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diff --git a/doc/rfc/rfc5442.txt b/doc/rfc/rfc5442.txt new file mode 100644 index 0000000..829cb05 --- /dev/null +++ b/doc/rfc/rfc5442.txt @@ -0,0 +1,843 @@ + + + + + + +Network Working Group E. Burger +Request for Comments: 5442 Consultant +Category: Informational G. Parsons + Nortel Networks + March 2009 + + + LEMONADE Architecture - Supporting Open Mobile Alliance (OMA) + Mobile Email (MEM) Using Internet Mail + +Status of This Memo + + This memo provides information for the Internet community. It does + not specify an Internet standard of any kind. Distribution of this + memo is unlimited. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents in effect on the date of + publication of this document (http://trustee.ietf.org/license-info). + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + + This document may contain material from IETF Documents or IETF + Contributions published or made publicly available before November + 10, 2008. The person(s) controlling the copyright in some of this + material may not have granted the IETF Trust the right to allow + modifications of such material outside the IETF Standards Process. + Without obtaining an adequate license from the person(s) controlling + the copyright in such materials, this document may not be modified + outside the IETF Standards Process, and derivative works of it may + not be created outside the IETF Standards Process, except to format + it for publication as an RFC or to translate it into languages other + than English. + +Abstract + + This document specifies the architecture for mobile email, as + described by the Open Mobile Alliance (OMA), using Internet Mail + protocols. This architecture was an important consideration for much + of the work of the LEMONADE (Enhancements to Internet email to + Support Diverse Service Environments) working group in the IETF. + This document also describes how the LEMONADE architecture meets + OMA's requirements for their Mobile Email (MEM) service. + + + +Burger & Parsons Informational [Page 1] + +RFC 5442 LEMONADE Architecture March 2009 + + +Table of Contents + + 1. Introduction ....................................................2 + 2. OMA Mobile Email (MEM) ..........................................2 + 2.1. OMA MEM Requirements .......................................2 + 2.2. OMA MEM Architecture .......................................3 + 2.2.1. OMA MEM Logical Architecture ........................3 + 2.2.2. OMA MEM Deployment Issues ...........................4 + 2.3. OMA MEM Technical Specification ............................6 + 3. IETF LEMONADE Architecture ......................................6 + 3.1. Relationship between the OMA MEM and LEMONADE Logical + Architectures ..............................................7 + 3.2. LEMONADE Realization of OMA MEM with + non-LEMONADE-Compliant Servers .............................9 + 3.2.1. LEMONADE Realization of OMA MEM with + non-LEMONADE IMAP Servers ...........................9 + 3.2.2. LEMONADE Realization of OMA MEM with non-IMAP + Servers ............................................10 + 4. Filters and Server-to-Client Notifications and LEMONADE ........11 + 5. Security Considerations ........................................13 + 6. Acknowledgements ...............................................13 + 7. Informative References .........................................13 + +1. Introduction + + This document describes the architecture of OMA Mobile Email (MEM) + using Internet Mail protocols defined by the IETF. The LEMONADE + working group has enhanced many of these protocols for use in the + mobile environment. The LEMONADE profile [PROFILE] and its revision, + [PROFILE-bis], summarize such protocols and protocol use. This + document shows how the OMA MEM Requirements document [MEM-req], OMA + MEM Architecture [MEM-arch], and OMA MEM Technical Specification + [MEM-ts] relate to the work of LEMONADE in the IETF. + +2. OMA Mobile Email (MEM) + + The OMA Mobile Email (MEM) sub-working group has spent some time + studying the requirements and architecture of mobile email. IETF + LEMONADE has been liaising with them and has based much of its + Internet Mail enhancements on their input. This section summarizes + the output of the OMA. + +2.1. OMA MEM Requirements + + The OMA MEM activity collected a set of use cases and derived + requirements for a Mobile Email (MEM) enabler. The OMA MEM + Requirements document [MEM-req] summarizes this work. Some + requirements relate to email protocols, some involve other OMA + + + +Burger & Parsons Informational [Page 2] + +RFC 5442 LEMONADE Architecture March 2009 + + + technologies outside the scope of the IETF, and some relate to + implementations and normative interoperability statements for clients + and servers. + +2.2. OMA MEM Architecture + + This section introduces the OMA MEM Architecture. + +2.2.1. OMA MEM Logical Architecture + + The OMA MEM activity has derived a logical architecture from the + requirements and use cases described in [MEM-req]. A simplification + for illustrative purposes is shown in Figure 1, where arrows indicate + content flows. + + __________ + | Other | + +---| Mobile |<--+ + | | Enablers | | + | |__________| | + |ME-4 |ME-3 + _v____ ___v____ ________ + | |ME-1 | | | | + | MEM |-------->| MEM | I2 | Email | + |Client| ME-2| Server |<---->| Server | + |______|<--------|________| |________| + ^ + |ME-5 + | + + Figure 1: Basic OMA MEM Logical Architecture + + Figure 1 identifies the following elements: + + o The MEM client that implements the client-side functionality of + the OMA Mobile Email enabler. It is also responsible for + providing the mobile email user experience and interface to the + user and storing the email and data to be sent to the MEM server + when not connected. + + o The MEM server that implements the server-side functionality of + the OMA Mobile Email (MEM) enabler. + + o The MEM protocol between the MEM client and MEM server. It is + responsible for all the in-band data exchanges that take place + between the MEM client and server in order to update the MEM + + + + + +Burger & Parsons Informational [Page 3] + +RFC 5442 LEMONADE Architecture March 2009 + + + client with email server changes and the email server with changes + in the MEM client, and in order to send new email from the email + server. + + o Other OMA enablers that are needed to directly support the Mobile + Email enabler. They are out of the scope of the IETF but may + include support for: + + * Client provisioning and management for over-the-air + installation of the MEM client on the device, provisioning of + the client settings, and revocation of client privileges. + + * Messaging enablers for out-of-band notification, where out-of- + band notifications that are server-to-client event exchanges + are not transported by the MEM protocol but via other channels. + + * Billing, charging, and so on. + + OMA identifies different interfaces: + + o ME-1: MEM client interface to interact via the MEM protocol with + the MEM server. + + o ME-2: Corresponding interface of the MEM server. + + o ME-3: Out-of-band MEM server interfaces; for example, to support + generation of server-to-client notifications. + + o ME-4: Out-of-band MEM client interfaces (e.g., to receive server- + to-client notifications). + + o ME-5: Interface for management of MEM enabler server settings, + user preferences, and filters, globally and per account. + + The MEM server enables an email server. In a particular + implementation, the email server may be packaged with (internal to + it) the MEM server or be a separate component. In such cases, + interfaces to the email server are out of scope of the OMA MEM + specifications. In the present document, we focus on the case where + the backend consists of IETF IMAP and SUBMIT servers. However, we + also discuss the relationship to other cases. The I2 interface is an + OMA notation to designate protocol / interfaces that are not + specified by the MEM enabler but may be standardized elsewhere. + +2.2.2. OMA MEM Deployment Issues + + The OMA MEM Architecture document [MEM-arch] further identifies + deployment models. + + + +Burger & Parsons Informational [Page 4] + +RFC 5442 LEMONADE Architecture March 2009 + + +2.2.2.1. OMA MEM Proxy + + The OMA MEM Architecture document [MEM-arch] identifies OMA MEM + server proxies as server components that may be deployed ahead of + firewalls to facilitate firewall traversal. + +2.2.2.2. OMA MEM Deployment Cases + + OMA MEM identifies that each component (MEM client, MEM servers, + other enablers, and the email server) may be deployed in different + domains, possibly separated by firewalls and other network + intermediaries. MEM proxies may be involved in front of a firewall + that protects the MEM server domain. + + OMA MEM targets support of configurations where: + + o All components are within the same domain, such as in a mobile + operator. + + o The MEM client and other enablers are in the mobile operator + domain, there is a MEM proxy, and the MEM server and email server + are in the domain of the email service provider. + + o The MEM client and other enablers as well as a MEM proxy are in + the mobile operator domain, and the MEM server and email server + are in the domain of the email service provider. + + o The MEM client and other enablers are in the mobile operator + domain, a MEM proxy is in a third-party service provider domain, + and the MEM server and email server are in the domain of the email + service provider. + + o The MEM client, other enabler, and MEM server are in the mobile + operator domain, and the email server is in the domain of the + email service provider. + + o The MEM client and other enablers are in the mobile operator + domain, the MEM server is in a third-party service provider + domain, and the email server is in the domain of the email service + provider. + + The email service provider can be a third-party service provider, a + network service provider, or an enterprise email service. + + + + + + + + +Burger & Parsons Informational [Page 5] + +RFC 5442 LEMONADE Architecture March 2009 + + +2.3. OMA MEM Technical Specification + + The OMA MEM activity will conclude with a specification for a Mobile + Email (MEM) enabler. The ongoing work is in the OMA MEM Technical + Specification [MEM-ts]. LEMONADE is a basis for the mechanism. + However, some additional details that are outside the scope of the + IETF will also be included. + + OMA provides ways to perform provisioning via OMA client provisioning + and device management. Other provisioning specifications are + available (e.g., SMS based). + + OMA provides enablers to support out-of-band notification mechanisms, + filter specifications (such as XDM), and remote deactivate devices, + and to perform other non-Internet activities. + +3. IETF LEMONADE Architecture + + This section introduces the LEMONADE Architecture. + + The IETF LEMONADE activity has derived a LEMONADE profile + [PROFILE-bis] with the logical architecture represented in Figure 2, + where arrows indicate content flows. + + ______________ + | | + _________| Notification | + | | Mechanism | + | |______________| + |Notif. ^ + |Protocol | + | ___|______ + | | | _____ + __v__ IMAP | LEMONADE | ESMTP | | + | |<----------->| IMAP |<---------------| MTA | + | MUA |- | Store | |_____| + |_____| \ |__________| + \ | + \ |URLAUTH + \SUBMIT | + \ ____v_____ + \ | | _____ + \ | LEMONADE | ESMTP | | + ---->| Submit |--------------->| MTA | + | Server | |_____| + |__________| + + Figure 2: LEMONADE logical architecture + + + +Burger & Parsons Informational [Page 6] + +RFC 5442 LEMONADE Architecture March 2009 + + + The LEMONADE profile [PROFILE] assumes: + + o IMAP protocol [RFC3501], including LEMONADE profile extensions + [PROFILE]. + + o SUBMIT protocol [RFC4409], including LEMONADE profile extensions. + + o LEMONADE profile compliant IMAP store connected to an MTA (Mail + Transfer Agent) via the ESMTP [EMAIL]. + + o LEMONADE profile compliant submit server connected to an MTA, + often via the ESMTP. + + o Out-of-band server-to-client notifications relying on external + notification mechanisms (and notification protocols) that may be + out of the scope of the LEMONADE profile. + + o LEMONADE-aware MUA (Mail User Agent). While use of out-of-band + notification is described in the LEMONADE profile, support for the + underlying notifications mechanisms/protocols is out of the scope + of the LEMONADE specifications. + + Further details on the IETF email protocol stack and architecture can + be found in [MAIL]. + +3.1. Relationship between the OMA MEM and LEMONADE Logical + Architectures + + Figure 3 illustrates the mapping of the IETF LEMONADE logical + architecture on the OMA MEM logical architecture. + + + + + + + + + + + + + + + + + + + + + +Burger & Parsons Informational [Page 7] + +RFC 5442 LEMONADE Architecture March 2009 + + + _____________________ + | Other_Mob. Enablers | + | |--------------| | + _________| Notification | | + | | | Mechanism | | + | | |______________| | + |Notif. |____________^________| + |Protocol ______|__________ + ME-4 | | ___|_ME-3_ | + ___|____ | | | | _____ + | __v__ | IMAP | | LEMONADE | | ESMTP | | + || |<----------->| IMAP |<-----------| MTA | + || MUA || ME-2a | | Store | | |_____| + ||_____||\ME-1 | |__________| | + | MEM | \ | | | + | Client| \ | |URLAUTH | + |_______| \SUBMIT | | + \ | ____v_____ | + \ | | | | _____ + \ | | LEMONADE | | ESMTP | | + ---->| Submit |----------->| MTA | + ME-2b | | Server | | |_____| + | |__________| | + |MEM Email | + |Server Server| + |_________________| + ^ + |ME-5 + | + + Figure 3: Mapping of LEMONADE Logical Architecture + onto the OMA MEM Logical Architecture + + As described in Section 3, the LEMONADE profile assumes LEMONADE + profile compliant IMAP stores and SUBMIT servers. Because the + LEMONADE profile extends the IMAP store and the SUBMIT server, the + mobile enablement of email provided by the LEMONADE profile is + directly provided in these servers. Mapping to the OMA MEM logical + architecture for the case considered and specified by the LEMONADE + profile, we logically combine the MEM server and email server. + However, in LEMONADE we split them logically into a distinct LEMONADE + message store and a LEMONADE SUBMIT server. ME-2 consists of two + interfaces. ME-2a is IMAP extended according to the LEMONADE + profile. ME-2b is SUBMIT extended according to the LEMONADE profile. + + The MUA is part of the MEM client. + + + + + +Burger & Parsons Informational [Page 8] + +RFC 5442 LEMONADE Architecture March 2009 + + + The external notifications mechanism is part of the OMA enablers + specified by the OMA. + +3.2. LEMONADE Realization of OMA MEM with non-LEMONADE-Compliant + Servers + + The OMA MEM activity is not limited to enabling LEMONADE-compliant + servers. It explicitly identifies the need to support other + backends. This is, of course, outside the scope of the IETF LEMONADE + activity. + +3.2.1. LEMONADE Realization of OMA MEM with non-LEMONADE IMAP Servers + + Figure 4 illustrates the case of IMAP servers that are not LEMONADE- + compliant. In such case, the I2 interface between the MEM server + components and the IMAP store and SUBMIT server are IMAP and SUBMIT + without LEMONADE extensions. + + It is important to note the realizations are of a schematic nature + and do not dictate actual implementation. For example, one could + envision collocating the LEMONADE MEM enabler server and the submit + server shown in Figure 4 in a single instantiation of the + implementation. Likewise, we consciously label the LEMONADE MEM + enabler as neither an IMAP proxy nor an IMAP back-to-back user agent. + LEMONADE leaves the actual implementation to the developer. + + + + + + + + + + + + + + + + + + + + + + + + + + +Burger & Parsons Informational [Page 9] + +RFC 5442 LEMONADE Architecture March 2009 + + + ______________ + | | + _________| Notification | + | | Mechanism | + | |______________| + |Notif. ^ + |Protocol | + | ___|______ _____________ + | | LEMONADE | | | _____ + __v__ IMAP | MEM | IMAP |NON-LEMONADE | ESMTP | | + | |<--------->|Enabler |<------>|IMAP |<----->| MTA | + | MUA |\ ME-2a | Server | |Store | |_____| + |_____| \ |__________| |_____________| + \ | + \ |URLAUTH + \SUBMIT | + \ ____v_____ _____________ + \ | | | | _____ + \ | LEMONADE | SUBMIT |NON-LEMONADE | ESMTP | | + -->| MEM | |Submit | | | + | Enabler |------->|Server |------>| MTA | + ME-2b | Server | | | |_____| + |__________| |_____________| + + Figure 4: Architecture to Support Non-LEMONADE IMAP Servers + with a LEMONADE Realization of an OMA MEM Enabler + +3.2.2. LEMONADE Realization of OMA MEM with non-IMAP Servers + + Figure 5 illustrates the cases where the message store and submit + servers are not IMAP store or submit servers. They may be Post + Office Protocol (POP3) servers or other proprietary message stores. + + + + + + + + + + + + + + + + + + + +Burger & Parsons Informational [Page 10] + +RFC 5442 LEMONADE Architecture March 2009 + + + ______________ + | | + _________| Notification | + | | Mechanism | + | |______________| + |Notif. ^ + |Protocol | + | ___|______ _____________ + | | LEMONADE | | | _____ + __v__ IMAP | MEM | I2 |Proprietary | ESMTP | | + | |<--------->|Enabler |<------>|Message |<----->| MTA | + | MUA |\ ME-2a | Server | |Store | |_____| + |_____| \ |__________| |_____________| + \ | + \ |URLAUTH + \SUBMIT | + \ ____v_____ _____________ + \ | | | | _____ + \ | LEMONADE | I2 |Proprietary | ESMTP | | + -->| MEM | |Submit | | | + | Enabler |------->|Server |------>| MTA | + ME-2b | Server | | | |_____| + |__________| |_____________| + + Figure 5: Architecture to Support Non-IMAP Servers with a LEMONADE + Realization of OMA MEM Enabler + + I2 designates proprietary adapters to the backends. + +4. Filters and Server-to-Client Notifications and LEMONADE + + OMA MEM Requirements [MEM-req] and Architecture [MEM-arch] emphasize + the need to provide mechanisms for server-to-client notifications of + email events and filtering. Figure 6 illustrates how notification + and filtering works in the LEMONADE profile [PROFILE]. + + + + + + + + + + + + + + + + +Burger & Parsons Informational [Page 11] + +RFC 5442 LEMONADE Architecture March 2009 + + + ______________ + | | + _________| Notification | + | | Mechanism | + | |______________| + |Notif. ^ + |Protocol -------\ _|__ + | ______| ___\>|NF|____ + | | | ---- | _____ + __v__| IMAP |__ LEMONADE |___ ESMTP __| | + | |<-------->|VF| IMAP |DF |<--------|AF| MTA | + | MUA |\ ME-2a |-- Store |--- --|_____| + |_____| \ |_____________| ^ + \_\_______________|_______| + \ |URLAUTH + \SUBMIT | + \ ____v_____ + \ | | _____ + \ | LEMONADE | ESMTP | | + ---->| Submit |--------------->| MTA | + ME-2b | Server | |_____| + |__________| + + Figure 6: Filtering Mechanism Defined in LEMONADE Architecture + + In Figure 6, we define four categories of filters: + + o AF: Administrative Filters - The email service provider usually + sets administrative filters. The user typically does not + configure AF. AF applies policies covering content filtering, + virus protection, spam filtering, etc. + + o DF: Deposit Filters - Filters that are executed on deposit of new + emails. They can be defined as SIEVE filters [SIEVE]. They can + include vacation notices [RFC5230]. As SIEVE filters, one can + administer them using the SIEVE management protocol [MANAGESIEVE]. + + o VF: View Filters - Filters that define which emails are visible to + the MUA. View filters can be performed via IMAP using the + facilities described in [NOTIFICATIONS]. + + o NF: Notification Filters - Filters that define for what email + server event an out-of-band notification is sent to the client, as + described in [NOTIFICATIONS]. + + Refer to the aforementioned references for implementation and + management of the respective filters. + + + + +Burger & Parsons Informational [Page 12] + +RFC 5442 LEMONADE Architecture March 2009 + + +5. Security Considerations + + We note there are security risks associated with: + + o Out-of-band notifications + + o Server configuration by client + + o Client configuration by server + + o Presence of MEM proxy servers + + o Presence of MEM servers as intermediaries + + o Measures to address the need to traverse firewalls + + We refer the reader to the relevant Internet Mail, IMAP, SUBMIT, and + Lemonade documents for how we address these issues. + +6. Acknowledgements + + The authors acknowledge and appreciate the work and comments of the + IETF LEMONADE working group and the OMA MEM working group. We + extracted the contents of this document from sections of + [PROFILE-bis] by Stephane Maes, Alexey Melnikov, and Dave Cridland, + as well as sections of [NOTIFICATIONS] by Stephane Maes and Ray + Cromwell. + +7. Informative References + + [EMAIL] Klensin, J., "Simple Mail Transfer Protocol", + RFC 5321, October 2008. + + [MAIL] Crocker, D., "Internet Mail Architecture", Work + in Progress, October 2008. + + [MANAGESIEVE] Melnikov, A. and T. Martin, "A Protocol for Remotely + Managing Sieve Scripts", Work in Progress, + January 2009. + + [MEM-arch] Open Mobile Alliance, "Mobile Email Architecture + Document", OMA, + http://member.openmobilealliance.org/ftp/ + public_documents/mwg/MEM/Permanent_documents/ + OMA-AD-Mobile_Email-V1_0_0-20070614-D.zip, + June 2007. + + + + + +Burger & Parsons Informational [Page 13] + +RFC 5442 LEMONADE Architecture March 2009 + + + [MEM-req] Open Mobile Alliance, "Mobile Email Requirements + Document", OMA, http://www.openmobilealliance.org/, + Oct 2005. + + [MEM-ts] Open Mobile Alliance, "Mobile Email Technical + Specification", OMA, Work in Progress, + http://www.openmobilealliance.org/, Oct 2007. + + [NOTIFICATIONS] Gellens, R. and S. Maes, "Lemonade Notifications + Architecture", Work in Progress, July 2008. + + [PROFILE] Maes, S. and A. Melnikov, "Internet Email to Support + Diverse Service Environments (Lemonade) Profile", + RFC 4550, June 2006. + + [PROFILE-bis] Cridland, D., Melnikov, A., and S. Maes, "The + Lemonade Profile", Work in Progress, September 2008. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [RFC4409] Gellens, R. and J. Klensin, "Message Submission for + Mail", RFC 4409, April 2006. + + [RFC5230] Showalter, T. and N. Freed, "Sieve Email Filtering: + Vacation Extension", RFC 5230, January 2008. + + [SIEVE] Guenther, P. and T. Showalter, "Seive: An Email + Filtering Language", RFC 5228, January 2008. + + + + + + + + + + + + + + + + + + + + + + +Burger & Parsons Informational [Page 14] + +RFC 5442 LEMONADE Architecture March 2009 + + +Authors' Addresses + + Eric W. Burger + Consultant + New Hampshire + USA + + Phone: + Fax: +1 530-267-7447 + EMail: eburger@standardstrack.com + URI: http://www.standardstrack.com + + + Glenn Parsons + Nortel Networks + 3500 Carling Avenue + Ottawa, ON K2H 8E9 + Canada + + Phone: +1 613 763 7582 + EMail: gparsons@nortel.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Burger & Parsons Informational [Page 15] + |