1. Point-to-Point Network Switching
Computer Networks
Term A16

2. Network Switching Outline
Circuit Switching, Message Switching, Packet Switching, Cell Switching
Multiplexing
TDM and FDM
Connection-Oriented versus Connectionless Protocols
Virtual Circuit versus Datagram Networks
External/Internal Subnet Abstractions
Computer Networks Network Switching

3. Computer Networks Network Switching
Circuit Switching
Seeking out and establishing a physical copper path from end-to-end [historic definition] .
Circuit switching implies the need to first set up a dedicated, end-to-end path for the connection before the information transfer takes place.
Once the connection is made, the only delay is propagation time.
Computer Networks Network Switching

4. Computer Networks Network Switching
Circuit Switching
Figure (a) Circuit switching. (b) Packet switching.
Tanenbaum
Computer Networks Network Switching

5. Network Core: Circuit Switching
End-end resources reserved for “call”
link capacity, router buffer space
dedicated resources: no sharing
circuit-like (guaranteed) performance
call setup required
Computer Networks Network Switching

6. Store-and-Forward Networks
Intermediate processors (IMPS, nodes, routers, gateways, switches) along the path store the incoming block of data.
Each block is received in its entirety at the router, inspected for errors, and retransmitted along the path to the destination.
This implies buffering at the router and one transmission time per hop.
Computer Networks Network Switching

7. Store-and-Forward Routers
Computer Networks Network Switching

8. Computer Networks Network Switching
‘Cut Through’ Routers
Computer Networks Network Switching

9. Computer Networks Network Switching
Message Switching
A store-and-forward network where the block of transfer is a complete message.
Since messages can be quite large, this can cause:
buffering problems at the router.
high mean delay times.
Computer Networks Network Switching

10. Computer Networks Network Switching
Packet Switching
A store-and-forward network where the block of transfer is a complete packet**.
A packet is a variable length block of data with a fixed upper bound.
**Using packets improves mean message delay.
Computer Networks Network Switching

11. Computer Networks Network Switching
Cell Switching
53 bytes
A network where the unit of transfer is a small, fixed-size block of data (i.e., a cell).
ATM (Asynchronous Transfer Mode) networks use 53-byte cells.
Computer Networks Network Switching

12. Multiplexing Multiplexing {general definition} ::
Sharing a resource over time.
(a)
(b) A A A
Trunk
group A B B B
MUX
MUX B C C C C
Leon-Garcia & Widjaja:
Communication Networks
Computer Networks Introduction to the Physical Layer

13. Computer Networks Introduction to the Physical Layer
Frequency Division Multiplexing (FDM) vs Time Division Multiplexing (TDM)
4 users
Example:
FDM
frequency
time
TDM
frequency
time
Two simple multiple access control techniques.
Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling.
As we will see, used in AMPS, GSM, IS-54/136
K & R
Computer Networks Introduction to the Physical Layer

14. Frequency Division Multiplexing
Figure (a) The original bandwidths. (b) The bandwidths raised in frequency. (c) The multiplexed channel.
Tanenbaum
Computer Networks Introduction to the Physical Layer

15. T1 - TDM Link TDM: each host gets same slot in revolving TDM frame
TDM:: each host gets a fixed slot in revolving TDM frame
TDM: each host gets same slot in revolving TDM frame
Figure 2-33.T1 Carrier (1.544Mbps)
Tanenbaum
Computer Networks Introduction to the Physical Layer

16. Packet Switched Networks
Connection-Oriented Protocols
A setup stage is used to determine the end-to-end path before a connection is established.
Data flow streams are identified by some type of connection indicator (e.g. OSI, X.25, SNA, ATM).
Computer Networks Network Switching

17. Connection-Oriented Virtual Circuits
Figure 5-45.Internetworking using concatenated
virtual circuits.
Tanenbaum
Computer Networks Network Switching

18. Packet Switched Networks
Connectionless Protocols
No set up is needed.
Each packet contains information which allows the packet to be individually routed hop-by-hop through the network.
Bifurcated and adaptive routing techniques are possible.
Computer Networks Network Switching

19. Connectionless Internetworking
Figure A connectionless internet.
Tanenbaum
Computer Networks Network Switching

20. Datagram vs Virtual Circuit
Datagram Routing
Each datagram packet may be individually routed.
Virtual Circuit Routing
In virtual circuit, set up is required.
All packets in a virtual circuit follow the same path through the network.
Computer Networks Network Switching

21. Transmission Event Timing
DCC 6th Ed., W. Stallings, Figure 10.3
Computer Networks Network Switching

22. External Virtual Circuit And Datagram Operation DCC 6th Ed.,
W. Stallings,
Figure 10.4

23. Internal Virtual Circuit And Datagram Operation DCC 6th Ed.,
W. Stallings,
Figure 10.5

24. Networking Switching Summary
Circuit-switching and message switching are now obsolete!!
Store-and- forward, datagram packet switching (IP routers) dominates the Internet.
Cell switching and virtual circuits (ATM switches) still exists in ATM networks.
The external protocol abstraction to the subnet may differ from the internal subnet view.
e.g. TCP is connection-oriented protocol that runs on top of a datagram IP protocol.
Computer Networks Network Switching