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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group L. Wood 3 Internet-Draft Surrey alumni 4 Intended status: Experimental P. Holliday 5 Expires: November 7, 2014 PS&E 6 May 6, 2014 8 Using HTTP for delivery in Delay/Disruption-Tolerant Networks 9 draft-wood-dtnrg-http-dtn-delivery-08 11 Abstract 13 This document describes how to use the Hypertext Transfer Protocol, 14 HTTP, for communication across delay- and disruption-tolerant 15 networks, by making every transit node in the network HTTP-capable, 16 and doing peer HTTP transfers between nodes to move data hop-by-hop 17 or subnet-by-subnet towards its final destination. HTTP is well- 18 known and straightforward to implement in these networks. 20 Status of This Memo 22 This Internet-Draft is submitted to IETF in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on November 7, 2014. 37 Copyright Notice 39 Copyright (c) 2014 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. 49 Table of Contents 51 1. Background and Introduction . . . . . . . . . . . . . . . . . 2 52 2. Adapting the HTTP delivery mechanism for DTNs . . . . . . . . 4 53 3. Other useful proposed additional HTTP headers . . . . . . . . 7 54 4. Other suggestions on using MIME in DTN networks . . . . . . . 8 55 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 56 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 57 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 58 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 59 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 60 8.2. Informative References . . . . . . . . . . . . . . . . . 9 61 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 63 1. Background and Introduction 65 Delay- and Disruption-Tolerant Networks (DTNs) are networks where 66 conditions are such that links between nodes are not always 67 permanent, may be of very long delay or exist only during very short 68 contact periods where the link is up, and may change over time 69 [RFC4838]. Some DTNs can be thought of as sparse ad-hoc networks, 70 with nodes communicating intermittently only when they come into 71 contact. Store-and-forward delivery of data is a useful way of 72 communicating across these networks. 74 This document outlines how the well-known Hypertext Transfer Protocol 75 (HTTP) [RFC2616] can be used for store-and-forward communication 76 across DTNs. HTTP is not used end-to-end as it is on the web. 77 Instead, applications running on each node in the network communicate 78 with their neighbours using dedicated hop-by-hop or subnet-by-subnet 79 HTTP transfers to effect local data delivery. 81 A specialised store-and-forward protocol for DTN delivery has been 82 proposed in the IRTF DTN research group (DTNRG) - the Bundle Protocol 83 [RFC5050]. Criticisms of the Bundle Protocol's lack of reliability 84 and its complexity have been made [I-D.irtf-dtnrg-bundle-checksum]. 85 The Bundle Protocol is itself intended to be a routable data format, 86 but the supporting architectures for node and application naming/ 87 addressing, automated routing, security, QoS, and resource discovery 88 have not yet been agreed upon or in some cases even significantly 89 worked on. These things already exist for the Internet Protocol, and 90 can in many cases be easily leveraged for DTN networks [Wood09a]. 92 Additional HTTP header information adds context for onward forwarding 93 and delivery to destination endpoints, and provides the reliability 94 and support for error-detection currently missing from the 95 alternative Bundle Protocol. 97 It must be stressed that this proposed use is distinct from proxy 98 caching methods prevalent in the traditional web. Caching commands 99 are not used; end-to-end HTTP requests are not intercepted by 100 intermediate caches that attempt to fulfil them in the traditional 101 web caching sense. 103 Although HTTP-DTN use as as a hop-by-hop message carrier between 104 caches implementing some form of routing protocol between them, the 105 distinction between client, server and proxy is replaced by peer 106 intermediate caches using HTTP to communicate in separate sessions 107 that together combine over time to make the full path between 108 original source and final destination for the data. 110 HTTP is a session layer, running over a transport layer providing 111 reliable delivery of the HTTP stream between hops. This transport 112 layer is commonly (and almost universally) TCP in the terrestrial 113 Internet, although alternative transport layers, such as SCTP, can 114 also be used under HTTP [I-D.natarajan-http-over-sctp]. For long- 115 delay networks, or for network conditions where TCP or an equivalent 116 is not suitable, an alternative transport layer such as Saratoga 117 [I-D.wood-tsvwg-saratoga] can be used under HTTP instead in hop-by- 118 hop communications between nodes. HTTP requires only reliable 119 streaming that can be used to provide ordered delivery; how that 120 reliable streaming is provided is up to the local transport layer in 121 the local subnet, and multiple different transport layers can be used 122 across the multiple hops between nodes to transfer data from source 123 to final destination. 125 Steve Deering has often described IP as 'the waist in the hourglass' 126 [Deering98] - what is above and touching on IP can be changed, what 127 is below and touching on IP can be changed, but provided the new 128 elements continue to interface to and work with IP, the hourglass 129 remains complete and the network stack remains functional. Here, 130 HTTP is the waist in this particular hourglass; applications can use 131 HTTP to communicate, provided HTTP runs over a reliable transport 132 stream. The applications can vary. The transport stream can be 133 changed; HTTP does not have to run over TCP/IP, but could even be 134 made to run directly over e.g. HDLC or a CCSDS reliable bitstream. 135 Given the prevalence of IP in many networks, it is likely that two 136 waists exist; IP and HTTP are likely choices, but the transport 137 protocol and physical enviroment will vary more. An expansion of 138 this argument is given in [Wood09b]. 140 Separation of HTTP from the underlying transport layer to make HTTP a 141 layer in its own right is increasingly likely to happen; this is 142 analogous to the use of different "convergence layers" under the 143 Bundle Protocol. Being able to set what transport layer to use 144 depending on conditions is useful, and one simple configuration 145 approach to this, able to support HTTP-DTN, was outlined in 146 [I-D.wood-tae-specifying-uri-transports]. 148 HTTP use here relies on the three P's - Persistence, Pipelining and 149 the PUT directive. These are all present in the HTTP/1.1 150 specification. 152 This document contains an overview of how HTTP can be simply adapted 153 to the DTN environment by the use of HTTP/1.1 with persistence and 154 pipelining, the PUT and GET directives, and some trivial extra HTTP 155 headers needed to indicate e.g. a destination in the DTN network. 157 The remainder of this specification uses 'file' as a shorthand for 158 'binary object', which may be an HTTP 'object', file with an 159 associated MIMEtype, or other type of contiguous binary data. 161 A significant benefit to use of HTTP is that the well-known MIMEtype 162 mechanism, integral to HTTP, provides hints on what received files 163 are, and what applications should do with them [RFC2045]. The Bundle 164 Protocol does not support MIMEtypes, or any similar mechanism. HTTP/ 165 1.1's use of MIME is specified in [RFC2616] rather than in the 166 separate MIME documents. 168 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 169 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 170 document are to be interpreted as described in RFC 2119. [RFC2119] 172 2. Adapting the HTTP delivery mechanism for DTNs 174 Here, HTTP is used as a peer-to-peer protocol in the sense that 175 multiple files may be transferred in both directions simultaneously 176 between two communicating nodes using HTTP for DTN use. There is not 177 intended to be a strict client/user-agent to server relationship as 178 there is in the web. Instead, sending data across a path of six 179 nodes, four nodes between source and destination, will require a 180 minimum of five separate per-hop HTTP transactions between each pair 181 of nodes to move the data onwards to the next node. This breaks the 182 traditional end-to-end control loop and transfer into separate 183 control loops and transfers suitable for the DTN environment. 185 When two nodes come into contact across a local hop or a subnet, a 186 request for files to be copied, stored, and carried onwards can be 187 made by the receiving node issuing an HTTP GET request. 188 Alternatively, the sending node can simply issue a series of HTTP PUT 189 requests once a connection is established, if it believes that 190 putting the data to the receiving node moves it closer to its 191 eventual destination. The receiving node can always reject transfers 192 with error codes. 194 HTTP-DTN is a superset of HTTP/1.1. HTTP/1.1 pipelining and 195 persistence permits multiple PUTs to be made in sequence. Support 196 for these in implementations is beneficial to the mechanisms outlined 197 here. (Note that [I-D.natarajan-http-over-sctp] also takes advantage 198 of HTTP pipelining and persistence.) 200 The key to enabling HTTP use for DTN networking is an added Content- 201 Destination: header, which specifies the final destination of the 202 file, and can be used by routing in the HTTP-using applications to 203 decide over which available links the file should be sent. Content-* 204 headers are special, in that they may not be ignored (section 9.6 of 205 [RFC2616]). Recipients not understanding Content-Destination: will 206 generate a "501 (Not Implemented)" error code. This separates HTTP 207 use in DTNs described here from normal end-to-end HTTP web use. HTTP 208 DTN nodes MUST support the Content-Destination: header. Files that 209 are PUT are cached and then relayed onwards by intermediate peer to 210 the final destination that is indicated by the Content-Destination: 211 header. GET requests for files can be forwarded by intermediate 212 peers to that final destination that is indicated by the Content- 213 Destination: header. 215 The information provided in Content-Destination: identifying the 216 destination may be an IP address, DNS name, Bundle Endpoint 217 Identifier (EID) or other text-string identifier useful to the local 218 DTN routing mechanisms being used. 220 Similarly, a Content-Source: header provides a textual identification 221 of the original source of the data. HTTP-DTN nodes MUST support the 222 Content-Source: header. 224 For DTN use, DTN HTTP nodes MUST also implement and use Content- 225 Length: and Content-Range: headers. These permit partial delivery of 226 files and resends of missing pieces of files. The Content-MD5: 227 header must be supported. This provides a simple end-to-end 228 reliability check. The Content-MD5: header is intended to be 229 generated by the source node first sending the data, and is not 230 recomputed at other nodes. 232 The Content-Disposition: header is useful for specifying local 233 processing and preserving a filename and timestamp information 234 [RFC6266]. 236 DTN HTTP nodes MUST implement the Host: header, in line with current 237 HTTP specifications. This header field MAY be left blank to request 238 available files from the peer node, rather than identifying a desired 239 file from a distant source by hostname matching the advertised 240 Content-Source: header. A sender placing a new file into the DTN 241 network for onward transmission MUST have the Content-Source: field 242 of the data being sent match its Host: field. 244 Hop-by-hop HTTP headers MAY be implemented between peer nodes talking 245 directly. The headers described in section 13.5.1 of [RFC2616] are 246 available. New hop-by-hop headers MUST use the Connection: header 247 approach described in section 14.10 of [RFC2616]. 249 DTN HTTP nodes may optionally GET from and PUT to link-local IP 250 multicast addresses when used over IP subnets. This permits 251 efficient sharing of files on shared LANs, with recipients requesting 252 resends via Content-Range: and checking assembly of file pieces using 253 the Content-MD5: header. A GET to multicast can request a specific 254 file from any available node that has it. The response to a 255 multicast GET SHOULD be unicast, but a multicast HEAD MAY also be 256 sent to inform other nodes that the sender has the file of interest. 257 If other nodes also express interest in the file with GET requests to 258 the sender, that file may later be PUT to a multicast address. 260 (Note that in the alternative Bundle Protocol, the Bundle Endpoint 261 Identifier (EID) can identify a group of endpoints, rather than just 262 one; mapping the Bundle EID onto multicast IP adddresses on IP 263 subnets is possible. Placing textual EIDs directly in HTTP-DTN's 264 Content-Source: and Content-Destination: headers, or in a Host: 265 field, would be possible to interwork HTTP-DTN and bundling.) 267 The utility of HTTP with multicast has been recognised previously as 268 a method of simple service discovery later adopted for the universal 269 plug and play (UPnP) protocol [I-D.draft-goland-http-udp] 270 [I-D.draft-cai-ssdp-v1]. Rather than call out multicast and unicast 271 separately as different protocols to be used by HTTP, recognising 272 that a given destination or address indicates multicast or broadcast 273 use should suffice. 275 Many existing HTTP/1.1 headers are directly useful with HTTP-DTN. 276 For example, ETag: headers are useful for identifying unique copies 277 of files in the network, and can be used to provide globally unique 278 identifiers (GUIDs) for each version of a file. Age: headers are 279 useful for estimating the amount of time a MIME object has been in 280 the network - indicating both transmission and storage times. Last- 281 Modified: times refer to the times on the origin server - that is, 282 the Content-Source: - and should be preserved during onward 283 forwarding. Max-Forwards: provides a TTL hop count and propagation 284 limitation mechanism. 286 3. Other useful proposed additional HTTP headers 288 A number of other additional HTTP headers are proposed here, as 289 likely to be useful. These SHOULD be implemented. These would 290 benefit from being specified more completely, in line with the 291 suggestions in [RFC2774]. 293 An HTTP object is just one binary file; the ability to group objects 294 together is useful (and is done in bundles by the Bundle Protocol). 295 If we call a group of related objects sent from the same source to 296 the same destination a 'package' (a name chosen to avoid any 297 confusion with the Bundle Protocol specification), we can then define 298 simple headers to be sent before each object: 300 Package-ID: - provides a unique textual identifier for the package 302 Package-Item: n of m (e.g. 1 of 7) - order of this HTTP file in the 303 package 305 Package-MD5: - MD5 hash across all Content-MD5: headers added 306 together in order of Package-Item: precedence. 308 A way to request missing Package-Items (from the previous node or 309 from the source) is likely to be very useful. 311 Precedence: headers could set importance of objects - very-high, 312 high, normal low, very-low - to give simple quality of service and 313 prioritization. 315 Some sort of header protection may be a good idea; Content-MD5: 316 covers the message body (entity-body), but not the headers. Header- 317 MD5: could cover some important HTTP headers. Header-MD5 could be 318 preserved across hops if possible, avoiding unnecessary header 319 reordering. Changing timestamps would invalidate the Header-MD5: 320 end-to-end, however - this needs more thought, particularly on where 321 timestamps are placed in HTTP headers. 323 For larger files, stronger mechanisms than MD5 should be examined. 325 There may be a need to send HTTP-DTN transfers across paths that 326 include hops with unidirectional one-way links with no return path, 327 e.g. when a wireless sender knows that a receiver is available, but 328 cannot hear it. Using: Connection: cannot-hear-response could be 329 used across that hop to indicate that the sender cannot hear 330 receivers. 332 Timestamps and how they are handled needs to be examined here in 333 greater detail. HTTP has the same basic assumption as the Bundle 334 Protocol - that all nodes are expected to know the current UTC time. 336 4. Other suggestions on using MIME in DTN networks 338 x-application-dtn has previously been proposed as a MIMEtype 339 identifying Bundle Protocol bundles delivered by HTTP. This provides 340 a way to support Bundle Protocol implementations in an HTTP 341 infrastructure. 343 Moving HTTP transfers over DTN networks using the Bundle Protocol has 344 already been proposed [Ott06]. By changing how HTTP is used - hop- 345 by-hop rather than end-to-end - HTTP can be used directly in DTN 346 networks without using the Bundle Protocol at all. 348 HTTP is a popular way to carry MIME, but support for MIME exists in 349 other protocols, including email, SIP and BEEP. BEEP can be thought 350 of as a more formalised and exactly-specified replacement for HTTP 351 for machine-machine interaction - and this detailed formal 352 specification makes BEEP complex [RFC3080]. BEEP provides an 353 alternative to HTTP to support XML-RPC and SOAP. BEEP's 354 specification is formally intended to support multiple different 355 transports, but only TCP transport of BEEP has been agreed [RFC3081]. 356 HTTP's simplicity of use and popularity appear to be compelling 357 advantages over BEEP. 359 5. Security Considerations 361 Better-Than-Nothing Security [RFC5386][RFC5387] is likely to be 362 useful here for ad-hoc communications without the availability of an 363 existing authentication infrastructure. 365 Security considerations and detailed examination of HTTP over TLS 366 (HTTPS) [RFC2817][RFC2818] and secure HTTP [RFC2660] are required 367 here. 369 Many existing security mechanism for HTTP could be used unchanged for 370 HTTP-DTN, if local conditions permit and the supporting 371 infrastructure, e.g. DNS, is available. However, reusing these 372 directly protects a single-hop transfer between peer nodes. To 373 protect an end-to-end transfer, the security mechanisms would need to 374 be applied using the information used in the Content-Source: and 375 Content-Destination: headers, before applying the local security 376 mechanism for the first peer-peer HTTP transfer. 378 6. IANA Considerations 380 Despite the Content-* rule for rejecting unfamiliar headers that 381 separates HTTP-DTN peers from traditional HTTP servers, it may be 382 desirable to use a non-standard port for DTN HTTP use over IP, rather 383 than the well-known port 80. If so, such a port should be requested 384 from IANA. 386 It may be necessary to request a dedicated IPv4 all-hosts multicast 387 address and a dedicated IPv6 link-local multicast addresses for local 388 HTTP DTN use, if local HTTP multicast is considered a desirable 389 feature. 391 7. Acknowledgements 393 We thank Wes Eddy and Kevin Fall for their review comments. 395 Work on the Saratoga protocol inspired some of the concepts that are 396 reused here, and we thank everyone involved in Saratoga's development 397 and implementation. 399 8. References 401 8.1. Normative References 403 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 404 Requirement Levels", BCP 14, RFC 2119, March 1997. 406 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 407 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 408 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 410 [RFC2774] Nielsen, H., Leach, P., and S. Lawrence, "An HTTP 411 Extension Framework", RFC 2774, February 2000. 413 8.2. Informative References 415 [Deering98] 416 Deering, S., "Watching the Waist of the Protocol 417 Hourglass", keynote, IEEE International Conference on 418 Network Protocols (ICNP), Austin Texas, October 1998. 420 [I-D.draft-cai-ssdp-v1] 421 Goland, Y., Cai, T., Leach, P., Gu, Y., and S. Albright, 422 "Simple Service Discovery Protocol/1.0 Operating without 423 an Arbiter", draft-cai-ssdp-v1-03 (expired) , October 424 1999. 426 [I-D.draft-goland-http-udp] 427 Goland, Y., "Multicast and Unicast UDP HTTP Messages", 428 draft-goland-http-udp-01 (expired) , November 1999. 430 [I-D.irtf-dtnrg-bundle-checksum] 431 Eddy, W., Wood, L., and W. Ivancic, "Reliability-only 432 Ciphersuites for the Bundle Protocol", draft-irtf-dtnrg- 433 bundle-checksum-09 (work in progress), May 2011. 435 [I-D.natarajan-http-over-sctp] 436 Natarajan, P., Amer, P., Leighton, J., and F. Baker, 437 "Using SCTP as a Transport Layer Protocol for HTTP", 438 draft-natarajan-http-over-sctp-02 (work in progress), July 439 2009. 441 [I-D.wood-tae-specifying-uri-transports] 442 Wood, L., "Specifying transport mechanisms in Uniform 443 Resource Identifiers", draft-wood-tae-specifying-uri- 444 transports-08 (work in progress), May 2010. 446 [I-D.wood-tsvwg-saratoga] 447 Wood, L., Eddy, W., Smith, C., Ivancic, W., and C. 448 Jackson, "Saratoga: A Scalable Data Transfer Protocol", 449 draft-wood-tsvwg-saratoga-15 (work in progress), April 450 2014. 452 [Ott06] Ott, J. and D. Kutscher, "Bundling the Web: HTTP over 453 DTN", WNEPT 2006 Workshop on Networking in Public 454 Transport, QShine Conference, Ontario, August 2006. 456 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 457 Extensions (MIME) Part One: Format of Internet Message 458 Bodies", RFC 2045, November 1996. 460 [RFC2660] Rescorla, E. and A. Schiffman, "The Secure HyperText 461 Transfer Protocol", RFC 2660, August 1999. 463 [RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within HTTP/ 464 1.1", RFC 2817, May 2000. 466 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 468 [RFC3080] Rose, M., "The Blocks Extensible Exchange Protocol Core", 469 RFC 3080, March 2001. 471 [RFC3081] Rose, M., "Mapping the BEEP Core onto TCP", RFC 3081, 472 March 2001. 474 [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, 475 R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant 476 Networking Architecture", RFC 4838, April 2007. 478 [RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol 479 Specification", RFC 5050, November 2007. 481 [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing 482 Security: An Unauthenticated Mode of IPsec", RFC 5386, 483 November 2008. 485 [RFC5387] Touch, J., Black, D., and Y. Wang, "Problem and 486 Applicability Statement for Better-Than-Nothing Security 487 (BTNS)", RFC 5387, November 2008. 489 [RFC6266] Reschke, J., "Use of the Content-Disposition Header Field 490 in the Hypertext Transfer Protocol (HTTP)", RFC 6266, June 491 2011. 493 [Wood09a] Wood, L., Eddy, W., and P. Holliday, "A Bundle of 494 Problems", IEEE Aerospace Conference, Big Sky, Montana, 495 March 2009. 497 [Wood09b] Wood, L., Holliday, P., Floreani, D., and I. Psaras, 498 "Moving data in DTNs with HTTP and MIME: Making use of 499 HTTP for delay- and disruption-tolerant networks with 500 convergence layers", Workshop on the Emergence of Delay 501 -/Disruption-Tolerant Networks (e-DTN 2009), St 502 Petersburg, Russia, October 2009. 504 Authors' Addresses 506 Lloyd Wood 507 University of Surrey alumni 508 Sydney, New South Wales 509 Australia 511 Email: L.Wood@society.surrey.ac.uk 513 Peter Holliday 514 Professional Services and Engineering 515 Brisbane, Queensland 516 Australia 518 Email: peter@ps-e.com.au