Can Your Current Network Handle VoIP?

by Scott Kinka, Sr. VP – Network Services, Evolve IP
Computer Technology Review, April 16th, 2009

IT professionals and business owners alike are looking for ways to do more with less in today’s economy. As a result, businesses who have not yet installed a Voice over IP (VoIP) phone system or hosted service are now giving it serious consideration.

VoIP phone systems are capable of enhancing the productivity of an entire workforce. Mobility-enhancing unified messaging and true click-to-dial communications give employees more flexibility and time to produce to revenue.

What’s more, the convergence of voice and IP traffic (WAN and Internet) over the same connection provides immediate cost savings to businesses that previously maintained separate networks for traditional Time Division Multiplexing (TDM) voice services and IP.

However, as with any new technology, there are various items to account for when planning to implement VoIP on your current wide or local area network. Failure to do so can prove disastrous for the VoIP implementation and incredibly costly to the business, with the risk of essentially erasing any targeted financial advantage.

Preparing the Network

Convergence adds an entirely new responsibility to a business’s existing network: adding and moving voice through the network. Voice streams are more sensitive to network congestion than data. If access to a Web page is a millisecond slower today than yesterday, it’s unlikely you’ll ever notice. But a millisecond delay in delivering a voice packet reveals itself as a stutter or moment of silence.

There are three main factors that affect the quality of a VoIP deployment. The first is latency, or delay, which is the time it takes a voice stream to travel from end-point to end-point. Second is packet loss, which occurs when data congestion causes routers and switches to overflow. Last is jitter, the difference in time between the expected transmission rate of data and the time it actually arrives. Generally, jitter stems from dramatic changes in network traffic or load.

To avoid these issues and ensure your network has sufficient bandwidth (whether LAN or WAN) to smoothly and flawlessly carry voice, a thorough network assessment should be performed in advance of the implementation.

To size the amount of bandwidth needed to cover your voice usage, you will need to understand the CODEC (Compressor/De‐compressor) that your IP PBX or hosted service will use. CODECs convert audio signals into a digital format and compress them for transmission over the network.

Depending on the selected CODEC, your voice sessions will take between 28.8 kilobits per second (Kbps) and 93 Kbps of bandwidth. In other words, if you have 10 phone lines representing the maximum concurrent phone calls, you will utilize between 288 Kbps and 930 Kbps for voice on that link.  If you average more than 50 percent of your current bandwidth or regularly peak above 80 percent, you will need to upgrade bandwidth at that location to support VoIP.

Preparing the network for VoIP goes beyond bandwidth and network speed, however. Network managers must also be prepared to address end-to end Class and Quality of Service. Class of Service (CoS) refers to a network’s ability to classify and treat traffic differently based on the type of data being transmitted. Quality of Service (QoS) meanwhile, applies to the standards that can be placed on the classified traffic.

Once data is classified into groups (i.e. voice, data, video, etc.), it is prioritized into different service levels based on the availability of bandwidth, and treated in accordance to its need and the end‐user’s expectation of availability.

For instance, because of its delay-oriented nature, Internet browsing requires a very low QoS. A user makes a request, that request is transmitted, the server sends back the data, and the page is delivered to the user’s browser. As previously noted, if there is a slight delay in delivery, it is negligible, and may even be expected by the end user.

In contrast, VoIP requires a much higher QoS to ensure calls can be conducted with zero delay. VoIP data is transmitted as a stream, more evenly over greater periods of time.

Network managers must ensure that LAN switches are managed and capable of supporting QoS, and WAN links and service providers can provide bandwidth that honors QoS between sites by utilizing Multiprotocol Label Switching (MPLS).

Providing Power

Traditional handsets obtain inline power from POTS (Plain Old Telephone Service) phone lines, but because VoIP handsets are connected to the Ethernet instead of POTS, power must be provided by some other means.

One option is to add an adapter to plug the phones into a standard power outlet. However, in this case, phone service is vulnerable to power outages.

The second, more desirable option is to use POE (Power over Ethernet) switches which provide inline power over standard Ethernet lines. These switches can then be backed up with an on‐site UPS (Uninterruptable Power Supply) to ensure continued use of phones in the event of a power outage.

Protecting Against Threats

Unlike traditional phone systems, VoIP is susceptible to the same security threats as the rest of a business’s IP based systems, i.e. its servers, routers, switches, firewalls and databases. In addition, VoIP-specific vulnerabilities exist. These could be the high-jacking of your VoIP service for unauthorized use, eavesdropping on your private conversations, or a malicious and disruptive attack, such as Denial of Service.

To prepare and protect your network and phone service against these attacks, it is essential to have a comprehensive organizational security policy in place. There are no significant VoIP-specific protections that are needed, other than a fully vetted defense in depth policy that addresses all IP-related systems and services.

While these considerations should be taken seriously and are necessary to ensure your WAN or LAN is capable of a VoIP deployment, they should not be seen as obstacles. A well planned and executed VoIP strategy can deliver call quality ratings similar to or better than traditional implementations, and deliver on the productivity and financial advantages that prompted you to consider it in the first place.

Scott Kinka is the senior vice president of Network Services for Evolve IP.

Originally appeared in the Computer Technology Review - April 2009