Quality of Service
QOS = Method of giving priority to some specific traffic as moving over the network.
The basic aim of QoS is to have a consistent and predictable performance on your network.
General characteristics of today’s Converged Network:
- Small voice packet compete with bursty data packets, many different applications are using network as services
- Critical traffic must get priority over less critical traffic, without QoS, default behavior is First In First Out (FIFO)
- Voice and video traffics are time-sensitive
- Outages are not acceptable
Converged Network Quality issues:
- Lack of Bandwidth
- Packet Loss
- Maximum available bandwidth is the slowest link on the traffic paths
- On the same physical links (traffic paths), multiple flows compete for the same bandwidth, multiple applications sharing the same bandwidth
- Lack of bandwidth causes performance degradation on network applications
Packet loss due to Tail Drop: Queue only can so much packets and once it is full and more packets arrive at the tail end of the queue before the queue is emptied (due to link congestion etc.), the packets will be dropped, and this behavior is called ‘Tail Drop’. If the tail drop occurs to the time sensitive traffics such as voice and video, the effects are immediately felt by the users on the flow. If this happens to data traffic, it may interrupt file transfer and corrupt the file.
- Processing Delay – time taken by router to process packets from an input interface and put them into the output queue of output interface
- Queuing Delay – time a packet resides in the output queue of a router
- Serialization Delay – time taken to place bits on the wire
- Propagation Delay – time taken for packets to cross links from one end to the other end
- Packets from a source will reach a destination with different delay times
- Congestion on the network will cause jitter
- Congestion can occur at a router interface/Service Provider network if the circuits are not properly provisioned