Transcript Multimedia on Internet

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
Real-time protocols
RTP, RTCP, RTSP
QoS
Definitions
Goals
Traffic management
architectures
IntServ, Diffserv, RSVP
VoIP
H.323, SIP
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
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 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 realtime 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
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; realtime 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 keystone
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 perconversation)
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