What is QUALITY OF SERVICE (QOS) in Telecommunications

               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:

1. Streaming media specially  IPTV(internet protocol television), audio over ethernet and audio over IP.
2. IP telephony ( voice over IP)
3. Video conferencing
4. 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.

4G systems - What is 4G LTE Technology

4G systems was originally visioned by Defence Advanced Research Projects Agency  (DARPA). The DARPA selected the distributed architecture and end to end internet protocol (IP). They believed in an early age, in peer to peer networking in which every mobile device would be both a transreceiver and a router for other devices in the network ,this eliminates the need of spoke and the hub which are the weakness of  2g and 3g cellular systems. 

The traditional voice calling is replaced by IP telephony in 4g systems. The  specifications of 4G named as International Mobile Technology Advanced (IMT-A) was proposed by International Telecommunication Union Radio (ITU-R). The main aim of developing this technology is  speed requirements of 100 mbps for high mobility such as users in trains and a speed of 1 gbps for stationary users. The basic idea behind 4G is to use only packet switching and internet protocol based communication. 

The spread spectrum technique which is used in 3G is replaced by OFDMA in order to achieve desired speed.In order to fulfill these requirements pre 4G was launched which are the technologies named as LTE and wimax. The 1st vision of 4g with ITU was laid in 2002.  In 2008, HTC announced first Wimax enable mobile as MAX 4G. Unfortunately, these technologies are not able to meet the requirements of 4g as desired. 

In feb 2007, NTT DOCOMO the japanese company tested 4g and was able to achieve maximum packet transmission at a rate of 5gbps.  LTE advanced offering a downloading speed of 1 gbps and uploading speed of 500 mbps. In April 2012, Bharti Airtel is the company which successfully launched 4G first time in India. In dec 2012, telcel launched 4G LTE in nine  major cities of Mexico.