Teletraffic Engineering

Today I’m going to explain some important words and their definitions in Tele-traffic engineering. These terms are very important and extremely useful when calculating offered traffic in a trunk or getting calculations.

Congestion

Congestion occurs when the number of packets being transmitted through the network approaches the packet handling capacity of the network. Most networks starts dropping packets when they are overloaded and this phenomenon is called congestion.

Networks provide congestion –control mechanism to prevent this problem. Congestion control aims to keep number of packets below a level at which performance falls off dramatically.

The congestion in the packet switching network appears due to packet handling capacity of the network while transmission of the packets. When too many packets are present in the subnet the performance get reduced. Most networks start dropping packets when they are overloaded. It happens when packet arrival rate exceeds the outgoing link capacity. This is this is called congestion in handling of packets.

  

Choke packets

Choke packets refer to the packets sent to a transmitter to tell it that congestion exists and that should reduce its sending rate. This is a specialized packet that is used for flow control along a network. A router detects congestion by measuring the percentage of buffers in use, line utilization and average queue lengths. When it detects congestion, it sends choke packets across the network to all the data sources associated with the congestion. The sources respond by reducing the amount of data they are sending.

           But this is not strong enough to long distance and high speeds, the choke packets are not very effective and also these packets are a more direct way of telling the source to slow down. This controlling packet is generated at a congested node and transmitted to restrict traffic flow.

Random early discard

        Random early discard (RED), also known as random early detection or random early drop is an active queue management algorithm. It is also a congestion avoidance algorithm.

In the traditional tail drop algorithm, a router or other network component buffers as many packets as it can, and simply drops the ones it cannot buffer. If buffers are constantly full, the network is congested. Tail drop distributes buffer space unfairly among traffic flows. Tail drop can also lead to TCP global synchronization as all TCP connections "hold back" simultaneously, and then step forward simultaneously. Networks become under-utilized and flooded by turns. RED addresses these issues.

                       

Traffic Shaping

                            Traffic shaping is an attempt to control network traffic in order to optimize or guarantee performance, low-latency, and/or bandwidth. Traffic shaping deals with concepts of classification, queue disciplines, enforcing policies, congestion management, quality of service (QoS), and fairness.

                                  Traffic shaping is any action on a set of packets (often called a stream or a flow) which imposes additional delay on those packets such that they conform to some predetermined constraint (a contract or traffic profile).Traffic shaping provides a means to control the volume of traffic being sent into a network in a specified period (bandwidth throttling), or the maximum rate at which the traffic is sent (rate limiting).

       

Difference between two traffic shaping algorithms

                     

Leaky bucket and Token buket

Token bucket throws away tokens when the bucket is full but never discards packets while leaky bucket discards packets when the bucket is full. Unlike leaky bucket, token bucket allows saving, up to maximum size of bucket n. This means that bursts of up to n packets can be sent at once, giving faster response to sudden bursts of input. Leaky bucket forces bursty traffic to smooth out, token bucket permits burstiness but bounds it. Token bucket has no discard or priority policy.

          Token bucket when compared to leaky bucket, is easy to implement. Each flow needs just a counter to count tokens and a timer to determine when to add new tokens to the counter.

    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.