ALTO Working Group Y. Yang
Internet-Draft Yale University
Intended status: Standards Track October 24, 2021
Expires: April 27, 2022
ALTO Transport using HTTP/2
draft-yang-alto-http2-transport-01
Abstract
The ALTO base protocol [RFC7285] uses HTTP/1.x as the transport
protocol and hence ALTO transport includes the limitations of
HTTP/1.x. ALTO/SSE [RFC8895] addresses some of the limitations, but
is still based on HTTP/1.x. This document introduces ALTO/H2, which
provides the transport of ALTO information resources on top of
HTTP/2.
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
working documents as Internet-Drafts. The list of current Internet-
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 April 27, 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
Yang Expires April 27, 2022 [Page 1]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. ALTO/H2 Design Requirements . . . . . . . . . . . . . . . . . 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. Figure 1
shows the architecture and message flow of ALTO/SSE, which can be
considered as a more general transport protocol than the ALTO base
transport protocol. Although ALTO/SSE allows the concurrent
transport of multiple ALTO information resources, it has complexities
and limitations: (1) it requires that the server provide a separate
control URI, leading to complexity in management; (2) the data
Yang Expires April 27, 2022 [Page 2]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
connection still suffers HTTP/1.x problems such as head-of-line (HOL)
blocking.
------------------------------------------------------------------
| |
| +-------+ +-------+ 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.
This document specifies ALTO/H2, based on HTTP/2 [RFC7540]. 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 multiple TCP
connections (a control connection and a data connection) 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 connection,
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 Requirements
To realize the functions of ALTO/SSE, there are the following
requirements:
Yang Expires April 27, 2022 [Page 3]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
o R0: Client can request any resource using the connection, just as
using ALTO base protocol using HTTP/1.x.
o R1: The client can signal the addition (start) of incremental
updates to a resource.
o R2: The client can signal the deletion (stop) of incremental
updates to a resource.
o R3: The server can signal to the client the start or stop of
incremental updates to a resource.
o R4: The server can choose the type of each incremental update
endcoding, as long as the type is indicated to be acceptable by
the client.
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",
"media-type": "application/alto-costmap+json",
"accepts": "application/alto-costmapfilter+json",
Yang Expires April 27, 2022 [Page 4]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
"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": {
"my-network-map": "application/json-patch+json",
"my-routingcost-map": "application/merge-patch+json",
Yang Expires April 27, 2022 [Page 5]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
"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"
},
"support-stream-control": true
}
Yang Expires April 27, 2022 [Page 6]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
}
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>.
[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>.
Yang Expires April 27, 2022 [Page 7]
Internet-Draft ALTO Transport Using HTTP/2 October 2021
[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
Yang Expires April 27, 2022 [Page 8]