EDM01-02: DAG 4.2S Card User Guide
©2005
20
Version 7: May 2006
Process
, continued
Process
Description
Setting capture session
parameters.
Parameters are set with
dagfour
.
The card can operate in two modes, variable
length capture (
varlen
), and fixed length
capture (
novarlen
).
In variable length capture mode, a maximum
capture size is set with
slen=N
bytes. This
figure should be in the range 32 to 2048 and is
rounded down to the nearest multiple of 4.
Packets longer than
slen
are truncated. Packets
shorter than
slen
will produce shorter records,
saving bandwidth and storage space.
Full packet capture for example:
tools/dagfour –d dag0 varlen slen=1536
Setting fixed length
mode.
In fixed length mode, packets longer than the
selected
slen
are truncated to
slen
.
Packets shorter than slen produce records
padded out to
slen
length.
Large
slen
values in fixed length mode should
not be used because short packets arriving
produce large padded records, wasting
bandwidth and storage space.
An example, for fixed length 64-byte records,
choose
slen=48
(64 – ERF header size of 16):
is:
tools/dagfour –d dag0 novarlen slen=48
