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

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

Assured Service: Leaf Router Functionality

Marker function

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.

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.

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?

Premium Service: Leaf Router Functionality

Marker function

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.

Profile Meter at Border Router

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.

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

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 classesthey 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 rateThe delay or jitter experienced by premium packets should be very low.

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.