Subject: RE: [mobile-ip] Regional Registration Last Call Resolution Issue #4

From: Scott Corson <[email-masked]>
Date: Wed, 15 May 2002 08:12:58 -0400

> As currently specified it's not immediately obvious how the regional
> registration agents are compatible with the above guidelines.  

Phil,

The particulars of RegReg aside, it's not clear how MIP is consistent with
e2e either.

Your note raises a couple of issues infrequently discussed in this WG.

1) MIP breaks the end-to-end architecture of the Internet.

The HA is a stateful, single point of failure.  It is an architectural
compromise (an evil in the minds of purists), necessary only because of the
Internet routing infrastructure's inability to deal with prefix mobility.

What the current discussion over regional elements questions is whether
*another* such element should be added to the MIP standard.  The unfortunate
conclusion is probably *yes* for the following reasons.

2) Operators need a way to shield the effects of what is commonly termed
micro-mobility from each other's networks (i.e. mobility signalling).  That
is the *primary* reason for needing a regional MIP element, and not latency
or many of the other issues frequently discussed on this list.  What is
necessary is *separation* of the effects of localized domain/provider
mobility from global mobility/reachability at the network layer.

Two current mobile network architectures (e.g. 3GPP/3GPP2) achieve this
separation through the usage of L2 mobility mechanisms for micro-mobility
support.  This L2 mobility is hidden from the IP layer by the existence of
two IP-level boxes: GGSN/PDSN for 3GPP/3GPP2, respectively.  These are
stateful, single points of failure which (if visible in the MIP plane) would
represent the regional elements your note suggests are harmful.

It turns out that the PDSN and GGSN are extremely stateful (middleboxes of
the most complex kind involving not only network layer state, but L2 and
higher session layer state as well).  In accordance with the e2e principle,
their removal would be a good thing from what are obstensibly "all-IP"
networks.

The addition of regional elements to MIP is a step towards making this
removal feasible.   It would add the necessary localization/separation
properties MIP currently lacks to the standard, making MIP a deployable
control plane between operators and, when desired, within operator's
networks.  It would limit the architecturally-compromising effects of
stateful elements to the network layer, which is consistent with existing
MIP, as a compromise solution for a network-layer routing deficiency.  All
other layers would be free to operate in an e2e fashion.  As a consequence,
these MIP regional elements need only be network layer entities (i.e.
routers), thus far cheaper to build, maintain, etc, enabling the Internet to
function closer to the way e2e principle suggests.

It should also be noted that many of the desired properties currently
lacking in MIP can be realized in a less stateful manner through the use of
"nested" MIP as detailed in 

http://search.ietf.org/internet-drafts/draft-oneill-mip-nested-00.txt

However, additional capabilities/features are realizable through the use of
network layer-stateful entities as detailed in the recently submitted drafts
related to nested MIP.  There are many facets to this issue which are
explored in these drafts.

In short, MIP does not survive the e2e test, and some current network
architectures fail woefully as well.

Regards,

-Scott

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From: Behcet Sarikaya <[email-masked]>
Date: Wed, 15 May 2002 09:15:37 -0500

Hi Scott,
  Agreed.
  But you must underline the MIP without route optimization. If route 
optimization is achieved which probably is going to be the case with 
MIPv6, then the HA in the architecture is a necessary stateful network 
box to enable the route optimization to work.
  Also we can view MIPv4 regreg trying to help in the route optimization 
in its own way so its architecture has better e2e characteristic than 
MIPv4 in this sense.
  We must also add that these days it is a fashion to keep adding proxy 
boxes, the most recent one being  the STUN proxy that would also violate 
e2e principle. SIP servers are probably of this category. However like 
in route optimization, SIP uses them carefully in order to establish e2e 
communications.

  My 0.02 euro cents.

Regards,

-- 
Behcet

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From: "James Kempf" <[email-masked]>
Date: Sun, 19 May 2002 19:11:05 -0700

Scott,

> Internet routing infrastructure's inability to deal with prefix
mobility.

See my response to Phil's note for why I think this is different. The HA
is the exception that proves the rule.

> mobility from global mobility/reachability at the network layer.

What do you mean by shielding? That it reveals the network topology in
the foreign network to the home provider?

If so, I think there are other ways to do this that don't involve
routing proxies. They use FMIPv4 in a particular way so the localized
mobility management is handled closer to the edge, by routers.

In addition, our telco types don't cite this as a particular problem.
They want something more radical (and as far as I can determine,
undoable). They are more concerned that the source IP address on the
packet delivered to the CN will be an address in the MN's foreign
network, regardless of whether a routing proxy such as the GFA is
deployed. They don't want the CN to be able to determine the address in
the foreign network, and they don't want the home address there because
they don't want tunneling. They don't care about the network topology,
they don't want the foreign network revealed, period, and they don't
want tunneling, period. So whatever benefits address privacy or topology
hiding might be brought by the GFA are not of interest to Docomo (one
operator's viewpoint).

On the other hand, we do have an interest in limiting the number of
special purpose, stateful boxes that only achieve reliability by making
them 5 nine's reliable. These tend to be expensive. They start looking
like 3G-SN's or VLRs.

> their removal would be a good thing from what are obstensibly "all-IP"

There are two reasons why the 3G networks need these boxes:

1) Their deep radio access networks enforce a connection oriented
protocol on the "last" hop (last from the MN IP stack's view, actually
there is a lot going on). In 3GPP, this is the PDP context. In 3GPP2,
this is a PPP context. A pure MIP solution shouldn't need this.

2) These boxes act as anchors for AAA. For MIPv4, that function is
already handled by the FA. Adding a GFA will only complicate AAA.

> function closer to the way e2e principle suggests.

I disagree. I believe the required localized mobility management
function can be added using minor enhancements to the access routers or
other routers closer to the edge, at considerably less expense.

> explored in these drafts.

I have not yet read Alan's drafts but they are my short list.

            jak