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Multimedia on Internet

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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
Challenges - Build hardware and software
 infrastructure and applications to support
 multimedia
Outline
Real-time challenges   Traffic management
Real-time protocols     architectures
  RTP, RTCP, RTSP        IntServ, Diffserv,
                           RSVP
QoS
  Definitions
                        VoIP
                          H.323, SIP
  Goals
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
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           QoS- guarantee
 bandwidth                 quality
Provide multicast to       Reserve resource on
 reduce traffic              the internet
                            Transport protocols
Provide protocols that
 handle that that care    Presentation of the
 of timing issues          multimedia data
  Delay, Jitter           (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 all
Soft QoS - differentiated guarantess
Hard 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 payload
Source identification
  Audio conference
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
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
Recevier reports: feedback of data
 delivery
  Packet lost, jitter, timestamps
Sender report:
  Intermedia synchronization, number of bytes
   sent, packet counters
SDES, 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 identification
inter-media synchronization
control information scaling
  Limit control traffic (most 5 % of the overall
   session traffic)
RTP/RTCP features
Provides                   Provides not
  end-to-end real-time       timely delivery (needs
   data delivery               lower layer
   (functionality and          reservations)
   control mechanisms)        any form of reliability
  timestamps sequences        or flow/congestion
   numbering (up to the        control (RTCP)
   application to use it)   Not complete - new
Uses UDP                    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 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
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 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 authentification
Will 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 complementary
Not 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 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 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 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
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 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
Diffserv provider may dedicate resources
 support SLA
Statistical multiplexing
Dynamic 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 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

 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)
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
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
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 LAN
RAS (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

				
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posted:6/26/2012
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