h.323_notes

Signaling Protocol: H.323

Introduction to H.323 Protocol

H.323 is a ITU-T standard protocol.

Based on ISDN protocol (used in TDM network).

Vendor-neutral protocol.

H.323 is a peer-to-peer protocol.

Supports audio, video, and data.

Benefits of H.323 Protocol

Self contained Dial Plan.

Dial Plan should be configured both on Gateway (dial-peers) and CUCM (route patterns)

No additional dial plan requirement for SRST.

No dependency on CUCM.

No dependency on the software version of CUCM

Digit Manipulation can be explicitly configured on gateway.

ISDN Nonfacility Associated Signaling (NFAS) is supported.

One signaling channel for more than one TDM circuits.

Fax support is advanced.

Enhanced call preservation.

Preserve the call even if the communication to the CUCM is lost.

PSTN

H.323 Components

H.323 Terminal: End point that support real-time audio and even video (some supports data as well).

Gateway: Allows H.323 devices to communicate with other devices running different signaling protocol (s).

H.323 Gatekeeper: An optional H.323 Component which control other H.323 components.

performs address translation, admission control, etc..

H.323 Multipoint Control Units (MCUs): Used as Conference bridge which controls and mixes audio, video

and data in a rich multimedia conference session..

H.323 Gateways

H.323 gateways perform these services:

Translation between audio, video, and data formats

Conversion between call setup signals and procedures

Conversion between communication control signals and procedures

PSTNH.323

TDM Digital

An

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H.323 Call Setup

H.323 has two sub protocols: H.225 and H.245

H.225: Responsible for call setup procedure.

H.245: Responsible for capabilities negotiation (audio and video codec negotiation) and

open logical channel between endpoints for RTP flow.

H.323 supports two types of call setup: Slow Start and Fast Start

Slow Start: H.245 messages are sent after the call setup (H.225) messages are sent.

Fast Start: H.245 messages are sent along the setup messages

H.323 Call Setup: Slow Start

Calling PartyCalled Party

H.225 (TCP)

H.245 (TCP)

Media (UDP)

Q.931-Derived

Call Setup

Capabilities

Negotiation

Call Proceeding

Alerting

Capabilities Exchange

RTP Stream

RTP Stream

RTCP Stream

Call Setup

Connect

Master/Slave Determination

Open Logical Channels

Initiate Call

Ring Called Party

Answer CallRing Back Tone

21

3

5

8

9

7

4

6

12

10

11

Media RTP

H.323 Call Teardown: Slow Start


H.225 (TCP)

H.245 (TCP)

Close Logical Channel

Release Complete

RTP Stream

RTP Stream

RTCP Stream

End Session Command

Hang Up

2

3

4

6

1

Close Logical Channel ACK

End Session Command ACK 5

H.323 Call Setup: Fast Start (Fast Connect)


Call Proceeding

Alerting

RTP Stream

RTP Stream

RTCP Stream

Call Setup

Connect

Initiate Call

Ring Called Party

Answer Call

Ring Back Tone

21

3

5

87

46

9

H.225 Call Setup message carries multiple H.245

TCS/OLC combinations, based on the number of codecs.

H.225 Call Proceeding message carries confirmation for

one TCS variant and OLC information.

Configuring H.323 Gateways

Enable VoIP Services

H.323 is enable by default

Configure VoIP Dial Peers

Dial peers default to H.323 protocol

Configure Codecs

Tune H.323 Timers

H.225 settings

Router(config)# voice service voip

Router(conf-voi-serv)# h323

Router(conf-voi-serv)# no shutdown

Enables H.323. Enabled by default

Configuring H.323 Gateways (Configuring Dial Peers)

Router(config)#dial-peer voice 1 voip

Router(config-dialpeer)#destination-pattern 1

Router(config-dialpeer)#session target ipv4:172.16.10.245

Router(config-dialpeer)#preference 0

Router(config-dialpeer)#exit


Router(config-dialpeer)#destination-pattern 1

Router(config-dialpeer)#session target ipv4:172.16.10.246

Router(config-dialpeer)#preference 1

172.16.10.246

172.16.10.245

2001

1XXX

Configuring H.323 Gateways (Transport Protocol /Source IP/Time Outs)

Router(config)#voice service voip

Router(config-voi-serv)#h323

Router(config-serv-h323)#session transport udp

Default transport protocol for H.323 is TCP.

Use these commands to set the transport protocol to

UDP.

Router(config)#interface loopback 1

Router(config-if)#ip address 1.1.1.1 255.255.255.255

Router(config-if)# h323-gateway voip bind srcaddr 1.1.1.1

By default the ip address of the exit interface

will Be the source IP address of H.323

messages. To force H.323 to use a specific IP

address always, uses these commands.

Router(config)#voice class h323 10

Router(config-class)#h225 timeout tcp establish 3

Router(config-class)#h225 timeout setup value 5

Router(config-class)#exit


Router(config-dialpeer)#voice-class h323 10

Changes the TCP connection timeout to 3 seconds

(default is 15 Sec) and H.323 setup message

timeout to 5 sec (default 15 Sec)

Applies the Voice class to the dial-peer

Verifying H.323 Configuration

Router#show gateway

Router#debug h225 events

Router#debug cch323 h225

Router#debug cch323 h245

Router#debug h225 asn1

Router#debug ccapi inout

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