Switching to VoIP or an IP-PBX is a project that you should take into serious consideration. Voice over IP has many benefits, including reduced maintenance costs, integration of voice, data and video in one infrastructure as well as cost-effective and flexible solutions, among many other technical advantages. However, deployment cannot and should not take place without proper planning and careful network preparation to accommodate these mission critical services.
Voice services are very sensitive to delay, delay variation (jitter) and packet loss. The most important aspects that influence the outcome of these parameters are:
- Bandwidth requirements
- Security requirements
- Quality of Service controls
- Method of voice and data traffic separation
- Network resilience and high-availability
You really need to understand each one of the above aspects, so take this opportunity and learn about them in this article. When you hire us at Phonewire to join your project team, we will consult with you in each of these areas and their relationship with your business objectives.
How to Estimate Your Bandwidth Requirements for VoIP
A proper estimation of bandwidth consumption is very important and necessary for proper planning of needed connection trunks to accommodate VoIP traffic. Your bandwidth calculations should be based on the VoIP codec used. If more than one codec is used then you should consider the “worst-case” codec during the busy-hour where the number of concurrent voice calls is about one quarter of all the users in the network.
Let’s take a look at this example:
Worst-case codec in terms of bandwidth consumption: G.711
Packetization interval: 20 ms
Total VoIP users: 100
Using G.711 with a packetization interval of 20 ms, results in bandwidth utilization of about 90 kb/s per voice conversation. To calculate the bandwidth consumption under the above circumstances, you should multiply one quarter of the users (¼ *100) with the 90 kb/s, which results in bandwidth requirement of 2.25 Mb/s during the busy hour.
There are techniques that can further minimize the amount of bandwidth utilization. Voice activity detection (VAD) for example, is known to conserve about 30% of bandwidth by not transmitting packets during silence periods. In our example, if VAD is used the estimated bandwidth calculation would be 1.57 Mb/s.
Do not rely on this calculation alone. As many in IT know, bandwidth inconsistencies can often lead to a great difference between a provider’s quoted bandwidth and actual speed achieved consistently at all hours of the business day or insist on a provider with a Service Level Agreement (SLA) guaranteeing a consistent speed regardless of demand.
Security with VoIP
VoIP is susceptible to the same vulnerabilities as the IP data network. You can read more about network threats and vulnerabilities in articles on preventing network attacks and dealing with DoS attacks.
Two suggestions I have for you, regarding VoIP security are:
- Allow only specific IP addresses and transport layer ports for both Voice signaling and media with the use of access lists and restrict as much as you can the usable addresses and ports on the network.
- Use a dedicated internal firewall to monitor the traffic flow and secure your network from application level sophisticated threats.
Voice and Data Traffic Separation in VoIP
You should consider separating your data traffic from VoIP traffic. To accomplish this task, you will need to apply dedicated layer-2 VLANs to each traffic category. This way you can achieve traffic classification and you can easily apply different QoS profiles to each traffic category. Besides, layer-2 tagging of packets, voice packets can also be marked at the network layer. Nowadays, most IP phones support Differentiated-Services bit-marking. Therefore, traffic categorization can be achieved at the very beginning of the voice packet generation. This way, service quality can be maintained end-to-end. Of course, your VoIP provider if not trusting your QoS marking, should at least apply similar traffic categorization and prioritization to your VoIP traffic.
Quality of Service with VoIP
If your network is used to carry both data and voice packets, then you should definitely consider Quality of Service (QoS). For protecting your Voice streams and to prevent data traffic from overwhelming your voice conversations, policing and traffic shaping should be applied. Of course in small networks layer-2 tagging of packets is usually enough to provide highly acceptable level of quality. It is your VoIP provider’s responsibility to apply sophisticated Quality of Service methods to offer better service to you.
Network Resilience and High-Availability with VoIP
VoIP service cannot tolerate any kind of interruption. You must make sure that you have adequate uplink physical links to carry all your VoIP traffic even in case you lose one of those links. It’s even better if you have an alternative way to carry your traffic in case of losing your primary path. Hardware malfunction should also be considered.
More than one VoIP components should be used where appropriate either in load-sharing mode or even in active-standby mode. Moreover, configuration settings on your network devices should also be upgraded to adhere with VoIP service requirements. For example, Spanning Tree should be removed or upgraded to Rapid Spanning tree because of Spanning Tree’s 60 seconds of inactivity during connectivity changes. Also, an Uninterrupted Power Supply (UPS) unit should also be considered. You do not want your Ethernet switches and VoIP devices to go offline in case of power failure. My suggestion is to use Inline power over Ethernet switches. These switches are capable of powering up all attached devices by delivering power over the unused Ethernet wires. The switches can then be attached on a UPS, the later one being able to provide uninterrupted service for a reasonable amount of time until power failure is corrected.
Good luck and let us know if you have any questions!