Agilent Technologies 37907A Bedienungsanleitung PDF herunterladen (Seite 15)

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During the time that the cell table is not being sent, the ATM software

will send idle or unassigned cells. Send Control allows the contents of

cell table to be sent once or repetitively, or for AIS or idle cells to be

sent. The peak cell rate (PCR) of the cell table based traffic can be set

from zero to the following maximum values, all of which are 100%

utilization for that interface. Also, for ease of entry, a percent of

utilization can be entered, such as 50% in place of the cells per second

value.

• 353,207 cells per second for STM- 1/OC- 3

• 3,623 cells for DS1

• 4,528 cells for E1

To generate OAM cells, the user can use quick tests that include F4 and

F5 segment or end- to- end cells with user- defined VPI[- VCI] values, they

are transmitted from the traffic generator. To generate cell errors, modify

the quick tests to add corrupted cells to the cell table.

The fields of the generated ATM cell header can be specified as follows:

• VPI values from 0 to 255 (UNI), or 0 to 4095 (NNI)

• VCI values from 0 to 65,535

• GFC values from 0 to 15 (UNI only, not applicable in NNI)

• PTI values from 0 to 7

• CLP values of 0 or 1

• HEC can be set to good (automatically calculated), bad, or user

defined.

The generated ATM cell payload can be defined in hex, decimal,

ASCII, or ‘‘don’t care.’’ Errors can be inserted on any bit within any

byte of the payload.

ATM Quality of Service (QoS) and Policing Tests

The ATM software has the ability to do various real- time tests and

measurements to check the performance of ATM networks. These fall into

two main categories -- policing and traffic contract shaped test cell

generation, really mirror images of each other. In the case of policing,

the ATM software monitors live traffic and measures conformance to the

traffic contract. Test cell generation allows test traffic shaped to a traffic

contract to measure the network’s ability to deliver the promised QoS,

i.e. is the network meeting its SLA (service level agreement) obligations?

Policing, traffic shaping and traffic contract measurements

One of the most important premises of the deployment of ATM networks

is the ability to maintain a given level of QoS within the public ATM

network. ATM networks protect themselves by policing incoming traffic to

check its conformance with pre- determined traffic contract parameters.

Some cells may have to be discarded or ‘‘tagged’’ (marked to low

priority) in order to protect the traffic of other users of the ATM

network.

Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com

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