Univ. of TehranAdv. topics in Computer Network1 Advanced topics in Computer Networks University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Lecture 3: ATM: Flow & Traffic Control

Univ. of TehranAdv. topics in Computer Network2 Outline Information flows in ATM Traffic control

Univ. of TehranAdv. topics in Computer Network3 B-ISDN reference model Three planes User planes Control plane Management plane Physical layer ATM Layer ATM Adaptation layer Signaling Higher Layers Control Plane User Plane Management Plane Layer management Pane management

Univ. of TehranAdv. topics in Computer Network4 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.

Univ. of TehranAdv. topics in Computer Network5 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)

Univ. of TehranAdv. topics in Computer Network6 Management plane Monitor, control Plane management: related to the network as a whole: Layer management: the most important is operations and maintenance (OAM)

Univ. of TehranAdv. topics in Computer Network7 Traffic control/Resource management Quality of service Statistical sharing Level of control; Reactive and preventive controls Offered load Network throughput Without control With control ideal

Univ. of TehranAdv. topics in Computer Network8 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.

Univ. of TehranAdv. topics in Computer Network9 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.

Univ. of TehranAdv. topics in Computer Network10 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.

Univ. of TehranAdv. topics in Computer Network11 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).

Univ. of TehranAdv. topics in Computer Network12 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

Univ. of TehranAdv. topics in Computer Network13 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.

Univ. of TehranAdv. topics in Computer Network14 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+1) = T(n) +I if t(n) > T(n) => T(n+1) = t(n) +I Nonconforming cells are not counted in the calculation.

Univ. of TehranAdv. topics in Computer Network15 Generic Cell Rate Algorithm T(n) T(n)- L t(n) Too early, Nonconforming T(n) T(n)- L t(n) T(n) T(n)- L t(n) Early, but, conforming Late, conforming

Univ. of TehranAdv. topics in Computer Network16 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

Univ. of TehranAdv. topics in Computer Network17 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 Leak rate, R Ave. rate is R Instead of discarding, we can mark or tag

Univ. of TehranAdv. topics in Computer Network18 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.