July 2005 Lemonade Internet Draft: Mobile E-mail S. H. Maes Document: draft-maes-lemonade-mobile-email-04.txt Oracle Corporation Expires: January 2006 July 2005 Lemonade and Mobile e-mail Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC2026. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC2026. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Maes Expires - January 2006 [Page 1] July 2005 The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document describes the challenges with mobile e-mail in order to identify the challenges that are within the mobile profile of Lemonade. Conventions used in this document In examples, "M:", "I:" and "S:" indicate lines sent by the client messaging user agent, IMAP e-mail server and submit server respectively. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. An implementation is not compliant if it fails to satisfy one or more of the MUST or REQUIRED level requirements for the protocol(s) it implements. An implementation that satisfies all the MUST or REQUIRED level and all the SHOULD level requirements for a protocol is said to be "unconditionally compliant" to that protocol; one that satisfies all the MUST level requirements but not all the SHOULD level requirements is said to be "conditionally compliant." When describing the general syntax, some definitions are omitted as they are defined in [RFC3501]. Table of Contents Status of this Memo ........................................... 1 Abstract....................................................... 2 Conventions used in this document.............................. 2 Table of Contents.............................................. 2 1. Introduction................................................ 3 1.1. Definitions ........................................... 3 1.2. Main Expectations...................................... 3 1.3. Additional Considerations.............................. 4 1.4. Main Actors ........................................... 5 1.5. Other players in ecosystem............................. 5 2. Challenges.................................................. 5 2.1. Devices................................................ 5 2.2. Networks and operators................................. 5 Maes Expires - January 2006 [Page 2] July 2005 2.3. Enterprises and other e-mail service providers......... 7 3. Usage models................................................ 7 3.1. Usage Pattern.......................................... 7 3.2. Deployment models...................................... 8 3.3. Deployment model A..................................... 8 3.4. Deployment model B..................................... 9 3.5. Deployment model C..................................... 9 3.5.1. Deployment model C.1.............................. 9 3.5.2. Deployment model C.2.............................. 9 3.6. Deployment model D.....................................10 4. Recommendations on Lemonade work and specifications.........10 4.1. Scope recommendations..................................10 4.2. Objectives.............................................11 4.3. Principles.............................................11 4.4. Topics to explicitly address...........................12 4.5. Lemonade goals for mobile e-mail.......................12 Security Considerations........................................12 References.....................................................13 Version History................................................13 Acknowledgments................................................14 Authors Addresses..............................................14 Intellectual Property Statement................................14 Full Copyright Statement.......................................15 1. Introduction This document describes the challenges associated to mobile e-mail. 1.1. Definitions Mobile e-mail is defined as "Access to e-mail while mobile"; typically from a mobile device. 1.2. Main Expectations The main expectations for mobile e-mail are: - To receive quasi-instantaneous notification of new e-mails when within coverage (if setup this way) - To reflect quasi-instantaneously new e-mail or e-mail server events in the mobile client when within coverage - To send quasi-instantaneously e-mail composed on mobile client from appropriate e-mail server when within coverage or as soon that coverage is established otherwise - To efficiently manipulate e-mails / drafts / attachment as needed or as preferred - End-to-end secure when needed (e.g. e-mails may at no point be in clear outside enterprise domain) Maes Expires - January 2006 [Page 3] July 2005 - Low or at least bearable cost of usage (e.g. traffic / bandwidth optimization, predictable cost, manageable traffic, ...) Note that the notion of quasi-instantaneous refers to the impression of the user and not to a particular precise duration: the user has the feeling that something happens in a way that is quasi- instantaneous. This may be equivalent to some desktop user experience or sometimes be faster or slower than desktop. That is not important as the user can usually not compare. On the other hand, some overall behavior clearly violate this principle (e.g. if the client waits for the user to "browse" its mailbox with a client to download the headers or even the whole messages). 1.3. Additional Considerations The following considerations are also important for mobile e-mail: - Need for graceful degradation (e.g. being able to access e- mail while mobile through other channels like voice/DTMF, Messaging (SMS, MMS, IM, à), WAP Push and browsing - Need for server-to-client notifications that clients can display instead if acting on and that informs the user. - Format adaptation (attachments, page, ...): - Format conversion - Adaptation to device capabilities and form factor - streamed versus downloaded multi-media - DRM (Digital Right Management) rules: how to respect DRM rules like forward lock - Provisioning / setup: These are extremely challenging on mobile devices with limited or challenging input capabilities. Also average users are more easily confused and unable to correctly setup mobile phones - Charging: Operator want to maintain charging to create a viable business model. They may be less inclined to deploy or support mobile email solutions that do not permit charging for e-mail services. - Synchronization with other clients: - e.g. Peer to peer vs. with server (SyncML / OMA DS and other real time synchronization protocols, ...) and how to allow a same repository to sometimes access e-mail on the server via mobile access over the air and sometimes access it via synchronization with the email repository on a laptop that itself sometimes access email from the email server. - Relationship to PIM (agenda / Address Book): mobile e-mail can also support the exchange of PIM events as payload or attachments (e.g. considering the calendar or address book repository as another e-mail folder). Maes Expires - January 2006 [Page 4] July 2005 1.4. Main Actors The main actors are: - Users - Operators of the mobile network - E-mail service providers: - Service providers (e.g. Operators, other e-mail server providers) - Enterprises 1.5. Other players in ecosystem Other actors influence decisions related to mobile e-mail: - Device Manufacturers - Client software providers - E-mail server manufacturers: - E-mail server - Mobile e-mail enablement server 2. Challenges 2.1. Devices Devices present the following challenges that directly impact mobile e-mail: - Constrained memory / processing power (always improving): - Wide range to support - Limited battery life (will remain a problem for a long time): - Constrains processing capability - Constrains connectivity patterns (not always fully connected but may be awaken via outband notifications...) - Notifications / wake-up are to be supported by mobile e-mail - Constraints acceptable bandwidth - More exotic platforms: - Sometimes proprietary or closed - Challenging or controlled software distribution channels: - Installing, provisioning, supporting, upgrading,... - E.g. DRM trusted clients - Wide range of control models by: - Device manufacturer, operator, enterprise, user 2.2. Networks and operators Mobile networks and operators impose additional constraints that must be taken into account when designing mobile e-mail solutions: - Different underlying network technologies / bearers with different behavior / capabilities Maes Expires - January 2006 [Page 5] July 2005 - Intermittent connectivity: - Loss of coverage - Nature of mobility (e.g. radio turned off in planes) - Temporary IP addresses - Unreliable delivery (Connection) - Underlying network layer (up to transport) may drop at any time. Even if then re-established, sessions at the transport level are maintained only if the transport protocol provide mechanisms to maintain it when the network connection is re- established. Otherwise, additional mechanisms are needed at the application protocol layer to establish and maintain or recover session if a session is needed or assumed. - As a result notifications schemes like IDLE perform poorly when used as intended (i.e. without improvements) over a reliable network - Out band notification schemes - Unreliable - But can be used as "wake up / notification scheme" - Limited bandwidth: - Limited capabilities shared across all users - Roaming within and across domain / operators / technologies - Cost of usage: - Multiple cost models (free, unlimited, per packet, per service / type of service, ...) - In general, costly and in need of optimization to maintain cost acceptable enough to user and to allow operator to share network with enough users. - Controlled: - Walled garden: - Inbound and outbound traffic - Internal traffic - With its own authentication mechanisms etc... - Regulated: - QoS - Privacy - Exchanged data - Reachability - Logging - Accountability, support desk (inexperienced users, hard to provision) - ... - Huge subscriber sets - Server scalability is critical (e-mail server / Mobile e-mail Enabling Server / network) - Solutions that tie-up one or more ports per device or user are not easily scalable - e.g. IDLE sessions for each devices tie-up ports and create large queues. - Support desk challenges Maes Expires - January 2006 [Page 6] July 2005 - Time outs introduced by numerous intermediaries, firewalls, gateways etc 2.3. Enterprises and other e-mail service providers Enterprises must reconcile mobile e-mail deployments with the following requirements: - Walled garden intranets: - Firewalls, VPN, ... - IT Corporate security guidelines: - Wide range - in general VERY conservative e.g. - Require end-to-end security - Allowed applications / usages / content - Firewalls / ports / protocols - (e.g. only HTTP or HTTPS; no SSL/TLS) - Time-outs - No storage of company data outside intranet on defined servers (in clear or not). This is why MMS solutions are not acceptable. Current e-mail infrastructure with untraceable potential intermediate storage is accepted. - Regulated: - E.g. Journaling / Storage of all corporate e-mails - Control usage costs and support (including provisioning) - Need to integrate with existing IT infrastructure (instead of replacing them). - Similar scalability need of email servers / mobile email enabling servers. - Time outs introduced by firewalls etc... 3. Usage models 3.1. Usage Pattern The generic usage pattern model to support mobile e-mail includes: - Mobile e-mail server (backend e.g. IMAP server): - This is typically a regular e-mail server. It may consist of several servers (e.g. IMAP4 server and SMTP server or POP3 server and SMTP server). - Connector: - The connector includes any protocol adaptation required between the e-mail server and mobile e-mail enabling server. - Mobile e-mail enabling server: - The mobile e-mail enabler implements the server-side functionality of the mobile e-mail specifications. - Mobile e-mail client: - The mobile e-mail client implements the client-side functionality of the mobile e-mail specifications. Maes Expires - January 2006 [Page 7] July 2005 - The mobile e-mail protocol between the mobile e-mail client and mobile e-mail enabling server. - Mobile enablers that support functions needed by the OMA mobile e-mail enabler. E.g.: - Outband notifications - Provisioning - ... 3.2. Deployment models These different components may be deployed in different domains that may be separated by firewalls. Possible deployments include: A: Mobile e-mail by operators: "operator hosted e-mail service" - Device in network - Mobile "enabled" email server in OperatorÆs Domain - Roaming across compatible networks / operators B: Mobile e-mail by E-mail service provider (enterprise, ISP): - Device in operator network (including roaming) - Mobile "enabled" email E-mail server in service provider C: Outsourced mobile enablement of E-mail service provider: 1. By Operator (operator hosted) 2. By other third party service provider - Device in operator network (including roaming) - E-mail server in other domain D: As above, but with proxies in addition to the mobile e-mail enabling server. 3.3. Deployment model A Deployment A is characterized by: * In operator(s) domain: - Mobile e-mail server (backend e.g. IMAP server) - Connected (e.g. via IMAP) through a "connector" - to a mobile e-mail enabling server - Connected: - Via mobile e-mail protocol to a mobile e-mail client - Via other protocols to mobile enablers that support functions like: - Outband notifications - Provisioning - ... Firewalls may exist: - Between: - Mobile client and mobile e-mail enabling server - Mobile enablers and mobile e-mail enabling server Maes Expires - January 2006 [Page 8] July 2005 3.4. Deployment model B Deployment B is characterized by: * In E-mail Service Provider domain: - Mobile e-mail server (backend e.g. IMAP server) - Connected (e.g. via IMAP) through a "connector" - to a mobile e-mail enabling server - Connected: * In Operator(s) domain: - Via mobile e-mail protocol to a mobile e-mail client - Via other protocols to mobile enablers that support functions like: - Outband notifications - Provisioning - ... Firewalls may exist: - 1) Between connectors and mobile e-mail enabling server - 2) Between: - Mobile client and mobile e-mail enabling server - Mobile enablers and mobile e-mail enabling server 3.5. Deployment model C 3.5.1. Deployment model C.1 Deployment C.1 is characterized by: * In E-mail Service Provider domain: - Mobile e-mail server (backend e.g. IMAP server) - Connected (e.g. via IMAP) through a "connector" * In Operator(s) domain: - to a mobile e-mail enabling server - Connected: - Via mobile e-mail protocol to a mobile e-mail client - Via other protocols to mobile enablers that support functions like: - Outband notifications - Provisioning - ... Firewalls may exist: - 1) Between connectors and mobile e-mail enabling server - 2) Between: - Mobile client and mobile e-mail enabling server - Mobile enablers and mobile e-mail enabling server 3.5.2. Deployment model C.2 Maes Expires - January 2006 [Page 9] July 2005 Deployment C.2 is characterized by: * In E-mail Service Provider domain: - Mobile e-mail server (backend e.g. IMAP server) - Connected (e.g. via IMAP) through a "connector" * In third party service provider: - to a mobile e-mail enabling server - Connected: * In Operator(s) domain: - Via mobile e-mail protocol to a mobile e-mail client - Via other protocols to mobile enablers that support functions like: - Outband notifications - Provisioning - ... Firewalls may exist: - 1) Between connectors and mobile e-mail enabling server - 2) Between: - Mobile client and mobile e-mail enabling server - Mobile enablers and mobile e-mail enabling server 3.6. Deployment model D Proxies are involved in front of mobile e-mail enabling server. This allows protocol adaptation to possibly take place within the e-mail server domain while the proxy handles the firewall challenges [LEMONADEINTERMEDIARIES]. 4. Recommendations on Lemonade work and specifications <> 4.1. Scope recommendations LemonadeÆs raison dÆŠtre and charter [LEMONADECHARTER] is to enhance Internet email to support diverse service environments. Considering the attention paid by the industry to mobile and/or push e-mail and success of early proprietary solutions, it is natural that IETF Lemonade considers enhancing its internet mail protocols to support mobile email. As discussed above, and as illustrated by the user experience and features of todayÆs pioneer deployments, mobile e-mail is different from regular internet mail confronted to the specific constraints and limitations of the networks, the technologies and their deployments by multiple actors... Problems are no only technical; some may be rather linked to non-recommended deployments or usages of these Maes Expires - January 2006 [Page 10] July 2005 technologies because of a variety of technical, business or legal reasons. Other standard activities, like the OMA (Open Mobile Alliance), have started work on mobile e-mail. It is critical that a standard mobile e-mail solution be based on profiles and extensions of the Internet email and interoperate well with it rather completely different approaches that are not built on the Internet email protocols that may take much longer to be designed and deployed and may not benefit of the year of experience that IETF and the industry have acquired developing, implementing and deploying e-mail. From a timing point of view, IETF Lemonade work seems to be ideally placed to allow rapid development of specifications to support mobile e-mail. It is not clear that any other standard technology today can easily be used or extended to satisfy the requirements and expectation of an open standard mobile e-mail specification. 4.2. Objectives So the Lemonade working group MUST look at the problems of mobile e- mail in their entirety. Lemonade MUST specify or a mobile e-mail protocol or specify a set of optimizations "inspired" from mobile e-mail to address as much as can be within the scope of IETF. When issues are deemed beyond the scope of IETF, Lemonade SHOULD analyze options to address all of the issues via guidelines or recommendations to other standard activities. If needed LemonadeÆs charter [LEMONADECHARTER] MUST be updated to cover the above. 4.3. Principles As design principles, it is recommended that: - Lemonade MUST design its protocol to allow use of its messages and principles with other transport mechanisms (e.g. HTTP bindings, outband notification mechanisms, ...) when needed to address some of the mobile e-mail challenges identified in this document. - Accordingly, Lemonade MUST NOT make assumptions on the underlying network transport or design choices that would prevent addressing all these issues even if their resolution is outside the scope of IETF (network neutrality). This implies in particular allowing: - Compression at the application level - Encryption Maes Expires - January 2006 [Page 11] July 2005 - The possibility to bind Lemonade to HTTP/HTTPS. 4.4. Topics to explicitly address Lemonade should start investigation addressing or specifying: - IMAP protocol optimizations (to reduce traffic between client and server: - Reduction of roundtrip - Compression of data exchanges: - Transport level - Application level shown very useful for example when attachments are exchanged. - Support for notifications mechanisms: - Client to server - Server to server - Filtering (setup and changes): - Message filters - Notifications filters - Dealing with problems of intermediaries with respect to mobile e-mail (see also [LEMONADEINTERMEDIARIES]): - Implications on end-to-end security, compression and stability of the connection. - Realities of todayÆs deployment models and business models. - Attachment / body part adaptation: - Format conversions - Streaming - Adaptation to device capability and form factor - Attachment manipulation: - Forward without download - Others? - Improved reliability to connection / network drops - Efficient quick reconnect scheme - Provisioning 4.5. Lemonade goals for mobile e-mail The Lemonade WG must target to provide support via its Lemonade profile and protocol specifications to the mobile e-mail enabler specified by OMA. Requirements can be found as [OMA-ME-RD]. Security Considerations The Mobile e-mail protocols must address / support security issues raised by: - The different deployment models identified in section 3. In particular: Maes Expires - January 2006 [Page 12] July 2005 - End-to-end security with no message in the clear when the mobile e-mail enabling server is outside the e-mail service provider domain. - No storage of e-mail (in the clear or not) outside the control and domain of the e-mail service provider - Secure notifications when relevant information is carried the notifications. - Support for the restrictions introduced by the presence of firewalls with constraints typically met in such firewall deployments (e.g. corporate guidelines that open only HTTP or HTTPS ports). - On bandwidth limited mobile networks where users pay per data volumes and/or notifications, spam may become an important issue. It can be mitigated with appropriate filters and server-side spam prevention tools. References [LEMONADECHARTER] IETF Charter for ôEnhancements to Internet email to support diverse service environments (lemonade)", http://www.ietf.org/html.charters/lemonade-charter.html. [LEMONADEINTERMEDIARIES] Maes, S.H. and D. Crocker, ôLemonade and the challenges of Intermediaries", draft-maes-lemonade-intermediary- challenges-xx.txt, (work in progress). [LEMONADEPROFILE] Maes, S.H. and Melnikov A., "Lemonade Profile", draft-ietf-lemonade-profile-XX.txt, (work in progress). [OMA-ME-RD] Open Mobile Alliance Mobile Email Requirement Document, (Work in progress). http://www.openmobilealliance.org/ Version History Revision 03: [1] Removal of explicit text change requests in section 4. [2] Addition of proxy-based deployment models. [3] Reference to OMA mobile e-mail RD. Revision 03: [1] Editorial improvements throughout the document [2] Extension of section 4 on recommendations including proposed next steps for the charter and Lemonade WG activities. [3] Addition of references Revision 02: [1] Added time out issue more explicitly [2] Added recommendations Maes Expires - January 2006 [Page 13] July 2005 Revision 01: [1] Editorial improvements Acknowledgments This document is based on discussions at Oracle, with partners as well as in the context of mobile e-mail standard work at OMA (Open Mobile Alliance) and at IETF Lemonade. Authors Addresses Stephane H. Maes Oracle Corporation 500 Oracle Parkway M/S 4op634 Redwood Shores, CA 94065 USA Phone: +1-650-607-6296 Email: stephane.maes@oracle.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Maes Expires - January 2006 [Page 14] July 2005 Full Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. Maes Expires - January 2006 [Page 15]