ALTO Protocol
draft-ietf-alto-protocol-11
The information below is for an old version of the document.
| Document | Type | This is an older version of an Internet-Draft that was ultimately published as an RFC. | |
|---|---|---|---|
| Authors | Richard Alimi , Reinaldo Penno , Y. Richard Yang | ||
| Last updated | 2012-03-29 (Latest revision 2012-03-11) | ||
| Replaces | draft-penno-alto-protocol | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
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| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | AD is watching | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Martin Stiemerling | ||
| Send notices to | alto-chairs@tools.ietf.org, draft-ietf-alto-protocol@tools.ietf.org |
draft-ietf-alto-protocol-11
ALTO WG R. Alimi, Ed.
Internet-Draft Google
Intended status: Standards Track R. Penno, Ed.
Expires: September 12, 2012 Juniper Networks
Y. Yang, Ed.
Yale University
March 11, 2012
ALTO Protocol
draft-ietf-alto-protocol-11.txt
Abstract
Networking applications today already have access to a great amount
of Inter-Provider network topology information. For example, views
of the Internet routing table are easily available at looking glass
servers and entirely practical to be downloaded by clients. What is
missing is knowledge of the underlying network topology from the ISP
or Content Provider (henceforth referred as Provider) point of view.
In other words, what a Provider prefers in terms of traffic
optimization -- and a way to distribute it.
The ALTO Service provides network information (e.g., basic network
location structure, preferences of network paths) with the goal of
modifying network resource consumption patterns while maintaining or
improving application performance. The basic information of ALTO is
based on abstract maps of a network. These maps provide simplified,
yet enough information of a network for applications to effectively
utilize. Additional services are built on top the maps.
This document describes a protocol implementing the ALTO Service.
Although the ALTO service would primarily be provided by the network
(i.e., the ISP), content providers and third parties could also
operate this service. Applications that could use this service are
those that have a choice in connection endpoints. Examples of such
applications are peer-to-peer (P2P) and content delivery networks.
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.
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This Internet-Draft will expire on September 12, 2012.
Copyright Notice
Copyright (c) 2012 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Background and Problem Statement . . . . . . . . . . . . . 6
1.2. Design History and Merged Proposals . . . . . . . . . . . 6
1.3. Solution Benefits . . . . . . . . . . . . . . . . . . . . 7
1.3.1. Service Providers . . . . . . . . . . . . . . . . . . 7
1.3.2. Applications . . . . . . . . . . . . . . . . . . . . . 7
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Endpoint Address . . . . . . . . . . . . . . . . . . . 8
2.1.2. ASN . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.3. Network Location . . . . . . . . . . . . . . . . . . . 8
2.1.4. ALTO Information . . . . . . . . . . . . . . . . . . . 8
2.1.5. ALTO Information Base . . . . . . . . . . . . . . . . 8
2.2. ALTO Service and Protocol Scope . . . . . . . . . . . . . 8
3. Protocol Structure . . . . . . . . . . . . . . . . . . . . . . 10
3.1. ALTO Information Services . . . . . . . . . . . . . . . . 11
3.1.1. Map Service . . . . . . . . . . . . . . . . . . . . . 11
3.1.2. Map Filtering Service . . . . . . . . . . . . . . . . 12
3.1.3. Endpoint Property Service . . . . . . . . . . . . . . 12
3.1.4. Endpoint Cost Service . . . . . . . . . . . . . . . . 12
4. Network Map . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. PID . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Endpoint Addresses . . . . . . . . . . . . . . . . . . . . 13
4.2.1. IP Addresses . . . . . . . . . . . . . . . . . . . . . 13
4.3. Example Network Map . . . . . . . . . . . . . . . . . . . 14
5. Cost Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Cost Attributes . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Cost Type . . . . . . . . . . . . . . . . . . . . . . 15
5.1.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Cost Map Structure . . . . . . . . . . . . . . . . . . . . 16
5.3. Network Map and Cost Map Dependency . . . . . . . . . . . 17
6. Protocol Design Overview . . . . . . . . . . . . . . . . . . . 17
6.1. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.1.1. Existing Infrastructure . . . . . . . . . . . . . . . 18
6.1.2. ALTO Information Reuse and Redistribution . . . . . . 18
6.2. Protocol Design . . . . . . . . . . . . . . . . . . . . . 18
7. Protocol Specification . . . . . . . . . . . . . . . . . . . . 19
7.1. Notation . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.2. Basic Operation . . . . . . . . . . . . . . . . . . . . . 19
7.2.1. Discovering Information Resources . . . . . . . . . . 19
7.2.2. Requesting Information Resources . . . . . . . . . . . 20
7.2.3. Response . . . . . . . . . . . . . . . . . . . . . . . 20
7.2.4. Client Behavior . . . . . . . . . . . . . . . . . . . 20
7.2.5. Authentication and Encryption . . . . . . . . . . . . 21
7.2.6. HTTP Cookies . . . . . . . . . . . . . . . . . . . . . 21
7.2.7. Parsing . . . . . . . . . . . . . . . . . . . . . . . 21
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7.3. Information Resource . . . . . . . . . . . . . . . . . . . 21
7.3.1. Capabilities . . . . . . . . . . . . . . . . . . . . . 21
7.3.2. Input Parameters Media Type . . . . . . . . . . . . . 22
7.3.3. Media Type . . . . . . . . . . . . . . . . . . . . . . 22
7.3.4. Encoding . . . . . . . . . . . . . . . . . . . . . . . 22
7.4. ALTO Errors . . . . . . . . . . . . . . . . . . . . . . . 23
7.4.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 23
7.4.2. Resource Format . . . . . . . . . . . . . . . . . . . 24
7.4.3. Error Codes . . . . . . . . . . . . . . . . . . . . . 24
7.5. ALTO Types . . . . . . . . . . . . . . . . . . . . . . . . 25
7.5.1. PID Name . . . . . . . . . . . . . . . . . . . . . . . 25
7.5.2. Version Tag . . . . . . . . . . . . . . . . . . . . . 25
7.5.3. Endpoints . . . . . . . . . . . . . . . . . . . . . . 26
7.5.4. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 28
7.5.5. Cost Type . . . . . . . . . . . . . . . . . . . . . . 28
7.5.6. Endpoint Property . . . . . . . . . . . . . . . . . . 28
7.6. Information Resource Directory . . . . . . . . . . . . . . 29
7.6.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 29
7.6.2. Encoding . . . . . . . . . . . . . . . . . . . . . . . 29
7.6.3. Example . . . . . . . . . . . . . . . . . . . . . . . 30
7.6.4. Usage Considerations . . . . . . . . . . . . . . . . . 33
7.7. Information Resources . . . . . . . . . . . . . . . . . . 34
7.7.1. Map Service . . . . . . . . . . . . . . . . . . . . . 34
7.7.2. Map Filtering Service . . . . . . . . . . . . . . . . 39
7.7.3. Endpoint Property Service . . . . . . . . . . . . . . 45
7.7.4. Endpoint Cost Service . . . . . . . . . . . . . . . . 48
8. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 52
8.1. ALTO Client Embedded in P2P Tracker . . . . . . . . . . . 52
8.2. ALTO Client Embedded in P2P Client: Numerical Costs . . . 53
8.3. ALTO Client Embedded in P2P Client: Ranking . . . . . . . 54
9. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 55
9.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 55
9.2. Hosts with Multiple Endpoint Addresses . . . . . . . . . . 56
9.3. Network Address Translation Considerations . . . . . . . . 56
9.4. Mapping IPs to ASNs . . . . . . . . . . . . . . . . . . . 57
9.5. Endpoint and Path Properties . . . . . . . . . . . . . . . 57
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 57
10.1. application/alto-* Media Types . . . . . . . . . . . . . . 57
10.2. ALTO Cost Type Registry . . . . . . . . . . . . . . . . . 59
10.3. ALTO Endpoint Property Registry . . . . . . . . . . . . . 60
11. Security Considerations . . . . . . . . . . . . . . . . . . . 61
11.1. Privacy Considerations for ISPs . . . . . . . . . . . . . 61
11.2. ALTO Clients . . . . . . . . . . . . . . . . . . . . . . . 62
11.3. Authentication, Integrity Protection, and Encryption . . . 62
11.4. ALTO Information Redistribution . . . . . . . . . . . . . 63
11.5. Denial of Service . . . . . . . . . . . . . . . . . . . . 63
11.6. ALTO Server Access Control . . . . . . . . . . . . . . . . 63
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 64
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12.1. Normative References . . . . . . . . . . . . . . . . . . . 64
12.2. Informative References . . . . . . . . . . . . . . . . . . 65
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 66
Appendix B. Authors . . . . . . . . . . . . . . . . . . . . . . . 67
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 68
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1. Introduction
1.1. Background and Problem Statement
Today, network information available to applications is mostly from
the view of endhosts. There is no clear mechanism to convey
information about the network (e.g., preferences) to applications.
On the other hand, modern network applications can be adaptive, with
the potential to become more network-efficient (e.g., reduce network
resource consumption) and achieve better application performance
(e.g., accelerated download rate), by leveraging better network-
provided information.
The ALTO Service intends to provide a simple mechanism to convey
network information to applications. Its objective is to provide
basic, abstract but useful network information to applications. The
mechanism should include abstractions to achieve concise, flexible
network information expression.
The goal of this document is to specify a simple and unified protocol
that meets the ALTO requirements [I-D.ietf-alto-reqs] while providing
a migration path for Internet Service Providers (ISP), Content
Providers, and clients that have deployed protocols with similar
intentions (see below). This document is a work in progress and will
be updated with further developments.
1.2. Design History and Merged Proposals
The protocol specified here consists of contributions from
o P4P [I-D.p4p-framework], [P4P-SIGCOMM08],
[I-D.wang-alto-p4p-specification];
o ALTO Info-Export [I-D.shalunov-alto-infoexport];
o Query/Response [I-D.saumitra-alto-queryresponse],
[I-D.saumitra-alto-multi-ps];
o ATTP [ATTP];
o Proxidor [I-D.akonjang-alto-proxidor].
See Appendix A for a list of people that have contributed
significantly to this effort and the projects and proposals listed
above.
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1.3. Solution Benefits
The ALTO Service offers many benefits to both end-users (consumers of
the service) and Internet Service Providers (providers of the
service).
1.3.1. Service Providers
The ALTO Service enables ISPs to influence the peer selection process
in distributed applications in order to increase locality of traffic,
improve user-experience, amongst others. It also helps ISPs to
efficiently manage traffic that traverses more expensive links such
as transit and backup links, thus allowing a better provisioning of
the networking infrastructure.
1.3.2. Applications
Applications that use the ALTO Service can benefit in multiple ways.
For example, they may no longer need to infer topology information,
and some applications can reduce reliance on measuring path
performance metrics themselves. They can take advantage of the ISP's
knowledge to avoid bottlenecks and boost performance.
An example type of application is a Peer-to-Peer overlay where peer
selection can be improved by including ALTO information in the
selection process.
2. Architecture
Two key design objectives of the ALTO Protocol are simplicity and
extensibility. At the same time, it introduces additional techniques
to address potential scalability and privacy issues. This section
first introduces the terminology, and then defines the ALTO
architecture and the ALTO Protocol's place in the overall
architecture.
2.1. Terminology
We use the following terms defined in [RFC5693]: Application, Overlay
Network, Peer, Resource, Resource Identifier, Resource Provider,
Resource Consumer, Resource Directory, Transport Address, Host
Location Attribute, ALTO Service, ALTO Server, ALTO Client, ALTO
Query, ALTO Reply, ALTO Transaction, Local Traffic, Peering Traffic,
Transit Traffic.
We also use the following additional terms: Endpoint Address,
Autonomous System Number (ASN), and Network Location.
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2.1.1. Endpoint Address
An endpoint address represents the communication address of an
endpoint. An endpoint address can be network-attachment based (IP
address) or network-attachment agnostic. Common forms of endpoint
addresses include IP address, MAC address, overlay ID, and phone
number.
Each Endpoint Address has an associated Address Type, which indicates
both its syntax and semantics.
2.1.2. ASN
An Autonomous System Number.
2.1.3. Network Location
Network Location is a generic term denoting a single endpoint or
group of endpoints.
2.1.4. ALTO Information
ALTO Information is a generic term referring to the network
information sent by an ALTO Server.
2.1.5. ALTO Information Base
Internal representation of the ALTO Information maintained by the
ALTO Server. Note that the structure of this internal representation
is not defined by this document.
2.2. ALTO Service and Protocol Scope
An ALTO Server conveys the network information from the perspective
of a network region; the ALTO Server presents its "my-Internet View"
of the network region. In particular, an ALTO Server defines network
Endpoints (and aggregations thereof) and generic costs amongst them,
both from the network region's own perspective. A network region in
this context can be an Autonomous System, an ISP, or perhaps a
smaller region or set of ISPs; the details depend on the deployment
scenario and discovery mechanism.
To better understand the ALTO Service and the role of the ALTO
Protocol, we show in Figure 1 the overall system architecture. In
this architecture, an ALTO Server prepares ALTO Information; an ALTO
Client uses ALTO Service Discovery to identify an appropriate ALTO
Server; and the ALTO Client requests available ALTO Information from
the ALTO Server using the ALTO Protocol.
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The ALTO Information provided by the ALTO Server can be updated
dynamically based on network conditions, or can be seen as a policy
which is updated at a larger time-scale.
More specifically, the ALTO Information provided by an ALTO Server
may be influenced (at the operator's discretion) by other systems.
The ALTO Server aggregates information from multiple systems to
provide an abstract, unified, useful network view to applications.
Examples of other systems include (but are not limited to) static
network configuration databases, dynamic network information, routing
protocols, provisioning policies, and interfaces to outside parties.
These components are shown in the figure for completeness but outside
the scope of this specification.
Note that it may also be possible for ALTO Servers to exchange
network information with other ALTO Servers (either within the same
administrative domain or another administrative domain with the
consent of both parties) in order to adjust exported ALTO
Information. Such a protocol is also outside the scope of this
specification.
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+-------------------------------------------------------------------+
| ISP |
| |
| +-----------+ |
| | Routing | |
| +--------------+ | Protocols | |
| | Provisioning | +-----------+ |
| | Policy | | |
| +--------------+\ | |
| \ | |
| \ | |
| +-----------+ \+---------+ +--------+ |
| |Dynamic | | ALTO | ALTO Protocol | ALTO | |
| |Network |.......| Server | -------------------- | Client | |
| |Information| +---------+ +--------+ |
| +-----------+ / / |
| / ALTO SD Query/Response / |
| / / |
| +----------+ +--------------+ |
| | External | | ALTO Service | |
| | Interface| | Discovery | |
| +----------+ +--------------+ |
| | |
+-------------------------------------------------------------------+
|
+------------------+
| Third Parties |
| |
| Content Providers|
+------------------+
Figure 1: Basic ALTO Architecture.
3. Protocol Structure
The ALTO Protocol uses a simple extensible framework to convey
network information. In the general framework, the ALTO protocol
will convey properties on both Network Locations and the paths
between Network Locations.
In this document, we focus on a particular Endpoint property to
denote the location of an endpoint, and provider-defined costs for
paths between pairs of Network Locations.
The ALTO Protocol is built on a common transport protocol, messaging
structure and encoding, and transaction model. The protocol is
subdivided into services of related functionality. ALTO-Core
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provides the Map Service, which provides the core ALTO informtion to
clients. Other ALTO Information services can provide additional
functionality. There are three such services defined in this
document: the Map Filtering Service, Endpoint Property Service, and
Endpoint Cost Service. Additional services may be defined in
companion documents. Note that functionality offered in different
services are not totally non-overlapping (e.g., the Map Service and
Map Filtering Service).
.-----------------------------------------.
| ALTO Information Services |
| .-----------. .----------. .----------. |
| | Map | | Endpoint | | Endpoint | |
| | Filtering | | Property | | Cost | |
| | Service | | Service | | Service | |
| `-----------' `----------' `----------' |
| .-------------------------------------. |
| | Map Service | |
| | .-------------. .--------------. | |
| | | Network Map | | Cost Map | | |
| | `-------------' `--------------' | |
| `-------------------------------------' |
`-----------------------------------------'
Figure 2: ALTO Protocol Structure
3.1. ALTO Information Services
Multiple, distinct services are defined to allow ALTO Clients to
query ALTO Information from an ALTO Server. The ALTO Server
internally maintains an ALTO Information Base that encodes the
network provider's preferences. The ALTO Information Base encodes
the Network Locations defined by the ALTO Server (and their
corresponding properties), as well as the provider-defined costs
between pairs of Network Locations.
3.1.1. Map Service
The Map Service provides batch information to ALTO Clients in the
form of Network Map and Cost Map. The Network Map (See Section 4)
provides the full set of Network Location groupings defined by the
ALTO Server and the endpoints contained with each grouping. The Cost
Map (see Section 5) provides costs between the defined groupings.
These two maps can be thought of (and implemented as) as simple files
with appropriate encoding provided by the ALTO Server.
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3.1.2. Map Filtering Service
Resource constrained ALTO Clients may benefit from query results
being filtered at the ALTO Server. This avoids an ALTO Client
spending network bandwidth or CPU collecting results and performing
client-side filtering. The Map Filtering Service allows ALTO Clients
to query for the ALTO Server Network Map and Cost Map based on
additional parameters.
3.1.3. Endpoint Property Service
This service allows ALTO Clients to look up properties for individual
endpoints. An example endpoint property is its Network Location (its
grouping defined by the ALTO Server) or connectivity type (e.g.,
ADSL, Cable, or FTTH).
3.1.4. Endpoint Cost Service
Some ALTO Clients may also benefit from querying for costs and
rankings based on endpoints. The Endpoint Cost Service allows an
ALTO Server to return either numerical costs or ordinal costs
(rankings) directly amongst Endpoints.
4. Network Map
In reality, many endpoints are very close to one another in terms of
network connectivity, for example, endpoints on the same site of an
enterprise. By treating a group of endpoints together as a single
entity in ALTO, we can achieve much greater scalability without
losing critical information.
The Network Location endpoint property allows an ALTO Server to group
endpoints together to indicate their proximity. The resulting set of
groupings is called the ALTO Network Map.
The definition of proximity varies depending on the granularity of
the ALTO information configured by the provider. In one deployment,
endpoints on the same subnet may be considered close; while in
another deployment, endpoints connected to the same PoP may be
considered close.
As used in this document, the Network Map refers to the syntax and
semantics of the information distributed by the ALTO Server. This
document does not discuss the internal representation of this data
structure within the ALTO Server.
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4.1. PID
Each group of Endpoints is identified by a provider-defined Network
Location identifier called a PID. There can be many different ways
of grouping the endpoints and assigning PIDs.
A PID is an identifier that provides an indirect and network-agnostic
way to specify an aggregation of network endpoints that may be
treated similarly, based on network topology, type, or other
properties. For example, a PID may be defined by the ALTO service
provider to denote a subnet, a set of subnets, a metropolitan area, a
PoP, an autonomous system, or a set of autonomous systems.
Aggregation of endpoints into PIDs can indicate proximity and can
improve scalability. In particular, network preferences (costs) may
be specified between PIDs, allowing cost information to be more
compactly represented and updated at a faster time scale than the
network aggregations themselves.
Using PIDs, the Network Map may also be used to communicate simple
preferences with only minimal information from the Cost Map. For
example, an ISP may prefer that endpoints associated with the same
PoP (Point-of-Presence) in a P2P application communicate locally
instead of communicating with endpoints in other PoPs. The ISP may
aggregate endhosts within a PoP into a single PID in the Network Map.
The Cost Map may be encoded to indicate that peering within the same
PID is preferred; for example, cost(PID_i, PID_i) == c* and
cost(PID_i, PID_j) > c* for i != j. Section 5 provides further
details about Cost Map structure.
4.2. Endpoint Addresses
Communicating endpoints may have many types of addresses, such as IP
addresses, MAC addresses, or overlay IDs. The current specification
only considers IP addresses.
4.2.1. IP Addresses
The endpoints aggregated into a PID are denoted by a list of IP
prefixes. When either an ALTO Client or ALTO Server needs to
determine which PID in a Network Map contains a particular IP
address, longest-prefix matching MUST be used.
A Network Map MUST define a PID for each possible address in the IP
address space for all of the address types contained in the map. A
RECOMMENDED way to satisfy this property is to define a PID that
contains the 0.0.0.0/0 prefix for IPv4 or ::/0 (for IPv6).
Each endpoint MUST map into exactly one PID. Since longest-prefix
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matching is used to map an endpoint to a PID, this can be
accomplished by ensuring that no two PIDs contain an identical IP
prefix.
4.3. Example Network Map
Figure 3 illustrates an example Network Map. PIDs are used to
identify network-agnostic aggregations.
.-----------------------------------------------------------.
| ALTO Network Map |
| |
| .-----------------------------------. .---------------. |
| | NetLoc: PID-1 | | NetLoc: PID-2 | |
| | .------------------------------. | | ... | |
| | | 192.0.2.0/24 | | `---------------` |
| | | .--------------------------. | | |
| | | | Endpoint: 192.0.2.34 | | | .---------------. |
| | | `--------------------------` | | | NetLoc: PID-3 | |
| | `------------------------------` | | ... | |
| | .------------------------------. | `---------------` |
| | | 198.51.100.0/25 | | |
| | | .--------------------------. | | .---------------. |
| | | | Endpoint: 198.51.100.100 | | | | NetLoc: PID-4 | |
| | | `--------------------------` | | | ... | |
| | `------------------------------` | `---------------` |
| `-----------------------------------` |
| |
`-----------------------------------------------------------`
Figure 3: Example Network Map
5. Cost Map
An ALTO Server indicates preferences amongst network locations in the
form of Path Costs. Path Costs are generic costs and can be
internally computed by a network provider according to its own needs.
An ALTO Cost Map defines Path Costs pairwise amongst sets of source
and destination Network Locations. Each Path Cost is the end-to-end
cost from the source to the destination.
One advantage of separating ALTO information into a Network Map and a
Cost Map is that the two components can be updated at different time
scales. For example, Network Maps may be stable for a longer time
while Cost Maps may be updated to reflect dynamic network conditions.
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As used in this document, the Cost Map refers to the syntax and
semantics of the information distributed by the ALTO Server. This
document does not discuss the internal representation of this data
structure within the ALTO Server.
5.1. Cost Attributes
Path Costs have attributes:
o Type: identifies what the costs represent;
o Mode: identifies how the costs should be interpreted.
Certain queries for Cost Maps allow the ALTO Client to indicate the
desired Type and Mode.
5.1.1. Cost Type
The Type attribute indicates what the cost represents. For example,
an ALTO Server could define costs representing air-miles, hop-counts,
or generic routing costs.
Cost types are indicated in protocol messages as strings.
5.1.1.1. Cost Type: routingcost
An ALTO Server MUST define the 'routingcost' Cost Type.
This Cost Type conveys a generic measure for the cost of routing
traffic from a source to a destination. Lower values indicate a
higher preference for traffic to be sent from a source to a
destination.
Note that an ISP may internally compute routing cost using any method
it chooses (e.g., air-miles or hop-count) as long as it conforms to
these semantics.
5.1.2. Cost Mode
The Mode attribute indicates how costs should be interpreted.
Specifically, the Mode attribute indicates whether returned costs
should be interpreted as numerical values or ordinal rankings.
It is important to communicate such information to ALTO Clients, as
certain operations may not be valid on certain costs returned by an
ALTO Server. For example, it is possible for an ALTO Server to
return a set of IP addresses with costs indicating a ranking of the
IP addresses. Arithmetic operations that would make sense for
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numerical values, do not make sense for ordinal rankings. ALTO
Clients may handle such costs differently.
Cost Modes are indicated in protocol messages as strings.
An ALTO Server MUST support at least one of 'numerical' and 'ordinal'
costs. ALTO Clients SHOULD be cognizant of operations when a desired
cost mode is not supported. For example, an ALTO Client desiring
numerical costs may adjust behavior if only the ordinal Cost Mode is
available. Alternatively, an ALTO Client desiring ordinal costs may
construct ordinal costs given numerical values if only the numerical
Cost Mode is available.
5.1.2.1. Cost Mode: numerical
This Cost Mode is indicated by the string 'numerical'. This mode
indicates that it is safe to perform numerical operations (e.g.
normalization) on the returned costs.
5.1.2.2. Cost Mode: ordinal
This Cost Mode is indicated by the string 'ordinal'. This mode
indicates that the costs values to a set of Destination Network
Locations from a particular Source Network Location are a ranking,
with lower values indicating a higher preference. The values are
non-negative integers. Ordinal cost values from a particular Source
Network Location to a set of Destination Network Locations need not
be unique nor contiguous. In particular, from the perspective of a
particular Source Network Location, two Destination Network Locations
may have an identical rank (ordinal cost value). This document does
not specify any behavior by an ALTO Client in this case; an ALTO
Client may decide to break ties by random selection, other
application knowledge, or some other means.
It is important to note that the values in the Cost Map provided with
the ordinal Cost Mode are not necessarily the actual cost known to
the ALTO Server.
5.2. Cost Map Structure
A query for a Cost Map either explicitly or implicitly includes a
list of Source Network Locations and a list of Destination Network
Locations. (Recall that a Network Location can be an endpoint
address or a PID.)
Specifically, assume that a query has a list of multiple Source
Network Locations, say [Src_1, Src_2, ..., Src_m], and a list of
multiple Destination Network Locations, say [Dst_1, Dst_2, ...,
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Dst_n].
The ALTO Server will return the Path Cost for each communicating pair
(i.e., Src_1 -> Dst_1, ..., Src_1 -> Dst_n, ..., Src_m -> Dst_1, ...,
Src_m -> Dst_n). If the ALTO Server does not define a Path Cost for
a particular pair, it may be omitted. We refer to this structure as
a Cost Map.
If the Cost Mode is 'ordinal', the Path Cost of each communicating
pair is relative to the m*n entries.
5.3. Network Map and Cost Map Dependency
If a Cost Map contains PIDs in the list of Source Network Locations
or the list of Destination Network Locations, the Path Costs are
generated based on a particular Network Map (which defines the PIDs).
Version Tags are introduced to ensure that ALTO Clients are able to
use consistent information even though the information is provided in
two maps.
A Version Tag is an opaque string associated with a Network Map
maintained by the ALTO Server. When the Network Map changes, the
Version Tag MUST also be changed. (Thus, the Version Tag is defined
similarly to HTTP's Entity Tags; see Section 3.11 of [RFC2616].)
Possibilities for generating a Version Tag include the last-modified
timestamp for the Network Map, or a hash of its contents.
A Network Map distributed by the ALTO Server includes its Version
Tag. A Cost Map referring to PIDs also includes the Version Tag of
the Network Map on which it is based.
6. Protocol Design Overview
The ALTO Protocol design uses a REST-ful design with the goal of
leveraging current HTTP [RFC2616] implementations and infrastructure.
The REST-ful design supports flexible deployment strategies and
provides extensibility. ALTO requests and responses are encoded with
JSON [RFC4627].
6.1. Benefits
Benefits enabled by these design choices include easier understanding
and debugging, mature libraries, tools, infrastructure, and caching
and redistribution of ALTO information for increased scalability.
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6.1.1. Existing Infrastructure
HTTP is a natural choice for integration with existing applications
and infrastructure. In particular, the ALTO Protocol design
leverages:
o the huge installed base of infrastructure, including HTTP caches,
o mature software implementations,
o the fact that many P2P clients already have an embedded HTTP
client, and
o authentication and encryption mechanisms in HTTP and SSL/TLS.
6.1.2. ALTO Information Reuse and Redistribution
ALTO information may be useful to a large number of applications and
users. For example, an identical Network Map may be used by all ALTO
Clients querying a particular ALTO Server. At the same time,
distributing ALTO information must be efficient and not become a
bottleneck.
Beyond integration with existing HTTP caching infrastructure, ALTO
information may also be cached or redistributed using application-
dependent mechanisms, such as P2P DHTs or P2P file-sharing. This
document does not define particular mechanisms for such
redistribution. See [I-D.gu-alto-redistribution] for further
discussion.
Note that if caching or redistribution is used, the response message
may be returned from another (possibly third-party) entity.
6.2. Protocol Design
The ALTO Protocol uses a REST-ful design. There are two primary
components to this design:
o Information Resources: Each service provides network information
as a set of resources, which are distinguished by their media
types [RFC2046]. An ALTO Client may construct an HTTP request for
a particular resource (including any parameters, if necessary),
and an ALTO Server returns the requested resource in an HTTP
response.
o Information Resource Directory: An ALTO Server provides to ALTO
Clients a list of available resources and the URI at which each is
provided. This document refers to this list as the Information
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Resource Directory. This directory is the single entry point to
an ALTO Service. ALTO Clients consult the directory to determine
the services provided by an ALTO Server.
7. Protocol Specification
This section first specifies general client and server processing,
followed by a detailed specification for each ALTO Information
Resource.
7.1. Notation
This document uses an adaptation of the C-style struct notation to
define the required and optional members of JSON objects. Unless
explicitly noted, each member of a struct is REQUIRED.
The types 'JSONString', 'JSONNumber', 'JSONBool' indicate the JSON
string, number, and boolean types, respectively. 'JSONValue'
indicates a JSON value, as specified in Section 2.1 of [RFC4627].
Note that no standard, machine-readable interface definition or
schema is provided. Extension documents may document these as
necessary.
7.2. Basic Operation
The ALTO Protocol employs standard HTTP [RFC2616]. It is used for
discovering available Information Resources at an ALTO Server and
retrieving Information Resources. ALTO Clients and ALTO Servers use
HTTP requests and responses carrying ALTO-specific content with
encoding as specified in this document, and MUST be compliant with
[RFC2616].
7.2.1. Discovering Information Resources
To discover available resources, an ALTO Client may request the
Information Resource Directory, which an ALTO Server provides at the
URI found by the ALTO Discovery protocol.
Informally, an Information Resource Directory enumerates URIs at
which an ALTO Server offers Information Resources. Each entry in the
directory indicates a URI at which an ALTO Server accepts requests,
and returns either the requested Information Resource or an
Information Resource Directory that references additional Information
Resources. See Section 7.6 for a detailed specification.
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7.2.2. Requesting Information Resources
Through the retrieved Information Resource Directories, an ALTO
Client can determine whether an ALTO Server supports the desired
Information Resource, and if it is supported, the URI at which it is
available.
Where possible, the ALTO Protocol uses the HTTP GET method to request
resources. However, some ALTO services provide Information Resources
that are the function of one or more input parameters. Input
parameters are encoded in the HTTP request's entity body, and the
request uses the HTTP POST method.
Note that it is possible for an ALTO Server to employ caching for the
response to a POST request. This can be accomplished by returning an
HTTP 303 status code ("See Other") indicating to the ALTO Client that
the resulting Cost Map is available via a GET request to an alternate
URL (which may be cached).
When requesting an ALTO Information Resource that requires input
parameters specified in a HTTP POST request, an ALTO Client MUST set
the Content-Type HTTP header to the media type corresponding to the
format of the supplied input parameters.
7.2.3. Response
Upon receiving a request, an ALTO server either returns the requested
resource, provides the ALTO Client an Information Resource Directory
indicating how to reach the desired resource, or returns an error.
The type of response MUST be indicated by the media type attached to
the response (the Content-Type HTTP header). If an ALTO Client
receives an Information Resource Directory, it can consult the
received directory to determine if any of the offered URIs contain
the desired Information Resource.
The generic encoding for an Information Resource is specified in
Section 7.3.
Errors are indicated via either ALTO-level error codes, or via HTTP
status codes; see Section 7.4.
7.2.4. Client Behavior
7.2.4.1. Using Information Resources
This specification does not indicate any required actions taken by
ALTO Clients upon successfully receiving an Information Resource from
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an ALTO Server. Although ALTO Clients are suggested to interpret the
received ALTO Information and adapt application behavior, ALTO
Clients are not required to do so.
7.2.4.2. Error Conditions
If an ALTO Client does not successfully receive a desired Information
Resource from a particular ALTO Server, it can either choose another
server (if one is available) or fall back to a default behavior
(e.g., perform peer selection without the use of ALTO information).
An ALTO Client may also retry the request at a later time.
7.2.5. Authentication and Encryption
An ALTO Server MAY support SSL/TLS to implement server and/or client
authentication, as well as encryption. See [RFC6125] for
considerations regarding verification of server identity.
7.2.6. HTTP Cookies
If cookies are included in an HTTP request received by an ALTO
Server, they MUST be ignored.
7.2.7. Parsing
This document only details object members used by this specification.
Extensions may include additional members within JSON objects defined
in this document. ALTO implementations MUST ignore such unknown
fields when processing ALTO messages.
7.3. Information Resource
An Information Resource is an HTTP entity body received by an ALTO
Server that encodes the ALTO Information desired by an ALTO Client.
This document specifies multiple Information Resources that can be
provided by an ALTO Server. Each Information Resource has certain
attributes associated with it, indicating its data format, the input
parameters it supports, and format of the input parameters.
7.3.1. Capabilities
An ALTO Server may advertise to an ALTO Client that it supports
certain capabilities in requests for an Information Resource. For
example, if an ALTO Server allows requests for a Cost Map to include
constraints, it may advertise that it supports this capability.
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7.3.2. Input Parameters Media Type
An ALTO Server may allow an ALTO Client to supply input parameters
when requesting certain Information Resources. The format of the
input parameters (i.e., as contained in the entity body of the HTTP
POST request) is indicated by the media type [RFC2046].
7.3.3. Media Type
The media type [RFC2046] uniquely indicates the data format of the
Information Resource as returned by an ALTO Server in the HTTP entity
body.
7.3.4. Encoding
Though each Information Resource may have a distinct syntax, they are
designed to have a common structure containing generic ALTO-layer
metadata about the resource, as well as data itself.
An Information Resource has a single top-level JSON object of type
InfoResourceEntity:
object {
InfoResourceMetaData meta; [OPTIONAL]
[InfoResourceDataType] data;
} InfoResourceEntity;
with members:
meta meta-information pertaining to the Information Resource
data the data contained in the Information Resource
7.3.4.1. Meta Information
Meta information is encoded as a JSON object. This document does not
specify any members, but it is defined here as a standard container
for extensibility. Specifically, InfoResourceMetaData is defined as:
object {
} InfoResourceMetaData;
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7.3.4.2. ALTO Information
The "data" member of the InfoResourceEntity encodes the resource-
specific data; the structure of this member is detailed later in this
section for each particular Information Resource.
7.3.4.3. Example
The following is an example of the encoding for an Information
Resource:
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {},
"data" : {
...
}
}
7.4. ALTO Errors
If there is an error processing a request, an ALTO Server SHOULD
return additional ALTO-layer information, if it is available, in the
form of an ALTO Error Resource encoded in the HTTP response's entity
body.
If no ALTO-layer information is available, an ALTO Server may omit an
ALTO Error resource from the response. An appropriate HTTP status
code MUST be set.
It is important to note that the HTTP Status Code and ALTO Error Code
have distinct roles. An ALTO Error Code provides detailed
information about the why a particular request for an ALTO Resource
was not successful. The HTTP status code indicates to HTTP
processing elements (e.g., intermediaries and clients) how the
response should be treated.
7.4.1. Media Type
The media type for an Error Resource is "application/
alto-error+json".
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7.4.2. Resource Format
An Error Resource has the format:
object {
JSONString code;
JSONString reason; [OPTIONAL]
} ErrorResourceEntity;
where:
code An ALTO Error Code defined in Table 1
reason A (free-form) human-readable explanation of the particular
error
7.4.3. Error Codes
This document defines ALTO Error Codes to support the error
conditions needed for purposes of this document. Additional status
codes may be defined in companion or extension documents.
The HTTP status codes corresponding to each ALTO Error Code are
defined to provide correct behavior with HTTP intermediaries and
clients. When an ALTO Server returns a particular ALTO Error Code,
it MUST indicate one of the corresponding HTTP status codes in
Table 1in the HTTP response.
If multiple errors are present in a single request (e.g., a request
uses a JSONString when a JSONInteger is expected and a required field
is missing), then the ALTO Server MUST return exactly one of the
detected errors. However, the reported error is implementation
defined, since specifying a particular order for message processing
encroaches needlessly on implementation technique.
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+-------------------------+-------------+---------------------------+
| ALTO Error Code | HTTP Status | Description |
| | Code(s) | |
+-------------------------+-------------+---------------------------+
| E_SYNTAX | 400 | Parsing error in request |
| | | (including identifiers) |
| | | |
| E_JSON_FIELD_MISSING | 400 | Required field missing |
| | | |
| E_JSON_VALUE_TYPE | 400 | JSON Value of unexpected |
| | | type |
| | | |
| E_INVALID_COST_MODE | 400 | Invalid cost mode |
| | | |
| E_INVALID_COST_TYPE | 400 | Invalid cost type |
| | | |
| E_INVALID_PROPERTY_TYPE | 400 | Invalid property type |
+-------------------------+-------------+---------------------------+
Table 1: Defined ALTO Error Codes
7.5. ALTO Types
This section details the format for particular data values used in
the ALTO Protocol.
7.5.1. PID Name
A PID Name is encoded as a US-ASCII string. The string MUST be no
more than 64 characters, and MUST NOT contain any ASCII character
below 0x21 or above 0x7E or the '.' separator. The '.' separator is
reserved for future use and MUST NOT be used unless specifically
indicated by a companion or extension document.
The type 'PIDName' is used in this document to indicate a string of
this format.
7.5.2. Version Tag
A Version Tag is encoded as a US-ASCII string. The string MUST be no
more than 64 characters, and MUST NOT contain any ASCII character
below 0x21 or above 0x7E.
The type 'VersionTag' is used in this document to indicate a string
of this type.
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7.5.3. Endpoints
This section defines formats used to encode addresses for Endpoints.
In a case that multiple textual representations encode the same
Endpoint address or prefix (within the guidelines outlined in this
document), the ALTO Protocol does not require ALTO Clients or ALTO
Servers to use a particular textual representation, nor does it
require that ALTO Servers reply to requests using the same textual
representation used by requesting ALTO Clients. ALTO Clients must be
cognizant of this.
7.5.3.1. Address Type
Address Types are encoded as US-ASCII strings consisting of only
alphanumeric characters. This document defines the address type
"ipv4" to refer to IPv4 addresses, and "ipv6" to refer to IPv6
addresses. Extension documents may define additional Address Types.
The type 'AddressType' is used in this document to indicate a string
of this format.
7.5.3.2. Endpoint Address
Endpoint Addresses are encoded as US-ASCII strings. The exact
characters and format depend on the type of endpoint address.
The type 'EndpointAddr' is used in this document to indicate a string
of this format.
7.5.3.2.1. IPv4
IPv4 Endpoint Addresses are encoded as specified by the 'IPv4address'
rule in Section 3.2.2 of [RFC3986].
7.5.3.2.2. IPv6
IPv6 Endpoint Addresses are encoded as specified in Section 4 of
[RFC5952].
7.5.3.2.3. Typed Endpoint Addresses
When an Endpoint Address is used, an ALTO implementation must be able
to determine its type. For this purpose, the ALTO Protocol allows
endpoint addresses to also explicitly indicate their type.
Typed Endpoint Addresses are encoded as US-ASCII strings of the
format 'AddressType:EndpointAddr' (with the ':' character as a
separator). The type 'TypedEndpointAddr' is used to indicate a
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string of this format.
7.5.3.3. Endpoint Prefixes
For efficiency, it is useful to denote a set of Endpoint Addresses
using a special notation (if one exists). This specification makes
use of the prefix notations for both IPv4 and IPv6 for this purpose.
Endpoint Prefixes are encoded as US-ASCII strings. The exact
characters and format depend on the type of endpoint address.
The type 'EndpointPrefix' is used in this document to indicate a
string of this format.
7.5.3.3.1. IPv4
IPv4 Endpoint Prefixes are encoded as specified in Section 3.1 of
[RFC4632].
7.5.3.3.2. IPv6
IPv6 Endpoint Prefixes are encoded as specified in Section 7 of
[RFC5952].
7.5.3.4. Endpoint Address Group
The ALTO Protocol includes messages that specify potentially large
sets of endpoint addresses. Endpoint Address Groups provide a more
efficient way to encode such sets, even when the set contains
endpoint addresses of different types.
An Endpoint Address Group is defined as:
object {
EndpointPrefix [AddressType]<0..*>;
...
} EndpointAddrGroup;
In particular, an Endpoint Address Group is a JSON object with the
name of each member being the string corresponding to the address
type, and the member's corresponding value being a list of prefixes
of addresses of that type.
The following is an example with both IPv4 and IPv6 endpoint
addresses:
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{
"ipv4": [
"192.0.2.0/24",
"198.51.100.0/25"
],
"ipv6": [
"2001:db8:0:1::/64",
"2001:db8:0:2::/64"
]
}
7.5.4. Cost Mode
A Cost Mode is encoded as a US-ASCII string. The string MUST either
have the value 'numerical' or 'ordinal'.
The type 'CostMode' is used in this document to indicate a string of
this format.
7.5.5. Cost Type
A Cost Type is encoded as a US-ASCII string. The string MUST be no
more than 32 characters, and MUST NOT contain characters other than
alphanumeric characters, the hyphen ('-'), or the ':' separator.
Identifiers prefixed with 'priv:' are reserved for Private Use
[RFC5226]. Identifiers prefixed with 'exp:' are reserved for
Experimental use. All other identifiers appearing in an HTTP request
or response with an 'application/alto-*' media type MUST be
registered in the ALTO Cost Types registry Section 10.2.
The type 'CostType' is used in this document to indicate a string of
this format.
7.5.6. Endpoint Property
An Endpoint Property is encoded as a US-ASCII string. The string
MUST be no more than 32 characters, and MUST NOT contain characters
other than alphanumeric characters, the hyphen ('-'), or the ':'
separator.
Identifiers prefixed with 'priv:' are reserved for Private Use
[RFC5226]. Identifiers prefixed with 'exp:' are reserved for
Experimental use. All other identifiers appearing in an HTTP request
or response with an 'application/alto-*' media type MUST be
registered in the ALTO Endpoint Property registry Section 10.3.
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The type 'EndpointProperty' is used in this document to indicate a
string of this format.
7.6. Information Resource Directory
An Information Resource Directory indicates to ALTO Clients which
Information Resources are made available by an ALTO Server.
Since resource selection happens after consumption of the Information
Resource Directory, the format of the Information Resource Directory
is designed to be simple with the intention of future ALTO Protocol
versions maintaining backwards compatibility. Future extensions or
versions of the ALTO Protocol SHOULD be accomplished by extending
existing media types or adding new media types, but retaining the
same format for the Information Resource Directory.
An ALTO Server MUST make an Information Resource Directory available
via the HTTP GET method to a URI discoverable by an ALTO Client.
Discovery of this URI is out of scope of this document, but could be
accomplished by manual configuration or by returning the URI of an
Information Resource Directory from the ALTO Discovery Protocol
[I-D.ietf-alto-server-discovery].
7.6.1. Media Type
The media type is "application/alto-directory+json".
7.6.2. Encoding
An Information Resource Directory is a JSON object of type
InfoResourceDirectory:
object {
...
} Capabilities;
object {
JSONString uri;
JSONString media-types<1..*>;
JSONString accepts<0..*>; [OPTIONAL]
Capabilities capabilities; [OPTIONAL]
} ResourceEntry;
object {
ResourceEntry resources<0..*>;
} InfoResourceDirectory;
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where the "resources" array indicates a list of Information Resources
provided by an ALTO Server. Note that the list of available
resources is enclosed in a JSON object for extensibility; future
protocol versions may specify additional members in the
InfoResourceDirectory object.
Any URI endpoint indicated in an Information Resource Directory MAY
provide a response to an OPTIONS request that is in the format of an
Information Resource Directory. This provides ALTO Clients a means
to discover resources and capabilities offered by that URI endpoint.
ALTO Servers that reply with an HTTP 300 status code ("Multiple
Choices") SHOULD use the Information Resource Directory format in the
reply.
Each entry in the directory specifies:
uri A URI at which the ALTO Server provides one or more Information
Resources, or an Information Resource Directory indicating
additional Information Resources.
media-types The list of all media types of Information Resources
(see Section 7.3.3) available via GET or POST requests to the
corresponding URI or URIs discoverable via the URI.
accepts The list of all media types of input parameters (see
Section 7.3.2) accepted by POST requests to the corresponding URI
or URIs discoverable via the URI. If this member is not present,
it MUST be assumed to be an empty array.
capabilities A JSON Object enumerating capabilities of an ALTO
Server in providing the Information Resource at the corresponding
URI and Information Resources discoverable via the URI. If this
member is not present, it MUST be assumed to be an empty array.
If a capability for one of the offered Information Resources is
not explicitly listed here, an ALTO Client may either issue an
OPTIONS HTTP request to the corresponding URI to determine if the
capability is supported, or assume its default value.
If an entry has an empty list for "accepts", then the corresponding
URI MUST support GET requests. If an entry has a non-empty list for
"accepts", then the corresponding URI MUST support POST requests. If
an ALTO Server wishes to support both GET and POST on a single URI,
it MUST specify two entries in the Information Resource Directory.
7.6.3. Example
The following is an example Information Resource Directory returned
by an ALTO Server. In this example, the ALTO Server provides
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additional Network and Cost Maps via a separate subdomain,
"custom.alto.example.com". The maps available via this subdomain are
Filtered Network and Cost Maps as well as pre-generated maps for the
"hopcount" and "routingcost" Cost Types in the "ordinal" Cost Mode.
An ALTO Client can discover the maps available by
"custom.alto.example.com" by successfully performing an OPTIONS
request to "http://custom.alto.example.com/maps".
GET /directory HTTP/1.1
Host: alto.example.com
Accept: application/alto-directory+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-directory+json
{
"resources" : [
{
"uri" : "http://alto.example.com/serverinfo",
"media-types" : [ "application/alto-serverinfo+json" ]
}, {
"uri" : "http://alto.example.com/networkmap",
"media-types" : [ "application/alto-networkmap+json" ]
}, {
"uri" : "http://alto.example.com/costmap/num/routingcost",
"media-types" : [ "application/alto-costmap+json" ],
"capabilities" : {
"cost-modes" : [ "numerical" ],
"cost-types" : [ "routingcost" ]
}
}, {
"uri" : "http://alto.example.com/costmap/num/hopcount",
"media-types" : [ "application/alto-costmap+json" ],
"capabilities" : {
"cost-modes" : [ "numerical" ],
"cost-types" : [ "hopcount" ]
}
}, {
"uri" : "http://custom.alto.example.com/maps",
"media-types" : [
"application/alto-networkmap+json",
"application/alto-costmap+json"
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],
"accepts" : [
"application/alto-networkmapfilter+json",
"application/alto-costmapfilter+json"
]
}, {
"uri" : "http://alto.example.com/endpointprop/lookup",
"media-types" : [ "application/alto-endpointprop+json" ],
"accepts" : [ "application/alto-endpointpropparams+json" ],
"capabilities" : {
"prop-types" : [ "pid" ]
}
}, {
"uri" : "http://alto.example.com/endpointcost/lookup",
"media-types" : [ "application/alto-endpointcost+json" ],
"accepts" : [ "application/alto-endpointcostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-modes" : [ "ordinal", "numerical" ],
"cost-types" : [ "routingcost", "hopcount" ]
}
}
]
}
OPTIONS /maps HTTP/1.1
Host: custom.alto.example.com
Accept: application/alto-directory+json,application/alto-error+json
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HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-directory+json
{
"resources" : [
{
"uri" : "http://custom.alto.example.com/networkmap/filtered",
"media-types" : [ "application/alto-networkmap+json" ],
"accepts" : [ "application/alto-networkmapfilter+json" ]
}, {
"uri" : "http://custom.alto.example.com/costmap/filtered",
"media-types" : [ "application/alto-costmap+json" ],
"accepts" : [ "application/alto-costmapfilter+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-modes" : [ "ordinal", "numerical" ],
"cost-types" : [ "routingcost", "hopcount" ]
}
}, {
"uri" : "http://custom.alto.example.com/ord/routingcost",
"media-types" : [ "application/alto-costmap+json" ],
"capabilities" : {
"cost-modes" : [ "ordinal" ],
"cost-types" : [ "routingcost" ]
}
}, {
"uri" : "http://custom.alto.example.com/ord/hopcount",
"media-types" : [ "application/alto-costmap+json" ],
"capabilities" : {
"cost-modes" : [ "ordinal" ],
"cost-types" : [ "hopcount" ]
}
}
]
}
7.6.4. Usage Considerations
7.6.4.1. ALTO Client
This document specifies no requirements or constraints on ALTO
Clients with regards to how they process an Information Resource
Directory to identify the URI corresponding to a desired Information
Resource. However, some advice is provided for implementors.
It is possible that multiple entries in the directory match a desired
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Information Resource. For instance, in the example in Section 7.6.3,
a full Cost Map with "numerical" Cost Mode and "routingcost" Cost
Type could be retrieved via a GET request to
"http://alto.example.com/costmap/num/routingcost", or via a POST
request to "http://custom.alto.example.com/costmap/filtered".
In general, it is preferred for ALTO Clients to use GET requests
where appropriate, since it is more likely for responses to be
cacheable.
7.6.4.2. ALTO Server
This document indicates that an ALTO Server may or may not provide
the Information Resources specified in the Map Filtering Service. If
these resources are not provided, it is indicated to an ALTO Client
by the absence of a Network Map or Cost Map with any media types
listed under "accepts".
7.7. Information Resources
This section documents the individual Information Resources defined
in the ALTO Protocol.
7.7.1. Map Service
The Map Service provides batch information to ALTO Clients in the
form of two types of maps: a Network Map and Cost Map.
7.7.1.1. Network Map
The Network Map Information Resource lists for each PID, the network
locations (endpoints) within the PID. It MUST be provided by an ALTO
Server.
7.7.1.1.1. Media Type
The media type is "application/alto-networkmap+json".
7.7.1.1.2. HTTP Method
This resource is requested using the HTTP GET method.
7.7.1.1.3. Input Parameters
None.
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7.7.1.1.4. Capabilities
None.
7.7.1.1.5. Response
The returned InfoResourceEntity object "data" member of type
InfoResourceNetworkMap:
object {
EndpointAddrGroup [pidname]<0..*>;
...
} NetworkMapData;
object {
VersionTag map-vtag;
NetworkMapData map;
} InfoResourceNetworkMap;
with members:
map-vtag The Version Tag (Section 5.3) of the Network Map.
map The Network Map data itself.
NetworkMapData is a JSON object with each member representing a
single PID and its associated set of endpoint addresses. A member's
name is a string of type PIDName.
The returned Network Map MUST include all PIDs known to the ALTO
Server.
7.7.1.1.6. Example
GET /networkmap HTTP/1.1
Host: alto.example.com
Accept: application/alto-networkmap+json,application/alto-error+json
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HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-networkmap+json
{
"meta" : {},
"data" : {
"map-vtag" : "1266506139",
"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"
]
}
}
}
}
7.7.1.2. Cost Map
The Cost Map resource lists the Path Cost for each pair of source/
destination PID defined by the ALTO Server for a given Cost Type and
Cost Mode. This resource MUST be provided for at least the
'routingcost' Cost Type and 'numerical' Cost Mode.
Note that since this resource, an unfiltered Cost Map requested by an
HTTP GET, does not indicate the desired Cost Mode or Cost Type as
input parameters, an ALTO Server MUST indicate in an Information
Resource Directory a unfiltered Cost Map Information Resource by
specifying the capabilities (Section 7.7.1.2.4) with "cost-types" and
"cost-modes" members each having a single element. This technique
will allow an ALTO Client to determine a URI for an unfiltered Cost
Map of the desired Cost Mode and Cost Type.
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7.7.1.2.1. Media Type
The media type is "application/alto-costmap+json".
7.7.1.2.2. HTTP Method
This resource is requested using the HTTP GET method.
7.7.1.2.3. Input Parameters
None.
7.7.1.2.4. Capabilities
This resource may be defined for across multiple Cost Types and Cost
Modes. The capabilities of an ALTO Server URI providing this
resource are defined by a JSON Object of type CostMapCapability:
object {
CostMode cost-modes<0..*>;
CostType cost-types<0..*>;
} CostMapCapability;
with members:
cost-modes The Cost Modes ( Section 5.1.2) supported by the
corresponding URI. If not present, this member MUST be
interpreted as an empty array.
cost-types The Cost Types ( Section 5.1.1) supported by the
corresponding URI. If not present, this member MUST be
interpreted as an empty array.
An ALTO Server MUST support all of the Cost Types listed here for
each of the listed Cost Modes. Note that an ALTO Server may provide
multiple Cost Map Information Resources, each with different
capabilities.
7.7.1.2.5. Response
The returned InfoResourceEntity object has "data" member of type
InfoResourceCostMap:
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object DstCosts {
JSONValue [PIDName];
...
};
object {
DstCosts [PIDName]<0..*>;
...
} CostMapData;
object {
CostMode cost-mode;
CostType cost-type;
VersionTag map-vtag;
CostMapData map;
} InfoResourceCostMap;
with members:
cost-mode Cost Mode (Section 5.1.2) used in the Cost Map.
cost-type Cost Type (Section 5.1.1) used in the Cost Map.
map-vtag The Version Tag (Section 5.3) of the Network Map used to
generate the Cost Map.
map The Cost Map data itself.
CostMapData is a JSON object with each member representing a single
Source PID; the name for a member is the PIDName string identifying
the corresponding Source PID. For each Source PID, a DstCosts object
denotes the associated cost to a set of destination PIDs (
Section 5.2); the name for each member in the object is the PIDName
string identifying the corresponding Destination PID. An
implementation of the protocol in this document SHOULD assume that
the cost is a JSONNumber and fail to parse if it is not, unless the
implementation is using an extensions to this document that indicates
when and how costs of other data types are signaled.
The returned Cost Map MUST include the Path Cost for each (Source
PID, Destination PID) pair for which a Path Cost is defined. An ALTO
Server MAY omit entries for which a Path Cost is not defined (e.g.,
both the Source and Destination PIDs contain addresses outside of the
Network Provider's administrative domain).
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7.7.1.2.6. Example
GET /costmap/num/routingcost HTTP/1.1
Host: alto.example.com
Accept: application/alto-costmap+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {},
"data" : {
"cost-mode" : "numerical",
"cost-type" : "routingcost",
"map-vtag" : "1266506139",
"map" : {
"PID1": { "PID1": 1, "PID2": 5, "PID3": 10 },
"PID2": { "PID1": 5, "PID2": 1, "PID3": 15 },
"PID3": { "PID1": 20, "PID2": 15 }
}
}
}
7.7.2. Map Filtering Service
The Map Filtering Service allows ALTO Clients to specify filtering
criteria to return a subset of the full maps available in the Map
Service.
7.7.2.1. Filtered Network Map
A Filtered Network Map is a Network Map Information Resource
(Section 7.7.1.1) for which an ALTO Client may supply a list of PIDs
to be included. A Filtered Network Map MAY be provided by an ALTO
Server.
7.7.2.1.1. Media Type
See Section 7.7.1.1.1.
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7.7.2.1.2. HTTP Method
This resource is requested using the HTTP POST method.
7.7.2.1.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies the input parameters with a data format
indicated by the media type "application/alto-networkmapfilter+json",
which is a JSON Object of type ReqFilteredNetworkMap, where:
object {
PIDName pids<0..*>;
AddressType address-types<0..*>;
} ReqFilteredNetworkMap;
with members:
pids Specifies list of PIDs to be included in the returned Filtered
Network Map. If the list of PIDs is empty, the ALTO Server MUST
interpret the list as if it contained a list of all currently-
defined PIDs. The ALTO Server MUST interpret entries appearing
multiple times as if they appeared only once.
address-types Specifies list of address types to be included in the
returned Filtered Network Map. If the list of address types is
empty, the ALTO Server MUST interpret the list as if it contained
a list of all address types known to the ALTO Server. The ALTO
Server MUST interpret entries appearing multiple times as if they
appeared only once.
7.7.2.1.4. Capabilities
None.
7.7.2.1.5. Response
See Section 7.7.1.1.5 for the format.
The ALTO Server MUST only include PIDs in the response that were
specified (implicitly or explicitly) in the request. If the input
parameters contain a PID name that is not currently defined by the
ALTO Server, the ALTO Server MUST behave as if the PID did not appear
in the input parameters. Similarly, the ALTO Server MUST only
enumerate addresses within each PID that have types which were
specified (implicitly or explicitly) in the request. If the input
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parameters contain an address type that is not currently known to the
ALTO Server, the ALTO Server MUST behave as if the address type did
not appear in the input parameters.
7.7.2.1.6. Example
POST /networkmap/filtered HTTP/1.1
Host: custom.alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-networkmapfilter+json
Accept: application/alto-networkmap+json,application/alto-error+json
{
"pids": [ "PID1", "PID2" ]
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-networkmap+json
{
"meta" : {},
"data" : {
"map-vtag" : "1266506139",
"map" : {
"PID1" : {
"ipv4" : [
"192.0.2.0/24",
"198.51.100.0/24"
]
},
"PID2" : {
"ipv4": [
"198.51.100.128/24"
]
}
}
}
}
7.7.2.2. Filtered Cost Map
A Filtered Cost Map is a Cost Map Information Resource
(Section 7.7.1.2) for which an ALTO Client may supply additional
parameters limiting the scope of the resulting Cost Map. A Filtered
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Cost Map MAY be provided by an ALTO Server.
7.7.2.2.1. Media Type
See Section 7.7.1.2.1.
7.7.2.2.2. HTTP Method
This resource is requested using the HTTP POST method.
7.7.2.2.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies the input parameters with a data format
indicated by the media type "application/alto-costmapfilter+json",
which is a JSON Object of type ReqFilteredCostMap, where:
object {
PIDName srcs<0..*>;
PIDName dsts<0..*>;
} PIDFilter;
object {
CostMode cost-mode;
CostType cost-type;
JSONString constraints<0..*>; [OPTIONAL]
PIDFilter pids; [OPTIONAL]
} ReqFilteredCostMap;
with members:
cost-type The Cost Type ( Section 5.1.1) for the returned costs.
This MUST be one of the supported Cost Types indicated in this
resource's capabilities ( Section 7.7.2.2.4).
cost-mode The Cost Mode ( Section 5.1.2) for the returned costs.
This MUST be one of the supported Cost Modes indicated in this
resource's capabilities ( Section 7.7.2.2.4).
constraints Defines a list of additional constraints on which
elements of the Cost Map are returned. This parameter MUST NOT be
specified if this resource's capabilities ( Section 7.7.2.2.4)
indicate that constraint support is not available. A constraint
contains two entities separated by whitespace: (1) an operator,
'gt' for greater than, 'lt' for less than, 'ge' for greater than
or equal to, 'le' for less than or equal to, or 'eq' for equal to
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(2) a target numerical cost. The numerical cost is a number that
MUST be defined in the same units as the Cost Type indicated by
the cost-type parameter. ALTO Servers SHOULD use at least IEEE
754 double-precision floating point [IEEE.754.2008] to store the
numerical cost, and SHOULD perform internal computations using
double-precision floating-point arithmetic. If multiple
'constraint' parameters are specified, they are interpreted as
being related to each other with a logical AND.
pids A list of Source PIDs and a list of Destination PIDs for which
Path Costs are to be returned. If a list is empty, the ALTO
Server MUST interpret it as the full set of currently-defined
PIDs. The ALTO Server MUST interpret entries appearing in a list
multiple times as if they appeared only once. If the "pids"
member is not present, both lists MUST be interpreted by the ALTO
Server as containing the full set of currently-defined PIDs.
7.7.2.2.4. Capabilities
The URI providing this resource supports all capabilities documented
in Section 7.7.1.2.4 (with identical semantics), plus additional
capabilities. In particular, the capabilities are defined by a JSON
object of type FilteredCostMapCapability:
object {
CostMode cost-modes<0..*>;
CostType cost-types<0..*>;
JSONBool cost-constraints;
} FilteredCostMapCapability;
with members:
cost-modes See Section 7.7.1.2.4.
cost-types See Section 7.7.1.2.4.
cost-constraints If true, then the ALTO Server allows cost
constraints to be included in requests to the corresponding URI.
If not present, this member MUST be interpreted as if it specified
false. ALTO Clients should be aware that constraints may not have
the intended effect for cost maps with the 'ordinal' Cost Mode
since ordinal costs are not restricted to being sequential
integers.
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7.7.2.2.5. Response
See Section 7.7.1.2.5 for the format.
The returned Cost Map MUST NOT contain any source/destination pair
that was not indicated (implicitly or explicitly) in the input
parameters. If the input parameters contain a PID name that is not
currently defined by the ALTO Server, the ALTO Server MUST behave as
if the PID did not appear in the input parameters.
If any constraints are specified, Source/Destination pairs for which
the Path Costs do not meet the constraints MUST NOT be included in
the returned Cost Map. If no constraints were specified, then all
Path Costs are assumed to meet the constraints.
Note that ALTO Clients should verify that the Version Tag included in
the response is consistent with the Version Tag of the Network Map
used to generate the request (if applicable). If it is not, the ALTO
Client may wish to request an updated Network Map, identify changes,
and consider requesting a new Filtered Cost Map.
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7.7.2.2.6. Example
POST /costmap/filtered HTTP/1.1
Host: custom.alto.example.com
Content-Type: application/alto-costmapfilter+json
Accept: application/alto-costmap+json,application/alto-error+json
{
"cost-mode" : "numerical",
"cost-type" : "routingcost",
"pids" : {
"srcs" : [ "PID1" ],
"dsts" : [ "PID1", "PID2", "PID3" ]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {},
"data" : {
"cost-mode" : "numerical",
"cost-type" : "routingcost",
"map-vtag" : "1266506139",
"map" : {
"PID1": { "PID1": 0, "PID2": 1, "PID3": 2 }
}
}
}
7.7.3. Endpoint Property Service
The Endpoint Property Service provides information about Endpoint
properties to ALTO Clients.
7.7.3.1. Endpoint Property
The Endpoint Property resource provides information about properties
for individual endpoints. It MAY be provided by an ALTO Server. If
an ALTO Server provides the Endpoint Property resource, it MUST
provide and define at least the 'pid' property for each Endpoint.
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7.7.3.1.1. Media Type
The media type is "application/alto-endpointprop+json".
7.7.3.1.2. HTTP Method
This resource is requested using the HTTP POST method.
7.7.3.1.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies the data format of input parameteres with the
media type "application/alto-endpointpropparams+json", which is a
JSON Object of type ReqEndpointProp:
object {
EndpointProperty properties<1..*>;
TypedEndpointAddr endpoints<1..*>;
} ReqEndpointProp;
with members:
properties List of endpoint properties to returned for each
endpoint. Each specified property MUST be included in the list of
supported properties indicated by this resource's capabilities (
Section 7.7.3.1.4). The ALTO Server MUST interpret entries
appearing multiple times as if they appeared only once.
endpoints List of endpoint addresses for which the specified
properties are to be returned. The ALTO Server MUST interpret
entries appearing multiple times as if they appeared only once.
7.7.3.1.4. Capabilities
This resource may be defined across multiple types of endpoint
properties. The capabilities of an ALTO Server URI providing
Endpoint Properties are defined by a JSON Object of type
EndpointPropertyCapability:
object {
EndpointProperty prop-types<0..*>;
} EndpointPropertyCapability;
with members:
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prop-types The Endpoint Property Types ( Section 3.1.3) supported by
the corresponding URI. If not present, this member MUST be
interpreted as an empty array.
7.7.3.1.5. Response
The returned InfoResourceEntity object has "data" member of type
InfoResourceEndpointProperty, where:
object {
JSONString [EndpointProperty];
...
} EndpointProps;
object {
VersionTag map-vtag; [OPTIONAL]
EndpointProps [TypedEndpointAddr]<0..*>;
...
} InfoResourceEndpointProperty;
InfoResourceEndpointProperty has one member for each endpoint
indicated in the input parameters (with the name being the endpoint
encoded as a TypedEndpointAddr). The requested properties for each
endpoint are encoded in a corresponding EndpointProps object, which
encodes one name/value pair for each requested property, where the
property names are encoded as strings of type EndpointProperty and
the property values encoded as JSON Strings.
The ALTO Server returns the value for each of the requested endpoint
properties for each of the endpoints listed in the input parameters.
If the ALTO Server does not define a requested property for a
particular endpoint, then it MUST omit it from the response for only
that endpoint.
The ALTO Server MAY include the Version Tag (Section 5.3) of the
Network Map used to generate the response (if desired and applicable)
as the 'map-vtag' member in the response. If the 'pid' property is
returned for any endpoints in the response, the 'map-vtag' member is
REQUIRED instead of OPTIONAL.
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7.7.3.1.6. Example
POST /endpointprop/lookup HTTP/1.1
Host: alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-endpointpropparams+json
Accept: application/alto-endpointprop+json,application/alto-error+json
{
"properties" : [ "pid" ],
"endpoints" : [ "ipv4:192.0.2.34", "ipv4:203.0.113.129" ]
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-endpointprop+json
{
"meta" : {},
"data": {
"ipv4:192.0.2.34" : { "pid": "PID1" },
"ipv4:203.0.113.129" : { "pid": "PID3" }
}
}
7.7.4. Endpoint Cost Service
The Endpoint Cost Service provides information about costs between
individual endpoints.
In particular, this service allows lists of Endpoint prefixes (and
addresses, as a special case) to be ranked (ordered) by an ALTO
Server.
7.7.4.1. Endpoint Cost
The Endpoint Cost resource provides information about costs between
individual endpoints. It MAY be provided by an ALTO Server.
It is important to note that although this resource allows an ALTO
Server to reveal costs between individual endpoints, an ALTO Server
is not required to do so. A simple alternative would be to compute
the cost between two endpoints as the cost between the PIDs
corresponding to the endpoints. See Section 11.1 for additional
details.
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7.7.4.1.1. Media Type
The media type is "application/alto-endpointcost+json".
7.7.4.1.2. HTTP Method
This resource is requested using the HTTP POST method.
7.7.4.1.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies input parameters with a data format indicated
by media type "application/alto-endpointcostparams+json", which is a
JSON Object of type ReqEndpointCostMap:
object {
TypedEndpointAddr srcs<0..*>; [OPTIONAL]
TypedEndpointAddr dsts<1..*>;
} EndpointFilter;
object {
CostMode cost-mode;
CostType cost-type;
JSONString constraints; [OPTIONAL]
EndpointFilter endpoints;
} ReqEndpointCostMap;
with members:
cost-mode The Cost Mode ( Section 5.1.2) to use for returned costs.
This MUST be one of the Cost Modes indicated in this resource's
capabilities ( Section 7.7.4.1.4).
cost-type The Cost Type ( Section 5.1.1) to use for returned costs.
This MUST be one of the Cost Types indicated in this resource's
capabilities ( Section 7.7.4.1.4).
constraints Defined equivalently to the "constraints" input
parameter of a Filtered Cost Map (see Section 7.7.2.2).
endpoints A list of Source Endpoints and Destination Endpoints for
which Path Costs are to be returned. If the list of Source
Endpoints is empty (or not included), the ALTO Server MUST
interpret it as if it contained the Endpoint Address corresponding
to the client IP address from the incoming connection (see
Section 9.3 for discussion and considerations regarding this
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mode). The list of destination Endpoints MUST NOT be empty. The
ALTO Server MUST interpret entries appearing multiple times in a
list as if they appeared only once.
7.7.4.1.4. Capabilities
See Section 7.7.2.2.4.
7.7.4.1.5. Response
The returned InfoResourceEntity object has "data" member equal to
InfoResourceEndpointCostMap, where:
object EndpointDstCosts {
JSONValue [TypedEndpointAddr];
...
};
object {
EndpointDstCosts [TypedEndpointAddr]<0..*>;
...
} EndpointCostMapData;
object {
CostMode cost-mode;
CostType cost-type;
EndpointCostMapData map;
} InfoResourceEndpointCostMap;
InfoResourceEndpointCostMap has members:
cost-mode The Cost Mode used in the returned Cost Map.
cost-type The Cost Type used in the returned Cost Map.
map The Endpoint Cost Map data itself.
EndpointCostMapData is a JSON object with each member representing a
single Source Endpoint specified in the input parameters; the name
for a member is the TypedEndpointAddr string identifying the
corresponding Source Endpoint. For each Source Endpoint, a
EndpointDstCosts object denotes the associated cost to each
Destination Endpoint specified in the input parameters; the name for
each member in the object is the TypedEndpointAddr string identifying
the corresponding Destination Endpoint. An implementation of the
protocol in this document SHOULD assume that the cost is a JSONNumber
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and fail to parse if it is not, unless the implementation is using an
extensions to this document that indicates when and how costs of
other data types are signaled. If the ALTO Server does not define a
cost from a Source Endpoint to a particular Destination Endpoint, it
MAY be omitted from the response.
7.7.4.1.6. Example
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-endpointcostparams+json
Accept: application/alto-endpointcost+json,application/alto-error+json
{
"cost-mode" : "ordinal",
"cost-type" : "routingcost",
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv4:203.0.113.45"
]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-endpointcost+json
{
"meta" : {},
"data" : {
"cost-mode" : "ordinal",
"cost-type" : "routingcost",
"map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 1,
"ipv4:198.51.100.34" : 2,
"ipv4:203.0.113.45" : 3
}
}
}
}
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8. Use Cases
The sections below depict typical use cases.
8.1. ALTO Client Embedded in P2P Tracker
Many P2P currently-deployed P2P systems use a Tracker to manage
swarms and perform peer selection. P2P trackers may currently use a
variety of information to perform peer selection to meet application-
specific goals. By acting as an ALTO Client, an P2P tracker can use
ALTO information as an additional information source to enable more
network-efficient traffic patterns and improve application
performance.
A particular requirement of many P2P trackers is that they must
handle a large number of P2P clients. A P2P tracker can obtain and
locally store ALTO information (the Network Map and Cost Map) from
the ISPs containing the P2P clients, and benefit from the same
aggregation of network locations done by ALTO Servers.
.---------. (1) Get Network Map .---------------.
| | <----------------------> | |
| ALTO | | P2P Tracker |
| Server | (2) Get Cost Map | (ALTO Client) |
| | <----------------------> | |
`---------' `---------------'
^ |
(3) Get Peers | | (4) Selected Peer
| v List
.---------. .-----------.
| Peer 1 | <-------------- | P2P |
`---------' | Client |
. (5) Connect to `-----------'
. Selected Peers /
.---------. /
| Peer 50 | <------------------
`---------'
Figure 4: ALTO Client Embedded in P2P Tracker
Figure 4 shows an example use case where a P2P tracker is an ALTO
Client and applies ALTO information when selecting peers for its P2P
clients. The example proceeds as follows:
1. The P2P Tracker requests the Network Map covering all PIDs from
the ALTO Server using the Network Map query. The Network Map
includes the IP prefixes contained in each PID, allowing the P2P
tracker to locally map P2P clients into a PIDs.
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2. The P2P Tracker requests the Cost Map amongst all PIDs from the
ALTO Server.
3. A P2P Client joins the swarm, and requests a peer list from the
P2P Tracker.
4. The P2P Tracker returns a peer list to the P2P client. The
returned peer list is computed based on the Network Map and Cost
Map returned by the ALTO Server, and possibly other information
sources. Note that it is possible that a tracker may use only
the Network Map to implement hierarchical peer selection by
preferring peers within the same PID and ISP.
5. The P2P Client connects to the selected peers.
Note that the P2P tracker may provide peer lists to P2P clients
distributed across multiple ISPs. In such a case, the P2P tracker
may communicate with multiple ALTO Servers.
8.2. ALTO Client Embedded in P2P Client: Numerical Costs
P2P clients may also utilize ALTO information themselves when
selecting from available peers. It is important to note that not all
P2P systems use a P2P tracker for peer discovery and selection.
Furthermore, even when a P2P tracker is used, the P2P clients may
rely on other sources, such as peer exchange and DHTs, to discover
peers.
When an P2P Client uses ALTO information, it typically queries only
the ALTO Server servicing its own ISP. The my-Internet view provided
by its ISP's ALTO Server can include preferences to all potential
peers.
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.---------. (1) Get Network Map .---------------.
| | <----------------------> | |
| ALTO | | P2P Client |
| Server | (2) Get Cost Map | (ALTO Client) |
| | <----------------------> | | .---------.
`---------' `---------------' <- | P2P |
.---------. / | ^ ^ | Tracker |
| Peer 1 | <-------------- | | \ `---------'
`---------' | (3) Gather Peers
. (4) Select Peers | | \
. and Connect / .--------. .--------.
.---------. / | P2P | | DHT |
| Peer 50 | <---------------- | Client | `--------'
`---------' | (PEX) |
`--------'
Figure 5: ALTO Client Embedded in P2P Client
Figure 5 shows an example use case where a P2P Client locally applies
ALTO information to select peers. The use case proceeds as follows:
1. The P2P Client requests the Network Map covering all PIDs from
the ALTO Server servicing its own ISP.
2. The P2P Client requests the Cost Map amongst all PIDs from the
ALTO Server. The Cost Map by default specifies numerical costs.
3. The P2P Client discovers peers from sources such as Peer Exchange
(PEX) from other P2P Clients, Distributed Hash Tables (DHT), and
P2P Trackers.
4. The P2P Client uses ALTO information as part of the algorithm for
selecting new peers, and connects to the selected peers.
8.3. ALTO Client Embedded in P2P Client: Ranking
It is also possible for a P2P Client to offload the selection and
ranking process to an ALTO Server. In this use case, the ALTO Client
gathers a list of known peers in the swarm, and asks the ALTO Server
to rank them.
As in the use case using numerical costs, the P2P Client typically
only queries the ALTO Server servicing its own ISP.
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.---------. .---------------.
| | | |
| ALTO | (2) Get Endpoint Ranking | P2P Client |
| Server | <----------------------> | (ALTO Client) |
| | | | .---------.
`---------' `---------------' <- | P2P |
.---------. / | ^ ^ | Tracker |
| Peer 1 | <-------------- | | \ `---------'
`---------' | (1) Gather Peers
. (3) Connect to | | \
. Selected Peers / .--------. .--------.
.---------. / | P2P | | DHT |
| Peer 50 | <---------------- | Client | `--------'
`---------' | (PEX) |
`--------'
Figure 6: ALTO Client Embedded in P2P Client: Ranking
Figure 6 shows an example of this scenario. The use case proceeds as
follows:
1. The P2P Client discovers peers from sources such as Peer Exchange
(PEX) from other P2P Clients, Distributed Hash Tables (DHT), and
P2P Trackers.
2. The P2P Client queries the ALTO Server's Ranking Service,
including discovered peers as the set of Destination Endpoints,
and indicates the 'ordinal' Cost Mode. The response indicates
the ranking of the candidate peers.
3. The P2P Client connects to the peers in the order specified in
the ranking.
9. Discussions
9.1. Discovery
The discovery mechanism by which an ALTO Client locates an
appropriate ALTO Server is out of scope for this document. This
document assumes that an ALTO Client can discover an appropriate ALTO
Server. Once it has done so, the ALTO Client may use the Information
Resource Directory (see Section 7.6) to locate an Information
Resource with the desired ALTO Information.
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9.2. Hosts with Multiple Endpoint Addresses
In practical deployments, especially during the transition from IPv4
to IPv6, a particular host may be reachable using multiple addresses.
Furthermore, the particular network path followed when sending
packets to the host may differ based on the address that is used.
Network providers may prefer one path over another (e.g., one path my
have a NAT64 middlebox). An additional consideration may be how to
handle private address spaces (e.g., behind carrier-grade NATs).
To support such behavior, this document allows multiple types of
endpoint addresses. In supporting multiple address types, the ALTO
Protocol also allows ALTO Service Provider the flexibility to
indicate preferences for paths from an endpoint address of one type
to an endpoint address of a different type. Note that in general,
the path through the network may differ dependent on the types of
addresses that are used.
Note that there are limitations as to what information ALTO can
provide in this regard. In particular, a particular ALTO Service
provider may not be able to determine if connectivity with a
particular endhost will succeed over IPv4 or IPv6, as this may depend
upon information unknown to the ISP such as particular application
implementations.
9.3. Network Address Translation Considerations
At this day and age of NAT v4<->v4, v4<->v6 [RFC6144], and possibly
v6<->v6[I-D.mrw-nat66], a protocol should strive to be NAT friendly
and minimize carrying IP addresses in the payload, or provide a mode
of operation where the source IP address provide the information
necessary to the server.
The protocol specified in this document provides a mode of operation
where the source network location is computed by the ALTO Server
(i.e., the the Endpoint Cost Service) from the source IP address
found in the ALTO Client query packets. This is similar to how some
P2P Trackers (e.g., BitTorrent Trackers - see "Tracker HTTP/HTTPS
Protocol" in [BitTorrent]) operate.
The ALTO client SHOULD use the Session Traversal Utilities for NAT
(STUN) [RFC5389] to determine a public IP address to use as a source
Endpoint address. If using this method, the host MUST use the
"Binding Request" message and the resulting "XOR-MAPPED-ADDRESS"
parameter that is returned in the response. Using STUN requires
cooperation from a publicly accessible STUN server. Thus, the ALTO
client also requires configuration information that identifies the
STUN server, or a domain name that can be used for STUN server
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discovery. To be selected for this purpose, the STUN server needs to
provide the public reflexive transport address of the host.
9.4. Mapping IPs to ASNs
It may be desired for the ALTO Protocol to provide ALTO information
including ASNs. Thus, ALTO Clients may need to identify the ASN for
a Resource Provider to determine the cost to that Resource Provider.
Applications can already map IPs to ASNs using information from a BGP
Looking Glass. To do so, they must download a file of about 1.5MB
when compressed (as of October 2008, with all information not needed
for IP to ASN mapping removed) and periodically (perhaps monthly)
refresh it.
Alternatively, the Network Map query in the Map Filtering Service
defined in this document could be extended to map ASNs into a set of
IP prefixes. The mappings provided by the ISP would be both smaller
and more authoritative.
For simplicity of implementation, it's highly desirable that clients
only have to implement exactly one mechanism of mapping IPs to ASNs.
9.5. Endpoint and Path Properties
An ALTO Server could make available many properties about Endpoints
beyond their network location or grouping. For example, connection
type, geographical location, and others may be useful to
applications. This specification focuses on network location and
grouping, but the protocol may be extended to handle other Endpoint
properties.
10. IANA Considerations
10.1. application/alto-* Media Types
This document requests the registration of multiple media types,
listed in Table 2.
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+-------------+------------------------------+-----------------+
| Type | Subtype | Specification |
+-------------+------------------------------+-----------------+
| application | alto-directory+json | Section 7.6 |
| application | alto-networkmap+json | Section 7.7.1.1 |
| application | alto-networkmapfilter+json | Section 7.7.2.1 |
| application | alto-costmap+json | Section 7.7.1.2 |
| application | alto-costmapfilter+json | Section 7.7.2.2 |
| application | alto-endpointprop+json | Section 7.7.3.1 |
| application | alto-endpointpropparams+json | Section 7.7.3.1 |
| application | alto-endpointcost+json | Section 7.7.4.1 |
| application | alto-endpointcostparams+json | Section 7.7.4.1 |
| application | alto-error+json | Section 7.4 |
+-------------+------------------------------+-----------------+
Table 2: ALTO Protocol Media Types
Type name: application
Subtype name: This documents requests the registration of multiple
subtypes, as listed in Table 2.
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: Encoding considerations are identical to
those specified for the 'application/json' media type. See
[RFC4627].
Security considerations: Security considerations relating to the
generation and consumption of ALTO protocol messages are discussed
in Section 11.
Interoperability considerations: This document specifies format of
conforming messages and the interpretation thereof.
Published specification: This document is the specification for
these media types; see Table 2for the section documenting each
media type.
Applications that use this media type: ALTO Servers and ALTO Clients
either standalone or embedded within other applications.
Additional information:
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Magic number(s): n/a
File extension(s): This document uses the mime type to refer to
protocol messages and thus does not require a file extension.
Macintosh file type code(s): n/a
Person & email address to contact for further information: See
"Authors' Addresses" section.
Intended usage: COMMON
Restrictions on usage: n/a
Author: See "Authors' Addresses" section.
Change controller: See "Authors' Addresses" section.
10.2. ALTO Cost Type Registry
This document requests the creation of an ALTO Cost Type registry to
be maintained by IANA.
This registry serves two purposes. First, it ensures uniqueness of
identifiers referring to ALTO Cost Types. Second, it provides
references to particular semantics of allocated Cost Types to be
applied by both ALTO Servers and applications utilizing ALTO Clients.
New ALTO Cost Types are assigned after Expert Review [RFC5226]. The
Expert Reviewer will generally consult the ALTO Working Group or its
successor. Expert Review is used to ensure that proper documentation
regarding ALTO Cost Type semantics and security considerations has
been provided. The provided documentation should be detailed enough
to provide guidance to both ALTO Service Providers and applications
utilizing ALTO Clients as to how values of the registered ALTO Cost
Type should be interpreted. Updates and deletions of ALTO Cost Types
follow the same procedure.
Registered ALTO Cost Type identifiers MUST conform to the syntatical
requirements specified in Section 7.5.5. Identifiers are to be
recorded and displayed as ASCII strings.
Identifiers prefixed with 'priv:' are reserved for Private Use.
Identifiers prefixed with 'exp:' are reserved for Experimental use.
Requests to add a new value to the registry MUST include the
following information:
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o Identifier: The name of the desired ALTO Cost Type.
o Intended Semantics: ALTO Costs carry with them semantics to guide
their usage by ALTO Clients. For example, if a value refers to a
measurement, the measurement units must be documented. For proper
implementation of the ordinal Cost Mode (e.g., by a third-party
service), it should be documented whether higher or lower values
of the cost are more preferred.
o Security Considerations: ALTO Costs expose information to ALTO
Clients. As such, proper usage of a particular Cost Type may
require certain information to be exposed by an ALTO Service
Provider. Since network information is frequently regarded as
proprietary or confidential, ALTO Service Providers should be made
aware of the security ramifications related to usage of a Cost
Type.
This specification requests registration of the identifier
'routingcost'. Semantics for the this Cost Type are documented in
Section 5.1.1.1, and security considerations are documented in
Section 11.1.
10.3. ALTO Endpoint Property Registry
This document requests the creation of an ALTO Endpoint Property
registry to be maintained by IANA.
This registry serves two purposes. First, it ensures uniqueness of
identifiers referring to ALTO Endpoint Properties. Second, it
provides references to particular semantics of allocated Endpoint
Properties to be applied by both ALTO Servers and applications
utilizing ALTO Clients.
New ALTO Endpoint Properties are assigned after Expert Review
[RFC5226]. The Expert Reviewer will generally consult the ALTO
Working Group or its successor. Expert Review is used to ensure that
proper documentation regarding ALTO Endpoint Property semantics and
security considerations has been provided. The provided
documentation should be detailed enough to provide guidance to both
ALTO Service Providers and applications utilizing ALTO Clients as to
how values of the registered ALTO Endpoint Properties should be
interpreted. Updates and deletions of ALTO Endpoint Properties
follow the same procedure.
Registered ALTO Endpoint Property identifiers MUST conform to the
syntatical requirements specified in Section 7.5.6. Identifiers are
to be recorded and displayed as ASCII strings.
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Identifiers prefixed with 'priv:' are reserved for Private Use.
Identifiers prefixed with 'exp:' are reserved for Experimental use.
Requests to add a new value to the registry MUST include the
following information:
o Identifier: The name of the desired ALTO Endpoint Property.
o Intended Semantics: ALTO Endpoint Properties carry with them
semantics to guide their usage by ALTO Clients. For example, if a
value refers to a measurement, the measurement units must be
documented. For proper implementation of the ordinal Cost Mode
(e.g., by a third-party service), it should be documented whether
higher or lower values of the cost are more preferred.
o Security Considerations: ALTO Endpoint Properties expose
information to ALTO Clients. As such, proper usage of a
particular Endpoint Properties may require certain information to
be exposed by an ALTO Service Provider. Since network information
is frequently regarded as proprietary or confidential, ALTO
Service Providers should be made aware of the security
ramifications related to usage of an Endpoint Property.
This specification requests registration of the identifier 'pid'.
Semantics for the this Endpoint Property are documented in
Section 4.1, and security considerations are documented in
Section 11.1.
11. Security Considerations
11.1. Privacy Considerations for ISPs
ISPs must be cognizant of the network topology and provisioning
information provided through ALTO Interfaces. ISPs should evaluate
how much information is revealed and the associated risks. On the
one hand, providing overly fine-grained information may make it
easier for attackers to infer network topology. In particular,
attackers may try to infer details regarding ISPs' operational
policies or inter-ISP business relationships by intentionally posting
a multitude of selective queries to an ALTO server and analyzing the
responses. Such sophisticated attacks may reveal more information
than an ISP hosting an ALTO server intends to disclose. On the other
hand, revealing overly coarse-grained information may not provide
benefits to network efficiency or performance improvements to ALTO
Clients.
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11.2. ALTO Clients
Applications using the information must be cognizant of the
possibility that the information is malformed or incorrect. Even if
an ALTO Server has been properly authenticated by the ALTO Client,
the information provided may be malicious because the ALTO Server and
its credentials have been compromised (e.g., through malware). Other
considerations (e.g., relating to application performance) can be
found in Section 6 of [RFC5693].
ALTO Clients should also be cognizant of revealing Network Location
Identifiers (IP addresses or fine-grained PIDs) to the ALTO Server,
as doing so may allow the ALTO Server to infer communication
patterns. One possibility is for the ALTO Client to only rely on
Network Map for PIDs and Cost Map amongst PIDs to avoid passing IP
addresses of their peers to the ALTO Server.
In addition, ALTO clients should be cautious not to unintentionally
or indirectly disclose the resource identifier (of which they try to
improve the retrieval through ALTO-guidance), e.g., the name/
identifier of a certain video stream in P2P live streaming, to the
ALTO server. Note that the ALTO Protocol specified in this document
does not explicitly reveal any resource identifier to the ALTO
Server. However, for instance, depending on the popularity or other
specifics (such as language) of the resource, an ALTO server could
potentially deduce information about the desired resource from
information such as the Network Locations the client sends as part of
its request to the server.
11.3. Authentication, Integrity Protection, and Encryption
SSL/TLS can provide encryption of transmitted messages as well as
authentication of the ALTO Client and Server. HTTP Basic or Digest
authentication can provide authentication of the client (combined
with SSL/TLS, it can additionally provide encryption and
authentication of the server).
An ALTO Server may optionally use authentication (and potentially
encryption) to protect ALTO information it provides. This can be
achieved by digitally signing a hash of the ALTO information itself
and attaching the signature to the ALTO information. There may be
special use cases where encryption of ALTO information is desirable.
In many cases, however, information sent out by an ALTO Server may be
regarded as non-confidential information.
ISPs should be cognizant that encryption only protects ALTO
information until it is decrypted by the intended ALTO Client.
Digital Rights Management (DRM) techniques and legal agreements
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protecting ALTO information are outside of the scope of this
document.
11.4. ALTO Information Redistribution
It is possible for applications to redistribute ALTO information to
improve scalability. Even with such a distribution scheme, ALTO
Clients obtaining ALTO information must be able to validate the
received ALTO information to ensure that it was generated by an
appropriate ALTO Server. Support for this validation is not provided
in this document, but may be provided by extension documents.
11.5. Denial of Service
ISPs should be cognizant of the workload at the ALTO Server generated
by certain ALTO Queries, such as certain queries to the Map Filtering
Service and Ranking Service. In particular, queries which can be
generated with low effort but result in expensive workloads at the
ALTO Server could be exploited for Denial-of-Service attacks. For
instance, a simple ALTO query with n Source Network Locations and m
Destination Network Locations can be generated fairly easily but
results in the computation of n*m Path Costs between pairs by the
ALTO Server (see Section 5.2). One way to limit Denial-of-Service
attacks is to employ access control to the ALTO server. Another
possible mechanism for an ALTO Server to protect itself against a
multitude of computationally expensive bogus requests is to demand
that each ALTO Client to solve a computational puzzle first before
allocating resources for answering a request (see, e.g.,
[I-D.jennings-sip-hashcash]). The current specification does not use
such computational puzzles, and discussion regarding tradeoffs of
such an approach would be needed before including such a technique in
the ALTO Protocol.
ISPs should also leverage the fact that the the Map Service allows
ALTO Servers to pre-generate maps that can be useful to many ALTO
Clients.
11.6. ALTO Server Access Control
In order to limit access to an ALTO server (e.g., for an ISP to only
allow its users to access its ALTO server, or to prevent Denial-of-
Service attacks by arbitrary hosts from the Internet), an ALTO server
may employ access control policies. Depending on the use-case and
scenario, an ALTO server may restrict access to its services more
strictly or rather openly (see [I-D.stiemerling-alto-deployments] for
a more detailed discussion on this issue).
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12. References
12.1. Normative References
[IEEE.754.2008]
Institute of Electrical and Electronics Engineers,
"Standard for Binary Floating-Point Arithmetic", IEEE
Standard 754, August 2008.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, August 2010.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
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12.2. Informative References
[BitTorrent]
"Bittorrent Protocol Specification v1.0",
<http://wiki.theory.org/BitTorrentSpecification>.
[I-D.akonjang-alto-proxidor]
Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D.
Saucez, "The PROXIDOR Service",
draft-akonjang-alto-proxidor-00 (work in progress),
March 2009.
[I-D.gu-alto-redistribution]
Yingjie, G., Alimi, R., and R. Even, "ALTO Information
Redistribution", draft-gu-alto-redistribution-03 (work in
progress), July 2010.
[I-D.ietf-alto-reqs]
Previdi, S., Stiemerling, M., Woundy, R., and Y. Yang,
"Application-Layer Traffic Optimization (ALTO)
Requirements", draft-ietf-alto-reqs-08 (work in progress),
March 2011.
[I-D.ietf-alto-server-discovery]
Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and
S. Yongchao, "ALTO Server Discovery",
draft-ietf-alto-server-discovery-03 (work in progress),
March 2012.
[I-D.jennings-sip-hashcash]
Jennings, C., "Computational Puzzles for SPAM Reduction in
SIP", draft-jennings-sip-hashcash-06 (work in progress),
July 2007.
[I-D.mrw-nat66]
Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", draft-mrw-nat66-16 (work in progress),
April 2011.
[I-D.p4p-framework]
Alimi, R., Pasko, D., Popkin, L., Wang, Y., and Y. Yang,
"P4P: Provider Portal for P2P Applications",
draft-p4p-framework-00 (work in progress), November 2008.
[I-D.saumitra-alto-multi-ps]
Das, S., Narayanan, V., and L. Dondeti, "ALTO: A Multi
Dimensional Peer Selection Problem",
draft-saumitra-alto-multi-ps-00 (work in progress),
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October 2008.
[I-D.saumitra-alto-queryresponse]
Das, S. and V. Narayanan, "A Client to Service Query
Response Protocol for ALTO",
draft-saumitra-alto-queryresponse-00 (work in progress),
March 2009.
[I-D.shalunov-alto-infoexport]
Shalunov, S., Penno, R., and R. Woundy, "ALTO Information
Export Service", draft-shalunov-alto-infoexport-00 (work
in progress), October 2008.
[I-D.stiemerling-alto-deployments]
Stiemerling, M. and S. Kiesel, "ALTO Deployment
Considerations", draft-stiemerling-alto-deployments-06
(work in progress), January 2011.
[I-D.wang-alto-p4p-specification]
Wang, Y., Alimi, R., Pasko, D., Popkin, L., and Y. Yang,
"P4P Protocol Specification",
draft-wang-alto-p4p-specification-00 (work in progress),
March 2009.
[P4P-SIGCOMM08]
Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A.
Silberschatz, "P4P: Provider Portal for (P2P)
Applications", SIGCOMM 2008, August 2008.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
Appendix A. Acknowledgments
Thank you to Jan Seedorf for contributions to the Security
Considerations section.
We would like to thank the following people whose input and
involvement was indispensable in achieving this merged proposal:
Obi Akonjang (DT Labs/TU Berlin),
Alimi, et al. Expires September 12, 2012 [Page 66]
Internet-Draft ALTO Protocol March 2012
Saumitra M. Das (Qualcomm Inc.),
Syon Ding (China Telecom),
Doug Pasko (Verizon),
Laird Popkin (Pando Networks),
Satish Raghunath (Juniper Networks),
Albert Tian (Ericsson/Redback),
Yu-Shun Wang (Microsoft),
David Zhang (PPLive),
Yunfei Zhang (China Mobile).
We would also like to thank the following additional people who were
involved in the projects that contributed to this merged document:
Alex Gerber (AT&T), Chris Griffiths (Comcast), Ramit Hora (Pando
Networks), Arvind Krishnamurthy (University of Washington), Marty
Lafferty (DCIA), Erran Li (Bell Labs), Jin Li (Microsoft), Y. Grace
Liu (IBM Watson), Jason Livingood (Comcast), Michael Merritt (AT&T),
Ingmar Poese (DT Labs/TU Berlin), James Royalty (Pando Networks),
Damien Saucez (UCL) Thomas Scholl (AT&T), Emilio Sepulveda
(Telefonica), Avi Silberschatz (Yale University), Hassan Sipra (Bell
Canada), Georgios Smaragdakis (DT Labs/TU Berlin), Haibin Song
(Huawei), Oliver Spatscheck (AT&T), See-Mong Tang (Microsoft), Jia
Wang (AT&T), Hao Wang (Yale University), Ye Wang (Yale University),
Haiyong Xie (Yale University).
Appendix B. Authors
[[CmtAuthors: RFC Editor: Please move information in this section to
the Authors' Addresses section at publication time.]]
Stefano Previdi
Cisco
Email: sprevidi@cisco.com
Stanislav Shalunov
BitTorrent
Email: shalunov@bittorrent.com
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Richard Woundy
Comcast
Richard_Woundy@cable.comcast.com
Authors' Addresses
Richard Alimi (editor)
Google
1600 Amphitheatre Parkway
Mountain View CA
USA
Email: ralimi@google.com
Reinaldo Penno (editor)
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale CA
USA
Email: rpenno@juniper.net
Y. Richard Yang (editor)
Yale University
51 Prospect St
New Haven CT
USA
Email: yry@cs.yale.edu
Alimi, et al. Expires September 12, 2012 [Page 68]