WebSocket-based server-to-client notifications for the Application-Layer Traffic Optimization (ALTO) Protocol
draft-marocco-alto-ws-00

Internet Engineering Task Force                               E. Marocco
Internet-Draft                                            Telecom Italia
Intended status: Standards Track                              J. Seedorf
Expires: January 10, 2013                                            NEC
                                                            July 9, 2012

WebSocket-based server-to-client notifications for the Application-Layer
                  Traffic Optimization (ALTO) Protocol
                        draft-marocco-alto-ws-00

Abstract

   The Application-Layer Traffic Optimization (ALTO) protocol is
   designed to allow entities with knowledge about the network
   infrastructure to export such information to applications that need
   to choose one or more endpoints to connect to among large sets of
   logically equivalent ones.  The base protocol specification adopts a
   simple pull-based model, according to which the client retrieves the
   information encoded as JSON objects over HTTP directly from the
   server.

   This document proposes (for discussion) a mechanism for providing
   server-initiated information update notifications through a
   WebSocket-based ALTO protocol extension that easily integrates in the
   basic protocol model.

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
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   This Internet-Draft will expire on January 10, 2013.

Copyright Notice

   Copyright (c) 2012 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
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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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 4
   2.  Overview of operations  . . . . . . . . . . . . . . . . . . . . 4
   3.  Information Resource Directory (IRD) Extensions . . . . . . . . 5
     3.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Client-to-server Version Indication . . . . . . . . . . . . . . 6
   5.  Partial Updates Encoding  . . . . . . . . . . . . . . . . . . . 7
   6.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   The Application-Layer Traffic Optimization (ALTO) protocol
   [I-D.ietf-alto-protocol] is designed to allow entities with knowledge
   about the network infrastructure to export such information to
   applications that need to choose one or more endpoints to connect to
   among large sets of logically equivalent ones.  The base protocol
   specification adopts a simple pull-based model, according to which
   the client retrieves the information encoded as JSON objects over
   HTTP directly from the server.

   Such a pull-based model is well suited for use cases where the
   information does not change frequently, e.g. when it represents
   network and cost maps intended to provide a hint to peer-to-peer
   applications that have to perform initial peer selection (i.e. the
   primary use case that motivated the specification of the ALTO
   protocol).  However, over the years several similar use cases have
   emerged, but most of them with more stringent requirements in terms
   of information freshness.  Those use cases could also simply and
   effectively be addressed by the ALTO protocol, provided it features a
   mechanism for clients to receive server-initiated information update
   notifications.  This document proposes (for discussion) a mechanism
   for providing such notifications through a WebSocket-based [RFC6455]
   extension that easily integrates in the basic ALTO protocol model.

   The WebSocket protocol is only one option such extension could be
   based on.  Many altenatives can of course be considered, based on
   virtually any bi-directional protocol that provides some sort of
   publish/subscribe framework.  Among others, XMPP, BGP and SNMP have
   been proposed and to some extent discussed in different contexts as a
   basis for providing similar features.  The strenght points of the
   WebSocket protocol in this context -- and thus the reason why the
   extension proposed here is based on it -- include:

   o  WebSocket is explicitly intended to provide bi-directionality to
      HTTP, the transport the ALTO protocol is based on.  Main
      implication of this consists with the fact that both HTTP client
      and server libraries/frameworks ALTO implementations are likely
      based on natively support it (or, since the technology is very
      new, soon will);

   o  a resource representing an update notification service related to
      a particular resource instance made available by an ALTO server
      can simply be identified by a WebSocket URI and advertized in the
      Information Resource Directory (IRD) just as any other regular
      resource;

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   o  a resource representing an update notification service can be
      unambiguously defined through a MIME type, just as any other
      regular resource;

   o  reuse of HTTP authentication.

   o  [TODO: Is Origin-based security of any use here?]

   The most appropriate way for encoding partial updates of ALTO
   information is an open issue itself, at the time of writing,
   discussed in [I-D.schwan-alto-incr-updates].

1.1.  Requirements Language

   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].

2.  Overview of operations

   When an ALTO client wants to retrieve a particular piece of
   information made available by an ALTO server and then receive
   notifications about each subsequent change, it achieves that in the
   following steps:

   1.  retrieve the IRD of the ALTO service it is going to access;

   2.  find in the IRD the URI of the resource it is interested in,
       identifying it through the associated content type (e.g.
       application/alto-networkmap+json);

   3.  retrieve a copy of the resource it is interested in;

   4.  find in the IRD the WebSocket URI of the update notification
       service associated to the specific resource just retrieved;

   5.  establish a WebSocket connection against the URI of the update
       notification service;

   6.  indicate the version tag of the retrieved resource to the server;

   7.  process each subsequent updates received on the WebSocket
       connection in order to keep the local representation of the
       recource up-to-date.

   Steps 1 to 3 are regular ALTO operations, as defined in
   [I-D.ietf-alto-protocol].  The following section will discuss (and at

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   some point hopefully define) the missing pieces of specification
   needed for performing the remaining steps, namely:

   1.  a mechanism for identifying the WebSocket URI of the update
       notification service associated to a particular resource;

   2.  a mechanism for the client to tell the server the version of the
       resource stored locally;

   3.  a mechanism for encoding information updates.

   The mechanism discussed here is intended to allow steps from 4 to 7
   to be executed at an arbitrarily later stage in respect to steps 1-3
   (i.e. the mechanism needs to be able to update arbitrarily stale
   resource representations).

3.  Information Resource Directory (IRD) Extensions

   [NOTE: strawman proposal.]

   This document specifies the additional optional "updates" property
   for top-level IRD entries.  The new property is specifically defined
   as:

   updates  A WebSocket URI as defined in [RFC6455] at which the ALTO
      server provides dynamic updates of the corrensponding resource.

3.1.  Example

   The following is an example Information Resource Directory returned
   by an ALTO Server.  In this example, the ALTO Server provides both a
   network map and a cost map with corrensponding update notification
   services.

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      {
        "resources" : [
          .
          .
          .
          {
            "uri" : "http://alto.example.com/networkmap",
            "media-types" : [ "application/alto-networkmap+json" ],
            "updates" : "ws://alto.example.com/networkmap"
          }, {
            "uri" : "http://alto.example.com/costmap/num/routingcost",
            "media-types" : [ "application/alto-costmap+json" ],
            "capabilities" : {
              "cost-modes" : [ "numerical" ],
              "cost-types" : [ "routingcost" ]
            },
            "updates" : "ws://alto.example.com/costmap/num/routingcost"
          }
        ]
      }

4.  Client-to-server Version Indication

   As discussed in [I-D.schwan-alto-incr-updates], indication of the
   version of the locally stored resource can happen in two ways:

   o  after the WebSocket connection has been established, with an ad-
      hoc client-to-server signalling message such as:

         {"reference-tag": "1266506140"}

      The main drawback of such an approach consists with the added
      complexity both on the client side and on the server side (e.g.
      for handling error conditions, race conditions, etc.);

   o  in the WebSocket connection initiating GET request, by means of a
      HTTP header fields such as If-Modified-Since or If-None-Match.
      The advantage of such an approach consists with the fact that the
      data on the WebSocket connection flows on the server-to-client
      direction only, adding no additional complexity to a client
      already able to process partial updates.  The drawback consists
      with the fact that none of the existing HTTP headers seem to have
      the exact required semantic.

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5.  Partial Updates Encoding

   Possible encoding options for partial updates are discussed in
   [I-D.schwan-alto-incr-updates], for the case of client-initiated
   transactions.  The very same considerations also apply to the case of
   server-initiated notifications.  It seems therefore straightforward
   to assume that the same encoding will be adopted here.

6.  Example

   [TODO: Illustrate a full example, from the IRD, the retrievial of the
   resource and the establishment of the WS connection.]

7.  Security Considerations

   [TODO: A lot to be said here.]

8.  References

8.1.  Normative References

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-11 (work in progress),
              March 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, December 2011.

8.2.  Informative References

   [I-D.schwan-alto-incr-updates]
              Schwan, N. and B. Roome, "ALTO Incremental Updates",
              draft-schwan-alto-incr-updates-01 (work in progress),
              March 2012.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

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Authors' Addresses

   Enrico Marocco
   Telecom Italia
   Via Reiss Romoli, 274
   Torino,   10148
   Italy

   Phone:
   Email: enrico.marocco@telecomitalia.it

   Jan Seedorf
   NEC Laboratories Europe, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg,   69115
   Germany

   Phone: +49 (0) 6221 4342 221
   Email: jan.seedorf@nw.neclab.eu
   URI:   http://www.nw.neclab.eu

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