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RE: IPSec IP Telephony:End to End or Segment


The problem you'll encounter on making an end-to-end secure call where one
both of the end parties is on the PSTN is that there are no standards for
encryption over the PSTN.  Many companies (including mine) have products 
available for PSTN voice encryption, but they are not interoperable.  The
devices encrypt the vocoded speech and forward the digital data over the
lines using an integral modem, i.e. V.32.  For a call through an IP
gateway, the gateway would have to detect the modem tones, and translate the

underlying data into IP packets (like it would do for a FAX).  Until/unless
PSTN encryptors standardize on an interoperable protocol like the FAX
did years ago, I don't think end-to-end secure calls involving a gateway
occur.  The only other option would be for the gateway to encode the modem
using PCM (64 kbps), and leave them for the end terminal to decode, but this
messy too.

Frank Costantini

Anthony Walwyn wrote:

I've a question which I hope the experts on
this list can answer/give their opinion.

With respect to IP Telephony, should security be
end-to-end or does it make sense to have it on
just one segment, eg between two IP Telephony Gateways.

Phone--PSTN--IPGW--IP Network--IPGW--PSTN-Phone

If security is only implemented between the Gateways
is the security risk unacceptable ??

If the phones were Internet-Phones, security could be
implemented end-to-end using IPSec, but what happens if
one end is an Internet Phone and one end is a normal PSTN Phone ?

Anthony Walwyn                      Title: Senior Systems Engineer
ECI Telecom, UK DCME Development,   Voice: +44(0)1256 388065
ISIS House, Reading Road, Chineham  Fax  : +44(0)1256 388142
Basingstoke, Hampshire UK RG24 8TW  Email: anthony.walwyn@telematics.com