IF you really want to understand what's going on, install xplot from pkgsrc and read the tcp plots README. This is not trivial, but is IMHO the only reasonable way to truly become one with transport protocols. It's an interesting question whether your 3G system has loss that is natural, or whether the provider is randomly imposing loss to keep usage down (without overly having a quota), or whether there is something else going on. Server resources are partly about speed, but multiple connections means there are multiple connection blocks allocated, and multiple send buffers, one per connection. Whether it truly hurts much more than one fast user is a fair question, but there's no question that it offends server admins.
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