IntServ

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IntServ (Integrated Services) is a fine-grained Quality of Service (QoS) method for prioritizing IP data packets using a network scheduler . In contrast to the DiffServ method, the resources are requested for individual connections and not for traffic classes.

The Resource Reservation Protocol (RSVP) is used as the protocol for establishing the resource reservation . A router can keep records of its available capacities and respond to a request for QoS assurance with a positive or negative answer. In the event of a positive answer, the router guarantees compliance with the required characteristics for the entire duration of the session. Assurances once made must not be curtailed. In order to implement the prioritization, resources are reserved in each network element by means of a traffic contract with fixed parameters. Therefore, every node in the participating network (router, switches, etc.) must proceed according to the IntServ method and all available resources must be managed via it. IntServ places certain requirements on the network such as the maximum packet delay, bandwidth and resource reservation. Access management then takes place in accordance with the requirements made by the applications and the resources available. The specifications are signaled or exchanged using TSPEC (Traffic Descriptor) and RSPEC (Reservation Characteristics) in the TOS field (Type of Service) of the IP header ( IPv4 ). IntServ guarantees the QoS properties only as long as the applications send the data in accordance with the previously exchanged specifications.

The Intserv process knows two basic classes of service:

  • Guaranteed QoS (guaranteed quality of service) offers a guaranteed transmission rate and a quantitative statement about the maximum delay caused by queues in the network. It is also guaranteed that no packets are lost due to queues that are too full.
  • Controlled Load only makes the promise that a very large part of the incoming packets will not be discarded by the router and that the delay caused by the queue is close to zero. However, no precise commitments are expressed in numbers.

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