Faculty: Mr. Kiran Kumar Semester: 8th ‘B’

Subject: Multimedia Communication Sub.Code:10EC841

PART A
Question
Solution / 1.  With a neat diagram, explain the following terms relating to a switched telephone network: i) POTS, ii) Local Exchange/end office, iii) PBX, iv) Mobile switching center, and v) international gateway exchange.
Switched Telephone Network

•  Basic switched telephone service. POTS (plain old telephone service). 'Switched' means that a subscriber can make a call/switch to any other telephone that is connected to the total network.
•  Telephones located in Home/ Small Business is connected to Local Exchanges/End Office. Part of PSTN
•  Set of telephones located in Large office/site are connected to PBX( private switching office). It in-turn is connected to PSTN
•  Cellular phone networks (handsets) linked by radio access. Switches used are called Mobile Switching Centers (MSCs). Inturn connected to a switching office in a PSTN
•  International Calls routed to & switched by (IGEs) International gateway exchanges. / Marks
Solution / 2.  Explain ISDN, B-ISDN, ATM, audio-bridge and MCU?
•  ISDN (Integrated Services Digital Network) is a set of CCITT/ITU standards for digital transmission of voice, video, data, and other network services over the traditional circuits of the PSTN. ISDN offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 kbs.
•  Enhanced ISDNs is also known as broadband ISDN (B-ISDN). "Broadband" means it can support a bit rate (>2Mbps). All media types are converted into digital form and integrated together, and the resulting stream is divided into fixed-sized packets known as cells.
•  Different multimedia applications generate cell streams of different rates and hence the rate of transfer of cells through the network varies. This mode of transmission is known as asynchronous transfer mode (ATM), uses asynchronous time-division multiplexing.
•  Audio-bridge :Special purpose Audio conferencing unit, audio bridge used to support 6-48 participants. Connects two LANS. Used to schedule call.
•  MCU: Special purpose unit, multipoint control unit (MCU) is a centralized conference server for high volume & rate exchange). It consists of MC & MP. MC: Establish connection with conference participants on a agreed set of operational parameters like screen resolution, refresh rate etc. MP: Distribution of information streams generated during conference (mixing of different media streams, voice-activated switching, continuous)
3.  State the aim of all broadcast TV networks. With an aid of diagrams, explain how additional services are provided with a cable distribution network and a satellite/terrestrial broadcast network.
•  Aim: Designed to support the diffusion/transmission of analog television (and radio) programs throughout wide geographical areas. Example: Cable distribution network : for a town or city, Satellite network /Terrestrial broadcast network : for larger areas.
•  The traffic is taken to be 1-way or asymmetric. But it generally works with a low bit rate return channel offered by a cable network for interaction purposes to provide a range of additional services such as home shopping and games playing. The subscriber accesses the cable distribution network through a set-top box.

Broadcast television networks: (a) cable networks;
(b) satellite/terrestrial broadcast networks.

4.  Explain the different kind of multimedia applications which involve multiple media? Give application descriptions for different media.
Solution: Different kinds of multimedia applications are
1.  Interpersonal communications involve speech, image, text or video. In some cases a single medium, in others multiple.
2.  Interactive applications over the Internet
3.  Entertainment applications
Interpersonal communications
Category / Media / Application descriptions
Interpersonal
communications / Speech / Telephony, voice-mail,
teleconferencing
Image / Facsimile
Text / Electronic mail
Text and images / Computer-supported
cooperative working
Speech and video / Video telephoney, video mail, Videoconferencing
Text, image, audio
and video / Multimedia electronic mail,
multiparty video games etc.
Interactive applications
And
Entertainment Applications
Category / Media / Application
Interactive
applications over
the Internet / Text, image, audio
and video / Information retrieval (news, weather, books, magazines, video games, product literature etc.)
Electronic commerce
Entertainment
services / Text, image, audio and video / Audio/CD-on-demand
Movie/video-on-demand
Analog and digital broadcasts
Interactive television
PART B
5.  A. Explain different media types? Give examples?
B. Explain symmetric and asymmetric information flow in half-duplex and full duplex communications? Give examples?
Solution: An Internet media type is a standard identifier used on the Internet to indicate the type of data that a file contains. The information flow associated with the different applications can be either continuous or block mode.
continuous: The information stream is generated by the source continuously in a time-dependent way and played out directly as it is received at the destination.
E.g. real-time audio, video.
The source stream can be generated at a constant bit rate (CBR) or a variable bit rate (VBR). Digitized audio is generated constant bit-rate, determined by sampled rate & numbers of bits used digitize each sample. Individual pictures/frames make up a video are generated at constant rate. Due to compression and variable information variable rate is generated.
Block mode of operation: streaming Mode of operation: downloading The source information comprises a single block of information that is created in a time-independent way. E.g. text, image
Half-duplex: info flows in both directions, but alternately ( request made to remote server and request granted)
Full-duplex: info flows in both directions simultaneously (1-to-1 transmission). Two-way speech and video in video telephony.
In duplex communications, if the flow is in the 2 directions are equal; the information flow is symmetric (Video Telephony). Otherwise, it's asymmetric (Web Browsing).(Diagrams)
6.  With aid of a diagram explain the operation principle of CO packet-mode network. Include in your explanation the need for a virtual connection/circuit, a virtual circuit identifier and a routing table.
Solution. A connection-oriented network comprises of an interconnected set of packet-switching exchanges (PSEs). Prior to sending any information, a connection is first set up through the network using address of source & destination terminals.

The connection utilizes only a variable portion of the bandwidth of each link and hence it's known as a virtual connection or a virtual circuit (VC). Connection-oriented packet-switched networks imitate circuit-switched network. In order for two users to communicate a Virtual circuit or a Connection has to be first established by the network, then data transfer takes place. After a connection or virtual circuit is established between two nodes or application processes, a bit stream may be delivered between the nodes.

VCI used for setting up Virtual circuit. PSE = Source/Destination Address + VCI .
PSE determines the input link and outgoing link by using packet destination address & a free identifier (VCI). Information transfer phase can start with VC in place. Only VCI is needed in packet header instead of full n/w wide info.
7.  In relation to the CL packet-mode network, explain i) best effort service, ii) store-and-forward delay
Define BER probability of a transmission line/channel. How does it influence the maximum packet block size of the channel?
Solution: When a packet is forwarded to a PSE/router, it's stored in a buffer, checked, discarded if there is any problem (due to congestion or error), or else forwarded to next PSE/router if the outgoing link is available. Each PSE/router has a routing table and it's used to determine the outgoing link to which a packet from a particular incoming link should forward. This mode of operation results in delay, called store-and-forward delay as a packet has to wait in a PSE/router until the outgoing link is available.
The service offered by a packet-switched network is said to be a best-effort service as the transmission of a packet is not guaranteed to be successful.
The mean bit error rate (BER) of a channel is the probability of a bit being corrupted during its transmission across the channel in a defined time interval. Mean BER of 10⁻⁴ indicates for every 10000 bits transmitted, 1 of a bit is corrupted.
A packet is declared incorrect if at least one bit is erroneous. Information is partitioned into blocks during its transmission so as to minimize the propagation of error. Any blocks containing bit errors will be discarded. Hence prior to transmission source info is divided into blocks, whose max size is determined by mean BER of the channel.
Example: for BER 10⁻⁴, block size < < 10000 bits. Otherwise all the blocks will discarded if block size = 10000. Block of 100 bits may still contain error, but probability is less.
8.  With the aid of a diagram explain the meaning of QoS parameters i) packetization delay ii) mean packet transfer delay iii)jitter. Hence describe the effects on a constant bit stream rate and how can it be overcome by buffering?
•  Mean packet transfer delay is the summation of the store-and-forward delay that a packet experiences when it travels along the route.
•  Packetization delay is the delay incurred at the source to packetize the information. The larger the size of a packet, the larger the packetization delay is.
• 
Question / Marks
Question / Marks