ATOCA R.L. Barnes
Internet-Draft BBN Technologies
Intended status: Informational October 31, 2011
Expires: May 03, 2012

Scalable Robust Alerting Protocol (SCRAP)
draft-barnes-atoca-delivery-00.txt

Abstract

Emergency alerts need to be delivered reliably from one source to many recipients at once. TCP is unsuitable for this style of delivery, because the large number of acknowledgements would likely cause network congestion. This document defines a UDP-based protocol for delivering alerts that supports fragmentation and retransmission for reliability, and allows the sender of a datagram to control whether acknowledgements are sent.

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Status of this Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on May 03, 2012.

Copyright Notice

Copyright (c) 2011 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

1. Introduction

[TODO]

1.1. Open Questions

Should we include hash value in URI format? Or leave that to the metadata/configuration protocol?

Should we randomize the order in which fragments are transmitted in order to deal with correlated loss?

2. Definitions

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 RFC 2119 [RFC2119].

3. Packet Format

[Sent over UDP. Default port is XXX.]

[Payload format: Alert ID (2 octets / 16 bits); Fragment number (1 octet / 8 bits); Number of fragments in alert (1 octet / 8 bits); Alert data (remaining octets)]

[Content of reassembled packets MUST be an ESCAPE-formatted alert]

4. URI Format

[Specifies the format/source of an alert that will be sent]

[alert-src:[host/IP]:[srcport]?:[dstport]]

5. Sender Processing

[Choose an alert ID]

[Divide payload into fragments that will fit within an MTU]

[Attach headers to fragments]

[Transmit fragments in order]

[Re-transmit the sequence to deal with loss:]

[Probability of receipt given loss (p=P(success)), #fragments (F), #retransmissions (R), : q = (1 - (1-p)^R)^F]

[Number of retransmissions given loss (1-p), resilience (q), #fragments (F): R = log(1-q^(1/F)) / log(1-p)]

6. Receiver Processing

[Maintain a set of alert buffers identified by alert ID (possibly an empty set)]

[Alert buffer contents: alert id; fragments to be received; list of fragment numbers; list of fragments]

[When an alert packet arrives...]

[If there is a buffer for its ID, add it to the buffer; if the buffer is complete, re-assemble, validate ESCAPE, and deliver alert to higher layer]

[If there is not a buffer for its ID, then allocate a new one and add the fragment.]

[If all fragments for an alert do not arrive within T1 milliseconds, discard the buffer; default T1=5000]

7. IANA Considerations

[Default port number]

8. Security Considerations

[This protocol provides no security protections; security provided by ESCAPE.]

[Main concern is DOS, mitigated by buffer timeouts; at worst, have to buffer 2^32 octets, if all buffers full for all alert IDs. MAY impose limits on buffer size / number of buffers active simultaneously. ]

9. Acknowledgements

[TODO]

10. References

10.1. Normative References

[CAP] Botterell, A and E. Jones, "Common Alerting Protocol v1.1", October 2005.
[RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures", RFC 1421, February 1993.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L.P. and G. Randers-Pehrson, "GZIP file format specification version 4.3", RFC 1952, May 1996.
[RFC2045] Freed, N. and N.S. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
[RFC3370] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms", RFC 3370, August 2002.
[RFC4566] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, September 2009.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010.
[RFC5754] Turner, S., "Using SHA2 Algorithms with Cryptographic Message Syntax", RFC 5754, January 2010.

10.2. Informative References

[I-D.ietf-atoca-requirements] Schulzrinne, H, Norreys, S, Rosen, B and H Tschofenig, "Requirements, Terminology and Framework for Exigent Communications", Internet-Draft draft-ietf-atoca-requirements-02, October 2011.

Author's Address

Richard Barnes BBN Technologies 9861 Broken Land Parkway Columbia, MD 21046 US Phone: +1 410 290 6169