1. 7.1 Chapter 7 Transmission Media Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Transmission medium and physical layer 7.2 A transmission media defined as anything that carry information between a source to a destination - Located below the physical layer and are directly controlled by the physical layer

3. 7.3 Classes of Transmission Media

4. 7.4 7-1 GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Twisted –pair cables and coaxial cable: use metallic (copper) conductors that transport signals in the form of electric current Optical fiber : transport signals in the form of the light

5. 7.5 Twisted-pair cable One of the wire used to carry signal and the other as a ground. The receiver uses the difference between the two. If the two wires are parallel, the effect of interference noise and crosstalk is big Twisting the pair of wire balance the effect of unwanted signal and reduce it. The number of twists per unit of length effects on the quality of the cable

6. 7.6 Coaxial (Coax) cable  Coax cable carries signals of higher frequency ranges than those in Twisted pair cablebecause the two media are constructed quite differently  The outer conductor serves both as a shield against noise and as second conductor, which complete the circuit Applications of Twisted pair Used in 1.telephone lines to provide voice and data channels (local loop) 2.The DSL lines that are used by the telephone companies to provide high-data-rate connections 3.Local area networks, such as 10-base-Tand 100base-T

7. 7.7 Figure 7.6 UTP performance

8. 7.8 Coaxial cable  Coax cable carries signals of higher frequency ranges than those in Twisted pair cable because the two media are constructed quite differently.  The outer conductor serves both as a shield against noise and as second conductor, which complete the circuit

9. 7.9 Applications of coaxial cable 1.Analog telephone network where a single cable could carry 10,000 voice signals. Later it was used in Digital telephone networks where cable can carry 600Mbps 2.Cable TV network: hybrid network use coaxial cable only at the network boundaries, near the consumer. Cable TV use RG-59 3.Traditional Ethernet LANs.  10-base-2 or “Thin Ethernet”, uses RG-58 coax cable to transmit data at 10 Mbps with a range of 185m.  10-base-5,or “Thick Ethernet”, uses RG-11 to transmit 10 Mbps with rang of 500 m

10. 7.10 Figure 7.9 Coaxial cable performance

11. 7.11 Fiber Optic Cable Is made of glass or plastic and transmit signals in the form of light. Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance enters another substance of different density, the ray change direction as shown: I: angle of incidence: the angle the ray makes with line perpendicular to the interface between the two substances Critical angle: property of substance, its value differs from one substance to another

12. 7.12 Optical fiber Fiber Optical : uses reflection to guide light through a channel. A glass or plastic core is surrounded by a cladding of less dense glass or plastic

13. 7.13 Used in : 1.Cable TV network: hybrid network use a combination of optical fiber and coax cable. Optical provides the backbone while coaxial cable provide the connation to the user. 2.Local area networks such as 100base-FX(fast Ethernet) and 1000base-XLANs. 3.Backbone networks because its wide bandwidth Applications for Fiber Optic cable

14. 7.14 1.Higher Bandwidth 2.Less signal attenuation it needs repeater every 50km, where twisted and coaxial need it every 5km. 3.Immunity to electromagnetic interference (noise) 4.Resistance to corrosive materials. Glass is more resistance to corrosive material than copper 5.Light weight. Fiber cables are much lighter than copper cables 6.Greater immunity to tapping: copper cables create antenna effects that can easily be tapped Advantages of fiber-optical

15. 7.15 1.Installation and maintenance. It’s a new technology. Its installation and maintenance require expertise that is not yet available every where. 2.Unidirectional light propagation. If we need bidirectional, two fibers are needed. 3.Cost. The cable and the interfaces are more expensive than those of other guided media. If the demand of BW is not high, often use of optical fiber can not be justified Disadvantages of fiber-optical

16. McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 CH. 8: SWITCHING & DATAGRAM NETWORKS 7.16

17. Building large networks 7.17  A network is a set of connected devices.  When ever we have multiple devices, we have the problem of how to connect them!  Point-to-point (mesh or star topology): impossible for large networks.  Multipoint (bus topology): does not work for large network since the distances between devices and the total number of devices increase beyond the capacity of the media and equipments.

18. Switching is the solution 7.18  A switched network consists of a series of interlinked nodes, called switches.  Switches are devices capable of making temporary connections between any two or more devices connected to the switch.

19. 8.19 Figure 8.1 Switched network

20. 8.20 Figure 8.2 Taxonomy of switched networks

21. 8.21 8-1 CIRCUIT-SWITCHED NETWORKS A circuit-switched network consists of a set of switches connected by physical links. A connection between two stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on each link. Each link is normally divided into n channels by using FDM or TDM. Three Phases Efficiency Delay Circuit-Switched Technology in Telephone Networks Topics discussed in this section:

22. 8.22 A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided into n channels. Note

23. 8.23 Figure 8.3 A trivial circuit-switched network

24. CIRCUIT-SWITCHED NETWORKS 7.24 We need to emphasize several points here:  Circuit switching takes place at the physical layer.  Before starting communication, the stations must make a reservation for the resources to be used during the communication. These resources, such as channels (bandwidth in FDM and time slots in TDM), switch buffers, switch processing time, and switch input/output ports, must remain dedicated during the entire duration of data transfer until the teardown phase.  Data transferred between the two stations are not packetized (physical layer transfer of the signal). The data are a continuous flow sent by the source station and received by the destination station, although there may be periods of silence.  There is no addressing involved during data transfer. The switches route the data based on their occupied band (FDM) or time slot (TDM). Of course, there is end-to end addressing used during the setup phase, as we will see shortly.

25. circuit-switched network Three phases 7.25  Setup Phase  Before the two parties (or multiple parties in a conference call) can communicate, a dedicated circuit (combination of channels in links) needs to be established. The end systems are normally connected through dedicated lines to the switches, so connection setup means creating dedicated channels between the switches.  In the next step to making a connection, an acknowledgment from system receiver needs to be sent in the opposite direction to the sender.  Data Transfer Phase  After the establishment of the dedicated circuit (channels), the two parties can transfer data.  Teardown Phase  When one of the parties needs to disconnect, a signal is sent to each switch to release the resources.

26. 8.26 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

27. 8.27 Switching at the physical layer in the traditional telephone network uses the circuit-switching approach. Note

28. circuit-switched network Efficiency and delay 7.28  circuit-switched networks are not as efficient as the other two types of networks because resources are allocated during the entire duration of the connection.  These resources are unavailable to other connections.  a computer can be connected to another computer even if there is no activity for a long time.  There is no waiting time at each switch (the delay in this type of network is minimal).  The total delay is due to the time needed to create the connection, transfer data, and disconnect the circuit.

29. 8.29 8-2 DATAGRAM NETWORKS In data communications, we need to send messages from one end system to another. If the message is going to pass through a packet-switched network, it needs to be divided into packets of fixed or variable size. The size of the packet is determined by the network and the governing protocol. Routing Table Efficiency Delay Datagram Networks in the Internet Topics discussed in this section:

30. 8.30 In a packet-switched network, there is no resource reservation; resources are allocated on demand. Note

31. 8.31 Figure 8.7 A datagram network with four switches (routers)

32. DATAGRAM NETWORKS 7.32  In a datagram network, each packet is treated independently of all others(even if a packet is part of a multipacket transmission.  Datagram switching is normally done at the network layer.  This approach can cause the datagrams of a transmission to arrive at their destination out of order with different delays between the packets.  Packets may also be lost or dropped because of a lack of resources.  The datagram networks are sometimes referred to as connectionless networks.

33. 7.33  Each switch (or packet switch) has a routing table which is based on the destination address.  The routing tables are dynamic and are updated periodically.  The destination addresses and the corresponding forwarding output ports are recorded in the tables.  This is different from the table of a circuit switched network in which each entry is created when the setup phase is completed and deleted when the teardown phase is over. DATAGRAM NETWORKS Routing Table

34. 8.34 A switch in a datagram network uses a routing table that is based on the destination address. Note

35. 8.35 The destination address in the header of a packet in a datagram network remains the same during the entire journey of the packet. Note

36. 8.36 Figure 8.9 Delay in a datagram network Efficiency and delay There may be greater delay in a datagram network than in a virtual-circuit network. As not all packets in a message travel through the same switches, the delay is not uniform for the packets of a message. EX: The packet travels through two switches. There are three transmission times (3T), three propagation delays(3t), and two waiting times (WI + w2)' We ignore the processing time in each switch. The total delay is Total Delay =3T + 3t + WI + W2

37. 8.37 Switching in the Internet is done by using the datagram approach to packet switching at the network layer. Note

38. 8.38 8-3 VIRTUAL-CIRCUIT NETWORKS A virtual-circuit network is a cross between a circuit- switched network and a datagram network. It has some characteristics of both. Addressing Three Phases Efficiency Delay Circuit-Switched Technology in WANs Topics discussed in this section:

39. 7.39  A virtual-circuit network is a cross between a circuit-switched network and a datagram network. It has some characteristics of both. 1. As in a circuit-switched network, there are setup and teardown phases in addition to the data transfer phase. 2. Resources can be allocated during the setup phase, as in a circuit-switched network, or on demand, as in a datagram network. 3. As in a datagram network, data are packetized and each packet carries an address in the header. However, the address in the header has local jurisdiction not end-to-end jurisdiction. The reader may ask how the intermediate switches know where to send the packet if there is no final destination address carried by a packet. 4. As in a circuit-switched network, all packets follow the same path established during the connection. 5. A virtual-circuit network is normally implemented in the data link layer, while a circuit- switched network is implemented in the physical layer and a datagram network in the network layer.

40. 8.40 Figure 8.10 Virtual-circuit network

41. 8.41 Figure 8.11 Virtual-circuit identifier

42. 8.42 Figure 8.12 Switch and tables in a virtual-circuit network

43. 8.43 Figure 8.13 Source-to-destination data transfer in a virtual-circuit network

44. 8.44 Figure 8.14 Setup request in a virtual-circuit network

45. 8.45 Figure 8.15 Setup acknowledgment in a virtual-circuit network

46. 8.46 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 if resource allocation is on demand. Note

47. 7.47  resource reservation in a virtual-circuit network can be made during the setup or can be on demand during the data transfer phase.  There is one big advantage in a virtual-circuit network even if resource allocation is on demand. The source can check the availability of the resources, without actually reserving it.

48. 8.48 Figure 8.16 Delay in a virtual-circuit network

49. 8.49 Switching at the data link layer in a switched WAN is normally implemented by using virtual-circuit techniques. Note