QOS

 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


When there is no QOS the process implemented is First in First out ie whichever traffic comes in first goes out first.


Congestion occurs when the rate of incoming traffic is more then the rate of egress traffic, congestion leads to delay, jitter and packet loss.


Delay:- Delay is caused by the latency in the network.

Serialization /transmission

􀂃 Queuing delay is the time a packet spends at a queuing point before it is processed or forwarded. Queuing occurs

when the router experiences congestion. Packets may be queued both at the ingress and egress of a router. Queue

delay is proportional to the size of the buffer and is thus variable.

􀂃 Processing delay is the amount of time taken by the router to perform forwarding table lookups, encapsulation,

and any other packet manipulation required, before sending the packet to the egress port.

􀂃 Propagation delay is the time it takes for a packet (signal) to travel across a link (wire) from one router to another.

It is dependent on the characteristics of the transmission media (different media have different propagation

speeds) and the distance between the routers.

Jitter is the variation in the delay

There are two types of Jitter

Positive Jitter

Negative Jitter

Negative jitter signifies that packets are not transmitted out the router at the expected intervals. It can be the result

of significant queuing.

Positive jitter signifies that packets are transmitted “clumped” together, with a smaller than expected intervals

between them. It can result when packets that have been queued together are subsequently transmitted together.

Packet loss

packet corruption (unknown packets are often dropped). It can also result from faulty equipment or signal degradation

on the network media


QOS models:-

There are two services involved

Integrated Services(Inet Serv):- This model is not widely used as it treats each flows separately. This is extremely granular however it increases the load on the nodes. The protocol which is used is RSVP which reserves the resources in each and every node.

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