An End-to-End Service Architecture

1. An End-to-End Service Architecture • Provide assured service, premium service, and best effort service (RFC 2638) Assured service: provide reliable service even in time of network congestion • SLA specifies the rate and burst size for assured traffic • Customer decides how the applications share the bandwidth

2. Assured Service: Leaf Router Functionality • Leaf router: the router directly connected to a host in a customer network • Leaf routers configured with the traffic profile (rate and burst size) for assured flows • Leaf routers perform classification (based on packet header) and marking on arriving packets before forwarding them. • Marking: • A token present: packet considered as in profile, A-bit set to 1 • A token not present: packet considered as out of profile, A-bit set to 0

3. Assured Service: Leaf Router Functionality Marker function

4. Assured Service: Queue Management • All packets are put into an Assured Queue(AQ) managed by RIO (RED with In and Out) • RED (Random Early Detection): discarding packets before buffer space is exhausted • Router maintains a running average of the queue length • When the average queue length exceeds a threshold, pick a packet at random and drop it TCP flow control mechanisms at different end hosts will reduce send rates at different time. • RIO: two thresholds t1 an t2 for each queue. • When the queue length L < t1, no packets are dropped • When t1 < L < t2, only out packets are randomly dropped • When L > t2, both in and out packets are randomly dropped, but out packets are dropped more aggressively.

5. Premium Service • Provide low-delay and low-jitter service • The SLA specifies a peak rate for premium traffic • Customer responsible for not exceeding the peak rate: excess traffic will be dropped. • Customer decides how the applications share the bandwidth • Desirable for ISPs to support both static SLAs and dynamic SLAs. • Admission control needed for dynamic SLAs.

6. Implementation of Premium Service • The leaf routers perform classification and marking. • Marking: • Token present: packet has P-bit set • No token present: packet held until a token arrives (shaping) • Token bucket depth limited to one or two packets  create very regular traffic patterns and small queues. • All packets with the P-bit set enter a Premium Queue(PQ). • Packets in the PQ sent before packets in the AQ. • The exit routers of the customer domain may reshape the traffic to ensure that the traffic does not exceed the peak rate specified by the SLA. • Need Limit the total bandwidth requested by Premium traffic. Why?

7. Premium Service: Leaf Router Functionality Marker function

8. Border Router Functionality • The agreement between adjacent administrative domains specify a peak rate on P traffic and a rate & burst for A traffic • A Profile Meter (constructed from a token bucket) is required at the border routers of an ISP to ensure that packet flows are in compliance with their agreed-upon rates & burst sizes. • Non-compliant packets of Premium flows are discarded • Noncompliant packets of Assured flows have their A-bits reset. • Each input interface at a border router has its own profile meter corresponding to a particular class across the boundary.

9. Profile Meter at Border Router

10. Service Allocation in Customer Domains • Service allocation: deciding how the hosts in a customer domain share the services specified by the SLA • Bandwidth broker (BB) used to allocate resources in a customer domain • Before a host starts sending packets, it sends a message to BB to request for desired service • A request includes a service type, a target rate, a maximum burst, and the time period when service is required. • BB checks if there is sufficient bandwidth to meet the request • If BB grants the request, it sets the classification and marking rules at the leaf router directly connected to the sender • Dynamic SLA: BB must use a signaling protocol (e.g., RSVP) to request resources on demand from the ISP.

11. Resource Allocations in ISP Domains • Given the SLAs, ISP must configure the border routers with the classification and policing rules • Static SLA: border routers are manually configured • Dynamic SLA: • BB in customer domain sends a PATH message to BB in its ISP • BB in ISP makes an admission control decision • Grant: send PATH message to BB in the destination domain • Deny: send back error message • If BB in destination domain accepts the request, it configures its border router and sends RESV message back to BB in the ISP • When BB in the ISP receives the RESV message, it configures the border router and sends RESV to BB in customer domain • When BB in the customer domain receives RESV, it configures the leaf router

12. Uneven traffic • by admission control, the amount of premium traffic can be limited to a small percentage (say 10%) of the bandwidth of input links. • excess packets are dropped at the ingress routers of the networks Non-conformant flows cannot impact the performance of conformant flows. • premium packets are forwarded before packets of other classesthey can potentially use 100% of the bandwidth of the output links. • if premium traffic is distributed evenly among the links, these three factors should guarantee that the service rate of the PQ is much higher than the arrival rateThe delay or jitter experienced by premium packets should be very low.

13. Uneven traffic • uneven distribution of premium traffic may cause a problem for Premium Service. aggregation of premium traffic in the core may invalidate the assumption that the arrival rate of premium traffic is far below the service rate. • Differentiated Traffic Engineering/Constraint Based Routing must be used to avoid such congestion caused by uneven traffic distribution.