1. HW for Chapter 3
Exercises:
38, 45, 47, 48

2. MIDTERM 1 – WEEK OF MARCH 8th
Ch.1, Ch.2, 3.1 & 3.6, Ch.7,

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

4. Transmission medium and physical layer
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

5. Classes of Transmission Media

6. 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

7. 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

8. Applications of Twisted pair
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

9. Figure 7.6 UTP performance

10. 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

11. 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

12. Figure 7.9 Coaxial cable performance

13. 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

14. 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

15. Applications for Fiber Optic cable
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

16. Advantages of fiber-optical
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

17. Disadvantages of fiber-optical
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

18. HW for Chapter 7
Review Questions:
1, 2, 3, 4, 8

19. Ch. 8: Switching & Datagram Networks

20. Building large networks
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.

21. Switching is the solution
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.

22. Figure 8.1 Switched network

23. Figure 8.2 Taxonomy of switched networks

24. Topics discussed in this section:
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.
Topics discussed in this section:
Three Phases Efficiency Delay
Circuit-Switched Technology in Telephone Networks

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

26. Figure 8.3 A trivial circuit-switched network

27. Note
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.

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

29. Topics discussed in this section:
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.
Topics discussed in this section:
Routing Table Efficiency Delay
Datagram Networks in the Internet

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

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

32. Figure 8.8 Routing table in a datagram network

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

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

35. Figure 8.9 Delay in a datagram network

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

37. Topics discussed in this section:
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.
Topics discussed in this section:
Addressing Three Phases
Efficiency Delay
Circuit-Switched Technology in WANs

38. Figure 8.10 Virtual-circuit network

39. Figure 8.11 Virtual-circuit identifier

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

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

42. Figure 8.14 Setup request in a virtual-circuit network

43. Figure 8.15 Setup acknowledgment in a virtual-circuit network

44. Note
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.

45. Figure 8.16 Delay in a virtual-circuit network

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

47. HW for Chapter 2 Review Questions: Exercises: 11 (a,c), 14, 16, 17, 18
1, 2, 3, 4, 5, 6
Exercises:
11 (a,c), 14, 16, 17, 18