Deploying VoIP: Weigh the pros and cons of convergence

To converge or not to converge -- that is the question. When deploying VoIP in your organization, should you combine data and voice networks, or should you keep them separate? Deb Shinder weighs the benefits and drawbacks of each option.

If your organization is currently contemplating a VoIP implementation, one big decision you'll have to make is whether to keep the VoIP network separate from the data network or if convergence is the way to go. Convergence is one of the popular IT buzzwords right now, and the connotation is generally positive.

While there are certainly advantages to "putting it all together," there are also good reasons to keep the networks separated. Let's weigh the pros and cons of each option.

Should you deploy VoIP on an existing network?

There are obvious cost benefits to deploying VoIP on an existing network and using the same Internet connection used for data. However, prior to deploying VoIP, your organization needs to make an assessment of the network to determine how well it will support the addition of VoIP.

Network issues such as packet loss, latency, and jitter (i.e., variation in time between the arrival of packets) impact VoIP call quality much more than they affect data transfer. That's why it's important to know the extent of these factors on your network beforehand rather than making assumptions and being subject to unpleasant surprises later.

More bandwidth is often the solution to network problems, but just adding more bandwidth doesn't necessarily solve VoIP problems. Remember, it's the quality of the connection — not the speed — that poses many of the problems with dropped calls, poor voice quality, and so forth. In fact, because of its sensitivity, VoIP can be the first indicator of network problems you didn't know you had.

A number of vendors offer network testing products and services that specialize in conducting pre-deployment baseline assessments to simulate voice traffic on the network. These offerings can help determine whether deficiencies exist that you'll need to address before deploying VoIP. Here are three examples:

The assessment may show that your network is ready for VoIP or that you need to change a few key components. In some cases, companies find that they need to completely redesign the network to support VoIP.

Along with determining whether the network can handle the extra bandwidth needed for VoIP (which can be considerable in a large company with many employees who make a lot of calls), you need to ensure that the network supports Quality of Service (QoS). Are your network's routers and switches VoIP-compatible? Do you need software updates for network devices to use QoS effectively?

Remember that users won't be as tolerant of outages or problems with their telephone service as they are of data network downtime. PSTN performance has trained users to expect almost 100 percent reliability from phone systems.

A converged network allows you to manage voice and data communications as one, and it can save equipment and personnel costs — if you do it right. It also makes for easier deployment of unified communications; users can access messages of all types — including e-mail, voice mail, faxes, and so forth — from a single repository through a single interface. You may enjoy a greater return on investment by using much of your equipment for both voice and data — and have fewer devices to maintain and manage.

Or should you maintain separate networks?

The other option is to deploy a separate network dedicated to VoIP components. You can either create an entirely separate physical network, or you can use virtual local area network (VLAN) technology to logically separate the networks.

The primary reason for separating networks is security. VoIP is vulnerable to many of the same attacks, intrusions, and other security threats as data networks. If you have VoIP and data traffic combined on the same network, an attack on one can bring down the other.

It's annoying enough to users if their e-mail is inaccessible because the network is down due to a virus or denial-of-service (DoS) attack. But if both e-mail and telephone communications are unavailable, business may come to a halt, and the company loses money.

Regulatory compliance issues may also come into play. If you're in a business in which industry or government mandate determines how to secure the data on your network, separating the networks provides higher security and thus a greater level of compliance.

Bandwidth considerations provide another reason for separating voice and data networks. If your existing network doesn't have the bandwidth to support VoIP, installing a separate network for VoIP is one solution. You have more control over the quality of service, and you don't have to worry about other applications getting priority and causing problems for VoIP users. In fact, Cisco and other vendors recommend VLANs to separate VoIP and data in its best practices for securing VoIP networks.

However, separating the networks — whether completely or by setting up VLANs — can be expensive, and there are other alternatives to secure voice traffic, such as encryption. And with separate networks, you may have wasted bandwidth on both.


To converge or not to converge, that is the question. But the answer isn't as clear-cut as we'd like. There are many advantages to convergence, and it appears to be the wave of the future, especially in budget-conscious environments.

However, separating voice and data transmissions can provide better security for both. In addition, it may be a more cost-effective alternative — at least in the short run — if the existing network would require a complete redesign to support VoIP.

A single network can make management and troubleshooting easier if IT personnel have the proper training to deal with VoIP technology. But it also makes the network more complex, and there may be a learning curve before the company can realize the full benefits.

As with so many issues in IT, then, the answer to the question is that it depends. It depends on the network infrastructure you're starting with, your security requirements, budgetary considerations, personnel considerations, and many other factors. It's essential to perform an assessment — not just of the network but of your company's particular needs in regard to both data and voice and a projection of future needs — before you make the decision.

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Deb Shinder is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. She currently specializes in security issues and Microsoft products, and she has received Microsoft's Most Valuable Professional (MVP) status in Windows Server Security.

About Deb Shinder

Debra Littlejohn Shinder, MCSE, MVP is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. Deb is a tech editor, developmental editor, and contributor to over 20 add...

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