From: Steve Schear <azur@netcom.com>
Date: Mon, 20 Jan 1997 15:26:57 -0800 (PST)
To: Adam Back <aba@dcs.ex.ac.uk>
Subject: Re: GSM technology
Message-ID: <199701202326.PAB23017@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


>Steve Shear <azur@netcom.com> writes:
>> [very useful explanation of GSM TDMA, and the new HSCSD]
>
>64 kbit/s tied to ISDN is very nice technology.
>
>> ENCRYPTED GSM LINKS
>> If the GSM phone includes a data port, as some already do, just connect
>> your laptop, dial your ISP and 'push' the encrypted traffic over that link
>> (e.g., using TCP/IP and PGPfone).
>
>This would obviously be possible, but to my mind reduces the appeal of
>the system.  Not every one has a laptop.
[snip]

Retrofitting the stonger encryption (e.g., IDEA) to some existing GSM
phones may be practical (as I've discussed in previous postings), but
unless the service providers support the stonger crypto (seems very
unlikely at the moment)parties at the other end of the line will need an
Eric Blossom-like device or a laptop running PGPfone.  I can see no way
around this.

>
>Also, the cell phone tarriffs may be higher if you need higher
>bandwidth to get the software only voice codec implementations in
>PGPfone to produce equivalent full-duplex voice quality to that
>expected from a digital mobile phone.

I may be wrong, but the faster laptops are already able to support the GSM
codes and rates in PGPfone (or could).  However, most of the service
providers may only be offering 9.6kb/s GSM data links at this time, and
this would surely impact voice quality.  If or when 28.8kb/s data is common
via GSM voice links via PGPfone should be better than the default GSM coded
voice.

--Steve


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