Life in the fast lane for voice using femtocells

Bus LaneDo femtocells need a "bus lane" on your broadband internet connection to speed through voice calls and ensure high quality? With internet services becoming more congested these days, is best effort really good enough?

How is internet traffic coping these days?

Most internet traffic these days is handled on a "best effort" basis, which means that you can't quite be sure when (or even if) each packet of data will get to its destination. Many applications are designed to cope with this, retrying or skipping over glitches. Web browsing can cope with delays before showing or updating each new web page. Video streaming usually buffers a few seconds to accommodate any short outages. Voice services, such as Skype, use codecs which spread the information across several data packets so that individual losses don't cause total loss of the audio.

Internet performance is degrading for many domestic users 

But where congestion is heavy, something has to give. Voice calls over the internet or live video streaming woud be some of the first services to be noticeably degraded in these circumstances. I've found from my own experience that during peak hours (the evening), my wireline broadband service slows down dramatically. Voice calls using Skype can become unreliable and can drop out or fail; those using simpler VoIP codecs reduce the call quality to a point where its unintelligble. In some cases, it isn't obvious to both parties that voice quality has degraded because sometimes this affects only one direction. And it's not just my personal experience - I've also downloaded and listened to a few interviews initially recorded over Skype where this has happened.

Study confirms poor quality of experience for end users 

This poor internet experience has been confirmed by Epitiro , the internet quality of experience measurement people, who have conducted a range of qualitative tests of many ISPs and end users.

This contrasts with statements made by Orange, who have not found voice quality to be an issue on their UMA/WiFi dual mode service which is similar to femtocell services in many ways. It also contrasts with the many millions of Skype and VoIP users around the world, who successfully use these systems without noticeable quality or performance limitations.The femtocell industry is quick to disagree with these conclusions too, having not experienced issues in field trials to date.

What can be done to address this? 

There are three considerations here:

a) Prioritise voice traffic inside the broadband router: Voice calls can be prioritised and fast tracked through the network. Where femtocells have been integrated with a broadband modems, their traffic can be marked with a priority flags that allow it to jump to the front of the queue and so avoid latency and dropout problems. DSL modems often already do there where they have built in VoIP ports - the femtocell is simply treated as another VoIP priority input.This can prioritise the traffic within the domestic network (i.e. prioritise above other computers in the same house), but since the femtocell traffic is securely encapsulated in an IPsec tunnel, it can't easily be distinguished (and prioritised) by the ISP.

b) Use loss-tolerant voice codecs: Where voice codecs have been designed for use in situations with poor quality in mind, this may compensate for packet loss or delay. Mobile phone codecs have been designed for poor radio links, although some of the protection is built into the underlying radio bearer protocols rather than just the voice codec itself and so wouldn't apply for its journey over the wireline IP network.

c) Prioritise all traffic: We are likely to see wireline broadband providers charge extra for handline premium traffic in the future. Todays tariff plans for broadband seem to be differentiated mostly by the volume of data per month and/or the peak data rate. Those wanting higher dat rates and/or priority typically pay a higher price. My own ISP offers a $15/month premium option where all my traffic is prioritised - this is aimed more at businesses, and ensures that VoIP calls are all of high quality and that web browsing and streaming are much more responsive. Whilst its still best-effort to some extent (if everyone took out premium service, we'd all continue to share the same contention problems), this would be an immediate solution to my quality problems.

Looking further ahead, I've seen suggestions for IMS controlled networks that offer up to 8 classes of traffic handling, ranging from VoIP and video streaming through to best effort peer to peer filesharing. Femtocells could setup sessions to the femto gateway using IMS, with a higher priority to ensure high voice quality.

Summary 

I suspect that where femtocells are offered by networks who own or can agree priority traffic handling for voice call traffic, then this capability will improve the customer experience in congested networks. This may require the ISPs to implement some changes in their networks. Simply relying on best effort traffic handling may work in most cases, and will be better than some VoIP services. Given the high quality of the radio connection achieved by a domestic femtocell, it would be a shame to see the end user experience degraded in this way. More results from field trials are required to

 

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