beyond cable testing: ethernet performance and … cable testing: ethernet performance and...

Beyond Cable Testing: Ethernet performance and troubleshooting

Peter Schweiger Americas Business DevelopmentAgilent Technologies

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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

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

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

The Evolution of the Contractor

ELECTRICAL CONTRACTOR

DATACOMM CONTRACTOR

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?

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.

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 ?

?

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

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

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

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

RFC 2544 Tests: Test anywhere

WAN

Any Ethernet connection

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.

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

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

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

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.

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

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?

• 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

Testing Network QoS experienced by users Can now be done by anyone.

1

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

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

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

Want more information on Ethernet Testing?

RFC 2544 Testing White Paper

Where to get more information

Peter Schweiger 905 282 [email protected]

Agilent Call Center 1-800-829-4444

www.agilent.com

beyond cable testing: ethernet performance and … cable testing: ethernet performance and...

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