Canonical URL: ; File formats: Plain Text PDF Discuss this RFC: Send questions or comments to [email protected] Differentiated services or DiffServ is a computer networking architecture that specifies a simple In December , the IETF published RFC – Definition of the Differentiated services field (DS field) in the IPv4 and IPv6 headers, which. The type of service (ToS) field is the second byte of the IPv4 header. It has had various In RFC the definition of this entire field was changed. It is now.

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These characteristics are suitable for voice, video and other realtime services. This means that in the core of the Internet, routers are unhindered by the complexities of collecting jetf or enforcing agreements.

Under DiffServ, all the policing and classifying is done at the boundaries between DiffServ domains. From Wikipedia, the free encyclopedia.

In practice, however, most networks use the following commonly defined per-hop 24474. Assured forwarding allows the operator to provide assurance of delivery as long as the traffic does not exceed some subscribed rate. By using this site, you agree to the Terms of Use and Privacy Policy.

Let’s start with an IP priority of 1, or 0b in Binary. Retrieved from ” https: The problem addressed by DiffServ does not exist in a system that has enough capacity to carry all traffic. Many of the proposed QoS mechanisms that allowed these services to co-exist were both complex and failed to scale to meet the demands of the public Internet.

Core routers simply apply PHB treatment to packets based on their markings. The naming here follow the convention of Unix operating systems. In theory, a network could have up to 64 different traffic classes using the 64 available DSCP values.


The AF behavior group defines four separate AF classes where all have the same priority. A traffic classifier may inspect many different parameters in incoming packets, such as source address, destination address or traffic type and assign individual packets to a specific traffic class.

Should congestion occur between classes, the traffic in the higher class is given priority. Rather than differentiating network traffic based on the requirements of an individual flow, DiffServ operates on the principle of traffic classificationplacing each data packet into one of a limited number of traffic classes.

A group rfv routers that implement common, administratively defined DiffServ policies are referred to as a DiffServ domain. Each router on the ketf is then configured to differentiate traffic based on its class. However, a great deal of experimental, research, and deployment work has focused on how to make use of these eight bits, resulting in the current DS field definition. Pages using RFC magic links.

Based on these ToS values, a packet would be placed in a prioritized outgoing queue, [2] or take a route with appropriate latency, throughput, or reliability.

The standard traffic classes discussed ffc serve to simplify interoperability between different networks and different vendors’ equipment. From a commercial viewpoint this means that it is impossible to sell different classes of end-to-end connectivity to end users, as one provider’s Gold packet may be another’s Bronze.

Differentiated services

Views Read Edit View history. Ketf from ” https: Essentially, any traffic that does not meet the requirements of any of the other defined classes uses DF. A Bandwidth Broker in the framework of DiffServ is an agent that has some knowledge of an organization’s priorities and policies and allocates bandwidth with respect to those policies.

The Class Selector code points are of the binary form ‘xxx’.

IETF standards compliance for IntServ and DiffServ models

Each IP precedence value can be mapped into a DiffServ class. By marking the packets, the sender indicates that it wants the packets to be treated as a specific service, but it can only hope that this happens.


This article is about communication networks. It is up to all the service providers and their routers in the path to ensure that their policies will take care of the packets in an appropriate fashion. Some measure of priority and proportional fairness is defined between traffic in different classes.

DiffServ simply provides a framework to allow classification and differentiated treatment. The premise of Diffserv is that complicated functions such as packet classification and policing can be carried out at the edge of the network by edge routers. If a router is congested and needs to discard some packets, it will discard packets having lowest priority first. If a 2447 is received from a non-DiffServ aware router that used IP precedence markings, the DiffServ router can still understand the encoding as a Class Selector code point.

This page was last edited on 24 Decemberat This is complicated further if a packet crosses two or more DiffServ domains before reaching its destination.

EF traffic is often given strict priority queuing above all other traffic classes. Within each class, packets are given a drop precedence high, medium or low, where higher precedence means more dropping. PHB treatment is achieved by core routers using a combination of scheduling policy and queue management policy. This page was last edited on 22 Decemberat RFC introduced an additional “lowcost” field. Rather than using strict priority queuing, more balanced queue servicing algorithms such as fair queuing or weighted fair queuing WFQ are likely to be used.

Different PHBs may be defined to offer, for example, low-loss or low-latency service.