Slow query execution over WAN network

Hi,

I experience really slow query execution over remote networks,
especially for a query which returns a lot of columns (~255) caused by
joins.

Executing the same query over different networks gives the following times:
Local: 20ms
DSL: 400ms
UMTS: 1500ms

The query returns 12 rows, and 255 column - most of them with only
very little data. A wireshark-snapshot of a request is only ~30kb
large, so I guess there isn't a lot of data transported.

I've uploaded a netbeans-profiler screenshot as well as a wireshark profile to:
http://93.190.88.182/jdbc_traffic.wireshark
http://93.190.88.182/jdbc_profile.png

Any idea whats causing the high latency? Are there multiple
round-trips going on here?
I already tried adjusting fetch size, however didn't change anything.

Thank you in advance, Clemens

PS: I've asked the question already on pgsql-performance,
unfourtunatly there wasn't a lot of feedback. Sorry for cross-posting.