Specifications

Product Description
IP Office Release 7.0
© 2011 AVAYA All rights reserved.
Page 233
Issue 22.a.- (21 March 2011)
IP Office Turns VoIP into IP Telephony
In order to make use of VoIP, IP Office uses signaling protocols called H.323 , and Session Initiation Protocol
(SIP) which allow IP Office to establish end-to-end connections for the voice path through the IP network. It
ensures each end of the connection is able to transmit and receive voice and provides the network addressing
for end to end packet transmission. IP Office also allows for connecting between the different technologies by
translating the signals they use, for example an analog telephone may wish to connect to a VoIP destination.
This requires both the signaling and voice transmission to be translated – IP Office does this easily as it
contains technology elements called gateways and gatekeepers that enable translations to happen.
With a conventional telephone system you plug your analog or digital TDM telephone into an extension socket
connected to your PBX or Key System. With IP Telephony you connect your digital IP telephone to your IP PBX
via the LAN. There are two basic types of IP telephones:
· A physical telephone, which looks very similar to a standard telephone (IP Hard Phone)
· A software application (IP Office Video Softphone) which runs on the user's PC, allowing them to use
either a headset/microphone to make/receive calls anywhere they have IP connection
IP telephony has the advantage of allowing extensions to be deployed both locally and remotely through the
use of IP routing and IP VPN services.
When making use of IP telephony, there are a number of data centric considerations such as which data types
have priority on the IP network when there is contention. This is set with IP/TCP "quality of service" and should
not be ignored. In situations where LAN Bandwidth is limited, a quality of service capable LAN switch should be
used to ensure voice packets are transmitted with the required priority on the network. If not, the conversation
carried over IP appears as broken up (due to delays) or has unacceptable delays introduced in the conversation
(latency and jitter). With IP hardphones there is need for Power over Ethernet (PoE), or local phone power
supplies to be provided to the telephones as the IP telephones are no longer powered by IP Office – a list of
Avaya approved PoE options is available at the end of this section.
Gateways, Gatekeepers and H.323 - Technology Overview
IP Office uses the H.323 signaling protocol which has the following architectural components
· Telephones are H.323 service endpoint devices that can support Audio calls. Other types of H.323
devices can support video as part of H.323
· Gateways provide media translation to allow calls to be made to non-H.323 devices, for instance an
analog telephone or the public network to connect with a H.323 device
· Gatekeepers control the call processing and security for H.323 devices
· Multipoint Connection Units (MCU) for conferences by adding together media streams
These elements are grouped together in what is known as an H.323 zone (a zone is analogous to a PABX). Each
zone has a single Gatekeeper that can be considered as the brains of the system dealing with call distribution,
call control and the management of resources. On power-up, IP telephones, Gateways and MCU make
registration requests to a Gatekeeper which then authenticates (accepts or rejects) their request to become a
member of the zone. Once accepted, a telephone wishing to make a call sends a call set-up message to the
Gatekeeper which then determines how to route the call and will then send an alert to the called telephone, or if
the call is to a non-H.323 telephone establish the call via a Gateway within the zone.
The design of IP Telephony systems has been driven by open standards. Digital IP telephones, Gateways and
Gatekeepers all support the H.323 standard and it is this that allows devices from different manufacturers to
work together. IP Office has an optional integral Gateway (Voice Compression Modules) and Gatekeeper
functionality required to provide a fully functional IP Telephony solution.
SIP – Session Initiation Protocol
IP Office supports SIP, which is a signaling protocol used for creating session oriented connections between two
or more locations in an IP network. SIP trunking is a service offered by and ITSP (Internet Telephony Service
Provider) that permits businesses with an IP Office installed to use Voice-over-IP (VoIP) outside the enterprise
network by using the same connection as in Internet connection.