RE: 3gpp-analysis-04: Transition mechanisms at UEs; 3GPP IPv6 dep loyment

["Karim El-Malki (HF/EAB)" <karim.el-malki@ericsson.com>]

 > On Thu, 24 Jul 2003, Karim El-Malki (HF/EAB) wrote:
 > >  > On Thu, 24 Jul 2003, Karim El-Malki (HF/EAB) wrote:
 > >  > > You're assuming that roaming is done at L3. Roaming 
 > is normally
 > >  > > done at L2 so for example ISATAP is a relevant option.
 > >  > 
 > >  > (I think you should elaborate on "normally")
 > > 
 > > According to the 3gpp standard.
 > 
 > Are there known (or planned) deviations from this standard?

Not that I know of.

 > >  > OK.  If roaming is done at L2, then IP addresses etc. should 
 > >  > stay the same
 > >  > when you roam, right?  Then IPv6 addresses will stay too, 
 > >  > right?  So, why
 > >  > do you need ISATAP there then?
 > > 
 > > Imagine a situation in which you're roaming to another
 > > operator's network. The roaming user requests v6 connectivity
 > > (PDP Context) in the new network. If the new network doesn't
 > > support it, the roaming user won't get v6 connectivity.
 > 
 > Ok; this is not necessarily a huge problem in itself.
 > 
 > But let me try to rephrase this:
 > 
 > Imagine a situation in which you're moving under another 
 > GGSN in your 
 > operator's network.  The user requests v6 connectivity
 > (PDP Context) in the network. If the network doesn't
 > support it, the user won't get v6 connectivity.
 > 
 > I.e., to be able to use v6 everywhere under your own 
 > operator's network, 
 > is it required that all GGSN's in that operator's network 
 > support IPv6 PDP 
 > contexts?

You can make it work with just one GGSN if you really want to.

 > 
 > Or let me phrase this differently:
 > 
 >  Would roaming with 3GPP UE work if the roaming agreements 
 > would include 
 >  an indication whether the foreign network supports the same 
 > PDP context 
 >  types as the original network.
 > 
 > I.e. the user can prefer those roaming partners which 
 > provide the services 
 > they want.  That should be enough of an economic incentive.

Basically the UE won't know until it tries to activate
a v6 connection and it gets refused.

 > 
 > Or, i.e. we define that "roaming" is not "true roaming" 
 > unless you provide 
 > the support for the same PDP context types; that is, there 
 > is "partial 
 > roaming" as of today and "real roaming" of tomorrow.
 > 
 > IMHO, it seems ill-advised to call something "roaming" when 
 > they fail to 
 > provide critical infrastructure capabilities the users need.

Some people would see voice, IPv4 or MMS as critical so I don't
think it makes sense to get into a discussion here on what the word
"roaming" should mean.

 > 
 > > The PDP Context is a special L2 as described in RFC 3314.
 > 
 > Ok, let me try to clarify several ambiguous points: (there 
 > are probably 
 > more but from the top of my head)
 > 
 > Does the IP address of the UE change when it roams to 
 > another network?

The active PDP Context's address doesn't change as long
as this type of "connection survivability" roaming is allowed.
However note that roaming is also when I get off the plane
in another country and turn my mobile on. So the address is
likely to change.

 > Does the GGSN always change to a GGSN of the another network?
No.

 >   If not, how is IP address kept the same?
L2 tunnelling back to the home network.

 > 
 > When the user moves inside the same operator's network does 
 > the IP address 
 > change? (I don't think so)
No.

 >  - Does the GGSN change? (I don't think so)
No.

 > 
 > What determines which GGSN you end up using in the 
 > operator's network?
The type of service "APN" you request (more in RFC 3314)

 >  - How does this work in a network where some GGSN's are 
 > v6-capable and 
 > some not?

You create a v6 "APN" mapped to the IPv6 GGSN, but I don't think
this is important in practice. I think you are concentrating too
much on the GGSN issue. Although the GGSN is your default router,
in order to activate the PDP Context you need support also in the
SGSN for example. Whether you're roaming or not this holds true.
As a user you sit under two nodes: SGSN and GGSN. The SGSN has
geographical coverage. If I am under a SGSN that refuses the
v6 pdp context or a network where there is no IPv6 GGSN then I
can use tunnelling. That's all we're saying.

 > 
 > Figure 3 (typo: should be fig 4) in page 11 seems to 
 > indicate that UE can
 > have multiple PDP contexts, to multiple ISPs.  As long as UE 
 > opens the PDP
 > context to his own ISP which supports v6, you're fine.  But 
 > can the UE do 
 > that?

It can activate mutliple PDP Contexts. However the addressing
and forwarding is through the GGSN. So, the ISP may support IPv6
but the SGSN/GGSN don't. It's just like any access router. If your
ISP supports IPv6 and your current access router is IPv4-only you'll
still need to tunnel to get to your v6 ISP.

/Karim