Network design and VoIP call quality …

moonwalk“Where are you talking to me from – the Moon?”

VoIP telephone systems use Local Area Networks (LAN’s), consisting of routers, network switches, loads of cabling, and servers – just like your computers do. But, VoIP is easily upset by network shortfalls that might cause congestion and re-transmission!

That’s because data can be delayed, and bits & bytes can actually be lost and re-sent without effecting the web-page, e-mail, or file that appears at your computer – but when VoIP experiences these problems, you – and the person you are calling – really do hear it!

VoIP transmissions need to be real-time, with minimal data loss – otherwise your ear will easily detect a loss of ‘quality’ in a phone call.

This means that when you consider installing a VoIP telephone system, you need to ensure that it is running on a network with adequate [bandwidth] capacity, and one that will give voice ‘priority’ over other data traffic to ensure a good ‘Quality of Service’ (QoS). In the early days of VoIP, it was the lack of understanding of the importance of QoS, that gave it a bad reputation. VoIP systems were just meshed with existing networks and expected to work – with some very disappointing results!

The basics still apply, in that you do need to consider how much bandwidth you have in your Local Network and Internet connections, to ensure you can carry the phone calls you need to in the first place! Jump to our earlier article about ‘Vibe’ to see how we can get you more bandwidth from even basic broadband services …

QoS is becoming vital in modern network design due to the increase in real-time media that’s being transmitted on both company networks, and the Internet. It’s not only VoIP that’s sensitive, but video streaming and video-conferences are also becoming important. For these applications, we need to ‘tag’ the voice packets that are streaming across LAN components, with code that identifies them as having priority – and of course, we need network components that can recognise these tags and act like traffic lights at an intersection, giving the ‘green-light’ to priority traffic, while queuing everything else until it passes.

In general we ensure that 3CX VoIP PBX systems have two components that ensure good quality speech on the Local Network, and to & from the Internet:

netgear-smart-switch

Network ‘Smart-switches’ are installed to replace existing ‘standard’ Ethernet switches so that using a variety of mechanisms, tagged voice packets moving between; the phones, the VoIP server and the Internet router, are ‘classified’ as important, and allowed free & swift passage, while other traffic is queued to follow it. In real terms, the delay imparted to non-tagged data traffic is hardly noticeable – but without this in place, a service-pack download to a workstation for example, could make a phone call quite difficult! As an added bonus, we also install Power over Ethernet (PoE) versions of these smart-switches, so that phones can be powered through the same cat.5e data cable as is used to connect them to the network & server. This means less plug-packs at your desks, and also makes it easy to back-up mains power with a central UPS to keep the phones going if there’s a power cut.

While smart-switches do the job on the LAN, it’s also important to ensure that VoIP traffic has the ‘fast-lane’ on and off the Internet. This is where we need to be careful in our choice of Router. In small site installs, we use a dual-WAN router that allows configuration of load-balancing rules so that we can take two DSL services onto your network, and use one for voice, and the other for data. A simple set of rules ensures that one DSL broadband service is used just for VoIP – with all other traffic coming to and from your LAN via the other.

In larger installs where a single high-speed DSL service (e.g. a 10Mbps or 100Mbps leased line) may be used to carry both voice and data traffic, the router may be configured to perform a different QoS role, where it ‘recognises’ voice traffic and prioritises a pre-set amount of bandwidth in the DSL service, exclusively for the use of VoIP. This means that downloads etc. from the Internet to your LAN, will not cause Quality problems for your phone calls. Jump to this article to see how much bandwidth is needed to carry a VoIP call …

The last consideration is your choice of Internet Service Provider (ISP). If you connect to the Internet, via a different ISP than the company providing your SIP Trunk channels, then there is going to be a ‘leg’ of your call that transits public Internet, with high risk of loss of call quality. This element of the call carriage can be minimised if your DSL supplier, is the same company that provides your SIP Trunks. VoIP Telephony ISP’s should (if they are reputable) provide direct links from their Internet services to the media [SIP] servers providing onward connection to PSTN and mobile services.

Unless you are considering a completely separate and new network for your phone system (which actually has a lot of disadvantages!), you do need to plan network upgrades as part of the implementation of a VoIP phone system such as 3CX. Please contact us at Foxhall Solutions to talk about what’s needed to bring the flexibility and cost-savings of VoIP technology to your company …

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