ALTO WG R. Alimi, Ed.
Internet-Draft Google
Intended status: Standards Track R. Penno, Ed.
Expires: April 28, 2011 Juniper Networks
Y. Yang, Ed.
Yale University
October 25, 2010
ALTO Protocol
draft-ietf-alto-protocol-06.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 information such as preferences of network
resources with the goal of modifying network resource consumption
patterns while maintaining or improving application performance.
This document describes a protocol implementing the ALTO Service.
While such 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 [1].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Alimi, et al. Expires April 28, 2011 [Page 1]
Internet-Draft ALTO Protocol October 2010
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 28, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Alimi, et al. Expires April 28, 2011 [Page 2]
Internet-Draft ALTO Protocol October 2010
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 . . . . . . . . . . . . . . . . . . . . 6
1.3.1. Service Providers . . . . . . . . . . . . . . . . . . 6
1.3.2. Applications . . . . . . . . . . . . . . . . . . . . . 7
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Endpoint Address . . . . . . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Server Information Service . . . . . . . . . . . . . . . . 10
3.2. ALTO Information Services . . . . . . . . . . . . . . . . 11
3.2.1. Map Service . . . . . . . . . . . . . . . . . . . . . 11
3.2.2. Map Filtering Service . . . . . . . . . . . . . . . . 11
3.2.3. Endpoint Property Service . . . . . . . . . . . . . . 11
3.2.4. Endpoint Cost Service . . . . . . . . . . . . . . . . 11
4. Network Map . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. PID . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Endpoint Addresses . . . . . . . . . . . . . . . . . . . . 13
4.2.1. IP Addresses . . . . . . . . . . . . . . . . . . . . . 13
4.3. Example Network Map . . . . . . . . . . . . . . . . . . . 13
5. Cost Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Cost Attributes . . . . . . . . . . . . . . . . . . . . . 14
5.1.1. Cost Type . . . . . . . . . . . . . . . . . . . . . . 14
5.1.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Cost Map Structure . . . . . . . . . . . . . . . . . . . . 15
5.3. Network Map and Cost Map Dependency . . . . . . . . . . . 16
6. Protocol Design Overview . . . . . . . . . . . . . . . . . . . 16
6.1. Existing Infrastructure . . . . . . . . . . . . . . . . . 17
6.2. ALTO Information Reuse and Redistribution . . . . . . . . 17
7. Protocol Messaging . . . . . . . . . . . . . . . . . . . . . . 18
7.1. Notation . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.2. Message Format . . . . . . . . . . . . . . . . . . . . . . 18
7.2.1. Protocol Versioning . . . . . . . . . . . . . . . . . 18
7.2.2. Content Type . . . . . . . . . . . . . . . . . . . . . 19
7.2.3. Request Message . . . . . . . . . . . . . . . . . . . 19
7.2.4. Response Message . . . . . . . . . . . . . . . . . . . 20
7.3. General Processing . . . . . . . . . . . . . . . . . . . . 22
7.4. ALTO Status Codes . . . . . . . . . . . . . . . . . . . . 22
7.5. Client Behavior . . . . . . . . . . . . . . . . . . . . . 23
7.5.1. Successful Response . . . . . . . . . . . . . . . . . 23
Alimi, et al. Expires April 28, 2011 [Page 3]
Internet-Draft ALTO Protocol October 2010
7.5.2. Error Conditions . . . . . . . . . . . . . . . . . . . 24
7.6. HTTP Usage . . . . . . . . . . . . . . . . . . . . . . . . 24
7.6.1. Authentication and Encryption . . . . . . . . . . . . 24
7.6.2. Cookies . . . . . . . . . . . . . . . . . . . . . . . 24
7.6.3. Caching Parameters . . . . . . . . . . . . . . . . . . 24
7.7. ALTO Types . . . . . . . . . . . . . . . . . . . . . . . . 24
7.7.1. PID Name . . . . . . . . . . . . . . . . . . . . . . . 24
7.7.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 25
7.7.3. Cost Type . . . . . . . . . . . . . . . . . . . . . . 25
7.8. ALTO Messages . . . . . . . . . . . . . . . . . . . . . . 25
7.8.1. Server Information Service . . . . . . . . . . . . . . 26
7.8.2. Map Service . . . . . . . . . . . . . . . . . . . . . 30
7.8.3. Map Filtering Service . . . . . . . . . . . . . . . . 34
7.8.4. Endpoint Property Service . . . . . . . . . . . . . . 38
7.8.5. Endpoint Cost Service . . . . . . . . . . . . . . . . 41
8. Redistributable Responses . . . . . . . . . . . . . . . . . . 43
8.1. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 43
8.1.1. Service ID . . . . . . . . . . . . . . . . . . . . . . 43
8.1.2. Expiration Time . . . . . . . . . . . . . . . . . . . 44
8.1.3. Signature . . . . . . . . . . . . . . . . . . . . . . 44
8.2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 46
8.2.1. Response Redistribution Descriptor Fields . . . . . . 47
8.2.2. Signature . . . . . . . . . . . . . . . . . . . . . . 48
9. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.1. ALTO Client Embedded in P2P Tracker . . . . . . . . . . . 48
9.2. ALTO Client Embedded in P2P Client: Numerical Costs . . . 50
9.3. ALTO Client Embedded in P2P Client: Ranking . . . . . . . 51
10. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 51
10.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 52
10.2. Hosts with Multiple Endpoint Addresses . . . . . . . . . . 52
10.3. Network Address Translation Considerations . . . . . . . . 52
10.4. Mapping IPs to ASNs . . . . . . . . . . . . . . . . . . . 53
10.5. Endpoint and Path Properties . . . . . . . . . . . . . . . 53
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 53
11.1. application/alto Media Type . . . . . . . . . . . . . . . 54
11.2. ALTO Cost Type Registry . . . . . . . . . . . . . . . . . 55
12. Security Considerations . . . . . . . . . . . . . . . . . . . 56
12.1. Privacy Considerations for ISPs . . . . . . . . . . . . . 56
12.2. ALTO Clients . . . . . . . . . . . . . . . . . . . . . . . 56
12.3. Authentication, Integrity Protection, and Encryption . . . 57
12.4. ALTO Information Redistribution . . . . . . . . . . . . . 57
12.5. Denial of Service . . . . . . . . . . . . . . . . . . . . 58
12.6. ALTO Server Access Control . . . . . . . . . . . . . . . . 58
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 59
13.1. Normative References . . . . . . . . . . . . . . . . . . . 59
13.2. Informative References . . . . . . . . . . . . . . . . . . 59
Appendix A. TO BE MOVED . . . . . . . . . . . . . . . . . . . . . 61
A.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 61
Alimi, et al. Expires April 28, 2011 [Page 4]
Internet-Draft ALTO Protocol October 2010
A.2. P2P Peer Selection . . . . . . . . . . . . . . . . . . . . 61
A.2.1. Client-based Peer Selection . . . . . . . . . . . . . 62
A.2.2. Server-based Peer Selection . . . . . . . . . . . . . 62
A.2.3. Location-Only Peer Selection . . . . . . . . . . . . . 62
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 63
Appendix C. Authors . . . . . . . . . . . . . . . . . . . . . . . 64
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 64
Alimi, et al. Expires April 28, 2011 [Page 5]
Internet-Draft ALTO Protocol October 2010
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's preferences to applications. By
leveraging better network-provided information, applications have the
potential to become more network-efficient (e.g., reduce network
resource consumption) and achieve better application performance
(e.g., accelerated download rate). The ALTO Service intends to
provide a simple way to convey network information to applications.
The goal of this document is to specify a simple and unified protocol
that meets the ALTO requirements [11] 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 [12], [13];
o ALTO Info-Export [14];
o Query/Response [15], [16];
o ATTP [ATTP];
o Proxidor [17].
See Appendix B for a list of people that have contributed
significantly to this effort and the projects and proposals listed
above.
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,
Alimi, et al. Expires April 28, 2011 [Page 6]
Internet-Draft ALTO Protocol October 2010
improve user-experience, amongst others. It also helps ISPs to
efficiently engineer 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. After an
introduction to the terminology, the ALTO architecture and the ALTO
Protocol's place in the overall architecture are defined.
2.1. Terminology
We use the following terms defined in [18]: 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, ASN,
and Network Location.
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.
Alimi, et al. Expires April 28, 2011 [Page 7]
Internet-Draft ALTO Protocol October 2010
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"
[19] of the network region. 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.
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.
Examples 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.
Alimi, et al. Expires April 28, 2011 [Page 8]
Internet-Draft ALTO Protocol October 2010
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.
+-------------------------------------------------------------------+
| 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.
Alimi, et al. Expires April 28, 2011 [Page 9]
Internet-Draft ALTO Protocol October 2010
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
provides the Server Information Service and the Map Service to
provide ALTO Information. 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 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 Info Services | |
| | | | .-----------. .----------. .----------. | |
| | | | | Map | | Endpoint | | Endpoint | | |
| | | | | Filtering | | Property | | Cost | | |
| | | | | Service | | Service | | Service | | |
| | Server | | `-----------' `----------' `----------' | |
| | Info | | .-------------------------------------. | |
| | Service | | | Map Service | | |
| | | | | .-------------. .--------------. | | |
| | | | | | Network Map | | Cost Map | | | |
| | | | | `-------------' `--------------' | | |
| | | | `-------------------------------------' | |
| `----------' `-----------------------------------------' |
| |
`------------------------------------------------------------'
Figure 2: ALTO Protocol Structure
3.1. Server Information Service
The Server Capability Service lists the details on the information
that can be provided by an ALTO Server and perhaps other ALTO Servers
maintained by the network provider. The configuration includes, for
example, details about the operations and cost metrics supported by
the ALTO Server and other related ALTO Servers that may be usable by
an ALTO Client. The capability document can be downloaded by ALTO
Clients. The capability information could also be provisioned to
devices, but care must be taken to update it appropriately.
Alimi, et al. Expires April 28, 2011 [Page 10]
Internet-Draft ALTO Protocol October 2010
3.2. 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.
3.2.1. Map Service
The Map Service provides batch information to ALTO Clients in the
form of a 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.
3.2.2. 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.
3.2.3. 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 FioS).
3.2.4. 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
Alimi, et al. Expires April 28, 2011 [Page 11]
Internet-Draft ALTO Protocol October 2010
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.
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 a network aggregation. 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 compact and updated at a smaller 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.
Alimi, et al. Expires April 28, 2011 [Page 12]
Internet-Draft ALTO Protocol October 2010
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. A RECOMMENDED way to satisfy this property is to
define a PID containing the 0.0.0.0/0 prefix for IPv4 or ::/0 (for
IPv6).
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
Alimi, et al. Expires April 28, 2011 [Page 13]
Internet-Draft ALTO Protocol October 2010
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.
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.
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
Alimi, et al. Expires April 28, 2011 [Page 14]
Internet-Draft ALTO Protocol October 2010
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. An
ALTO Server return costs that are interpreted as either 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, such as summation, that would
make sense for 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 operation 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.
summation) 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.
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
Alimi, et al. Expires April 28, 2011 [Page 15]
Internet-Draft ALTO Protocol October 2010
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, ...,
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). 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 SHOULD also be changed. (Thus, the Version Tag is
defined similarly to HTTP's ETag.) Possibilities for generating a
Version Tag included 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-like interface with the goal of
leveraging current HTTP [2] [3] implementations and infrastructure,
as well as familiarity with existing REST-like services in popular
use. ALTO messages use JSON [4] to encode message bodies.
This document currently specifies both services and and the message
encoding in a descriptive fashion. Care is taken to make
descriptions precise and unambiguous, but it still lacks benefits of
automatic tooling that exists for certain encoding formats.
Alimi, et al. Expires April 28, 2011 [Page 16]
Internet-Draft ALTO Protocol October 2010
Standards such as WSDL 2.0 and WADL are capable of describing
available interfaces. JSON Schema [20] allows message encodings to
be specified precisely and messages may be verified against the
schema. It is not yet clear whether such an approach should be taken
in this document.
Other benefits enabled by these design choices include easier
understanding and debugging, flexible ALTO Server implementation
strategies, and more importantly, simple caching and redistribution
of ALTO information to increase scalability.
6.1. 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.
6.2. 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, but it does define the primitives (e.g., digital
signatures) needed to support such a mechanism. See [21] for further
discussion.
Note that if caching or redistribution is used, the Response message
may be returned from another (possibly third-party) entity. Reuse
and Redistribution is further discussed in Section 12.4. Protocol
support for redistribution is specified in Section 8.
Alimi, et al. Expires April 28, 2011 [Page 17]
Internet-Draft ALTO Protocol October 2010
7. Protocol Messaging
This section specifies client and server processing, as well as
messages in the ALTO Protocol. Details common to ALTO Server
processing of all messages is first discussed, followed by details of
the individual messages.
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.
This document only includes object members used by this
specification. It is possible that protocol extensions include
additional members to JSON objects defined in this document; such
additional members will be silently ignored by ALTO Servers and
Clients only implementing the base protocol defined in this document.
7.2. Message Format
Request and Response follow the standard format for HTTP Request and
Response messages [2] [3].
The following subsections provide an overview of how ALTO Requests
and Responses are encoded in HTTP, and discusses rationale for
certain design decisions.
7.2.1. Protocol Versioning
The ALTO Protocol uses a simple versioning approach that permits
evolution between versions even if ALTO information is being served
as static, pre-generated files.
It is assumed that a single host responding to ALTO Requests
implements a single protocol version. Virtual hosting may be used if
multiple protocol versions need to be supported by a single physical
server.
A common query (Server List, detailed in Section 7.8.1.1) to be
present in all ALTO protocol versions allows an ALTO Client to
discover additional ALTO Servers and the ALTO Protocol version number
of each.
This approach keeps the ALTO Server implementation free from parsing
Alimi, et al. Expires April 28, 2011 [Page 18]
Internet-Draft ALTO Protocol October 2010
and directing each request based on version number. Although ALTO
Requests are free from protocol version numbers, the protocol version
number is echoed in each ALTO Response to keep responses self-
contained to, for example, ease reading persisted or redistributed
ALTO responses.
Using virtual hosting with TLS may require the Server Name Indication
extension for TLS [5] [22].
This document specifies ALTO Protocol version 1.
7.2.2. Content Type
All ALTO Request and Response messages MUST set the Content-Type HTTP
header to "application/alto".
7.2.3. Request Message
An ALTO Request is a standard HTTP Request generated by an ALTO
Client, with certain components defined by the ALTO Protocol.
The basic syntax of an ALTO Request is:
<Method> /<Resource> HTTP/1.1
Host: <Host>
For example:
GET /info/capability HTTP/1.1
Host: alto.example.com:6671
7.2.3.1. Standard HTTP Headers
The Host header MUST follow the standard rules for the HTTP 1.1 Host
Header.
The Content-Length header MUST follow the standard rules defined in
HTTP 1.1.
The Content-Type HTTP Header MUST have value "application/alto" if
the Body is non-empty.
7.2.3.2. Method and Resource
Next, both the HTTP Method and URI-Path (denoted as Resource)
indicate the operation requested by the ALTO Client. In this
example, the ALTO Client is requesting basic capability information
from the ALTO Server.
Alimi, et al. Expires April 28, 2011 [Page 19]
Internet-Draft ALTO Protocol October 2010
7.2.3.3. Input Parameters
Certain operations defined by the ALTO Protocol (e.g., in the Map
Filtering Service) allow the ALTO Client to supply additional input
parameters. Such input parameters are encoded in a URI-Query-String
where possible and appropriate. However, due to practical
limitations (e.g. underlying HTTP implementations may have
limitations on the total length of a URI and the Query-String is
better-suited for simple unstructured parameters and lists), some
operations in the ALTO Protocol use input parameters encoded in the
HTTP Request Body.
7.2.4. Response Message
A Response message is a standard HTTP Response generated by an ALTO
Server with certain components defined by the ALTO Protocol.
The basic syntax of an ALTO Response is:
HTTP/1.1 <StatusCode> <StatusMsg>
Content-Length: <ContentLength>
Content-Type: <ContentType>
<ALTOResponse>
where the HTTP Response Body is an ALTOResponse JSON Object (defined
in Section 7.2.4.3). For example:
HTTP/1.1 200 OK
Content-Length: 1000
Content-Type: application/alto
{
"meta" : {
"version": 1,
"status" : {
"code" : 1,
"reason" : "Success"
},
...
},
"type" : "capability",
"data" : {
...
}
}
Alimi, et al. Expires April 28, 2011 [Page 20]
Internet-Draft ALTO Protocol October 2010
7.2.4.1. Standard HTTP Headers
The Content-Length header MUST follow the standard rules defined in
HTTP 1.1.
The Content-Type HTTP Header MUST have value "application/alto" if
the Body is non-empty.
7.2.4.2. Status Code and Message
Two sets of status codes are used in the ALTO Protocol. First, an
ALTO Status Code provides detailed information about the success or
failure of a particular operation. Second, an HTTP Status Code
indicates to HTTP processing elements (e.g., intermediaries and
clients) how the response should be treated.
7.2.4.3. HTTP Body
The Response body MUST encode a single top-level JSON object of type
ALTOResponse:
object {
RspMetaData meta;
JSONString type;
[RspDataType] data;
} ALTOResponse;
The ALTOResponse object has distinct sections for:
o meta information encoded in an extensible way,
o the type of ALTO Information to follow, and
o the requested ALTO Information.
7.2.4.3.1. Meta Information
Meta information is encoded as a JSON object with type RspMetaData:
object {
JSONString code;
JSONString reason; [OPTIONAL]
} RspStatus;
object {
JSONNumber version;
RspStatus status;
RspRedistDesc redistribution; [OPTIONAL]
Alimi, et al. Expires April 28, 2011 [Page 21]
Internet-Draft ALTO Protocol October 2010
} RspMetaData;
with members:
o version: the ALTO Protocol version
o status: an ALTO Status Code from Section 7.4 and corresponding
reason (free-form string) providing a human-readable explanation
of the particular status code.
o redistribution: see Section 8.
7.2.4.3.2. ALTO Information
If the Response is successful (see Section 7.4), then the "type" and
"data" members of the ALTOResponse object are REQUIRED. "type"
encodes a Response-specific string which indicates to the ALTO Client
the type of data encoded in the message. The "data" member encodes
the actual Response-specific data; the structure of this member is
detailed later in this section for each particular ALTO Response.
7.2.4.4. Signature
An ALTO Server MAY additionally supply a signature asserting that it
generated a particular response. See Section 8.2.2.
7.3. General Processing
The protocol is structured in such a way that, independent of the
query type, there are a set of general processing steps. The ALTO
Client selects a specific ALTO Server with which to communicate,
establishes a TCP connection, and constructs and sends ALTO Request
messages which MUST conform to Section 7.8. In response to Request
messages, an ALTO Server constructs and sends ALTO Response messages
which also MUST conform to Section 7.8.
7.4. ALTO Status Codes
This document defines ALTO Status Codes to support the operations
defined in this document. Additional status codes may be defined in
companion or extension documents.
An ALTO Server MUST return the SUCCESS status code if and only if the
Request message is successfully processed and the requested ALTO
information is returned by the ALTO Server.
The HTTP Status Codes corresponding to each ALTO Status Code are
defined to provide correct behavior with HTTP intermediaries and
Alimi, et al. Expires April 28, 2011 [Page 22]
Internet-Draft ALTO Protocol October 2010
clients. When an ALTO Server returns a particular ALTO Status Code,
it MUST indicate one of the corresponding HTTP Status Codes in
Table 1.
If multiple errors are present in a single ALTO 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.
+----------------------+------------------+-------------------------+
| ALTO Status Code | HTTP Status | Description |
| | Code(s) | |
+----------------------+------------------+-------------------------+
| SUCCESS | 2xx | Success |
| E_JSON_SYNTAX | 400 | JSON parsing error in |
| | | request |
| E_JSON_FIELD_MISSING | 400 | Required field missing |
| E_JSON_VALUE_TYPE | 400 | JSON Value of |
| | | unexpected type |
| E_INVALID_OPERATION | 501 | Invalid operation |
| | | requested |
| E_INVALID_COST_TYPE | 501 | Invalid cost type |
+----------------------+------------------+-------------------------+
Table 1: Defined ALTO Status Codes
Status codes described in Table 1 are a work in progress. This
document will be modified to update the available status codes as
implementation experience is gained. Feedback is welcomed.
In addition, feedback from implementers of ALTO Clients is welcomed
to identify if there is a need to communicate multiple status codes
in a single response.
7.5. Client Behavior
7.5.1. Successful Response
This specification does not indicate any required actions taken by
ALTO Clients upon receiving a successful response from 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.
Alimi, et al. Expires April 28, 2011 [Page 23]
Internet-Draft ALTO Protocol October 2010
7.5.2. Error Conditions
If an ALTO Client does not receive a successful response from the
ALTO Server, it can either choose another server 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.
7.6. HTTP Usage
7.6.1. Authentication and Encryption
An ALTO Server MAY support SSL/TLS to implement server and/or client
authentication, as well as encryption. See [6] for considerations
regarding verifcation of server identity.
An ALTO Server MAY support HTTP Digest authentication.
7.6.2. Cookies
Cookies MUST NOT be used.
7.6.3. Caching Parameters
If the Response generated by the ALTO Server is cachable, the ALTO
Server MAY include 'Cache-Control' and 'Expires' HTTP headers.
If a Response generated by the ALTO Server is not cachable, the ALTO
Server MUST specify the "Cache-Control: no-cache" HTTP Header.
7.7. ALTO Types
This section details the encoding for particular data values used in
the ALTO Protocol.
7.7.1. PID Name
A PID Name 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 or the '.' separator. The '.' separator is
reserved for future use and MUST NOT unless specifically indicated by
a companion or extension document.
The type 'PIDName' is used in this document to indicate a string of
this format.
Alimi, et al. Expires April 28, 2011 [Page 24]
Internet-Draft ALTO Protocol October 2010
7.7.2. 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.
7.7.3. 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 or the ':' separator.
Identifiers prefixed with 'priv:' are reserved for Private Use [7].
Identifiers prefixed with 'exp:' are reserved for Experimental use.
All other identifiers appearing in an ALTO Request or Response MUST
be registered in the ALTO Cost Types registry Section 11.
The type 'CostType' is used in this document to indicate a string of
this format.
7.8. ALTO Messages
This section documents the individual operations supported in the
ALTO Protocol. See Section 7.2.3 and Section 7.2.4 for
specifications of HTTP Request/Response components common to all
operations in the ALTO Protocol.
Table 2 provides an summary of the HTTP Method and URI-Paths used for
ALTO Requests:
Alimi, et al. Expires April 28, 2011 [Page 25]
Internet-Draft ALTO Protocol October 2010
+----------------+--------------+----------------------------+
| Service | Operation | HTTP Method and URI-Path |
+----------------+--------------+----------------------------+
| Server Info | List Servers | GET /info/servers |
| Server Info | Capability | GET /info/capability |
| | | |
| Map | Network Map | GET /map/core/pid/net |
| Map | Cost Map | GET /map/core/pid/cost |
| | | |
| Map Filtering | Network Map | POST /map/filter/pid/net |
| Map Filtering | Cost Map | POST /map/filter/pid/cost |
| | | |
| Endpoint Prop. | Lookup | GET /endpoint/prop/<name> |
| | | POST /endpoint/prop/lookup |
| | | |
| Endpoint Cost | Lookup | POST /endpoint/cost/lookup |
+----------------+--------------+----------------------------+
Table 2: Overview of ALTO Requests
7.8.1. Server Information Service
The Server Information Service provides information about available
ALTO Servers and their capabilities (e.g., supported services).
An ALTO Server MUST support the Server Information Service and MUST
implement all operations defined in this section.
7.8.1.1. Server List
The Server List request allows an ALTO Client to discover other ALTO
Servers provided by the ALTO Service Provider. Upon discovering an
additional ALTO Server, the ALTO Client may then query the server
capabilities (see Section 7.8.1.2) to test if it supports desired
functionality.
The Server List request is intended to help an ALTO Client find an
ALTO Server supporting the desired ALTO Protocol version and
capabilities. It is not intended to serve as a substitute for the
ALTO Server Discovery which helps an ALTO Client locate an initial
ALTO Server.
This operation MUST be supported by the ALTO Server.
7.8.1.1.1. Request Syntax
GET /info/servers HTTP/1.1
Host: <Host>
Alimi, et al. Expires April 28, 2011 [Page 26]
Internet-Draft ALTO Protocol October 2010
7.8.1.1.2. Response Syntax
HTTP/1.1 200 <StatusMsg>
Content-Length: <BodyLength>
Content-Type: application/alto
<ALTOResponse>
where the ALTOResponse object has "type" member equal to the string
"server-list" and "data" member of type RspServerList:
object {
JSONString uri;
JSONNumber version;
} ServerItem;
object {
ServerItem servers<0..*>;
} RspServerList;
RspServerList has members:
o servers: Array of available ALTO Servers, detailing the URI of the
ALTO Server and the ALTO Protocol version that it implements. The
array must at least contain an entry corresponding to the ALTO
Server at the URI from which it is retrieving the server list.
7.8.1.1.3. Example
GET /info/servers HTTP/1.1
Host: alto.example.com:6671
Alimi, et al. Expires April 28, 2011 [Page 27]
Internet-Draft ALTO Protocol October 2010
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "server-list",
"data" : {
"servers" : [
{
"uri": "http://alto.example.com:6671",
"version" : 1
}
]
}
}
7.8.1.2. Server Capability
The Server Capability request allows an ALTO Client to determine the
functionality supported by the queried ALTO Server.
This operation MUST be supported by the ALTO Server.
7.8.1.2.1. Request Syntax
GET /info/capability HTTP/1.1
Host: <Host>
7.8.1.2.2. Response Syntax
HTTP/1.1 200 <StatusMsg>
Content-Length: <BodyLength>
Content-Type: application/alto
<ALTOResponse>
where the ALTOResponse object has "type" member equal to the string
"capability" and "data" member of type RspCapability:
Alimi, et al. Expires April 28, 2011 [Page 28]
Internet-Draft ALTO Protocol October 2010
enum {
map,
map-filtering,
endpoint-property,
endpoint-cost
} ServiceType; [Note: encoded as JSONString's]
object {
ServiceType services<0..*>;
CostMode cost-modes<0..*>; [OPTIONAL]
CostType cost-types<0..*>; [OPTIONAL]
JSONBool cost-constraints; [OPTIONAL]
JSONString service-id; [OPTIONAL]
JSONString certificates<0..*>; [OPTIONAL]
} RspCapability;
RspCapability has members:
o services: Lists the services supported by the ALTO Server. The
service names defined in this document are are "map", "map-
filtering", "endpoint-property", and "endpoint-cost".
o cost-modes: Array of supported ALTO Cost Modes.
o cost-types: Array of supported ALTO Cost Types.
o cost-constraints: Indicates if the ALTO Server supports cost
constraints. The value 'false' is implied if this member is not
present.
o service-id: UUID [8] indicating an one or more ALTO Servers
serving equivalent ALTO Information.
o certificates: List of PEM-encoded X.509 certificates used by the
ALTO Server in the signing of responses.
If an ALTO Server denotes a response as redistributable, the
'service-id' and 'certificates' fields are REQUIRED instead of
OPTIONAL. See Section 8 for detailed specification.
7.8.1.2.3. Example
GET /info/capability HTTP/1.1
Host: alto.example.com:6671
Alimi, et al. Expires April 28, 2011 [Page 29]
Internet-Draft ALTO Protocol October 2010
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "capability",
"data" : {
"services" : [ "map", "map-filtering" ],
"cost-modes": [
"numerical",
"ordinal"
],
"cost-types": [
"routingcost",
"hopcount"
],
"cost-constraints": false
}
}
7.8.2. Map Service
The Map Service provides batch information to ALTO Clients in the
form of two maps: a Network Map and Cost Map.
An ALTO Server MUST support the Map Service and MUST implement all
operations defined in this section.
7.8.2.1. Network Map
The full Network Map lists for each PID, the network locations
(endpoints) within the PID.
7.8.2.1.1. Request Syntax
GET /map/core/pid/net HTTP/1.1
Host: <Host>
Alimi, et al. Expires April 28, 2011 [Page 30]
Internet-Draft ALTO Protocol October 2010
7.8.2.1.2. Response Syntax
HTTP/1.1 200 <StatusMsg>
Content-Length: <BodyLength>
Content-Type: application/alto
<ALTOResponse>
where the ALTOResponse object has "type" member equal to the string
"network-map" and "data" member of type RspNetworkMap:
object {
CIDRString [pidname]<0..*>;
...
} NetworkMapData;
object {
JSONString map-vtag;
NetworkMapData map;
} RspNetworkMap;
RspNetworkMap has members:
o map-vtag: The Version Tag of the Network Map (Section 5.3)
o map: The network map data itself.
NetworkMapData is a JSON object with each member representing a
single PID and its associated set of IP Prefixes (encoded as a string
in CIDR notation). A member's name is a PIDName string denoting the
PID's name.
7.8.2.1.3. Example
GET /map/core/pid/net HTTP/1.1
Host: alto.example.com:6671
Alimi, et al. Expires April 28, 2011 [Page 31]
Internet-Draft ALTO Protocol October 2010
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "network-map",
"data" : {
"map-vtag" : "1266506139",
"map" : {
"PID1" : [
"192.0.2.0/24",
"198.51.100.0/25"
],
"PID2" : [
"198.51.100.128/25"
],
"PID3" : [
"0.0.0.0/0"
]
}
}
}
7.8.2.2. Cost Map
The Map Service Cost Map query is a batch operation in which the ALTO
Server returns the Path Cost for each pair of source/destination PID
defined by the ALTO Server.
The ALTO Server provides costs using the default Cost Type
('routingcost') and default Cost Mode ('numerical').
7.8.2.2.1. Request Syntax
GET /map/core/pid/cost HTTP/1.1
Host: <Host>
Alimi, et al. Expires April 28, 2011 [Page 32]
Internet-Draft ALTO Protocol October 2010
7.8.2.2.2. Response Syntax
HTTP/1.1 200 <StatusMsg>
Content-Length: <BodyLength>
Content-Type: application/alto
<ALTOResponse>
where the ALTOResponse object has "type" member equal to the string
"cost-map" and "data" member of type RspCostMap:
object DstCosts {
JSONNumber [dstname];
...
};
object {
DstCosts [srcname]<0..*>;
...
} CostMapData;
object {
JSONString map-vtag;
CostType cost-type;
CostMode cost-mode;
CostMapData map;
} RspCostMap;
RspCostMap has members:
o map-vtag: The Version Tag of the Network Map used to generate the
Cost Map (Section 5.3).
o cost-type: Cost Type used in the map (Section 5.1.1)
o cost-mode: Cost Mode used in the map (Section 5.1.2)
o 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. DstCosts has a
single member for each destination PID in the map.
Alimi, et al. Expires April 28, 2011 [Page 33]
Internet-Draft ALTO Protocol October 2010
7.8.2.2.3. Example
GET /map/core/pid/cost HTTP/1.1
Host: alto.example.com:6671
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "cost-map",
"data" : {
"map-vtag" : "1266506139",
"cost-type" : "routingcost",
"cost-mode" : "numerical",
"map" : {
"PID1": { "PID1": 1, "PID2": 5, "PID3": 10 },
"PID2": { "PID1": 5, "PID2": 1, "PID3": 15 },
"PID3": { "PID1": 20, "PID2": 15, "PID3": 1 }
}
}
}
7.8.3. 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.
An ALTO Server MAY support the Map Filtering Service. If an ALTO
Server supports the Map Filtering Service, all operations defined in
this section MUST be implemented.
7.8.3.1. Network Map
ALTO Clients can query for a subset of the full network map (see
Section 7.8.2.1).
Alimi, et al. Expires April 28, 2011 [Page 34]
Internet-Draft ALTO Protocol October 2010
7.8.3.1.1. Request Syntax
POST /map/filter/pid/net HTTP/1.1
Host: <Host>
Content-Length: <BodyLength>
<ReqNetworkMap>
where:
object {
PIDName pids<0..*>;
} ReqNetworkMap;
The Body of the request encodes an array of PIDs to be included in
the resulting 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.
7.8.3.1.2. Response Syntax
The Response syntax is identical to that of the Map Service's Network
Map Response (Section 7.8.2.1.2).
The ALTO Server MUST only include PIDs in the Response that were
specified (implicitly or explicitly) in the Request. If the Request
contains 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
request.
Alimi, et al. Expires April 28, 2011 [Page 35]
Internet-Draft ALTO Protocol October 2010
7.8.3.1.3. Example
POST /map/filter/pid/net HTTP/1.1
Host: alto.example.com:6671
Content-Length: <BodyLength>
{
pids: [ "PID1", "PID2" ]
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "network-map",
"data" : {
"map-vtag" : "1266506139",
"map" : {
"PID1" : [
"192.0.2.0/24",
"198.51.100.0/24",
],
"PID2" : [
"198.51.100.128/24",
]
}
}
}
7.8.3.2. Cost Map
ALTO Clients can query for the Cost Map (see Section 7.8.2.2) based
on additional parameters.
7.8.3.2.1. Request Syntax
POST /map/filter/pid/cost?<URI-Query-String> HTTP/1.1
Host: <Host>
<ReqCostMap>
Alimi, et al. Expires April 28, 2011 [Page 36]
Internet-Draft ALTO Protocol October 2010
where:
object {
PIDName srcs<0..*>;
PIDName dsts<0..*>;
} ReqCostMap;
The Query String may contain the following parameters:
o type: The requested Cost Type (Section 5.1.1). If not specified,
the default value is "routingcost". This parameter MUST NOT be
specified multiple times.
o mode: The requested Cost mode (Section 5.1.2). If not specified,
the default value is "numerical". This parameter MUST NOT be
specified multiple times.
o constraint: Defines a constraint on which elements of the Cost Map
are returned. This parameter MUST NOT be used if the Server
Capability Response (Section 7.8.1.2) indicates that constraint
support is not available. A constraint contains two entities
separated by whitespace (before URL encoding): (1) an operator
either 'gt' for greater than , 'lt' for less than or 'eq' for
equal to with 10 percent on either side, (2) a target numerical
cost. The numerical cost is a number that MUST be defined in the
units specified in the Server Capability Response. If multiple
'constraint' parameters are specified, the ALTO Server assumes
they are related to each other with a logical AND. If no
'constraint' parameters are specified, then the ALTO Server
returns the full Cost Map.
The Request body MAY specify a list of Source PIDs, and a list of
Destination PIDs. If a list is empty, it is interpreted by the ALTO
Server as the full set of currently-defined PIDs. The ALTO Server
returns costs between each pair of source/destination PID. If the
Request body is empty, both lists are interpreted to be empty.
7.8.3.2.2. Response Syntax
The Response syntax is identical to that of the Map Service's Cost
Map Response (Section 7.8.2.2.2).
The Response MUST NOT contain any source/destination pair that was
not indicated (implicitly or explicitly) in the Request. If the
Request contains 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 request.
Alimi, et al. Expires April 28, 2011 [Page 37]
Internet-Draft ALTO Protocol October 2010
7.8.3.2.3. Example
POST /map/filter/pid/cost?type=hopcount HTTP/1.1
Host: alto.example.com:6671
{
"srcs" : [ "PID1" ],
"dsts" : [ "PID1", "PID2", "PID3" ]
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "cost-map",
"data" : {
"map-vtag" : "1266506139",
"cost-type" : "hopcount",
"cost-mode" : "numerical",
"map" : {
"PID1": { "PID1": 0, "PID2": 1, "PID3": 2 }
}
}
}
7.8.4. Endpoint Property Service
The Endpoint Property Lookup query allows an ALTO Client to lookup
properties of Endpoints known to the ALTO Server. If the ALTO Server
provides the Endpoint Property Service, the ALTO Server MUST define
at least the 'pid' property for Endpoints.
An ALTO Server MAY support the Endpoint Property Service. If an ALTO
Server supports the Endpoint Property Service, all operations defined
in this section MUST be implemented.
7.8.4.1. Endpoint Property Lookup
Alimi, et al. Expires April 28, 2011 [Page 38]
Internet-Draft ALTO Protocol October 2010
7.8.4.1.1. Request Syntax
POST /endpoint/prop/lookup?<URI-Query-String> HTTP/1.1
Host: <Host>
Content-Length: <BodyLength>
<ReqEndpointProp>
where:
object {
JSONString endpoints<0..*>;
} ReqEndpointProp;
The Query String may contain the following parameters:
o prop: The requested property type. This parameter MUST be
specified at least once, and MAY be specified multiple times
(e.g., to query for multiple different properties at once).
The body encodes a list of endpoints (IP addresses) as strings.
An alternate syntax is supported for the case when properties are
requested for a single endpoint:
GET /endpoint/prop/<Endpoint>?<URI-Query-String> HTTP/1.1
Host: <Host>
where the Query String is the same as in the first form.
7.8.4.1.2. Response Syntax
HTTP/1.1 200 <StatusMsg>
Content-Length: <BodyLength>
Content-Type: application/alto
<ALTOResponse>
where the ALTOResponse object has "type" member equal to the string
"endpoint-property" and "data" member of type RspEndpointProperty:
Alimi, et al. Expires April 28, 2011 [Page 39]
Internet-Draft ALTO Protocol October 2010
object {
JSONString [propertyname];
...
} EndpointProps;
object {
EndpointProps [endpointname]<0..*>;
...
} RspEndpointProperty;
RspEndpointProperty has one member for each endpoint indicated in the
Request. The requested properties for each endpoint are encoded in a
corresponding EndpointProps object, which encodes one name/value pair
for each requested property. Note that property values are JSON
Strings. 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.
7.8.4.1.3. Example
POST /endpoint/prop/lookup?prop=pid HTTP/1.1
Host: alto.example.com:6671
Content-Length: [TODO]
{
"endpoints" : [ "192.0.2.34", "203.0.113.129" ]
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "endpoint-property",
"data": {
"192.0.2.34" : { "pid": "PID1" },
"203.0.113.129" : { "pid": "PID3" }
}
}
Alimi, et al. Expires April 28, 2011 [Page 40]
Internet-Draft ALTO Protocol October 2010
7.8.5. Endpoint Cost Service
The Endpoint Cost Service allows ALTO Clients to directly supply
endpoints to an ALTO Server. The ALTO Server replies with costs
(numerical or ordinal) amongst the endpoints.
In particular, this service allows lists of Endpoint addresses to be
ranked (ordered) by an ALTO Server.
An ALTO Server MAY support the Endpoint Cost Service. If an ALTO
Server supports the Endpoint Cost Service, all operations defined in
this section MUST be implemented.
7.8.5.1. Endpoint Cost Lookup
7.8.5.1.1. Request Syntax
POST /endpoint/cost/lookup?<URI-Query-String> HTTP/1.1
Host: <Host>
Content-Length: <BodyLength>
<ReqCostMap>
The request body includes a list of source and destination endpoints
that should be assigned a cost by the ALTO Server. The allowed Query
String parameters are defined identically to Section 7.8.3.2.
The request body MUST specify a list of source Endpoints, and a list
of destination Endpoints, using an structure identical to
Section 7.8.3.2 with the exception that identifiers are endpoints
instead of PIDs. If the list of source Endpoints is empty (or it is
not included), the ALTO Server MUST treat it as if it contained the
Endpoint address of the requesting client. The list of destination
Endpoints MUST NOT be empty. The ALTO Server returns costs between
each pair of source/destination Endpoint.
7.8.5.1.2. Response Syntax
HTTP/1.1 200 <StatusMsg>
Content-Length: <BodyLength>
Content-Type: application/alto
<ALTOResponse>
where ALTOResponse is encoded identically to Section 7.8.2.2.2 with
the following exceptions:
Alimi, et al. Expires April 28, 2011 [Page 41]
Internet-Draft ALTO Protocol October 2010
o ALTO Response's "type" member must be equal to "endpoint-cost-
map",
o The "map-vtag" member of RspCostMap MUST be omitted, and
o Identifiers refer to endpoints instead of PIDs.
7.8.5.1.3. Example
POST /endpoint/cost/lookup?mode=ordinal HTTP/1.1
Host: alto.example.com:6671
Content-Length: [TODO]
{
"src": [ "192.0.2.2" ],
"dst": [ "192.0.2.89", "198.51.100.34", "203.0.113.45" ]
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto
{
"meta" : {
"version" : 1,
"status" : {
"code" : 1
}
},
"type" : "endpoint-cost-map",
"data" : {
"cost-type" : "routingcost",
"cost-mode" : "ordinal",
"map" : {
"192.0.2.2": {
"192.0.2.89" : 1,
"198.51.100.34" : 2,
"203.0.113.45" : 3
}
}
}
}
Alimi, et al. Expires April 28, 2011 [Page 42]
Internet-Draft ALTO Protocol October 2010
8. Redistributable Responses
This section defines how an ALTO Server enables certain responses to
be redistributed by ALTO Clients. Concepts are first introduced,
followed by the protocol specification.
8.1. Concepts
8.1.1. Service ID
The Service ID is a UUID that identifies a set of ALTO Servers that
would provide identical ALTO Information for any ALTO Request for any
ALTO Client. Each ALTO Server within such a set is configured with
an identical Service ID.
If a pair of ALTO Servers would provide different ALTO Information in
response to a particular ALTO Client request, then the pair of ALTO
Servers MUST have a different Service ID.
8.1.1.1. Rationale
For scalability and fault tolerance, multiple ALTO Servers may be
deployed to serve equivalent ALTO Information. In such a scenario,
ALTO Responses from any such redundant server should be seen as
equivalent for the purposes of redistribution. For example, if two
ALTO Servers A and B are deployed by the service provider to
distribute equivalent ALTO Information, then clients contacting
Server A should be able to redistribute ALTO Responses to clients
contacting Server B.
To accomplish this behavior, ALTO Clients must be able to determine
that Server A and Server B serve identical ALTO Information. One
technique would be to rely on the ALTO Server's DNS name. However,
such an approach would mandate that all ALTO Servers resolved by a
particular DNS name would need to provide equivalent ALTO
information, which may be unneccessarily restrictive. Another
technique would be to rely on the server's IP adddress. However,
this suffers similar problems as the DNS name in deployment scenarios
using IP Anycast.
To avoid such restrictions, the ALTO Protocol allows an ALTO Service
Provider to explicitly denote ALTO Servers that provide equivalent
ALTO Information by giving them identical Service IDs. Service IDs
decouple the identification of equivalent ALTO Servers from the
discovery process.
Alimi, et al. Expires April 28, 2011 [Page 43]
Internet-Draft ALTO Protocol October 2010
8.1.1.2. Server Capability Response
If an ALTO Server generates redistributable responses, the Server
Capability response's 'service-id' field MUST be set to the ALTO
Server's Service ID.
8.1.1.3. Configuration
To help prevent ALTO Servers from mistakenly claiming to distribute
equivalent ALTO Information, ALTO Server implementations SHOULD by
default generate a new UUID at installation time or startup if one
has not explicitly been configured.
8.1.2. Expiration Time
ALTO Responses marked as redistributable should indicate a time after
which the information is considered stale and should be refreshed
from the ALTO Server (or possibly another ALTO Client).
If an expiration time is present, the ALTO Server SHOULD ensure that
it is reasonably consistent with the expiration time that would be
computed by HTTP header fields. This specification makes no
recommendation on which expiration time takes precedence, but
implementers should be cognizant that HTTP intermediaries will obey
only the HTTP header fields.
8.1.3. Signature
ALTO Responses marked as redistributable include a signature used to
assert that the ALTO Server Provider generated the ALTO Information.
8.1.3.1. Rationale
Verification of the signature requires the ALTO Client to retrieve
the ALTO Server's public key. There are multiple possibilities
through which the ALTO Protocol could be designed to retrieve it:
o SSL/TLS connection with the ALTO Server: The public key algorithm
and public key may be retrieved from the ALTO Server's X.509
Certificate used on an HTTPS connection between the ALTO Server
and ALTO Client.
o Included in ALTO Server's Server Capability Response: An X.509
certificate (including the public key and public key algorithm)
can be included in the Server Capability Response. This could be
achieved even if the ALTO Server and ALTO Client do not have a
SSL/TLS channel.
Alimi, et al. Expires April 28, 2011 [Page 44]
Internet-Draft ALTO Protocol October 2010
To reduce requirements on the underlying transport (i.e., requiring
SSL/TLS), the ALTO Protocol uses the latter option.
8.1.3.2. Certificates
8.1.3.2.1. Local Certificate
The ALTO Server's public key is encoded within an X.509 certificate.
The corresponding private key MUST be used to sign redistributable
responses. This certificate is termed the Local Certificate for an
ALTO Server.
8.1.3.2.2. Certificate Chain
To ease key provisioning, the ALTO Protocol is designed such that
each ALTO Server with an identical Service ID may have a unique
private key (and hence certificate).
The ALTO Service Provider may configure a certificate chain at each
such ALTO Server. The Local Certificate for a single ALTO Server is
the bottom-most certificate in the chain. The Certificate Chains of
each ALTO Server with an identical Service ID MUST share a common
Root Certificate.
Note that there are two simple deployment scenarios:
o One-Level Certificate Chain (Local Certificate Only): In this
deployment scenario, each ALTO Server with an identical Service ID
may provisioned with an identical Local Certificate.
o Two-Level Certificate Chain: In this deployment scenario, a Root
Certificate is maintained for a set of ALTO Servers with the same
Service ID. A unique Local Certificate signed by this CA is
provisioned to each ALTO Server.
There are advantages to using a Certificate Chain instead of
deploying the same Local Certificate to each ALTO Server.
Specifically, it avoids storage of the CA's private key at ALTO
Servers. It is possible to revoke and re-issue a key to a single
ALTO Server.
8.1.3.2.3. Server Capability Response
If an ALTO Server generates redistributable responses, the Server
Capability response's 'certificates' field MUST be populated with the
ALTO Server's full certificate chain. The first element MUST be the
ALTO Server's Local Certificate, followed by the remaining
Certificate Chain in ascending order to the Root Certificate.
Alimi, et al. Expires April 28, 2011 [Page 45]
Internet-Draft ALTO Protocol October 2010
8.1.3.3. Signature Verification
ALTO Clients SHOULD verify the signature on any ALTO information
received via redistribution before adjusting application behavior
based on it.
An ALTO Client SHOULD cache its ALTO Server's Service ID and
corresponding Certificate Chain included in the Server Capability
response. Recall that the last certificate in this chain is the Root
Certificate. The retrieval of the Service ID and certificates SHOULD
be secured using HTTPS with proper validation of the server endpoint
of the SSL/TLS connection [6].
An ALTO Response received via redistribution from Service ID S is
declared valid if an ALTO Client can construct a transitive
certificate chain from the certificate (public key) used to sign the
ALTO Response to the Root Certificate corresponding to Service ID S
obtained by the ALTO Client in a Server Capability response.
To properly construct the chain and complete this validation, an ALTO
Client may need to request additional certificates from other ALTO
Clients. A simple mechanism is to request the certificate chain from
the ALTO Client that received the ALTO Response. Note that these
additional received certificates may be cached locally by an ALTO
CLient.
ALTO Clients SHOULD verify ALTO Responses received via
redistribution.
8.1.3.4. Redistribution by ALTO Clients
ALTO Clients SHOULD pass the ALTO Server Certificate, Signature, and
Signature Algorithm along with the body of the ALTO Response. The
mechanism for redistributing such information is not specified by the
ALTO Protocol, but one possibility is to add additional messages or
fields to the application's native protocol.
8.2. Protocol
An ALTO Server MAY indicate that a response is suitable for
redistribution by including the "redistribution" member in the
RspMetaData JSON object of an ALTO Response message. This additional
member, called the Response Redistribution Descriptor, has type
RspRedistDesc:
Alimi, et al. Expires April 28, 2011 [Page 46]
Internet-Draft ALTO Protocol October 2010
object {
JSONString service-id;
JSONString request-uri;
JSONValue request-body;
JSONString expires;
} RspRedistDesc;
The fields encoded in the Response Redistribution Descriptor allows
an ALTO Client receiving redistributed ALTO Information to understand
the context of the query (the ALTO Service generating the response
and any input parameters) and to interpret the results.
Information about ALTO Client performing the Request and any HTTP
Headers passed in the request are not included in the Response
Redistribution Descriptor. If any such information or headers
influence the response generated by the ALTO Server, the response
SHOULD NOT be indicated as redistributable.
8.2.1. Response Redistribution Descriptor Fields
This section defines the fields of the Response Redistribution
Descriptor.
8.2.1.1. Service ID
The 'service-id' member is REQUIRED and MUST have a value equal to
the ALTO Server's Service ID.
8.2.1.2. Request URI
The 'request-uri' member is REQUIRED and MUST specify the HTTP
Request-URI that was passed in the HTTP Request.
8.2.1.3. Request Body
If the HTTP Request body was non-empty, the 'request-body' member
MUST specify full JSON value passed in the HTTP Request (note that
whitespace may differ, as long as the JSON Value is identical). If
the HTTP Request was empty, then the 'request-body' MUST NOT be
included.
8.2.1.4. Expiration Time
The 'expires' element is RECOMMENDED and, if present, MUST specify a
time in UTC formatted according to [9].
Alimi, et al. Expires April 28, 2011 [Page 47]
Internet-Draft ALTO Protocol October 2010
8.2.2. Signature
The Hash Algorithm, Signature Algorithm, and Signature are included
as either HTTP Headers or Trailers. Headers may be useful if
Responses are pre-generated, while Trailers may be useful if
Responses are dynamically generated (e.g., to avoid buffering large
responses in memory while the hash value is computed).
The following HTTP Headers (the ALTO Server MAY specify them as HTTP
Trailers instead) MUST be used to encode the Signature parameters for
redistributable ALTO Responses:
ALTO-HashAlgorithm: <HashAlgorithm>
ALTO-SignatureAlgorithm: <SignatureAlgorithm>
ALTO-SignatureDigest: <Signature>
where <HashAlgorithm> and <SignatureAlgorithm> are an integer values
from the IANA TLS HashAlgorithm and SignatureAlgorithm registries,
and <Signature> is the corresponding PEM-encoded signature.
9. Use Cases
The sections below depict typical use cases.
9.1. 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.
Alimi, et al. Expires April 28, 2011 [Page 48]
Internet-Draft ALTO Protocol October 2010
.---------. (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.
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.
Alimi, et al. Expires April 28, 2011 [Page 49]
Internet-Draft ALTO Protocol October 2010
9.2. 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.
.---------. (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.
Alimi, et al. Expires April 28, 2011 [Page 50]
Internet-Draft ALTO Protocol October 2010
9.3. 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.
.---------. .---------------.
| | | |
| 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.
10. Discussions
Alimi, et al. Expires April 28, 2011 [Page 51]
Internet-Draft ALTO Protocol October 2010
10.1. 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 Server List
query Section 7.8.1.1 to locate an ALTO Server with capabilities
necessary for its application.
10.2. 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 perfer 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).
Note that to support such behavior, Endpoints must be associated with
a particular address type (e.g., IPv4 or IPv6). One simple
possibility may be to prefix each endpoint address with its type
(e.g., "ipv4:198.51.100.128/25"). However, we may want to discuss if
a more efficient/compact encoding is possible in some cases (e.g.,
all addresses in the same PID are IPv6).
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.
Exploration of these issues is being considered in a separate
Internet Draft [23]. Once a suitable solution emerges, it will be
included in this document.
10.3. Network Address Translation Considerations
At this day and age of NAT v4<->v4, v4<->v6 [24], and possibly
v6<->v6[25], 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 (via
the Endpoint Property Lookup interface) from the source IP address
found in the ALTO Client query packets. This is similar to how some
Alimi, et al. Expires April 28, 2011 [Page 52]
Internet-Draft ALTO Protocol October 2010
P2P Trackers (e.g., BitTorrent Trackers - see "Tracker HTTP/HTTPS
Protocol" in [26]) operate.
The ALTO client SHOULD use the Session Traversal Utilities for NAT
(STUN) [10] 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
discovery. To be selected for this purpose, the STUN server needs to
provide the public reflexive transport address of the host.
10.4. 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.
10.5. 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. The current draft focuses on network location and
grouping, but the protocol may be extended to handle other Endpoint
properties.
11. IANA Considerations
Alimi, et al. Expires April 28, 2011 [Page 53]
Internet-Draft ALTO Protocol October 2010
11.1. application/alto Media Type
This document requests the registration of a new media type:
"application/alto":
Type name: application
Subtype name: alto
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: Encoding considerations are identical to
those specified for the 'application/json' media type. See [4].
Security considerations: Security considerations relating to the
generation and consumption of ALTO protocol messages are discussed
in Section 12.
Interoperability considerations: This document specifies format of
conforming messages and the interpretation thereof.
Published specification: This document.
Applications that use this media type: ALTO Servers and ALTO Clients
either standalone or embedded within other applications.
Additional information:
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.
Alimi, et al. Expires April 28, 2011 [Page 54]
Internet-Draft ALTO Protocol October 2010
Change controller: See "Authors' Addresses" section.
11.2. 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 [7]. 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 7.7.3. 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:
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.
Alimi, et al. Expires April 28, 2011 [Page 55]
Internet-Draft ALTO Protocol October 2010
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 12.1.
12. Security Considerations
12.1. 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.
12.2. 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 [18].
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
Alimi, et al. Expires April 28, 2011 [Page 56]
Internet-Draft ALTO Protocol October 2010
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.
12.3. 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
protecting ALTO information are outside of the scope of this
document.
12.4. 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. Further, to prevent the ALTO Server from
being a target of attack, the verification scheme must not require
ALTO Clients to contact the ALTO Server to validate every set of
information. Contacting an ALTO server for information validation
would also undermine the intended effect of redistribution and is
therefore not desirable.
Note that the redistribution scheme must additionally handle details
such as ensuring ALTO Clients retrieve ALTO information from the
correct ALTO Server. See [21] for further discussion. Details of a
particular redistribution scheme are outside the scope of this
document.
To fulfill these requirements, ALTO Information meant to be
redistributable contains a digital signature which includes a hash of
Alimi, et al. Expires April 28, 2011 [Page 57]
Internet-Draft ALTO Protocol October 2010
the ALTO information signed by the ALTO Server with its private key.
The corresponding public key is included in the Server Capability
response Section 7.8.1.2, along with the certificate chain to a Root
Certificate generated by the ALTO Service Provider. To prevent man-
in-the-middle attacks, an ALTO Client SHOULD perform the Server
Capability Query over SSL/TLS and verify the server identity
according to [6].
The signature verification algorithm is detailed in Section 8.1.3.3.
12.5. 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., [27]). 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.
12.6. 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 [28] for a more detailed discussion on
this issue).
13. References
Alimi, et al. Expires April 28, 2011 [Page 58]
Internet-Draft ALTO Protocol October 2010
13.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[3] 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.
[4] Crockford, D., "The application/json Media Type for JavaScript
Object Notation (JSON)", RFC 4627, July 2006.
[5] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, April 2006.
[6] 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)",
draft-saintandre-tls-server-id-check-10 (work in progress),
October 2010.
[7] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[8] Leach, P., Mealling, M., and R. Salz, "A Universally Unique
IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[9] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[10] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session
Traversal Utilities for (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-18 (work in progress), July 2008.
13.2. Informative References
[11] Kiesel, S., Popkin, L., Previdi, S., Woundy, R., and Y. Yang,
"Application-Layer Traffic Optimization (ALTO) Requirements",
draft-kiesel-alto-reqs-01 (work in progress), November 2008.
[12] 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.
Alimi, et al. Expires April 28, 2011 [Page 59]
Internet-Draft ALTO Protocol October 2010
[13] 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.
[14] Shalunov, S., Penno, R., and R. Woundy, "ALTO Information
Export Service", draft-shalunov-alto-infoexport-00 (work in
progress), October 2008.
[15] Das, S. and V. Narayanan, "A Client to Service Query Response
Protocol for ALTO", draft-saumitra-alto-queryresponse-00 (work
in progress), March 2009.
[16] Das, S., Narayanan, V., and L. Dondeti, "ALTO: A Multi
Dimensional Peer Selection Problem",
draft-saumitra-alto-multi-ps-00 (work in progress),
October 2008.
[17] Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D.
Saucez, "The PROXIDOR Service", draft-akonjang-alto-proxidor-00
(work in progress), March 2009.
[18] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693, October 2009.
[19] Yang, Y., Popkin, L., Penno, R., and S. Shalunov, "An
Architecture of ALTO for P2P Applications",
draft-yang-alto-architecture-00 (work in progress), March 2009.
[20] Zyp, K., "A JSON Media Type for Describing the Structure and
Meaning of JSON Documents", draft-zyp-json-schema-02 (work in
progress), March 2010.
[21] Yingjie, G., Alimi, R., and R. Even, "ALTO Information
Redistribution", draft-gu-alto-redistribution-03 (work in
progress), July 2010.
[22] 3rd, D., "Transport Layer Security (TLS) Extensions: Extension
Definitions", draft-ietf-tls-rfc4366-bis-12 (work in progress),
September 2010.
[23] Penno, R. and J. Medved, "ALTO and IPv4/IPv6 Co-existence and
Transition", draft-penno-alto-ipv4v6-00 (work in progress),
June 2010.
[24] Baker, F., Li, X., and C. Bao, "Framework for IPv4/IPv6
Translation", draft-baker-behave-v4v6-framework-02 (work in
progress), February 2009.
Alimi, et al. Expires April 28, 2011 [Page 60]
Internet-Draft ALTO Protocol October 2010
[25] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Address
Translation (NAT66)", draft-mrw-behave-nat66-02 (work in
progress), March 2009.
[26] "Bittorrent Protocol Specification v1.0",
http://wiki.theory.org/BitTorrentSpecification, 2009.
[27] Jennings, C., "Computational Puzzles for SPAM Reduction in
SIP", draft-jennings-sip-hashcash-06 (work in progress),
July 2007.
[28] Stiemerling, M. and S. Kiesel, "ALTO Deployment
Considerations", draft-stiemerling-alto-deployments-05 (work in
progress), October 2010.
[29] H. Xie, YR. Yang, A. Krishnamurthy, Y. Liu, and A.
Silberschatz., "P4P: Provider Portal for (P2P) Applications",
In SIGCOMM 2008.
Appendix A. TO BE MOVED
The text in this section is intended to be moved to a more
appropriate document.
A.1. Discovery
Some ISPs have proposed the possibility of delegation, in which an
ISP provides information for customer networks which do not wish to
run ALTO Servers themselves. A consideration for delegation is that
customer networks may wish to explicitly configure such delegation.
A.2. P2P Peer Selection
This section discusses possible approaches to peer selection using
ALTO information (Network Location Identifiers and associated Costs)
from an ALTO Server. Specifically, the application must select which
peers to use based on this and other sources of information. With
this in mind, the usage of ALTO Costs is intentionally flexible,
because:
Different applications may use the information differently. For
example, an application that connects to just one address may have
a different algorithm for selecting it than an application that
connects to many.
Though initial experiments have been conducted [29], more
investigation is needed to identify other methods.
Alimi, et al. Expires April 28, 2011 [Page 61]
Internet-Draft ALTO Protocol October 2010
In addition, the application might account for robustness, perhaps
using randomized exploration to determine if it performs better
without ALTO information.
A.2.1. Client-based Peer Selection
One possibility is for peer selection using ALTO costs to be done
entirely by a P2P client. The following are some techniques have
been proposed and/or used:
o Prefer network locations with lower ordinal rankings (i.e., higher
priority) [17] [14].
o Optimistically unchoking low-cost peers with higher probability
[14].
A.2.2. Server-based Peer Selection
Another possibility is for ALTO costs to be used by an Application
Tracker (e.g., BitTorrent Tracker) when returning peer lists. The
following are techniques that have been proposed and/or used:
o Using bandwidth matching (e.g., at an Application Tracker) and
choosing solution (within bound of optimal) with minimal network
cost [29].
A.2.3. Location-Only Peer Selection
This section discusses a promising peer selection algorithm that was
recently used in experiments with a P2P live streaming application.
Experiments in the context of live streaming have shown significant
benefits of a simple "location-only" algorithm that primarily makes
use of the Network Map. A benefit of this algorithm is that it can
provide a simple integration path for applications wishing to utilize
ALTO.
In particular, the algorithm proceeds as follows to select an ordered
list of peers for a particular incoming (or existing peer):
1. Insert into the result list a number (up to a threshold) of peers
from the same PID as the incoming peer.
2. Insert into the result list a number (up to a threshold) of peers
from the same ISP as the incoming peer.
3. Insert into the result list a number (up to a threshold) of peers
from different ISPs than the incoming peer.
Alimi, et al. Expires April 28, 2011 [Page 62]
Internet-Draft ALTO Protocol October 2010
In the experiments, this algorithm was implemented at a tracker and
executed for peer selection when peers initially join and when
requesting new peers.
This algorithm makes two assumptions about the preferences
communicated by the Network Map:
o The ISP prefers peers within the same PID to peer with each other
(see Section 4); and
o The ALTO Client can distinguish between peers within the same ISP
and peers outside of the ISP. In implementation at the ALTO
Client, it may may estimate a threshold based on costs read from
the Cost Map.
Appendix B. Acknowledgments
Thank you to Jan Seedorf for contributions to the Security
Considerations section. We would like to thank Yingjie Gu and Roni
Even for helpful input and design concerning ALTO Information
redistribution.
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),
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:
Alimi, et al. Expires April 28, 2011 [Page 63]
Internet-Draft ALTO Protocol October 2010
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 C. Authors
[[Comment.1: 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
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
Alimi, et al. Expires April 28, 2011 [Page 64]
Internet-Draft ALTO Protocol October 2010
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 April 28, 2011 [Page 65]
