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DiffServ is an abbreviation for differentiated services, which is a network management system. Differentiated service allows users to set up a system of classes and mark their network information based on content. Routers using DiffServ protocols then arrange those packets based on their markings. Some packets, such as voice transmissions, have a higher priority and will always go through immediately. Other packets are held for later transmission or dropped entirely.
Information sent over a standard network is divided into packets. Each of these packets contains a small portion of the total information. One computer takes the information and divides it into packets containing the information, its network address and the address where is it going. This information is sent in rapid pulses across the network or over the Internet. When it gets where it’s going, the receiving computer reassembles the packets into the original data.
A DiffServ system adds an additional marker to the packets when they are first made. This marker designates the packet based on pre-defined characteristics. These characteristics are devised by the user and may be anything from the content of the information to its associated addresses. These markers are used to assure users that certain information will always have priority over others.
Any system that is able to handle DiffServ packets may make judgments on the importance of packets as they travel over the network. When a group of packets enters the differentiated services router, it looks at the individual markers and prioritizes them based on the user-defined listings. The packets then move through in order of priority. If more high-priority packets come into the system, lower-priority packets keep being pushed back.
In general, a DiffServ system guarantees the proper and timely delivery of one or two types of data, or two markers, and the best effort on the rest. This means that one or two types of marked packets will arrive on time and in order without fail, but other packets may not. In networking, best effort means that the system will do its best to move the information, but it won’t guarantee anything. The packets may arrive slowly or may never transmit at all.
This is one of the largest drawbacks to DiffServ. When packets are held up, it can cause a lot of problems on both ends of the system. If the packets arrive corrupted or out of order, the receiving computer will have to request the information again. This request makes the sending computer send out all the necessary information again, effectively doubling the amount of low-priority information being sent. This increases used bandwidth on both ends with no guarantee that the second transmission will work.