Mobile Phone Quality: It’s Not Just the Handset

By Charlie Baker

Director, Product Management

Brix Networks

As consumers, we tend to blame the poor sound quality we may encounter with our mobile phones on the phone itself. But, it takes a lot more than a high-quality handset to make a high-quality phone call.

Unlike the good ol’ days of always-available wireline service, our devices have been untethered from the network and rely on over-the-air radio transmissions to carry time-sensitive voice traffic. Add to this the transforming of voice calls into IP-routed traffic, microphones and speakers disconnected from the device via Bluetooth, high-bandwidth competition from e-mail, data, and video downloads, and multiple hand-offs between network elements, like routers, switches, and gateways, and you have a lot of places in the transaction where voice quality can  get degraded. 

At the same time, new converged services are being added to the mix. Comcast and Sprint recently announced their new “4-in-1” Pivot service, for example, which links your Sprint mobile phone to your Comcast digital services, such as high-speed Internet and mobile TV. And new similar converged services will continue to tax the bandwidth that network operators currently offer.

What is a network operator to do? Most are promoting quality based on the percent of dropped calls, network reliability, and the speed of their wireless cloud. But what really concerns them is providing the highest quality of experience (QoE) to a customer, no matter how that customer is accessing the network. While most operators have systems in place for measuring things like a handset’s RF signal strength, it’s not enough information to identify a host of other potentially damaging quality issues.

Much work is already being done behind the scenes to migrate infrastructure to higher bandwidth and higher speed connections to the base stations. Carriers are working hard to create and enforce service level agreements (SLAs) between network providers and network peers in order to measure the customer experience across the network. The goal is to proactively identify performance degradations before they impact users, satisfy contractual SLAs, and cost-effectively troubleshoot user-impacting problems when they do occur.

To this end, network operators who take quality seriously are rolling out converged service assurance solutions for voice that address the user’s QoE two different ways: passive (live) monitoring of traffic and active (on-demand) testing.

Passive monitoring assesses voice traffic across the network to discover quality trends before the problems become widespread. Active testing injects traffic between network segments to isolate disruptions before they affect the user's perceived voice quality.

In both testing approaches, the mobile handset is key to understanding voice quality issues. One passive monitoring approach is to deploy software agents on handsets to measure quality using measurement standards like a Mean Opinion Score (MOS), R-factor, echo, and jitter. But, agent technology requires handset manufacturers to install the operator’s software on every device they ship. This may be good for the operator, but it can be a pain for the manufacturer and thus a contract stumbling block.

A simpler passive alternative is for the handset manufacturer to adopt standard protocols, such as Request for Comments (RFC) 3611, RTP Control Protocol Extended Reports (RTCP-XR), which provides a way to measure and manage voice performance by reporting detailed RTP and VoIP metrics.

Operators can combine RTCP-XR with the SIP Service Quality Reporting Event, a draft standard specification popularly called the Johnson draft spec from the Internet Engineering Task Force (IETF). With these standards, operators can define a method for retrieving voice quality information at the end of every user’s call. The typical approach is to have a SIP message send quality metrics at the conclusion of a call to a service assurance system to correlate information across multiple points in the network and generate targeted reports on voice quality. While few operators are using SIP all the way to handsets today, they definitely will as they migrate towards IP Multimedia Subsystem–based (IMS-) networks. 

Adding another wrinkle to the wireless environment mix is the emerging picocell/femtocell market. Picocells are wireless communication devices that cover a small area, such as the home, through which mobile phone users can access the operator’s network wirelessly through their home broadband connection rather than over-the-air to the cell tower. It’s similar to a WiFi access point, but for mobile handsets, and operators such as Sprint and T-Mobile have already announced offerings.

Picocells will become another point in the network where operators will need to know about quality. Using the same passive agent or protocol-based approaches will enable operators to extend quality testing to another point in the network where their customers may experience voice quality issues.

The other approach is active (on-demand) testing. And here, too, standards are key enabling technologies. With active testing, an operator triggers a transaction to the user’s handset or picocell – completely undetectable by the user – to measure quality. Standards used by the operator and handset manufacturer include RTCP-XR, and the IETF drafts for SIP Media Loopback and the Two-Way Active Measurement (TWAMP) protocol. 

Typically, the operator deploys a service assurance appliance in the middle of its network. This appliance initiates a call to the customer’s device, with protocols looping the payload back to the appliance so that it can be measured.

The active testing approach enables operators to test devices across the network 24/7, and identifies potential problems before customers detect them and either call for assistance or return their equipment to the store.

The combination of active testing and passive monitoring provides carriers with visibility to service performance across their network, resulting in reduced truck rolls and tighter SLA enforcement, and gives consumers higher quality calls every time they dial. 

 Today, not everyone is confident enough to drop his or her landline completely. But, with great service assurance coverage, that day is rapidly approaching.

About the Author:

Charlie Baker is director, product management at Chelmsford, Mass.-based Brix Networks (www.brixnet.com).  He holds a Bachelor's of Science in Management from the United States Air Force Academy, and an MBA from Boston University