Trace Utilities Isolate Data Flow Problems Between Stations (103889)

SUMMARY

A number of problems can occur in the data flow path between two network stations and they can cause errant, restricted or even halted communication. Trace utilities make it possible to find problems in vertical interfaces or peer protocols so that proper network communications can be restored.

VERTICAL INTERFACE TRACE UTILITIES

Since layer entities within a station call layer entities above and below through established service access points (SAPs) in order to pass a defined interface data unit (IDU) structure, interface trace utilities can be written to:

• "Hook" the SAP entry point, saving the original entry point
• Gain control when the SAP entry point is called
• Examine the IDU structure being passed, "snapshot" all or part of the IDU and write the snapshot to a buffer or log file
• Pass control to the original SAP entry point

If the data flow problem is due to an errant layer entity (passing incorrect or incorrectly formatted ICI information, "freezing up," etc.), an examination of the log generated by the interface trace utility should reveal the cause of the problem. An example of a vertical interface trace utility used for LAN Manager troubleshooting is the NBTRAP (NetBIOS interface trace) utility.

PEER PROTOCOL TRACE UTILITIES

A specially configured computer can connect to the physical medium to receive and examine all frames sent to and from specified network addresses. If you set the computer software to display frame header information at any selected functional layer, then you can examine peer protocol conversations between selected stations to see if the data flow problem is due to peer protocol errors. An example of a peer protocol trace utility is the Sniffer from Network General.