Differentiated Services

Differentiated Services
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Motivation

Properties of IP:
- "Cross traffic" is unpredictable and impacts traffic on other paths
- IP provides best effort service (i.e., no service guarantees)
Possible Improvements:
- Service guarantees (e.g., for real-time applications)
- Service classes

Comparison to Integrated Services

Important Concepts

DiffServ (DS) Domain:
- A (contiguous) portion of the network administered by a single entity
Router Types:
- Edge (Ingress and Egress) - police and classify (using the Differentiated Service Code Point in the DS field)
- Core - process packets based on DSCP and implement Per-Hop Behavior

Roles of the Service Provider

Bandwidth Broker:
- Allocates and controls available bandwidth within a DS domain
- Communicates with brokers in neighboring domains
Policing:
- Operates a traffic classifier and traffic conditioner at the DS domain's edger router

Policing Operations

Traffic Classification:
- Determines the appropriate class of the traffic
Traffic Conditioning:
- Meter - measures traffic
- Marker - marks/unmarks packets to track state information
- Shaper - delays non-compliant packets
- Dropper - drops violating packets

Agreements

Types of Service (i.e., Per-Hop Behavior)

Best Effort:
- No assurances
Assured Forwarding:
- Higher assurance than best effort
- High throughput
Expedited Forwarding (a.k.a. Premium Service):
- Low loss
- Low latency
- Ensured bandwidth