Integrated Service in the Internet Architecture

1. Integrated Service in the Internet Architecture RFC 1633

2. Introduction • The Internet only offers simple QoS (quality of service)—best effort • Real-time applications do not work well across the Internet because of: • Variable queueing delays • Congestion losses • The Internet infrastructure must be modified to support real-time QoS

3. Introduction • Real-time QoS is the issue for a next generation of traffic management in the Internet • The term integrated services(IS) for an Internet service model includes: • Best-effort service • Real-time service • Controlled link sharing

4. Elements of the Architecture • The fundamental service model of the Internet—best effort has been unchanged for 20 years • Change the service model of the Internet is a major undertaking • New components will supplement but not replace the basic IP service • Only to extend the original architecture

5. Integrated Service Model • Two sorts of service targeted towards real-time traffic: • Guaranteed service • Predictive service • It integrate with controlled link-sharing • The resources (e.g., bandwidth) must be explicitly managed

6. The arguments against resource guarantees • Bandwidth will be infinite • In the future, the bandwidth will be so abundant, ubiquitous, and cheap? • Simple priority is sufficient • Simply giving higher priority to real-time traffic is enough? • Applications can adapt

7. Integrated Service Model • There is an inescapable requirement for routers to be able to reserve resources • Provide special QoS for specific user packet streams, or flows • Use the existing internet-layer protocol (e.g., IP or CLNP) for real-time data

8. Reference Implementation Framework • Propose a reference implementation framework to realize the IS model • The framework includes 4 components: • Packet scheduler • Admission control • Classifier • Reservation setup protocol

9. Traffic control • For integrated services, a router must implement an appropriate QoS for each flow • The router function that creates different qualities of service is called “traffic control” • Implemented by: the packet scheduler, the classifier and admission control

10. Traffic control • Packet Scheduler • An experimental scheduler—CSZ scheduler • Classifier • Packets are mapped into some classes • Packets in same class get the same treatment form packet scheduler • Admission Control • The decision algorithm used by router

11. The 4th component—reservation setup protocol • Create and maintain flow-specific state in the endpoint hosts and in routers along the path of a flow • RSVP (ReSerVation Protocol) is used to reserve the resource

12. Implementation Reference Model for Routers Reservation Setup Agent Management Agent Routing Agent Admission Control [ Routing ] [ Traffic Control Database ] [ Database ] ========================================== Classifier Packet Scheduler Input Driver Internet Forwarder Output Driver

13. Implementation Reference Model for Routers • The forwarding path is divided into 3 sections : • Input driver,internet forwarder,output driver • Internet forwarder interprets the internetworking protocol header (e.g., IP header for TCP/IP) • The output driver implements the packet scheduler

14. Implementation Reference Model for Routers • In routers, integrated service will require changes to both the forwarding path and the background functions • The forwarding path may depend upon hardware acceleration for performance—difficult and costly to change

15. Quality of Service Requirements • Per-packet delay is the central quantity about which the network makes QoS commitments • Real-time applications • Need the data in each packet by a certain time, or the data will be worthless • Elastic applications • Always wait for data to arrive

16. Real-time applications • Playback applications • The source takes some signal, packetizes it, and then transmits over the network • Receiver has to buffer the incoming data and then replay the signal at some fixed offset delay form the original departure time • The performance is measured by • Latency and fidelity

17. Real-time applications • Delay can affect the performance of playback applications in two ways: • The value of the offset delay • The delays of individual packets can decrease the fidelity of the playback by exceeding the offset delay

18. Real-time applications • Intolerant applications • Must use a fixed offset delay • Set the upper bound on max delay • Be called as guaranteed service • Tolerant applications • Can tolerate some late packets • Vary offset delays according to the experience in the recent past • Be called as predictive service

19. Elastic applications • Always wait for data to arrive • Example applications: • Interactive burst — Telnet • Interactive bulk burst — FTP • Asynchronous bulk transfer — E-mail • An appropriate service model for these applications is to provide as-soon-as-possible service (i.e., best-effort service)

20. Resource-sharing requirements • Multi-entity link-sharing • When the link is underloaded, any one of the entities could utilize all idle bandwidth • Multi-protocol link-sharing • Prevent one protocol family from overloading the link • Multi-service sharing • Limit the amount real-time traffic to avoid preempting elastic traffic

21. Other remarks • Packet dropping • Some of the packet within a flow could be marked as preemptable • Router use this mark to drop packets • Usage feedback • Prevent abuse of network resources • Reservation model • Describe how an application negotiates for a QoS level

22. Traffic Control Mechanisms • Basic functions: • Packet scheduling • Packet dropping • Packet classification • Admission control • An example: The CSZ scheme

23. Packet scheduling • Reorder the output queue • One approach is a priority scheme • Packets are ordered by priority • Highest priority packets leave first • An alternative scheme is round-robin • Gives different classes of packets access to a share of the link

24. Packet dropping • A router must drop packets when its buffers are all full • Dropping the arriving packet is simple but may cause undesired behavior • In real-time service, dropping one packet will reduce the delay of all the packet behind it • Dropping and scheduling must be coordinated

25. Packet classification • The classifier implementation issues are complexity and processing overhead • One approach is to provide a flow-id field in the Internet-layer packet header • Reduce the overhead of classification • Engineering is required to choose the best design of this concept

26. Admission control • Admission control—the design about resource availability • The router has to understand the demands that are currently being made on its assets • A recent proposal is to program the router to measure the actual usage by existing packet flows, then use this information for the admitting of new flow

27. The CSZ scheme • At the top level, CSZ node use WFQ to separate guaranteed flows for each other • Predictive and best-effort service are separated by priority • Inside each predictive sub-class, FIFO queueing is used to mix the traffic

28. The CSZ scheme • Within the best-effort class, WFQ is used to provide link sharing • Within each link share of the best-effort class, priority is used to permit more time-sensitive elastic traffic • The CSZ node uses both WFQ and priority in an alternating manner to build the mechanism

29. Reservation Setup Protocol • Requirements for the design of a reservation setup protocol: • designed for a multicast environment • accommodate heterogeneous service needs • can add/delete one sender/receiver to an existing set • robust and scale well to large multicast groups • advanced reservation of resources, and for the preemption

30. RSVP • Flowspecs and Filter Specs • RSVP reservation request specifies the amount of resources to be reserved • The resource quantity is specified by a flowspec • The packet subset to receive those resources is specified by a filter spec • The service model presented to an app. must specify how to encode flowspecs and filter specs

31. RSVP—reservation styles • Offers several different reservation styles • Wildcard • All packet destined for the session may use a common pool of reserved resource • Fixed-filter • Can not be changed during its life time without re-invoking admission control • Dynamic-filter • Receiver can modify its choice of resource without additional admission control

32. RSVP—reservation styles • Wildcard uses a filter spec that is not source-specific • The other two use filter specs that select particular sources • The wildcard reservation is useful in support of an audio conference

33. RSVP—initiation • Sender knows the qualities of the traffic stream it can send • Receiver knows what it wants to (or can) receive • Sender initiation scales poorly for large, dynamic multicast delivery trees and for heterogeneous receivers • Thus, RSVP uses Receiver-Initiation

34. RSVP—initiation • Receiver Initiation • Natural choice for multicast sessions • But may appear weaker for unicast sessions • Except real-time app. will have its higher-level signalling and protocol • Then this protocol can be used to signal the receiver to initiate a reservation

35. RSVP—states • Hard state approach • Connection-oriented • Soft state approach • Connectionless • RSVP takes the Soft State approach • Regards the reservation as cached information that is installed and periodically refreshed by the end hosts

36. RSVP—routing issues • Find a route that support resource reservation • Find a route that has sufficient unreserved capacity for new flow • Adapt to a route failure • Adapt to a route change (without failure) • The last issue is provide by mobile hosts

37. Conclusion • The Integrated services framework has four main components : • Packet scheduler • Admission control • Classifier • Reservation setup protocol • RSVP is used to reserve the resource for the session belongs to high class level