EDM01-36v10 DAG_9.2X2_Card_User_Guide - Using your DAG card
©2010 - 2012 Endace Technology Ltd. Confidential - Version 10 - May 2012
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Capturing data at high speed
As the DAG card captures packets from the network link, it writes a record for each packet into a buffer
in the host computer’s main memory.
To avoid packet loss, the user application reading the record, such as
dagsnap
, must be able to read
records out of the buffer as fast or faster than they arrive. If not the buffer will eventually fill and packet
records will be dropped by the DAG card.
If the user process is writing records to hard disk, it may be necessary to use a faster disk or disk array.
If records are being processed in real-time, a faster host CPU may be required.
When the computer buffer fills the “Data Capture” LED on the card will flash or flicker, or may go OFF
completely.
In Windows no screen message displays to indicate when the buffer is full. Please contact Endace
Customer Support at
for further information on detecting buffer overflow and
packet loss in Windows.
Detecting packet drops
Once the buffer fills, any new packets arriving will be discarded by the DAG 9.2X2 card until some data is
read out of the buffer to create free space.
You can detect any such losses by observing the Loss Counter (
lctr
field) of the Extensible Record
Format (ERF), or examining the stream drop counters. See
Stream drop count
(page 31) and
Data
Formats
(page 65) for more information.
Increasing buffer size
You can increase the size of the host computer buffer to enable it to cope with bursts of high traffic load
on the network link.
For information on increasing the buffer size, see
buffer_size
(page 26).
For information on calculating the required stream buffer size, see
Guidance for stream buffer sizing
(page 71).
Capturing packets using Enhanced Packet Processing v2
For information on capturing packets using Enhanced Packet Processing v2, refer to
EDM04-31 Enhanced
Packet Processing v2
.
Filtering data
This DAG card uses the dagfilter-loader software with Enhanced Packet Processing v2. For details on
dagfilter-loader, refer to
EDM04-30 dagfilter-loader Software Guide
.
