What is QoS?

Quality of Service or QoS is a method of providing better service for selected types of traffic on various types of packet-switched networks. The network medium used can be any of several types of technology, from Ethernet to wireless networks and Frame Relay. QoS provides a method for determining which traffic should have priority on a network segment.

Quality of service provides better service for selected types of traffic on various types of packet-switched networks.

An example of an environment that uses QoS would be an Internet-based phone system on an organization’s network. Suppose an organization creates a packet-switched network with ten computers using Ethernet as a backbone. The company then connects a router and other hardware to connect to the public Internet.

QoS is not really affected by this scenario, because all traffic is basically the same type. When a company decides to attach a new phone system to its network using Voice Over IP technology, QoS becomes a factor.

The main function of QoS is to ensure that all technologies get the bandwidth they need to function at the desired level. In this case, the phones would be getting enough bandwidth to avoid choppy calls and the computers would be getting enough bandwidth to browse the internet and perform tasks to avoid appearing slow to their users.

QoS employs resource reservation control mechanisms to allow administrators to define a desired level of service for each type of network traffic. By allowing phone traffic to have a higher QoS than internet traffic, there will be much less interference when using the phone because the network will anticipate phone calls and adjust bandwidth to all devices accordingly.

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Computer networking technologies must also account for things like congestion. When two users in the example above are on the Internet and three phone calls are received, the network must be able to decide what to do with all the traffic being directed to it. Often a good deal of traffic will be handled by a technology called queuing, which allows traffic to be stored until it can be processed, depending on the queuing method used. Think of queues like this: Suppose there are five phone lines coming into the organization, but only two people are available to answer any call at any given time. A queuing system would receive all incoming calls and route two calls to available employees, while continuing to handle the other calls.

Two of the common queuing types used with QoS are first-in-first-out (FIFO) queuing and priority queuing. The FIFO queue allows the first traffic in the queue to be the first to leave. In our telephone example, this would allow the third caller to be the next call answered, even if the remaining two lines become full. Priority queuing allows different types of traffic to be assigned priority and bandwidth assigned to that traffic as the need increases.

If telephony traffic has a higher priority than data traffic in our organization, as employees start using the phone, the Internet will start to slow down for other users. Non-telephone traffic will be restricted to allow for better quality of service for telephone calls.

QoS and the need for technology to manage multiple traffic types on the same network are growing and will become more commonplace in the future.

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