One document matched: draft-roome-alto-incr-update-sse-00.txt
ALTO WG W. Roome
Internet-Draft Alcatel-Lucent
Intended status: Standards Track X. Shi
Expires: April 30, 2015 Y. Yang
Yale University
October 27, 2014
ALTO Incremental Updates Using Server-Sent Events (SSE)
draft-roome-alto-incr-update-sse-00
Abstract
The goal of Application-Layer Traffic Optimization (ALTO) [RFC7285]
is to bridge the gap between network and applications by providing
network related information to non-priviledged, application-level
clients. This allows applications to make informed decisions, for
example when selecting a target host from a set of candidates.
Therefore an ALTO Server provides network and cost maps to its
clients. However, those maps can be very large, and portions of
those maps may change frequently (cost maps in particular).
This draft presents a method to provide incremental updates for these
maps. The goal is to reduce the load on the ALTO Client and Server
by transmitting just the updated portions of those maps.
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].
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."
Roome, et al. Expires April 30, 2015 [Page 1]
Internet-Draft ALTO Incremental Updates October 2014
This Internet-Draft will expire on April 30, 2015.
Copyright Notice
Copyright (c) 2014 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
(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.
Roome, et al. Expires April 30, 2015 [Page 2]
Internet-Draft ALTO Incremental Updates October 2014
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Incremental Update Message Format . . . . . . . . . . . . . . 4
2.1. JSON Merge Patch . . . . . . . . . . . . . . . . . . . . . 4
2.2. JSON Merge Patch Applied to Network Map Messages . . . . . 5
2.3. JSON Merge Patch Applied to Cost Map Messages . . . . . . 7
3. Server-Sent Events . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Overview of SSEs . . . . . . . . . . . . . . . . . . . . . 8
3.2. ALTO SSE Update Messages . . . . . . . . . . . . . . . . . 9
3.3. Keep-Alive Messages . . . . . . . . . . . . . . . . . . . 10
4. Update Stream Service . . . . . . . . . . . . . . . . . . . . 10
4.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 10
4.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . . 10
4.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.6. Event Order Requirements . . . . . . . . . . . . . . . . . 11
4.7. Response . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.8. Client Actions When Receiving Update Messages . . . . . . 12
5. Filtered Update Stream Service . . . . . . . . . . . . . . . . 13
5.1. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 13
5.2. Accept Input Parameters . . . . . . . . . . . . . . . . . 13
5.3. Response . . . . . . . . . . . . . . . . . . . . . . . . . 14
6. IRD Example . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Design Decisions and Discussion . . . . . . . . . . . . . . . 18
7.1. Not Allowing Stream Restart . . . . . . . . . . . . . . . 18
7.2. Is Incremental Update Useful for Network Maps? . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
Roome, et al. Expires April 30, 2015 [Page 3]
Internet-Draft ALTO Incremental Updates October 2014
1. Introduction
The Application-Layer Traffic Optimization (ALTO) [RFC7285] protocol
provides network related information to client applications so that
clients may make informed decisions. An ALTO Server provides network
and cost maps, which may be very large and change very frequently.
Instead of having the clients request for a new complete network map
or cost map every time, an incremental update from the server is much
more efficient. The goals are to reduce the load on the ALTO Client
and Server by efficiently transmitting only the updated portions of
those maps, and to provide timely updates to clients.
This draft uses the JSON Merge Patch message format [RFC7386] to
encode the incremental update messages for network maps and cost
maps, and uses Server-Sent Events (SSE) as the transport mechanism to
deliver those updates to clients.
2. Incremental Update Message Format
2.1. JSON Merge Patch
[RFC7386] defines JSON Merge Patch format and transport, which
enables applications to update the server resources via the PATCH
method [RFC5789] of HTTP. This draft adopts the format of the Merge
Patch messages to encode our incremental updates objects, but uses a
different transport mechanism.
The process of applying a Merge Patch is defined by the following
algorithm, as specified in [RFC7386]:
Roome, et al. Expires April 30, 2015 [Page 4]
Internet-Draft ALTO Incremental Updates October 2014
define MergePatch(Target, Patch) {
if Patch is an Object {
if Target is not an Object {
Target = {} # Ignore the contents and
# set it to an empty Object
}
for each Name/Value pair in Patch {
if Value is null {
if Name exists in Target {
remove the Name/Value pair from Target
}
} else {
Target[Name] = MergePatch(Target[Name], Value)
}
}
return Target
} else {
return Patch
}
}
Note that null as the value of a name/value pair will remove the pair
with "name" in the original JSON document.
2.2. JSON Merge Patch Applied to Network Map Messages
Section 11.2.1.6 of [RFC7285] defines the format of a Network Map
message. Here is a simple example:
Roome, et al. Expires April 30, 2015 [Page 5]
Internet-Draft ALTO Incremental Updates October 2014
{
"meta" : {
"vtag": {
"resource-id": "my-default-network-map",
"tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785"
}
},
"network-map" : {
"PID1" : {
"ipv4" : [
"192.0.2.0/24",
"198.51.100.0/25"
]
},
"PID2" : {
"ipv4" : [ "198.51.100.128/25" ]
},
"PID3" : {
"ipv4" : [ "0.0.0.0/0" ],
"ipv6" : [ "::/0" ]
}
}
}
When applied to that message, the following Merge Patch update
message adds the ipv6 prefix "2000::/3" to "PID1", deletes "PID2",
and assigns a new "tag" to the Network Map:
{
"meta" : {
"vtag" : {
"tag" : "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
}
},
"network-map": {
"PID1" : {
"ipv6" : [ "2000::/3" ]
},
"PID2" : null
}
}
Here is the updated Network Map:
Roome, et al. Expires April 30, 2015 [Page 6]
Internet-Draft ALTO Incremental Updates October 2014
{
"meta" : {
"vtag": {
"resource-id": "my-default-network-map",
"tag": "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
}
},
"network-map" : {
"PID1" : {
"ipv4" : [
"192.0.2.0/24",
"198.51.100.0/25"
],
"ipv6" : [ "2000::/3" ]
},
"PID3" : {
"ipv4" : [ "0.0.0.0/0" ],
"ipv6" : [ "::/0" ]
}
}
}
2.3. JSON Merge Patch Applied to Cost Map Messages
Section 11.2.3.6 of [RFC7285] defines the format of a Cost Map
message. Here is a simple example:
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "my-default-network-map",
"tag": "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
}
],
"cost-type" : {"cost-mode" : "numerical",
"cost-metric": "routingcost"
}
},
"cost-map" : {
"PID1": { "PID1": 1, "PID2": 5, "PID3": 10 },
"PID2": { "PID1": 5, "PID2": 1, "PID3": 15 },
"PID3": { "PID1": 20, "PID2": 15 }
}
}
The following Merge Patch message updates that cost map so that (1)
PID1->PID2 is 9 instead of 5; (2) PID3->PID1 is no longer available;
and (3) PID3->PID3 is now 1:
Roome, et al. Expires April 30, 2015 [Page 7]
Internet-Draft ALTO Incremental Updates October 2014
{
"cost-map" : {
"PID1" : { "PID2" : 9 },
"PID3" : { "PID1" : null, "PID3" : 1 }
}
}
Here is the updated Cost Map:
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "my-default-network-map",
"tag": "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
}
],
"cost-type" : {"cost-mode" : "numerical",
"cost-metric": "routingcost"
}
},
"cost-map" : {
"PID1": { "PID1": 1, "PID2": 9, "PID3": 10 },
"PID2": { "PID1": 5, "PID2": 1, "PID3": 15 },
"PID3": { "PID1": 20, "PID3": 1 }
}
}
3. Server-Sent Events
3.1. Overview of SSEs
Server-Sent Events [SSE] enable a server to send new data to a client
by pushing messages to the client. To summarize the protocol, the
client establishes an HTTP connection to the server, and keeps the
connection open. The server continually sends messages. Messages
are delimited by two new-lines (this is a slight simplification of
the full specification), and contain three fields: an event type, an
id, and data. All fields are strings. The data field may contain
new-lines; the other fields cannot. The event type and id fields are
optional.
Here is a sample SSE stream, starting with the client request. The
server sends three events and then closes the stream.
Roome, et al. Expires April 30, 2015 [Page 8]
Internet-Draft ALTO Incremental Updates October 2014
GET /stream HTTP/1.1
Host: example.com
Accept: text/event-stream
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: start
data: hello there
event: middle
data: let's chat some more ... and more ...
event: end
data: good bye
3.2. ALTO SSE Update Messages
In our events, the data field is a JSON object. There two types of
data objects. One is a message describing an ALTO resource, such as
a Network Maps or Cost Map, as defined in [RFC7285]. We will refer
to these as full-map messages. The other type is a Merge Patch
message to apply to an ALTO resource.
Our event types have two sub-fields: the media-type of the JSON
message in the data field, and the resource-id of the ALTO resource.
The media-types for ALTO resource messages are defined by [RFC7285],
and include "application/alto-networkmap+json" for Network Map
messages and "application/alto-costmap+json" for Cost Map messages.
The media-type for a Merge Patch message is "application/
merge-patch+json", and is defined by [RFC7285].
We do not use the SSE id field.
Because commas (character code 0x2c) are not allowed in media-type
names, we encode the event type sub-fields as
media-type , resource-id
Here examples of ALTO update events:
Roome, et al. Expires April 30, 2015 [Page 9]
Internet-Draft ALTO Incremental Updates October 2014
event: application/alto-networkmap+json,my-network-map
data: { ... full Network Map message ... }
event: application/alto-costmap+json,my-routingcost-map
data: { ... full Cost Map message ... }
event: application/merge-patch+json,my-routingcost-map
data: { ... Merge Patch update for previous Cost Map ... }
3.3. Keep-Alive Messages
An SSE event with an empty event type is a keep-alive message. An
ALTO Server MAY send keep-alive messages as needed. An ALTO Client
MUST ignore any keep-alive messages.
4. Update Stream Service
An Update Stream Service returns a stream of SSE messages, as defined
in Section 3.2.
4.1. Media Type
The media type of an ALTO Update Stream resource is "text/
event-stream".
4.2. HTTP Method
An ALTO Update Stream resource is requested using the HTTP GET
method.
4.3. Accept Input Parameters
None.
4.4. Capabilities
The capabilities are defined by an object of type
UpdateStreamCapabilities:
object {
JSONString events<1..*>;
} UpdateEventStreamCapabilities;
The strings in the array are the event types (see Section 3.2) sent
by this Update Stream.
If an Update Event Service's event capability list has an event with
Roome, et al. Expires April 30, 2015 [Page 10]
Internet-Draft ALTO Incremental Updates October 2014
a media-type of "text/merge-patch+json" for a resource-id, then the
event capability list MUST also have an full-map event for that
resource-id. For example, suppose "my-costmap" is the resource-id of
a Cost Map. Then if the event list has "text/
merge-patch+json,my-costmap", it MUST also have the event
"application/alto-costmap+json,my-costmap".
4.5. Uses
An array with the resource-ids of the resources for which this stream
sends updates. This array MUST contain the resource-ids of every
event type in the "events" capability.
4.6. Event Order Requirements
There are several requirements on the order in which an ALTO Server
sends SSE Update messages on the event stream:
o For any given resource-id, the ALTO Server MUST send a full-map
update event (media-type "application/alto-networkmap+json" or
"application/alto-costmap+json") before the first Merge Patch
event (media-type "application/merge-patch+json") for that
resource-id.
o The ALTO Server SHOULD send full-map update events for all
resource-ids covered by this Update Stream resource as soon as
possible after the client initiates the connection.
o If the event list contains a resource-id R0 on which resource-id
R1 depends, when R0 changes, the ALTO Server MUST send the update
for R0 before sending the update for R1. For example, suppose the
event list includes a Network Map resource and its dependent Cost
Map resources. When the Network Map changes, the ALTO Server MUST
send an update event for that Network Map before sending the
update events for the dependent Cost Maps.
o If the event list contains a resource-id R0 on which resource-id
R1 depends, the ALTO Server SHOULD send an update for R1 as soon
as possible after sending the update for R0. For example, when a
Network Map changes, the ALTO Server SHOULD send update events for
all dependent Cost Maps as soon as possible after the update event
for the Network Map.
4.7. Response
Here is an example of a client's request and the server's immediate
response, using the Update Stream resource "my-routingcost-update-
stream" defined in the IRD in Section 6. This assumes the Update
Roome, et al. Expires April 30, 2015 [Page 11]
Internet-Draft ALTO Incremental Updates October 2014
Stream service sends updates for a Network Map with resource-id "my-
network-map" and an associated Cost Map with resource-id "my-
routingcost-map":
GET /updates/routingcost HTTP/1.1
Host: alto.example.com
Accept: text/event-stream
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: application/alto-networkmap+json,my-network-map
data: { ... full Network Map message ... }
event: application/alto-costmap+json,my-routingcost-map
data: { ... full Cost Map message ... }
After sending those two events immediately, the ALTO Server will send
additional events as the maps change. For example, the following
represents a small change to the Cost Map:
event: {"resource-id":"my-routingcost-map",
"media-type":"application/merge-patch+json"}
data: {"cost-map": {"PID1" : {"PID2" : 9}}}
If a major change to the Network Map occurs, the ALTO Server MAY
choose to send full Network and Cost Map messages rather than Merge
Patch messages:
event: application/alto-networkmap+json,my-network-map
data: { ... full Network Map message ... }
event: application/alto-costmap+json,my-routingcost-map
data: { ... full Cost Map message ... }
4.8. Client Actions When Receiving Update Messages
In general, when a client receives a full-map update message for a
resource, the client should replace the current version with the new
version. When a client receives a Merge Patch update message for a
resource, the client should apply those patches to the current
version of the resource.
However, because resources can depend on other resources (e.g., Cost
Maps depend on Network Maps), an ALTO Client MUST NOT use a dependent
resource when the resource on which it depends changes. There are at
least two ways a client may do that. We will illustrate these
Roome, et al. Expires April 30, 2015 [Page 12]
Internet-Draft ALTO Incremental Updates October 2014
techniques by referring to Network and Cost Map messages, although
these techniques apply to any dependent resources.
One approach is for the ALTO Client to save the Network Map update
message in a buffer, and continue to use the previous Network Map,
and the associated Cost Maps, until the client receives the update
messages for all dependent Cost Maps. The client then applies all
Network and Cost Map updates atomically.
Alternatively, the client MAY update the Network Map immediately. In
this case, the client MUST mark each dependent Cost Map as
temporarily invalid, and MUST NOT use that map until the client
receives a Cost Map update message with the new Network Map version
tag. Note that the client MUST NOT delete the Cost Maps, because the
server may send Merge Patch update messages.
The ALTO Server SHOULD send updates to dependent resources in a
timely fashion. However, if the client does not receive the expected
updates, the client MUST close the Update Stream connection, discard
the dependent resources, and reestablish the Update Stream. If the
client uses the Filtered Update Stream service, the client MAY retain
the version tag of the last version of any tagged resources, and give
those version tags when requesting the new Update Stream. In this
case, if a version is still current, the ALTO Server will not re-send
that resource.
Although not as efficient as possible, this recovery method is simple
and reliable.
5. Filtered Update Stream Service
The Filtered Update Stream service is similar to the Update Stream
service, except that the client can select the types of update
events. Specifically, except as noted below, the Filtered Update
Stream service is identical to the Update Stream service (Section 4).
5.1. HTTP Method
A Filtered ALTO Update Stream resource is requested using the HTTP
POST method.
5.2. Accept Input Parameters
An ALTO Client supplies filtering parameters by specifying media type
"application/alto-updatestreamfilter+json" with HTTP POST body
containing a JSON object of type ReqFilteredUpdateStream, where:
Roome, et al. Expires April 30, 2015 [Page 13]
Internet-Draft ALTO Incremental Updates October 2014
object {
[UpdateEventType events<1..*>;]
[VersionTag vtags<1..*>;]
[ResourceInputs inputs<1..*>;]
} ReqFilteredUpdateStream;
object-map {
ResourceID -> JSONObject;
} ResourceInputs;
The "events" field gives the types of the events the ALTO Client
wishes to receive. These events MUST be a subset of the "events"
capability of this resource. If the "events" list is omitted, the
ALTO Server MUST send all event types in the "events" capability of
this resource.
The "vtags" field gives the version tags, as defined in Section 10.3
of [RFC7285], for any resources which the client already has. If
those versions are still current, the server SHOULD NOT send the full
version of that resource at startup.
The "inputs" field gives the client input needed for any POST-mode
resources requested by the client. The value is a JSON object; the
key is the resource-id of the POST-mode resource, and the value is
the JSON object that it requires as "accepts" input.
If a client requests Merge Patch update events for a given
resource-id, the client MUST also request the corresponding full map
update events for that resource-id.
If a client requests the full-map update event for given resource-id,
but does not request the Merge Patch update event for that
resource-id, then the ALTO Server MUST send full-map update events
whenever the map changes. For Network Map resources, the ALTO Server
SHOULD send the full map as soon as it would have sent the Merge
Patch event. For Cost Map and other resources, the ALTO Server MAY
delay sending the full-map until more changes are available.
5.3. Response
Here is an example of a client's request and the server's immediate
response, using the Filtered Update Stream resource "my-allresources-
update-stream" defined in the IRD in Section 6. The client requests
updates for the Network Map and the "routingcost" Cost Map, but does
not want updates for the "hopcount" Cost Map. The "vtags" field gives
the client's version of the Network Map. Because that version is
still current, the server does not send the full Network Map update
event at the beginning of the stream:
Roome, et al. Expires April 30, 2015 [Page 14]
Internet-Draft ALTO Incremental Updates October 2014
POST /updates/allresources HTTP/1.1
Host: alto.example.com
Accept: text/event-stream
Content-Type: application/alto-updatestreamfilter+json
Content-Length: ###
{ "events": [
"application/alto-networkmap+json,my-network-map",
"application/alto-costmap+json,my-routingcost-map",
"application/merge-patch+json,my-routingcost-map"
],
"vtags": [
"resource-id": "my-network-map", "tag": "314159265359"}
]
}
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: application/alto-costmap+json,my-routingcost-map
data: { ... full Cost Map message ... }
After that, the ALTO Server sends updates for the Network Map and
"routingcost" Cost Map as they become available.
As another example, here is how a client can request updates for the
property "priv:ietf-bandwidth" for a set of endpoints. The ALTO
Server immediately sends a full-map message with the property values
for all endpoints. After that, the server sends update events for
the individual endpoints as their property values change.
Roome, et al. Expires April 30, 2015 [Page 15]
Internet-Draft ALTO Incremental Updates October 2014
POST /updates/allresources HTTP/1.1
Host: alto.example.com
Accept: text/event-stream
Content-Type: application/alto-updatestreamfilter+json
Content-Length: ###
{ "events": [
"application/alto-endpointprop+json,my-properties",
"application/merge-patch+json,my-properties"
],
"inputs": {
"my-properties": {
"properties" : [ "priv:ietf-bandwidth" ],
"endpoints" : [
"ipv4:1.0.0.1",
"ipv4:1.0.0.2",
"ipv4:1.0.0.3"
]
}
}
}
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: application/alto-endpointprop+json,my-properties
data: { "endpoint-properties": {
data: "ipv4:1.0.0.1" : { "priv:ietf-bandwidth": "13" },
data: "ipv4:1.0.0.2" : { "priv:ietf-bandwidth": "42" },
data: "ipv4:1.0.0.3" : { "priv:ietf-bandwidth": "27" }
data: } }
event: text/merge-patch+json,my-properties
data: { "endpoint-properties":
data: {"ipv4:1.0.0.1" : {"priv:ietf-bandwidth": "3"}}
data: }
event: text/merge-patch+json,my-properties
data: { "endpoint-properties":
data: {"ipv4:1.0.0.3" : {"priv:ietf-bandwidth": "38"}}
data: }
Roome, et al. Expires April 30, 2015 [Page 16]
Internet-Draft ALTO Incremental Updates October 2014
6. IRD Example
Here is an example of an IRD that offers both regular and Filtered
Update Stream services. The unfiltered Update Stream provides
updates for the Network Map and "routingcost" Cost Map. The Filtered
Update Stream provides update to both those maps, plus the "hopcount"
Cost Map and the Endpoint Properties service.
"my-network-map": {
"uri": "http://alto.example.com/networkmap",
"media-type": "application/alto-networkmap+json",
},
"my-routingcost-map": {
"uri": "http://alto.example.com/costmap",
"media-type": "application/alto-costmap+json",
"uses": ["my-networkmap+json"],
"capabilities": {
"cost-type-names": ["num-routingcost"]
}
},
"my-hopcount-map": {
"uri": "http://alto.example.com/costmap",
"media-type": "application/alto-costmap+json",
"uses": ["my-networkmap+json"],
"capabilities": {
"cost-type-names": ["num-hopcount"]
}
},
"my-properties": {
"uri": "http://alto.example.com/properties",
"media-type": "application/alto-endpointprops+json",
"accepts": "application/alto-endpointpropparams+json",
"capabilities": {
"prop-types": ["priv:ietf-bandwidth"]
}
},
"my-routingcost-update-stream": {
"uri": "http://alto.example.com/updates/routingcost",
"media-type": "text/event-stream",
"uses": ["my-network-map", "my-routingcost-map"],
"capabilities": {
"events": [
"application/alto-networkmap+json,my-network-map",
"application/alto-costmap+json,my-routingcost-map",
"application/merge-patch+json,my-routingcost-map"
]
}
},
Roome, et al. Expires April 30, 2015 [Page 17]
Internet-Draft ALTO Incremental Updates October 2014
"my-allresources-update-stream": {
"uri": "http://alto.example.com/updates/allresources",
"media-type": "text/event-stream",
"uses": [
"my-network-map",
"my-routingcost-map",
"my-hopcount-map",
"my-properties"
],
"accepts": "application/alto-updatestreamfilter+json",
"capabilities": {
"events": [
"application/alto-networkmap+json,my-network-map",
"application/alto-costmap+json,my-routingcost-map",
"application/merge-patch+json,my-routingcost-map"
"application/alto-costmap+json,my-hopcount-map",
"application/merge-patch+json,my-hopcount-map"
"application/alto-endpointprops+json,my-properties",
"application/merge-patch+json,my-properties"
]
}
}
7. Design Decisions and Discussion
7.1. Not Allowing Stream Restart
If an update stream is closed accidentally, when the client
reconnects, the server must resend the full maps. This is clearly
inefficient. To avoid that inefficiency, the SSE specification
allows a server to assign an id to each event. When a client
reconnects, the client can present the id of the last successfully
received event, and the server restarts with the next event.
However, that mechanism adds a lot of complication. The server would
have to save SSE messages in a buffer, in case clients reconnect.
But that mechanism will never be perfect: if the client waits too
long to reconnect, or if the client's last id is bogus, then the
server will have to resend the complete maps anyway.
In short, using event ids to avoid resending the full map adds a lot
of complication to avoid a situation which is hopefully very rare.
Hence we decided to keep it simple.
The Filtered Update Stream service does allow the client to specify
the vtag of the last received Network Map, and if that is still
current, the server can avoid retransmitting the Network Map.
Roome, et al. Expires April 30, 2015 [Page 18]
Internet-Draft ALTO Incremental Updates October 2014
7.2. Is Incremental Update Useful for Network Maps?
It is not clear whether incremental update (that is, Merge Patch
update) is useful for Network Maps. For minor changes, such as
moving a prefix from one PID to another, it might be useful. But
more involved changes to the Network Map are likely to be "flag
days": they represent a completely new Network Map, rather than a
simple, well-defined change.
This is not to say that Network Map updates are not useful. Clearly
Network Maps will change, and update events are necessary to inform
clients of the new map. But we expect most Network Map updates will
be full updates with full Network Map message, rather than
incremental Merge Patch updates.
Note that while we allow a server to use Merge Patch on Network Maps,
we do not require the server to do so.
8. Security Considerations
Allowing persistent update stream connections does enable a new class
of Denial-of-Service attacks. An ALTO Server MAY choose to limit the
number of active streams, and reject new requests when that threshold
is reached. In this case the server should return the HTTP status
"503 Service Unavailable".
Alternatively an ALTO Server MAY return the HTTP status "307
Temporary Redirect" to redirect the client to another ALTO Server
which can better handle a large number of update streams.
This extension does not introduce any privacy issues not already
present in the ALTO protocol.
9. IANA Considerations
This draft defines a new media-type, "application/
alto-updatestreamfilter+json", as described in Section 5.2. That
type must be registered with IANA.
All other media-types used in this document have already been
registered, either for ALTO or JSON Merge Patch.
10. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Roome, et al. Expires April 30, 2015 [Page 19]
Internet-Draft ALTO Incremental Updates October 2014
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
[RFC7285] Almi, R., Penno, R., Yang, Y., Kiesel, S., Previdi, S.,
Roome, W., Shalunov, S., and R. Woundy, "Application-Layer
Traffic Optimization (ALTO) Protocol", RFC 7285,
September 2014.
[RFC7386] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7386,
October 2014.
[SSE] Hickson, I., "Server-Sent Events (W3C)", December 2012.
Authors' Addresses
Wendy Roome
Alcatel-Lucent/Bell Labs
600 Mountain Ave, Rm 3B-324
Murray Hill, NJ 07974
USA
Phone: +1-908-582-7974
Email: w.roome@alcatel-lucent.com
Xiao Shi
Yale University
51 Prospect Street
New Haven, CT 06511
USA
Email: xiao.shi@yale.edu
Y. Richard Yang
Yale University
51 Prospect St
New Haven CT
USA
Email: yang.r.yang@gmail.com
Roome, et al. Expires April 30, 2015 [Page 20]
| PAFTECH AB 2003-2026 | 2026-04-24 05:54:04 |