TCPDUMP via Cross Cable with my Laptop

[yihwen]

Can we use Wireshark to get a TCPDUMP of a SPA2102 device via my laptop using a cross cable?

Reason is it has all my SIP credentials embedded in the devices and I am trying to sniff the traffic so that I would be able to retrieve the username and password. Any idea how can I do it via Wireshark?

I am totally novice to wireshark so a step by step would be good.