Flow Controlby

Md.Javedul Ferdous

East West University

Flow Control

Flow control is the process of managing

the rate of data transmission between two

nodes to prevent a fast sender from

outrunning a slow receiver. It provides a

mechanism for the receiver to control the

transmission speed, so that the receiving

node is not overwhelmed with data from

transmitting node.

So why need it

? ? ? ? ?

Prevent degradation and loss of

efficiency due to overload.

Prevent degradation and loss of

efficiency due to overload.

Deadlock avoidance.

Prevent degradation and loss of

efficiency due to overload.

Deadlock avoidance.

Fair allocation of resources among

competing users.

Prevent degradation and loss of

efficiency due to overload.

Deadlock avoidance.

Fair allocation of resources among

competing users.

Speed matching between the network

and its attached users.

Type of ‘Flow Control’

Stop-and-wait

Type of ‘Flow Control’

Stop-and-wait

Sliding Window

Stop-and-wait

Fundamental technique to provide

reliable transfer under unreliable packet

delivery system

Stop-and-wait

Fundamental technique to provide

reliable transfer under unreliable packet

delivery system

Simplest form of flow control

Stop-and-wait

Fundamental technique to provide

reliable transfer under unreliable packet

delivery system

Simplest form of flow control

Inefficiencies when sending longer

transmissions

Stop-and-wait

Sliding Window

Technique for controlling transmitted

data packets between two network

computers where reliable and sequential

delivery of data packets is required.

Sliding Window

Technique for controlling transmitted

data packets between two network

computers where reliable and sequential

delivery of data packets is required.

Best utilized when the buffer size is

limited and pre-established.

Sliding Window

Technique for controlling transmitted

data packets between two network

computers where reliable and sequential

delivery of data packets is required.

Best utilized when the buffer size is

limited and pre-established.

Better Performance.

Sliding Window

Levels of Flow Control

Hop Level

Levels of Flow Control

Hop Level

Entry-to-Exit Level

Levels of Flow Control

Hop Level

Entry-to-Exit Level

Network Access Level

Levels of Flow Control

Hop Level

Entry-to-Exit Level

Network Access Level

Transport Level

Hop Level

Prevent store and forward buffer

congestion and its consequences

Hop Level

Prevent store and forward buffer

congestion and its consequences

Maintain a smooth flow of traffic

between two neighboring nodes In a

computer network

Entry-to-Exit Level

Implement as a protocol between the

source and destination switch

Entry-to-Exit Level

Implement as a protocol between the

source and destination switch

Protect the exit node from congestion

Network Access Level

Throttle external inputs based on

measurements of internal network

congestion.

Transport Level

Efficient and reliable transmission of

messages within each user session and

the efficient sharing of common network

resources by several user sessions

Transport Level

Efficient and reliable transmission of

messages within each user session and

the efficient sharing of common network

resources by several user sessions

Events destination buffer congestion

and overflow is known as transport level

flow control

Problem of ‘Flow Control’

Can’t send too slow or too fast

Problem of ‘Flow Control’

Can’t send too slow or too fast

Too slow

Problem of ‘Flow Control’

Can’t send too slow or too fast

Too slow

wastes time

Problem of ‘Flow Control’

Can’t send too slow or too fast

Too slow

wastes time

Too fast

Problem of ‘Flow Control’

Can’t send too slow or too fast

Too slow

wastes time

can lead to buffer overflow