"The P/S-CSCF specifies a dedicated port, or it inserts a unique header parameter or username parameter in its SIP URL Path and Record-Route headers. The P/S-CSCF utilizes this information to detect the direction of the request. "
http://www.3gpp.org/ftp/tsg_cn/tsg_cn/TSGN_16/Docs/PDF/NP-02...

Without further context, the sentence you posted:
P/S-CSCFにおいては、新規INVITE等のリクエストを受信した際、その方向性(送信してきたノード)によって、実施する処理を変える必要がある。

would be translated something like this:

In the case of P/S-CSCF systems, when a new request, such as an INVITE is received, depending on its direction (the node from which it was sent) it may be necessary to modify the process for execution.


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Note added at 12 hrs (2006-12-07 14:59:13 GMT) Post-grading
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Hamo: If you read the question again, you will see that the asker was unsure whether the node was the origin or just a viapoint on the sending path of the request. I wanted to clarify that with the long explanation.
Thank you for offering an additional option, I added that to the glossary.