Advanced topics in Computer Networks

1. Advanced topicsinComputer Networks Lecture 6: Switching University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Adv. topics in Computer Network

2. Outline • Introduction • What are switches? • Basic concepts • Design factors • Performance factors Adv. topics in Computer Network

3. Node incoming links outgoing links Memory Switches • A means to create connectivity • Why switching? Efficient utilization of resources • Store and forward scheme Adv. topics in Computer Network

4. Basic concepts • An ideal switch: route all incoming packet to their requested outputs with the following conditions: • No loss • Minimum delay • Preserving order • Output contention: At least two input goes to one output. we need buffer and queuing (how much?) • Congestion: no buffer space left. Drop packet Adv. topics in Computer Network

5. Design Factors • Throughput • Max throughput- Nx line speed where N is the # of input line • Ave throughput – At random is %60. • Packet per second (PPS)- # of packets switched per second • Throughput depends on the traffic. • Quality of service: • Ave delay of cells • Jitter • Reliability in switching cells. Adv. topics in Computer Network

6. Design Factors • Scalability: how the architecture scale, linear? Square? • Regarding the speed of input line • Regarding the # of input port. • Cost: • # of logic gates • Mem. • Bandwidth or # of pines Adv. topics in Computer Network

7. Performance Factors • Traffic pattern: • Packet arrival rate. • Destination distribution • Addressing and operation: • Unicast or multicast operation • Priority- Differentiation among packets Adv. topics in Computer Network

8. Functional requirement • User plane: • Data is carried transparently • Header are processed and VPI/VCI is used for routing. 0 0 LC SFC IPP LC OPP … … Central unit Adv. topics in Computer Network

9. Functional requirement (cont) • Control plane: Signaling • Identified by VPI/VCI, 5/0 is for call admission. • May use SFC for transporting data to CAC. IPP+ SFC+ OPP Store and forward system. CAC LC SFC IPP LC OPP … … CAC- Call Admission Control Adv. topics in Computer Network

10. Functional requirement (cont) • Management plane: System Management (SM) must handle management cell. • Should support Network wide operations. • May use SFC for transporting management cells. SM LC SFC IPP LC OPP … … Adv. topics in Computer Network

11. Functional requirement(cont) • Management plane: must support the following operations • Fault management • Performance management • Security • Accounting • Traffic Management • Configuration • OAM cell is filtered out in IPP and sent to SM. Adv. topics in Computer Network

12. Functional requirement (cont) • Traffic Control: This part is generally regarded part of SM. Must do the following: • Call Admission control • Usage/Network parameter control • Congestion control • Traffic shaping. Adv. topics in Computer Network

13. Switch Architecture • General “Divide and conquer” policy. • Different partitioning policy. • Generally the following functional blocks • Input port processor (IPP) module • Output Port Processor (OPP) module • Switch Fabric Chip (SFC) module • Connection Admission Control (CAC) module. • System Management (SM) module. Adv. topics in Computer Network

14. IPP module • Extract ATM (or IP) cells initially and prepare them for switching. • Conversion of the optical signal into electrical. • Recovery of digital bit stream. • Processing physical line header (overhead) • Cell delineation • Cell rate decoupling (Discarding empty cell). • These are mostly on line card and done in the first step. Adv. topics in Computer Network

15. IPP module (cont) • In the second steps, cells are prepared for routing through SFC. • Error Check, using HEC in the header. • Translation of VPI/VCI • Determination of Output port • Sorting data, management and signaling cells • Usage/Network parameter control for policing • Adding internal tags. Adv. topics in Computer Network

16. OPP module • Usually done the reverse of IPP • Remove internal tags. • Translation of VPI/VCI (why?) • Generating HEC field • Cell rate decoupling (Adding empty cells) • Generating physical line (SONET) overhead. • Converting into optical signal. Adv. topics in Computer Network

17. SFC module • Route, switch, cells • Cell buffering (output contention) • Traffic concentration and multiplexing • Multicast or broadcasting cells • Cell scheduling based on delay priorities. • Selective cell discarding. • Congestion monitoring and back pressure. Adv. topics in Computer Network

18. CAC module • Establishment, modification and termination of connections • Higher layer signaling protocols. • Resource allocation • Admission/rejections decision • Generating of UPC/NPC parameters; Adv. topics in Computer Network

19. SM module • It is complex and do many things. • Physical and ATM layer OAM • Configuration of components. • Security control • Traffic management • Accounting Adv. topics in Computer Network