METRODATA NetTESTER FAMILY USER MANUAL
76-02-107 Rev.A
Page 46 of 133
In addition, packets carrying an IP payload will have their source/destination IP
addresses swapped, the TTL field reset to a value of 32 and the IP checksum
recalculated, as per the Layer 3 loopback.
Further, packets carrying a UDP payload will have their UDP source/destination
ports swapped and the UDP checksum set to zero.
The Layer 4 mode is intended for use where the traffic comes from a Metrodata
device operating in 'Layer 3' tester mode (see below).
10.3 Tester Function
In tester mode, the SAM becomes a packet generator and analyser.
Packets up to 10k bytes can be generated, with complete control over packet type
and header values. The packet stream can include a mix of up to 5 different packet
sizes.
Packets can be generated up to full wire-speed, and with sophisticated timing
controls to allow simulation of real-world traffic characteristics such as burstiness.
Hardware-based timestamping is used to record packet transmission and reception
times, providing high-accuracy delay measurements for every packet.
10.3.1
Test Regimes
A 'manual' mode is provided that allows direct access to the tester functions.
However, this is complicated to use and not recommended, except for specialised
applications.
For general use, the unit offers a suite of 'scripted' tests, supporting different service
activation test methodologies (referred to as 'regimes'). As well as simplifying the
setup process, these offer:
•
Test parameters that are tailored to each regime;
•
Test setups that are saved as part of the unit configuration;
•
The ability to define multiple tests that will run sequentially;
•
A common system for identifying peer (loopback) devices, with the option to
operate in a Layer 2 (MAC address) or Layer 3 (IP address) environment;
•
A simple interface to the standard SLA system (also used for performance
monitoring and flow policing);
•
Report generation and handling system, allowing test results to be viewed as
they are generated or after the test has completed, and uploaded as text files
to a TFTP server.
