Why won't you use simple HTTP protocol? That's exactly the case for which it was invented - moving resources accross the Web.
Install lightweight HTTP server on the access point, if you don't have one there already. For example, boa is very lightweight, single-tasking HTTP server, which could be more than enough for this purpose.
Then, just:
- let the tcpdump store the file in the server directory tree at the access point
- on the server, use HTTP module of node.js to download the file
- store it in the database.
That's it. There's no need nor is it a good idea to convert your binary data into JSON!