Standards%20for%20Multimedia%20Communications

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• Standards for Multimedia Communications

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Introduction

• Most Multimedia Applications involve a number of
  media types that are together in some way
• Standards are necessary because it is essential
  that the two or more items of equipment that are
  used for the application interpret the integrated
  information stream in the same way
• Reference model is a common framework used for
  defining the various standards used in multimedia
  communications

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Reference Models

• Standards are required at both the application
  level and the networking level

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• The functionality of each set of standards is as
  follows application standards, network interface
  standards and internal network standards
• The internal network standards are concerned
  solely with networking issues and are said to be
  within the networking environment
• The network interface standards operate over the
  access circuit to the network and are said to
  have local significance
• Application standards are independent of the
  network and define the communications between two
  terminals/computer. These communications are said
  to have end-to-end significance

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• Each standard has a set of procedures associated
  with them to perform a particular function
• A procedure set will have information such as
• - content and structure of the source
  information stream associated with an application
• - how the information stream is formatted
• - the way of transmission error detection
• - the procedure to obtain another copy of
  the corrupted block
• Both the communicating parties must adhere to
  the same set of procedures and collectively these
  form the communications protocol relating to that
  function

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Reference Models Standards for entertainment
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TCP/IP Reference Model

• Application of the general structure of the
  modified model in relation to the various
  standards identified

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Standards relating to interpersonal
communications

• Most of the standards relating to the
  interpersonal communications are defined by the
  ITU-T and there are separate standards for the
  circuit and packet switched networks
• A typical session may start with a telephone
  conversation and during this conversion they may
  want to bring a third person who is not known to
  one of the communicating parties. Hence they may
  convert to a videoconferencing call.
• This shows that the initial conversation started
  with a speech only then speech with data, then
  speech with video and finally speech, video, and
  user data
• With ISDN each media type is allocated a fixed
  portion of the channel bandwidth, but with
  packet-switched network the appropriate amount of
  bandwidth is allocated on-demand as the session
  progresses

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Standards Relating to Interpersonal Communications
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Circuit-mode networks

• The network interface standards relate primarily
  to the physical connection to the network
  termination and with the procedure to set up and
  clear a connection
• The basic transport layer function is provided
  by the multiplexer/demultiplexer
• The multiplexer merges the source information
  from the audio, video and user data and the
  system control application into a single stream
  for transmission over the constant bit rate
  channel
• The system control application is concerned
  with negotiating and agreeing on the operational
  parameters to be used with the call/session,
  based on the capabilities of the end system
  involved.
• e.g with the PSTN, the system control function
  includes the management of the available
  transmission bandwidth during a call

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Circuit-mode networks

• The audio and video codecs each use a particular
  compression algorithm which is appropriate for
  the application and within the bandwidth limits
  provided by the network
• The codecs also achieve audio and video
  synchronization (e.g. lip-sync)
• If the user data is to be shared between the
  various members of a conference, the application
  uses the service provided by a protocol known as
  a multimedia communications service (MCS)

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H.320

• The H.320 standard is intended for use in end
  systems that support a range of multimedia
  applications over an ISDN
• Audio The choice of audio/speech is determined
  primarily by the amount of transmission bandwidth
  available
• Video A constant output bit rate from the
  encoder is obtained by varying the quantization
  threshold that is used dynamically
• User Data The same standard is used with all the
  different types of circuit-mode network
• System control/call setup Concerned primarily
  with the negotiation of the bandwidth/bit rate to
  be used for each stream
• Multiplexing The fixed portions of the
  available bandwidth are allocated using a
  technique known as time division multiplexing
  (TDM). The role of H.221 is to ensure that each
  input stream is placed into its allocated
  position in the output bitstream

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H.324

• The H.324 standard is intended for use in end
  systems that support a range of interpersonal
  communication applications over low bit rate
  switched networks such as PSTN
• Video The H.263 standard uses the same
  compression technique as H.261 but contains a
  number of more advanced coding features in order
  to operate over lower bit rate channels
• Audio The G.723.1 standard is the most common
  and operates at a bit rate of either 5.3 or 6.3
  kbps
• Adaptive Additional bytes are added by the
  transmitter to enable the receiver to detect the
  presence of errors
• System control Concerned with the overall
  control of the end system and this involves many
  functions

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H.324 - Multiplexing

• The channel bandwidth is divided into a number of
  separate logical channels each of which is
  identified by means of a logical channel number
  (LCN)
• The LCN0 is used to carry the control stream and
  each of the remaining channels carries a separate
  media stream
• The allocation of LCN is controlled by the
  transmitter and when it wishes to open a new
  channel, it sends an H.245 control message which
  includes the media type and the type of codec
  used

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Circuit-mode networks H.223 Multiplex Principles

• The role of the multiplexer is to merge the
  stream that are currently present into the
  available bandwidth by using what is known as
  bit-oriented protocol

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H.324 - Multiplexing

• The transmitted bitstream is treated as a string
  of bytes and this is divided into a number of
  separate information fields
• Each field comprises a variable number of bytes
  and is separated by one or more flag bytes
• These have a bit pattern 01111110 and a technique
  known as zero bit insertion and deletion is used
  to ensure that this pattern cannot be present at
  the information field
• At the start of the information field is a
  header field which includes a multiplex code
  which specifies a particular mix of media and
  control logic channels
• The multiplex code is 4 bits in length and forms
  the index to a table known as the multiplex table

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Circuit-mode networks H.223 Multiplex
Principles Multiplex table usage

• At the start of each information field is the
  header (byte) and the combined header plus
  information field is known as a multiplex
  protocol data unit

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H.321/H.310

• Intended for use with terminals that provide a
  range of multimedia applications over a B-ISDN (
  known as ATM network)
• The H.321 standard is an adaptation of the H.320
  standard simplifying the interworking across both
  types of network and the only difference is that
  the network interface layers associated with
  H.321 relate to interfacing the end system to a
  B-ISDN rather than an ISDN
• The H.310 standard is intended for use with end
  systems that support not only interpersonal
  applications but also interactive and
  entertainment applications, it includes the H.321
  set and additional standards (MPEG-1 audio and
  MPEG 2 video) plus their associated multiplex
  standard H.222
• The H.322 standard is intended for use with end
  systems that supports interpersonal communication
  applications over a LAN that provides
  communication channels of a guaranteed
  bandwidth/QoS

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Packet-switched networks

• Two alternative sets of protocols have been
  defined for providing interpersonal communication
  services over packet-switched networks, one
  defined by the ITU in recommendation H.323 and
  the other by the IETF
• The H.323 standard pertaining to
  packet-switched networks relates primarily to how
  interpersonal communications are achieved between
  end systems that are attached either to the same
  LAN or to different LANs that are interconnected
  together in some way
• Unlike the H.322, the H.323 standard is intended
  for use with LANs that provide a non-guaranteed
  QoS
• The H.323 standard comprises components for the
  packetization and synchronization of the audio
  and video streams, an admission control procedure
  for end systems to join a conference, multipoint
  conference control, and interworking with
  terminals that are connected to the different
  types of circuit-switched networks

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Packet-switched networks

• The H.323 standard is independent of the
  underlying transport and network interface
  protocols and hence can be used with any type of
  LAN
• Normally the transport layer provides both the
  reliable and unreliable service which in practice
  is the case for most LANs
• With the end system connected to a LAN and
  communicating over an intranet or the Internet,
  the network layer protocol is the IP, the
  unreliable transport service is provided by the
  user datagram protocol (UDP) and the reliable
  transport service by the TCP

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Packet-switched networks
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H.323

• Audio and video coding Allows a variety of
  coding options to be used in order to simplify
  interworking with terminals/computers attached to
  the different types of circuit-mode networks
• prior to a call commencing an agreed coding
  standard must be negotiated to avoid the
  necessity of transcoding the audio and video
  streams
• The output streams of both the audio and video
  codecs are formatted into packets for transfer
  over the network using the real-time transport
  protocol (RTP)

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H.323

• Call setup In order to limit the number of
  concurrent calls that involve multimedia, a
  device called an H.323 gatekeeper can
  (optionally) be used
• During the setting up of a multimedia
  conferencing call, each end system involved in
  the conference must obtain permission from the
  gatekeeper
• Then depending on the current level of usage of
  the LAN, the gatekeeper decides whether the call
  can take place
• If an increase in the allocated bandwidth is
  required during a call, again prior permission
  must be obtained from the gatekeeper

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Packet-switched networks Two-party call setup
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H.323 gatekeeper

• Setting up of the call is carried out in two
  stages
• First the end system initiating the call obtains
  a permission from the gatekeeper to set up a call
  by sending an access request (ARQ) message to the
  gatekeeper and the gatekeeper responding with
  either an access confirm or reject
• Assuming permission is received for a two-party
  call the initiating terminal then sends a setup
  request message directly to the called end system
• The called system sends a call proceeding
  message directly to the initiating end system and
  then proceeds to obtain permission from the
  gatekeeper to take part in the call by means of
  the exchange of ARQ and ACF
• Assuming permission is granted the called end
  system sends an alerting message directly to the
  initiating end system
• Finally a connect message is sent directly to
  the initiating system
• Above are part of the Resource Access Service
  (RAS) protocol

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Packet-switched networks Interworking
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H.323 gateway

• In addition to the operation of the end systems,
  the H.323 standard also defines interworking with
  end systems that are attached to a circuit-mode
  network
• This is through a device known as an H.323
  gateway
• The role of the gateway is to provide
  translations between the different procedures
  associated with each network type
• Translators are necessary for call-set up and
  clearing, system control, and for the two
  different multiplexing
• If the two communicating end systems are using
  different audio and video codec standards, then
  transcoding between two different coding
  techniques must be carried out
• A second function associated with a gateway
  relates to address translation (e.g LAN the end
  systems are referred to by an IP address while
  PSTN or an ISDN the address is a conventional
  telephone number

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Internet Engineering Task Force (IETF)

• The IETF standard provides a versatile facility
  supporting both multiparty conferencing and
  broadcast services
• It uses a different signalling protocol set from
  that used with H.323 session initiation protocol
  (SIP) and the related session description
  protocol (SDP), these replace the RAS and system
  control protocols. The SIP provides services for
  user location, call establishment, and call
  participation management
• Examples of SIP request messages (commands or
  methods)
• - Options sent to solicit the capabilities
  supported by a host
• - Invite sent to invite the user of a host
  to join in a call/session
• - Bye sent when the user of a host intends
  to leave a call/session
• Users are identified by a symbolic name similar
  to an email address which is converted into an
  actual IP address and port number by a server
  call the domain name server (DNS)

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Electronic mail

• The two basic components associated with a
  text-based email system that uses the Internet
  are the email client and the email server
• Email client is normally a desktop PC which runs
  a program known as the user agent (UA)
• This provides the user interface to the email
  system to create, send and delete messages from
  the users mailbox
• The email server is a server computer that
  maintains an IN and OUT mailbox for all the
  users/clients that are registered with it
• The server has software to transfer mail
  messages over the Internet. This software is
  known as the message transfer agent (MTA). This
  is responsible for the sending and receiving of
  messages over the Internet

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Electronic mail

• A copy of the user agent software runs in each
  client (UA client) and this communicates with a
  similar piece of software in the email server
  (the UA server) in order to log in to the server
  and to deposit and retrieve mail into/from the
  mailbox of the client
• The set of mail boxes in the server are
  contained in a database known as the message
  store (MS)
• The UA client periodically retrieves any
  received mail from the message store and transfer
  this to its own local mailbox ready for reading
  by the user
• An example protocol associated with the user
  agent function is the post office protocol,
  version 3, (POP3) which is defined in RFC 1939

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Electronic mail

• The standard structure of text-based mail
  associated with the Internet is defined in RFC
  822
• An email message comprises a header and a
  message body. The structure of the header is
  defined in RFC 821
• The application protocol associated with the
  transfer of messages between the MTA in two
  servers is the simple mail transfer protocol
  (SMTP) defined in RFC 821
• A email message is transferred by the MTA in the
  sending server by it first establishing a TCP
  connection to the MTA in the recipient server
• As the email addresses are in the form of
  symbolic names the sending MTA requests another
  application protocol known as the domain name
  server (DNS) for the related Internet address of
  the recipient server

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Electronic mail

• This then uses this together with its own
  Internet address to create an Internet packet
  known as a datagram
• The routing of packets over the Internet is
  carried out by the IP and hence the Internet
  address is known as the IP address
• Each Internet packet contains the IP address of
  both the sending and recipient servers at its
  head and the email message as its contents
• The IP address of the recipient is used to route
  the packet over the Internet and, on receipt, the
  MTA in the server deposits the message contained
  in the packet into the recipients mailbox

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Electronic mail

• An email client is a desktop which runs a
  program known as the user agent (UA) that
  provides the user interface to the email system
  and related services

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Electronic mail
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Email gateways

• The email gateway is used in general to overcome
  two problems within company/enterprise networks
  the format of the mail messages and the
  application protocols are often different when
  trying to use other networks
• The email gateway has a number of interfaces, one
  for connecting to the local email server at the
  site and the others for connecting to those
  networks with which the employees at the site
  wish to communicate
• To transfer a message first the email server
  transfers it to the email gateway using the
  protocol stack associated with the company
  network
• The email address in the header of the message
  is then read by an application-level program to
  determine the network over which the mail should
  be forwarded

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Email gateways

• Assuming the external network is the Internet,
  the program proceeds to reformat the message into
  the RFC 822 format and then forwards this using
  the TCP/IP protocol stack
• A similar procedure is followed at the reverse
  direction except the message format has to be
  changed from RFC 822 to the format used by the
  company network
• Using SMTP/TCP/IP protocols the email gateways
  can be removed

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Electronic Commerce

• When you want to purchase something over the web
  you send your credit card details to a server
• This is an example of e-commerce
• When you send your card details using a mobile
  handset then this is called the m-commerce
• The normal standard used to pass information from
  the client to the server is via forms
• The standard for use at the server for processing
  the received information is known as the common
  gateway interface (CGI)

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Electronic Commerce
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Integrated Management Architecture for IP-based
Networks

• There are five functional areas related to the
  integrated management architecture
• - Performance management
• - Fault management
• - Configuration management
• - Security management
• - accounting and billing management

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Performance management

• This the the process of converting IP traffic
  measurements into meaningful performance measures
• It can be divided into real-time and long-term
  management
• The real-time performance management process is a
  mechanism to guarantee that enough bandwidth is
  reserved for time-sensitive IP voice traffic,
  while other applications sharing the same link
  get their share without interfacing with the
  mission traffic
• Another example is constant monitoring of
  high-priority customer services as well as
  customers who have been complaining about the
  performance of their services
• Long-term performance management supports studies
  that monitor the ability of the existing IP
  networks to meet service objectives

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Performance management

• The purpose of the performance management is to
  identify situations where corrective planning is
  necessary
• This is needed when objectives are not being
  satisfied and, where possible, to provide early
  warning of potential service degradation so that
  a corrective plan can be formulated before
  service is affected

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• Examples of IP performance traffic measurements
  include the following
• - Number of packets received per interface
• - Number of packets transmitted per
  interface
• - Number of packets dropped due to mild and
  severe congestion per interface
• - Number of packets dropped due to protocol
  errors
• - Amount of time a network element is in a
  mild or a severe congestion state
• - Number of times a network element enters
  a mild or severe congestion state

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Fault Management

• This process is similar to the real-tie
  performance process except that it uses the
  collected alarms and fault statistics to detect
  and correct problems by pointing and correlating
  faults through the system
• It simplifies the service providers ability to
  monitor customer services by providing the status
  of the subscribed services
• It is very challenging to represent the action
  that the network should consider in order to
  relieve a potential servicing problem before the
  service is affected
• This may include rerouting, load balancing, and
  congestion control

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Configuration Management

• It delas with the physical and geographical
  interconnections of various IP network elements,
  such as routers, switches, multiplexers and lines
• It includes the procedure for initializing,
  operating, setting and modifying the set of
  parameters that control the day-to-day operation
  of the networks
• Configuration management also delas with service
  provisioning, user profile management and
  collection of operational data, which is the
  basis for recognizing changes in the state of the
  network
• The main functions are creation, deletion and
  modification of network elements and network
  resources
• This includes the action of setting up an IP
  network or extending an already existing network,
  setting various parameters, defining threshold
  values, allocating names to managed IP objects

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Security Management

• This process includes authentication,
  authorization and other essential secure
  communication issues
• Authentication establishes the identity of both
  the sender and the receiver of information
• Integrity checking of confidential information is
  often done if the identity of the sending or
  receiving party is not properly established
• Authorization establishes what a user is allowed
  to do after the user is identified
• Issues related to authentication and
  authorization include the robustness of the
  methods used in verifying an entitys identity,
  the establishment of trusted domains to define
  authorization boundaries and the requirement of
  namespace uniqueness

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Accounting and Billing management

• This process deals with the generation and
  processing functions of end-user usage
  information
• This includes measuring the subscribers and
  possibly the network resources for auditing
  purposes and managing call detail information
  generated during the associated call processing
• The records created in the application servers
  are of growing importance in IP networks. They
  contain the contents and the services delivered
  by the network
• These usage details can then be transferred to a
  billing system to render invoices to the
  subscribers that use IP services
• Fraud detection and subscriber-related profile
  information, such as authorization to charge, are
  also a function of accounting and billing
  management