Internet Protocols for Multimedia

DS VT-00 Jerry Eriksson

Multimedia Networking

Animation, voice and video - not only textdistance learning, distributed simulation,

distribute work groupsMultimedia networks may replace

telephone, television, etcChallenges - Build hardware and software

infrastructure and applications to support multimedia

Outline

Real-time challenges

Real-time protocols RTP, RTCP, RTSP

QoS Definitions Goals

Traffic management architectures IntServ, Diffserv,

RSVP

VoIP H.323, SIP

Real-time Challenges

High bandwidthAudio and video must be played

back at the rate they were sampled (voice may be even more difficult)

Multimedia data streams are bursty

Internet

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

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

Best-effort - No gurantees at allSoft QoS - differentiated guarantessHard QoS - full guarantees

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

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

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

Payload type identifier specifies the payload format as well as

encoding/compression schemes The application then knows how to

interpret the payloadSource identification

Audio conference

Where is RPT reside

RPT is typically run on top of UDP Uses UDP’s multiplexing and checksum

functionsRPT is usually implemented within

the application (Lost packets and congestion control have to be implemented in the application level

RTCP - Real Time Control Protocol

Designed to work together with RTPIn 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

Recevier reports: feedback of data delivery Packet lost, jitter, timestamps

Sender report: Intermedia synchronization, number of

bytes sent, packet countersSDES, BYE, APP

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)

Source identificationinter-media synchronizationcontrol information scaling

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

RTP/RTCP features

Provides 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

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

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 establish and controls streamsA media server provides playback or

recording servicesA client requests continues media

data from the media serverRTSP is the network is the ”network

remote control” between the server and the client

RTSP provides

Retrieval of media from media serverInvitation of a media server to a

conferenceAdding media to an existing

presentationSimilar services on streamed audio

and video, just as HTTP does for text and graphics

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

Any QoS better than best-effort. Routing delays and congestion losses

Real-time traffic

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

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 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

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 authentificationWill play an important role for charging

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 complementaryNot suitable for high volume traffic

(speech)

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

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

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

Internet control protocol - not routing protocolRuns on top of IP and UDPKey concepts: flows and reservationsApplies 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 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 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;

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

Only implemented for UNIX platformsMust be implemented on each node

from ’end’-end’ - not scalableNo secure policy mechanismsProtecting multimedia - most traffic

still are non-multimediaClose to death, September 1997

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

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

The combination of RSVP signalingwith aggregate traffic handling mechanismsis able to address the deficiencies of theexclusively top-down provisioned approachwithout incurring the scalability problemsof classical RSVP/intserv usage

Enhancing efficiency within diffserv Network

Diffserv provider may dedicate resources support SLA

Statistical multiplexingDynamic signalling at certain key

points; dynamic admission control

Yoram Bernet

When managing a network to offer QoS, the manager is faced with certain trade-offs. A given network and its QoS mechanisms canoffer a certain quality of guarantees at a certainlevel 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

Despite the astounding rate at which netorkcapacity is increasing, we find ourselvescontending with congested networks today andcan expect ot do be doing so for theforeseeable future

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; conferencingSingle network

Internet telephony standards

Still immature; latency major issueITU-T: H.323 (set of protocols)SIP used to initate a session between

users. Simple, cheap. Limited, but popular

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

Components Gateway Gatekeeper MCU

Interwork with SS7

Signalling within H.323

H.323 uses a logicla channel on the LANRAS (Registration, admission and status)

Gatekeeper Discovery Endpoint registration Call management Admission procedures and several more

VoIPoW (over wireless (wcdma))

Rather important reserach in Ericsson

Challenge cube