[lwip-users] Why the delay after ARP?

[JM]

I am using lwIP 1.3.0 and it works great, but I've always wondered where there's an approx. three second delay after the ARP response before lwIP sends the SYN.  In other words:

1. I initiate a TCP connection
2. lwIP sends an ARP request almost immediately
3. The host responds (relatively) immediately
4. lwIP waits about three seconds before sending the SYN

When the MAC is in the ARP cache, this doesn't happen, but still, what is it doing during that time?  Incidentally, I've noticed uIP does the same.