SIPped, the Polycom fork of SIPp (https://github.com/SIPp/polycom-sipped) has improved the command, adding the ability to wait for a return code and verify it, as well as output tracing. It would be good to get this merged into the main SIPp code.

It looks as though the relevant commits are 9013201, bca0bcc and 2a23974 for return code verification (which might be a good task for a new dev) and 9013201, 571793a, f7d2e97, 1c9f029 and ba9f6b7 for improved tracing.