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.
