Differentiated Services

Differentiated Services (DiffServ or DS) provide a method that attempts to guarantee quality of service in large networks, such as the Internet.

To provide this quality of service, IP packets are classified into different classes based on different QoS terms that will have special relevance for the connection. Example: packets used in streaming transmissions of multimedia content, which will require a low packet loss ratio and latency, and will be classified under the EF PHB (Expedited Forwarding) category.

To specify the class of each packet, 6 bits are used, entered in specific fields, which are:

• For IPv4: The old 8-bit TOS field is used, being the first six for DS, and the last two for ECN (Explicit Congestion Notification, identifier to detect network congestion without using specific packages for it).

• For IPv6: A specific field is used for this called the 8-bit Traffic Class, the first six for DS, and the last two for ECN.

Differentiated Services analyzes multiple data streams instead of single connections or resource pools. This means that a negotiation will be made for all packages sent by an organization, whether it is a university, an Internet service provider or a company. The contracts resulting from those negotiations are called Service Level Agreements (SLAs), and they inevitably involve an onerous exchange. These SLAs specify what classes of traffic will be provided, what guarantees are given for each class, and how much data is considered for each class.