TECHNIQUES OF ACHIEVING GOOD QUALITY OF SERVICESATYA PRAKASH JOSHI

QOS

• Quality of service (QoS) is the overall performance of a telephony or computer network, particularly the performance seen by the users of the network.• QoS considered, such as error rates, bit

rate, throughput, transmission delay, relaibilty, jitter, etc.

RELIABILITY

• Lack of reliability means losing a packet or acknowledgement, entails retransmission. • How ever sensitivity of all application

program not same. i.e email, file transfer, and internet access have reliable transmission than telephony and audio conferencing.

DELAY

• Source to destination delay is another flow characteristics.• In this case telephony, audio conferencing,

video conferencing, and remote login need minimum delay While in file transfer or email Is less importance.

JITTER

• Jitter is the variation in delay for packets belonging to the same flow. High jitter means the different between delays is large; low jitter means the variation is small.

OVER-PROVISIONING

• An alternative to complex QoS control mechanisms is to provide high quality communication by generously over-provisioning a network so that capacity is based on peak traffic load estimates. • This approach is simple for networks with

predictable peak loads. The performance is reasonable for many applications. 

• This might include demanding applications that can compensate for variations in bandwidth and delay with large receive buffers, which is often possible for example in video streaming.

TRAFFIC SHAPING

• It is the mechanism to control the amount and the rate of the traffic sent to the network.

• The rate at which water leaks from a bucket does not depend on the rate at which the water is input to the bucket • The input rate varies but the output remains

constant, similarly, network can smooth out burst traffic.

TOKEN BUCKET

• Leaky bucket does not taken into account idle host, if a host is not sending for a while , it’s buckets becomes empty• If the host has bursty data, leaky buckets allows only

average rate. • Token bucket takes into account the idle time with each

clock tick the token are added to bucket, when the data needs to be send, it collects token from bucket and then send the data packets consisting of data = no of tokens.

BUFFRING• Multimedia data are large in size and reside on disks. • When users retrieve large multimedia data, in-

memory buffers are used to reduce the number of disk I/Os, since memory is significantly faster than disk. The problem to be studied is to efficiently make use of buffers in the multimedia system to reduce the number of I/Os in order to get a better performance when multiple users are retrieving multiple multimedia data simultaneously. • Existing works on multimedia data buffering focus on

either the replacement algorithms to lower the number of cache misses or the buffer sharing algorithms when many simultaneous clients reference the same data item in memory