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

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Multiplexing
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.
1 link, n channels
n signals (input)
M U X
D E M U X
n signals (output)
Multiplexer
Demultiplexer

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Multiplexing
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)
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Frequency Division Multiplexing (FDM)
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 Time f3 f2 f1
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Conceptual View of FDM
Channel 3
Channel 2
Channel 1 f1 f2 f3
Frequency
Time

6. FDM: Multiplexing Process
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FDM: Multiplexing Process

7. FDM: Demultiplexing Process
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FDM: Demultiplexing Process

8. Analog Hierarchy Used by AT&T … … 12 voice channels F D M F D M F D M
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Analog Hierarchy
Used by AT&T
4 kHz
48 kHz 12 voice channels
12 voice channels
4 kHz …
240 kHz 60 voice channels
group F D M
2.52 MHz
600 voice channels
5 groups
supergroup F D M …
10 supergropus
master group
MHz
3600 voice channels F D M
6 master groups
Jumbo group F D M

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

10. Time Division Multiplexing (TDM)
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Time Division Multiplexing (TDM)
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
one unit
T D M A B C
Frame
Time slot

11. Conceptual View of TDM M U X 1 2 3 1 Data flow 2 D E M U X 3 Time
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Conceptual View of TDM
M U X 1 2 3 1
Data flow 2 3 2 1 3 2 1 3 2 1
D E M U X 3
Time
Frequency
Channel 3
Channel 2
Channel 1

12. TDM Frames A frame consists of one complete cycle of time slots
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TDM Frames
A frame consists of one complete cycle of time slots

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Interleaving
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

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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

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Data rate matching
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
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Multi-Level Multiplexing

17. Multiple-slot multiplexing
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Multiple-slot multiplexing

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Pulse stuffing

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Synchronization
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.

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Framing bits

21. DS Services and T Lines DS-0, DS-1, etc, are services
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DS Services and T Lines
DS-0, DS-1, etc, are services
T lines are used to implement these services
Service
Line
Rate (Mbps)
Voice Channels
DS-1
T-1
1.544 24
DS-2
T-2
6.312 96
DS-3
T-3
44.736
672
DS-4
T-4
4032

22. T Lines and Analog Signals
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T Lines and Analog Signals

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T-1 Frame Structure

24. E Lines European's version of T lines Also used in Thailand E Line
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E Lines
European's version of T lines
Also used in Thailand
E Line
Rate (Mbps)
Voice Channels
E-1
2.048 30
E-2
8.448
120
E-3
34.368
480
E-4
1920

25. Statistical Time-Division Multiplexing
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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
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Synchronous and statistical TDM

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

28. Frequency-Hopping SS "FHSS" – Frequency-Hopping Spread Spectrum
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Frequency-Hopping SS
"FHSS" – Frequency-Hopping Spread Spectrum
Used in Bluetooth technology

29. FHSS Cycles
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30. Direct-Sequence SS "DSSS" – Direct-Sequence Spread Spectrum
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Direct-Sequence SS
"DSSS" – Direct-Sequence Spread Spectrum
Used in Wireless LANs

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

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DSSS Example

33. Introduction to switching
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Introduction to switching
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

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A Switched network

35. Taxonomy of switched networks
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Taxonomy of switched networks

36. Circuit switched Networks
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Circuit switched Networks
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

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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. Delay in a circuit switched network
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Delay in a circuit switched network

39. Datagram Networks Each packet is treated independently of all others.
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Datagram Networks
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. A datagram network with four switches (routers)
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A datagram network with four switches (routers)

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Routing Table
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. Routing table in a datagram network
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Routing table in a datagram network

43. Delay is more in datagram network than in virtual circuit network
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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. Delay in a datagram network
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Delay in a datagram network

45. Virtual Circuit Networks
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Virtual Circuit Networks
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. Virtual-circuit network
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Virtual-circuit network

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

48. Three phases Data Transfer phase
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Three phases
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. Source-to-destination data transfer in a virtual-circuit network
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Source-to-destination data transfer in a virtual-circuit network

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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

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Acknowledgement
A special fram,called acknowledgement frame,completes the entries in the switching tables.

52. Delay in a virtual-circuit network
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Delay in a virtual-circuit network

53. Thank You……