CEN 4500 - Network Fundamentals
Chapter 5
The Network Layer
The Network Layer
• Congestion Control
–Two Types of Congestion Control
• Open Loop
• Closed Loop
• Open Loop CC algorithms tends to be proactive; that is, they are designed to
ensure that congestion does not occur in the first place
•Tools used in Open Loop include
–Deciding when to accept new traffic
–Packet-discard policies
–Scheduling decisions at various points along the network
•One Open Loop approach to congestion control is traffic shaping
•Used to offset the ‘burstiness’ of data communications, traffic shaping is about
regulating the average rate of data transmission
•Works essentially by the customer and carrier agreeing beforehand what the
customer’s transmission pattern will be
•The carrier then monitors the customer’s traffic to ensure the average throughput
agreed is being maintained; this is known as traffic policing
•Common Open Loop congestion algorithms are
–The Leaky Bucket Algorithm
–The Token Bucket Algorithm
•Note however, that once a network connection is up and running, no further
congestion-corrections are made if Open Loop is utilized
