H.323 Protocol

Introduction to H.323

H.323 is an ITU-T recommendation that defines protocols for multimedia communication over packet-based networks. It was one of the first VoIP protocols and remains important in video conferencing.

H.323 Architecture

Components

Terminals

End-user devices supporting real-time communications.

Gateways

Interface between H.323 and other networks (PSTN, SIP).

Gatekeepers

Optional components providing: - Address translation - Admission control - Bandwidth management - Zone management

MCU (Multipoint Control Unit)

Enables conferences between three or more endpoints.

Protocol Stack

Signaling Protocols

• H.225.0 - Call signaling and RAS (Registration, Admission, Status)
• H.245 - Control protocol for multimedia communication

Media Protocols

• RTP/RTCP - Real-time media transport
• T.120 - Data conferencing

Call Flow

Basic Call Setup

1. RAS Exchange - Registration with gatekeeper
2. H.225 Setup - Call establishment
3. H.245 Negotiation - Capability exchange
4. Media Flow - RTP streams
5. Call Termination - Release procedures

H.323 vs SIP

H.323 Advantages

• Mature and stable
• Strong video conferencing support
• Comprehensive feature set
• Good interoperability

SIP Advantages

• Simpler protocol
• Text-based messages
• Web integration
• Faster development

Common H.323 Systems

• Cisco TelePresence
• Polycom RealPresence
• Avaya Communication Manager
• GNU Gatekeeper

Security Features

• H.235 security framework
• Authentication
• Encryption
• Integrity checking