1. 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 6: Switching

2. Univ. of TehranAdv. topics in Computer Network2 Outline Introduction What are switches? Basic concepts Design factors Performance factors

3. Univ. of TehranAdv. topics in Computer Network3 Switches A means to create connectivity Why switching? Efficient utilization of resources Store and forward scheme incoming linksoutgoing links Node Memory

4. Univ. of TehranAdv. topics in Computer Network4 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

5. Univ. of TehranAdv. topics in Computer Network5 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.

6. Univ. of TehranAdv. topics in Computer Network6 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

7. Univ. of TehranAdv. topics in Computer Network7 Performance Factors Traffic pattern: Packet arrival rate. Destination distribution Addressing and operation: Unicast or multicast operation Priority- Differentiation among packets

8. Univ. of TehranAdv. topics in Computer Network8 Functional requirement User plane: Data is carried transparently Header are processed and VPI/VCI is used for routing. LC IPP SFC OPP LC 0 0 … … Central unit

9. Univ. of TehranAdv. topics in Computer Network9 Functional requirement (cont) Control plane: Signaling Identified by VPI/VCI, 5/0 is for call admission. May use SFC for transporting data to CAC. LC IPP SFC OPP LC … … IPP+ SFC+ OPP Store and forward system. CAC CAC- Call Admission Control

10. Univ. of TehranAdv. topics in Computer Network10 Functional requirement (cont) Management plane: System Management (SM) must handle management cell. Should support Network wide operations. May use SFC for transporting management cells. LC IPP SFC OPP LC … … SM

11. Univ. of TehranAdv. topics in Computer Network11 Functional requirement(cont) 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.

12. Univ. of TehranAdv. topics in Computer Network12 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.

13. Univ. of TehranAdv. topics in Computer Network13 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.

14. Univ. of TehranAdv. topics in Computer Network14 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.

15. Univ. of TehranAdv. topics in Computer Network15 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.

16. Univ. of TehranAdv. topics in Computer Network16 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.

17. Univ. of TehranAdv. topics in Computer Network17 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.

18. Univ. of TehranAdv. topics in Computer Network18 CAC module Establishment, modification and termination of connections Higher layer signaling protocols. Resource allocation Admission/rejections decision Generating of UPC/NPC parameters;

19. Univ. of TehranAdv. topics in Computer Network19 SM module It is complex and do many things. Physical and ATM layer OAM Configuration of components. Security control Traffic management Accounting