Why do we experience poor VoIP quality?

March 26th, 2018, Published in Articles: EngineerIT

Voice over internet protocol (VoIP) relates to phone service over the internet. This facility is its greatest asset but is also frequently the cause of frustration and poor quality of service. However, the problem is the network over which many companies run their VoIP communication services. Ideally there would be a totally separate dedicated network configured for VoIP, but that is often not economically viable, so the voice network is shared with all other data services.

Poor voice quality tends to be caused by an expected high call volume (a standard cliché on call centre calls). While a network may be correctly configured, a suddenly larger-than-normal call rate will introduce network delays and result in poor voice quality, sometimes to the detriment to normal conversation. Some vendors don’t walk the talk and often neglect their own voice services.

VoIP is extremely bandwidth- and delay-sensitive. For VoIP transmissions to be intelligible to the receiver, voice packets should not be dropped, excessively delayed, or suffer varying delay (otherwise known as jitter). The International Telecommunication Union (ITU) specification G114 provides guidance on the effect of end-to-end one-way delay (sometimes termed latency), and an upper bound one-way network delay. The ITU G.114 specification recommends less than 150 ms one-way end-to-end delay for high-quality real-time voice traffic. Jitter buffers (used to compensate for varying delay) further add to the end-to-end delay, and are usually only effective on delay variations of less than 100 ms. Jitter must therefore be minimised.

Jitter is a very common hiccup. Because the packets travel by a different path from sender to receiver, they can arrive in a different order, resulting in poor or scrambled sound. Jitter buffers will solve this issue, as they temporarily store incoming packets in order to lessen delay variations. Latency is another frequently experienced issue and often sounds like an echo.

There are three types of delays commonly found in today’s VoIP networks:

  • Propagation delay: A fibre network stretching halfway around the world (21 000 miles) induces a one-way delay of about 70 ms. Although this delay is almost imperceptible to the human ear, propagation delays in conjunction with handling delays can cause noticeable speech degradation.
  • Handling delay: Devices that forward the frame through the network cause handling delay. Handling delays can impact traditional phone networks, but these delays are a larger issue in packetised environments.
  • Queuing delay: When packets are held in a queue because of congestion on an outbound interface, the result is queuing delay. This occurs when more packets are sent than can be handled by the interface at a given interval.

Security can also be an issue. One of the most common threats is a denial of service (DoS) attack that takes out a network’s servers. DoS attacks aren’t directed at the VoIP services themselves but create overloads on servers’ requests, thus creating excessive delays in the network.

For added security, encryption will thwart hackers attempting to tap into a company’s communications. Some vendors recommend a solution that lets users set encryption options on a call-by-call basis, and sends a message to their desktop telling them that the encryption service is up and running.

Prioritising VoIP traffic over the network yields latency and jitter improvements. Policy-based network management, bandwidth reservation, type of service, class of service, and multi-protocol label switching (MPLS) are all widely used techniques for prioritising VoIP traffic and ensuring a quality call.

The long road to VoIP in SA

VoIP dates back to around 1996 when it was introduced in the call centre industry, but in South Africa it was out of bounds, except for Telkom and Vodacom. The restrictive telecommunications policies prevented value added network service (VANS) providers to set up their own networks and forced them to buy their connectivity from the state-owned Telkom. Early access to VoIP would have liberated the communications industry and offered South Africans many communications choices.

A landmark court case in 2008 changed the face of the communication industry in South Africa. On 18 April 2006 the Electronic Communication Act (ECA) of 2005 was signed into law by parliament. Its aim was to:

  • Promote convergence in the broadcasting, broadcasting signal distribution, and telecommunications sectors.
  • Provide the legal framework for convergence of these sectors.
  • Make new provision for the regulation of electronic communications services, electronic communications network services and broadcasting services.
  • Provide for the granting of new licences and new social obligations.
  • Provide for the control of the radio frequency spectrum.
  • Provide for the continued existence of the Universal Service Agency and the Universal Service Fund.

The ECA of 2005 would allow licensees to build their own networks but those licences could only be granted by the Independent Communications Authority of South Africa (ICASA) upon authorisation by the then Minister of Communications, Dr. Ivy Matsepe-Casaburri. Was the minister going to continue with her fight to protect the unpopular policy of managed liberalisation? Altech took the matter to court. They argued that companies who had a VANS licence should automatically have these converted into Electronic Communication Service licenses. The judge ruled in favour of Altech and overnight South Africa had over 300 communication network licensees. Clearly a defeated ministry made the wise decision not to take the matter on review. The industry was ready and almost overnight offered VoIP services, from complete networks, to PBXs, call centre services and other hosted VoIP services. South Africa had arrived!