Fibre channel network integrity testing, Interfaces, Applications – Atec EXFO-FTB-8120-8130NGE User Manual

Page 8: Latency, Buffer-to-buffer credit estimation, Login testing

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FTB-8120NGE/8130NGE Power Blazer

fiBrE channEl nEtWorK intEgrity tESting

EXFO’s FTB-8120NGE/8130NGE Power Blazer modules allow comprehensive testing capabilities for Fibre Channel network
deployment.

Interfaces

These modules support multiple Fibre Channel interfaces:

Applications

Since most SANs cover large distances and Fibre Channel has stringent performance attributes that must be respected, it is
imperative to test at each phase of network deployment to ensure appropriate service levels. EXFO’s FTB-8120NGE/8130NGE
Fibre Channel option provides full wire-speed traffic generation at FC-0, FC-1 and FC-2 logical layers, allowing BER testing for
link integrity measurements. Latency, buffer-to-buffer credit measurements for optimization, and login capabilities that enable end-
to-end Fibre Channel network testing features are also supported.

Latency

Transmission of frames in a network is not instantaneous and is subject to multiple delays caused by the propagation delay in the
fiber and by processing time inside each piece of network equipment. Latency is the total accumulation of delays between two
end points. Some applications such as VoIP, video and storage area networks are very sensitive to excess latency.

It is therefore critical for service providers to properly characterize network latency when offering Fibre Channel services. From the
latency measurement that they perform, the FTB-8120NGE/8130NGE modules estimate buffer-to-buffer credit value requirements.

Buffer-to-Buffer Credit Estimation

The buffer credit mechanism is the flow-control engine for Fibre Channel. This is a crucial configuration parameter for optimal
network performance. Usually, network administrators calculate the value by taking the distance traveled and the data rate into
consideration; however, since latency issues are not considered, poor accuracy is to be expected. The FTB-8120NGE/8130NGE
modules are capable of estimating buffer credit values with respect to latency by calculating the distance according to the round-
trip latency time.

Login Testing

Most new-generation transport devices (xWDM or SONET/SDH MUX) supporting Fibre Channel are no longer fully transparent;
they also have increased built-in intelligence, acting more as Fibre-Channel switches. With switch fabric login ability, the FTB-
8120NGE/8130NGE modules support connections to a remote location through a fabric or semi-transparent networks.

The login process not only permits the unit to connect through a fabric, but it also exchanges some of the basic port characteristics
(such as buffer-to-buffer credit and class of service) in order to efficiently transport the traffic through the network.

The login feature allows automatic detection of port/fabric login, login status (successful login, in progress, failure and logout) and
response to remote buffer-to-buffer advertised credit.

INTERFACE

RATE (G

BIT

/

S

)

1x

1.0625

2x

2.125

4x

4.25

10x

10.51875

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