the network affandi singaren, singapore doug pearson indiana university internet2 commons site...
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![Page 1: The Network Affandi Singaren, Singapore Doug Pearson Indiana University Internet2 Commons Site Coordinator Training December 3, 2003 National University](https://reader036.vdocuments.site/reader036/viewer/2022062321/56649da05503460f94a8bd02/html5/thumbnails/1.jpg)
The Network
Affandi Singaren, Singapore
Doug PearsonIndiana University
Internet2 Commons Site Coordinator TrainingDecember 3, 2003National University of Singapore
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A Sample University Network
LAN
Building network
Campus backbone
WAN intranet
Internet
Internet2
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Sample Network
UNIVERSITY3rd floor
2nd floor
1st floor
Ethernet switch horizontal wiring station cable device
router
WAN
Campus Backbone
datajack
iMac
risers
CommercialInternet
LAN and Building Network
intranet
Internet2
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Wiring and Station Cables
3rd floor
Ethernet switch horizontal wiring station cable devicedatajack
iMac
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 +
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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.
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Ethernet LAN
3rd floor
2nd floor
1st floor
Ethernet switch horizontal wiring station cable device
router
datajack
iMac
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Ethernet LAN
10 / 100 / 1000 Mbps
Full- and Half-Duplex• Half-duplex: send or receive, one at a time.• Full-duplex: send and receive simultaneously.• 10 Mbps Ethernet supports half-duplex; full-duplex is not consistently implemented.
• 100 Mbps supports half- and full-duplex.
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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.
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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!
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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
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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
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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).
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LAN: Duplex Mismatch – Detection
Microsoft Windows doesn’t display the auto-negotiated duplex setting.
Some routers re-negotiate Auto-duplex, which introduces jitter.
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LAN: Ethernet Duplex Mismatch
switch device switch device
auto auto auto autohalf half half halffull full full full
auto full BAD! half fullfull auto BAD! full half
auto half half halfhalf auto half half
SETTINGS RESULTS
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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
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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
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Router
3rd floor
2nd floor
1st floor
Ethernet switch
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
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Router
WAN
Campus Backbone
intranet Internet2intranetInternet2
CommercialInternet
Provides interface to the WAN.• Intranet, commercial
Internet, and Internet2 connections.
• Typically, every networked device at an Internet2-connected institution has connectivity to Internet2.
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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.
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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.
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VLAN
3rd floor
2nd floor
1st floor
Campus Backbone
3rd floor
2nd floor
1st floor
Building A Building B
Router
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VLAN
Modern campus network architectures are tending to move away from traditional router-for-a-building design, to VLAN designs.
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Old Design Included a lot of Routers
UNIVERSITY3rd floor
2nd floor
1st floor
Ethernet switch horizontal wiring station cable device
router
WAN
Campus Backbone
datajack
iMac
risers
CommercialInternet
LAN and Building Network
intranet
Internet2routers
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New Design Includes VLAN Router
router
UNIVERSITY3rd floor
2nd floor
1st floor
Ethernet switch horizontal wiring station cable device
WAN
Campus Backbone
datajack
iMac
risers
CommercialInternet
LAN and Building Network
intranet
Internet2
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WAN Segments
Service Speed Sample Uses
T1 1.5 Mbps remote building; extension center
DS3 45 Mbps inter-campus; Internet (I1) connection
OC3 155 Mbps inter-campus; I1 & Internet2 connection
OC12 622 Mbps I1 backbones; Internet2 connection
OC48 2.4 Gbps I1 and Internet2 backbones
GigabitEthernet
1 Gbps advanced inter-campus connections when have access to dark fiber
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Indiana University Abilene NOC Weathermap
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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
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Traffic on the Network
Typical university today:• IP
– TCP– UDP
• IPX [diminishing]• Appletalk [diminishing]
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Traffic on the LAN
Unicast : one-to-one
Multicast: one-to-many
Broadcast: one-to-every
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Unicast
Most common traffic
Common applications: mail, Web browsing, file transfer, etc.
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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
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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.
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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.
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Broadcast
A healthy network should have less than 100 broadcast packets per second.
Check using a network traffic and protocol analyzer tool.
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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.
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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.
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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.
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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.
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NATs
Difficult to use H.323 behind NATs.
Some videoconferencing terminals provide features to work with NAT – refer to videoconferencing terminal documentation.
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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.
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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.
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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
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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?
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Packet Loss
Packet loss is typically due to congested links and routers.
• 1% is noticeable
• 5% becomes intolerable
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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.
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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.
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QoS
Caution!•The wrong implementation could result in unwanted tradeoffs, e.g., packet loss improves but jitter gets worse.
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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.
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The End-to-End Performance Problem
Problem• How do the users get timely, useful assistance?• How is network problem resolution coordinated?
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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.
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The End-to-End Performance Problem
Solutions• Articulate the E-2-E problem to network management and engineers on all campuses.
• Establish reliable communication tools, and insist that engineers utilize the tools.
• Hold regular meetings; bring all engineers together in one place and time to share information.
• Have good network documentation for all networks.
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H.323 is Network Sensitive!
The big problems are:• Half/Full-duplex mismatches• Packet loss• Jitter• Substandard horizontal wiring or station cables• Multicast leaks• High broadcast rates
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Tools
Ping – availability, loss, roundtrip time Traceroute – path discovery Pingplot – graphical traceroute/ping MRTG – graph link/port utilization & errors Iperf – bandwidth, loss and jitter Gnuplotping – visualize jitter Sniffer – inspect traffic on the LAN VideNet Scout – bandwidth, loss and jitter Internet2 Detective – detect I2 connection H.323. Beacon –protocol-specific tests
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Tools: Ping
Test for availability, loss, and roundtrip time
ICMP Echo Request• Plus optional dummy payload – only in the direction of the ping, i.e., source destination
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Tools: Sample Ping from Windows
C:\WINDOWS>ping 10.1.1.1 Pinging 10.1.1.1 with 32 bytes of data: Reply from 10.1.1.1: bytes=32 time=88ms TTL=112 Reply from 10.1.1.1: bytes=32 time=72ms TTL=112 Reply from 10.1.1.1: bytes=32 time=69ms TTL=112 Reply from 10.1.1.1: bytes=32 time=69ms TTL=112 Ping statistics for 10.1.1.1: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds: Minimum = 69ms, Maximum = 88ms, Average = 74ms C:\WINDOWS>
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Tools: Sample Ping from Windows
C:\WINDOWS>ping -l 40000 10.1.1.1
Pinging 10.1.1.1 with 40000 bytes of data:
Reply from 10.1.1.1: bytes=40000 time=2412ms TTL=112
Reply from 10.1.1.1: bytes=40000 time=2721ms TTL=112
Reply from 10.1.1.1: bytes=40000 time=2761ms TTL=112
Reply from 10.1.1.1: bytes=40000 time=2714ms TTL=112
Ping statistics for 10.1.1.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 2412ms, Maximum = 2761ms, Average = 2652ms
C:\WINDOWS>
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Tools: Ping Big and Fast on Linux
ping -c2000 -i.03 -s1470 -q [destination]• Count of 2000 packets• Interval of .03 seconds between packet starts• Packet size of 1470 bytes• (2000)(.03) = 60 second long test• (1/(.03 sec/packet))(1470 bytes/packet)(8 bits/byte) = 392 Kbps
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Tools: Ping Big and Fast on Linux
$ ping -c2000 -i.03 -s1470 -q [hostname]
PING [hostname] ([hostaddr]) from [hostaddr2] : 1470(1498) bytes of data.
--- [hostname] ping statistics ---2000 packets transmitted, 2000 packets received, 0% packet loss
round-trip min/avg/max = 4.8/5.1/13.2 ms
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Tools: Traceroute
Used to discover the layer-3 network path (routers) between the two endpoints
Doesn’t identify layer-2 devices (switches)
Must run from one of the discovery endpoints – it can’t act as a third party.
Take baselines – know what your path should be in advance of trouble
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Tools: Traceroute
Microsoft tracert uses ICMP packets, whereas Unix traceroute uses UDP; may be of importance in networks where routers are configured to not respond to ICMP; or if ICMP is blocked.
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Tools: Traceroute; Sample Output
[dodpears@huck dodpears]$ traceroute www.internet2.edu traceroute to www.internet2.edu (209.211.239.208), 30 hops max, 38 byte
packets
1 wcc-sub5-hp1 (129.79.5.253) 11.726 ms 0.627 ms 0.571 ms 2 iub-gw (129.79.8.10) 3.133 ms 0.717 ms 0.651 ms 3 156.56.249.22 (156.56.249.22) 2.544 ms 3.138 ms 2.538 ms 4 abilene-iupui.abilene.ucaid.edu (198.32.11.13) 5.245 ms 3.402 ms 3.493
ms 5 clev-ipls.abilene.ucaid.edu (198.32.8.26) 9.381 ms 9.586 ms 9.244 ms 6 nycm-clev.abilene.ucaid.edu (198.32.8.30) 23.198 ms 21.963 ms 21.775
ms 7 border-abilene-oc3.advanced.org (209.211.237.97) 23.448 ms 23.268 ms
23.052 ms 8 www.internet2.edu (209.211.239.208) 23.559 ms 23.478 ms 23.234 ms
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Tools: Traceroute
8 www.internet2.edu (209.211.239.208) 23.559 ms 23.478 ms 23.234 ms
Hop
Router/host name
Router/host address
Round-trip times of each of three probes
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Tools: Traceroute – Example Uses
Identify the path, and then perform pings along the path segments to isolate troublesome segments.
Insure that Internet2 is being used for a connection, rather than commercial Internet.
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Tools: Ping Plotter
Shareware tool; $15• http://www.pingplotter.com
Performs a visual traceroute and ping tests along the entire path
Permits identification of bottlenecks along a path
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Tools: Ping Plotter
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Tools: MRTG
Multi Router Traffic Grapher
Collect and graph scalar, time-based data, e.g., router and link performance data.
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Tools: MRTG
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Tools: MRTG
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Tools: Iperf
http://dast.nlanr.net/Projects/Iperf/
Client/server application that• Measures maximum TCP bandwidth• Facilitates tuning of TCP and UDP parameters• Reports bandwidth, jitter, and packet loss
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Tools: IperfExample on Intercampus DS3
At server, invoke:
iperf -fk -i30 -u -s(f)ormat reports in kbps
(i)nterval for reporting = 30 seconds
(u)dp
(s)erver mode
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Tools: IperfExample on Intercampus DS3
At client, invoke:
iperf -u -b800k -t3600 -c [hostname-server](u)dp
(b)andwidth = 800kbps
(t)ime of run = 3600 seconds
(c)lient mode
[hostname-server] = server to target
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Tools: IperfExample on Intercampus DS3
[dodpears@vc-iperf iperf]$ iperf -fk -i30 -u -s
------------------------------------------------------------
Server listening on UDP port 5001
Receiving 1470 byte datagrams
UDP buffer size: 64.0 KByte (default)
------------------------------------------------------------
[ 3] local 149.166.197.80 port 5001 connected with 129.79.92.230 port 1031
[ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
[ 3] 0.0-30.0 sec 3000 KBytes 819 Kbits/sec 0.300 ms 0/ 2090 (0%)
[ 3] 30.0-60.0 sec 3000 KBytes 819 Kbits/sec 0.242 ms 0/ 2090 (0%)
[ 3] 60.0-90.0 sec 3000 KBytes 819 Kbits/sec 0.338 ms 0/ 2090 (0%)
[...]
[ 3] 0.0-90.0 sec 9000 KBytes 819 Kbits/sec 0.263 ms 0/ 6393 (0%)
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Iperf- Example on Intercampus DS3
MRTG utilization graph showed bandwidth peaking at capacity ~ 10:00a – 2:00p
As utilization peaked on the DS3, jitter measured by Iperf rose to unacceptable level
Iperf also reported periodic high packet loss, with no apparent correlation to the low-resolution MRTG utilization reports
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Iperf- Example on Intercampus DS3
Second day, utilization as reported by MRTG is staying reasonable.
Jitter measured by Iperf is staying low.
The periodic high packet loss remains, until noon when network engineer adjusted the QoS settings.
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Third day, utilization peaking at 3:00p.
As utilization peaked jitter measured by Iperf also rising.
Still no packet loss.QoS fixed the packet loss
problem, but still not certain about the jitter – more analysis needed.
Iperf- Example on Intercampus DS3
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Tools: Gnuplotping
Pings multiple hosts in parallel with graphical display (gnuplot) of the delay distribution.
Runs on Unix/X-Windows
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Tools: gnuplotping
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Tools: Network Traffic Analyzer
Reveals the traffic on a LAN
Protocol analysis
Reports such as utilization, protocols, conversations, nodes, etc.
Network General Sniffer
WildPackets EtherPeek
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Tools: ViDeNet Scout
Scout is a web-based, distributed network performance analysis tool developed at the University of North Carolina at Chapel Hill.
Scout makes use of the Chariot performance testing engine developed by NetIQ.• http://scout.video.unc.edu/
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Tools: Internet2 Detective
I2 Detective is a small application.
Detects Internet2 connection.
Measures connection bandwidth (using Iperf).
Detects multicast connection.• http://detective.internet2.edu/
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Tools: H.323 Beacon
Used to measure, monitor and qualify the performance of an H.323 Videoconference session.
Provides H.323-protocol specific evidence and other information necessary to troubleshoot H.323 application performance problems in the network and at the host (end-to-end) • http://www.itecohio.org/beacon/
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Recommendations
Develop a close relationship with the network engineers and NOC. Make sure they understand what’s being done with videoconferencing and the network sensitivity of IP-based video.
Articulate the End-to-End Performance Problem to network engineering and operations management. Champion ways to reduce the problem.
Be sure to open trouble tickets with your NOC so that a problem history is maintained.
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Recommendations
Use switched Ethernet.
Watch out for duplex mismatches.
Keep an eye on utilization of WAN links, packet loss, and jitter.
Make sure you don’t have broadcast or multicast leaking problems.
Make sure wiring is up to the task.
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Recommendations
Have engineers in the videoconferencing support group trained to understand networking issues and tools.