In the field of computer networking and other packet-switched telecommunication networks, the traffic engineering term quality of service (QoS) refers to resource reservation control mechanisms rather than the achieved service quality. Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. For example, a required bit rate, delay, jitter, packet dropping probability and/or bit error rate may be guaranteed. Quality of service guarantees are important if the network capacity is insufficient, especially for real-time streaming multimedia applications such as voice over IP, online games and IP-TV, since these often require fixed bit rate and are delay sensitive, and in networks where the capacity is a limited resource, for example in cellular data communication.
3.1.1 INTEGRATED SERVICES
In computer networking, IntServ or integrated services is an architecture that specifies the elements to guarantee quality of service (QoS) on networks. IntServ can for example be used to allow video and sound to reach the receiver without interruption. IntServ specifies a fine-grained QoS system, which is often contrasted with DiffServ’s coarse-grained control system.The idea of IntServ is that every router in the system implements IntServ, and every application that requires some kind of guarantees has to make an individual reservation.
The IntServ architecture model (RFC 1633, June 1994) was motivated by the needs of real-time applications such as remote video, multimedia conferencing, visualization, and virtual reality. It provides a way to deliver the end-to-end Quality of Service (QoS) that real-time applications require by explicitly managing network resources to provide QoS to specific user packet streams (flows). It uses “resource reservation” and “admission control” mechanisms as key building blocks to establish and maintain QoS.
IntServ uses Resource Reservation Protocol (RSVP) to explicitly signal the QoS needs of an application’s traffic along the devices in the end-to-end path through the network. If every network device along the path can reserve the necessary bandwidth, the originating application can begin transmitting.
3.1.2 DIFFERENTIATED SERVICES
The second and currently accepted approach is “Diff Serv” or differentiated services. In the DiffServ model, packets are marked according to the type of service they need. Routers supporting DiffServ use multiple queues for packets awaiting transmission from bandwidth constrained (e.g., wide area) interfaces. Router vendors provide different capabilities for configuring this behavior, to include the number of queues supported, the relative priorities of queues, and bandwidth reserved for each queue.
Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying, managing network traffic and providing Quality of Service (QoS) guarantees on modern IP networks. DiffServ , for example, can be used to provide low-latency to critical network traffic such as voice or video while providing simple best-effort traffic guarantees to non-critical services such as web traffic or file transfers.
DiffServ operates on the principle of traffic classification, where each data packet is placed into a limited number of traffic classes, rather than differentiating network traffic based on the requirements of an individual flow. Each router on the network is configured to differentiate traffic based on its class. Each traffic class can be managed differently, ensuring preferential treatment for higher-priority traffic on the network.
One advantage of DiffServ is that all the policing and classifying is done at the boundaries between DiffServ clouds. This means that in the core of the Internet, routers can get on with doing the job of routing, and not care about the complexities of collecting payment or enforcing agreements. That is, DiffServ requires no advance setup, no reservation, and no time-consuming end-to-end negotiation for each flow, as with integrated services. This leads DiffServ services to be relatively easy to implement.
SELF ASSESSMENT EXERCISE
What are the difference between the Integrated and Differentiated Services?
Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. It is important to note that IntServ specifies a fine-grained QoS system, which is often contrasted with DiffServ’s coarse-grained control system.
This unit provided an overview of the Quality of Service in Multimedia technology. It highlighted the two types of services available which are the IntServ and the DiffServ. We hope you found this unit enlightening.
6.0 TUTOR MARKED ASSIGNMENT
1).Give a concise definition of Quality of Service (Qos)
2). List at least 4 features each of the Integrated Service and the differentiated Service.
3).What is the relevance of QoS in Multimedia Technology