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Differentiated Services
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Motivation
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  • 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
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  • Simpler:
    • Uses per-class queues and rates instead of per-flow queues and rates
  • Less Powerful:
    • Many flows share the same queue, state and capacity
  • Scope:
    • Domain rather than end-to-end
Important Concepts
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  • 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
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  • 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
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  • 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
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  • Service-Level Agreement (SLA):
    • Indicates the type of forwarding service
  • Traffic Conditioning Agreement (TCA):
    • Detailed description of the service
Types of Service (i.e., Per-Hop Behavior)
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  • 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
There's Always More to Learn
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