Best-Effort Service Model; Intserv Service Model; Diffserv Service Model; Qos Techniques Overview - 3Com S7906E Configuration Manual

Best-Effort Service Model

Best effort is a single service model and also the simplest service model. In the best effort service
model, the network delivers the packets at its best effort but does not guarantee delay or reliability.
The best-effort service model is the default model in the Internet and is applicable to most network
applications. It is implemented through FIFO queuing.

IntServ Service Model

IntServ is a multiple services model that can accommodate multiple QoS requirements. In this model,
an application must request a specific kind of service from the network before it can send data. The
request is made by RSVP signaling. RSVP runs on each device from the source end to the destination
end, and monitors each data flow to prevent each data flow from consuming more resources than the
requested, reserved, and pre-purchased resources. The Inter-Serv model can definitely identify and
guarantee QoS for each data flow, and provides the most granularly differentiated QoS.
However, the Inter-Serv model imposes extremely high requirements on devices. In a network with
heavy data traffic, the Inter-Serv model imposes very great pressure on the storage and processing
capabilities of devices. On the other hand, the Inter-Serv model is poor in scalability, and therefore, it is
hard to be deployed in the core Internet network.
For more information about RSVP, refer to MPLS TE Configuration in the MPLS Volume.

DiffServ Service Model

DiffServ is a multiple services model that can satisfy diverse QoS requirements. Unlike IntServ, DiffServ
does not require an application to signal the network to reserve resources before sending data. DiffServ
is easy to implement and extend.
All QoS techniques mentioned in this document are based on the Diff-Serv model.

QoS Techniques Overview

The QoS techniques include traffic classification, traffic policing, traffic shaping, line rate, congestion
management, and congestion avoidance. The following part briefly introduces these QoS techniques.
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