beyond cable testing: ethernet performance and … cable testing: ethernet performance and...
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Beyond Cable Testing: Ethernet performance and troubleshooting
Peter Schweiger Americas Business DevelopmentAgilent Technologies
0 50 100 150 200 250 300 350-100
-90
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MHzN
ext,
dB
NEXT, pair 1 to 2
NEXT plotsNEXT plots
Cat 6 ChannelCat 6 ChannelLimitLimit
Page 2
The facts
Internet Traffic Growth Slows by Half in 2005 After 10 years of hyper growth, the rate is slowing. Global internet traffic grew by just 49 percent in 2005, down from 103 percent in 2004.
Fact: Increased traffic reduces network performanceData is becoming business, not just business critical
Page 3
The OSI Model - Open Systems Interconnection
Network Application Software. File transfer and email working with L6 & 5.
Translates different formats into a uniform format so that two different applications may function during a session.Synchronization signaling - this layer will decide which of the many nodes can transmit, at what time, and for how long.Has the primary Flow Control and Error Correction responsibility.
Network Routers: Routing methods, filtering rules, security and device identifiers such as IP addresses are very important on this layer. Media Access Control (MAC addresses). This layer groups data into packets, and transfers them after adding source and destination addressesAll of the connectivity - Cable, Connectors, Signaling and Voltage.Physical
Application
Presentation
Session
Transport
Network
Data Link
Layer
7
6
5
4
3
2
1
Page 4
Required Measurements –Category 3/5 vs. 5e vs. 6WiremapLengthInsertion Loss (Attenuation)NEXT (pair to pair)
ELFEXT (power sum) Propagation DelayDelay SkewReturn LossNEXT (power sum) ELFEXT (pair to pair)
Category 3 - 16MHzCategory 5 - 100MHz
Ethernet
Category 5E - 100 MHzCategory 6 - 250 MHz
Fast EthernetGigabit Ethernet
Page 6
The Burning Issue:We can measure cabling,
but can you measure a Ethernet network’s
Quality of Service (QoS)?
1. As Defined in your service level agreements (SLA’s)?2. As Experienced by your users?
Page 7
What is driving the issue?
• Ethernet is a “best effort” un-guaranteed service• Business customers require service level agreements• Summary: Contractors and IT professionals are being asked
to do more than check wiring. They are being asked to check connectivity and network performance.
Page 8
Good Performance?
Definition – Getting the expected performanceDo I measure it? E.g. You are paying for 100Mbps1. Rely on manufacturer’s specifications ?2. Assume since the cabling passes, the network is perfect3. Measure performance in a lab and compare to
performance once deployed ?
?
Page 9
Painting an Ethernet Picture: Frames
Preamble(8)
DestinationAddress
(6)
SourceAddress
(6)Type
(2)Data (46 - 1500 bytes) FCS
(4)
Ethernet 802.3
Frames vary in size from 64 Bytes to over 1500 Bytes in Length
Page 10
Ethernet Network Performance and affects. • Bandwidth
• File transfer speed, email, web downloads• Are all parts at the same speed? (Over subscription)• High utilization can cause delays
• Delay • 10-100ms is typical. VOIP quality is affected by >100ms delay
• Ethernet Data/Frame Loss • Some applications have retransmission• Streaming apps like Video and VOIP need low Frame loss.
• Burst support –• Improved file transfers or web page downloads
10MB/s
100MB/s
Page 11
Testing Network QoS of Ethernet Links Network availability and repair times are agreed to, but what about bandwidth, delay times, burst performance and data integrity?In 1999 Internet Engineering Task Force (IETF) created a suite of tests called RFC 2544 to:•Benchmark performance to compare later•Allow customers to define SLA’s with service providers
Page 12
Types of Network Performance tests.
RFC-2544 tests link capability (any 2 points in a network)• Bandwidth measurement – Throughput • Network delay - Latency • Error frames – Frame Loss • Burst support –Back to Back frames
Page 14
RFC-2544 Tests: Throughput ~Maximum amount of data transported in one second. Smaller size frames have a lower throughput because of pre-amble and inter-packet gap bytes.
Page 15
RFC-2544 Tests: Latency~Total Time taken for a frame to travel to it’s destination. = the sum of processing delays in network elements.
Affects VOIP quality
Page 16
Frame Loss~The number of frames transmitted but never received as the network load is increased. - Referred to as frame loss rate.- Expressed as a percentage of the total frames transmitted.
E.G: 1000 frames transmitted. 900 were received. Frame loss rate is: (1000 – 900) / 1000 x 100% = 10%.
Frames can be lost, or dropped, for a number of reasons including:•Errors (FCS)•Over-subscription of bandwidth e.g. (Ethernet Rate > SONET Rate)•Excessive Delay (2s)•Overloading devices (Routers)
Affects VOIP quality
Page 17
Back to Back test~Sends a counted burst of frames with minimum inter-frame gaps to the other tester and counts the # of frames returned. It increases and decreases the length depending on the results.
The back-to-back value is the maximum number of frames that can be transmitted successful from source to destination using a minimum inter-frame gap
Verify network can support bursts of traffic
Useful to verify you can use the bandwidth
Page 18
Testing Network QoS experienced by users Testing network resources vs. just the network.
The challenge is to: - Test in a repeatable way - Test in a way that simulates use.- Know what the results mean or see trends.- Isolate problems to resolve them.- Not be an expert on every test and resource.
Page 19
Types of Network Resources and services
Remote NetworkIP NetworkIP NetworkLocal Network
Gigabit UplinksGigabit Uplinks
10/100 Ethernet
Gigabit Backbone Switch/Router
Network services – DHCP, DNS, Routing• Background tasks executed but not visible to the user• Effects many different end user applicationsNetwork resources – file, email, print, and web servers• Directly noticeable by users
Page 20
Trouble Shooting Performance Problems
• Network is slow• User complaint is unclear• Network evolution may have overloaded
resources• Unsure what users and resources are on
the network.• How do I isolate performance problems?
Page 21
• Network Auto-discovery passively or actively discovers what’s on your network. See network utilization and errors
Discovering your networkFinding Network Resources
Handheld Ethernet Tester
Page 23
Application Performance – Web Accesss
Problem : Time to display web page is slowBreak operation into individual operationsName lookup – is the delay the DNS? serverPing – is the delay the network?Page download
How long did it take to get the 1st byte of the page? (this would indicate server not network delay)
How long did it take to get the entire page download
Page 24
Ethernet Tools: Check for connectivity and find the cause of problems.
Ping, Trace Route verify the resource is availableSNMP Queries reads and reports MIB informationStatistics displays utilization, top talker, traffic types Traffic Generator test under heavy traffic loads Performance tests include RFC-2544 Throughput, Latency, Frame Loss and Back-to-Back tests as well as IP and MAC Loopback. Blink Hub Port locates live network cable connectionError Log reports network configuration errors
Page 25
SummaryThe burning issue is testing Quality of Service of networks and how users experience it.RFC 2544 testing and an Ethernet tool kit –is a good way to test a network.In order to satisfy needs today and tomorrow, we must go beyond cable test to troubleshoot and measure a users network experience
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