Congestion Control in Networks

ATM and TCP

Balazs Attila-Mihaly

Outline

What is congestion?

Myths about congestion

Congestion control possibilities

ATM Vocabulary

ATM Congestion Control

ATM CC evaluation

TCP

TCP Congestion Control

TCP CC evaluation

Bibliography

What is congestion?

network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates - Wikipedia

QoSPacket loss

Queuing delay

Jitter

Low troughput

Congestion control possibilities

Admission control

Traffic access control

Packet scheduling (prioritization)

Buffer management

Flow control (speed matching)

QoS routing

Congestion control possibilities

Admission control

Traffic access control

Packet scheduling (prioritization)

Buffer management

Flow control (speed matching)

QoS routing

Congestionprevention

avoidance

recovery

CC Objectives

Scalability

FairnessMax-Min

Min + Equal share

Maximum of the previous too

Allocation proportional with Min

Weighted allocation

Robustness

Implementability

ATM

Protocol implemented over different media

Fixed sized cells (53 bytes 48 byte of data)

Vocabulary:VCI Virtual Circuit Identifier

PCR Peak Cell Rate

SCR Sustained Cell Rate

MBR Maximum Burst Size

MCR Minimum Cell Rate

ATM

VocabularyCTD Cell Transfer Delay (maximum / mean)

CDV Cell Delay Variation (peak-to-peak / instant.)

CLR Cell Loss Ratio

Service categoriesCBR Constant Bit Rate

rt-VBR Real-Time Variable Bit Rate

nrt-VBR Non-Real-Time Variable Bit Rate

UBR Unspecified Bit Rate

ABR Available Bit Rate

ATM Congestion Control

Admission control CAC (Call Access Control)Hard or soft (statistical) limits

Traffic access control GCRA (Generic Cell Rate Algorith)TAT Theoretical Arrival Time

I Increment

L - Limit

Cell arrival at tt