ALTO/H2: The ALTO Protocol using HTTP/2
draft-ietf-alto-new-transport-01
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| Authors | Roland Schott , Y. Richard Yang , Kai Gao , Jingxuan Zhang | ||
| Last updated | 2022-07-11 | ||
| Replaces | draft-schott-alto-new-transport | ||
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draft-ietf-alto-new-transport-01
ALTO Working Group R. Schott
Internet-Draft Deutsche Telekom
Intended status: Standards Track Y. Yang
Expires: 12 January 2023 Yale University
K. Gao
Sichuan University
J. Zhang
Tongji University
11 July 2022
ALTO/H2: The ALTO Protocol using HTTP/2
draft-ietf-alto-new-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 new
transport, which provides the transport functions of ALTO/SSE on top
of HTTP/2, for more efficient ALTO transport.
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 12 January 2023.
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Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ALTO/H2 Design Requirements . . . . . . . . . . . . . . . . . 4
3. ALTO/H2 Design Overview . . . . . . . . . . . . . . . . . . . 4
4. Transport Queue . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Transport Queue Operations . . . . . . . . . . . . . . . 7
4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Incremental Updates Queue . . . . . . . . . . . . . . . . . . 10
5.1. Incremental Updates Queue Operations . . . . . . . . . . 11
5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Individual Updates . . . . . . . . . . . . . . . . . . . . . 12
6.1. Individual Updates Operations . . . . . . . . . . . . . . 12
6.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Receiver Set . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Receiver Set Operations . . . . . . . . . . . . . . . . . 16
7.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 17
8. ALTO/H2 Stream Management . . . . . . . . . . . . . . . . . . 17
8.1. Objectives . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Client -> Server [Create Transport Queue] . . . . . . . . 17
8.3. Client -> Server [Close Transport Queue] . . . . . . . . 18
8.4. Client -> Server [Request on Data of a Transport Queue on
Stream SID_tq] . . . . . . . . . . . . . . . . . . . . . 18
8.5. Server -> Client [PUSH_PROMISE for Transport Queue on
Stream SID_tq] . . . . . . . . . . . . . . . . . . . . . 18
8.6. Concurrency Management . . . . . . . . . . . . . . . . . 18
9. ALTO/H2 Information Resource Directory (IRD) . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
13.1. Normative References . . . . . . . . . . . . . . . . . . 22
13.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Outlook to ALTO with HTTP/3 . . . . . . . . . . . . 23
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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 can issue only 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. For example, it requires that the server provide a
separate control URI, leading to complexity in management.
------------------------------------------------------------------
| |
| +-------+ +-------+ 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.
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This document specifies ALTO/H2, which realizes ALTO/SSE but takes
advantage of new HTTP capabilities provided by HTTP/2 [RFC7540].
2. ALTO/H2 Design Requirements
ALTO/H2 is designed to satisfy a set of requirements. First, it
should satisfy the following requirements to realize the functions of
ALTO/SSE:
* R0: Client can request any resource using the connection, just as
using ALTO base protocol using HTTP/1.x.
* R1: The client can request the addition (start) of incremental
updates to a resource.
* R2: The client can request the deletion (stop) of incremental
updates to a resource.
* R3: The server can signal to the client the start or stop of
incremental updates to a resource.
* R4: The server can choose the type of each incremental update
encoding, as long as the type is indicated to be acceptable by the
client.
Following the ALTO framework [RFC7285] [RFC7971], ALTO/H2 should
still be HTTP based:
* R5: The design follows the basic principle of HTTP---
Representational State Transfer and hence can use only HTTP verbs
(GET, POST, PUT, DELETE, HEAD).
* R6: The design takes advantage of HTTP/2 design features such as
parallel transfers and respects HTTP/2 semantics such as the
semantics of PUSH_PROMISE.
To allow flexible deployment, the new transport protocol should be
flexible, in particular,
* R7: The design should support capability negotiation.
3. ALTO/H2 Design Overview
A key design of ALTO/H2 is to distinguish between information about
ALTO resources and information about ALTO transport. It introduces
the following transport information structures to distribute ALTO
information resources:
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* The transport state from the ALTO server to an ALTO client (or a
set of clients) for an ALTO information resource is conceptually
through a transport queue. A static ALTO information resource
(e.g., Cost Map, Network Map) has a single transport queue, and a
dynamic ALTO information resource (e.g., Filtered Cost Map) may
create a queue for each unique filter request.
* Each transport queue maintains two states: (1) the incremental
update message queue, which includes a sequence of incremental
update messages and (2) the receiver set, which includes the set
of receivers receiving incremental push updates from the ALTO
server.
* The transport queue state is exposed to clients through views;
that is, a client can see only a virtual view of the server state.
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.
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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 Information Structure.
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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 Information Structure.
4. 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.
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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/H2 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"
}
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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):
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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. Incremental Updates Queue
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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:
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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. Individual Updates
6.1. Individual Updates Operations
A client can only read an individual update. The read can be either
pull read issued by the client or a push from the server to the
client.
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Client pull read: A client uses HTTP GET method on the incremental
updates queue concatenated by a sequence number to pull an individual
update.
Server push read: a client starts to receive server push when it is
added to the receiver set. A client can add itself to the receiver
set when creating the transport queue, or add itself explicitly to
the receiver set (see the next section).
The work flow of server push of individual updates is the following:
* Initialization: the first update pushed from the server to the
client MUST be the later of the following two: (1) the last
independent update in the incremental updates queue; and (2) the
following entry of the entry that matches the tag when the client
creates the transport queue. The client MUST set
SETTINGS_ENABLE_PUSH to be consistent.
* Push state: the server MUST maintain the last entry pushed to the
client (and hence per client, per connection state) and schedule
next update push accordingly.
* Push management: The client MUST NOT cancel (RST_STREAM) a
PUSH_PROMISE to avoid complex server state management.
6.2. Examples
The first example is a client pull example, in which the client
directly requests an individual update.
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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.
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Instead of directly requesting, the client can wait for the server
for incremental push, where the server first sends PUSH_PROMISE with
the GET URI as above.
Server -> client PUSH_PROMISE in current stream:
PUSH_PROMISE
- END_STREAM
Promised Stream 4
HEADER BLOCK
:method = GET
:scheme = https
:path = /tqs/2718281828459/uq/101
host = alto.example.com
accept = application/alto-error+json,
application/alto-costmap+json
Server -> client content Stream 4:
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 }
}
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}
Server -> client PUSH_PROMISE in current stream:
PUSH_PROMISE
- END_STREAM
Promised Stream 6
HEADER BLOCK
:method = GET
:scheme = https
:path = /tqs/2718281828459/uq/102
host = alto.example.com
accept = application/alto-error+json,
application/merge-patch+json
Server -> client content Stream 6
HEADERS
+ END_STREAM
+ END_HEADERS
:status = 200
content-type = application/merge-patch+json
content-length = TBD
DATA
+ END_STREAM
{ ...}
7. Receiver Set
7.1. Receiver Set Operations
Among the CRUD operations, a client can add to or delete itself from
the receiver set of a transport queue. It can also read the status
of the receiver set.
Creat: A client can add itself in the receiver set by using the HTTP
PUT method: PUT transport-queue/rs/self
Read: A client can see only itself in the receiver set. The
appearance of self in the receiver set (read does not return "not
exists" error) is an indication that push starts.
Delete: A client can delete itself (stops receiving push) either
explicitly or implicitly.
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* Explicit delete: A client deletes itself using the HTTP DELETE
method: DELETE transport-queue/rs/self.
* Implicit delete: Transport queue is connection ephemeral: the
close of connection or stream for the transport queue deletes the
transport queue (from the view) for the client.
7.2. Examples
A client can stop incremental push updates from the server to itself
by sending the request:
DELETE /tqs/2718281828459/rs/self HTTP/2
Accept: application/alto-transport+json
HTTP/2 200 OK
8. ALTO/H2 Stream Management
8.1. Objectives
A main benefit of using HTTP/2 for ALTO is to take advantage of
HTTP/2 streams. In particular, the objectives of ALTO/H2 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/H2 MUST satisfy the following stream
management requirements in all 4 phases specified in the next 4
subsections.
8.2. 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.
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8.3. 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.
8.4. 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.
8.5. Server -> Client [PUSH_PROMISE for Transport Queue on Stream
SID_tq]
The server push MUST satisfy the following requirements:
* PUSH_PROMISE MUST be sent in stream SID_tq to serialize to allow
the client to know the push order;
* Each PUSH_PROMISE chooses a new server-selected stream ID, and the
stream is closed after push.
8.6. Concurrency Management
* ALTO/H2 must allow concurrency control using the
SETTINGS_MAX_CONCURRENT_STREAMS option in HTTP/2.
* 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.
* From the server to the client direction, each push needs to open a
new stream and this should be controlled bu
SETTINGS_MAX_CONCURRENT_STREAMS.
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9. ALTO/H2 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/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",
"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
}
},
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"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": {
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"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/H2 based
connection, and this is indicated by the media-type "application/
alto-transport+json". 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.
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10. Security Considerations
The properties defined in this document present no security
considerations beyond those in Section 15 of the base ALTO
specification [RFC7285].
11. IANA Considerations
IANA will need to register the application/alto-transport+json media
type under ALTO registry as defined in [RFC7285].
12. Acknowledgments
The authors of this document would also like to thank many for the
reviews and comments.
13. References
13.1. 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>.
[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, "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>.
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[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>.
13.2. 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>.
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:
* Minimizing connection establishment and overall transport latency
for applications, starting with HTTP/2
* Providing multiplexing without head-of-line blocking
* Requiring only changes to path endpoints to enable deployment
* Enabling multipath and forward error correction extensions
* Providing always-secure transport, using TLS 1.3 by default
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.
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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
Email: Roland.Schott@telekom.de
Y. Richard Yang
Yale University
51 Prospect St
New Haven, CT 06520
United States of America
Email: yry@cs.yale.edu
Kai Gao
Sichuan University
Chengdu
201804
China
Email: kgao@scu.edu.cn
Jingxuan Jensen Zhang
Tongji University
4800 Cao'An Hwy
Shanghai
201804
China
Email: jingxuan.n.zhang@gmail.com
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