Subject: [Enum] Comments on "e212" enumservice and "e212" parameters for Tel URI

From: "Fullbrook Kim (UK)" <[email-masked]>
Date: Thu, 24 May 2007 10:19:12 +0100

INTRODUCTION
The ENUM Group within the GSM Association is a technical working group dedicated to the discussion and agreement of ENUM-related issues that affect GSM operators. The GSM Association represents the interests of GSM operators worldwide.

Some ENUM group members became aware of certain draft proposals from the IETF ENUM group and were concerned about their content. These proposals have been discussed within the GSMA ENUM group and the results are summarised in this email.

PROPOSALS
The IETF has published two recent draft proposals:

1) E.212 ENUMService Type Definition draft-lewis-enum-enumservice-e212-00.txt
2) E.212 Parameters for the "tel" URI draft-lewis-enum-teluri-e212-00.txt

GSMA ENUM Group members have serious concerns about these proposals. 

ENUM GROUP COMMENTS - PROPOSAL 1
Firstly it is described as potentially providing, for example, the ability to identify the service provider for a telephone number for billing purposes by using the "Mobile network code" (MNC) and "mobile country code" (MCC) parameters.

The MNC does not identify a service provider. In many GSM networks there are multiple service providers providing service to customers, each sharing the single MNC used by the Network Operator. It is therefore not possible to identify the service provider based on MNC.

Secondly an additional parameter has been included in the definition - Mobile Subscriber Identification Number (MSIN). Together MNC, MCC and MSIN define the IMSI (International Mobile Subscriber Identity). 

Divulging IMSIs facilitates fraud or abuse at the expense of mobile operators' customers. The design of GSM systems has therefore included special measures to protect an IMSI from being revealed unintentionally by using temporary identities such as TMSIs and P-TMSIs. GSM operators have been consulted about this proposal and unanimously declared that they:
- do not want to see IMSI held in a DNS 
- wish to see MSIN and IMSI removed from this ENUMservice Type Definition.

ENUM GROUP COMMENTS - PROPOSAL 2
Comments on proposal 2)
GSM operators have similar comments to proposal 1). They have declared unanimously that they do not want the ability to store IMSI in a DNS because of security concerns. There are no security concerns around storage of MNC and MCC. However GSM operators are unconvinced about the value of storing them in a Tel URI and wish to see some use cases as a justification. As in the previous section they have noted that MNC cannot be used to indicate a billing relationship for an E.164 number.

WAY FORWARD
The GSMA ENUM group recommends the IETF to:
i) abandon these proposals in their present form due to the short-falls detailed above;
ii) Provide rationale, along with examples, to support any future ENUM-related proposals that include Mobile Network Code and Mobile Country Code.

Kim Fullbrook, 
O2 UK, 
Chair GSMA ENUM Group

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