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Versions: 00                                                            
ALTO Working Group                                               Y. Yang
Internet-Draft                                           Yale University
Intended status: Standards Track                           July 12, 2021
Expires: January 13, 2022


                      ALTO Transport using HTTP/2
                   draft-yang-alto-http2-transport-00

Abstract

   The ALTO base protocol and ALTO/SSE are based on HTTP/1.x, and they
   introduce complexities to address limitations of HTTP/1.x.  The
   deployment of HTTP/2 allows this document to design ALTO/H2, which
   benefits from the additional capabilities of HTTP/2 to provide
   services for ALTO.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 13, 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  ALTO/H2 Design Overview . . . . . . . . . . . . . . . . . . .   3
   3.  ALTO/H2 Information Resource Directory (IRD)  . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  ALTO based on HTTP/3 Considerations . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Application-Layer Traffic Optimization (ALTO) provides a means for
   network applications to obtain network status information.  The ALTO
   base protocol [RFC7285] is based on the sequential request and
   response model of HTTP/1.1 [RFC7230]; hence, in the base protocol, an
   ALTO client only can issue a sequence of requests on network
   information resources, and the ALTO server sends the information
   resources one-by-one, in the order of the request sequence.  To
   address the use cases where an ALTO client may need to efficiently
   monitor changes to a set of network information resources and the
   protocol is still based on the HTTP/1.1 model, the ALTO Working Group
   introduces ALTO/SSE (ALTO Incremental Update based on Server-Sent-
   Event) [RFC8895], so that an ALTO client can manage (i.e., add and
   remove) a set of requests maintained at an ALTO server, and the
   server can continuously, concurrently, and incrementally push updates
   whenever a monitored network information resource changes.  ALTO/SSE
   can be considered a more general protocol of the ALTO base protocol
   to transport network information.  Figure 1. shows the architecture
   and message flow of ALTO/SSE.







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    ------------------------------------------------------------------
   |                                                                  |
   |          +-------+         +-------+ 1. init request  +------+   |
   |          |       |         |       | <-------------   |      |   |
   |          |       |         |       | ------------->   |      |   |
   | 3.add/   |       |         |       | 1'. control uri  |      |   |
   | remove   |       |         |       |                  |      |   |
   | resource |Stream |         |Update |                  |      |   |
     -------->|Control| private |Stream | 2a. data update  |Client| --
              |Server |<------->|Server | messages         |      |
     -------- |       |         |       | -------------->  |      | <-
   | response |       |         |       | -------------->  |      |   |
   |          |       |         |       | 2b.control update|      |   |
   |          +-------+         +-------+ messages         +------+   |
   |                                                                  |
    ------------------------------------------------------------------


             Figure 1: ALTO SSE Architecture and Message Flow.

   With the wide deployment of newer HTTP (e.g., HTTP/2 [RFC7540]), this
   document specifies ALTO transport based on HTTP/2, referred to as
   ALTO/H2.  The newer transport can provide multiple benefits:

   o  ALTO based on HTTP/2 natively supports multiple concurrent
      requests pending at the server, realizing a main design goal of
      ALTO SSE.  At the same time, instead of using two TCP connections
      (a control channel and a data channel) as ALTO/SSE does, ALTO
      based on HTTP/2 can use a single TCP connection, achieving a
      design with only one connection.

   o  ALTO based on HTTP/2 can take advantage of the benefit provided by
      HTTP/2 to avoid head-of-line blocking in the data channel,
      reducing latency.

   o  ALTO based on HTTP/2 can take advantage of other benefits of
      HTTP/2, including potentially higher encoding efficiency and
      stronger enforcement of security (i.e., using https).

2.  ALTO/H2 Design Overview

   There are multiple design points.

   o  First, how to transport incremental update messages to a monitored
      resource (e.g., in a single HTTP/2 stream or each update uses a
      unique HTTP/2 stream)?  Since there is sequential dependency among
      the incremental updates to a single information resource, there is
      no concurrency gain in separating them into different streams.



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      Creating multiple streams, on the other hand, has overhead.
      Hence, ALTO/H2 uses a single HTTP/2 stream to carry the
      incremental updates to each monitored request.  An implication of
      the preceding design is that to allow flexibility, ALTO/SSE allows
      different types of incremental update encodings (e.g., merge patch
      vs JSON patch), and hence ALTO/H2 needs to solve the same problem:
      it needs a header layer above HTTP/2 to indicate the media type of
      each incremental update.

   o  Second, how to distinguish between an ALTO service that sends a
      one-shot response and one that sends incremental updates.  Instead
      of introducing ALTO/H2 to completely replace the ALTO base
      protocol [RFC7285] and ALTO/SSE [RFC8895], ALTO/H2 can run in
      parallel with them, to support incremental deployment.  A single
      ALTO server can provide multiple resources in its IRD, and an
      ALTO/H2 resource is indicated in the ALTO IRD, consistent with
      ALTO base protocol and ALTO/SSE.

3.  ALTO/H2 Information Resource Directory (IRD)

   Extending the IRD example in Section 8.1 of [RFC8895], Figure 2 is
   the IRD of an ALTO server supporting ALTO base protocol, ALTO/SSE,
   and ALTO/H2.

   In particular,

     "my-network-map": {
       "uri": "https://alto.example.com/networkmap",
       "media-type": "application/alto-networkmap+json",
     },
     "my-routingcost-map": {
       "uri": "https://alto.example.com/costmap/routingcost",
       "media-type": "application/alto-costmap+json",
       "uses": ["my-networkmap"],
       "capabilities": {
         "cost-type-names": ["num-routingcost"]
       }
     },
     "my-hopcount-map": {
       "uri": "https://alto.example.com/costmap/hopcount",
       "media-type": "application/alto-costmap+json",
       "uses": ["my-networkmap"],
       "capabilities": {
         "cost-type-names": ["num-hopcount"]
       }
     },
     "my-filtered-cost-map": {
       "uri": "https://alto.example.com/costmap/filtered/constraints",



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       "media-type": "application/alto-costmap+json",
       "accepts": "application/alto-costmapfilter+json",
       "uses": ["my-networkmap"],
       "capabilities": {
         "cost-type-names": ["num-routingcost", "num-hopcount"],
         "cost-constraints": true
       }
     },
     "my-simple-filtered-cost-map": {
       "uri": "https://alto.example.com/costmap/filtered/simple",
       "media-type": "application/alto-costmap+json",
       "accepts": "application/alto-costmapfilter+json",
       "uses": ["my-networkmap"],
       "capabilities": {
         "cost-type-names": ["num-routingcost", "num-hopcount"],
         "cost-constraints": false
       }
     },
     "my-props": {
       "uri": "https://alto.example.com/properties",
       "media-type": "application/alto-endpointprops+json",
       "accepts": "application/alto-endpointpropparams+json",
       "capabilities": {
         "prop-types": ["priv:ietf-bandwidth"]
       }
     },
     "my-pv": {
       "uri": "https://alto.example.com/endpointcost/pv",
       "media-type": "multipart/related;
                      type=application/alto-endpointcost+json",
       "accepts": "application/alto-endpointcostparams+json",
       "capabilities": {
         "cost-type-names": [ "path-vector" ],
         "ane-properties": [ "maxresbw", "persistent-entities" ]
       }
     },
     "update-my-costs": {
       "uri": "https://alto.example.com/updates/costs",
       "media-type": "text/event-stream",
       "accepts": "application/alto-updatestreamparams+json",
       "uses": [
          "my-network-map",
          "my-routingcost-map",
          "my-hopcount-map",
          "my-simple-filtered-cost-map"
       ],
       "capabilities": {
         "incremental-change-media-types": {



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           "my-network-map": "application/json-patch+json",
           "my-routingcost-map": "application/merge-patch+json",
           "my-hopcount-map": "application/merge-patch+json"
         },
         "support-stream-control": true
       }
     },
       "update-my-costs-h2": {
       "uri": "https://alto.example.com/updates-h2/costs",
       "media-type": "application/alto-h2",
       "accepts": "application/alto-updatestreamparams+json",
       "uses": [
          "my-network-map",
          "my-routingcost-map",
          "my-hopcount-map",
          "my-simple-filtered-cost-map"
       ],
       "capabilities": {
         "incremental-change-media-types": {
           "my-network-map": "application/json-patch+json",
           "my-routingcost-map": "application/merge-patch+json",
           "my-hopcount-map": "application/merge-patch+json"
         },
         "support-stream-control": true
       }
     },

     "update-my-props": {
       "uri": "https://alto.example.com/updates/properties",
       "media-type": "text/event-stream",
       "uses": [ "my-props" ],
       "accepts": "application/alto-updatestreamparams+json",
       "capabilities": {
         "incremental-change-media-types": {
           "my-props": "application/merge-patch+json"
         },
         "support-stream-control": true
       }
     },
     "update-my-pv": {
       "uri": "https://alto.example.com/updates/pv",
       "media-type": "text/event-stream",
       "uses": [ "my-pv" ],
       "accepts": "application/alto-updatestreamparams+json",
       "capabilities": {
         "incremental-change-media-types": {
           "my-pv": "application/merge-patch+json"
         },



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         "support-stream-control": true
       }
     }

   Note that it is straightforward for an ALTO sever to run HTTP/2 and
   support concurrent retrieval of multiple resources such as "my-
   network-map" and "my-routingcost-map" using multiple HTTP/2 streams
   with the need to introducing ALTO/H2.

   The resource "update-my-costs-h2" provides an ALTO/H2 based
   connection, and this is indicated by the media-type "application/
   alto-h2".  For an ALTO/H2 connection, the client can send in a
   sequence of control requests using media type application/alto-
   updatestreamparams+json.  The server creates HTTP/2 streams and
   pushes updates to the client.

4.  Security Considerations

   The properties defined in this document present no security
   considerations beyond those in Section 15 of the base ALTO
   specification [RFC7285].

5.  ALTO based on HTTP/3 Considerations

   One consideration of the ALTO/H2 design is the pending deployment of
   HTTP3.

6.  IANA Considerations

   IANA will need to register the alto-h2 media type under ALTO registry
   as defined in [RFC7285].

7.  Acknowledgments

   The authors of this document would also like to thank many for the
   reviews and comments.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997, <https://www.rfc-editor.org/info/
              rfc2119>.






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   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing", RFC
              7230, DOI 10.17487/RFC7230, June 2014, <https://www.rfc-
              editor.org/info/rfc7230>.

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI
              10.17487/RFC7540, May 2015, <https://www.rfc-
              editor.org/info/rfc7540>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8895]  Roome, W. and Y. Yang, "Application-Layer Traffic
              Optimization (ALTO) Incremental Updates Using Server-Sent
              Events (SSE)", RFC 8895, DOI 10.17487/RFC8895, November
              2020, <https://www.rfc-editor.org/info/rfc8895>.

8.2.  Informative References

   [RFC7971]  Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
              S. Previdi, "Application-Layer Traffic Optimization (ALTO)
              Deployment Considerations", RFC 7971, DOI 10.17487/
              RFC7971, October 2016, <https://www.rfc-editor.org/info/
              rfc7971>.

Author's Address

   Y. Richard Yang
   Yale University
   51 Prospect St
   New Haven, CT  06520
   USA

   Email: yry@cs.yale.edu









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