Lecture 15: Routers and QoS - Home | Computer Science

Lecture 15: Routers and QoS"

CSE 123: Computer Networks Alex C. Snoeren

HW 4 due next Tuesday!

Lecture 15 Overview"

Router Basics Buffer Management Traffic Policing/Scheduling Quality of service basics

CSE 123 ? Lecture 15: Routers and QoS

2

Whats in a Router?"

Physical components

One or more input interfaces that receive packets One or more output interfaces that transmit packets A chassis (box + power) to hold it all

Functions

Forward packets Drop packets (congestion, security, QoS) Delay packets (QoS) Transform packets? (Encapsulation, Tunneling)

CSE 123 ? Lecture 15: Routers and QoS

3

Router Architecture"

Firewall

Reservation/ Admission Control

Routing Protocols

Classification Rules

Routing Table

Control Plane ? Complex ? Per-control action ? May be slow

Forwarding Table

Data plane ? Simple

? Per-packet

Packet Classification

Switching

Output Scheduling

? Must be fast

4

Key Router Challenges"

Buffer management: which packet to drop when?

We only have finite-length queues

Scheduling: which packet to transmit next?

flow 1

1

Classifier

flow 2

Scheduler

2

flow n

Buffer management

CSE 123 ? Lecture 15: Routers and QoS

5

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