Circuit Switching - Data Communications - Lecture Slides, Slides of Data Communication Systems and Computer Networks

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Chapter 10

Circuit Switching and Packet Switching

Switching Networks

• Long distance transmission is typically done over a network of switched nodes
• Nodes not concerned with content of data
• End devices are stations —Computer, terminal, phone, etc.
• A collection of nodes and connections is a communications network
• Data routed by being switched from node to node

Simple Switched Network

Circuit Switching

• Dedicated communication path between two stations
• Three phases —Establish —Transfer —Disconnect
• Must have switching capacity and channel capacity to establish connection
• Must have intelligence to work out routing

Public Circuit Switched

Network

Telecomms Components

• Subscriber — Devices attached to network
• Subscriber line — Local Loop — Subscriber loop — Connection to network — Few km up to few tens of km
• Exchange — Switching centers — End office - supports subscribers
• Trunks — Branches between exchanges — Multiplexed

Circuit Switch Elements

Circuit Switching Concepts

• Digital Switch —Provide transparent signal path between devices
• Network Interface
• Control Unit —Establish connections - Generally on demand - Handle and acknowledge requests - Determine if destination is free - construct path —Maintain connection —Disconnect

Space Division Switching

• Developed for analog environment
• Separate physical paths
• Crossbar switch —Number of crosspoints grows as square of number of stations —Loss of crosspoint prevents connection —Inefficient use of crosspoints - All stations connected, only a few crosspoints in use —Non-blocking

Space Division Switch

Three Stage Space Division

Switch

Time Division Switching

• Modern digital systems rely on intelligent control of space and time division elements
• Use digital time division techniques to set up and maintain virtual circuits
• Partition low speed bit stream into pieces that share higher speed stream

Control Signal Sequence

• Both phones on hook
• Subscriber lifts receiver (off hook)
• End office switch signaled
• Switch responds with dial tone
• Caller dials number
• If target not busy, send ringer signal to target subscriber
• Feedback to caller — Ringing tone, engaged tone, unobtainable
• Target accepts call by lifting receiver
• Switch terminates ringing signal and ringing tone
• Switch establishes connection
• Connection release when Source subscriber hangs up

Switch to Switch Signaling

• Subscribers connected to different switches
• Originating switch seizes interswitch trunk
• Send off hook signal on trunk, requesting digit register at target switch (for address)
• Terminating switch sends off hook followed by on hook (wink) to show register ready
• Originating switch sends address