CIS679: Scheduling, Resource Configuration and Admission Control

Review of Last lecture Scheduling Resource configuration Admission control

Review of last lecture

Scheduling Mechanisms

Scheduling: choosing the next packet for transmission on a link can be done following a number of policies;

FIFO: in order of arrival to the queue; packets that arrive to a full buffer are either discarded, or a discard policy is used to determine which packet to discard among the arrival and those already queued

Scheduling Policies Priority Queuing: classes have different priorities; class

may depend on explicit marking or other header info, eg IP source or destination, TCP Port numbers, etc.

Transmit a packet from the highest priority class with a non-empty queue

Preemptive and non-preemptive versions

Scheduling

Scheduling: FIFO Priority Scheduling (static priority) Round Robin Weight Fair Queuing (WFQ)

Priority-driven Scheduler

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

Round Robin

Round Robin: scan class queues serving one from each class that has a non-empty queue

WFQ

Weighted Fair Queuing: is a generalized Round Robin in which an attempt is made to provide a class with a differentiated amount of service over a given period of time

WFQ (more)

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.

WFQ

token rate, r

bucket size, b

per-flowrate, R

D = b/Rmax

arrivingtraffic

Resource Configuration

Traffic engineering QoS routing Resource provisioning

Network planning Network design

Admission Control

Session must first declare its QOS requirement and characterize the traffic it will send through the network

R-spec: defines the QOS being requested T-spec: defines the traffic characteristics A signaling protocol is needed to carry the R-

spec and T-spec to the routers where reservation is required; RSVP is a leading candidate for such signaling protocol

Admission Control

Call Admission: routers will admit calls based on their R-spec and T-spec and base on the current resource allocated at the routers to other calls.

Conclusion

Scheduling: Decide the order of packet transmission

Resource configuration Admission control