Advanced topics in Computer Networks

1. Advanced topicsinComputer Networks Lecture 3: ATM: Flow & Traffic Control University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Adv. topics in Computer Network

2. Outline • Information flows in ATM • Traffic control Adv. topics in Computer Network

3. Management Plane Control Plane User Plane Pane management Higher Layers Signaling Layer management ATM Adaptation layer ATM Layer Physical layer B-ISDN reference model • Three planes • User planes • Control plane • Management plane Adv. topics in Computer Network

4. User plane • Consists of physical layer, ATM layer, AAL and higher layer. • Physical layer consists of transmission path, digital section and regenerating section. • ATM is subdivided into virtual path and virtual channel • User data cells are carried transparently. Adv. topics in Computer Network

5. Control plane • Is responsible for connection consisting of establishment, supervision and release • Signaling cells are transported in the same manner as user data. • Signaling is done in reserved VCI (5 for NNI and 0 for UNI) Adv. topics in Computer Network

6. Management plane • Monitor, control • Plane management: related to the network as a whole: • Layer management: the most important is operations and maintenance (OAM) Adv. topics in Computer Network

7. Traffic control/Resource management • Quality of service • Statistical sharing • Level of control; • Reactive and preventive controls ideal Network throughput With control Without control Offered load Adv. topics in Computer Network

8. QoS • Supported classes • Class A- circuit emulation and CBR services • Class B: for VBR like video and speech • Class C:for connection-oriented • Class D: for connectionless data. Adv. topics in Computer Network

9. Classes of Service • CBR (Constant bit rate): User declares required rate. Throughput, delay and delay variation guaranteed. • VBR (Variable bit rate): User declares average and max rate. – rt-VBR (Real-time variable bit rate): Conferencing. Max delay and delay variation guaranteed. – nrt-VBR (non-real time variable bit rate): Stored video. • ABR (Available bit rate): Follows feedback instructions Network gives maximum throughput with minimum loss. • UBR (Unspecified bit rate): User sends whenever it wants. No feedback mechanism. No guarantee. Cells may be dropped during congestion. Adv. topics in Computer Network

10. Traffic Management Functions • Connection Admission Control (CAC): Can requested bandwidth and quality of service be supported? • Traffic Shaping: Limit burst length. Space-out cells. • Usage Parameter Control (UPC): Monitor and control traffic at the network entrance. • Network Resource Management: Scheduling, Queuing, virtual path resource reservation • Selective cell discard: Cell Loss Priority (CLP) = 1 cells may be dropped Cells of non-complient connections may be dropped • Frame Discarding • Feedback Controls: Network tells the source to increase or decrease its load. Adv. topics in Computer Network

11. Traffic control • Reactive control • Feedback based control (TCP) • Not good for real time application • Limited to propagation delay. • Preventive control: remain in a bound. • Connection admission control • Usage parameter control (UPC). Adv. topics in Computer Network

12. Connection Admission Control • Negotiating a new connection • Admitting/rejecting a new connection • Allocating network resources • Important issues • Characterization of the traffic and it QoS • Admitting/rejecting policy Adv. topics in Computer Network

13. Traffic contract • Traffic description: like peak rate, ave. rate, max burst length • Cell delay variation tolerance • Conformance definition • Important traffic parameter must be simple such as high and low priority. Adv. topics in Computer Network

14. Generic Cell Rate Algorithm • Define parameters of a cell stream to connection setup as well as rate enforcement • GCRA(I, L): I increment and Limit L: Actual arrival of cell n t(n) and theoretical T(n) with each cell distancing I • If t(n) > T(n) –L, the cell is conforming • Nonconforming otherwise. • If Conforming and t(n) < T(n) => T(n+1) = T(n) +I if t(n) > T(n) => T(n+1) = t(n) +I • Nonconforming cells are not counted in the calculation. Adv. topics in Computer Network

15. t(n) T(n) T(n)- L Generic Cell Rate Algorithm Too early, Nonconforming t(n) Early, but, conforming T(n) T(n)- L t(n) Late, conforming T(n) T(n)- L Adv. topics in Computer Network

16. Traffic shaping • Ensure conformance to the traffic contract and avoid cell loss. • Reduce burstiness of VBR traffice • Leaky Bucket Algorithm is used to regulate traffic: GCRA is equivalent to a continuious leaky bucket Adv. topics in Computer Network

17. Leaky Bucket • B Buffer of size B, containing tokens is drained at rate R • Arrival cell adds one token. If buffer full cell is discarded. cells cells • Ave. rate is R • Instead of discarding, • we can mark or tag Leak rate, R Adv. topics in Computer Network

18. Congestion control • Congestion is still possible due to buffers overloads • Selective discarding • Delay and loss priority: CLP bit in the ATM header • Explicit forwarding congestion indication: to inform down stream user from congestion. Adv. topics in Computer Network