VoIP Deployment


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VoIP Deployment

Deploying new applications and technologies in your business is always a challenge for management. They have to balance productivity with costs, and integrate it all with the existing infrastructure.

Taking all possible deployment scenarios into consideration is too ambitious in the context of this document. So we have taken the example of deploying VoIP on a LAN. Many organizations, today, are considering converging voice and data on the same LAN and need to ensure that their existing networks can take on this additional load. For this, you'd have to analyze your existing network for congestion, and in case you're planning to use VoIP over your WAN links, then you'll have to work out the bandwidth requirements for it. This analysis will also vary depending upon the specific application you're planning.

How much bandwidth?
This is the most commonly asked question on a VoIP network. That's because voice is much more sensitive to traffic congestion, on the network, than data. When implementing VoIP over a LAN, you have plenty of bandwidth at your disposal. Therefore, you can configure VoIP devices to use a more bandwidth-intensive codec, such as the G.711, which consumes up to 87.2 kbps of NEB (Nominal Ethernet Bandwidth) in one direction. This will ensure better voice quality. In addition to this, you would also need to analyze the existing traffic patterns on your network.

Ethernet 10
Base T
Fast Ethernet
100 Base T
Available bandwidth 10,000 Kbps 100,000 Kbps 1,000,000 Kbps
Bandwidth Required Per Call 100Kbps 100Kbps 100Kbps
Total Calls Possible 100 1,000 10,000

Figure 1 – Basic bandwidth availability for different LAN technology

The above chart shows how much bandwidth is available in various LAN configurations. This is an oversimplification just to provide an idea of how much bandwidth is available for VoIP calls in a typical LAN. Of course considerations must be made for other data traffic on the LAN. Consideration must be given to the actual telephone call usage and the actual busiest times of day when that usage occurs. The design must accommodate usage for the busiest hour during the day. Most businesses experience the busiest time at about 10:00 am and 2:00 pm. During the busiest peak usage times, there will be a percentage of employees using the telephone. Using this number, a calculation can then be made on how much capacity is required during the busiest time. Typically about 25 percent of the employees are on the phone at any given time. So in the case of a 100 employee business, normal usage would be about 25 simultaneous calls at busy hour. If the business involves a busy call center, then everything changes. Since the investment in a communication system may last 5 to 10 years, make sure that you allow for growth.

The key issue in deploying VoIP over WAN links is that you have limited bandwidth. You have to start by determining how many simultaneous voice calls you'd want to hold over your WAN links. Then determine how much bandwidth would be consumed by each voice call. For this, you have to take into account the compression technique to use, the payload size of voice packets, and the type of link used for VoIP communication. There are a lot of different codecs that can be used for VoIP communication, supporting bit rates that range from 5.3 Kbps to 64 Kbps.

Ensuring Quality of Service
Once you have calculated the bandwidth required for VoIP, you have to ensure you're your voice calls get that much bandwidth. This is when you have to enforce the QoS policies, or you may experience poor quality reception, delays, jitters, missed speech or even dropped calls. QoS is normally controlled at the router level. Therefore, you'll need a router that let's you configure QoS for VoIP packets on your WAN links.

You can also deploy switches that support QoS for VoIP on your LAN. There are also some bandwidth-management solutions available that support QoS policies.

All of the bandwidth calculations and planning should be completed by someone with knowledge of routers, PBX/Key Systems, and networking.



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