Chapter 12 - Packet Switching Introduction Sharing Saves Money –Arranging for multiple devices to share a single transmission path lowers cost because it uses fewer wires and fewer switching machines Sharing Introduces Delays –Granting one party exclusive access of a shared transport path can be impractical because it can delay all other parties Sharing Wires Selectable Channels (unique frequencies) Sharing By Taking Turns

Chapter 12 - Packet Switching Packet Switching Avoids Delays Each Packet Must Be Labeled (uses header) Computers Have Addresses (IP Addresses) –Each computer attached to a network is assigned a unique number called its address. A packet contains the address of the computer that sent it and the computer to which it is sent. Packets Are Not All the Same Size Packet Transmission Seems Instantaneous –A packet switching system permits multiple pairs of computers to communicate across a shared network with minimal delay because it divides each conversation into small packets and arranges for the computers that share a network to take turns sending packets.

Chapter 12 - Packet Switching Sharing Is Automatic –Because packet switching systems adapt instantly as computers become ready to send data or others finish sending data, each computer receives a fair share of network resources at any given time. Network Hardware Handles Sharing –From a computer's point of view obtaining fair access to a shared network is automatic - the network hardware handles all the details. Many Devices Can Use Packet Switching –Although many types of devices can connect directly to a computer network, each such device must contain a small computer that handles communications.

Chapter 12 - Packet Switching Relevance To The Internet –All data is transferred across the Internet in packets. A sender divides a message or document into packets and transfers the packets across the Internet. A receiver reassembles the original message from the packets that arrive. Packets from many machines traverse the Internet at the same time. Terms –destination address –network printer –packet –packet switching –source address