Subject: [Ecrit] FW: Comments on draft-schulzrinne-ecrit-unauthenticated-access-03 - Section 1

From: <[email-masked]>
Date: Thu, 20 Nov 2008 22:28:29 +0200

Regarding unauthenticated emergency access, the authors had some
off-list message exchanges and a new version of the draft was posted. I
was asked to forward this mail exchange to the list to help start
discussion on it.

Therefore, we would welcome comments.

Henning did have answer to my comments, but I let him decide whether it
wants to forward that to the list or not.

- Gabor

-----Original Message-----
From: 'Bajko Gabor'
Sent: Saturday, November 01, 2008 1:40 AM
To: 'ext Henning Schulzrinne'; Hannes Tschofenig
Cc: Stephen McCann
Subject: RE: Comments on
draft-schulzrinne-ecrit-unauthenticated-access-03 - Section 1

Isn't it a safe assumtion that in case of NAA, the existence of a VSP
does not matter? I.e., when the ISP gives access to an NAA device for
emergency calls purposes, it is expected to provide additional
assistance for the end host to place the emergency call, without
requiring the end host to have a VSP.

In NVP case the ISP has no means to know that it needs to provide
emergency call related additional assistance to the end host. The end
host is pretty much on its own and needs to have a way to determine its
location and find a LoST server, even in case RFC5223 is not supported
by the ISP.
Or, have a separate requirement that ISPs committed to assist end hosts
in emergency calling, need to support RFC5223. Or, as described in
section 5, have an ESRP which routes the call to the PSAP to which that
access network belongs to. 

The ZBP case can be split into either NVP or regular VoIP emergency call
through a VoIP service provider, depending on whether the VSP is
required by regulation to provide emergency calling services to such
customers or not.

I think it is good to have these definitions, but at the end it all
comes down to what assistance an ISP needs to provide to an end host in
the NAA case, or what the end host is supposed to do when it does have
network access, but does not have a VSP which could assist it in
emergency calling.

- Gabor

  >-----Original Message-----
  >From: ext Henning Schulzrinne [mailto:[email-masked]]
  >Sent: Tuesday, October 28, 2008 2:31 PM
  >To: Hannes Tschofenig
  >Cc: Bajko Gabor (Nokia-CIC/MtView); Stephen McCann
  >Subject: Comments on
draft-schulzrinne-ecrit-unauthenticated-access-03 -
  >Section 1
  >
  >I think the current terminology is really confusing, as it commingles
  >access authorization and VSP authorization, which have rather
  >different consequences. Thus, if this is the WiMax terminology, I
  >think they are just wrong and we shouldn't propagate their confusing
  >terminology.
  >
  >I'm not sure about my attempt below, so I'd appreciate comments. In
  >particular, there might be a better name instead of ZBP.
  >
  >---
  >
  >Second paragraph and following:
  >
  >Roughly speaking, the IETF emergency services architecture [bcp]
  >divides responsibility for handling emergency calls between the
access
  >network (ISP), the VoIP service provider (VSP) and the provider of
  >emergency signaling services, the emergency service network (ESN).
The
  >access network may provide location information to end systems, but
  >does not have to provide any VoIP signaling functionality. The
  >emergency caller can reach the ESN either directly or through the
VoIP
  >provider's outbound proxy. Any of the three parties can provide the
  >mapping from location to PSAP URI by offering LoST [RFC] services.
  >
  >In general, a set of automated configuration mechanisms allows a
  >device to function in a variety of architectures, without the user
  >being aware of the details on who provides location, mapping services
  >or call routing services. However, if emergency calling is to be
  >supported when the calling device lacks access network authorization
  >or does not have a VoIP provider, one or more of the providers may
  >need to provide additional services and functions.
  >
  >In all cases, the end device MUST be able to perform a LoST lookup
and
  >otherwise conduct the emergency call in the same manner as when the
  >three exceptional conditions discussed below do not apply.
  >
  >We distinguish between three conditions:
  >
  >(1) No access authorization (NAA): The current access network
requires
  >access authorization and the caller does not have valid user
  >credentials. (This includes the case where the access network allows
  >pay-per-use, as is common for wireless hotspots, but there is
  >insufficient time to pay for access.)
  >
  >(2) No VoIP provider (NVP): The caller does not have a VoIP service
  >provider (VSP) at the time of the call.
  >
  >(3) Zero-balance VoIP provider (ZBP): The caller has valid
credentials
  >with a VSP, but is not allowed to place calls, e.g., because the user
  >has a zero balance in a prepaid account.
  >
  >A user may well suffer from both NAA and NVP or ZBP at the same time.
  >Depending on local policy and regulations, it may not be possible to
  >place emergency calls in the NAA case. Unless local regulations
  >require user identification, it should always be possible to place
  >calls in the NVP case, with minimal impact on the ISP. Unless the ESN
  >requires that all calls traverse a known set of VSPs, a caller should
  >be able to place an emergency call in the ZBP case. We discuss each
  >case in separate sections below.
  >
  >----
  >
  ><section>No Access Authorization (NAA)
  >
  >In the NAA (No Access Authorization) case, the emergency caller does
  >not posses valid credentials for the access network. If local
  >regulations or policy allows or require, the access network may or
  >needs to cooperate in providing emergency calling services.
Generally,
  >the ISP will want to ensure that devices do not pretend to place
  >emergency calls, but then abuse the access for obtaining more general
  >services fraudulently.
  >
  >In particular, the ISP MUST allow emergency callers to acquire an IP
  >address and to reach a LoST server, either provided by the ISP or
some
  >third party. It SHOULD also provide location information via one of
  >the mechanisms specified in [bcp] without requiring authorization
  >unless it can safely assume that all nodes in the access network can
  >determine their own location, e.g., via GPS.
  >
  >The details of how filtering is performed depends on the details of
  >the ISP architecture and are beyond the scope of this document. We
  >illustrate a possible model. If the ISP runs its own LoST server, it
  >would maintain an access control list including all IP addresses
  >contained in responses returned by the LoST server, as well as the
  >LoST server itself. (It may need to translate the domain names
  >returned to IP addresses and hope that the resolution captures all
  >possible DNS responses.) Since the media destination addresses are
not
  >predictable, the ISP also has to provide a SIP outbound proxy so that
  >it can determine the media addresses and add those to the filter
list.
  >
  ><section>No VoIP Service Provider (NVP)
  >
  >In the second case, the emergency caller has no current VoIP service
  >provider (VSP). This case poses no particular difficulties unless it
  >is assumed that only VSPs provide LoST server or that ESNs only
accept
  >calls that reach it through a set of known VSPs. However, since the
  >calling device cannot obtain configuration information from its VSP,
  >the ISP MUST provide the address of a LoST server via DHCP [rfc] if
  >this model is to be supported. The LoST server may be operated either
  >by the ISP or a third party.
  >
  ><section>Zero-Balance VoIP Service Provider (ZBP)
  >
  >In the case of zero-balance VoIP service provider, the VSP can
  >authenticate the caller, but the caller is not authorized to place
  >regular VoIP calls, e.g., because the contract has expired or the
  >prepaid account for the customer has been depleted. Naturally, a VSP
  >can simply disallow access by such customers, so that all such
  >customers find themselves in the NVP situation described above. If
  >VSPs desire or are required by regulation to provide emergency
calling
  >services to such customers, they need to provide LoST services to
such
  >customers and may need to provide outbound SIP proxy services. As
  >usual, the calling device looks up the LoST server via SIP
  >configuration.
  >
  >Unless the emergency call traverses a PSTN gateway or the VSP charges
  >for IP-to-IP calls, there is little potential for fraud. If the VSP
  >also operates the LoST server, the outbound proxy MAY restrict
  >outbound calls to the SIP URIs returned by the LoST server. It is NOT
  >RECOMMENDED to rely on a fixed list of SIP URIs, as that list may
  >change.
  >
  >---
  >
  >Henning
  >
  >
  >
  >
  >
  >
  >
  >
  >

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