When it comes to IP telephony, a little quality control goes a long way.

me type of intelligent controls in the network, all traffic will receive equal delivery treatment, and voice and data traffic could compete with and undermine each other. For a long time, IP telephony (IPT) was held back by the fear that large voice packets would overwhelm the capacity of data networks and unruly data traffic would impede delay-sensitive voice traffic.

That changed with the emergence of Quality of Service (abbreviated in technical circles as "QoS"), which are standard-based tools or mechanisms designed to eliminate conflicts in network transmissions.

Companies need to apply Quality of Service to intelligently identify and route traffic based on its priority. By guaranteeing that voice traffic gets the bandwidth it needs, Quality of Service helps ensure good voice quality in your business's telecommunications. Here's how.

1. Quality of Service provides the "smarts" across the network.

A Quality of Service solution is not implemented in a single device. In order to work effectively, all of the equipment that has a role in forwarding traffic through the network (for example, routers and switches) should support Quality of Service.

Even more importantly, these different network components must have the same understanding of how traffic is to be classified and prioritized. Otherwise there will be a breakdown in communication — and probable congestion — somewhere in the system. Fortunately, industry standards from groups like the Internet Engineering Task Force (IETF) help devices talk a common Quality of Service language.

2. Quality of Service takes a holistic approach.

Quality of Service is mainly a set of techniques that manages different conditions in any transmission "pipe" or line, including:

• Bandwidth (the "width" of the pipe)
• Delay (the "length" of the pipe)
• Jitter (the "variation in the length" of the pipe)
• Packet loss (the "leakage" in the pipe)

The performance of any application depends on how much it gets or experiences in the way of bandwidth, delay, jitter, and packet loss. Therefore, in Quality of Service, the goal is to manage each of these conditions by:

• Prioritizing one type of traffic over another.
• Preventing or delaying the transmission of low-priority traffic, as needed, to avoid network congestion.
• Controlling the rate at which individual application streams transmit their packets.

Traffic is prioritized based on the application's importance to the company's business. "Packetized" voice traffic, for example, must be guaranteed bandwidth because a voice connection can be annoyingly poor or totally incomprehensible if it is subjected to too much delay, jitter, or packet loss.

Quality of Service is a team effort

In addition to different network devices working cooperatively, Quality of Service is also about different Quality of Service mechanisms working cooperatively. Different types of applications require different Quality of Service techniques.

In addition, different Quality of Service mechanisms are applied at different points in the packets' journey through the network. For example, packets are classified and marked, then shaped or policed, and finally queued or dropped depending on their priority.

Mechanisms can also be used in combination. For example, congestion avoidance and congestion management can be used in combination to give preference to high-priority flows while regulating low-priority flows so they slow down.

Quality of Service mechanisms generally perform one of the following functions:

• Packet classification, a way to recognize application packets moving across a network.
• Marking, which utilizes classification data to tell network equipment how to handle packets.
• Enforcement, which establishes policing schemes that establish and ensure different classes of service.

Quality of Service is a multidimensional tool

The benefits of Quality of Service are as multidimensional as the mechanisms available to implement it.

A good end-to-end Quality of Service monitoring and enforcement solution also provides insights into who is using the network, when, and with what types of traffic, and can contribute to security by helping protect against denial of service attacks.

Most of all, Quality of Service is the key to getting maximum return from network resources and maximum productivity from applications.