Multimedia Communications

1. Electrical Communication Engineering, Indian Institute of Science, Bangalore – 560012, India Multimedia Communications

2. Objectives To know the networking evolution. To understand the network types. To discuss multimedia requirements in the communication systems. To understand the basics of a multimedia communication system. To illustrate multimedia networks. To know the Internet protocol suite for multimedia communications.

3. The network formed by the co-operative interconnection of a large number of computer networks. Every person who makes a connection owns a slice of the Internet. The connected networks use the TCP/IP protocol.

4. Application of Internet Telnet-Remote login File Transfer Protocol (FTP) Electronic Mail (Email) Gopher Internet Relay Chat (IRC) Usenet News World Wide Web (WWW)

5. Computer Network A communication system for connecting computers / hosts Why? Better communication Better sharing of resources Bring people together

6. Types of Computer Networks Local Area Network (LAN) Connects hosts within a relatively small geographical area. Same room Same building Same campus It is Faster: speeds- 10 Mbps to 10 Gbps Cheaper-1 crore for a hundred node LAN (one-time cost)

7. Network Topologies Evolution LAN Linear topology- Single segment LAN in linear topology. Ethernets and token rings were cables connecting each station Star-wired-to avoid rewiring, Multistation access units (MAUs) introduced. Hubs were used. Multisegment-Bridges and routers connected several LANs. Backbone-connected-Backbone network Switched-backbone-Replacement of backbone with high bandwidth Switch.

8. Internetworking Devices Hub- Extends the span of a single LAN. Bridge / Layer-2 Switch Connects two or more LANs together. Works at data link layer level. Router / Layer-3 Switch Connects any combination of LANs and WANs. Works at network layer level.

9. Types of LANs

10. WAN Wide Area Network (WAN) Hosts may be widely dispersed Across campuses Across cities / countries/ continents It is faster and cheaper Typical speeds- 64 Kbps to 8 Mbps Typical cost- 30 lakhs (recurring cost)

12. Internet

13. How to get connected to internet

14. Gateway access- Level one connection, Access to internet from a network that is not on internet. ISP defines the limitations. Good example of network with Level One connectivity within India is that of VSNL (Videsh Sanchar Nigam Limited). All access to Internet from India are through VSNL gateway. Dial up connection- Level two connection. Computer that provide Connection to internet is called host and computer that receives the Access is client. Also called remote modem access. Leased connection-Direct internet access or level three connection. Secure, dedicated expensive connection.Leased internet connections Are connections limited to large corporations and universities that Can afford the cost.

15. Circuit Switching A dedicated communication path is required between two stations. The path follows a fixed sequence of intermediate links.

16. In circuit switching, three steps are required for communication: Connection establishment Required before data transmission. Data transfer Connection termination

17. Drawbacks: Channel capacity gets dedicated during the entire duration of communication. Acceptable for voice communication. Very inefficient for bursty traffic. There is an initial delay. For connection establishment.

18. Packet Switching Network resources are not dedicated. A link can be shared. Data are transmitted in short packets(~ Kbytes). A longer message is broken up into smaller chunks. The chunks are called packets. Every packet contains a header. Relevant information for routing, etc.

19. Packet switching is based on store-and-forward concept. Each intermediate network node receives a whole packet. Decides the route. Forwards the packet along the selected route.

20. Advantages: Links can be shared; so link utilization is better. Suitable for computer-generated traffic. Typically bursty in nature. Buffering and data rate conversion can be performed easily. Some packets may be given priority over others, if desired.

21. How are the packets transmitted? Two alternative approaches: Virtual Circuits: Similar in concept to circuit switching. A route is established before packet transmission starts. All packets follow the same path. The links comprising the path are not dedicated. Datagram:No route is established beforehand. Each packet is transmitted as an independent entity. Does not maintain any history.

22. Every intermediate node has to take routing decisions dynamically. Makes use of a routing table. Every packet must contain source and destination addresses. Problems: Packets may be delivered out of order. If a node crashes momentarily, all of its queued packets are lost. Duplicate packets may also be generated.

23. Advantages: Faster than virtual circuit for smaller number of packets. No route establishment and termination. More flexible. Packets between two hosts may follow different paths. Can handle congestion/failed link.

24. Three types of delays must be considered: Propagation Delay: Time taken by a data signal to propagate from one node to the next. Transmission Time: Time taken to send out a packet by the transmitter. Processing Delay: Time taken by a node to “process” a packet.

25. Multimedia Requirements For smooth running of multimedia applications over networks, three issues need to be addressed. To develop schemes for multi-access networks which can provide performance guarantees. To develop a distribute route-selection strategy for point-to-point networks. Real-time multimedia applications require guaranteed performance communication services, such as throughput, delay, delay jitter and loss rate. The characteristics of a source, such as peak and average rate, are known at channel establishment time. Channel parameters have to be predicted in live continuous video sources.

26. Communication Service for Multimedia Quality-of-service (QoS) support and group communication system: establishment and take-down of appropriately configured channels; negotiation of QOS levels between end-systems, intermediate systems, and network control; and control of the agreed QOS level bandwidth, delay, delay jitter (variance), and reliability. Audio/Video groups can: have static or dynamic memberships during their lifetime, have centrally (typically sender) or distributively (typically receiver) controlled membership, consist of members with homogeneous or be heterogeneous characteristics and requirements.

27. Multimedia Communication System Multimedia Communication system (MCS) – system that handles more than one media stream in synchronized way from user's point of view. Communication system-A system or facility capable of providing information transfer between persons and equipment. It consist of collection of communication networks, transmission system, relay stations, tributary stations and terminal equipment.

28. Multimedia Application Environment

29. Terms and definitions Bandwidth-is a measurement of bit-rate of available or consumed data communication resources expressed in bits per second or multiples of it (bit/s, kbit/s, Mbit/s, Gbit/s, etc.). CD-ROM: “Compact disk read-only memory.” most popular method of delivery of MM materials. Client-Server Model: A client makes a request and a server fulfills that request. Composite Video: Analog video signals can be broken down into parts such as luminance (Black & White) and chrominance (color).

30. Multimedia File types Here are some examples of file types: Text Files: .txt, .doc, .rtf Audio Files: .au, .aif, .wav Graphic files: .jpg, .gif, .tif, .bmp, .pict, .pcx Moving video files: .qt, .mov, .avi Animation: .fli, .flc

31. Multimedia Communication System Interactive Multimedia Design- Interactive multimedia is becoming increasingly popular in education, entertainment, and business. Because of the capability of incorporating various media, and of supporting interactivity and learner control, multimedia is often used in delivering instruction. Interleaved-synchronization of audio and video- lip synchronization with audio. Interlacing-A TV video signal is interlaced, meaning each full screen of information is actually made up of two separate fields—the odd field and the even field. First, the odd lines are painted on the screen. Then, before the odd lines fade, the even lines are painted in between the odd lines. This all happens faster than the human eye can perceive

33. Multimedia may be broadly divided into linear and non-linear categories. Linear active content progresses without any navigation control for the viewer such as a cinema presentation. Non-linear content offers user interactivity to control progress as used with a computer game or used in self-paced computer based training. Hypermedia is an example of non-linear content. Presentation Multimedia-combination of digitized audio, video, graphics, etc.

34. Multimedia Communication System LAN Access Method Routing Frame and Packet Structures Packet Discrimination Identify packets that require special handling. Be capable of accommodating those special requirements. Bandwidth Requirement, Reservation and Conservation High bandwidth and low latency

35. Multimedia Communication System Architecture The ability to manage dynamically the achieved QoS of each service component The possibility for users to select some resources that best meet their needs. The possibility to interact with another user whose equipment has differing characteristics. The communications network must allow any user to select the service components he/she wants: The possibility for users to join in or withdraw from a communication session according to certain policies, such as agreement of all interacting partners before admitting a new user. The possibility to set such quality of service parameters as the synchronization tolerance between the service components, the echo sensitivity, the burst sensitivity, and so on.

36. Multimedia Networks Technical Issues Network transmission is liable to errors and Data loss. Excess of loss in video transmission affects performance of video quality. Video quality can be enhance by proper frame synchronization between video and audio streams. Admission control: takes into account resource reservation request and available capacity whether to accept a new request with its QoS requirements. Scheduling: provides QoS by allocating resources depending on the service requirements. This requires mapping of user defined QoS requirement to resouce allocations for providing the service.

37. Resource management: Efficient resource management is a cost effective solution for the provider and it ensures that applications will get the specified QoS during the course of their execution. Congestion control: is required to avoid anything bad from happening inside a network domain. Some applications may not follow the standard protocol description and try to steal resources, thereby deteriorating the QoS of other applications. Policing/Shaping:Users might send traffic at a rate higher than that agreed on. Policing is necessary to monitor these situations and shaping makes the traffic smooth and reduces its variations over time.

38. Multimedia Network reference model Hypothetical multimedia network reference model (MNRM). The MNRM must have monitoring and real time control, management, communication, and abstraction primitives that are organized and real time control, management architecture, information transport architecture and tele-base architecture respectively. Subdivision of MNRM based controls and communications a. Management and traffic control architecture b. Information transport architecture Reference model is organized into five planes :N plan, M- plane, C-plan, U-plane.

39. Multimedia Network Reference Model

40. N-plane: Management architecture resides in the network management or N-plane and covers the functional areas of network management- configuration, performance, fault, accounting and security management, manager and agents. M-plane-comprises the entities and mechanism for resource control such as cell scheduling, call admission, and call routing. C-plane- comprise the entities and mechanism responsible for connection management and control. D-plane-Telebase architecture resides here and implements the principles of data sharing for network monitoring, control and communication primitives. U-plane- The information transport architecture is located in the user transport or U plane and it models the protocols and entities for transport of user information.

41. Multimedia Hardware/Software Difference between steaming and non-streaming media is streaming allow playback in RT. Non streaming media require the whole file to be downloaded before playback. Audio/Video Hardware Digital Video (DV) Eliminates inefficient method of converting analogue video to Digital by capturing video digitally. Analog to Digital devices: Converts analoge video signals to digital video. Built-in Hardware:Most PCs come equipped with CD ROM drives and microphones.

42. Digital Video Software: Video format of widows computer is AVI(audio video interleaved) files. Video file are compressed using codecs so that they are small enough to deliver over the internet. Multimedia Software: combines various elements of audio , graphics and video that allow creation of shock-wave, director, quick-time(video format), real-media etc.

43. Comparison of Stacks TCP/IP five layer reference model is a widely accepted model For designing network protocols. To single out the mm characteristics, we logically partition the Five layer reference model into four layer mm design model that Includes application layer, mm integration control and synchronization layer (MICS) layer., the inter process communication and synchronization layer (IPCS) and network layer.

44. Comparison of Stacks

45. IPCS layer-Consist of foundation of the MM communication environment. Provides flexible set of communication and synchronization primitives. It crates set of mechanisms that allow location independent exchange of MM information between two processes and provide the adequate tools for synchronization. MICS layer: Is responsible for integrating different types of related communication media, preserving the timing relations. Provides control operations required by supported applications. Application layer: provides set of user interaction functionality to handle different types of user defined objects. This layer is characterized by a coarse level of synchronization which has direct implications on process scheduling and object manipulation.

46. Multimedia Internet Protocols Multimedia over TCP: in mm application multicast method used, TCP supports point to point. Reliable connection, client has to wait for packets so delays. Multimedia over UDP: connection less, best effort delivery. Support Multi-casting and Best effort is required for MM applications.

47. RTP Real-time Transport Protocol (RTP) provides support for the transport of real-time data such as video and audio streams. RTP needs support from lower layers that actually have control over resources in switches and routers RTP/RTCP provides functionality and control mechanisms necessary for carrying real-time content. RTP/RTCP itself is not responsible for the higher-level tasks like assembly and synchronization. These have to be done at application level.

48. RTCP Real-Time Control Protocol extends RTP In an RTP session, participants periodically send RTCP packets to convey feedback on quality of data delivery and information of membership. Packets defined for carrying control information: SR: Sender report, for transmission and reception statistics from session participants that are active senders. RR: Receiver report, for reception statistics from session participants, that are not active senders. SDES: Source description items, including CNAME BYE: Indicates end of participation APP: Application specific functions

49. Multimedia Internet Protocols SAP & SDP-Session announcement protocol, Session description protocol. Peer to peer communication, the concept of session. SIP Signalling mechanisms that are necessary to establish a session and to negotiate the parameters to be used in it, such as codecs, media, location, etc. MBONE Tools (Multicast Backbone)-allows us to participate in different kinds of VC and meetings using IP MultiCast as network technology

50. SDR-session directory tool -TV guide Shows all plans and MBONE sessions., VIC-Video conferencing tool used for video transmission with great variety of codecs available. This can be used on every platform and compatible with standards for capturing video. VAT and RAT-Video and Robust audio tool for video and audio conferencing used in many platforms. WB- white board that can be used by participants and same functionality as blackboard in classroom. NTE-Network text editor and offers the functionality of distributed word processor. It supports tokens for asking permission to write and quite comprehensions.