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CIS679: Two Planes and Int-Serv Model

CIS679: Two Planes and Int-Serv Model. Review of Last Lecture Two planes Integrated Service Model. Review of last lecture. RSVP PATH and RESV messages Soft-state. Two Planes. Control-Plane Call management (setup, signaling (RSVP) and tear-down) Admission control (delay computation etc)

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CIS679: Two Planes and Int-Serv Model

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  1. CIS679: Two Planes and Int-Serv Model • Review of Last Lecture • Two planes • Integrated Service Model

  2. Review of last lecture • RSVP • PATH and RESV messages • Soft-state

  3. Two Planes • Control-Plane • Call management (setup, signaling (RSVP) and tear-down) • Admission control (delay computation etc) • and resource provisioning (off-line), path determination (shortest-path routing, MPLS) etc. • Data-Plane: • Packet forwarding (controlled by schedulers, such as rate-based schedulers, e.g. WFQ and priority-based schedulers, e.g. Static Priority)

  4. Integrated Services (Int-Serv) • An architecture for providing QOS guarantees in IP networks for individual application sessions • relies on resource reservation, and routers need to maintain state info (Virtual Circuit??), maintaining records of allocated resources and responding to new Call setup requests on that basis

  5. Integrated Services: Classes • Guaranteed QOS: this class is provided with firm bounds on queuing delay at a router; envisioned for hard real-time applications that are highly sensitive to end-to-end delay expectation and variance • Controlled Load: this class is provided a QOS closely approximating that provided by an unloaded router; envisioned for today’s IP network real-time applications which perform well in an unloaded network

  6. Worst case traffic arrival: leaky-bucket-policed source Complex in terms of having per-flow isolation mechanism, hence needing per-flow state maintenance and resource reservation at per-element: WFQ couple QoS control to the core-router. Simple in terms of having mathematically provable bound on delay, which makes admission control simple. D = b/R max Packet forwarding with WFQ token rate, r arriving traffic bucket size, b per-flow rate, R WFQ

  7. packets are transmitted according to their priorities; within the same priority, packets are served in FIFO order. Complex in terms of no provable bounded delay due to no flow isolation Simple in terms of no per-flow management: SP make it possible to decouple QoS control from the core-router. D = ?? max Packet forwarding with Priority-driven Scheduler

  8. IntServ is not scalable • Solutions demonstrated “in the small” may not work “in the large” • per-callsignaling and management at per-element: too complex? • do-able in “small” networks • modest backbone router sees 250K flows/min Priority-based Rate-based Control Plane Scalable Not Scalable Data Plane Not Scalable Scalable

  9. Differentiated Services (Diff-Serv) Model • Basic Idea • Services classification • Flow aggregation • Relative Differentiated Services • provide per-hop, per-class relative services • Absolute Differentiated Services: • provide IntServ-type end-to-end absolute performance • guarantees without per-flow state in the network core

  10. Differentiated Services • Intended to address the following difficulties with Intserv and RSVP; • Scalability: maintaining states by routers in high speed networks is difficult sue to the very large number of flows • Flexible Service Models: Intserv has only two classes; want to provide ‘relative’ service distinction (Platinum, Gold, Silver, …) • Simpler signaling: (than RSVP) many applications and users may only want to specify a more qualitative notion of service

  11. Differentiated Services • Approach: • Only simple functions in the core, and relatively complex functions at edge routers (or hosts) • Do not define service classes, instead provides functional components with which service classes can be built

  12. Edge Functions • At DS-capable host or first DS-capable router • Classification: edge node marks packets according to classification rules to be specified (manually by admin, or by some TBD protocol) • Traffic Conditioning: edge node may delay and then forward or may discard

  13. Core Functions • Forwarding: according to “Per-Hop-Behavior” or PHB specified for the particular packet class; such PHB is strictly based on class marking (no other header fields can be used to influence PHB) • BIG ADVANTAGE: No state info to be maintained by routers!

  14. Classification and Conditioning • Packet is marked in the Type of Service (TOS) in IPv4, and Traffic Class in IPv6 • 6 bits used for Differentiated Service Code Point (DSCP) and determine PHB that the packet will receive • 2 bits are currently unused

  15. Classification and Conditioning • It may be desirable to limit traffic injection rate of some class; user declares traffic profile (eg, rate and burst size); traffic is metered and shaped if non-conforming

  16. Forwarding (PHB) • PHB result in a different observable (measurable) forwarding performance behavior • PHB does not specify what mechanisms to use to ensure required PHB performance behavior • Examples: • Class A gets x% of outgoing link bandwidth over time intervals of a specified length • Class A packets leave first before packets from class B

  17. Conclusion • Two planes • IntServ • DiffServ

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