Telesis PX24 IP PBX Business Phone System
Design and manufacture IP PBX Business Phone System, Switching System, VoIP Gateway, and Signaling Converter  

H.323 Protocol

Telesis Systems Offering H.323 Protocol

  • Telesis Business Phone Systems:
    • PX24N (Telesis Nano) IP PBX SoHo System
    • PX24M Hybrid IP PBX Business Phone System
    • PX24X Hybrid IP PBX Business Phone System
  • Telesis Switching Systems:
    • X1 Large Capacity TDM - IP Telephony Switch
  • Combined VoIP Gateway and Signaling Converters:
    • Stillink 200
    • Stillink 800
    • Stillink 3200
  • Large Capacity IP PBX for Enterprises
    • Stillink 3200


The applied standards for H.323 umbrella protocol are H.225.0 (07/2003) version 5, H.235 (05/2003) version 3, H.245 (07/2003) version 12, H.450 (09/1997), AES FIPS PUB 197.


Telesis systems integrate both packet and circuit switching technology. A Telesis system featuring an integrated gatekeeper provides an economical way for administrators to manage a central database of phone numbers without the expense of a separate-box gatekeeper solution. Number/IP translation is performed through Telesis advanced routing algorithm. Together with the integrated gatekeeper, call authorization, call management, enhanced billing functions, flexible routing algorithms and extensive business telephony features make a Telesis system serve as a feature-rich communication platform. Integrated gatekeeper allows calls to be placed direct or gatekeeper routed between H.323 entities in various circumstances.

Telesis systems are with an integrated H.323 gatekeeper

The integrated H.323 gatekeeper may serve to numerous H.323 users

Telesis systems can register to multiple H.323 gatekeepers at the same time. This allows address resolution of a Telesis system from either side and results in flexibility for multipath VoIP access applications.

Telesis systems can register to multiple H.323 gatekeepers

Capability of registering to multiple H.323 gatekeepers at the same time provides multipath VoIP access


 Telesis systems support numerous H.323 users (entities) which can be terminals, gatekeepers or gateways.

Telesis systems support numerous H.323 entities

H.323 entities may be terminals, gatekeepers, gateways at the same time

Furthermore, Telesis systems are with media proxying capabilities. The integrated media proxy provides a transit point for media (audio) streams between H.323 entities. The media proxy operates only for the integrated gatekeeper routed calls in some circumstances.

While voice bridging distant offices over the IP, security of a VoIP call is guaranteed with the encryption (optional) of voice according to 256 bit AES (AES-256).

Media can be encrypted with AES 256 among Telesis systems if H.323 protocol is used

Telesis systems support AES 256 media encryption over H.323

While connecting to the long distance call operator over the IP, the Telesis system may register to an external gatekeeper of the operator as an option. With the advanced routing algorithms and alternate routing capability, TDM calls from a terminal equipment of the system may be routed to a selected operator over the IP or PSTN. Alternate routing capability provides automatic fall back to the PSTN if the IP network is unaccessible.

Automatic fall back to PSTN if all routes to IP fail

Advanced routing algorithms and alternate routing capability ensure call progress

Layers and Options

The physical layer of H.323 protocol in Telesis systems is 10/100 BaseT Ethernet. Several ethernet and other properties for H.323 are programmable.

Audio Codecs

A Telesis system is equipped with well-known audio codecs featuring audio compression as well. Audio codec preference list and properties such as silence suppression (VAD-Voice Activity Detection), frame length are programmable for the system. Currently available codecs for VoIP calls are:

  • G.711 (A and u)
  • G.723.1 (5.3kbps, 6.4kbps)
  • G.729
  • G.729AB

Echo Cancellation

An AT&T certified G.168 echo canceler meets and exceeds G.168-2002 standards. The echo canceler can operate with delays as high as 128msec. It is better than industry standard cancelers under the most important and difficult conditions like double-talk and the presence of background noise.

Route and Routeset Configuration

In a Telesis system, an H.323 endpoint may have its own route number. It is possible to define numerous distinct routes. A given route to a particular destination and its accompanying alternate routes are grouped in a routeset. Each route in a routeset has a priority order. Alternate routes may be H.323 endpoints or TDM (PSTN) lines. Routing to the next priority alternate route is possible in the event that a route becomes unavailable.

Call Routing

As an IP-TDM gateway, the Telesis system routes a call from the TDM network to the IP network according to:

  • Dialed digits (called number)
  • DPC
  • Calling party number and information elements whenever available, such that:

    • Category of calling party
    • NOA of calling party
    • Numbering plan of calling party
    • Presentation status of calling party
    • Screening status of calling party

H.450 Supplementary Services

Telesis systems support various H.450.x series supplementary services in H.323 protocol stack, such as:

  • H.450.1 Generic functional protocol for the support of supplementary services in H.323
  • H.450.2 Call transfer supplementary service for H.323
  • H.450.4 Call hold supplementary service for H.323

Related Readings

We recommend you to visit Telesis WiKi Pages for technical readings. 


Copyright Telesis A.S. 2006-2013
STB Design Services