One way to improve the quality of service is to reduce the overall delay. This can be done in two ways:
- Design the network structure in such a way that the delay in it is minimal;
- Reduce the processing time in the gateway.
The first way is realized by reducing the number of transit sections between the routers, and in high-traffic areas use high-speed channels. If it is necessary to reduce the spread of delays, then it is necessary to use effective methods of traffic management, for example, reservation mechanisms.
In IP networks, the information is transmitted on the principle of “best effort” (regardless of the type of information). In this model, all available network resources are used without the allocation of separate traffic classes and regulation. It is believed that the best mechanism for providing QoS is to increase throughput. The Best Effort Service model, even with large reserves, allows overloading in the event of sudden surges of traffic.
Integrated Service (IntServ)
Integrated Service (Integrated Service) is divided into two types of guaranteed level of service:
- with controlled loading;
- with guaranteed service.
Required elements located in each node that supports IntServ:
- Classifier – it sends all incoming packets to one of the classes of service based on the information in the package. The service class is implemented as a separate queue. Packages that are within the same class of service should receive the same QoS;
- the package manager – extracts from each queue the packets and sends them to the link layer;
- Access control unit – makes decisions about the possibility of receiving the required amount of traffic-by-traffic, without affecting the previously provided guarantees. Access control is performed on each node to accept or reject a resource allocation request along the entire flow path;
- Resource reservation protocol (RSVP) – Informs the connection participants (sender, recipient, intermediate routers) about the required service parameters.
The most significant disadvantage of IntServ is related to the scalability of RSVP, especially in high-speed backbone networks. RSVP provides redundancy for only one information stream.
Differentiated Service (DiffServ)
The Differentiated Service model has a high scalability in packet networks. For this reason, this model has a place on the backbone and high-speed sections of the network. DiffServ provides non-protocol-based QoS parameters, but based on the requirements of different user groups, differentiating traffic by the established class number. Such a mechanism reduces the amount of overhead information in comparison with the IntServ architecture.
The DiffServ model supports the following services:
- guaranteed service;
- service with preference;
- service with maximum effort.
The disadvantage of this model is that, despite the high priority, the data can still be subject to unpredictable delays in case of network overload.
Integrated Service Operation over Differentiated Service Networks (Int-DiffServ)
This model describes the principles of organizing the interaction between IntServ and DiffServ to provide the required level of service. This is achieved due to the fact that the weaknesses of one model are compensated by the corresponding solutions of the other. On the one hand, a simpler DiffServ can replace poorly scalable IntServ on backbone sections of the network; on the other hand, using RSVP can solve the problem with the uncertainty of the received service in the DiffServ network.
In MPLS-networks on the basis of labels, transmission with a quality of service quality of the network (QoS) is conveniently implemented. Within the MPLS domain, the transmission of various data streams is absolutely safe because of its clear logical separation. To increase the reliability in MPLS technology, Fast Reroute and LSP Protection functions are implemented that allow creating duplicate switching routes in advance and in case of failure of the main path to switch to a backup route without loss of transmitted data.
The introduction and maintenance of MPLS networks are more unified and simplified compared to conventional IP networks through the use of LDP and RSVP. The first of them is intended for automatic routing of new paths in the MPLS-domain. The RSVP protocol allows you to manage the allocation of bandwidth between virtual channels on the network, providing a guaranteed required level of quality of service.