EE3414 Multimedia Communication Systems I

EE3414EE3414

Multimedia Communication Systems IMultimedia Communication Systems I

• Communication networks and services

• Digital transmission fundamentals

• Circuit switching and telephone network

Communication networks and servicesCommunication networks and services

• Types of networks

• Types of applications

• Matching of applications needs/traffic to networking modes

• Types of delays

• What is a protocol?

• Four forces of importance

TYPES OF NETWORKS (1)• What's a network?

♣ It is a set of equipment and facilities that allows for a transfer of data from one endpoint to another.

♣ Links are the transmission lines. The simplest network is one point-to-point link.

♣ Nodes are switches/routers. A switch interconnects many links allowing for data to be switched from one link to another.

♣ Multiplexers are used to multiplex data bits from different communication sessions on to one link. Examples include Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM)/ Wavelength Division Multiplexing (WDM).

♣ Access network is the network used to provide end users access to services and connectivity to other end users

♣ Backbone network interconnects access networks

♣ LANs: Local Area Networks (typically deployed in offices/campus buildings)

♣ WANs: Wide Area Networks (interconnects offices, buildings, homes, regions)

TYPES OF NETWORKS (2)

• Communication networks are analogous to transportation networks.

• There are four types of transportation networks in existence today:♣ roadways♣ shipping♣ railroads♣ airways

• Similarly, there are multiple types of communication networks:

♣packet-switched connectionless (e.g., Internet - IP protocol based)

♣circuit-switched (e.g., Telephone network)

♣packet-switched connection-oriented (e.g., ATM: Asynchronous Transfer Mode)


♣TV networks are more like utility networks (power, water, etc.)

♣ Internet operates much like the postal system, where an envelope is sent in the mail with a destination address. Each intermediate post office determines the next hop post office based on this address. Intermediate post offices are comparable to IP routers.

S w itch ing M odes\N etw orkingm odes

C onnection less C onnection -O riented

P acket Sw itch ing e.g ., IP ,S S 7 e.g ., X .25 , A T M

C ircu it Sw itching e.g ., S O N E T , W D M O X C basedn etw ork s, T elep h on y n etw ork

• What defines packet-switching and circuit-switching:♣Packet-switching (PS): switching based on information in

packet headers♣Circuit-switching (CS): switching based on the "position" of

arriving bits, where "position" is defined by space (port), timeand wavelength

• Most textbooks define circuit switching as a mode in which a circuit is first set up before data is sent. However, this is not the "defining" attribute of circuit switching, but rather that of "connection-oriented (CO)" networking, since packet-switched CO networks also require a set up phase prior to data transfer.


• What defines connectionless and connection-oriented networking:

♣ In connectionless (CL) networking, packet headers carry destination addresses and routing through the network is based on the destination address

♣ In connection-oriented (CO) networking, a "connection" is set up prior to data transfer and released after data transfer. By reservation of a connection, we mean that a route is selected, and bandwidth, and if applicable, buffer space, is assigned for the connection


TYPES OF APPLICATIONS (1)We classify applications to check if any single networking mode can handle all applications

Sending end\Receivingend Live Stored

LiveInteractive(two-way)Streaming(one-way)

Recording (e.g.,Replay, TiVo)

Stored Streaming Non-real-time

• An end is considered "live" if the data is consumed immediately after the transfer either by a human user or computer user; Otherwise the data is"stored" for future use

• A communication session is considered real-time if either end is "live."

• Traffic characteristics: bursty traffic within a communication session in case of voice and video

• QoS requirements of real-time applications: constraints on delay and jitter

• One-way delay requirement for telephony traffic is 25ms if there are no echo cancellers on the path, 150ms with an echocanceller for excellent quality voice, and 400ms with an echocanceller for acceptable quality voice.

• Delay in transmitting a voice packet on a packet-switched network consists of packetization delay (time to fill the packet), emission delay on the links (packet size divided by transmission rate), propagation delay on the links (length of the link divided by the speed of light in the link medium),queueing delays, and playout delays at the receiver.

• Voice codec rates vary; PCM codecs generate data at 64kbps, Truespeech codecs at 8.5kbps, etc.

TYPES OF APPLICATIONS (2)

• Examples:♣ Interactive: Telephony♣ Streaming from live source: Radio, television, real-audio broadcasts

of radio/TV channels over the Internet♣ Streaming from stored source: Some of the Internet courses offered

at Poly have stored audio files that are only accessible to students in streaming mode; a real-audio streaming device (in Poly's case milestone.poly.edu) plays the audio out in streamed fashion. Students listen to it, but it doesn't get stored at the receiving PC. Buffering is done at the receiving PC to reduce jitter (variation in delay).

♣ Recording applications: Replay and TiVo are two appliances that would allow a set of hard disks to record TV programs, and play it out at the viewer's convenience (sophisticated VCRs).

♣ Non-real-time: a file download using http (hyper-text transfer protocol), ftp (file transfer protocol), smtp (simple mail transfer protocol)

TYPES OF APPLICATIONS (3)

Matching of applications needs/traffic to networking modes

• Bursty traffic: best served by packet-switched networks• Continuous traffic: best served by circuit-switched networks• Delay-sensitive traffic: best served by CO networks• Short delay-insensitive transfers: best served by CL

networks

Conclusions:• Interactive, streaming and recording applications best served

by packet-switched CO networks;• Short non-real-time transfers: best served by (packet-

switched) CL networks• Large non-real-time transfers: best served by circuit-

switched networks

Types of delays

• Packetization delay: time to fill a packet with user data; e.g., using a 64kbps PCM voice codec, it will take 10msec to fill a 80B packet.

• Emission or transmission delay: time taken by the transmitter to "emit" a data block, such as a packet, on to a physical link; e.g., to emit the 80B packet on a 10Mb/s link will take 64microseconds.

• Propagation delay: time to send a bit from one end of a physical medium to the other end; e.g., on a 100m fiber in which light travels at V m/s will take 100/V m/s.

What is a protocol

• It is a set of rules that governs how two communicating parties are to interact.

Four forces of importance to communication network evolution (1)

Market♣ For network based services, there has to be a critical mass of

subscribers'♣ Types of businesses in communications/networking:

• Service providers

• Telecommunications service providers, e.g., AT&T, Bell Atlantic, etc.

• History: After divestiture in 1984, seven Regional Bell Operating Companies (RBOCs) were created to offer local service, and AT&T offered long-distance service. Bellcore (Bell Communications Research) was created as the R&D labs for all 7 RBOCs, and Bell Labs. remained the R&D for AT&T. Now, some of the RBOCs have merged with each other.

• In 1996, AT&T split to form AT&T (the services company), Lucent Technologies (the equipment vendor) and NCR (computer company).

• Internet service providers, e.g., AOL, AT&T Worldnet, @home, etc.

• Increasingly, these classifications are no longer true, with telcos offering data services and ISPs offering telephony service


Market♣ Types of businesses in communications/networking:

• Equipment vendors• Telecommunications equipment vendors

• Examples include Nortel (Canada), Lucent (US), Siemens (Germany),Ericsson (Sweden), Alcatel (France), etc.

• Equipment: Circuit switches, SS7 nodes (Signaling Transfer Points), Operations Support Systems, Transmission equipment, cellular telephony infrastructure systems (base stations, mobile switching centers), etc.

• Internet equipment vendors

• Cisco, Bay Networks, 3COM, etc.

• Equipment: Ethernet switches, IP routers, etc.

• Increasingly, these classifications are not true, with traditional telcomequipment vendors selling IP routers, ethernet switches, and Internet equipment providers entering the voice market.


Standards

• In telecommunications, the ITU-T (International Telecommunications Union-Telecommunications) provides recommendations for many interfaces. Many national standards bodies, such as the ANSI (American National Standards Institute), ETSI (European Telecommunication Standards Institute), Japan, and other countries send representatives to ITU-T meetings to create recommendations.

• Internet standards have been largely defined by the IETF (Internet Engineering Task Force). See http://www.ietf.org. Most protocols, TCP, IP, OSPF, BGP, etc. have been defined in this organization.

• ATM Forum http://www.atmforum.com has been active in defining ATM specifications. It's an adhoc body consisting of industry members.

• IEEE defines LAN standards, such as IEEE 802.3 (which is ethernetlike), IEEE 802.11 (wireless LAN standard), etc.

• Check out the IETF and ATM Forum web sites to see how these organizations function.

Technology• Clearly, advances in technology drives the networking market and

services. For example, physicists working on fibers recently demonstrated the AllWave technology, which increases the range of wavelengths at which low attenuation can be achieved by drawing water molecules out of fiber! This will change how effective Wavelength Division Multiplexing (WDM) technology will be in data networks

• Until recently, IP packet header processing and IP forwarding was implemented in kernel-level software. Packet delays and router throughputs were consequently bottlenecks. Only, three or four years ago, some companies demonstrated that IP packet header processing and IP forwarding can be implemented in hardware. This has led to the birth of very large routers that operate at "wire-speeds." Differences between connectionless packet-switching and connection-oriented packet switching have been dramatically affected by this technological advance.



Regulation

• Most governments have agencies that regulate telecommunications services. For example, the use of electro-magnetic spectrum for communication purposes, i.e., frequency allocations for various services, needs to be done centrally. FCC (Federal Communications Commission) is the body that oversees telecommunications in the US.

Digital transmission fundamentalsDigital transmission fundamentals

• Digital representation of information: block-oriented, stream-oriented

• Why digital communications?• Line coding• Modulation

Digital representation of information: block-oriented, stream-oriented

Block-oriented

• Text: ASCII (7bits for each character) and EBCDIC; extended ASCII uses 8 bits per character

♣ Compression techniques: "the" "e" occur a lot

• Images:

♣ Fax of an 8" by 10" page with 400 by 400 pixels per sq. inch results in 38.4Mbytes if three bytes are used, one each to represent R, G, and B.

♣ GIF: lossless compression

♣ JPEG: lossy compression


Stream-oriented

• Voice: PCM (Pulse Code Modulation); 8000 samples/sec; with 8 bits/sample, it results in 64Kbps.

♣ Compression techniques:

♣ ADPCM - 32 Kbps

♣ Residual excited linear predictive coding - 8-16 kbps

• Audio (music): needs 32-384Kbps

• Video:

♣ H.261 coding: 176 by 144 or 352 by 258 frames at 10-30 frame/sec

♣ Full motion MPEG-2

♣ HDTV - 1920 by 1080 frames at 30 frames/sec (aspect ratio is important 16:9 vs. 4:3)


Requirements of different traffic types

• Audio: sensitive to delay and jitter (delay variation)♣ Transmission (emission) delay is L/R where L bits needs to be

transferred over a channel operating at R bits/sec♣ Propagation delay is distance divided by speed of light in medium of

the channel♣ Packetization delay: time to create an audio packet to send on a

packet-switched network or to create a voice sample to send on a circuit-switched network; depends on the codec rate; for example, G.711 codecs operate at 64Kbps

♣ For telephony traffic, the one-way delay should be ♣ Less than 25ms for excellent quality voice without echo cancellers♣ Less than 150ms for excellent quality voice with echo cancellers♣ Less than 400ms for acceptable quality voice with echo cancellers

• Text/data: sensitive to loss

Why digital communications?

• Advantages of digital communication over analog communication

• Analog communication: all details must be reproducedvs. digital communication: only a discrete set of levels need to be reproduced


• Analog repeaters vs. Digital repeaters• Analog repeaters: Amplifier and equalizer

♣ The amplifier amplifies both the signal and noise. High frequencies attenuate more than low frequencies; also delays are frequency-dependent.

♣ The equalizer removes these differences. The signal on the output of the repeater has noise and signal components.

• Digital repeaters: Amplifier/equalizer

♣ Output is fed into a timing recovery circuit and a decision circuit and signal regenerator; the output signal is regenerated to a string of 1s and 0s.

♣ There can still be errors, i.e., a 1 can appear as a 0 or vice versa, but there is no degradation as in the analog case.

♣ This makes digital communications cheaper, because transmission can be achieved to longer distances at the same power, or at the same distance with lower power.


• Basic properties of digital transmission systems

• Concept of "Bandwidth of a channel:"

♣ The bandwidth W of a channel is the range of frequencies that is passed by the channel.

♣ The amplitude response function of a low pass channel is such that past W, the ampliture drops off to zero - see Fig. 11 of your textbook.



• Nyquist rate:

♣ The fastest rate at which pulses can be transmitted into a channel of bandwidth W is given by the Nyquist rate, which is 2W pulses/sec. It is also the minimum rate at which a signal of maximum bandwidth W needs to be sampled.

♣ In case of multi-level transmission, where there are m bits/pulse, which corresponds to M=2m levels, the Nyquist rate is 2Wm bits/sec. This seems to indicate that by increasing the number of levels, the rate at which pulses are sent on a channelcan be arbitrarily increased. This is not true because as the number of levels increases, it becomes harder to detect levels accurately; this leads to higher noise levels



• Concept of "Signal to Noise Ratio:"

It is the ratio of the average signal power to the average noisepower.

SNR (dB) = 10 log10 SNR;

SNR is typically expressed in decibels (dB).



• Shannon's channel capacity: The maximum rate at which bits can be transferred reliably.

C=W log2(1+SNR) bits/sec when W is expressed in hertz.SNR is the signal to noise ratio at the receiver

Example:

If SNR expressed in dB is 20dB, it means that SNR is 100; To find log2 x, find (log10x)/log102.If 2y = 101, take log10 of both sides, then y log102 = log10101.


• Unipolar vs. bipolar:

In unipolar coding, only positive voltages are used, not negative ones

Line coding: how 1s and 0s in a binary string are converted into a digital signal in a digital communications systems


• NRZ vs. RZ (Non-return to zero vs. return to zero): Midway through the bit time, RZ will return to zero.

♣ Frequency of RZ signals are twice as much as NRZ; hence RZ coding is not good for bandwidth limited channels

♣ But it is good for synchronous systems since clock recovery is easier.

♣ RZ: A 1 is represented as a transition as is a 0.

♣ Manchester coding, a RZ coding scheme is used in Ethernet; 1: transition from +A/2 to -A/2; 0: transition from -A/2 to A/2 within the bit time.

Line coding: how 1s and 0s in a binary string are converted into a digital signal in a digital communications systems

Modulation

• If a channel is not low pass, it may pass a set of frequencies [f1, f2] centered around some frequency fc. The bandwidth of such a channel is f2-f1.

• To transmit a signal on such a channel, the signal needs to be modulated on to a carrier frequency fc.

• Three forms of modulation: ASK (Amplitude Shift Keying), FSK (Frequency Shift Keying), PSK (Phase Shift Keying).

Modulation

• Consider a PSK signal:

♣ If the information bit is 1, +ACos(2πfct) is sent

♣ If the information bit is 0, - ACos(2πfct) is sent

♣ The baseband signal, a digital string of 1s and 0s is denoted Ak. The modulated signal is AkCos(2πfct) for k (k −1)Τ< t < kΤ.

Modulation

• To demodulate, multiply by 2 Cos (2πφχτ), and then send through a low-pass filter

• The reason this works is that

♣ Ak Cos (2πfct) x2 Cos (2πfct) = Ak (1+Cos (4πfct))♣ 2Cos2ρ = 1 + Cos 2ρ

• The second component will not be passed through the filter and the string of 1s and 0s is output.

♣ The filter is a low pass filter of band W.

♣ The baseband signal Ak is of bandwidth W, which is the range of frequencies around fc that the medium can carry.

♣ The second term is another band of +/- W around 2fc. This will be filtered out by the low pass filter.

Circuit switching and telephone networkCircuit switching and telephone network

• Why are switches needed?

• What are circuit switches?

• Space division circuit switches

• Time-division multiplexed switch

• Telephone network

Why are switches needed?

• To connect N endpoints with each other, we need O(N2) lines

• By connecting N endpoints to a switch, we only need O(N) lines.

• The switch then needs to be configured for communication between any two endpoints

What are circuit switches?

• These are switches that perform switching action based on the "position" of arriving bits

• "Position" is defined by space (port number), time and wavelength.

Space division circuit switches

•A space division circuit switch is one in which all bits arriving on an input port are switched to a given output port.


•Crossbar switch• N inputs and N outputs; can connect any

input to any output • Non-blocking: if the output line that you are

trying to reach is free, the switch itself should not block the call.

• Need N2 crosspoints


•Multistage switch

• To decrease the number of crosspoints and hence complexity of the switch, a new design idea is to use multiple stages.



• The book shows a three-stage switch. Assume the switch has N input lines and N output lines. Divide each set into groups of n lines. The input stage has (N/n) small switches, each of which is an (n xk) switch. An (n x k) switch has n input lines and k output lines. The intermediate stage has k switches, each of which is an (N/n x N/n) switch. The output stage has (N/n) small switches, each of which is a (k x n) switch.



• Question: why bother with this multi-stage switch? Answer: to achieve a simpler design (with fewer crosspoints), while keeping the switch non-blocking.



• What should k be for the switch to be non-blocking? Answer: 2n-1.

• How? Assume an input line I wants to be connected to an output line O. I is in competition with n-1 lines that are in the same "n" group as itself. This is so because if these n-1 lines take all the outputs from its input stage switch to the intermediate stage, then the input line I cannot enter the intermediate stage. Similarly, the output line O is incompetition with n-1 lines in its "n" group. If these n-1 lines use n-1 of the intermediate stages that are disjoint from the n-1 stages used by the input line I's n-1 neighbors, then if there are 2(n-1) intermediate stages, in the worst case, the connection between I and O cannot be made. If there is one extra stage, i.e., 2(n-1)+1 = 2n-1, the switch will be non-blocking, assuring any I of connecting to any O, provided O is free. Therefore k has to minimally be 2n-1 for the switch to be non-blocking.



• How many crosspoints does this multistage switch have?The input stage has (N/n) switches, each with (n x k)crosspoints. There are k intermediate stages, each with (N/n x N/n) crosspoints. The output stage is the same as the input stage. Therefore the total number of crosspoints is 2(N/n)(n x k) + k(N/n)2. For k=2n-1, this number is 2N(2n-1) + (2n-1)N 2/n 2 = 4Nn - 2N + 2N 2/n - N 2/n 2.

.



• To find the order of increase in the number of crosspointsfor this switch relative to N, find the minimum value for the above polynomial. Find the differential of the polynomial for the number of crosspoints with respect to n, and set it to 0. This becomes 4n3 - 2nN + 2N = 0. Solving this results in n being approximately equal to square root (N/2). Therefore the number of crosspoints grows in the order of N1.5rather than N2 as in the cross-bar switch.

•See derivation for why the number of crosspoints only grows in the order of N1.5.

.

Time-division multiplexed switch

•Time slot interchange reads bits from incoming slots in each frame and writes these into a register. Call setup would have created a permutation table for how the contents are read out.

Time-division multiplexed switch

•T-S-T switch:• Replace the first stage of (n x k) switches in the 3-stage space-

division switch with (n x k) TSIs, i.e., each incoming line carries n time slots; these are read into k separate output lines in the first stage switch.

• At time slot 1, all N/n input stages send data to the 1st intermediate stage, which crossconnects them. At time slot 2, all N/n input stages send data to the 2nd intermdiate stage and so on. So instead of having k (N/n x N/n) intermediate stages, have only one (N/n x N/n) intermediate stage but reprogram it on every time slot. This is called a time-shared space switch.

• See Fig. 29 in chapter 4 of the book. Look for other ways of providing the same crossconnections. Here's another way.

Example of how a circuit switch is programmed to realize four connections

2 x 3

2 x 3

3 x 2

B1

B1

C1

C1

3 x 2

D1

D1

D1 C1

B1 A1D1 C1

B1 A1

A talks to C; B talks to D

Connected to A and B

Connected to C and D Connected

to C and D

Connected to A and B

A1

A1

• Lines, trunks, analog vs. digital, phone calls, addressing, NANP

• Digital cross-connects, Central Office and Toll switches, PBXs

• PDH, SONET/SDH, ISDN BRI and PRI

• Relation between OSI reference model and the telephone network/circuit switching

Telephone network

B B

C C

A A

B

C

A

B

C

A

MUXMUX

(a) (b)Trunkgroup

Figure 4.1

A CBf

Cf

Bf

Af

W

W

W

0

0

0

(a) Individual signals occupy W Hz

(b) Combined signal fits into channel bandwidth

Figure 4.2

(a) Each signal transmits 1 unit every 3T seconds

(b) Combined signal transmits 1 unit every T seconds

tA1 A2

tB1 B2

tC1 C2

3T0T 6T

3T0T 6T

3T0T 6T

tB1 C1 A2 C2B2A1

0T 1T 2T 3T 4T 5T 6T

Figure 4.3

2

24

1

MUXMUX

1

2

24

24 b1 2 . . .b2322

frame

24 . . .

. . .

Figure 4.4

12345 12345

t

Figure 4.6

MUX DEMUX MUX DEMUX

MUX DEMUX

(a) pre-SONET multiplexing

removetributary

inserttributary

ADM

removetributary

inserttributary

(b) SONET Add-Drop multiplexing

Figure 4.9

a

b

c

d

a

b

c

d

(a) Dual ring (b) Loop-around in response to fault

Figure 4.12

Inter-OfficeRings

MetroRing

RegionalRing

Figure 4.13

STE: Section Terminating Equipment, e.g. a repeaterLTE: Line Terminating Equipment, e.g. a STS-1 to STS-3 multiplexerPTE: Path Terminating Equipment, e.g. an STS-1 multiplexer

optical

section

optical

sectionoptical

section

optical

sectionline

optical

sectionline

optical

sectionlinepath

optical

sectionlinepath

(a)

(b)

STSPTE

LTESTE

STS-1 Path

STS LineSection Section

Mux Muxreg reg regSONETTerminal

STE STELTE

STSPTE

SONETTerminal

Figure 4.14

B BB 87B

InformationPayload 9 Rows

125 µsTransportoverhead

90 bytes

SectionOverhead 3 rows

6 rowsLineOverhead

Figure 4.15

Pointer87 columns

9rows

first column is path overhead

SynchronousPayload

Envelope

framek

framek+1

Pointer

first octet

last octet

Figure 4.16

STS-1 STS-1

STS-1 STS-1

STS-1 STS-1

Map

Map

Map

STS-1 STS-1

STS-1 STS-1

STS-1 STS-1B

yteInterleave

STS-3

IncomingSTS-1 Frames

Synchronized NewSTS-1 Frames

Figure 4.17

λ1

λ2

λm

OpticalMUX

λ1

λ2

λm

OpticaldeMUX

λ1 λ2. λm

Opticalfiber

Figure 4.18

(a) WDM chain networka b c d

(b) WDM ring network

a

b

c

3 ADMs

Figure 4.20

User 1

SwitchLink

User n

User n-1

(a) Network

(b) Switch Control

123

N

123

N

Connectionof inputs to outputs

Figure 4.21

N

1 2

1

N

2

N-1

Figure 4.22

N

1 2

1

N

2

N-1

Figure 4.22

nxk

nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

kxn1

2

N/n

Ninputs

1

2

3 3

N/n

Noutputs

1

2

k

2(N/n)nk + k (N/n)2 crosspoints

kxn

kxn

kxn

Figure 4.23

nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

kxn1

N/n

Desiredinput

1

jm

N/n

Desiredoutput

1

2n-1

kxn

kxn

n-1

N/n x N/nn+1

N/n x N/n2n-2

free path freepath

n-1busy

n-1busy

Figure 4.24

12

24

12

24

FromTDM

DeMUX

ToTDMMUX

24 23 12

2 241 23

Read slots inpermuted order

Figure 4.25

nxk

nxk

nxk

nxk

N/n x N/n kxn1

2

N/n

Ninputs

1

3

1

12n

input TDM frame with n slots

output TDM frame with k slots

Figure 4.26

nxk N/n x N/n

N/n x N/n

N/n x N/n

kxn1 1

2

N/n

1

2

k

kxn

kxn

nxk2

nxkN/n

first slot

kth slot

first slot

kth slot

Figure 4.27

nxk

nxk

nxk

nxk

N/n x N/nTime-Shared

SpaceSwitch

kxn1

2

N/n

Ninputs

1

2

3 3

N/n

Noutputs

TDMn slots

n slots

n slots

n slots

kxn

kxn

kxn

TDMk slots TDM

k slots

TSI Stage TSI StageSpace Stage

Figure 4.28

2x3

2x3

3x21

2

1

23x2D1

B1 A1B2 A2

C1D2 C2

B1 A1

C1D1

A1

B1

C1

D1

A1 C1

B1 D1

Figure 4.29

Figure 4.30

Signal

Source

Signal

Release

Signal

Destination

GoAhead Message

Figure 4.31

(a) Routing in a typical metropolitan area

(b) Routing between two LATAs

1

2 3

4

5

LATA 1 LATA 2

net 1

net 2

A B

C D

Figure 4.32

local telephone office

Dis

tribu

tion

Fram

e

Serving Area I/f

Serving Area I/f

Pedestal

feeder cable

Switchdistribution cable

Figure 4.33

Original signal

Hybrid transformer

Received signal

Echoed signal

Receive pair

Transmit pair

Figure 4.34

SPC

Control Signaling Message

Figure 4.38

STP

STP

STP

STP

SSP SSP

Transport Network

Signaling Network

SSP = Service switching point (signal to message)STP = Signal transfer point (message transfer)SCP = Service control point (processing)

SCP

Figure 4.40

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EE3414 Multimedia Communication Systems I