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Internet Protocols for Multimedia. DS VT-00 Jerry Eriksson. Multimedia Networking. Animation, voice and video - not only text distance learning, distributed simulation, distribute work groups Multimedia networks may replace telephone, television, etc

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Internet protocols for multimedia

Internet Protocols for Multimedia

DS VT-00 Jerry Eriksson

Multimedia networking
Multimedia Networking

  • Animation, voice and video - not only text

  • distance learning, distributed simulation, distribute work groups

  • Multimedia networks may replace telephone, television, etc

  • Challenges - Build hardware and software infrastructure and applications to support multimedia


Real-time challenges

Real-time protocols





Traffic management architectures

IntServ, Diffserv, RSVP


H.323, SIP


Real time challenges
Real-time Challenges

  • High bandwidth

  • Audio and video must be played back at the rate they were sampled (voice may be even more difficult)

  • Multimedia data streams are bursty


  • Primary reason: Platform for most networking activities

  • Integrated data and multimedia service over a single network (investments)

  • Not suitable for real-time traffic

    • Offers only best-effort quality

Problems to solve

Provide enough bandwidth

Provide multicast to reduce traffic

Provide protocols that handle that that care of timing issues

Delay, Jitter

QoS- guarantee quality

Reserve resource on the internet

Transport protocols

Presentation of the multimedia data (WAP, Voice)

Charging and policing mechaninsm

Problems to solve

Qos definitions
QoS Definitions

  • Qos is a set of technologies that enables network administrators to manage the effects of congestion on application traffic by using network resources optimally

  • or, allocate different resourses for different data flows

Qos classes
QoS classes

  • Best-effort - No gurantees at all

  • Soft QoS - differentiated guarantess

  • Hard QoS - full guarantees

Rtp real time transport protocols
RTP- Real-time transport protocols

  • Ip-based protocol providing

    • time-reconstruction

    • loss detection

    • security

    • content identification

  • Designed primarily for multicast of real-time data (also unicast, simplex, duplex)

Rtp development
RTP - development

  • December 1992, Henning Schulzrinne, GMD Berlin, published RPT version 1

  • Proposed (version 2) as standard November,1995

  • Netscape and Microsoft uses RTP

How does rtp works
How does RTP works

  • Timestamping - most important information for real-time applications.

    • The sender timestamp according to the instant the first octet in the packet was sampled.

    • The receiver uses timestamp to reconstruct the original timing

    • Also used for synchronize different streams; audio an video in MPEG. ( Application level responsible for the actual synchronization)

How does rtp work
How does RTP work

  • Payload type identifier

    • specifies the payload format as well as encoding/compression schemes

    • The application then knows how to interpret the payload

  • Source identification

    • Audio conference

Where is rpt reside
Where is RPT reside

  • RPT is typically run on top of UDP

    • Uses UDP’s multiplexing and checksum functions

  • RPT is usually implemented within the application (Lost packets and congestion control have to be implemented in the application level

Rtcp real time control protocol
RTCP - Real Time Control Protocol

  • Designed to work together with RTP

  • In an RTP session the participants periodically send RTCP packet to give feedback on the quailty of the data.

  • Comparable to flow and congestion control of other transport protocols.

  • RTP produces sender and receivers reports; statistics and packet counts

Rtct packet types
RTCT packet types

  • Recevier reports: feedback of data delivery

    • Packet lost, jitter, timestamps

  • Sender report:

    • Intermedia synchronization, number of bytes sent, packet counters


Rtcp provides the following services
RTCP provides the following services

  • QoS monitoring and congestion control

    • Primary function: QoS feedback to the application

    • The sender can adjust its transmission

    • The receiver can determine if the congestion is local, regional, or global

    • Network managers can evaluate the network performance for multicast distribution

Rtcp provides the following services cont
RTCP provides the following services (Cont)

  • Source identification

  • inter-media synchronization

  • control information scaling

    • Limit control traffic (most 5 % of the overall session traffic)

Rtp rtcp features


end-to-end real-time data delivery (functionality and control mechanisms)

timestamps sequences numbering (up to the application to use it)

Uses UDP

Provides not

timely delivery (needs lower layer reservations)

any form of reliability or flow/congestion control (RTCP)

Not complete - new payload format

RTP/RTCP features

What is streaming
What is Streaming?

  • Streaming breaks data into packets; real-time data through the transmission, decompressing just like a water stream.

    • A client can play the first packet, decompress the second, while receiving the third.

    • The user can start enjoying the multimedia without waiting to the end of the transmission

Rtsp real time streaming protocol
RTSP - real time streaming protocol

  • Client-server multimedia presentation protocol to enable controlled delivery

    • provides ”vcr”-style remote control functionality of streamings over IP.

    • RTSP is an application-level protocol designed to work with RTP (and RSVP) to provide a complete streaming service over internet

    • It provides means for choosing channels (UDP etc) and delivery mechanisms (RTP)

  • Developed by RealNetworks, netscape, and columbia university (still an internet draft)

Rtsp operations and methods
RTSP operations and methods

  • RTSP establish and controls streams

  • A media server provides playback or recording services

  • A client requests continues media data from the media server

  • RTSP is the network is the ”network remote control” between the server and the client

Rtsp provides
RTSP provides

  • Retrieval of media from media server

  • Invitation of a media server to a conference

  • Adding media to an existing presentation

  • Similar services on streamed audio and video, just as HTTP does for text and graphics

Http rtsp differences
HTTP/RTSP differences

  • HTTP stateless protocol; an RTSP server has to maintain ”session states”

  • HTTP is asymmetric; in RTSP both client and server can issue requests

  • It uses URL, like HTTP

Resources reservation and prioriations
Resources reservation and prioriations

  • Any QoS better than best-effort.

    • Routing delays and congestion losses

  • Real-time traffic

Now ip qos networking integrated services
Now IP QoS Networking -Integrated services

  • Defined by an IETF working group to be a key-stone

  • IS was developed to optimize network and resource utilization which require QoS.

  • Divided traffic between into different QoS classes.

  • An internet router must be able to provide an appriopriate QoS for each flow. (according to a service model)

Router function traffic control
Router function: Traffic control

  • Packet scheduler manages forwarding of different packet streams.

    • Service class, queue management, algorithms

    • Police and shape traffic

    • must be implemented at the point where the packets are queued.

Router function traffic control1
Router function: Traffic control

  • Packet classifier indentifies packets of an IP flow in hosts and routers that will receive a certian level of service.

    • Each packet is mapped by the classifier into a specific class. (same class, same treatment)

    • The choice of class is based upon the source and destination, and port number in packet header

Admission control
Admission control

  • Decision algorithms that a router uses to determine if there are routing resources to accept the requested QoS for a flow

    • If the flow is accepted; the packet classifier and packet scheduler reservs the requested Qos for this flow.

  • Checks user authentification

  • Will play an important role for charging

Intserv cont
IntServ (cont)

  • Communicates with RSVP to create and maintain flow-specific states in the endpoint hosts and in routers along the path of a flow

  • RSVP/Intserv are complementary

  • Not suitable for high volume traffic (speech)

Differentiated services
Differentiated services

  • IETF working group (draft, no RFC)

  • Simplify scheduling and classification using the priority bits in the IP header.

  • Packet flow must be marked according to SLA; Servive Level Agreements at the edge of the network

  • The ISP must assures that a user gets his requsted QoS.

  • Improves scalability greatly.

Mechanisms needed
Mechanisms needed

  • Setting bits in DS at the network edges and administrative boundaries

  • Using those bits to determine how packets are treated by routers inside the network

  • DS architecture is currently asymmetric;

    • on-going research for symmetric architecture

Diffserv architecture
Diffserv architecture

  • Static and long-term

    • Not need to set up QoS reservation for specific data packets

    • DS routing example (it is not that easy)

  • Handle aggregate traffic (not per-conversation)

    • require significantly less sates and processing power than per-conversation.

Rsvp reservation protocol
RSVP - reservation protocol

  • Internet control protocol - not routing protocol

  • Runs on top of IP and UDP

  • Key concepts: flows and reservations

  • Applies for a specific flow of data packets on a specific path. Each flow has a flow descritpor.

  • Both unicast and multicast.

  • Doesn’t understand the content of the flow descriptor

Rsvp reservation protocol1
RSVP - reservation protocol

  • Simplex protocol; reservation is done in one direction;

  • Receiver-initiated. The sender sends QoS wanted to the receiver which sends an RSVP message back to the sender.

  • The sender does not need to know the capabilities along the path or at the receiver

Rsvp reservation protocol2
RSVP - reservation protocol

  • The RVSP daemon

    • checks admission and policy control. If either fails the RSVP returns error

    • sets parameters in the packet classifier and packet scheduler

    • communicates with the routing process to determine path

Reservation messages path and resv
Reservation messages PATH and RESV;

  • PATH messages are periodically from the sender to the receiver and contains a flow spec

    • data format, source address, source port

    • traffic characteristics

  • RECV is generated by the receiver and contains flow spec and filter spec

    • follows the exact reverse path setting up reservations for one or or more senders at each node

Intserv drawbacks
Intserv drawbacks

  • Only implemented for UNIX platforms

  • Must be implemented on each node from ’end’-end’ - not scalable

  • No secure policy mechanisms

  • Protecting multimedia - most traffic still are non-multimedia

  • Close to death, September 1997

Rsvp renaissance today
RSVP renaissance today

  • Availability of RSVP signaling on a large number of hosts (Windows 2000)

  • Use Diffserv as well.

  • Availability of policy components and products from many vendors.

  • Recent work on RSVP signalling handle non-multimedia much better

Top down provisioning
Top-down provisioning

  • Low overhead and aggregate traffic handling. Bilateral agreements

  • Difficulty learning the classification criteria that should be configured to specify specific traffic

  • Cannot offer high-quality guarantees required for multimedia applications, unless the network is overdimensioned

  • Top-down provisioning to coordinate traffic handling along a specific path

Youram bernet
Youram Bernet

The combination of RSVP signaling

with aggregate traffic handling mechanisms

is able to address the deficiencies of the

exclusively top-down provisioned approach

without incurring the scalability problems

of classical RSVP/intserv usage

Enhancing efficiency within diffserv network
Enhancing efficiency within diffserv Network

  • Diffserv provider may dedicate resources support SLA

  • Statistical multiplexing

  • Dynamic signalling at certain key points;

    • dynamic admission control

Yoram bernet
Yoram Bernet

When managing a network to offer QoS,

the manager is faced with certain trade-offs.

A given network and its QoS mechanisms can

offer a certain quality of guarantees at a certain

level of efficiency.

Quality efficiency

  • Trade-off; An on-going debate

    • Over-provision the network;Efficiency decreases

    • Lower the resourses;Decrease QoS.

  • It is impossible to aviod the overhead of more sophisticated QoS mechanisms unless on is willing to compromise in the trade-off just mentioned

Yoram bernet qos expert microsoft
Yoram Bernet, QoS expert Microsoft

Despite the astounding rate at which netork

capacity is increasing, we find ourselves

contending with congested networks today and

can expect ot do be doing so for the

foreseeable future

Why ip telephony voip
Why IP telephony (VoIP)

  • Regarded far too unreliable for mass market, but now reliability and quality have quickly improved

  • Advantages: Cheaper

    • No inter-connect charges; 6-8 kb/s (packet) vs 64kb/s

    • Regulation costs

  • New value-added features; conferencing

  • Single network

Internet telephony standards
Internet telephony standards

  • Still immature; latency major issue

  • ITU-T: H.323 (set of protocols)

  • SIP used to initate a session between users. Simple, cheap. Limited, but popular

H 323 standard architectures
H.323 Standard architectures

  • Protocol stack (fig. 9-4)

    • Audio, video over RTP/RTCP/UDP

    • Data over TCP

    • System Control over TCP

H 323 architecture
H.323 Architecture

  • Components

    • Gateway

    • Gatekeeper

    • MCU

  • Interwork with SS7

Signalling within h 323
Signalling within H.323

  • H.323 uses a logicla channel on the LAN

  • RAS (Registration, admission and status)

    • Gatekeeper Discovery

    • Endpoint registration

    • Call management

    • Admission procedures

    • and several more

Voipow over wireless wcdma
VoIPoW (over wireless (wcdma))

  • Rather important reserach in Ericsson

  • Challenge cube