On Friday, October 12, 2001, at 08:58 , mats_at_mobiledreams.com wrote:
> benjamin wrote:
>> That is quite interesting, given that PHS does not
>> have a roaming protocol nor any mode/means to
>> interoperate with GSM/MAP. Possible, NTT
>> have hacked something, but perhaps this follows the
>> >rent-a-handset-and-roam model by which manual/static
>> call diversion is used to deliver calls
> I don't know the handset, but it could also be "2 handsets in one",
> where the user has 2 subscriptions and chooses manually which "phone"
> to use; at least that's how DoCoMo made (still make?) their PDC/PHS
The GSM/PHS handset developed by NTT and NEC switches automatically
between the two modes. Thus if you are abroad i.e. in Europe it would
switch into GSM mode. If you are in Japan it switches into PHS mode.
This is similar to the way how PHS handsets switch between public and
The problem with a roaming service is that a GSM network would want to
send an authentication and roaming request to the home network's HLR
using the GSM/MAP protocol.
Roaming between GSM and CDMA for example uses a gateway that translates
such signalling from one standard to the other.
The difficulty with PHS is that PHS has not equivalent roaming
international roaming functionality and therefore such a gateway cannot
simply translate but it would also have to provide all the missing
However, the ZEBRA roaming protocol has this functionality already
built-in because it caters to situations where home networks do not
support ZEBRA. This is called non-cooperative mode. There is also no
need to deliver incoming calls via GSM/MAP because when the user signs
in to a foreign network they are assigned a local account and a local
phone number which is then sent back to the home network. If the home
network wants to provide this service they can then use an ordinary call
forwarding service to deliver incoming calls to their roaming customer.
The home network need not even be a mobile network. A fixed network can
also participate. Thus, you could have a PHS cordless phone (without
public PHS service) and if it was a GSM/PHS dual mode handset then you
could roam via ZEBRA into a GSM network and receive incoming calls to
your house or office on your mobile while roaming, or have voicemail
forwarded to yourself.
PHS is widely adopted as a cordless standard in Asia. Latin America and
the Middle East. Therefore, GSM/PHS roaming using this wireless/cordless
mode could be quite interesting even outside of Japan.
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Received on Fri Oct 12 16:46:17 2001