“ DESIGN OF A CALL/CONNECTION INTERFACE FOR REAL
TIME TRANSFER OF VOICE OVER INTERNET PROTOCOL
BETWEEN TWO H.323 TERMINALS ”
(PROJECT REPORT)
Submitted in Partial Fulfillment of the Requirements
For the Award of the Degree of
BACHELOR OF ENGINEERING
IN
COMPUTER SCIENCE & ENGINEERING
UNDERTAKEN AT
BIT MESRA, RANCHI
BY
NISHIT KUMAR (41/96)
B. SIDHARTH (43/96)
TUSHAR VRIND (44/96)
K. RAMATHREYA (61/96)
Project Co-ordinator & Guide
DR. P. K. MAHANTI
Head of the Department
Dept. Of Computer Science & Engineering
BIRLA INSTITUTE OF TECHNOLOGY
Mesra, Ranchi - 835215
Packet Based Multimedia Communication
Systems
H.323 & Voice Over IP
Outline
1. H.323 Components
2. H.323 Zone
3. Protocols specified by H.323
4. Terminal Characteristics
5. Gatekeeper Characteristics
6. H.225 RAS
7. H.225 Signaling and H.245 Control Signaling
8. Connection Procedures
1. H.323 Components
Terminals
Gateways
Gatekeepers
Multi-point Control Units (MCUs)
1.1. H.323 Terminals
Runs an H.323 Stack and multi-media applications.
Audio Communications a must (hence a key role in IP telephony),
Video/Data Communications is optional.
May be used in multi-point conferences.
Interworking with H.310 terminals on B-ISDN, H.320 terminals
on ISDN, H.321 terminals on B-ISDN, H.322 terminals on QoS
guaranteed LANs & H.324 terminals on SCN and Wireless
Networks
1.2. H.323 Gateways
Connects two dissimilar networks (H.323 and non-H.323)
Translates protocols for call setup and release.
Converts media formats between different networks
Transfers information between the networks connected by the
gateway.
 A gateway is not required for communication between two terminals on an
H.323 network
1.3. H.323 Gatekeepers
Brain of the H.323 Network.
Provide services like addressing, authorization and
authentication of terminals and gateways.
Bandwidth management, accounting, billing and charging.
May also provide call routing services.
 A gatekeeper is not ALWAYS required in an H.323 Network.
1.4. H.323 Multi-point Control Units
Support for conference of three or more H.323 Terminals.
Manages conference resources, negotiates between terminals
for audio/video codec selection and may handle media
streams.
2. H.323 Zone
Zone
T1
T2
GK
T3
GW
R
T4
R
T5
MCU
T1521220-96
Collection of all terminals (Tx), Gateways (GW), and Multipoint
Control Units (MCUs) managed by a single Gatekeeper (GK).
Includes at least one terminal, and may or may not include
Gateways or MCUs.
Has one and only one Gatekeeper.
May be independent of network topology and may be
comprised of multiple network segments which are connected
using routes (R) or other devices.
3. Protocols Specified by H.323
Audio Codecs.
Video Codecs
H.225 Registration Admission and Status (RAS)
H.225 Call Signaling
H.245 Control Signaling
Real Time Transport Protocol (RTP)
Real Time Transport Control Protocol (RTCP)
3.2. H.225 Registration Admission and Status
Protocol between endpoints (terminal & gateways) and
gatekeeper.
Performs registration, admission control, bandwidth changes,
status, and disengage procedures between endpoints and
gatekeepers.
A signaling RAS channel is opened between an endpoint and a
gatekeeper prior to the establishment of any other channels
3.3. H.225 Call Signaling
Used to establish a connection between two H.323 endpoints.
Achieved by exchanging H.225 protocol messages on the call
signaling channel.
The call signaling channel is opened between two H.323
endpoints or between an endpoint and a gatekeeper.
3.4. H.245 Control Signaling
Used to exchange end-to-end control messages governing the
operation of the H.323 endpoint.
Capabilities Exchange
Opening and Closing of logical channels used to carry media
streams.
Flow control messages
General Commands and Indication.
3.5. Real Time Transport Protocol
End-to-end delivery services of real time audio and video.
RTP is typically used to transfer data via UDP; RTP together
with UDP provides transport protocol functionality.
RTP provides Payload type identification
RTP provides Sequence Numbering
RTP provides Timestamping
RTP provides Delivery Monitoring
UDP provides multiplexing and checksum services.
 RTP can be used with other transport protocols as well.
3.6. Real Time Transport Control Protocol
Provides feedback on the quality of RTP data distribution.
Carries a transport-level identifier for an RTP source, called a
canonical name, which is used by receivers to synchronize
audio and video.
4. Terminal Characteristics
H.245 for exchanging terminal capabilities and creation of
media channels
H.225 for call signaling and call setup.
RAS for registration and other admission control with a
gatekeeper
RTP/RTCP for sequencing audio and video packets.
G.711 audio codec
 Optional components include video codecs, T.120 data-conferencing
protocols and MCU capabilities.
5. Gatekeeper Characteristics
Mandatory
Address Translation
Admission Control
Bandwidth Control
Zone Management
Optional
Call Control Signaling
Call Authorization
Call Management
6. H.225 RAS
Gatekeeper Discovery (GRQ)
Endpoint Registration
Endpoint Location
Admission Control
Access Tokens
7. H.225 Call Signaling and H.245 Control
Signaling
H.225 Call Signaling
Gatekeeper-Routed Call Signaling
Direct Call Signaling
H.245 Control Signaling
Capabilities Exchange
Logical Channel Signaling
8. Connection Procedures
8.1 H.323 Call Establishment
Endpoint 1
Gatekeeper 1
Endpoint 2
ARQ (1)
ACF/ARJ (2)
Setup (3)
Call proceeding (4)
ARQ (5)
ACF/ARJ (6)
Alerting (7)
Connect (8)
T1527160-97
RAS Messages
Call Signalling Messages
8.2 H.323 Control Signaling
8.3 H.323 Media Stream and Media Control Flows
8.3 H.323 Call Release