2b switching in networks
- 3. 8.3 Types of switched networks
- 4. 8.4 CIRCUIT-SWITCHED NETWORKSCIRCUIT-SWITCHED NETWORKS A circuit-switched network consists of a set of switchesA circuit-switched network consists of a set of switches connected by physical links. A connection between twoconnected by physical links. A connection between two stations is a dedicated path made of one or more links.stations is a dedicated path made of one or more links. However, each connection uses only one dedicatedHowever, each connection uses only one dedicated channel on each link. Each link is normally dividedchannel on each link. Each link is normally divided into n channels by using FDM or TDM.into n channels by using FDM or TDM.
- 5. 8.5 A trivial circuit-switched network
- 6. 8.6 In circuit switching, the resources need to be reserved during the setup phase; the resources remain dedicated for the entire duration of data transfer until the teardown phase. Note
- 7. 8.7 As a trivial example, let us use a circuit-switched network to connect eight telephones in a small area. Communication is through 4-kHz voice channels. We assume that each link uses FDM to connect a maximum of two voice channels. The bandwidth of each link is then 8 kHz. Figure shows the situation. Telephone 1 is connected to telephone 7; 2 to 5; 3 to 8; and 4 to 6. Of course the situation may change when new connections are made. The switch controls the connections. Example
- 8. 8.8 Circuit-switched network used in Example
- 9. 8.9 Delay in a circuit-switched network
- 10. 8.10 Switching at the physical layer in the traditional telephone network uses the circuit-switching approach. Note
- 11. 8.11 DATAGRAM NETWORKSDATAGRAM NETWORKS In data communications, we need to send messagesIn data communications, we need to send messages from one end system to another. If the message isfrom one end system to another. If the message is going to pass through a packet-switched network, itgoing to pass through a packet-switched network, it needs to be divided into packets of fixed or variableneeds to be divided into packets of fixed or variable size. The size of the packet is determined by thesize. The size of the packet is determined by the network and the governing protocol.network and the governing protocol.
- 12. 8.12 In a packet-switched network, there is no resource reservation; resources are allocated on demand. Note
- 13. 8.13 A datagram network with five switches (routers) Packets may also be lost/dropped due to lack of resources
- 14. 8.14 In a packet-switched (connectionless)network , there are no setup or teardown phases. Each packet is treated the same regardless of its source or destination. Note
- 15. 8.15 Routing table in a datagram network
- 16. 8.16 A switch (router) in a datagram network uses a routing table that is based on the destination address. The routing tables are updated dynamically or statically. Note
- 17. 8.18 Delay in a datagram network
- 18. 8.19 Switching in the Internet is done by using the datagram approach to packet switching at the network layer. Note
- 19. Comparison of circuit switched and packet-switched networks
- 20. 8.21 VIRTUAL-CIRCUIT NETWORKSVIRTUAL-CIRCUIT NETWORKS A virtual-circuit network is a cross between a circuit-A virtual-circuit network is a cross between a circuit- switched network and a datagram network. It hasswitched network and a datagram network. It has some characteristics of both.some characteristics of both.
- 21. 8.22 One
- 23. 8.24
- 25. 8.26
- 26. 8.27 Switch and switching tables in a virtual-circuit network
- 27. 8.28 Setup request frame from source to destination in a virtual-circuit network B assigns a VCI if ready to receive frames from A
- 28. 8.29 A special Setup acknowledgment frame completes the table entries
- 29. 8.30 Source-to-destination data transfer in a virtual-circuit network
- 30. 8.31 • In virtual-circuit switching, all packets belonging to the same source and destination travel the same path; but the packets may arrive at the destination with different delays due to: — Varying packet queue lengths in the network nodes — Varying load from other users sharing the same network resources
- 31. 8.32 Delay in a virtual-circuit network
- 32. 8.33 Switching at the data link layer in a switched WAN is normally implemented by using virtual-circuit techniques. Note
- 33. 8.34 STRUCTURE OF A SWITCHSTRUCTURE OF A SWITCH We use switches in circuit-switched and packet-We use switches in circuit-switched and packet- switched networks. We will see the structures of theswitched networks. We will see the structures of the switches used in packet-switched networks.switches used in packet-switched networks.
- 35. 8.36 Input port
- 36. 8.37 Output port
- 37. 8.38
- 38. 8.39 Crossbar switch with three inputs and four outputs ni xmo Crosspoints. Impractical & Inefficient
- 39. 8.40 A banyan switch – more realistic For in=out =n,log2 nstages with n/2 microswitches at each stage. Routing based on output port represented as binary string
- 40. 8.41 Examples of routing in a banyan switch b. Try Input 5 to Output 2
- 41. 8.42 Examples of routing in a banyan switch