Quality of Service (QoS) refers to the ability of a network to provide higher priority services, including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics, to selected network traffic over various WAN, LAN and Man technologies. At the same time, making sure that providing priority for one class of traffic does not make other flows fail.
Typically, there are three levels / classes of QoS:
- Best-effort servicebasic connectivity with no guarantees of traffic delivery, and speed and order of delivery.
- Differentiated service (Class of Service) - Some traffic is treated better than the rest (faster handling, more average bandwidth, and lower average loss rate). This is a statistical preference, not guaranteed service, which is typically provided by classification of traffic.
- Guaranteed service -This is an absolute reservation of network resources for specific traffic. This is provided through QoS tools RSVP in the packet network. The traditional PSTN network uses circuit switch with guaranteed link connection and bandwidth allocation to ensure QoS.
QoS technologies covers the following three areas:
- QoS identification and marking techniques for coordinating QoS from end to end between network elements, which is accomplished through packet/traffic classification and bandwidth reservation. Common methods of identifying flows include access control lists (ACLs), policy-based routing, committed access rate (CAR), and network-based application recognition (NBAR).
- QoS within a single network element: which includes technologies of congestion management, queue management, link efficiency, and shaping/policing tools provide QoS within a single network element.
- QoS policy, management, and accounting functions to control and administer end-to-end traffic across a network: this includes baseline the network with devices such as RMON probes, Deploy QoS techniques when the traffic characteristics have been obtained and an application(s) has been targeted for increased QoS and Evaluate the results by testing the response of the targeted applications to see whether the QoS goals have been reached.
QoS: Quality of Service
Related Terms: CoS (Class of Service), Traffic Management, Service Level Agreement
Reference Links: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/qos.htm: Quality of Service