Lecture Notes on Internet Quality of Service

Overview of Quality of Service (QoS) Architectures

• Two main architectures covered:
  • Integrated Service Architecture (IntServ)
  • Differentiated Service Architecture (DiffServ)

Key Differences between IntServ and DiffServ

• IntServ Architecture:

  • Provides guaranteed service based on Service Level Agreements (SLAs).
  • Each router coordinates to ensure requested QoS is met, requiring resource reservations.
  • Can be complex due to the scale of the internet and the need for coordination between millions of routers.
  • Example: If SLA states delay should be no more than 10 milliseconds, the network must ensure packets rarely exceed this delay.

• DiffServ Architecture:

  • Offers a best-effort service and does not guarantee QoS.
  • It aims to optimize QoS based on the network status, but results can vary depending on congestion.
  • Example: Similar to airport security queues; during peak times, service quality may suffer.

Integrated Service Architecture (IntServ)

Key Components

1. Admission Control:

   • Uses the Resource Reservation Protocol (RSVP) for reserving resources for new flows.

2. Routing Control:

   • Routing decisions based on QoS parameters such as load on routers.

3. Queuing Strategies:

   • Different strategies manage different flow requirements, including congestion avoidance.

4. Traffic Control Database:

   • Provides instructions on how packets should be treated.

Forwarding Plane in Routers

• Classifier & Route Selection:

  • Classifies incoming packets into traffic classes and selects routes.

• Packet Scheduler:

  • Determines how packets are treated based on their classification and routing information.

Resource Reservation Protocol (RSVP)

• RSVP allows the receiver to request guaranteed QoS for data flows.
• It should not be confused with routing protocols; rather, it works in conjunction with them.
• RSVP maintains per-flow states at intermediate routers, which can introduce scalability concerns.

RSVP Terminologies

• Flowspec:

  • Specifies the desired level of QoS (e.g., peak bandwidth, latency).

• Filterspec:

  • Defines packets eligible for QoS treatment and corresponds to queuing mechanisms.

Differentiated Service Architecture (DiffServ)

Key Features

• Coarse-grained, Class-based System:
  • Uses a fixed set of traffic classes defined by the Differentiated Services Code Point (DSCP).
• Fixed Roles:
  • Unlike IntServ, DiffServ does not maintain per-flow state, simplifying the process.
• Per Hop Behaviour (PHB):
  • Defines forwarding properties for incoming packets based on their DSCP classification.

Traffic Conditioning in DiffServ

• Components include: Meter, Marker, Shaper, Dropper.
• Meter measures compliance with traffic profiles; Marker can adjust priority; Shaper controls traffic flow; Dropper discards non-compliant packets.

Service Level Agreements (SLAs)

• Traffic Conditioning Agreement: Specifies rules for traffic classification.
• Service Level Agreement: Defines expected QoS parameters for traffic streams.

Working Steps in DiffServ Domains

1. Users contact ISPs to establish SLAs.
2. Requests are sent through routers to bandwidth brokers that either accept or deny requests based on available bandwidth.
3. Traffic is then marked according to its priority classes.
4. Edge routers enforce compliance with SLAs through policing.
5. Core routers process packets based on DSCP values.

Conclusion

• This lecture provided an overview of Quality of Service in the internet, focusing on IntServ and DiffServ architectures.
• Additional resources include links to further documentation and deeper readings on Cisco QoS implementation.

References

• Cisco documentation and resources on QoS implementation.

• Links provided in the lecture to gain more insights into QoS topics.