Voip migration

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Migrating to VoIP Technology

The most favorable scenario for the private user or company wanting to use VoIP telephony consists of planning and installing a system from scratch. No legacy constraints to meet and the freedom to lay down and thoroughly test the system before release. Migrating an existing system on the other hand presents many additional intricacies as users all have their idea about how the system should work and high expectations for the delivered one. Phones are the most widely used communication system and should be considered a "mission critical" service. The migration should be regarded, planned and executed with the proper care avoiding any disservice as much as possible.

Performing a Preliminary Analysis

The first step when planning a migration of a traditional telephone system (PSTN) to VoIP technology consists of an analysis of the existing infrastructure. At least three aspects should be covered:

  • Talk to users.
  • Create or update an inventory of the equipment.
  • Map the cabling and equipment used for the data and telephony networks.

Talk to Users

Final users are an invaluable source of information and prove to be very useful to configure the telephone system. By talking to them you'll understand how and how much they use it in their day to day activities. What services are to be regarded as fundamental, which can be upgraded, which can be added in order to improve the service and which are obsolete and can be ignored or eventually decommissioned. Meeting your users is the easiest way to collect information to correctly size the network ans servers to manage it.

Equipment Inventory

A small organization will probably possess a limited number of servers and will host not so many telephone related services like call waiting, call forwarding or voice mail. As the company grows so do the number of services and the complexity of their configuration. it is therefore essential to know how many devices are installed and what is running on them, where are they located and how do they talk to each other. Once collected, this information will aid you in the planning stage to properly size and configure VoIP devices and how to schedule and organize the migration for example buying and distributing the VoIP phones to replace old analog ones.

Special care should be taken in managing fax machines and similar equipment like multifunction printers. They require special care because such machines are hard to migrate. The T.38 VoIP fax transmission standard protocol is quite recent and poorly supported by traditional fax vendors. Moreover transmitting a fax the traditional way hardly fits VoIP protocols, that can suffer from data loss due to lack of bandwidth. You are strongly encouraged to decommission old fax machines replacing them with an Internet Fax: a software emulating a fax that delivers documents directly to an e-mail account as an attachment. A similar open source fax server software is HylaFAX. Were fax decommissioning impossible, you are strongly recommended to connect such machines directly to the phone line eventually recurring to a gateway.

Network Mapping

One of the migration goals consists of merging data and voice traffic into a unique stream. It is important to check for both cabling and network port availability in every room to suffice for the additional equipment required. Otherwise you'll have to fix the issue upgrading the network adding cabling, adding one or more wireless access points and upgrading or replacing routers and switches accordingly. Obviously the opportunity should be considered a convenient time to put some order in the network and put the basis for future evolutions. While designing the new network it is a good practice to slightly oversize it planning a reasonable margin for growth. You should avoid to find yourself in need of network ports while migrating and at the same time anticipate the need for a quick addition of a new phone or other device.

Interfacing to Traditional Lines

It is not always possible or advisable to cut every tie to the traditional telephone network. There are many reasons not to execute a full switch off. Technical reasons such as a poor VoIP network coverage by the local telephone company. Convenience reasons such as not changing a phone number which served you for years, which is well known to customers and used as the target contact of recent campaigns: switch it off and you'll loose the potential gain in new leads.

When it is not possible to execute a full transition from the traditional telephone network and some analog or ISDN lines are required you'll need:

  • Equipment designed to make the VoIP network to talk to the analog or ISDN one. This interfacing equipment is commonly called gateway.
  • Carefully count the number of analog or ISDN lines you'll need.

The first issue can be easily solved. Many VoIP hardware vendors sell the equipment needed to connect their devices to analog lines. A quick search in the Internet should return an almost endless list of devices and products in order to solve your every need at a reasonable cost. The second entry can be somewhat more awkward. Many calls can be concurrently transmitted through the same VoIP line. An analog line means one and only one call at a time. The needed line number equals the maximum number of concurrent calls the system is supposed to handle. Suppose for example you'd like to provide a phone service for a marketing office consisting of 8 persons performing commercial call all day long, then you'll have to plan for 8 analog lines otherwise some of the personnel will be prevented from performing their duties.


The outcome of the analysis will prove to be very useful to schedule the service migration. Once again you'll have to proceed step by step in order to organize every task coherently with day to day activities. The first step consists of every action needed to resize, redesign, update and evolve the data network. It is possible, but strongly discouraged to start the migration while the infrastructure is still a work in progress. Temporary solutions tend to be the perfect path to disaster and consequent project failure. When unplanned issues arise it is better to check with the customer and eventually agree on a less aggressive timeline that addresses the issues.

The following step consists of installing and configuring servers and other communication equipment. Once you are finished with hardware, add some bogus user and test everything. Tests are the perfect way to check for network efficiency. It is better to test every telephone and telephone related service to make certain of every functionality to work well when migrating users. Work is finished when every test executed with bogus users exit successfully and every quirk has been ironed out.

Before starting the migration you'll have to distribute SIP phones, fax machines and PC peripherals used to replace analog phones. When every piece of equipment is in place it is time to configure phone numbers on the VoIP PBX and to register the corresponding SIP phone, PC soft phone, smart phone, etc.. You are encouraged to split work in batches of users an to fully test every group before moving to the next. The most chaotic part of the activity is the period of coexistence when both the old and the new technology are in use. The situation will get stabler and stabler as the migration reaches its end and all issues should inevitably disappear when the great majority of users will be running the new system.

Further Service

A successful migration is not concluded with delivery. Some kind of support is needed and should cover the first few months of use. Moreover users will need some sort of training.


Decommissioning a technology in favor of a newer one rich of functionality presents no benefit if users are not trained to take advantage of the new potential offered. As good practice plan some meetings with the people on staff describing them the new features and benefits VoIP offers and how to use them at best. Some selected users should be assigned higher privileges than usual thus enabling them to help their colleagues with the new technology. For large companies you must divide users into groups and organize training sessions for each one coordinating with the migration progresses.


Training and documentation are tightly tied to each other especially for large companies where it is not always possible and often impractical to reach one and every user. An official centralized source of documentation can be an invaluable source of information about phone and service use. A web server and a content management software represent an easy and cost effective way to build the documentation repository where to store manuals, whitepapers, FAQs and suggestions to users. Using a web server presents users with a familiar interface: one they are accustomed and familiar with, moreover the information is stored and managed in a centralized way and every update is immediately available to everyone and finally its possible to get users involved in writing, checking and correcting the documentation. Another benefit is the opportunity to link the VoIP equipment configuration interfaces to the related manuals.


The present paper introduced some cues and ideas to help in the migration of a traditional telephone system to a VoIP based one. A potential path for the migration was presented along with the subsequent services needed to achieve the goal.

To contact me or leave me your feedback, Please e-mail at studiosg [at] giustetti [dot] net.

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Languages: English - Italiano