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Versions: 00 01 02 03 04 05 06 07 08                                    
Network Working Group                                            L. Wood
Internet-Draft                                             Cisco Systems
Intended status: Experimental                          December 19, 2008
Expires: June 22, 2009

   Specifying transport mechanisms for retrieval or delivery of URIs

Status of this Memo

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

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   This Internet-Draft will expire on June 22, 2009.

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   This document describes a simple extension of the URI format to allow
   preferred transport mechanisms and interfaces to be specified.  This

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   explicit configuration is beneficial for separation of HTTP from
   underlying transports, which has been increasingly recognised as
   useful.  Explicit configuration in the URI for programs is valuable
   when TCP, traditionally used to carry HTTP, is not present or not
   desired, or when other methods of determining or negotiating the
   appropriate transport method to use, e.g. the Domain Name System
   (DNS), are absent.

Table of Contents

   1.  Background and Introduction . . . . . . . . . . . . . . . . . . 3
   2.  Extending the URI scheme to indicate transports and
       interfaces  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Related work  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Background and Introduction

   Desire to separate the Hypertext Transfer Protocol (HTTP) [RFC2616]
   from its traditional transport of the Transmission Control Protocol
   (TCP) is increasing.

   There are environments where TCP is not suitable, or absent, yet HTTP
   can still be used as a method to transfer data.  Being able to
   indicate the desired transport and interface to use in the URI for a
   program to interpret when executing HTTP GETs or PUTs is useful when
   a choice of mechanisms and interfaces are available.

   This document outlines how the desired transport and interface can be
   indicated in the Uniform Resource Identifier (URI) format [RFC3986]
   by a simple extension to that format using existing syntax.

   This syntax is useful for carrying HTTP over different transport
   protocols.  HTTP can be thought of a session layer, running over a
   transport layer providing reliable delivery of the HTTP stream
   between hops.  This transport layer is commonly (and almost
   universally) TCP in the terrestrial Internet, although alternative
   transport layers, such as SCTP, can also be used under HTTP
   [I-D.natarajan-httpbis-sctp].  For long-delay networks, or for
   network conditions where TCP or an equivalent is not suitable, an
   alternative transport layer such as Saratoga
   [I-D.wood-tsvwg-saratoga] can be used under HTTP instead in hop-by-
   hop communications between nodes.  This has been described in detail
   [I-D.wood-dtnrg-http-dtn-delivery].  HTTP requires only reliable
   streaming that can be used to provide ordered delivery to the
   application; how that reliable streaming is provided is up to the
   local transport layer in the local network.  TCP or SCTP would be
   used to carry HTTP over the congestion-sensitive public Internet,
   while Saratoga would be used for HTTP across private links.

   Steve Deering has often described IP as 'the waist in the hourglass'
   [Deering98] - what is above and touching on IP can be changed, what
   is below and touching on IP can be changed, but provided the new
   elements continue to interface to and work with IP, the hourglass
   remains complete and the network stack remains functional.  Here,
   HTTP is the waist in this particular hourglass; applications can use
   HTTP to communicate, provided HTTP runs over a reliable transport
   stream.  The applications can vary.  The transport stream can be
   changed; HTTP does not have to run over TCP/IP, but could even be
   made to run directly over something else entirely.  Given the
   prevalence of IP in many networks, it is likely that two waists
   exist; IP and HTTP are likely choices, but the transport protocol and
   physical enviroment will vary more.

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   Being able to specify how HTTP or other schemes are carried is useful
   when a variety of methods are available to choose from.  The syntax
   described here is useful for local configuration, e.g. in a scripting
   language that is aware of the local host and remote host's shared
   support of a given transport protocol.  It is less useful on the
   public world-wide web, because users (and web page design) are not
   generally capable of determining which transport protocol(s) are
   supported by their web browser, operating system, or network.

2.  Extending the URI scheme to indicate transports and interfaces

   The URI format syntax ([RFC3986], section 3.1) defines the scheme as:

   scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )

   To quote [RFC2718], section 2.2.2:

   "When a scheme is associated with a network protocol, the
   specification should completely describe how URLs are translated into
   protocol actions in sufficient detail to make the access of the
   network resource unambiguous.  If an implementation of the URL scheme
   requires some configuration, the configuration elements must be
   clearly identified."

   Within these constraints, this draft proposes that schemes can be
   extended to indicate transport and interface, in the format:

   scheme = scheme name [ "+" port ] [ "-" transport ] ["." interface ]

   where the optionally-included +port is a description mapping to the
   default IANA-assigned port number, or the equivalent name, indicating
   the desired behaviour over a transport.  The optionally-included
   -transport is the transport name or IANA protocol identifier number
   that that name maps to.  The optionally-included .interface can
   contain a locally-meaningful specifier identifying that interface.

   This would permit http-sctp:// or http+saratoga-udp:// for the uses
   outlined in [I-D.natarajan-httpbis-sctp] and
   [I-D.wood-dtnrg-http-dtn-delivery].  Port and internet protocol
   numbers assigned by IANA are accepted as equivalent to assigned names
   for these underlying protocols, so http+7542-17:// specifies HTTP
   over Saratoga over UDP. http-132 is equivalent to http-sctp in
   specifying HTTP over SCTP.  As is usual, these are case insensitive,
   so that http-sctp, HTTP-sctp, and HtTp-ScTp are all equivalent.

   If required, the port the scheme is actually run over, which the
   behaviour of the specified default port is mapped to, is still

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   indicated later in the URI as :number, e.g. :80.  When this is not
   specified the default port is used.

   Knowing that a higher-layer protocol is always associated with TCP or
   UDP would mean that -tcp or -udp could be omitted. http by itself is
   taken to mean http-tcp, and is therefore backwards-compatible with
   current use.

   Being able to specify the local interface to initiate a transaction
   on when a choice of interfaces is available on a multihomed device is
   useful, e.g. http+saratoga.serial0://.

3.  Related work

   [I-D.jennings-http-srv] has proposed a DNS lookup of a SRV record to
   return a dynamic port value, as well as an address.  Rather than
   overloading existing use of "http://", this could be specially
   indicated via e.g. http-srv://.  Alternatively, some new DNS record
   type returning address, port and other access information could be
   explicitly accessed via e.g. http-dns://.

   Other work on evolving the URI format to enable service discovery
   with DNS for different transport protocols is in e.g.  [Uruena05].

   It should be possible to combine the static configuration in the
   parseable scheme format described here with getting other
   configuration information that is not explicitly given, but that is
   needed to access the URI dyamically, from DNS records when

4.  Security Considerations

   No additional security concerns have been thought of at this time.

5.  IANA Considerations

   No additional IANA considerations have been thought of at this time.

6.  References

6.1.  Normative References

   [RFC2718]  Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
              "Guidelines for new URL Schemes", RFC 2718, November 1999.

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   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

6.2.  Informative References

              Deering, S., "Watching the Waist of the Protocol
              Hourglass", keynote, IEEE International Conference on
              Network Protocols (ICNP), Austin Texas, October 1998.

              Jennings, C., "DNS SRV Records for HTTP",
              draft-jennings-http-srv-00 (work in progress), July 2008.

              Natarajan, P., Amer, P., Leighton, J., and F. Baker,
              "Using SCTP as a Transport Layer Protocol for HTTP",
              draft-natarajan-httpbis-sctp-00 (work in progress),
              October 2008.

              Wood, L. and P. Holliday, "Using HTTP for delivery in
              Delay/Disruption-Tolerant Networks",
              draft-wood-dtnrg-http-dtn-delivery-02 (work in progress),
              October 2008.

              Wood, L., McKim, J., Eddy, W., Ivancic, W., and C.
              Jackson, "Saratoga: A Scalable File Transfer Protocol",
              draft-wood-tsvwg-saratoga-02 (work in progress),
              October 2008.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

              Uruena, M. and D. Larrabeiti, "Nested Uniform Resource
              Identifiers", Proceedings of the 31st EUROMICRO Conference
              on Software Engineering and Advanced Applications, pp.
              380-385 , August 2005.

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Author's Address

   Lloyd Wood
   Cisco Systems
   11 New Square Park, Bedfont Lakes
   Feltham, Middlesex  TW14 8HA
   United Kingdom

   Phone: +44-20-8824-4236
   Email: lwood@cisco.com

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