MULTIMEDIA SERVICES OVER IP NETWORKS

Coursework for IP Networks and Protocols
MULTIMEDIA SERVICES OVER IP
NETWORKS
Submitted by:
YatishBathla
Bruno Iniguez

INDEX OF MULTIMEDIA SERVICES IN IP NETWORKS
• Introduction to multimedia services in IP
network
• Problem statement
• Types of solutions
• SIP Protocol Basics
- Introduction
- Session Descriptions and SDP
- Message Format
- Session initiation
• SIP Based Application: IMS
2A. Introduction of IMS
- IMS Requirements
- Protocols used in the IMS
- IMS Architecture
2B. Session Control in the IMS
- Prerequisites Operation
- Session Setup
• H.323
3A. Introduction
• Network Architecture
• Network Elements
– Terminals
– MCU’s
• Gateways
– Gatekeepers
– Border Elements and Peer
Elements
• Protocols/Codecs
• 3B. Network Signaling
i. RAS Signaling
ii. H.225.0 Call Signaling
iii. H.245 Call Control
– Capability Negotiation
– Master/Slave
Determination
– Logical Channel Signaling
– Fast Connect

INTRODUCTION
• Today with the rise of multimedia and network technologies,
multimedia has become an indispensable feature on the Internet.
• Animation, voice and video clips become more and more popular on
the Internet. Multimedia networking products like Internet telephony,
Internet TV, video conferencing have appeared on the market.
• In the future, people would enjoy other multimedia products in
distance learning, distributed simulation, distributed work groups and
other areas.
• The Internet has experienced tremendous expansion in the past
several years. Demands for IP based multimedia services are emerging.
At the same time, cellular networks are evolving from circuit-switched,
voice-centric networks to third generation (3G) wireless networks that
support high-speed IP-based data, voice, and multimedia services.

PROBLEM?

• H. 323
• SIP
TYPE OF SOLUTION

Introduction of SIP Protocol
• SIP is based on HTTP and,
so, is a textual request-
response protocol.
• main goal of SIP is to deliver
a session description to a
user at their current
location
• Based on Offer/Answer
Model
• User register its complete
URI in Registrar server
• SIP makes mapping
between Public URI and
current URI

Session Description Protocol
• The most common format
for describing multimedia
sessions is the Session
Description Protocol (SDP).
a textual format to describe
multimedia sessions
• SDP description consists of
two parts: session-level
information and media-level
information

SIP Message Body
• SIP messages can carry any
type of body using MIME
(Multipurpose Internet Mail
Extensions) encoding
• Sender Terminal or / Server sends
SIP request called Request Line
Request line consist method
name, the Request-URI, the
protocol version and Header.
• Receiving Terminal or/ Server
reply SIP response called Status
Line
The status line contains the
protocol version ,the status of the
transaction and Header

SIP Message Body
• Right after the start line, SIP
messages contain a set of
header fields
• Six mandatory header fields
that appear in every SIP
message. They are
To, From, Cseq, Call-ID, Max-
Forwards, and Via

Session Initiation SIP
• Alice registers her current location
sip:alice@pda.com
• with the registrar at domain.com.
Alice sends a REGISTER request
indicating that requests addressed
to the URI in the To header field
sip:Alice.Smith@domain.com
• At a later time, Bob invites Alice to
an audio session. Bob sends an
INVITE request using Alice’s public
URI
• If, in the middle of the session,
they wanted to make any changes
to the session (e.g., add video), all
they would need to do would be to
issue another INVITE request with
an updated session description

SIP APPLICATION: IMS
• Third Generation (3G) networks aim to merge two of the most
successful paradigms in communications: cellular networks
and the Internet
• IMS to provide ubiquitous cellular access to all the services
that the Internet provides. Picture yourself accessing your
favorite web pages, reading your email, watching a movie, or
taking part in a videoconference wherever you are by simply
pulling a 3G hand-held device out of your pocket.
• IP Multimedia Subsystem is a Session Initiation Protocol
(SIP)-based IP Multimedia infrastructure that provides a
complete architecture and framework for real-time and non-
real-time IP multimedia services on the top of Packet
Switched (PS) core while still preserving the Circuit Switched
(CS) telephony services

IMS REQUIREMENT
• Support for establishing IP Multimedia Sessions.
• Support for a mechanism to negotiate Quality of Service
(QOS).
• Support for inter-working with the Internet and circuit-
switched networks.
• Support for roaming.
• Support for strong control imposed by the operator with
respect to the services delivered to the end-user.
• Support for rapid service creation without requiring
standardization.

PROTOCOL USED IN IMS
• Session Initiation Protocol (SIP):. SIP was chosen as the session
control protocol for the IMS. Since SIP is based on HTTP, SIP service
developers can use all the service frameworks developed for HTTP,
such as CGI (Common Gateway Interface) and Java servlets.
• Authentication, Authorization, and Accounting (AAA) protocol:
Diameter Protocol was chosen to be the AAA (Authentication,
Authorization, and Accounting) protocol in the IMS.
• Common Open Policy Service (COPS): used to transfer policies
between PDPs (Policy Decision Points) and PEPs (Policy Enforcement
Points)
• H.248: Its packages are used by signaling nodes to control nodes in
the media plane (e.g., a media gateway controller controlling a media
gateway).
• Real-Time Protocol (RTP) and Real-Time Control Protocol
(RTCP): transport media data such as video and audio.

IMS ARCHITECTURE

Session Initiation: Prerequisite Operation Of IMS
• IP CAN: fixed environments are DSL,
Dial-up Lines, enterprise LAN, etc. In
wireless environments we have
Packet Data Access networks such as
GPRS or WLAN
• P-CSCF Discovery:
P-CSCF discovery may take place in
different ways:
a) integrated into the procedure that
gives access to the IP-CAN;
b) as a stand-alone procedure

SESSION SETUP: IMS

H.323
• H.323* is a multimedia conferencing protocol, which includes voice, video,
and data conferencing, for use over packet networks
• Standard recommended by ITU-T
• Collection of Standards.
• H.323 belongs to the H.32x class of standards for videoconferencing
applications.
* H.323 is “ITU-T Recommendation H.323: Packet-based multimedia communications systems”
What is H.323?

H.323 Architecture
RR
Router
Gatekeeper
MCU
RR
RR
PSTN
Enterprise
Wireless
ISND
Gateway
Terminals
IP Network
• Terminals
• Gateways
• Multipoint Control Units
• Gatekeepers
• Border Elements
Endpoints

H.323: Terminals
• H.323 client endpoints
• They could be:
• Telephones
• Voicemail Systems
• “Soft phones” (e.g., NetMeeting®)
• Multimedia PCs
• Any stand-alone device
• Expectation by H.323:
• Must support audio communication.
• Video, data support optional

H.323: Gateways
ptional Component of H.323 implementation.
sed as interface between different networks e.g. LAN & PSTN
unctions:
• Data format translation
• Audio/video codec translation
• Call setup, termination from both sides of the network

H.323: Multipoint Control Unit (MCU)
ultipoint conferences (two or more endpoints engaged in a conference)
CUs are also optional in a H.323 implementation
eeded only when multiparty conferences are desired
unctions:
• Provides capability of video-conferencing with more than one party.
• Acts as a coordinator of multiparty conferences

H.323: Gatekeepers
Brains” of a H.323 network
xpectation by H.323:
• Address translation
• Admissions Control
• Bandwidth Control
• Zone Management
• Routing Capabilities
he Gatekeeper is an optional component in the H.323 system which is primarily used
for admission control and address resolution
he gatekeeper may allow calls to be placed directly between endpoints or it may
route the call signaling through itself to perform functions such as follow-me/find-me
and forward on busy

H.323: Border Elements and Peer Elements
• Peer Elements, which are often co-located with a Gatekeeper, exchange
addressing information and participate in call authorization within and
between administrative domains
• Peer Elements may aggregate address information to reduce the volume of
routing information passed through the network
• Border Elements are a special type of Peer Element that exists between two
administrative domains
• Border Elements may assist in call authorization/authentication directly
between two administrative domains or via a clearinghouse

Typical H.323 Protocol Stack
H.323
IP
UDP
RTP
RTCP
TCP/UDP TCP UDPUDP TCP
Audio
Codecs
G.711
G.723.1
G.729
..
Video
Codecs
H.261
H.263
H.264
..V.150 T.120
TCP/UDP
T.38
H.225.0
Call
Signaling
H.245
H.225.0
RAS
Terminal Control and Management
Data
Applications
Media Control
Multimedia Applications, User Interface

H.225.0 Call Signaling
Terminal
Setup
Call Proceeding
Connect
Release Complete
Terminal
Alerting
H.245 Session Establishment
H.245 Session Release
Media Exchange
Allows an endpoint to initiate and terminate a call with another endpoint

H.323 call establishment

Registration, Admission, and Status - RAS Signaling
• Defined in H.225.0
• Allows an endpoint to request authorization to place or accept a call
• Allows a Gatekeeper to control access to and from devices under its control
• Allows a Gatekeeper to communicate the address of other endpoints
• Allows two Gatekeepers to easily exchange addressing information
GatekeeperTerminal Gatekeeper
GRQ
GRJ
GCF
GK discovery
GRQ
GRQ

Endpoints use the RAS protocol in order to communicate with a gatekeeper. Likewise, gatekeepers use RAS
to communicate with peer gatekeepers. RAS is a fairly simple protocol composed of just a few messages
• Gatekeeper request, reject, and confirm messages (GRx)
• Registration request, reject, and confirm messages (RRx)
• Unregister request, reject, and confirm messages (URx)
• Admission request, reject, and confirm messages (ARx)
• Bandwidth request, reject, and confirm message (BRx)
• Disengage request, reject, and confirm (DRx)
• Location request, reject, and confirm messages (LRx)
• Resource availability indication and confirm (RAx)
• Admission confirm sequence (ACS)

GatekeeperTerminal
RRQ
RCF
URQ
UCF
／／／／

ARQ
ACF
Setup
ACF
／／／／／／
ARQ
DRQ
DCFDCF
DRQ
TerminalTerminal Gatekeeper

URQ
UCF

H.245 Call Control
• Provide more extensive control over the conference.
• H.245 provides capabilities such as capability
negotiation, master/slave determination, opening and closing of "logical channels"
(i.e., audio and video flows), flow control, and conference control.
Capability Negotiation
• Enables devices to communicate without having prior knowledge of the capabilities
of the remote entity.
Master/Slave Determination
• Once capabilities are exchanged, the endpoints negotiate master and slave roles.
• The master in a point to point conference really only has the power to indicate when
channels are in conflict (e.g., when one the other terminal tries to open a channel
that is not compatible)
• The slave device must yield to the requests of the master device and reconfigure
channels appropriately

H.245 Call Control
Logical Channel Signaling
•Once capabilities are exchanged and master/slave determination steps have completed,
devices may then open "logical channels" or media flows. This is done by simply sending
an Open Logical Channel (OLC) message and receiving an acknowledgement message.
Upon receipt of the acknowledgement message, an endpoint may then transmit audio or
video to the remote endpoint.
Fast Connect
•Fast Connect (also improperly referred to as “fast start”, after the name of the
associated field) is a means of establishing an H.323 call with as few as two
messages.With the use of Fast Connect, there is no need to open an H.245 channel, as
long as all needed media can be negotiated via Fast Connect

H.245 Call Control

Use Cases
H.323 and Voice over IP services
ITU-T Recommendation H.323 is one of the standards used in VoIP.
H.323 and Videoconference services
Supports advanced videoconferencing features, including:
•Cascading MCUs
•MCU control over audio and video mixing
•Far-end camera control

MULTIMEDIA SERVICES OVER IP NETWORKS

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