Queue Management and Quality of Service (QOS)

Traffic and Resource Management

Resources statistically shared

Overload causes congestion
packet delayed or dropped
application performance suffer
Local vs. network wide
Transient vs. persistent
Challenge
high resource utilization
high application performance

Resource Management Approaches

Increase resources
install new links, faster routers
capacity planning, provisioning, traffic engineering
happen at longer timescale
Reduce or delay demand
Reactive approach: encourage everyone to reduce or delay demand
Reservation approach: some requests will be rejected by the network

More Ideas on Traffic Management

Improve TCP
Stay with end-point only architecture
Enhance routers to help TCP
Random Early Discard
Enhance routers to control traffic
Rate limiting
Fair Queueing
Provide QoS by limiting congestion

Typical Internet Queuing

FIFO + drop-tail
Simplest choice
Used widely in the Internet
FIFO (first-in-first-out)
Implies single class of traffic
Drop-tail
Arriving packets get dropped when queue is full regardless of flow or importance
Important distinction:
FIFO: scheduling discipline
Drop-tail: drop policy

Active Queue Management

Design active router queue management to aid congestion control
Why?
Router has unified view of queuing behavior
Routers see actual queue occupancy (distinguish queue delay and propagation delay)
Routers can decide on transient congestion, based on workload

Congestion Control Summary

Architecture: end system detects congestion and slow down
Starting point:
slow start/congestion avoidance
packet drop detected by retransmission timeout (RTO) as congestion signal
fast retransmission/fast recovery
packet drop detected by three duplicate acks
Router support
RED: early signaling
ECN: explicit signaling

Reference: http://studentbank.in/report-queue-manag...z4GAM5v4Ic