1. Ethernet Congestion Management Brad Booth, Intel September 2004

2. IEEE 802.3 CMSG Interim Meeting2 Supporters

3. September 2004IEEE 802.3 CMSG Interim Meeting3 Issue Ethernet not adequate for low latency applications Ethernet not adequate for low latency applications Ethernet frame loss is inefficient Ethernet frame loss is inefficient Markets impacted Markets impacted Clustering and grid computing (RDMA, iWARP) Clustering and grid computing (RDMA, iWARP) Storage (iSCSI) Storage (iSCSI) Backplanes (802.3ap, ATCA) Backplanes (802.3ap, ATCA) Video (Video over IP) Video (Video over IP) Telecom and voice (VoIP) Telecom and voice (VoIP) Others? Others?

4. September 2004IEEE 802.3 CMSG Interim Meeting4 Market Need Decreased latency Decreased latency Critical for storage and clustering Critical for storage and clustering Reduces buffer requirements; therefore impacts cost of components Reduces buffer requirements; therefore impacts cost of components Reduced frame loss Reduced frame loss Important in all network applications Important in all network applications Prevent oversubscription with no latency impact Prevent oversubscription with no latency impact Improves performance of the system Improves performance of the system

5. September 2004IEEE 802.3 CMSG Interim Meeting5 Overview Oversubscription occurs in MAC Client 802.3x could assist, but halts all flows Preference is to keep 802.3 simple and rely on MAC Client to resolve 802.3 PHY 802.3 MAC 802.3 MAC Client MAC Client Service Interface

6. September 2004IEEE 802.3 CMSG Interim Meeting6 802.3x Pros Pros Proactive for oversubscription Proactive for oversubscription Cons Cons Halting all flows is not desirable Halting all flows is not desirable Removes control from upper layer protocols Removes control from upper layer protocols Adds latency to all flows Adds latency to all flows A feature no one uses A feature no one uses

7. September 2004IEEE 802.3 CMSG Interim Meeting7 MAC Client Many varieties of MAC Clients Many varieties of MAC Clients 802.1 (bridging) 802.1 (bridging) TCP/IP, UDP, etc. TCP/IP, UDP, etc. MAC Clients are reactive MAC Clients are reactive Wait for oversubscription to occur Wait for oversubscription to occur Protocols force rate limiting when oversubscription occurs Protocols force rate limiting when oversubscription occurs Buffers used to prevent transient congestion from becoming oversubscription Buffers used to prevent transient congestion from becoming oversubscription

8. September 2004IEEE 802.3 CMSG Interim Meeting8 The Evil Trade-off Buffers vs. frame loss Buffers vs. frame loss Frame loss is considered bad Frame loss is considered bad MAC Clients can control which frames are lost MAC Clients can control which frames are lost Buffers decrease frame loss, add latency Buffers decrease frame loss, add latency Trade-off Trade-off Increase latency and reduce frame loss Increase latency and reduce frame loss Or, reduce latency and increase frame loss Or, reduce latency and increase frame loss No win situation for latency & frame loss sensitive applications No win situation for latency & frame loss sensitive applications

9. September 2004IEEE 802.3 CMSG Interim Meeting9 Solution Provide a means for MAC Client to be proactive Provide a means for MAC Client to be proactive Decreases need for buffers Decreases need for buffers Reduces latency Reduces latency How? How? 802.3x was close 802.3x was close Permit MAC Clients to exchange congestion information via an 802.3 control messages Permit MAC Clients to exchange congestion information via an 802.3 control messages

10. September 2004IEEE 802.3 CMSG Interim Meeting10 Value Opens up latency and frame loss sensitive markets to Ethernet Opens up latency and frame loss sensitive markets to Ethernet Empower the Ethernet standards with support for improved congestion control in 802.3 L2 subnets Empower the Ethernet standards with support for improved congestion control in 802.3 L2 subnets Increase performance of MAC Clients Increase performance of MAC Clients Reduced frame loss decreases re-transmissions Reduced frame loss decreases re-transmissions Decrease cost of Ethernet components Decrease cost of Ethernet components Reduction in buffer requirements has a direct correlation to cost of components and systems Reduction in buffer requirements has a direct correlation to cost of components and systems

11. September 2004IEEE 802.3 CMSG Interim Meeting11 Recommendation Change the Objectives to better align with this strategy Change the Objectives to better align with this strategy Thanks to Shimon Muller for his feedback on the Objectives Thanks to Shimon Muller for his feedback on the Objectives

12. September 2004IEEE 802.3 CMSG Interim Meeting12 Current Objectives

13. September 2004IEEE 802.3 CMSG Interim Meeting13 Current Objectives Point-to-point links A mechanism to support exchange of congestion control information

14. September 2004IEEE 802.3 CMSG Interim Meeting14 Proposed Objectives Support point-to-point links only Specify a mechanism to support the exchange of congestion control information Specify a mechanism to limit the rate of transmitted data Preserve the MAC/PLS service interfaces Preserve the 802.3/Ethernet frame format at the MAC Client service interface Support full duplex operation only

15. Thank you! Questions?