1 Lecture 15 Internet resource allocation and QoS Resource Reservation Protocol Integrated Services Differentiated Services

2 QoS in a datagram network ? Packet Classification. Buffer acceptance algorithms. Explicit Congestion Notification. Flow measurements

3 A QoS Capable Router

4 Packet classification Identify the flow the packet belongs to. The edge routers may be able to do that. MPLS – multi protocol label switch. Add an extra header in front of the IP header. Now a router decides the output link based upon the input link and the MPLS header.

5 Buffer acceptance algorithms Tail Drop. RED – Random Early Detection RIO – Random Early Detection with In and Out packet dropping strategies.

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7 Explicit Congestion Notification (ECN) Routers could prevent congestion by informing the source of the packets when they become lightly congested, but before they start dropping packets. This strategy is called source quench.

8 Source quench A router sets a congestion notification flag in the IP header to inform the destination that signs of congestion are visible. The destination informs the source by setting a flag in the TCP header of segments carrying acknowledgments.

9 Problems with ECN (1) TCP must be modified to support the new flag. (2) Routers must be modified to distinguish between ECN-capable flows and those who do not support ECN. (3) IP must be modified to support the congestion notification flag. (4) TCP should allow the sender to confirm the congestion notification to the receiver, because acknowledgments could be lost.

10 Flow measurements How to choose the measurement interval to accommodate bursty traffic? Token bucket

11 The token bucket filter Characterized by : (1) A token rate R, and (2) The depth of the bucket, B Basic idea the sender is allocated tokens at a given rate and can accumulate tokens in the bucket until the bucket is filled. To send a byte the sender must have a token. The maximum burst can be of size B because at most B token can be accumulated.

12 Example Flow A: generates data at a constant rate of 1 Mbps. Its filter will support a rate of 1 Mbps and a bucket depth of 1 byte, Flow B: alternates between 0.5 and 2.0 Mbps. Its filter will support a rate of 1 Mbps and a bucket depth of 1 Mbps Note: a single flow can be described by many token buckets.

13 Example

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15 Token bucket L = packet length C = # of tokens in the bucket if ( L <= C ) { accept the packet; C = C - L; } else drop the packet;

16 A shaping buffer delays packets that do not confirm to the traffic shape if ( L <= C ) { accept the packet; C = C - L;} else { /* the packet arrived early, delay it */ while ( C < L ) { wait; } transmit the packet; C = C - L;}

17 Packet Scheduling PS and GPS – Processor Sharing & Generalized Processor Sharing Round Robin, Weighted Round Robin Priority Scheduling Weighted Fair Queuing – practical version of GPS. Transmits packets in the order of their finishing time.

18 Weighted queuing

19 RSVP- Resource Reservation Protocol Used to establish a path for a flow and reserve resources along the path. Requirements: Accommodate faults – soft state. Support unicast as well as multicast. PATH messages  issued by sender includes TSpec RESV messages  issued by the receiver includes RSpec

20 RSVP

21 RSVP message

22 RSVP multicast

23 Integrated Services Support fine-grain QoS for individual flows. Mechanisms: Specification of flow requirements - Flowspecs Admission decisions Resource reservation and policing Policy enforcement

24 Flowspecs TSpec – specify the traffic characteristics Rspec – describe services required from network.

25 Admission decisions Two classes: Guaranteed Services – based upon token buckets Controlled Load – approximates a best effort model in a lightly loaded network.

26 Integrated Service Router

27 Differentiated Services Two classes of traffic Regular Premium Edge routers mark the packets. Premium packets enjoy EF – Expedited Forwarding AF – Assured Forwarding