Transcript Chapter 12 - Packet Switching

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
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destination address
network printer
packet
packet switching
source address