QUALITY OF SERVICE (QOS)
In 1994, International Telecommunication Union defined Quality of service in the field of telephony. It comprises of services like response time , signal to noise ratio, cross talk, loudness levels etc.Quality of service is the ability to provide different priorities to different applications , users and data flow or to guarantee a certain level of performance to the data flow. This can be explained as a required bit rate, jitter and delay etc may be guaranteed.
HISTORY—conventional internet resources and LAN switches operate on a best effort basis because this equipment is less expensive, less complex and faster thus more popular than the complex ones offering QOS. There are 4 type of service bits and three precedence bits added in each IP packet header but it is not respected. These bits are later redefined as differential services code points (DSCP) and are used in modern internet. With the adventure of IPTV and IP telephony QOS is available to the users. In ethernet, VLAN virtual local area networks may be used to differentiate different QOS levels. One VLAN may be used for internet access (low priority), one for IP t.v (high priority) and IP telephony (high priority).In packet switched networks quality of service is affected by many factors which includes both human and technical factors.Human factors are stability of service, availability of service and user information.Technical factors include relaibilty, effectiveness and maintainability.
APPLICATIONS:
- Streaming media specially IPTV(internet protocol television), audio over ethernet and audio over IP.
- IP telephony ( voice over IP)
- Video conferencing
- Ethernet/ Ip
END TO END QOS:
It can require a method of coordinating resoure allocation between. One autonomous system and the other. The Internet Engineering Task Force defined the resourse reservation protocolfor bandwidth reservation, as proposed standard in 1997. RSVP is an end to end reservation protocol.
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