System information

System Administration Guide

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Revised: March 28, 2007

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8 Remote Allworx Server Multi-Site Calling

Note: This is an optional feature that requires a feature key. The necessary key is referred to as the Internet

Call Access Feature Key and is the same key that enables SIP Proxy and SIP Gateway functionality

described in the previous chapter.

8.1 Introduction

The Allworx server products support VoIP calling between servers connected in a peer-to-peer manner.

These peer Allworx servers are typically located at different sites. For example, a small business with three

office locations may have a dedicated Allworx server at each location where each site is configured to be able

to place VoIP calls to each of the two other sites without using conventional circuit switched voice trunks. In

addition to these sites each with their own Allworx server, additional site(s) can be serviced via individual

remote phones that are each associated with a specific site’s Allworx server. See the Remote IP Phone

section for more details on configuring remote IP phones that are not associated with a local Allworx server.

8.2 Quality of Service Between Sites

To take advantage of multi-site calling it is important to take into consideration the quality of the network data

connection that spans between each set of sites that will be calling each other. The quality of the data

connection will have a direct impact on the observed voice quality between the sites. While the raw

bandwidth requirements are not particularly cumbersome for each call that is set up, limiting the number of

calls to within the bandwidth available is important to enforce. In addition and perhaps more importantly,

having a good understanding of the typical packet latency and loss rates are also key to accurately accessing

the voice quality one would expect to observe on a day to day basis.

The best arrangement to have is to use a managed data service from a quality service provider to be able to

deliver a guaranteed level of service according to an agreed upon Service Level Agreement (SLA). Barring

that, many best effort services, such as an ordinary Internet access service delivered to each site will likely

provide acceptable voice quality a majority of the time – but the performance can vary widely depending on

many different factors which are beyond the scope of this document. If you are unfamiliar with such

considerations, Allworx suggests you read the Allworx VoIP Tutorial white paper available on

www.allworx.com/support/downloads/default.asp as a starting point for your investigation into such topics.

8.3 Limiting Total Number of Calls Between Sites

It is important to limit the maximum number of allowed calls that will simultaneously exist between the local

site and all other sites. This limit is set on the Servers / VoIP Server web page under the parameter Maximum

Active Remote Calls. The default value is eight, but you should select a value based on the total amount of

bandwidth you are willing to dedicate to voice calls. See the Allworx VoIP Tutorial white paper available on

www.allworx.com/support/downloads/default.asp for some tips about computing a reasonable value for this

parameter.

8.4 Defining Remote Allworx Sites

It is actually quite straightforward to configure site-to-site connectivity. For each pair of sites you wish to be

able to communicate with each other, you simply need to define a remote site on each system to point to its

symmetrical peer. To define the peer, go to Phone System / Outside Lines and under the Remote Allworx

section of the page select Add New Remote Allworx. Once each remote site is defined, you can use the

associated Modify link to adjust any settings as needed. Here is a description of each required parameter to

define a pair of sites:

Description

– A friendly administrative name for the remote site.