Subject Name:COMPUTER NETWORKS-1 Subject Code: 10CS55

1. Subject Name:COMPUTER NETWORKS-1 Subject Code:10CS55 Prepared By:Shruthi N, Krishna sowjanya.k, santhiya Department: CSE

2. Multiplexing Engineered for Tomorrow 1 link, n channels n signals(input) MUX DEMUX n signals(output) Multiplexer Demultiplexer • Multiplexing is the simultaneous transmission of multiple signals across a single data link. • In a multiplexed system, n lines share the bandwidth of one link.

3. Multiplexing Engineered for Tomorrow • Multiplexing is the simultaneous transmission of multiple signals across a single data link. • In a multiplexed system, n lines share the bandwidth of one link • There are three basic multiplexing techniques: • frequency-division multiplexing. • wavelength-division multiplexing. • time-division multiplexing.

4. Frequency Division Multiplexing (FDM) Engineered for Tomorrow • Medium BW > Channel BW • Each signal is modulated to a different carrier frequency • E.g., broadcast radio • Channel allocated even if no data An analog multiplexing technique to combine signals

5. Conceptual View of FDM Channel 3 Channel 2 Channel 1 f3 f2 f1 Time Frequency Engineered for Tomorrow

6. FDM: Multiplexing Process Engineered for Tomorrow

7. FDM: Demultiplexing Process Engineered for Tomorrow

8. Analog Hierarchy 4 kHz 4 kHz group 12 voice channels … supergroup 5 groups 4 kHz 10 supergropus mastergroup … 6 master groups Jumbogroup Engineered for Tomorrow • Used by AT&T 48 kHz12 voice channels 240 kHz60 voice channels F D M 2.52 MHz 600 voice channels F D M 16.984 MHz 3600 voice channels F D M F D M

9. Wavelength Division Multiplexing (WDM) 1 1 WDM WDM 2 2 1+2+3 3 3 1+2+3 Fiber-optic cable Multiplexer Demultiplexer Engineered for Tomorrow An analog multiplexing technique to combine optical signals • WDM is a special case of FDM 1 1 2 2 3 3

10. Time Division Multiplexing (TDM) A Frame one unit B TDM C B A C B A C B A C Time slot Engineered for Tomorrow A digital multiplexing technique to combine data • Medium Data Rate > Signal Data Rate • Multiple digital signals interleaved in time • Time slots • are preassigned to sources and fixed • are allocated even if no data • do not have to be evenly distributed among sources

11. Conceptual View of TDM 1 2 MUX Channel 3 Channel 3 Channel 3 Channel 2 Channel 2 Channel 2 Channel 1 Channel 1 Channel 1 3 Time Frequency Engineered for Tomorrow 1 Data flow 2 3 2 1 3 2 1 3 2 1 DEMUX 3

12. TDM Frames Engineered for Tomorrow • A frame consists of one complete cycle of time slots

13. Interleaving Engineered for Tomorrow • Multiplexing side:As the switch opens in front of a connection, that connection has the opportunity to send a unit onto the path. This process is called interleaving. • Demultiplexing side: as the switch opens in front of a connection, that connection has the opportunity to receive a unit from the path

14. Engineered for Tomorrow Data Rate Management • Not all input links maybe have the same data rate. • Some links maybe slower. There maybe several different input link speeds • There are three strategies that can be used to overcome the data rate mismatch: multilevel, multislot and pulse stuffing 6.14

15. Data rate matching Engineered for Tomorrow • Multilevel: used when the data rate of the input links are multiples of each other. • Multislot: used when there is a GCD between the data rates. The higher bit rate channels are allocated more slots per frame, and the output frame rate is a multiple of each input link. • Pulse Stuffing: used when there is no GCD between the links. The slowest speed link will be brought up to the speed of the other links by bit insertion, this is called pulse stuffing.

16. Multi-Level Multiplexing Engineered for Tomorrow

17. Engineered for Tomorrow Multiple-slot multiplexing

18. Engineered for Tomorrow Pulse stuffing

19. Synchronization Engineered for Tomorrow • To ensure that the receiver correctly reads the incoming bits, i.e., knows the incoming bit boundaries to interpret a “1” and a “0”, a known bit pattern is used between the frames. • The receiver looks for the anticipated bit and starts counting bits till the end of the frame. • Then it starts over again with the reception of another known bit. • These bits (or bit patterns) are called synchronization bit(s). • They are part of the overhead of transmission.

20. Engineered for Tomorrow Framing bits

21. DS Services and T Lines Engineered for Tomorrow • DS-0, DS-1, etc, are services • T lines are used to implement these services

22. T Lines and Analog Signals Engineered for Tomorrow

23. T-1 Frame Structure Engineered for Tomorrow

24. E Lines Engineered for Tomorrow • European's version of T lines • Also used in Thailand

25. Engineered for Tomorrow Statistical Time-Division Multiplexing • In statistical time-division multiplexing, slots are dynamically allocated to improve bandwidth efficiency. Only when an input line has a slot's worth of data to send is it given a slot in the output frame. • In statistical multiplexing, the number of slots in each frame is less than the number of input lines. • The multiplexer checks each input line in roundrobin fashion; it allocates a slot for an input line if the line has data to send; otherwise, it skips the line and checks the next line.

26. Synchronous and statistical TDM Engineered for Tomorrow

27. Spread Spectrum Engineered for Tomorrow • Spread signal to use larger bandwidth • To prevent eavesdropping • To reduce effect from interference

28. Frequency-Hopping SS Engineered for Tomorrow • "FHSS" – Frequency-Hopping Spread Spectrum • Used in Bluetooth technology

29. FHSS Cycles Engineered for Tomorrow

30. Direct-Sequence SS Engineered for Tomorrow • "DSSS" – Direct-Sequence Spread Spectrum • Used in Wireless LANs

31. DSSS and Interference Amplitude Narrow Band Signal Narrow Band Interference Spread Spectrum Signal Frequency Engineered for Tomorrow

32. DSSS Example Engineered for Tomorrow

33. Introduction to switching Engineered for Tomorrow Switched networks • Long distance transmission between stations (called “end devices”) is typically done over a network of switching nodes. • Switching nodes do not concern with content of data. Their purpose is to provide a switching facility that will move the data from node to node until they reach their destination (the end device). • A collection of nodes and connections forms a communications network. • In a switched communications network, data entering the network from a station are routed to the destination by being switched from node to node

34. A Switched network Engineered for Tomorrow

35. Taxonomy of switched networks Engineered for Tomorrow

36. Circuit switched Networks Engineered for Tomorrow • Circuit switching: • There is a dedicated communication path between two stations (end-to-end) • The path is a connected sequence of links between network nodes. On each physical link, a logical channel is dedicated to the connection. • Communication via circuit switching has three phases: • Setup phase • Resource allocation (FDM or TDM) • Data transfer phase • Tear down phase • Deallocate the dedicated resources • The switches must know how to find the route to the destination and how to allocate bandwidth (channel) to establish a connection

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

38. Engineered for Tomorrow Delay in a circuit switched network

39. Datagram Networks Engineered for Tomorrow • Each packet is treated independently of all others. • Packets in this approach are referred to a datagrams • Datagram switching is normally done at the network layer. • Datagram networks are also referred to as connectionless networks. • There are no setup or tear down phases.

40. Engineered for Tomorrow A datagram network with four switches (routers)

41. Routing Table Engineered for Tomorrow In datagram networks,each switch has a routing table which is based on the destination address. Routing tables are dynamic and are updated periodically. The destination address and the corresponding forwarding output ports are recorded in the tables

42. Engineered for Tomorrow Routing table in a datagram network

43. Engineered for Tomorrow Destination address • Every packet in datagram network carries a header that contains destination address of the packet • When switch recieves packet,this destination address is examined,routing table is consulted to find path. Efficiency • Efficiency of datagram network is better than of circuit switche network as resources are allocated only when there are packets to be transferred. Delay • Delay is more in datagram network than in virtual circuit network

44. Engineered for Tomorrow Delay in a datagram network

45. VirtualCircuit Networks Engineered for Tomorrow A virtual-circuit network is a cross between a circuit-switched network and a datagram network. There are setup and teardown phases in addition to data transfer phase. Resources can be allocated during setup phase or on demand Data are packetized and each packet carries an address in the header.but address in header has local jurisdiction. All packets follow the same path established during the connection Virtual circuit network is implemented in the data link layer. Two types of addressing are used:global and local

46. Engineered for Tomorrow Virtual-circuit network

47. Virtual circuit Identifier Engineered for Tomorrow The identifier used for data tranfer is called virtual circuit identifier(VCI)

48. Threephases Engineered for Tomorrow Data Transfer phase • To transfer a frame from source to destination,all switches need to have a table entry for this virtual circuit • Fig shows a frame arriving at port1 with a VCI of 14

49. Engineered for Tomorrow Source-to-destination data transfer in a virtual-circuit network

50. Engineered for Tomorrow Setup phase • In setup phase,a switch creates an entry for a virtual circuit.Two steps are required • Setup request • A setup request is sent from the source to the destination as shown