Chapter 11 - 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
- Packet Switching Avoids Delays
- Each Packet Must Be Labeled
- Computers Have 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.
- Sharing Is Automatic
Because packet switching systems adapt instantly as compters 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.
- 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.
