Multi-Stage Clos Networks in Router Architecture [Scholarly Paper Presentation]

1. Multi-Stage Clos Networks In Router Architecture Scholarly Paper Presentation (In partial fulfillment for MS Degree in Computer Engineering) Advisor: Dr. Jeremy Allnutt Co-advisor: Dr BijanJabbari George Mason University, Fairfax, Virginia Lawrence Awuah lawuah@gmu.edu ljawuah@ieee.org Fall 2007

3. Packet Forwarding and ASIC Design

4. Switch Fabric Implementation

6. Four operationally independent, identical and active switch planes.

8. Each cable is connected to each of the five parallel switch planes (four active, one redundant as discussed above )

10. Egress PFE drops packets if cells missing (assigned sequence #s).

12. The TX Matrix platform functions as the switching core of a routing matrix - the second stage of the Clos switch fabric.

13. The TX Matrix platform contains five SIB cards connected to the T640-SIB cards in each T640 routing node by way of inter-chassis fiber-optic array cables.

15. Mathematical Analysis Multi-stage Clos networks Theory of 3-stage Clos networks applications in switching fabric. Non-blocking condition k ≥ 2n-1.

17. flow control and congestion control, queuing algorithm – RED, WDRR.Single-stage crossbar switch

18. Multi-stage Clos networks (3-stage) Non-blocking condition k ≥ 2n-1 <=> assuming that; (i) all the other n-1 input lines are already engaged in connections; (ii) all the other n-1 output lines connections are already engaged in connections; (iii) and all these 2n-2 intermediate-stage switches are occupied For i input and j output lines to be connected, there must be at least 2n-2 + 1 (= 2n-1) intermediate-stage switches hence the condition k ≥ 2n-1.

19. Clos Switch Fabric Implementation Number of crosspoints for (2t-1)-stage switch:

21. The main goal of RED gateways is to provide congestion avoidance by controlling the average queue size developed in the network.

22. As avg (average queue size) varies from min.th to max.th, the packet marking probability pb varies linearly from 0 to maxp.Pb = maxp * (avg – min.th) (max.th – min.th) The final packet-marking probability pa given by: Pa = pb / (1 – count * pb) Where count is the number of non-marked packet since last marked packet. Using bytes rather than packets then: Pb = PacketSize * maxp * (avg – min.th) MaxPacketSize (max.th – min.th)

23. RED Algorithm