b.bharat shetty 4 th semester cs&e sjce defnition: multimedia is often described as a holy grail...
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DEFNITION: Multimedia is often described as a holy grail by some people.Literally the term multimedia is just two or more media.To be precise “Multimedia” generally means the combination of two or more continuous media i.e. media that has to be played during some well defined interval usually with some user defined interaction.
Before Proceeding concept of a protocol must be clear to you
Multimedia Networking Applications
Streaming stored audio and videoRTSP
Protocols for Real-Time Interactive Applications
RTP
RTCP
SIP.
RSVP
H.323 standard
Summary
MM Networking Applications
Fundamental characteristics:
• Typically delay sensitive.• End-to-end delay.• Delay jitter.
• But loss tolerant: infrequent losses cause minor glitches.
• Antithesis of data, which are loss intolerant but delay tolerant.
Classes of MM applications:
1) streaming stored audio and video
2) streaming live audio and video
3) real-time interactive audio and video
Jitter -the variability of packet delays within the same packet stream
Multimedia, Quality of Service: What is it?
Multimedia applications: network audio and video(“continuous media”)
level of performance needed for application to function.
QoS
Streaming Stored Multimedia
• Streaming: • media stored at source• transmitted to client• streaming: client playout begins before
all data has arrived• timing constraint for still-to-be
transmitted data: in time for playout
SSM: What Is It?
1. videorecorded
2. videosent
3. video received,played out at client
Cum
ula
tive
data
streaming: at this time, client playing out early part of video, while server still sending laterpart of video
networkdelay
time
Streaming Stored Multimedia: Interactivity
functionality similar to a VCR: client can pause, rewind, FF, push slider
bar• 10 sec initial delay causes no problem• 1-2 sec until command effect OK• RTSP often used
• timing constraint for still-to-be transmitted data: in time for playout
Streaming Live Multimedia
Examples:• Talk shows over the web.• Events brought live to home.Streaming.• Playback buffer.• Playback can lag tens of seconds after
transmission.• Still have timing constraint.Interactivity.• Fast forward impossible.• Rewind, pause possible!
Video servers
ATM or SONET Backbone network
LDN*
Local spooling server
switchCustomer’s
House
LDN-local distribution network
User Control of Streaming Media: RTSP
RTSP: • Client-server application layer protocol.
• User can control display: rewind, fast forward, pause, resume, repositioning, etc…
Disadvantages:
• Does not define how audio/video is encapsulated for streaming over network.
• No restrictions on how sm is transported. It can be transported over UDP or TCP.
• No specifications on how the media player buffers audio/video.
Real-time Protocol (RTP)
RTP specifies a packet structure for packets carrying audio and video data.RFC 1889.RTP packet provides.
Payload type identification.Packet sequence numbering.Timestamping.
RTP runs in the end systems.RTP packets are encapsulated in UDP segments.Interoperability: if two internet phone applications run RTP, then they may be able to work together.
RTP Runs on Top of UDP
RTP libraries provide a transport-layer interface that extend UDP:
• port numbers, IP addresses
• payload type identification
• packet sequence numbering
• time-stamping
RTP Header
Payload Type (7 bits): Indicates type of encoding currently being used. If sender changes encoding in middle of conference, sender informs the receiver through this payload type field.
•Payload type 0: PCM mu-law, 64 kbps•Payload type 3, GSM, 13 kbps•Payload type 7, LPC, 2.4 kbps•Payload type 26, Motion JPEG•Payload type 31. H.261•Payload type 33, MPEG2 video
Sequence Number (16 bits): Increments by one for each RTP packet sent, and may be used to detect packet loss and to restore packet sequence.
Real-time Control Protocol (RTCP)
Works in conjunction with RTP. Each participant in RTP session
periodically transmits RTCP control packets to all other participants.
Each RTCP packet contains sender and/or receiver reports.
Key things:-Number of packets sent.
-Number of packets lost. -Inter arrival jitter.
RTCP - Continued
- RTP session typically has a single multicast address; all RTP and RTCP packets belonging to the session use the multicast address.
- RTP and RTCP packets are distinguished from each other through the use of distinct port numbers.
- To limit traffic, each participant reduces his RTCP traffic as the number of conference participants increases.
RTCP Packets
Receiver report packets: Fraction of packets lost, last sequence number, average interarrival jitter.
Sender report packets: SSRC of the RTP stream,the current
time,the number of packets sent and the number of bytes sent.Source description packets:
E-mail address of sender,sender's name, SSRC of associated RTP stream.
Enable mapping between the SSRC and the user/host name.
SIP
• Session initiation protocol.• Comes from IETF.
• Usually a single module suitable for internetworking.
• People are identified by names or e-mail addresses, rather than by phone numbers.
• You can reach the callee, no matter where the callee roams, no matter what IP device the callee is currently using.
Calling a Known IP Address• Alice’s SIP invite message indicates her port number & IP address. Indicates encoding that Alice prefers to receive
• Bob’s 200 OK message indicates his port number, IP address & preferred encoding (GSM)
• SIP messages can be sent over TCP or UDP; here sent over RTP/UDP. •Default SIP port number is 5060.
time time
Bob'stermina l rings
A lice
167.180.112.24
Bob
193.64.210.89
port 38060
Law audio
G SMport 48753
Example of SI P message
INVITE sip:bob@domain.com SIP/2.0 Via: SIP/2.0/UDP 167.180.112.24 From: sip:alice@hereway.com To: sip:bob@domain.com Call-ID: a2e3a@pigeon.hereway.com Content-Type: application/sdp Content-Length: 885 c=IN IP4 167.180.112.24 m=audio 38060 RTP/AVP 0 Notes:
r HTTP message syntax
r sdp = session description protocol
r Call-I D is unique f or every call.
• Here we don’t know Bob’s I P address. I ntermediate SI P servers will be necessary.
• Alice sends and receives SI P messages using the SI P def ault port number 506. • Alice specifies in Via: header that SI P client sends and receives SI P messages over UDP More details
Definition of H.323 standard
H.323 is a standard that specifies the components, protocols and procedures that provide multimedia communication services—real-time audio, video, and data communications—over packet networks, including Internet protocol (IP)–based networks. H.323 is part of a family of ITU—T recommendations called H.32x that provides multimedia communication services over a variety of networks
-Emergence of voice-over–IP (VoIP) applications and IP telephony
-The absence of a standard for voice over IP meant products that were incompatible.
- Such requirements forced the need for a standard for IP telephony.
E.g.:Version 2 of H.323—packet-based multimedia communications systems
H.323 - lications
H.323 is applied in a variety of mechanisms
Audio only (I P telephony) Audio and video (video telephony) Audio and data and audio Video and data.
H.323 can also be applied to multipoint- multimedia communications. H.323 provides myriad services and, therefore, can be applied in a wide variety of areas— consumer, business, and entertainment application The features being added currently include fax- over- packet networks, gatekeeper- gatekeeper.
Data Link Protocol
IP
TCPUDP
H.225(RAS)H.225(RAS)
RTCPRTCP
Physical Layer Protocol
H.245(call control)Q.931
RTP
ControlSpeech
INTERNET
GATEWAY
TELEPHONENETWORK
The H.323 architectural Model for Internet Telephony
Terminal
Gatekeeper
ZONE
Allow two Party and multiparty calls
Support parameter negotiation
Support Encryption
Support Media transport on RTP/RTCP protocols
Feature sets are almost similar
Similarities b/w H.323 and SIPSimilarities b/w H.323 and SIP
H.323 SIP
ITU ITEF
Yes Largely
No Yes
Monolithic Modular
Full Protocol Stack Handles only setup
Binary ASCII
Yes No
Host or Telephone no URL
No Yes
Large and complex Moderate
1400 pages 250 pages
ITEM
Designed By
Compatibility with PSTN
Compatibility with net
Architecture
Completeness
Message Format
Multimedia conferences
Addressing
Instant Messaging
Implementation
Standards size
RSVP designed at
-MIT
-PARC
-California University.
RSVP Features:
RSVP is a novel signaling protocol in at least 4 ways:
1. It accommodates multicast, not just point-to-multipoint (one-to-many) reservations.
2. QoS routing can be deployed separately (in more operations, and so is
3. relatively low cost
4. Scalability.
RESERVATION IMPLEMENTATIONS
Reservations are implemented through two types of RSVP messages:
PATH and RESV.
The PATH messages are sent periodically from the sender to the multicast address. A PATH message contains flow spec to describe sender template (data format, source address, source port) and traffic characteristics.
RESV messages are generated by the receivers and contains reservation parameters including flow spec and filter spec.
Multimedia Networking: Summary
Video conferencing,distance learning.Distributed networking and sharing of data and info resources.Future holds so much promise.Virtual reality,digital animation,net telephony.Interactivity enabled in all sectors.Next generation internet: Intserv, RSVP, Diffserv.
Graphical Analysis Ahead
Multimedia market A graphical analysis
0 20 40 60 80 100 120 140 160
Market Value in Billions
Telecom
Computers
Publishing
Catalog
TV/Radio
Cable networks
Home video
Info servers
CDs/Tapes
Video
Arcades
Movies
Worldwide Statistics of multimedia market compiled by NASDAQ
Values in Billions
The real-time challenges
However, multimedia networking is not a trivial task. We can expect at least three difficulties.
1. When compared with traditional textual applications, multimedia applications usually require much higher bandwidth.
2. Most multimedia applications require the real-time traffic
3. In addition to the delay, network congestion also has more serious effects on real-time traffic
4. Multimedia data stream is usually bursty
Books:
1.Multimedia Handbook- Jessica Keyes-TMH
2.Computer networks – Andrew Tanenbaum
3.Multimedia systems- a perspective (IEEE)
Internet:
1.www.cis.ohio-state.edu/~jain/
2.www.google.com
3.University of colombia website.
4.IEEE papers on net
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