1. Network Diagnostic Tool (NDT) Duplex-Mismatch detection update Fall Member Meeting Sept 21, 2005 Rich Carlson RCarlson@internet2.edu

2. 7/20/05 2 Motivation for work  Measure performance to users desktop  Identify real problems for real users Network infrastructure is the problem Host tuning issues are the problem  Make tool simple to use and understand  Make tool useful for users and network administrators

3. 7/20/05 3 Mismatches can occur anywhere

4. 7/20/05 4 Typical Campus infrastructure  Desktop/Laptop computer connects to building switch via (cat 5 twisted pair cable). Building Switch Desktop Laptop computer Building Wire Uplink to campus backbone Other hosts

5. 7/20/05 5 Ethernet transmission strategy  Half Duplex Use carrier sense signal to determine if link in use If not, send frame at head of queue Else, wait for frame to end and send frame Use collision detection signal to determine if other station also sends  Full Duplex Send packet at head of queue Disable carrier sense Disable collision detection

6. 7/20/05 6 Duplex Mismatch Detection  Condition exists due to configuration error User ‘Knows’ full duplex is faster than half duplex Administrator ‘prevents problems’ by fixing switch  Developing analytical model to describe how network operates  Expanding model to describe UDP and TCP flows  Test models in LAN, MAN, and WAN environments NIH/NLM grant funding

7. 7/20/05 7 Test environment  Receiver is put is various states Switch = full & Host = full or half Switch = half & Host = full or half Switch NDT Srv Source 100 Mbps Full Duplex NDT Clt Receiver 100 Mbps Mismatch Data Packets Ack Packets

8. 7/20/05 8 Results for TCP flows  Source is Full and Destination is Half Data packets lost Ack packets delayed or lost Expect poor performance due to large number of retransmissions  Source is Half and Destination if Full Data packets delayed or lost Ack packets lost Expect poor performance with large number of duplicate acks

9. 7/20/05 9 Analytical Loss-Model Loss vs Transmission rate

10. 7/20/05 10 TCP Operation on LAN  Observed behavior depends on direction of TCP flow and direction of mismatch  Losing ACKs has bigger effect than losing Data packets

11. 7/20/05 11 Four Cases of Duplex Setting FD-FD FD-HD HD-FDHD-HD

12. 7/20/05 12 Duplex Mismatch Switch is Full & Host is Half

13. 7/20/05 13 Tentative Mismatch Detection  Full to Half mismatch detection Large percentage of duplicate ACKs Connection spends majority of the time in CwndLimited state

14. 7/20/05 14 Duplex Mismatch Switch is Half & Host is Full

15. 7/20/05 15 Tentative Mismatch Detection  Half to Full mismatch detection Large number of timeouts causes long idle time (RTO x timeout value) Connection spends majority of the time in CwndLimited state

16. 7/20/05 16 Next Steps  Test proposed detection algorithms in LAN, MAN, and WAN environments  Test proposed detection algorithms with multiple clients (Windows, Mac, *nix)  Refine tool to report possible/probable problems

17. 7/20/05 17 Availability  Open Source Development project http://www.sourceforge.net/projects/ndt  Tools available via from http://e2epi.internet2.edu/ndt/download.html Contains source code  Email discussion list ndt-users@internet2.edundt-users@internet2.edu Goto http://e2epi.internet2.edu/ndt web site and clickhttp://e2epi.internet2.edu/ndt –ndt-users – General discussion on NDT tool –ndt-announce – Announcements on new features