1. Switching A Network Layer Function
Switched network with interlinked nodes called switches
Traditional Switching Methods:
Circuit, Packet, and Message switching
New Switching Strategies:
Asynchronous transfer Mode (ATM)
Frame Relaying
11/14/2018
Lin - Swicthing

2. Circuit Switching Designed for voice communication
Circuit switch device:
A device with n inputs and m outputs
Temporary connector for input and output links
Full-duplex mode
n x n folded switches
n phones
11/14/2018
Lin - Swicthing

3. A Four Switch Example Hosts or computers: H1 through H7
H1 --| |-- S3 (1-to-2) --| -- H4
H2 --|--- S-1 (4-to-1) -- S2 (1-to-2) --| | -- H5
H3 --| |-- S4 (1-to-2) --| -- H6
H4 --| | | -- H7
Hosts or computers: H1 through H7
Switches: S-1 through S4
11/14/2018
Lin - Swicthing

4. Circuit Switching (continue)
Switching technology:
Space-division switches (SDS)
Instantaneous connection, require crosspoints
Time-division switches (TDS)
Time delay, no crosspoints
Combination of SDS and TDS
11/14/2018
Lin - Swicthing

5. Space-Division Switches
Analog + digital networks
Crossbar switches (n x m)
Multistage switches
Multipaths connections
Blocking – during period of heavy traffic
11/14/2018
Lin - Swicthing

6. Time-division switches
Time-division multiplexer and
Time-slot interchange (TSI)
A TDS Example
H1 --| |-- H4
H2 --|--- TDM -- TSI -- TDM --- |-- H5
H3 --| |-- H6
H4 --| |-- H7
11/14/2018
Lin - Swicthing

7. Disadvantages of Circuit Switching
More idle time: low utilization rate
One data rate: can’t interconnect a variety of digital devices
Inflexible: fixed circuit connection
Cannot setup priority
Less well suited for data communication
11/14/2018
Lin - Swicthing

8. Packet Switching Packets Variable length of data blocks Header Data
Priority
Control info
Destination address
Source address
Data
11/14/2018
Lin - Swicthing

9. Packet Switching (continue)
Two methods
Datagram
Virtual Circuit
11/14/2018
Lin - Swicthing

10. Datagram Approach Datagram is also known as packet
Each packet is treated independently
Packets may arrive at the destination in any order
Packets can be carried simultaneously by either TDM or FDM
May use multiple channels
11/14/2018
Lin - Swicthing

11. Virtual Circuit Approach
A single route between sender and receiver is chosen for the session
All packets travel on the same route
Can have multiplexing at the switches
Two formats
Switched virtual circuit (SVC)
Permanent virtual circuit (PVC)
11/14/2018
Lin - Swicthing