The Network

1. Dave Devereaux-Weber University of Wisconsin-Madison Internet2 Commons Site Coordinator Training March 22, 2004 Indianapolis, Indiana The Network

2. A Sample University Network • LAN • Building network • Campus backbone • WAN intranet • Internet • Internet2

3. Sample Network

4. Wiring and Station Cables • Common practice is unshielded twisted-pair (UTP) according to the specs: • CAT 3 [old] supports 10 Mbps Ethernet (10base-T) • CAT 5 [modern] supports 10base-T, 100 Mbps (100base-TX) and 1000 Mbps (1000base-T) Ethernet • CAT 6 [new] supports CAT 5 applications +

5. Wiring and Station Cables • Actual wire used and quality of installation may vary widely – know your wiring! • Important to consider the station cables • Don’t use sub-CAT 5 station cables for 100 Mbps connections. • Silver Satin telephone line cords are not CAT 5.

6. Ethernet LAN

7. Ethernet LAN • 10 / 100 / 1000 Mbps • Full- and Half-Duplex • Half-duplex: send or receive, one at a time (listens for collision). • Full-duplex: send and receive simultaneously (does not listen for collision). • 10 Mbps Ethernet supports half-duplex; full-duplex is not consistently implemented. • 100 Mbps supports half- and full-duplex. • Modern Ethernet devices can auto-sense speed and duplex.

8. LAN: Switches vs. Repeaters • Repeaters (hubs) are old technology. • A repeater sends (repeats) packets that are incoming on one port, out all other ports (I know you’re out there somewhere!). • Can only operate in half-duplex mode. • Bandwidth and jitter provided to any single device is highly dependent on the LAN traffic.

9. LAN: Switches vs. Repeaters • A switch learns the MAC addresses of the devices connected to it, and sends packets directly and only to the target end-point. • Provides much more consistent bandwidth and latency (low jitter). • A well-designed switched LAN is important for videoconferencing. Repeater-based LANs should be upgraded to switched for videoconferencing!

10. LAN: Ethernet Duplex Mismatch • “One of the most common causes of performance issues on 10/100Mb Ethernet links is when one port on the link is operating at half-duplex while the other port is operating at full-duplex.” • http://www.cisco.com/warp/public/473/3.html

11. LAN: Ethernet Duplex Mismatch • “There is a silent performance-killer out there, one so inconspicuous that it is hardly ever looked for or even suspected. You could suffer from it and never know it, as it robs a site of performance but not connectivity. This performance-killer has a name: Ethernet duplex mismatch.” • http://www.hostingtech.com/nm/01_01_mismatch.html

12. LAN: Ethernet Duplex Mismatch • If one end of a connection (device or Ethernet switch) is set for auto-negotiation, and fails to see auto-negotiation at the other end, the former sets itself to the default, half-duplex. • Auto-negotiation can sometimes fail, even when both sides are set to auto (although this isn’t as prevalent as in the past).

13. LAN: Duplex Mismatch – Detection • Microsoft Windows doesn’t display the auto-negotiated duplex setting. • Some routers re-negotiate auto-speed or auto-duplex, which can introduce jitter.

14. LAN: Ethernet Duplex Mismatch

15. LAN: Duplex Mismatch – Detection • Show port statistics on the Ethernet switch. When mismatched, the full-duplex end will report a high level of CRC or alignment errors; the half-duplex end will report a high number of late collisions. • Port Align FCS Xmit Rcv UnderSize • Err Err Err Err • 2/11 - 0 0 3077 0 • Port Single- Multi- Late- Excess- CarriSen Runts Giants • Coll Coll Coll Coll • 2/11 3233 0 2588 0 0 2489 0

16. LAN: Duplex Mismatch- Prevention • Always configure switches and devices according to your local policy. An example policy is: • If building wiring is sub-CAT 5, then set switch ports to 10/half • If building wiring is CAT 5 or better, then set switch ports and devices to Auto. • Monitor switch port stats and logs

17. Router • Segments LANs into distinct networks and subnetworks, e.g., the distinct red, green, and blue LANs with distinct network numbers. • Segments LANs into broadcast domains

18. Router • Provides interface to the WAN. • Intranet, commercial Internet, and Internet2 connections. • Typically, every networked device at an Internet2-connected institution has connectivity to Internet2.

19. VLAN • A single, physical LAN can be logically segmented into multiple logical LANs; and, • Physically separate LANs can be made to behave and appear as a single LAN.

20. VLAN • Packets are tagged according to LAN membership, e.g., green LAN, red LAN, and blue LAN. • Ethernet switches establish broadcast domains according to the defined VLAN boundaries. • Routers establish multiple VLANs on a single interface.

21. VLAN

22. VLAN • Modern campus network architectures are tending to move away from traditional router-for-a-building design, to VLAN designs.

23. Old Design Included a lot of Routers routers

24. New Design Includes VLAN Router router

25. WAN Segments

26. Indiana University Abilene NOC Weathermap

27. High Performance Research and Education Networks • Internet2 / Abilene • http://www.internet2.edu • http://www.abilene.iu.edu • STARTAP and International Networks • http://www.startap.net • US Government-Sponsored Networks • http://www.startap.net/NETWORKS

28. Traffic on the Network • Typical university today: • IP • TCP • UDP • IPX [diminishing] • Appletalk [diminishing]

29. Traffic on the LAN • Unicast : one-to-one • Multicast: one-to-many • Broadcast: one-to-every

30. Unicast • Most common traffic • Common applications: mail, Web browsing, file transfer, etc.

31. IP Multicast • A one-to-many mode of transmission • Network numbers 224.0.0.0 through 239.255.255.255 are reserved for multicast. • Examples of multicast applications: • Vic/rat videoconferencing • Centralized PC software administration tools such as Symantec Ghost

32. IP Multicast – Leak Problems • Beware: high rates of unpruned multicast can adversely affect videoconference performance. • Use a network traffic and protocol analyzer to identify this problem.

33. Broadcast • A one-to-every mode of transmission • Used by network protocols including ARP and IPX, NetBIOS system discovery, and name resolution. • All devices on the network must process every broadcast packet; high broadcast rates can divert processing capacity. • If the broadcast domain is too large or unusually active, the activity required at the end-point to deal with the broadcasts could diminish performance.

34. Broadcast • A healthy network should have less than 100 broadcast packets per second. • Check using a network traffic and protocol analyzer tool.

35. Firewalls • A firewall is a network node that acts to enforce an access control policy between two networks, e.g., between a university intranet and the commercial Internet. • Used to secure IT resources against external attacks and break-ins. • Network-layer firewalls typically make their decisions based upon port numbers and source/destination addresses. • Application-layer firewalls act as proxies.

36. Firewalls • H.323 uses the IP ports: • Statically-assigned TCP ports 1718 – 1720 and 1731 for call setup and control. • Dynamically-assigned UDP ports in the range of 1024 – 65535 for video and audio data streams. • Firewalls don’t allow unrestricted ports. Typical modern firewalls and H.323 don’t get along so well.

37. Firewalls – Solutions for H.323 • [bad; non-scaleable] Allow unrestricted ports for specific, known, external IP-addresses. • [better, but still not so good] Use feature of some videoconferencing clients to confine dynamic ports to a specific, narrow range. • [OK, but extra admin work and cost] Use an H.323 application proxy. • [best] Use a firewall that snoops on the H.323 call set-up channels (static ports) and opens ports for the audio/video (dynamic ports) as needed.

38. NATs • Allows multiple computers behind the NAT to share one external network address. • Uses: • Alleviate shortage of IP addresses • Security – obscures view of the network from outside • Flexible network administration • Not commonly used at universities on the campus level. Used somewhat in corporations. Common in small offices and at home – behind DSL, cable modem, or ISDN network service.

39. NATs • Difficult to use H.323 behind NATs. • Some videoconferencing terminals provide features to work with NAT – refer to videoconferencing terminal documentation.

40. Latency • Latency is the time required for a packet to traverse a network from source to destination. • Components of latency include: • Propagation delay: the time it takes to traverse the distance of the transmission line; controlled by the speed of light in the media; rule-of-thumb: 20ms San Francisco to New York.

41. Latency • Transmission delay: the time it takes for the source to put a packet on the network. Rule-of-thumb: < 1ms. • Store-and-forward delay: the cumulative length of time it takes the internetworking devices along the path to receive, process, and resend the packets. Rule-of-thumb: variable, and depends upon network load.

42. Latency • Rule of thumb: • A one-way delay of: • 0 – 150 ms provides excellent interactivity • 150 – 300 ms is OK • 300 – 400 ms is bad • 400+ ms is unacceptable

43. Jitter • Jitter is variation in latency over time. • If the endpoints are on switched LANs, then the primary source of jitter is variation in the store-and-forward time, resulting from network load. • H.323, particularly audio, is adversely affected by high levels of jitter. • What is high? Rule of thumb?

44. Packet Loss • Packet loss is typically due to congested links and routers. • 1% is noticeable • 5% becomes intolerable

45. QoS • Not currently feasible on commercial Internet and Internet2 networks for production, regular use. Internet2 is working on QoS plans, but the current over-provisioned Internet2 network doesn’t dictate need. • Is useful on over-utilized intranet WAN links.

46. QoS • How: • Some videoconferencing terminals can set the IP precedence bits. Use that for marking and priority queuing on the WAN. • Or: • Use a H.323 Proxy for consolidation of traffic to a single address, router access list for marking, and priority queuing on the WAN.

47. QoS • Caution! • The wrong implementation could result in unwanted tradeoffs, e.g., packet loss improves but jitter gets worse.

48. The End-to-End Performance Problem • Scenario • Users on two different campuses of a university are experiencing poor video and audio in a conference. • Each user is supported by a different group of videoconferencing engineers. • Each campus is supported by a different group of network engineers. • The wide-area network is supported by a third group of network engineers.

49. The End-to-End Performance Problem • Problem • How do the users get timely, useful assistance? • How is network problem resolution coordinated?

50. The End-to-End Performance Problem • Obstacles • Different groups, schedules, and priorities. • No one engineer has a complete understanding of the entire network path. • No one engineer can gain access to all the network nodes (routers, switches) along the path to inspect for trouble. • Communications are inconsistent from engineer to engineer.