Clicks, Pops, and Dropouts: VoIP Quality of Service Issues

The quality and clarity of properly designed and configured VoIP service is indistinguishable from that of traditional wire line service. There are, however, a number of issues that can cause VoIP quality to deteriorate to the level of cellular service in a fringe area – noise, loss of portions of conversation, and disconnects. Fortunately, there are reasonable solutions for these problems.

The primary cause of VoIP quality problems is a lack of adequate bandwidth required for the service to perform properly. Internet calls require approximately 30 kilobits per second of bandwidth while faxes require around 80 kilobits per second. There are three areas where bandwidth constrictions are likely to occur: on the customer premise, in the “last mile” (the connection between the customer’s location and the Internet service provider’s (ISP) equipment location), and the connection from the ISP to the Internet.

The cause of bandwidth restrictions on customer premises differs significantly between residential customers and business customers. Residential VoIP applications are dependent on “statistical” bandwidth availability - most of the time there will be adequate bandwidth for telephone conversations. Certain applications, such as downloading large files, streaming audio or video, and automatic updates for software may consume enough bandwidth to cause deterioration in VoIP quality. You may want to refrain from watching the latest Paris Hilton hamburger video while talking to your friends. While bandwidth issues for very small business customers are much the same as those of residential customers, the problems for medium and large businesses are more complex and difficult to manage. Bandwidth restrictions for these customers can be associated with application issues, LAN capacity, design issues, and management issues. All of these issues can be successfully resolved as long as the customer’s IT organization has a good understanding of the VoIP application and has the time and resources to devote to it. If your IT resources are stretched to the limit, it may be advisable to stay with more traditional communications technologies. Finally, undetected viruses and worms may disrupt VoIP services for both residential and business customers. It is a good practice to update your operating system, applications and virus blocker with the latest security patches before implementing VoIP.

“Last mile” bandwidth constraints for residential and very small business customers generally originate with the technology being employed and are aggravated by design and deployment issues. The ADSL technology deployed by many telephone companies for residential customers is much more problematic for use with VoIP than cable based Internet access. There are two reasons for this: first, the bandwidth available with ADSL is generally less than that available with cable, and second, the available bandwidth drops off significantly with distance from the telephone company’s central office. “Last mile” VoIP issues are best addressed by using cable or “fiber to the home” service for residential and very small business customers. Medium and large businesses have fewer last mile problems because they generally use a dedicated 1.5 megabit per second T1 to connect to the Internet.

The final are prone to bandwidth constriction is the connection from the ISP to the Internet. This problem can happen with all access technologies (ADSL, cable, and dedicated T1s) but is less likely with large ISPs and Tier 1 carriers who have the funds and engineering resources to properly size their Internet connections. The problem is more likely with “mom and pop” ISPs because these companies sometimes overload their connections to the Internet in order to offer low prices.

VoIP service is more sensitive to bandwidth restrictions than most applications. You can assure service quality by properly managing your computing environment, choosing an appropriate access technology, and using a large ISP or Tier 1 carrier to provide your Internet access.

David Hughart
VoIP Article #2 (Bus. & Res. QOS)
July 5, 2005