ALTO WG R. Penno, Ed.
Internet-Draft Juniper Networks
Intended status: Standards Track Y. Yang, Ed.
Expires: January 14, 2010 Yale University
July 13, 2009
ALTO Protocol
draft-penno-alto-protocol-02.txt
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Abstract
Applications already have access to great amount of underlying
network topology information. For example, views of the Internet
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routing table are easily available at looking glass servers and
entirely practical to downloaded by clients. What is missing is
network side information such as the network preference information
-- what an ISP or Content Provider actually prefers -- 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].
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Background and Problem Statement . . . . . . . . . . . . . 6
1.2. Design History and Merged Proposals . . . . . . . . . . . 6
1.3. Solution Benefits . . . . . . . . . . . . . . . . . . . . 6
1.3.1. Service Providers . . . . . . . . . . . . . . . . . . 7
1.3.2. P2P Applications . . . . . . . . . . . . . . . . . . . 7
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Endpoint Address . . . . . . . . . . . . . . . . . . . 7
2.1.2. Network Location . . . . . . . . . . . . . . . . . . . 8
2.2. ALTO Service and Protocol Scope . . . . . . . . . . . . . 8
2.3. Query Types . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1. Server Capability . . . . . . . . . . . . . . . . . . 9
2.3.2. Endpoint Property . . . . . . . . . . . . . . . . . . 10
2.3.3. Reverse Property Map . . . . . . . . . . . . . . . . . 10
2.3.4. Path Property Lookup . . . . . . . . . . . . . . . . . 10
3. Network Map . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. PID . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Example Network Map . . . . . . . . . . . . . . . . . . . 11
3.3. Endpoint PID Query . . . . . . . . . . . . . . . . . . . . 12
3.4. Reverse Network Map Query . . . . . . . . . . . . . . . . 12
4. Path Rating . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Path Cost . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1.1. Cost Type . . . . . . . . . . . . . . . . . . . . . . 12
4.1.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Path Rating Query . . . . . . . . . . . . . . . . . . . . 13
4.2.1. Cost Map . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.2. Ranking List . . . . . . . . . . . . . . . . . . . . . 13
4.2.3. Implicit Source Network Location . . . . . . . . . . . 14
4.2.4. Implicit Destination Network Location . . . . . . . . 14
4.2.5. Network Map and Cost Map Dependency . . . . . . . . . 14
5. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Design Approach . . . . . . . . . . . . . . . . . . . . . 14
5.1.1. Use of Existing Infrastructure . . . . . . . . . . . . 14
5.1.2. ALTO Information Reuse and Redistribution . . . . . . 15
5.2. Message Format . . . . . . . . . . . . . . . . . . . . . . 15
5.2.1. Query Message . . . . . . . . . . . . . . . . . . . . 15
5.2.2. Response Message . . . . . . . . . . . . . . . . . . . 16
5.2.3. Query and Response Body Encoding . . . . . . . . . . . 16
6. Protocol Messaging . . . . . . . . . . . . . . . . . . . . . . 17
6.1. Client Processing . . . . . . . . . . . . . . . . . . . . 17
6.1.1. General Processing . . . . . . . . . . . . . . . . . . 17
6.1.2. General Error Conditions . . . . . . . . . . . . . . . 17
6.2. Server Processing . . . . . . . . . . . . . . . . . . . . 17
6.2.1. General Error Conditions . . . . . . . . . . . . . . . 17
6.3. ALTO Queries . . . . . . . . . . . . . . . . . . . . . . . 18
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6.3.1. Server Capability . . . . . . . . . . . . . . . . . . 18
6.3.2. Endpoint Property Lookup . . . . . . . . . . . . . . . 19
6.3.3. Reverse Property Lookup . . . . . . . . . . . . . . . 21
6.3.4. Path Rating Lookup . . . . . . . . . . . . . . . . . . 22
7. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.1. ALTO Client Embedded in P2P Tracker . . . . . . . . . . . 26
7.2. ALTO Client Embedded in P2P Client: Numerical Costs . . . 28
7.3. ALTO Client Embedded in P2P Client: Ranking . . . . . . . 29
8. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 30
8.2. Network Address Translation Considerations . . . . . . . . 30
8.3. Mapping IPs to ASNs . . . . . . . . . . . . . . . . . . . 31
8.4. Endpoint and Path Properties . . . . . . . . . . . . . . . 31
8.5. P2P Peer Selection . . . . . . . . . . . . . . . . . . . . 31
8.5.1. Client-based Peer Selection . . . . . . . . . . . . . 32
8.5.2. Server-based Peer Selection . . . . . . . . . . . . . 32
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
10. Security Considerations . . . . . . . . . . . . . . . . . . . 32
10.1. ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.2. ALTO Clients . . . . . . . . . . . . . . . . . . . . . . . 32
10.3. ALTO Information . . . . . . . . . . . . . . . . . . . . . 33
10.4. ALTO Information Redistribution . . . . . . . . . . . . . 33
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
11.1. Normative References . . . . . . . . . . . . . . . . . . . 33
11.2. Informative References . . . . . . . . . . . . . . . . . . 34
Appendix A. Data Types . . . . . . . . . . . . . . . . . . . . . 35
A.1. Endpoint Name . . . . . . . . . . . . . . . . . . . . . . 35
A.2. PID Name . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.3. Property Name . . . . . . . . . . . . . . . . . . . . . . 35
A.4. IP Prefix . . . . . . . . . . . . . . . . . . . . . . . . 35
A.5. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . 35
A.6. Cost Mode . . . . . . . . . . . . . . . . . . . . . . . . 36
A.7. Constraint . . . . . . . . . . . . . . . . . . . . . . . . 36
Appendix B. XML Encoding . . . . . . . . . . . . . . . . . . . . 36
B.1. Server Configuration . . . . . . . . . . . . . . . . . . . 36
B.2. Endpoint . . . . . . . . . . . . . . . . . . . . . . . . . 37
B.3. Endpoint List . . . . . . . . . . . . . . . . . . . . . . 37
B.4. PID . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
B.5. PID List . . . . . . . . . . . . . . . . . . . . . . . . . 37
B.6. Cost Map Specification . . . . . . . . . . . . . . . . . . 37
B.7. Cost Row . . . . . . . . . . . . . . . . . . . . . . . . . 37
B.8. Cost Map . . . . . . . . . . . . . . . . . . . . . . . . . 37
Appendix C. Additional Protocol Message Examples . . . . . . . . 38
C.1. Endpoint Property Lookup . . . . . . . . . . . . . . . . . 38
C.2. Reverse Property Lookup . . . . . . . . . . . . . . . . . 39
C.3. Path Cost Lookup . . . . . . . . . . . . . . . . . . . . . 41
Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 41
Appendix E. Acknowledgements . . . . . . . . . . . . . . . . . . 44
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 44
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1. Introduction
1.1. Background and Problem Statement
Today, network information available to applications is mostly from
the view of endhosts. There is no clear mechanism to convey
information about the network's preferences to applications. By
leveraging better network-provided information, applications have
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 the protocol specified in this document is to provide a
simple, unified protocol that meets the ALTO requirements [5],
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 [6],[7];
o ALTO Info-Export [8];
o Query/Response [9],[10];
o ATTP [ATTP].
o Proxidor [Proxidor].
The people listed here should be viewed as co-authors of this
document: Obi Akonjang, Richard Alimi, Saumitra M. Das, Syon Ding,
Anja Feldmann, Doug Pasko, Reinaldo Penno, Laird Popkin, Stefano
Previdi, Satish Raghunath, Stanislav Shalunov, Albert Tian, Yu-Shun
Wang, Richard Woundy, Y. Richard Yang, David Zhang, and Yunfei Zhang.
Due to the limit of 5 authors per draft, the complete list of authors
were moved to the contributors section at this point.
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).
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1.3.1. Service Providers
The ALTO Service enables ISPs to influence the neighborhood selection
process of overlay networks to increase locality of traffic and also
regain the ability to efficiently engineer traffic that traverses
more expensive links such as backbone and transit links, thus
allowing a better provisioning of the networking infrastructure.
1.3.2. P2P 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.
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. Below we start
with an introduction to the terminology. Then we define the overall
architecture and how the ALTO Protocol fits into the architecture.
At the end of this section, we specify the simple, but general
protocol framework which demonstrates its extensibility.
2.1. Terminology
We use the following terms defined in [11]: 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 and
Network Location.
2.1.1. Endpoint Address
An endpoint address represents the communication address of an end
point. 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.
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2.1.2. Network Location
Network Location is a generic concept denoting a single endpoint or
group of endpoints. Whenever we say Network Location, we refer to
either a single endpoint or a group of endpoints.
2.2. ALTO Service and Protocol Scope
An ALTO Server conveys the network information from the perspective
of a network region. We say that the ALTO Server presents its "my-
Internet View" [12] of the network region. A network region in this
context can be an Autonomous System, an ISP, perhaps a smaller
region, or perhaps a 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 Client uses ALTO Service Discovery to
identify an appropriate ALTO Server; an ALTO Server prepares ALTO
Information; 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.
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+-------------------------------------------------------------------+
| ISP |
| |
| +-----------+ |
| | Routing | |
| +--------------+ | Protocols | |
| | Provisioning | +-----------+ |
| | Policy | | |
| +--------------+\ | |
| \ | |
| \ | |
| +-----------+ \+---------+ +--------+ |
| |Dynamic | | ALTO | ALTO Protocol | ALTO | |
| |Network |.......| Server | -------------------- | Client | |
| |Information| +---------+ +--------+ |
| +-----------+ / / |
| / ALTO SD Query/Response / |
| / / |
| +----------+ +--------------+ |
| | External | | ALTO Service | |
| | Interface| | Discovery | |
| +----------+ +--------------+ |
| | |
| | Figure 1: Basic ALTO Architecture. |
| | |
+-------------------------------------------------------------------+
|
+------------------+
| Third Parties |
| |
| Content Providers|
+------------------+
ALTO Architecture
2.3. Query Types
As a general framework, ALTO Information is provided via the ALTO
Protocol by answering the following four types of queries:
2.3.1. Server Capability
It lists the details on the information that can be provided by an
ALTO Server.
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2.3.2. Endpoint Property
Given an endpoint, it gives the set of network-aware properties
associated with the endpoint. An example endpoint property is its
Network Location property or connectivity type (e.g., ADSL, Cable, or
FioS).
2.3.3. Reverse Property Map
It is the reverse of the preceding. In particular, given a property,
it lists the endpoints with the property.
2.3.4. Path Property Lookup
It gives information on the properties of paths among Network
Locations.
3. Network Map
The preceding section specifies a simple, extensible ALTO Protocol
framework. In this section, we focus on a particular endpoint
property named Network Map. In the next section, we introduce a
particular path property named Path Rating.
In reality many endpoints are very close to one another in terms of
network connectivity, for example, endpoints on the same site of an
enterprise. By treating a group of endpoints together as a single
entity in ALTO, we can achieve much greater scalability without
loosing any 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 Network Map may also be used to communicate simple preferences.
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.
Note that the definition of proximity varies depending on the
granularity of the ALTO algorithm. 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.
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3.1. PID
Each group can be identified by a Network Location identifier called
a PID. There can be many different ways of grouping the endpoints
and assigning PIDs.
Thus, a PID is an identifier providing 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. Also, aggregation 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.
3.2. Example Network Map
Figure 1 illustrates an example Network Map. PIDs are used to
identify network-agnostic aggregations.
.--------------------------------------------------------.
| ALTO Network Map |
| |
| .--------------------------------. .---------------. |
| | NetLoc: PID-1 | | NetLoc: PID-2 | |
| | .---------------------------. | | ... | |
| | | 128.36.0.0/16 | | `---------------` |
| | | .-----------------------. | | |
| | | | Endpoint: 128.36.9.8 | | | .---------------. |
| | | `-----------------------` | | | NetLoc: PID-3 | |
| | `---------------------------` | | ... | |
| | .---------------------------. | `---------------` |
| | | 130.132.0.0/16 | | |
| | | .-----------------------. | | .---------------. |
| | | | Endpoint: 130.132.1.2 | | | | NetLoc: PID-4 | |
| | | `-----------------------` | | | ... | |
| | `---------------------------` | `---------------` |
| `--------------------------------` |
| |
`--------------------------------------------------------`
Figure 1: Example Network Map
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3.3. Endpoint PID Query
The Endpoint Property query against the Network Map allows an ALTO
Client to retrieve the PID of a given endpoint.
3.4. Reverse Network Map Query
The Reverse Property Map query for Network Map allows an ALTO Client
to obtain a map from PIDs to lists of endpoints: for each PID, the
map includes its list of endpoints.
4. Path Rating
In this section we define a particular path property named Path
Rating.
4.1. Path Cost
Path Rating is based on Path Cost, which conveys the preference of an
ALTO Server on communication among Network Locations. Path Costs
have attributes:
o Type: identifies what the costs represent;
o Mode: identifies how the costs should be interpreted (numerical or
ordinal interpretation).
4.1.1. 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 alphanumeric
strings. An ALTO Server MUST at least define the routing cost type
denoted by the string 'routingcost'.
Note that an ISP may internally compute routing cost using any method
it chooses (including air-miles or hop-count).
If an ALTO Client requests a Cost Type that is not available, the
ALTO Server responds with an error as specified in Section 6.2.1.2.
4.1.2. Cost Mode
The Mode attribute indicates how costs should be interpreted. For
example, an ALTO Server could return costs that should be interpreted
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as numerical values or ordinal rankings.
It is important to communicate such information to ALTO Clients, as
certain operations may not be valid on certain costs returned by an
ALTO Server. For example, it is possible for an ALTO Server to
return a set of IP addresses with costs indicating a ranking of the
IP addresses. Arithmetic operations, such as summation, that would
make sense for numerical values, do not make sense for ordinal
rankings. ALTO Clients may want to handle such costs differently.
Cost Modes are indicated in protocol messages as alphanumeric
strings. An ALTO Server MUST at least define the modes 'numerical'
and 'ordinal'.
If an ALTO Client requests a cost Mode that is not supported, the
ALTO Server MUST reply with costs having Mode either 'numerical' or
'ordinal'. Thus, an ALTO Server must implement at least one of
'numerical' or 'ordinal' Costs, but it may choose which to support.
ALTO Clients may choose how to handle such situations. Two
particular possibilities are to use the returned costs as-is (e.g.,
treat numerical costs as ordinal rankings) or ignore the ALTO
information altogether.
4.2. Path Rating Query
The Path Rating Query consists of a Cost Type, a Cost Mode, a list of
Source Network Locations (note that a Network Location can be an
endpoint address or a PID), and a list of Destination Network
Locations.
Specifically, assume that a Path Rating 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], then the ALTO Server will compute 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).
4.2.1. Cost Map
We refer to the Response containing the m*n entries as a Cost Map.
If the Cost Type is ordinal, the ranking of each communicating pair
is relative to the m*n entries.
4.2.2. Ranking List
If there is a single Source Network Location and the Cost Mode is
ordinal, we also say that the response is a Ranking List.
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4.2.3. Implicit Source Network Location
If the Source Network Location is not specified in the Query message,
it is inferred by the ALTO server as the address of the Query message
sender.
4.2.4. Implicit Destination Network Location
If the Destination Network Location is not specified in the Query
message, it is inferred by the ALTO server as the list of all PIDs.
4.2.5. Network Map and Cost Map Dependency
Note that if a Path Rating query contains any PID in the list of
Source Network Locations or the list of Destination Network
Locations, we say that the particular Path Rating is generated based
on a particular Network Map. Version Tags are introduced to ensure
that ALTO Clients are able to use consistent information even though
the information is provided in two maps. 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.
5. Protocol Overview
5.1. Design Approach
The ALTO Protocol design uses a RESTful interface using a lightweight
XML encoding, with the goal of leveraging current HTTP [2] [3]
implementations and infrastructure. ALTO messages are denoted with
HTTP Content-Type "application/alto".
These design decisions make the protocol easy to understand and
debug, and allows for flexible ALTO Server implementation strategies.
More importantly, however, this enables use of existing
implementations and infrastructure, and allows for simple caching and
redistribution of ALTO information to increase scalability.
5.1.1. Use of Existing Infrastructure
An important design consideration for the ALTO Protocol is easy
integration with existing applications and infrastructure. As
outlined above, HTTP is a natural choice. In particular, this ALTO
Protocol design leverages:
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o the huge installed base of HTTP infrastructure, including HTTP
caches,
o mature software implementations for both HTTP and XML,
o the fact that many P2P clients already have an embedded HTTP
client, and
o authentication and encryption mechanisms in HTTP and SSL.
5.1.2. ALTO Information Reuse and Redistribution
ALTO information may be useful to a large number of applications and
users. Distributing ALTO information must be efficient and not
become a bottleneck. Therefore, the ALTO Protocol specified in this
document integrates with existing HTTP caching infrastructure to
allow reuse of ALTO information by ALTO Clients and reduce load on
ALTO servers. ALTO information may also be cached or redistributed
using application-dependent mechanisms, such as P2P DHTs or P2P file-
sharing.
For example, a Cost Map amongst PIDs may be reused by all ALTO
Clients within a particular Source Grouping [12]. A full Network Map
may be reused by all ALTO Clients using the ALTO Server.
5.2. Message Format
The ALTO Protocol uses a RESTful design operating over HTTP. Both
Query and Response follow the standard format for HTTP Request and
Response messages [2] [3]. This section provides an overview of the
components of a Query message sent from an ALTO Client to an ALTO
Server, as well as the components of a Response message returned by
an ALTO Server. Note that if caching or redistribution is used, the
Response message may be returned from another (possibly third-party)
entity. Reuse and Redistrubution is further discussed in
Section 10.4.
5.2.1. Query Message
A Query message is generated by an ALTO Client and sent to an ALTO
Server. The ALTO Protocol employs the following components of the
HTTP request message:
Method: Indicates operation requested by the ALTO Client (along with
URI Path).
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URI Path: Indicates the operation requested by the ALTO Client
(along with Method).
URI Query String Parameters: Indicates parameters for the requested
operation. Note that in the messaging specification in Section 6,
we abbreviate these as 'URI QS Params'. Order of query string
parameters is not specified. Some parameters are restricted in
how many times they appear. We use the notation 'min..max' to
denote the the minimum and maximum times they may appear, where
'max' may be '*' to denote unbounded.
Headers: Indicates encoding of the Body.
Body: Indicates additional request parameters that are not concisely
representable as Query String parameters.
5.2.2. Response Message
A Response message is generated by an ALTO Server, which corresponds
to a particular Query message. The ALTO Protocol employs the
following components of the HTTP Response message:
Status Code: Indicates either success or an error condition.
Headers: Indicates encoding of the Body and caching directives.
Body: Contains data requested by the ALTO Client.
5.2.3. Query and Response Body Encoding
When the Body of a Query or Response message is not empty, it MUST
contain a well-formed XML document and it SHOULD contain an encoding
declaration in the XML declaration. If the charset parameter of the
MIME content type declaration is present and it is different from the
encoding declaration, the charset parameter takes precedence. Every
application conforment to this specification MUST accept the UTF-8
character encoding to ensure maximum interoperability. The namespace
for the elements defined in this specification is
urn:ietf:params:xml:ns:p2p:alto.
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
...
</alto>
Example XML Document Carried by ALTO Protocol Messages
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6. 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. Note that the primary focus of the current
draft is the architecture and protocol operations. This section will
be updated as revisions are made to protocol details and encodings.
For clarity of the examples, details such as URL encoding have been
omitted.
6.1. Client Processing
6.1.1. General Processing
An ALTO Client implementing the ALTO protocol can make use of a set
of queries, each for a different purpose. 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 to communicate with and establishes a TCP connection. The
ALTO protocol on top of this TCP connection can be secured through
SSL/TLS. The client then decides which query to use and formats it
as specified in Section 6.3, which includes HTTP request-line,
headers and body. Finally the client sends it down the TCP/IP stack.
All HTTP encoding rules apply, as well as TCP transport
considerarions.
6.1.2. General Error Conditions
In the case the client does not receive an appropriate response from
the server it can choose another server to communicate or fall back
to perform peer selection without the use of ALTO information.
6.2. Server Processing
6.2.1. General Error Conditions
This section specifies ALTO Server behavior when it recevies a Query
message that cannot be processed due to a problem with processing the
Query message itself.
6.2.1.1. Invalid Query Format
If any component of the Query message is formatted incorrectly (i.e.,
it does not follow the formats in Section 6.3), the ALTO Server MUST
return HTTP Status Code 400.
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6.2.1.2. Unsupported Query
If an ALTO Server does not support the operation indicated in the
Query message, the ALTO Server MUST return HTTP Status Code 501.
6.3. ALTO Queries
6.3.1. Server Capability
The Server Capability query allows an ALTO Client to determine the
configuration of a particular ALTO Server. The configuration
includes, for example, details about the operations and cost metrics
supported by the ALTO Server. The returned document can be
downloaded by ALTO Clients or provisioned into devices.
6.3.1.1. Query
The Query message MUST follow:
Method : 'GET'
URI Path : '/capability'
URI QS Params : MUST be empty
Headers : None required
Body : MUST be empty
6.3.1.2. Response
The Response message MUST follow:
Status Code : '200'
Headers : 'Content-Encoding: application/alto'
Body : See Below
The Body MUST be an XML document containing the Server Configuration
XML structure in Appendix B.1.
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6.3.1.3. Example Query and Response
GET /capability HTTP/1.1
Host: alto.example.com
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<configuration instance-name="alto.example.com">
<alto-server uri="http://alto.example.com:6671"/>
<cost type="latency" units="ms"/>
<cost type="pDistance" units="scalar"/>
<cost type="bandwidth" units ="kbps"/>
<constraint-support value="false"/>
</configuration>
</alto>
6.3.2. Endpoint Property Lookup
The Endpoint Property Lookup query allows an ALTO Client to query for
properties of Endpoints known to the ALTO Server.
6.3.2.1. Query
There are multiple forms of the Query message. The Query message
from the ALTO Client MUST follow one of the forms.
The first form allows an ALTO Client to query for properties of a
single endpoint:
Method : 'GET'
URI Path : '/endpoint/[endpointname]'
URI QS Params : 'prop=[propertyname]' (multiplicity: 1..*)
Headers : None Required
Body : MUST be empty
Note that the '[endpointname]' and '[propertyname]' strings above are
placeholders to be substituted with valid values indicated in
Appendix A.1 and Appendix A.3, respectively.
Also note that the 'prop' parameter may be specified multiple times
to query for multiple properties simultaneously. For example, the
query string could be 'prop=pid&prop=bandwidth'.
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The second form allows an ALTO Client to query for properties of
multiple endpoints:
Method : 'POST'
URI Path : '/endpoint/m'
URI QS Params : 'prop=[propertyname]' (multiplicity: 1..*)
Headers : 'Content-Encoding: application/alto'
Body : See Below
In the second form, the Body MUST be an XML document containing the
Endpoint List XML structure in Appendix B.3, with the additional
requirement that 'endpoint' elements specify no attributes except for
'name'.
6.3.2.2. Response
The Response message MUST follow:
Status Code : '200' if all property types are supported
'501' if at least one property is not supported
Headers : 'Content-Encoding: application/alto'
Body : See Below
The Body MUST be an XML document containing the Endpoint List XML
structure in Appendix B.3.
6.3.2.3. Example Query and Response
For additional message examples, see Appendix C.1.
GET /endpoint/ipv4:128.36.1.34?prop=pid HTTP/1.1
Host: alto.example.com
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<endpoint name="ipv4:128.36.1.34" pid="PID1"/>
</alto>
Example Query for Single Endpoint
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6.3.3. Reverse Property Lookup
The Reverse Property Lookup query allows an ALTO Client to query for
Endpoints with common properties. This draft focuses on the case
where an ALTO Client wishes to determine the Endpoints within a PID.
For scalability, the Endpoints within a PID may be enumerated using
IP Prefixes.
6.3.3.1. Query
There are multiple forms of the Query message. The Query message
from the ALTO Client MUST follow one of the forms.
The first form allows an ALTO Client to query for the IP prefixes
within a specific PID defined by the ALTO Server:
Method : 'GET'
URI Path : '/prop/pid/[pidname]'
URI QS Params : MUST be empty
Headers : None Required
Body : MUST be empty
Note that the '[pidname]' string above is a placeholder to be
substituted with valid values indicated in Appendix A.2.
The second form allows an ALTO Client to query for the IP prefixes
within all PIDs defined by the ALTO Server:
Method : 'GET'
URI Path : '/prop/pid'
URI QS Params : MUST be empty
Headers : None Required
Body : MUST be empty
The third form allows an ALTO Client to query for the IP prefixes
within a specific set of PIDs:
Method : 'POST'
URI Path : '/prop/pid/m'
URI QS Params : MUST be empty
Headers : 'Content-Encoding: application/alto'
Body : See Below
In the second form, the Body MUST be an XML document containing the
PID List XML structure in Appendix B.5, with the additional
requirement that 'pid' elements specify no attributes except for
'name'.
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6.3.3.2. Response
The Response message MUST follow:
Status Code : '200' if all PIDs specified in request are
valid, or no PIDs are specified in request.
'404' if at least one PID specified in request
is not valid.
Headers : 'Content-Encoding: application/alto'
Body : See Below
The Body MUST be an XML document containing the PID List XML
structure in Appendix B.5.
6.3.3.3. Example Query and Response
For additional message examples, see Appendix C.2.
GET /prop/pid/PID1 HTTP/1.1
Host: alto.example.com
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<pid name="PID1" size="3">
<cidr4 name="128.36.1.0/24"/>
<cidr4 name="132.130.1.0/24"/>
<cidr4 name="132.130.2.0/24"/>
</pid>
</alto>
Example Query for Single PID
6.3.4. Path Rating Lookup
The Path Rating Lookup query allows ALTO Clients to query for Costs
amongst Network Locations.
6.3.4.1. Query
There are multiple forms of the Query message. The Query message
from the ALTO Client MUST follow one of the forms.
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The first form allows an ALTO Client to query for costs amongst all
PIDs defined by the ALTO Server:
Method : 'GET'
URI Path : '/cost/map'
URI QS Params : 'type=[costtype]' (multiplicity: 0..1)
'mode=[costmode]' (multiplicity: 0..1)
'constraint=[constraint]' (multiplicity: 0..*)
Headers : None Required
Body : MUST be empty
Note that the '[costtype]', '[costmode]', '[constraint]' strings
above are placeholders to be substituted with valid values indicated
in Appendix A.5, Appendix A.6, and Appendix A.7 respectively.
The 'constraint' parameter is optional and is to be used only if the
ALTO service supports it. It allows a client to specify a target
numerical cost. The constraint contains two entities: (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 ALTO service configuration document obtained
from ALTO service discovery. These cost constraints allows a
resource constrained ALTO client to filter query results at the ALTO
server instead of spending network bandwidth and multiple round trips
collecting results and performing client side filtering. If multiple
'constraint' parameters are specified, the ALTO Server assumes they
are related to each other with a logical AND.
If the query does not specify the 'type' and 'mode' query string
parameters, then the server assumes the type to be 'routingcost' and
the mode to be 'numerical'. A Query MUST contain no more than one
'type' parameter, and no more than one 'mode' parameter.
The second form allows an ALTO Client to query for costs from a
single Endpoint or PID to all other PIDs:
Method : 'GET'
URI Path : '/cost/row'
URI QS Params : 'srcpid=[pidname]' (multiplicity: 0..*)
'srcendp=[endpointname]' (multiplicity: 0..*)
'type=[costtype]' (multiplicity: 0..1)
'mode=[costmode]' (multiplicity: 0..1)
'constraint=[constraint]' (multiplicity: 0..*)
Headers : None Required
Body : MUST be empty
Note that in this form, exactly one of 'srcpid' and 'srcendp' query
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string parameters MUST be specified.
The third form allows an ALTO Client to query for costs amongst an
arbitrary set of sources and destinations:
Method : 'POST'
URI Path : '/cost/m'
URI QS Params : 'type=[costtype]' (multiplicity: 0..1)
'mode=[costmode]' (multiplicity: 0..1)
'constraint=[constraint]' (multiplicity: 0..*)
Headers : 'Content-Encoding: application/alto'
Body : See Below
In the third form, the Body MUST be an XML document containing the
Cost Map Specification XML structure in Appendix B.6.
6.3.4.2. Response
The Response message MUST follow:
Status Code : '200' if all PIDs specified in request are
valid, or no PIDs are specified in request.
'404' if at least one PID specified in request
is not valid.
'501' if specified cost type is not supported
'501' if constraints not supported but are
included
Headers : 'Content-Encoding: application/alto'
Body : See Below
The Body MUST be an XML document containing the Cost Map XML
structure in Appendix B.8.
Note that the ALTO Server is not required to return a 501 code
(unsupported query) if an unsupported cost type or cost mode is
specified. In such a case, the ALTO Server MAY instead reply with
Costs for a default type.
6.3.4.3. Examples of Query and Response
We give two examples. For additional message examples, see
Appendix C.3.
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GET /cost/map HTTP/1.1
Host: alto.example.com
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<costmap type="routingcost" mode="ordinal">
<row srcpid="PID1" size="2">
<pid name="PID2" cost="5"/>
<pid name="PID3" cost="10"/>
</row>
<row srcpid="PID2" size="2">
<pid name="PID1" cost="5"/>
<pid name="PID3" cost="15/>
</row>
<row srcpid="PID3" size="2">
<pid name="PID1" cost="20"/>
<pid name="PID2" cost="15"/>
</row>
</costmap>
</alto>
Example Query for Cost Map for All PIDs
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POST /cost/m?mode=ordinal HTTP/1.1
Host: alto.example.com
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<costmapspec>
<srcs size="1">
<endpoint name="ipv4:128.36.22.1"/>
</srcs>
<dsts size="3">
<endpoint name="ipv4:128.30.24.89"/>
<endpoint name="ipv4:130.132.33.4"/>
<endpoint name="ipv4:12.32.67.3"/>
</dsts>
</costmapspec>
</alto>
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<costmap type="routingcost" mode="ordinal">
<row srcendp="ipv4:128.36.22.1" size="2">
<endpoint name="ipv4:130.132.33.4" cost="1"/>
<endpoint name="ipv4:128.30.24.89" cost="2"/>
<endpoint name="ipv4:12.32.67.3" cost="3"/>
</row>
</costmap>
</alto>
Example Query for Specific Destinations (Ranking List)
7. Use Cases
The sections below depict typical use cases.
7.1. 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
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ALTO information as an additional information source to enable more
network-efficient traffic patterns and improve application
performance.
A particular requirement of many P2P trackers is that they must
handle a large number of P2P clients. A P2P tracker can obtain and
locally store ALTO information (the Network Map and Cost Map) from
the ISPs containing the P2P clients, and benefit from the same
aggregation of network locations done by ALTO Servers.
.---------. (1) Get Network Map .---------------.
| | <----------------------> | |
| ALTO | | P2P Tracker |
| Server | (2) Get Cost Map | (ALTO Client) |
| | <----------------------> | |
`---------' `---------------'
^ |
(3) Get Peers | | (4) Selected Peer
| v List
.---------. .-----------.
| Peer 1 | <-------------- | P2P |
`---------' | Client |
. (5) Connect to `-----------'
. Selected Peers /
.---------. /
| Peer 50 | <------------------
`---------'
Figure 2: ALTO Client Embedded in P2P Tracker
Figure 2 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 Reverse Property Lookup 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
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sources.
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.
7.2. 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 3: ALTO Client Embedded in P2P Client
Figure 3 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.
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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.
7.3. 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 Path 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 4: ALTO Client Embedded in P2P Client: Ranking
Figure 4 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 its ALTO Server, including discovered
peers as the set of Destination Network Locations, and indicates
the 'ordinal' Cost Mode. The returned Cost Map indicates the
ranking of the candidate peers.
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3. The P2P Client connects to the peers in the order specified in
the ranking.
8. Discussions
8.1. Discovery
The particular mechanism by which an ALTO Client discovers its ALTO
Server is an important component to the ALTO architecture and
numerous techniques have been discussed [13] [14]. However, the
discovery mechanism is out of scope for this document.
Some ISPs have proposed the possibility of delegation, in which an
ISP provides information for customer networks which do not wish to
run Portal Servers themselves. A consideration for delegation is
that customer networks may wish to explicitly configure such
delegation.
8.2. Network Address Translation Considerations
At this day and age of NAT v4<->v4, v4<->v6 [15], and possibly
v6<->v6[16], 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
(the GetCostMap-Source interface) where the source NL-ID 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 P2P Trackers (e.g., BitTorrent Trackers - see
"Tracker HTTP/HTTPS Protocol" in [17]).
The ALTO client SHOULD use the Session Traversal Utilities for NAT
(STUN) [4] to determine a public IP address to use as a source NL-ID.
If using this method, the host MUST 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.
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8.3. 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, Reverse Property Lookup query 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.
8.4. 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.
8.5. 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 [18], more
investigation is needed to identify other methods.
In addition, the application might account for robustness, perhaps
using randomized exploration to determine if it performs better
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without ALTO information.
8.5.1. 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) [19] [8].
o Optimistically unchoking low-cost peers with higher probability
[8].
8.5.2. 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 [18].
9. IANA Considerations
This document request the registration of a new media type:
"application/alto"
10. Security Considerations
10.1. 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. In
particular, providing overly fine-grained information may make it
easier for attackers to infer network topology. On the other hand,
revealing overly coarse-grained information may not provide benefits
to network efficiency or performance improvements to ALTO Clients.
10.2. ALTO Clients
Applications using the information must be cognizant of the
possibility that the information is malformed or incorrect. Even
when it is correct, its use might harm the performance. When an
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application concludes that it would get better performance
disregarding the ALTO information, the decision to discontinue the
use of ALTO information is likely best left to the user.
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.
The use of SSL/TLS can make it easier for clients to verify the
origin of ALTO information.
10.3. ALTO Information
An ALTO Server may optionally use authentication and encryption to
protect ALTO information. Authentication and encryption may be
provided using HTTP Basic or Digest Authentication and/or SSL/TLS.
10.4. 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 actually generated by
the correct 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 fulfill these requirements, ALTO Information meant to be
redistributable contains a digital signature which includes a hash of
the ALTO information encrypted by the ALTO Server's private key. The
corresponding public key should either be part of the ALTO
information itself, or it could be included in the interface
descriptor. The public key SHOULD include the hostname of the ALTO
Server and it SHOULD be signed by a trusted authority.
11. References
11.1. 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.
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[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] 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.
11.2. Informative References
[5] 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.
[6] 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.
[7] 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.
[8] Shalunov, S., Penno, R., and R. Woundy, "ALTO Information
Export Service", draft-shalunov-alto-infoexport-00 (work in
progress), October 2008.
[9] Das, S. and V. Narayanan, "A Client to Service Query Response
Protocol for ALTO", draft-saumitra-alto-queryresponse-00 (work
in progress), March 2009.
[10] 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.
[11] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement",
draft-marocco-alto-problem-statement-04 (work in progress),
February 2009.
[12] 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.
[13] Garcia, G., Tomsu, M., and Y. Wang, "ALTO Discovery Protocols",
draft-wang-alto-discovery-00 (work in progress), March 2009.
[14] Song, H., Even, R., Pascual, V., and Y. Zhang, "Application-
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Layer Traffic Optimization (ALTO): Discover ALTO Servers",
draft-song-alto-server-discovery-00 (work in progress),
March 2009.
[15] Baker, F., Li, X., and C. Bao, "Framework for IPv4/IPv6
Translation", draft-baker-behave-v4v6-framework-02 (work in
progress), February 2009.
[16] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Address
Translation (NAT66)", draft-mrw-behave-nat66-02 (work in
progress), March 2009.
[17] "Bittorrent Protocol Specification v1.0",
http://wiki.theory.org/BitTorrentSpecification, 2009.
[18] H. Xie, YR. Yang, A. Krishnamurthy, Y. Liu, and A.
Silberschatz., "P4P: Provider Portal for (P2P) Applications",
In SIGCOMM 2008.
[19] Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D.
Saucez, "The PROXIDOR Service", draft-akonjang-alto-proxidor-00
(work in progress), March 2009.
Appendix A. Data Types
A.1. Endpoint Name
TBD.
A.2. PID Name
TBD.
A.3. Property Name
TBD.
A.4. IP Prefix
TBD.
A.5. Cost Type
TBD.
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A.6. Cost Mode
TBD.
A.7. Constraint
TBD.
Appendix B. XML Encoding
B.1. Server Configuration
The Response contains a 'configuration' XML element which contains
the configuration information for an ALTO. service. The
'configuration' element MUST have the following attributes:
o name of the ALTO service
The 'configuration' element MAY contain the following child elements:
o specifies in its 'uri' attribute, the Base URI at which the ALTO
Server can be reached. An ALTO Client uses this URI (e.g.,
'http://alto.example.com:6671/') as a prefix placed before URI
Paths when querying an ALTO Server. More than one 'alto-server'
element may be present for load balancing, and an ALTO Client can
choose any one at random.
o specifies a cost metric supported by the ALTO Server. It MUST
have a 'type' attribute indicating the name of the metric, and
MUST have a 'units' attribute indicating the measurement units.
If the metric does not have any units, then the units attribute
must have the value 'none'. unit. If the no 'cost' element is
present, then the ALTO Server is assumed to support the default
'routingcost' Cost metric. Multiple 'cost' elements MAY be
included, but a single Cost Type MUST NOT appear more than once.
o specifies whether the ALTO Server supports Cost constraints in the
Path Cost Lookup Query Section 6.3.4. This element MUST contain a
'value' attribute with value either 'true' or 'false'. The
'constraint-support' element MUST NOT appear more than once. If
the 'constraint-support' element is not present, the ALTO Client
MUST assume that the ALTO Server does not support Cost
constraints.
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B.2. Endpoint
An Endpoint is represented by the XML element 'endpoint'. The
following attributes are REQUIRED:
name: Indicates the name of the Endpoint. The value of this
attribute MUST be formatted according to Appendix A.1.
The 'endpoint' element MAY contain additional attributes indicating
endpoint properties and their values. In this case, the attribute
name is the property name, and the attribute value is the value of
the property. Note that 'name' is not a valid property name.
B.3. Endpoint List
A list of Endpoints is represented by the XML element 'endpoints'.
The following attributes are REQUIRED:
size: Specifies the number of endpoints contained in the list as a
non-negative integer.
The 'endpoints' element MAY contain child elements. The following
elements are allowed:
element: Specifies a single endpoint in the list. The number of
'endpoint' elements MUST equal the value of the 'size' attribute
for the containing 'endpoints' element.
B.4. PID
TBD.
B.5. PID List
TBD.
B.6. Cost Map Specification
TBD.
B.7. Cost Row
TBD.
B.8. Cost Map
TBD.
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Appendix C. Additional Protocol Message Examples
C.1. Endpoint Property Lookup
POST /endpoint/m?prop=pid HTTP/1.1
Host: alto.example.com
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<endpoints size="2">
<endpoint name="ipv4:128.36.1.34"/>
<endpoint name="ipv4:130.132.1.100"/>
</endpoints>
</alto>
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<endpoints size="2">
<endpoint name="ipv4:128.36.1.34" pid="PID1"/>
<endpoint name="ipv4:130.132.1.100" pid="PID2"/>
</endpoints>
</alto>
Example Query for Multiple Endpoints
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C.2. Reverse Property Lookup
GET /prop/pid/ HTTP/1.1
Host: alto.example.com
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<pids size="3">
<pid name="PID1" size="3">
<cidr4 name="128.36.1.0/24"/>
<cidr4 name="132.130.1.0/24"/>
<cidr4 name="132.130.2.0/24"/>
</pid>
<pid name="PID2" size="1">
<cidr4 name="130.132.3.0/24"/>
</pid>
<pid name="PID3" size="1">
<cidr4 name="0.0.0.0/0"/>
</pid>
</pids>
</alto>
Example Query for All PIDs
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POST /prop/pid/m HTTP/1.1
Host: alto.example.com
Content-Length: [...]
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<pids size="2">
<pid name="PID1"/>
<pid name="PID2"/>
</pids>
</alto>
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<pids size="2">
<pid name="PID1" size="3">
<cidr4 name="128.36.1.0/24"/>
<cidr4 name="132.130.1.0/24"/>
<cidr4 name="132.130.2.0/24"/>
</pid>
<pid name="PID2" size="1">
<cidr4 name="130.132.3.0/24"/>
</pid>
</pids>
</alto>
Example Query for Specific PIDs
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C.3. Path Cost Lookup
GET /cost/row?srcendp=ipv4:128.36.22.1 HTTP/1.1
Host: alto.example.com
HTTP/1.1 200 OK
Date: Fri, 31 Dec 1999 23:59:59 GMT
Content-Type: application/alto
Content-Length: [...]
<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="config-schema.rnc" type="compact"?>
<alto xmlns="urn:ietf:params:xml:ns:p2p:alto">
<costmap type="routingcost" mode="ordinal">
<row srcendp="ipv4:128.36.22.1" size="2">
<pid name="PID1" cost="1"/>
<pid name="PID2" cost="5"/>
<pid name="PID3" cost="10"/>
</row>
</costmap>
</alto>
Example Query for Cost Map from a Single Endpoint
Appendix D. Contributors
The people listed here should be viewed as co-authors of the
document. Due to the limit of 5 authors per draft the co-authors
were moved to the contributors section at this point.
Obi Akonjang
DT Labs/TU Berlin/
EMail: obi@net.t-labs.tu-berlin.de
Richard Alimi
Yale University
EMail: richard.alimi@yale.edu
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Saumitra M. Das
Qualcomm Inc.
EMail: saumitra@qualcomm.com
Syon Ding
China Telecom
EMail: syding@chinatelecom.com
Doug Pasko
Verizon
EMail: pasko@verizon.com
Laird Popkin
Pando Networks
EMail: laird@pando.com
Stefano Previdi
Cisco
EMail: sprevidi@cisco.com
Satish Raghunath
Juniper Networks
satishr@juniper.net
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Stanislav Shalunov
BitTorrent
EMail: shalunov@bittorrent.com
Albert Tian
Ericsson/Redback
EMail: alberttian@gmail.com
Yu-Shun Wang
Microsoft Corp.
yu-shun.wang@microsoft.com
Richard Woundy
Comcast
Richard_Woundy@cable.comcast.com
David Zhang
PPLive
davidzhang@pplive.com
Yunfei Zhang
China Mobile
zhangyunfei@chinamobile.com
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Appendix E. Acknowledgements
We would like to thank the following additional people who were
involved in the projects that contributed to this merged document:
Alex Gerber (AT&T), Chris Griffiths (Comcast), Ramit Hora (Pando
Networks), Arvind Krishnamurthy (University of Washington), Marty
Lafferty (DCIA), Erran Li (Bell Labs), Jin Li (Microsoft), Y. Grace
Liu (IBM Watson), Jason Livingood (Comcast), Michael Merritt (AT&T),
Ingmar Poese (DT Labs/TU Berlin), James Royalty (Pando Networks),
Damien Saucez (UCL) Thomas Scholl (AT&T), Emilio Sepulveda
(Telefonica), Avi Silberschatz (Yale University), Hassan Sipra (Bell
Canada), Georgios Smaragdakis (DT Labs/TU Berlin), Haibin Song
(Huawei), Oliver Spatscheck (AT&T), See-Mong Tang (Microsoft), Jia
Wang (AT&T), Hao Wang (Yale University), Ye Wang (Yale University),
Haiyong Xie (Yale University).
Authors' Addresses
Reinaldo Penno (editor)
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, CA
USA
Email: rpenno@juniper.net
Y. Richard Yang (editor)
Yale University
Email: yry@cs.yale.edu
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