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MULTIMEDIA SYSTEMS NETWORKING. SOFTWARE. SERVER. NETWORK. CLIENT. MULTIMEDIA SYSTEM. WE CONSIDER MULTIMEDIA SYSTEMS BUILT-UP ON LARGE SCALE: REACHING PRACTICALLY EVERYBODY, LIKE TV, RADIO AND TELEPHONE TODAY, THAT IS THOUSANDS AND MILIONS OF USERS MULTIMEDIA MEANS BROADBAND

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MULTIMEDIA SYSTEMS NETWORKING


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    1. MULTIMEDIA SYSTEMSNETWORKING

    2. SOFTWARE SERVER NETWORK CLIENT MULTIMEDIA SYSTEM

    3. WE CONSIDER MULTIMEDIA SYSTEMS BUILT-UP ON LARGE SCALE: REACHING PRACTICALLY EVERYBODY, LIKE TV, RADIO AND TELEPHONE TODAY, THAT IS THOUSANDS AND MILIONS OF USERS • MULTIMEDIA MEANS BROADBAND STREAMING AND INTERACTIVITY

    4. MAIN PROBLEMS IN NETWORKING • NETWORKS FOR MULTIMEDIA REQUIRE: • SUFFICIENT/CONTROLLED BANDWIDTH • RESERVATION OF NETWORK RESOURCES (WE CAN NOT LOSE DATA) • STREAMING • FAST INTERACTIVITY DELIVERY CAN BE WIRED OR WIRELESS: WIRED - USES PHYSICAL LINKS WIRELESS – USES RADIO

    5. A MODEL OF INTERACTIVE SYSTEM IS INTERNET • A MODEL OF BROADBAND STREAMING ARE TV, RADIO • MULTIMEDIA SYSTEMS WOULD BE SOMETHING LIKE INTEGRATION OF THEM BOTH • SOMETHING LIKE BECAUSE WE CAN NOT PREDICT IN DETAIL WHAT IT MIGHTBE

    6. COMMUNICATION SERVICE TYPES • BROADCAST: SINGLE SOURCE, MANY USERS – LIKE TV, 1-WAY DISTRIBUTION - MULTICAST: LIKE BROADCAST BUT USERS SIGN TO A SESSION, ONE WAY CONNECTION • RETRIEVAL, UNICAST –ASYMMETRIC CONNECTION, USERS RECEIVE MUCH MORE THAN SEND, E.G. WWW

    7. COMMUNICATIVE SERVICE – SYMMETRIC 2-WAY CONNECTION LIKE TELEPHONE IN MULTIMEDIA SYSTEMS WE ARE MOSTLY INTERESTED IN THE RETRIEVAL AND COMMUNICATIVE SERVICES WITH HIGH BIT RATE

    8. STREAMING STREAMING MEANS DATA ARE SEND SYNCHRONOUSLY IN TIME AND WILL REACH USER PRESERVING THEIR TIME ORGANIZATION. NO DATA LOSS OR DELAYS ARE ALLOWED. EXAMPLE: TELEPHONE NETWORK IN MULTIMEDIA STREAMING IS ABSOLUTELY NECESSARY

    9. THIS IS VERY MUCH RELATED TO THE PROBLEM OF NETWORK RESOURCE MANAGEMENT AND CONTROL • THERE ARE TWO TYPES OF NETWORKS • CONNECTION-ORIENTED • CONNECTIONLESS • IN CONNECTION-ORIENTED NETWORK RESOURCES ARE ALLOCATED BEFORE

    10. THE DATA TRANSFER IS STARTED. IN CONNECTIONLESS NETWORK RESERVATION IS NOT DONE: DATA MAY BE TRANSFERRED WITHOUT ANY GUARANTEE OF RESOURCE ALLOCATION, OR WITH SOME GUARANTEE ONLY.

    11. HOW STREAMING CAN BE ENSURED IN NETWORKING? THERE ARE THREE BASIC TYPES OF NETWORKING • CIRCUIT SWITCHING - CONNECTION IS ’SWITCHED’ BEFORE SENDING DATA (”PHONE”) • PACKET SWITCHING – DATA ARE ORGANIZED IN PACKETS. EACH PACKET CARRIES ADDRESSES

    12. - CELL SWITCHING – BETWEEN CIRCUIT AND PACKET SWITCHING ”PACKETS ARE SWITCHED” (TECHNOLOGY CALLED ATM – ASYNCHRONOUS TRANSFER MODE) ALL THESE SYSTEMS HAVE VARIOUS POSIIVE AND NEGATIVE ASPECTS FOR MULTIMEDIA

    13. IN CIRCUIT SWITCHING NETWORK RESOURCES ARE FULLY RESERVED FOR STREAM TRANSMISSION IN PACKET SWITCHING PACKETS ARE FLOWING IN LITTLE CONTROLLED WAY MAKING STREAMING PROBLEMATIC IN CIRCUIT SWITCHING INTERACTIVITY IS SLOW (TIME FOR CONNECTION NEEDED) IN PACKET SWITCHING INTERACTIVITY IS FAST

    14. EXAMPLES: • TELEPHONE SYSTEM – SWITCHING (connection establishment) IS DONE IN EXCHANGES, SWITCHBOARDS OR SWITCHING CENTERS • INTERNET - PACKETS ARE DIRECTED IN ROUTERS WHICH READ THEIR ADDRESSES AND DIRECT THEM The difference is that only circuit switching fully guarantees streaming but it is expensive

    15. ADVANTAGES OF CIRCUIT SWITCHING: • GUARANTEED DATA DELIVERY • STREAMING AND TIMING OF DATA NO PROBLEM • DISADAVANTAGES: • CIRCUIT ESTABLISHMENT (”call”) TAKES TIME - EXPENSIVE INFRASTRUCTURE

    16. PACKET SWITCHING EXAMPLE: INTERNET DATA ARE ORGANIZED IN PACKETS PACKETS CARRY HEADERS WITH SOURCE AND DESTINATION ADDRESS PACKETS ARE ROUTED IN THE NETWORK BASING ON THE ADDRESSESS

    17. ADVANTAGES OF PACKET SWITCHING - SIMPLICITY, EVEN A PC CAN BE ROUTER • PACKETS CAN BE ROUTED IMMEDIATELY • PACKETS CAN BE SEND USING DIFFERENT ROUTES, OR STORED EASY ADAPTATION TO THE AMOUNT OF TRAFFIC - IDEAL FOR TIME NON-CRITICAL DATA

    18. DISADVANTAGES: • NO GUARANTEE FOR PACKET DELIVERY • NO GUARANTEE FOR RESOURCES NO GUARANTEE FOR PACKET DELIVER ON-TIME, NO STREAMING

    19. EXAMPLE – WWW. WE GET INSTANT RESPONSE FROM THE PS INTERNET IF THE INTERNET WOULD BE CS, WE WOULD NEED TO WAIT FOR CONNECTION ESTABLISHMENT. BUT THERE IS NO RESOURCE RESERVATION FOR STREAMS IN PS A SOLUTION FOR THIS PROBLEM COULD BE INTELLIGENT PACKET SWITCHING AND NETWORKING

    20. IN INTELLIGENT PS PACKETS HAVE PRIORITIES ASSIGNED, MULTIMEDIA PACKETS GET HIGH PRIORITY SO THEY WILL NOT BE DISTURBED BY OTHER PACKETS IF THE NETWORK WOULD HAVE ENOUGH CAPACITY, MULTIMEDIA PACKETS WILL FLOW IN STREAMS (if there is not enough capacity, no help)

    21. THUS PACKET SWITCHING CAN BE IN PRINCIPLE BETTER BECAUSE OF STREAMING AND FAST INTERACTIVITY • CURRENT NETWORKING IS THUS EVOLVING IN THIS DIRECTION (INTERNET IS BECOMING VERY POWERFUL)

    22. CELL SWITCHING OVERVIEW • THIS TECHNOLOGY IS REALIZED IN ONE PARTICULAR FORM CALLED • ATM – ASYNCHRONOUS TRANSFER • MODE IT IS A COMBINATION OF CIRCUIT SWITCHING AND PACKET SWITCHING PACKETS HAVE CONSTANT, VERY SHORT LENGTH – 48DATA+5HEADER=53BYTES/PACKET

    23. ATM ENABLES COMBINATION OF CIRCUIT AND PACKET SWITCHING • BASIC CONCEPTS ARE VIRTUAL CHANNEL AND VIRTUAL PATH H PAYL. H PAYL. H PAYL. H FLOW OF ATM CELLS H – HEADER 5 BYTES PAYLOAD 48 BYTES

    24. HEADERS ESTABLISH WHERE THE PACKETS ARE TRANSMITTED STRUCTURE OF ATM CELL HEADER: GFC VPI VCI PT CL HEC 4 8 16 3 1 8 bits GFC - GENERIC FLOW CONTROL VPI - VIRTUAL PATH IDENTIFIER VCI - VIRTUAL CIRCUIT IDENTIFIER PT - PAYLOAD TYPE CL - CALL LOSS PRIORITY HEC – HEADER ERROR CHECK

    25. FOR MULTIMEDIA DATA ONE VP COULD BE ALLOCATED AND SEVERAL VC FOR E.G. VC=1 VIDEO VP=5 VC=2 AUDIO VC=3 TEXT

    26. IN THE ATM NETWORK THERE ARE SWITCHES WHICH DIRECT PACKETS ACCORDING TO THEIR VP AND VC VP=6 VC=13 VP=4 VC=2 VP=1 VC=5 SWITCH 1 SWITCH 2 VP AND VC BETWEEN THE SWITCHES (THERE CAN BE MANY OF THEM HAS TO BE ASSIGNED TO ENABLE END-TO-END TRANSMISSION

    27. HOW THE ASSIGNMENT IS DONE? IT CAN BE DONE BY HAND OR IT CAN BE DONE AUTOMATICALLY USING SPECIAL SYSTEM FOR MAPPING END POINT NUMBERS TO VP AND VC OF INTERMEDIATE SWITCHES

    28. IN ATM THIS IS SOLVED IN A WAY WHICH IS SIMILAR TO TELEPHONE NETWORKS IT IS POSSIBLE TO ESTABLISH CONNECTION BETWEEN ANY END-POINTS BECAUSE THEY HAVE UNIQUE NUMBERS

    29. THE ATM CALLS CAN SPECIFY BANDWIDTH AND OTHER PARAMTERS THERE ARE SEVERAL CLASSES OF SERVICES AAL – ATM ADAPTATION LAYER AAL1- CONSTANT BITRATE WITH TIMING

    30. AAL2 – VARIABLE BIT RATE WITH TIMING • AAL3/4- VARIABLE BIT RATE WITH NO TIMING • AAL5 VARIABLE BIT RATE WITH NO TIMING, CONNECTIONLESS • FOR THESE AAL’S IT IS SPECIFIED HOW DIFFERENT PROTOCOLS ARE MAPPED ON THEM

    31. FOR EXAMPLE MPEG-2 TRANSPORT STREAM IS MAPPED INTO 2 X188 MPEG-2 PACKETS -> 8 ATM CELLS AAL2 IS IDEAL FOR MULTIMEDIA BUT IT IS DIFFICULT TO IMPLEMENT (TIMING) LARGE ATM NETWORKS ONLY RARELY ARE IMPLEMENTED

    32. BUT IN NEW THIRD GENERATION WIRELESS NETWORKS - WIRELESS LAN - WIRELESS CELLULAR ATM AND AAL2 (WIRELESS) IS SPECIFIED AND IMPLEMENTED THUS, THEY MAY OPERATE IN THE ATM MODE

    33. PACKET SWITCHING – IP INTERNET IN STANDARD PACKET SWITCHING THERE IS NO NETWORK RESOURCE RESERVATION BEFORE THE PACKETS ARE SEND. THE BASIC METHOD OF TRANSFERRING PACKETS ON THE INTERNET IS THE UDP – USER DATAGRAM PROTOCOL

    34. IPv4 Header Structure Ip version Tos Header_length Total length Identification Flags and fragmentation Protocol Header check sum TTL 32 bit Source Ip address 32 bit Destination address Options(if any) Data

    35. UDP/IP PACKETS ARE ROUTED ACCORDING TO THEIR ADRESSES, ONCE SENT, THEY ARE UNCONTROLLED THIS CAN BE VERY UNRELIABLE BUT ON RELIABLE AND HIGH BANDWIDTH LINKS IT CAN BE SUFFICIENT FOR MULTIMEDIA

    36. THE TCP/IP PROTOCOL IS USED TO PROVIDE INFORMATION THAT PACKETS REACHED THEIR DESTINATION, THERE IS CONFIRMATION SEND ABOUT THEIR RECEPTION • IF THERE IS NO CONFIRMATION, PACKETS ARE RESEND • TCP/IP IS GOOD FOR NON-TIME CRITICAL DATA (EMAIL)

    37. IP NETWORKING FOR MULTIMEDIA • FOR MULTIMEDIA DATA PACKET SWITCHING INTERNET CAN BE VERY BAD • ON THE OTHER HAND INTERNET IS CHEAP, AVAILABLE AND UBIQUITOUS

    38. FOR SOLVING PROBLEMS WITH MULTIMEDIA DATA OVER IP PACKET NETWORK, THERE ARE THREE APPROACHES: • INTRODUCING RESOURCE RESERVATION, PROTOCOL CALLED RSVP – RESOURCE RESERVATION PROTOCOL AIMS TO DO IT - INTRODUCE PACKET PRIORITY LABELLING (DONE IN ROUTERS)

    39. BOTH WOULD REQUIRE IMPLEMENTATION IN ROUTERS AND ARE COMPLICATED • THIRD APPROACH - SIMPLER • TRYING TO FOLLOW HOW PACKETS ARE FLOWING THROUGH THE NETWORK AND SEND INFORMATION TO THE SENDING SIDE

    40. REAL-TIME PROTOCOL RTP IN THIS PROTOCOL EACH PACKET GETS TIME STAMP AND NUMBER WHEN IT IS SEND. ON THE RECEIVING SIDE IT IS POSSIBLE TO DETECT IF PACKETS ARE LOST AND WHAT ARE THE PACKETS DELAYS. THECOMPLETE PACKET LOOKS LIKE THIS

    41. THERE IS A PROTOCOL CALLED RTCP – REAL TIME CONTROL PROTOCOL WHICH COLLECTS STATISTICAL INFORMATION ABOUT PACKET DELAYS AND LOSS AND SENDS IT TO THE SENDING SIDE WHICH MAY REACT IN SOME WAY

    42. THE RTP/RTCP COMBINATION IS SIMPLE AND REALISTIC FOR THE CURRENT INTERNET: • DOES NOT CHANGE ANYTHING IN THE SYSTEM • PROVIDES CONCISE REPORTING • SENDING SIDE MAY ESTIMATE QUALITY OF CONNECTION AND REACT E.G. BY REDUCING BITRATE

    43. RTP INTRODUCTION • provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio or video. • does not address resource reservation and does not guarantee quality-of-service for real-time services. • independent of the underlying transport and network layers. • RTP packet consists fixed RTP header, a possibly empty list of contributing sources and the payload data

    44. RTP header T V P X CC M PT SEQUENCE NUMBER TIMESTAMP SYNCHRONIZATION SOURCE IDENTIFIER (SSRS) CONTRIBUTING SOURCE IDENTIFIERS (CSRC) ...

    45. RTP header • Version (2 bits) identifies the version of RTP • Padding (1 bit) packet contains one or more additional padding octets • Extension (1 bit) the fixed header must be followed by one header extension • CSRC Count (4 bits) contains the number of CSRC identifiers that follow the fixed header. V P X CC

    46. RTP header • Marker (1 bit) the packet contains marker bits • Payload Type (7 bits) identifies the format of the RTP payload • Sequence number (16 bits) increments by one for each RTP data packet sent, and may be used by the receiver to detect packet loss and to restore packet sequence. M PT SEQUENCE NUMBER

    47. RTP header • Timestamp (32 bits) reflects the sampling instant of the first octet in the RTP data packet • SSRC (32 bits) field identifies the synchronization source. • CSRC list (0 to 15 items, 32 bits each) identifies contributing sources for the payload. The number of identifiers is given by the CC field. TIMESTAMP SYNCHRONIZATION SOURCE IDENTIFIER (SSRS) CONTRIBUTING SOURCE IDENTIFIERS (CSRC) ...

    48. RTP Applications • Designed for multiparticipant multimedia conferences • Storage of continuos data • Interactive distributed simulation • Control and measurement applications

    49. Implementation of RTP • Typically integrated into application processing • No direct coupling at the RTP level between different media • For example, audio and video are in different sessions • Enables the choice of receiving only audio signal • With UDP, RTP uses an even port number and the corresponding RTCP stream uses the next higher odd port number

    50. RTP/UDP/IP