1. Data Communication
Flow Control
by
Md.Javedul Ferdous
East West University

2. 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.

3. So why need it
?????

4. 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.

5. Type of ‘Flow Control’
• Stop-and-wait
• Sliding Window

6. Stop-and-wait
• Fundamental technique to provide reliable
transfer under unreliable packet delivery
system
• simplest form of flow control
• inefficiencies when sending longer
transmissions

7. Stop-and-wait

8. 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

10. Levels of Flow Control
Hop Level
Entry-to-Exit Level
Network Access Level
Transport Level

11. 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

12. Entry-to-Exit Level
Implement as a protocol between the source
and destination switch
Protect the exit node from congestion

13. Network Access Level
Throttle external inputs based on
measurements of internal network
congestion.

14. 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

15. Problem of ‘Flow Control’
Can’t send too slow or too fast
Too slow
wastes time
Too fast
can lead to buffer overflow