>

7. IEEE 802 LAN Layers

8. <ul><li>IEEE 802.3 Ethernet LANs </li></ul><ul><ul><li>The MAC layer uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection) technology. </li></ul></ul><ul><ul><ul><li>When a computer wants to transmit a frame it: </li></ul></ul></ul><ul><ul><ul><ul><li>Listens for a frame on the cable, if busy, the computer waits for a random time and attempts transmission again. This is known as Carrier Sense . </li></ul></ul></ul></ul><ul><ul><ul><ul><li>If the cable is quiet, the computer begins to transmit. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Two computers could transmit at the same time. To prevent this happening, the transmitting computer listens to what it is sending. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>If what it hears is different to what it is sending, then a collision has occurred. This is known as Collision Detection . </li></ul></ul></ul></ul>

9. <ul><li>Contd…….. </li></ul><ul><ul><li>When a computer wants to receive a frame it: </li></ul></ul><ul><ul><ul><li>Listens to all frames traveling on the cable. </li></ul></ul></ul><ul><ul><ul><li>If the frame address is the same as the computer’s address or the same as the group address of the computers of which it is a member, it copies the frame from the cable. </li></ul></ul></ul><ul><ul><ul><li>Otherwise it just ignores the frame. </li></ul></ul></ul><ul><ul><ul><li>Note: Ethernet LAN is a broadcast network. It is possible to </li></ul></ul></ul><ul><ul><ul><ul><li>Unicast a frame from one computer to any other computer connected to the same cable. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Broadcast a frame from one computer to all other computers connected to the same cable. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Multicast a frame from one computer to a subset of the computers connected to the same cable. </li></ul></ul></ul></ul>

10. <ul><li>Carrier Sense Multiple Access with Collision Detection (CSMA/CD) </li></ul><ul><li>  </li></ul><ul><li>The basic idea: </li></ul><ul><li>When a station has a frame to transmit: </li></ul><ul><li>1)   Listen for Data Transmission on Cable (Carrier Sense) </li></ul><ul><li>2)   When Medium is Quiet (no other station transmitting): </li></ul><ul><ul><li>a)   Transmit Frame, Listening for Collision </li></ul></ul><ul><ul><li>b)   If collision is heard, stop transmitting, wait random time, and transmit again. </li></ul></ul>Frame format This portion must be at least 64 bytes for the Ethernet to work correctly

12. <ul><li>IEEE 802.3 Cabling Standards </li></ul><ul><ul><li>The following is a list of the commonly used cables in 802.3 LANs. </li></ul></ul>Cable Name Cable Type Transmission Rate Max. length before repeater needed Max. No. of Computer 10Base5 Thick coaxial 10Mbsec 500 metres 100 per segment 10Base2 Thin coaxial cable 10Mbsec 200 metres 30 per segment 10BaseT Twisted Pair 10/100 Mbsec 100 metres 1024 per segment 10BaseF Fiber Optic cable 100/1000 Mbsec 2000 metres 1024 per segment

13. <ul><li>IEEE 802.3 Cabling Standards </li></ul><ul><ul><li>10Base5 </li></ul></ul><ul><ul><li>Bus topology is used. </li></ul></ul><ul><ul><ul><li>Connections are made using tap to a thick coaxial cable. </li></ul></ul></ul><ul><ul><ul><li>This results in a poor connection between the computer and the coaxial cable. </li></ul></ul></ul><ul><ul><li>10Base2 </li></ul></ul><ul><ul><ul><li>This was the most popular 802.3 cable because it was cheap and there was a good connection between the computer and the coaxial cable. </li></ul></ul></ul>

14. <ul><ul><li>10BaseT </li></ul></ul><ul><ul><li>star topology is used. </li></ul></ul><ul><ul><li>Stations are connected to a hub via two pairs of twisted cable. </li></ul></ul><ul><ul><ul><li>Currently most popular since it is easy to maintain but is more expensive. </li></ul></ul></ul><ul><ul><li>10BaseF </li></ul></ul><ul><ul><ul><li>Good for high speed connections between buildings. </li></ul></ul></ul>

15. 10Base5 10Base2 10Base

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