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QoS prioritizes certain types of traffic over packet switched networks, using resource reservation control mechanisms to ensure each technology gets the bandwidth it needs. Queuing is used to handle congestion, with FIFO and priority queuing being common types. QoS is becoming increasingly important as networks handle multiple types of traffic.
Quality of Service or QoS is a method of providing better service for selected types of traffic over various types of packet switched networks. The network medium used could be any of several types of technology ranging from Ethernet networks to Wireless and Frame Relay networks. QoS provides a method for determining which traffic should be prioritized on a network segment.
An example of an environment that uses QoS might be an Internet-based telephone system on an organization’s network. Let’s say an organization creates a packet switched network with ten computers using Ethernet as the 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 mostly of the same type. When the business decides to connect a new phone system to its network using Voice Over IP technology, QoS becomes a factor.
The primary function of QoS is to ensure that all technologies get the bandwidth they need to operate at the desired level. In this case, phones would get enough bandwidth to avoid choppy calls, and computers would get enough bandwidth to browse the Internet and perform tasks to avoid seeming slow to users.
QoS uses resource reservation control mechanisms to allow administrators to set a desired level of service for each type of traffic on the network. 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.
Computer networking technologies must also take into account factors such as congestion. When two users in the previous example are on the Internet and three phone calls come in, the network must be able to decide what to do with all the traffic that is routed to it. Many times a good portion of the traffic will be handled using a technology called queuing, which allows traffic to be stored until it can be processed, depending on the queuing method used. Think of queuing like this: Suppose there are five phone lines coming into your organization, but only two people available to take any call at any given time. A queuing system will receive all incoming calls and route two calls to available employees, while still handling the other calls.
Two of the common types of queuing used with QoS are FIFO (First in First Out) queuing and priority queuing. FIFO queuing allows the first traffic in queue to be the first traffic outgoing. In our telephone example, this would allow the third caller to be the next call even if the remaining two lines fill up. Priority queuing allows you to prioritize different types of traffic and allocate bandwidth to this traffic as the need increases.
If phone traffic is given a higher priority than data traffic in our organization, when employees start using the phone, the Internet will start to slow down for other users. Non-telephone traffic will be limited to allow telephone calls to have a better quality of service.
QoS and the need for technology to handle multiple types of traffic on the same network are growing and will become more common in the future.
