VoIP over WiMAX demands close attention to QoS

By Basharat Ashai

VoIP over WiMAX is different than traditional VoIP over DSL or cable. In a VoIP over WiMAX offering, there are two sets of network contingencies: one being the number of base stations and the other, how far away a subscriber is from the base station. At a basic service level, VoIP over WiMAX requires that service providers pay attention to QoS and mobility issues.

The 802.16-2004 based equipment currently on the market has been certified and tested by the WiMAX Forum for data services. WiMAX Forum has not completed the certification process for the QoS profile that handles VoIP. For instance the 802.16-2004 testing in the WiMAX Forum labs considers the Unsolicited Grant Service (UGS) QoS class as optional. UGS is one of the five QoS service types defined in the IEEE 802.16 WiMAX. UGS is designed to support real-time service flows that generate fixed-size data packets on a periodic basis, such as VoIP without silence suppression. There is a lot of momentum going on in terms of QoS improvements over WiMAX networks. Later in 2009 we expect to see an evolution towards the PCRF (Policy and Charging Rules Function), a QoS IMS module that WiMAX is going to adopt and use for QoS.

The initial standards only address the basic RADIUS interface for the bandwidth management. There should be sufficient bandwidth to handle the number of voice channels. The bandwidth crunch is always in the access network whether it happens to be DSL or WiMAX. That is the area of the network most subjected to the kinds of impairments that make the service acceptable or not as far as the end user is concerned. In general, it is important wireless networks deliver a low latency as it relates to both signaling and media and any network that introduces significant amounts of delay in excess of few fractions of a second can result in an impaired subscriber experience.

VoIP over WiMAX is going to be an upsell to an existing broadband service. If WiMAX really is seen as a broadband replacement technology then the ARPU increase is going to be relatively low. This comes mainly from a perception that voice is becoming free, with Skype as the main example. To see an increase in ARPU, VoIP over WiMAX service needs to be positioned as more of a wireline replacement technology and should be marketed as a prime solution for CPE-based residential phone service. WiMAX ARPU is about three times higher than the mobile ARPU for residential services. The increased usage and features enabled by VOIP-capable mobile Internet devices (MIDs) with embedded WiMAX can greatly increase ARPU.

In many emerging markets, VoIP will be a baseline service requirement that WiMAX service providers will have to offer. This indicates that offering VoIP will not necessarily double a service provider's ARPU. In developed countries, the situation is likely to be different as the cost of broadband access and voice services are comparable, and customers are more likely to be attracted by discounted bundled services and the convenience of a consolidated bill.

Both fixed and mobile VoIP over WiMAX markets are still in their infancy. The number of VoIP over WiMAX users is very low compared to the overall user base within WiMAX. In fact, WiMAX networks have an estimated 269,690 cumulative worldwide VOIP subscribers. But WiMAX players are not really positioning VoIP over WiMAX as a voice replacement technology. The majority of service providers do not foresee a high market penetration for voice in the near future.

The challenge for mobile VoIP over 802.16e-2005 networks is that many MIDs are not yet available, since the technology is still evolving. There are a number of WiMAX service providers such as Neo-Sky in Spain that have delayed  VoIP deployment plans until mobile phones/MIDs with embedded WiMAX, such as the Nokia N810 at 3.5 GHz,  hit the marketplace.

Handsets will be vital to making voice a major component of WiMAX based on an 802.16e-2005 network. HTC has just launched the first GSM/WiMAX phone, the HTC Max 4G. However, the key to VoIP over WiMAX success is to have a range of handsets and devices available -- one device alone is not going drive the market. The expansion of WiMAX networks and the increasing availability of WiMAX VoIP-enabled devices will mean an increase in customer choices for mobile phone services.

The future of VoIP over WiMAX and broadband wireless in general looks promising for the next few years. Although LTE is still some years away from commercial availability, it will be interesting to see how 3G operators package VoIP in their future offerings, and to what extent VoIP will cannibalize their circuit-switch voice business.

Basharat Ashai is the APAC & Middle East analyst for Maravedis, a research and analysis firm focusing on broadband wireless technologies including WiMAX, 802.20, TD-CDMA and wireless local loop systems. Learn more at www.maravedis-bwa.com.