CSCI 465 D ata Communications and Networks Lecture 14 Martin van Bommel CSCI 465 Data Communications & Networks 1

Packet Switching circuit switching designed for voice packet switching designed for data transmitted in small packets – packets contains user data and control info – user data may be part of a larger message – control information includes routing (addressing) packets are received, stored briefly (buffered) and passed on to the next node CSCI 465 Data Communications & Networks 2

Packet Switching (2) CSCI 465 Data Communications & Networks 3

Packet Switching (3) Advantages – Better line efficiency - shared by many – Can adjust data rates for different devices – Signals can always be routed (with delay) – Prioritization option - high priority packets first Disadvantages – Transmission delay in nodes - buffers & processing – Variable delays can cause jitter – Overhead for address and network status info CSCI 465 Data Communications & Networks 4

Packet Switching Techniques station breaks long message into packets – packets sent one at a time to the network packets can be handled in two ways: – datagram each packet is treated independently with no reference to previous packets – virtual circuit a preplanned route is established before any packets are sent CSCI 465 Data Communications & Networks 5

Virtual Circuit preplanned route established for all packets – similar to circuit switching, but the circuit is not dedicated to one connection – each packet contains virtual circuit identifier extra overhead to establish route, but no dynamic routing required – faster error control can be performed at each node if link goes down, no alternative available Figure CSCI 465 Data Communications & Networks 6

Datagram each packet treated independently and referred to as a datagram – must each contain addressing information packets may take different routes – may arrive out of sequence no call setup overhead - done dynamically more flexible - adapt to changing conditions Figure CSCI 465 Data Communications & Networks 7

There is a significant relationship between Packet Size and transmission time.

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