Internet-Draft ALTO/H2 October 2022
Schott, et al. Expires 24 April 2023 [Page]
Workgroup:
ALTO Working Group
Internet-Draft:
draft-ietf-alto-new-transport-02
Published:
Intended Status:
Standards Track
Expires:
Authors:
R. Schott
Deutsche Telekom
Y. Yang
Yale University
K. Gao
Sichuan University
J. Zhang
Tongji University

ALTO New Transport: ALTO Transport Information Structures

Abstract

The ALTO base protocol [RFC7285] defines both the ALTO information resources and their transport from the server to the client. Using HTTP/1.x as the transport protocol, the ALTO transport in the base protocol includes the limitations of HTTP/1.x. ALTO/SSE [RFC8895] defines a new transport design addressing some of the limitations, but is still based on HTTP/1.x. This document introduces ALTO new transport, which introduces ALTO transport information structures (TIS) at an ALTO server. The introduction of ALTO TIS allows at least two types of efficient transport using HTTP: (1) HTTP/2/3 independent client (long) poll allowed by non-blocking, newer HTTP, and (2) HTTP/2 specific server push. This document defines ALTO TIS and the first design. A companion document defines server-push ALTO transport based on ALTO TIS.

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 https://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 24 April 2023.

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Table of Contents

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, the base protocol cannot support well the use cases where an ALTO client may need to efficiently monitor the changes to a set of network information resources. If the client opens a single HTTP connection, the request for one resource may block the request for the next resource.

To address the issue using a protocol that is still based on the HTTP/1.1 transport 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. For example, it requires that the server provide a separate control URI, leading to complexity in management; it needs its own envelop protocol on top of HTTP encoding to indicate message types.


 ------------------------------------------------------------------
|                                                                  |
|          +-------+         +-------+ 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 New Transport, which realizes ALTO/SSE functions but takes advantage of newer versions of HTTP (e.g., HTTP/2 [RFC7540]) that support concurrent, non-blocking transport of multiple streams in the same HTTP connection.

2. ALTO New Transport Design Requirements

ALTO New Transport is designed to satisfy a set of requirements. First, it should satisfy the following requirements to realize the functions of ALTO/SSE:

Following the ALTO framework [RFC7285] [RFC7971], ALTO New Transport should still be HTTP based:

ALTO New Transport should be designed to take advantage of newer HTTP design features, in particular, parallel transfers, but be as transparent to versions (HTTP/2, HTTP/3) as possible. If a design is based on a particular HTTP version, it should respect its semantics:

To allow flexible deployment, the new transport protocol should be flexible, in particular,

3. ALTO New Transport Design Overview

A key design of ALTO New Transport is to distinguish between information about ALTO resources and information about ALTO transport. The latter information is called transport management information, which provides meta information about the transport of ALTO information resources:

Figure 2 shows an example illustrating the aforementioned information. Each ALTO client (Client 1, Client 2, or Client 3) maintains a single HTTP/2 connection with the ALTO server.


Information Resource:

a) Static resource (#1) such as NetworkMap
b) Filterable resource (#3) such as FilteredCostMap


                              +-------------+
                              |             |
         +--------------------| ALTO Server |-----------+
         |                  +-|             |-+         |
         |                  | +-------------+ |         |
         |                  |                 |         |
---------|------------------|-----------------|---------|------------
         |                  |                 |         | Information
         |                  |                 |         | Resource
+-------------+   +-------------+   +-------------+   +-------------+
| Information |   | Information |   | Information |   | Information |
| Resource #1 |   | Resource #2 |   | Resource #3 |   | Resource #4 |
+-------------+   +-------------+   +-------------+   +-------------+
       |                              /    \
-------|-----------------------------/------\------------------------
       |                            /        \            Transport
       |                      +----/          \------+    Queues
       |                      |                      |
  +--------+             +--------+             +--------+
  |   tq1  |-----+       |   tq2  |-----+       |   tq3  |-----+
  +----|---+     |       +----|---+     |       +----|---+     |
       |         |            |         |            |         |
  +----|---+ +---|----+  +----|---+ +---|----+  +----|---+ +---|----+
  | tq1/uq | | tq1/rs |  | tq2/uq | | tq2/rs |  | tq3/uq | | tq3/rs |
  +--------+ +--------+  +--------+ +--------+  +--------+ +--------+
       |\       /\              |         /           |          |
-------|-\-----/--\-------------|--------/------------|----------|---
       |  \   /    +-------+    |       /             |          |
       |   +-/-----------+  \   |      /              |          |
       |    /             \  \  |     /   A           +          +
       |   /            +--\--\-|----/--+ single       \        /
       |  /             +---\--\|---/---+ http2/3       \      /
   +----------+             +----------+  connection   +----------+
   | Client 1 |             | Client 2 |               | Client 3 |
   +----------+             +------- --+               +----------+

tqi    = transport queue i
tqi/uq = incremental updates queue of transport queue i
tqi/rs = receiver set of transport queue i
Figure 2: ALTO New Transport Transport Management Information.

The basic work flow of a client connecting to an ALTO server is the following:



    Client opens a connection to the server
    Client opens/identifies a transport queue tq
      // pull mode
      Client requests transport queue status of tq
      Client requests an element in the incremental update queue

      // push mode
      Client becomes a receiver
      Client receives incremental push updates
    Client closes the transport queue tq
    Client closes the connection
Figure 3: ALTO New Transport Transport Management Information.

4. Transport Information: Transport Queue

4.1. Transport Queue Operations

A transport queue supports three basic operations (CRD): create, read (get status), and delete.

Create a transport queue: An ALTO client creates a transport queue using the HTTP POST method with ALTO SSE AddUpdateReq ([RFC 8895] Sec. 6.5) as the parameter:


    object {
        ResourceID   resource-id;
        [JSONString  tag;]
        [Boolean     incremental-changes;]
        [Object      input;]
     } AddUpdateReq;

A successful POST request MUST return the URI for the transport queue. Unless the request has incremental-changes to be false, the client is added to receiver set as well, indicating that the client will receive automatic, incremental push updates.

Read a transport queue: A client reads the status of a transport queue by issuing a GET request to the transport queue URI returned from the POST method.

Delete a transport queue: a transport queue exposed to a client can be closed (deleted) either explicitly or implicitly.

  • Explicit delete: A client uses the HTTP DELETE method to explicitly delete a transport queue. If successful, the transport queue is deleted from the local view of the client, although the server may still maintain the transport queue for other client connections.
  • Implicit delete: Transport queue for a client is ephemeral: the close of the HTTP connection between the client and the server deletes the transport queue from the client's view --- when the client reconnects, the client MUST NOT assume that the transport queue is still valid.

Error codes: ALTO New Transport uses HTTP error codes.

4.2. Examples

The first example is a client creating a transport queue.

   Client -> server request

   HEADERS
     - END_STREAM
     + END_HEADERS
       :method = POST
       :scheme = https
       :path = /tqs
       host = alto.example.com
       accept = application/alto-error+json,
                    application/alto-transport+json
       content-type = application/alto-transport+json
       content-length = TBD

   DATA
    - END_STREAM
    {
       "resource-id": "my-routingcost-map"
    }



   Server -> client response:

   HEADERS
     - END_STREAM
     + END_HEADERS
       :status = 200
       content-type = application/alto-transport+json
       content-length = TBD

   DATA
     - END_STREAM
      {"tq": “/tqs/2718281828459”}

The client can then read the status of the transport queue using the read operation (GET) in the same HTTP connection. Below is an example (structure of incremental updates queue will be specified in the next section):

   Client -> server request

   HEADERS
     - END_STREAM
     + END_HEADERS
       :method = GET
       :scheme = https
       :path = /tqs/2718281828459
       host = alto.example.com
       accept = application/alto-error+json,
                    application/alto-transport+json

   Server -> client response:

   HEADERS
     - END_STREAM
     + END_HEADERS
       :status = 200
       content-type = application/alto-transport+json
       content-length = TBD

   DATA
     - END_STREAM
    { "uq":
       [
         {“seq”:        101,
          "media-type": "application/alto-costmap+json",
          “tag”:        "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe" },
         {“seq”:        102,
          "media-type": "application/merge-patch+json",
          “tag”:        "cdf0222x59740b0b2e3f8eb1d4785acd42231bfe" },
         {“seq”:        103,
          "media-type": "application/merge-patch+json",
          “tag”:        "8eb1d4785acd42231bfecdf0222x59740b0b2e3f",
          "link":       "/tqs/2718281828459/snapshot/2e3f"}

       ],
     "rs": ["self"]
    }

5. Transport Information: Incremental Updates Queue

5.1. Incremental Updates Queue Operations

Among the CRUD operations, an incremental updates queue supports only the read operation: a client cannot create, update, or delete incremental updates queue directly---it is read only, and associated with transport queue automatically.

Reads an incremental updates queue: A client reads the status of an incremental updates queue using the HTTP GET method: GET transport-queue-uri/uq, where the transport-queue-uri is the URI returned in the transport queue create method.

The response informs the client the backlog status, and potential direct links. Specifically, the response is a JSON array, with each element being one incremental update, with three required fields and one optional field:

  • "seq": a required JSON integer indicating the sequence number of the incremental update; As JSON allows a large integer space, when the server reaches the largest integer, the server SHOULD close the incremental update queue;
  • "media-type", a required JSON string giving the type of the incremental update (see ALTO/SSE);
  • "tag": a required JSON string giving a unique tag (see [RFC7285];
  • "link": an optional JSON string giving an optional link for a client to directly request a resource as a complete snapshot (not through incremental updates).

Note that the server determines the state (window of history and type of each update) in the incremental updates queue, as specified by [R4].

5.2. Examples

Assume the same example in the preceding section. The client can check the status of the incremental updates queue of a transport queue from the same connection:

   Client -> server request:

   HEADERS
     - END_STREAM
     + END_HEADERS
       :method = GET
       :scheme = https
       :path = /tqs/2718281828459/uq
       host = alto.example.com
       accept = application/alto-error+json,
                    application/alto-transport+json

   Server -> client response:

   HEADERS
     - END_STREAM
     + END_HEADERS
       :status = 200
       content-type = application/alto-transport+json
       content-length = TBD

   DATA
     - END_STREAM
    {
       [
         {“seq”:        101,
          "media-type": "application/alto-costmap+json",
          “tag”:        "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe" },
         {“seq”:        102,
          "media-type": "application/merge-patch+json",
          “tag”:        "cdf0222x59740b0b2e3f8eb1d4785acd42231bfe" },
         {“seq”:        103,
          "media-type": "application/merge-patch+json",
          “tag”:        "8eb1d4785acd42231bfecdf0222x59740b0b2e3f",
          "link":       "/tqs/2718281828459/snapshot/2e3f"}

       ],

    }

6. Information Resource Information: Client Pull Individual Updates

6.1. Individual Updates Operations

A client can only read an individual update: A client uses HTTP GET method on the incremental updates queue concatenated by a sequence number to pull an individual update.The server push model, however, depends on HTTP specific version. The companion document specifies server push for HTTP/2.

6.2. Examples

The first example is a client pull example, in which the client directly requests an individual update.

   Client -> server request:

   HEADERS
     + END_STREAM
     + END_HEADERS
       :method = GET
       :scheme = https
       :path = /tqs/2718281828459/uq/101
       host = alto.example.com
       accept = application/alto-error+json,
                    application/alto-costmap+json

   Server -> client response:

   HEADERS
     - END_STREAM
     + END_HEADERS
       :status = 200
       content-type = application/alto-costmap+json
       content-length = TBD

   DATA
     + END_STREAM
    {
      "meta" : {
         "dependent-vtags" : [{
            "resource-id": "my-network-map",
            "tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785"
          }],
         "cost-type" : {
           "cost-mode"  : "numerical",
           "cost-metric": "routingcost"
         },
         "vtag": {
           "resource-id" : "my-routingcost-map",
           "tag" : "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
         }
      },
      "cost-map" : {
        "PID1": { "PID1": 1,  "PID2": 5,  "PID3": 10 },
        "PID2": { "PID1": 5,  "PID2": 1,  "PID3": 15 },
        "PID3": { "PID1": 20, "PID2": 15  }
      }
   }

Note from the transport queue state that the 103 message has an OPTIONAL link to a complete snapshot, which a client can request.

One important design is that the "seq" must be sequentially increasing. Hence, by issuing a request on the next sequence number, the client realizes long poll.

7. ALTO New Transport Stream Management

7.1. Objectives

A main benefit of ALTO New Transport is to take advantage of concurrent streams in newer versions of HTTP (HTTP/2 and later). In particular, the objectives of ALTO New Transport include:

  • Allow stream concurrency to reduce latency
  • Minimize the number of streams created
  • Enforce dependency among streams (so that if A depends on B, then A should be sent after B)
  • Encode dependency to enforce semantics (correctness)

To realize the objectives, ALTO New Transport MUST satisfy the following stream management requirements in all 4 phases specified in the next 4 subsections.

7.2. Client -> Server [Create Transport Queue]

Each request to create a transport queue (POST) MUST choose a new client selected stream ID (SID_tq), with the following requirements:

  • Stream Identifier of the frame is a new client-selected stream ID; Stream Dependency in HEADERS is 0 (connection) for an independent resource, the other transport queue if the dependency is known.
  • Invariant: Stream keeps open until close or error.

7.3. Client -> Server [Close Transport Queue]

DELETE to close a transport queue (SID_tq) MUST be sent in SID_tq, with the following requirements:

  • Stream Identifier of the frame is SID_tq, and Stream Dependency in HEADER is 0 (connection), so that a client cannot close a different stream.
  • HEADERS indicates END_STREAM; server response SHOULD close the stream.

7.4. Client -> Server [Request on Data of a Transport Queue on Stream SID_tq]

The request and response MUST satisfy the following requirements:

  • The Stream Identifier of the frame is a new client-selected stream ID, and Stream Dependency in HEADERs MUST be SID_tq, so that a client cannot issue request on a closed transport queue;
  • Both the request and the response MUST indicate END_STREAM.

7.5. Concurrency Management

  • ALTO New Transport must allow concurrency control.
  • From the client to the server direction, there MUST be one stream for each open transport queue, and hence a client can always close a transport queue (which it uses to open the stream) and hence can also close, without the risk of deadlock.

8. ALTO New Transport Information Resource Directory (IRD)

Extending the IRD example in Section 8.1 of [RFC8895], below is the IRD of an ALTO server supporting ALTO base protocol, ALTO/SSE, and ALTO New Transport.

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",
    "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",
        "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-transport+json",
    "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
    }
  }

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 New Transport based connection, and this is indicated by the media-type "application/alto-transport+json". For an ALTO New Transport 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.

9. Security Considerations

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

10. IANA Considerations

IANA will need to register the application/alto-transport+json media type under ALTO registry as defined in [RFC7285].

11. Acknowledgments

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

12. References

12.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <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, , <https://www.rfc-editor.org/info/rfc7285>.
[RFC7540]
Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8895>.

12.2. 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, , <https://www.rfc-editor.org/info/rfc7971>.

Appendix A. Outlook to ALTO with HTTP/3

This draft is focusing on HTTP/2 enhancement of the ALTO protocol and the design takes advantage of HTTP/2 design features such as parallel transfer and respects HTTP/2 semantics (e.g., PUSH_PROMISE). Since QUIC and HTTP/3 respectively are coming up for various protocols on the Internet it is understandable that the question arises, if ATLO could also take advantage of the advantages of HTTP/3. QUIC can be seen as a replacement for TCP+TLS+HTTP2. HTTP/3 bases on the QUIC transport protocol and uses UDP instead of a TCP connection.

QUIC has been developed by the IETF QUIC Working Group with the following goals:

If HTTP/3 is not supported, it automatically runs on HTTP/2. The prerequisite for HTTP/3 is that both client and server support it.

The basic assumption is that an implementation that runs on HTTP/2 should also run-on HTTP/3. This should be transparent. HTTP/3 uses "well known port" UDP 443 analogous to TCP 443. The network between client and server must not filter HTTP/3.

Since many applications still using HTTP/2 it is mandatory for ALTO to support this protocol first. This ensures compatibility. Therefore, this document describes the update of ALTO from HTTP/1.x to HTTP/2. The usage of HTTP/3 will be described in a separate document so that compatibility of ALTO with HTTP/3 will be ensured in a later stage.

Authors' Addresses

Roland Schott
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
64295 Darmstadt
Germany
Y. Richard Yang
Yale University
51 Prospect St
New Haven, CT 06520
United States of America
Kai Gao
Sichuan University
Chengdu
201804
China
Jingxuan Jensen Zhang
Tongji University
4800 Cao'An Hwy
Shanghai
201804
China