I googled "com.ibm.websphere.sib" and, interestingly, your post was the #6 entry in the list which Google gave me. The answer is in the #7 entry.
Joined: Nov 06, 2003
Paul - thank you - "Service Integration Bus". I feel a bit of a numpty now! That said, I too googled and there are a lot of entries that don't give the full name. I couldn't even find it under the search "com.ibm.websphere.sib site:ibm.com". (I have now found via "Service Integration Bus" site:ibm.com.