L5PacketsFrames6 - Part 2 Packet Transmission Part 2 Packet...

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1 Part 2 – Packet Transmission Module Contents and Structure Part 1: data transmission Part 2: packet transmission Part 3: internetworking Part 4: applications Part 2 – Packet Transmission Part 2: Packet Transmission Packets, frames Local area networks (LANs) Wide area networks (LANs) Hardware addresses Bridges and switches Routing and protocols Part 2 – Packet Transmission Packets, Frames and Error Detection Gail Hopkins Part 2 – Packet Transmission Introduction ± Packets and frames ± Control data and byte stuffing ± Error detection Ð Parity bits Ð Checksums Ð Cyclic redundancy checks Part 2 – Packet Transmission Packets ± Most networks transmit data in small blocks called packets Ð helps in detecting transmission errors Ð gives fair access for a shared connection between many computers ± These are packet networks or packet switching networks Part 2 – Packet Transmission An Example of Fair Access A wants to send a 5 megabyte file to C B wants to send a 10 kilobyte file to D network speed is 56,000 bits per second 5000000x8 = 40000000bits 40000000/56000=714s /60 = 11.9 min 10000x8 = 80000bits 80000/56000=1.43s shared resource B A C D 1000 byte packet 8000/56000=0.143s
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2 Part 2 – Packet Transmission Packets and Time Division Multiplexing ± Packet networks use a form of TDM computer 1 computer 2 computer 3 computer 1 computer 2 computer 3 multiplexing occurs Computer 1 using channel to send a packet Computer 2 using channel to send a packet (a) (b) Part 2 – Packet Transmission Packets and Hardware Frames ± Each type of hardware defines its own format/wrapping for a packet called a frame Ð Packet is logical Ð Frame is actual A Simple Example of Framing ± A frame may include “unused” control data values to mark both its beginning and end ± Advantage is error detection: Ð transmitter crashes => eot will not arrive Ð receiver crashes => soh marks next valid frame ± Disadvantages: Ð requires two extra characters per frame Ð cannot carry arbitrary values (e.g, soh and eot) eot soh block of data in frame
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This note was uploaded on 08/14/2011 for the course ELECTRONIC G52CCN taught by Professor Professorgail during the Spring '09 term at Uni. Nottingham.

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L5PacketsFrames6 - Part 2 Packet Transmission Part 2 Packet...

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