Skip to main content

Considerations on the AS-Level Application-Layer Traffic Optimization
draft-asai-cross-domain-overlay-03

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Hirochika Asai , Hiroshi Esaki , 百瀬 剛
Last updated 2011-12-17 (Latest revision 2011-06-16)
RFC stream (None)
Formats
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date (None)
Responsible AD (None)
Send notices to (None)
draft-asai-cross-domain-overlay-03
Internet Engineering Task Force                                  H. Asai
Internet-Draft                                                  H. Esaki
Intended status: Informational                   The University of Tokyo
Expires: June 3, 2012                                          T. Momose
                                                           Cisco Systems
                                                                Dec 2011

 Considerations on the AS-Level Application-Layer Traffic Optimization
                   draft-asai-cross-domain-overlay-03

Abstract

   Application-layer or overlay routing has been applied to various
   distributed systems such as content delivery networks and live media
   streaming systems.  The problems with these systems for the layer 3
   network providers, such as Internet service providers, are that these
   systems utilize higher-cost network resources (e.g., transit links)
   from the viewpoint of the layer 3 network providers but the operators
   have difficulties in controlling and optimizing the traffic of these
   systems because these systems construct their own networks over the
   layer 3 network.  The ALTO Working Group has worked on application-
   layer traffic optimization to fill the gaps in routing policies
   between the layer 3 network and applications by providing the
   underlay network topology and cost information to these systems.
   However, there are considerations on applying application-layer
   traffic optimization techniques to cross-domain traffic because the
   cost is assumed to be configured by each AS although ASes are
   autonomously operated.  This document summarizes general problems
   with overlay networks and considerations on the AS-level application-
   layer traffic optimization from the viewpoint of inter-AS economics.
   The main concerns on the AS-level application-layer traffic
   optimization are unfair policy configuration between distinct
   administrative domains and asymmetric economic policies on transit
   links.  The underlying problem inducing these concerns is that the
   economic policies between interconnected ASes are non-disclosure due
   to commercial contracts.  This document also discusses the
   conceivable approaches to solve the problems and considerations.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

Asai, et al.              Expires June 3, 2012                  [Page 1]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 3, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Asai, et al.              Expires June 3, 2012                  [Page 2]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.1.  AS Relationships . . . . . . . . . . . . . . . . . . .  4
       1.1.2.  Transit  . . . . . . . . . . . . . . . . . . . . . . .  5
       1.1.3.  Peering  . . . . . . . . . . . . . . . . . . . . . . .  5
       1.1.4.  Overlay Network  . . . . . . . . . . . . . . . . . . .  5
   2.  Cross-Domain Traffic Optimization Problems and
       Considerations . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.1.  Problems with Overlay Networks . . . . . . . . . . . . . .  6
     2.2.  Considerations on AS-Level Application-Layer Traffic
           Optimization . . . . . . . . . . . . . . . . . . . . . . .  8
       2.2.1.  Unfair policy configuration  . . . . . . . . . . . . .  8
       2.2.2.  Asymmetric economic policies . . . . . . . . . . . . .  9
   3.  Solution Approaches  . . . . . . . . . . . . . . . . . . . . . 12
     3.1.  Inference-based Global Policy Map  . . . . . . . . . . . . 12
     3.2.  End-to-End Cost Map Exchange . . . . . . . . . . . . . . . 13
     3.3.  Path-Vector Policy Advertisement . . . . . . . . . . . . . 14
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
   7.  Informative References . . . . . . . . . . . . . . . . . . . . 19
   Appendix A.  The Impact of Cross-domain Policy Conflicts . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24

Asai, et al.              Expires June 3, 2012                  [Page 3]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

1.  Introduction

   Many distributed systems, such as content delivery networks (CDNs)
   and live media streaming systems, have introduced application-layer
   overlay routing for their communication scheme to avoid excessive
   server load and to achieve effective and high-quality communication
   (e.g., high throughput, fault tolerance).  Server-client type
   distributed systems as well as peer-to-peer applications have also
   introduced application-layer overlay routing on their back-end.
   Today, the traffic generated by these applications using application-
   layer overlay routing becomes a significant amount of the Internet
   traffic [RFC5693].  Since these applications construct their own
   network topology (a.k.a. overlay network) over the Internet,
   generally without taking into account the layer 3 network topology,
   these applications frequently utilize a larger amount of network
   resources than network providers expect.  Moreover, they may utilize
   a detoured path that cannot be expected by layer 3 network
   providers [Ho09].

   The ALTO Working Group has worked on application-layer traffic
   optimization to fill the gaps between the layer 3 network and
   applications by providing the underlay network topology and cost
   information to these applications for their overlay network
   construction.  However, there exist considerations on inter-AS
   economic policy conflicts when we focus on the AS-level application-
   layer traffic optimization.

   This document summarizes general problems with overlay networks and
   considerations on the AS-level application-layer traffic optimization
   from the viewpoint of inter-AS economics, which are not discussed
   in [RFC5693].  The main concerns on the AS-level application-layer
   traffic optimization are unfair policy configuration between distinct
   layer 3 network domains (i.e., ASes) and asymmetric economic policies
   on transit links.  The underlying problem inducing these concerns is
   that the economic policies between interconnected ASes are non-
   disclosure information due to commercial contracts.  This document
   also discusses the conceivable approaches to solve the problems and
   considerations.

1.1.  Terminology

   We use the following terms in this document.

1.1.1.  AS Relationships

   AS relationships represent commercial relationships between
   interconnected ASes.  AS relationships are categorized into two major
   types: transit and peering.  There are typical inter-AS routing

Asai, et al.              Expires June 3, 2012                  [Page 4]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   policies by each type of AS relationships [Wang03].

1.1.2.  Transit

   Transit is a type of AS relationships, in which a customer AS
   purchases Internet access from its transit provider(s) over transit
   link(s) by paying some amount of money according to the actual
   bandwidth usage.  Transit relationships are also called provider-
   customer relationships.

1.1.3.  Peering

   Peering is a type of AS relationships, in which two peering ASes are
   equal.  Traffic exchanged over peering links is free of charge.

1.1.4.  Overlay Network

   Overlay networks are constructed by application-layer nodes such as
   peer-to-peer application nodes over the layer 3 network (i.e., IP
   network) that is operated by network providers.  The topology and
   routing of overlay networks are controlled by applications that
   construct overlay networks but not by the layer 3 network providers.

Asai, et al.              Expires June 3, 2012                  [Page 5]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

2.  Cross-Domain Traffic Optimization Problems and Considerations

   This section discusses the general problems with overlay networks and
   considerations on the AS-level application-layer traffic optimization
   in terms of cross-domain traffic and economics.  They are categorized
   into two; 1) problems with overlay networks, and 2) considerations on
   AS-level application-layer traffic optimization.  The former category
   presents the general problems that overlay networks do not take into
   account the layer 3 network economics and routing policies.  The
   latter category presents the considerations that the AS-level
   application-layer traffic optimization has difficulties in applying
   it to the real Internet because of conflicts of cross-domain policies
   that are autonomously determined or configured by each administrative
   domain (i.e., AS).

2.1.  Problems with Overlay Networks

   The Internet consists of thousands of ASes operated by distinct
   network providers such as commercial ISPs, companies and
   universities.  Each AS generally connects with multiple ASes, and
   there are distinct charging policies for each inter-AS link.  These
   charging policies are roughly categorized into two major types of
   relationships; transit (with charge) and peering (without any
   charge).  From the economic viewpoint, network providers want to
   reduce the traffic volume exchanged with transit providers as much as
   possible, and consequently, they manage BGP routing policies as
   explained in [Wang03].

   However, overlay networks are not sometimes aware of these routing
   policies and generate more expensive cross-domain traffic.  On the
   other hand, network providers cannot optimize the cross-domain
   traffic generated by applications on overlay networks.  This is
   because the traffic is controlled by a set of application-specific
   algorithms that determines overlay network topology and traffic
   delivery paths, such as peer, neighbor, or path selection algorithms.

                    +------+ provider
                    | AS 1 |----------------------+
           provider +------+                      | transit
                       | transit                  |
                       v                          v
           customer +------+ peering +------+  +------+ customer
                    | AS 2 |<------->| AS 3 |  | AS 4 |
                    +------+         +------+  +------+

   AS 2 purchases Internet access from AS 1 via a transit link.  On the
   contrary, the link between AS 2 and AS 3 is peering, which is a lower
          cost link from the viewpoint of AS 2 network operators.

Asai, et al.              Expires June 3, 2012                  [Page 6]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

      Figure 1: An example of AS-level topology with AS relationships

   We show an example of the problem with the unawareness of the layer 3
   network economics and cross-domain traffic generated by overlay
   networks.  An example of interconnections of ASes and their
   relationships is shown in Figure 1.  Suppose remote nodes of a peer-
   to-peer content delivery network that provide a certain content file
   exist in both AS 3 and AS 4, and a local node that downloads the file
   in AS 2 is to retrieve the file from one of these remote nodes, a
   remote node in AS 3 should be selected to reduce transit charge for
   both ASes of the local node and the remote node, but today's peer-to-
   peer content delivery networks that are unaware of AS relationships
   often select other remote nodes.

   Thus, overlay networks often utilize higher-cost network resources
   (i.e., transit links from/to transit providers) from the economic
   viewpoint of network providers.  Moreover, especially on peer-to-peer
   overlay networks, the connectivity of most of end-point nodes (i.e.,
   peers) is provided by residential ISPs, and most of residential ISPs
   are not transit providers but transit customers.  Therefore, it is
   significantly important to control the transit traffic not to
   increase their charge to their providers though these kinds of
   application-layer traffic are hardly controlled by network providers.
   [RFC5693] also claims this problem with cross-domain traffic in terms
   of transit cost as well as congestion in intra-domain networks.

                 +------+ provider
                 | AS 1 |-----------------------------+
        provider +------+                             | transit
                    | transit                         |
                    v                                 v
        customer +------+ peering +------+ peering +------+ customer
                 | AS 2 |<------->| AS 3 |<------->| AS 4 |
                 +------+         +------+         +------+

   According to the typical BGP routing policies, the path from AS 2 to
     AS 4 is to be AS 2->AS 1->AS 4.  The path AS 2->AS 3->AS 4 is not
   usually allowed because AS 3 relays traffic from AS 2 to AS 4 without
                    any charge if this path is allowed.

      Figure 2: An example of AS-level detouring by overlay networks

   Another problem with overlay networks is that overlay networks may
   utilize a detoured path that cannot be expected by layer 3 network
   providers [Ho09].  For example, in Figure 2, the traffic from AS 2 to
   AS 4 can pass through AS 3 if a node of an overlay network exists in
   AS 3 and relays the traffic, but this is usually disallowed by the
   routing policy of AS 3.

Asai, et al.              Expires June 3, 2012                  [Page 7]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   In summary, overlay networks have following problems from the
   economic viewpoint of network providers.

   o  Overlay networks usually do not take into account the layer 3
      network economics to construct their network topology and to
      exchange traffic between end-point nodes.  Therefore, they utilize
      higher-cost network resources from the economic viewpoint of
      network providers.

   o  Overlay networks may enable AS-level traffic detouring that is
      disallowed by the layer 3 network routing policies.  This problem
      possibly increases transit expenses or induces free-riding.

2.2.  Considerations on AS-Level Application-Layer Traffic Optimization

   The ALTO Working Group has worked on application-layer traffic
   optimization to fill the gaps in routing policies between the layer 3
   network and overlay networks.  It has worked on solving the problems
   stated in [RFC5693], but [RFC5693] misses some considerations on the
   AS-level (cross-domain) application-layer traffic optimization.  We
   summarize the missing considerations as follows.

   o  Unfair policy configuration between distinct administrative
      domains: ASes hardly cooperate with each other in fairly
      regulating policies of distinct ASes because inter-AS policies are
      complicated and each AS operates its network under its own policy.

   o  Asymmetric economic policies on transit links: It is difficult to
      regulate the asymmetric economic policies on transit links because
      transit customers' policies run counter to transit providers;
      i.e., customers want to reduce the traffic exchanged with their
      providers to reduce their expense though providers want to
      increase the traffic exchanged with their customers to increase
      their income.

   The details of these problems are explained in the following
   sections.

2.2.1.  Unfair policy configuration

   The ALTO Working Group has proposed a protocol to distribute end-to-
   end network cost between peers [I-D.ietf-alto-protocol] to
   applications.  This protocol does not intend to define the cost
   computation algorithm, but it assumes that the cost is computed by
   network providers.  Two oracle-based cost computation algorithms,
   [Aggarwal07] and [Xie08], have been proposed and evaluated in the
   research area.  [Aggarwal07] computes the AS-level cost according to
   AS hop count between two end-point nodes.  So, it ignores the

Asai, et al.              Expires June 3, 2012                  [Page 8]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   information on AS relationships (i.e., transit cost).  [Xie08]
   computes the AS-level cost according to the configured parameters
   (e.g., `local preference' in BGP) in routers.  This takes into
   account AS relationships.  However, there is a problem with this
   algorithm when it is applied to the Internet (i.e., multi-domain
   system).  Charging policies for exchanged inter-AS traffic volume are
   so complicated that different ASes hardly cooperate with each other
   in computing and fairly balancing cost.  The hot potato problem
   stated in [RFC4277] shows the difficulty in regulating policies of
   distinct ASes.

                    +------+ provider
                    | AS 1 |----------------------+
           provider +------+ 5                    | transit
                     5 | transit (1$/Mbps)        |  (2$/Mbps)
                    30 v                          v 10
           customer +------+                   +------+ customer
                    | AS 2 |                   | AS 3 |
                    +------+                   +------+

                    Each number represents egress cost.

             Figure 3: An example of unfair cost configuration

   For example, suppose egress cost of each inter-AS link is configured
   autonomously (i.e., each AS sets cost according to its own policies)
   as shown in Figure 3, then the cost of the path from AS 2 to AS 1
   becomes larger than that of the path from AS 3 to AS 1 though the
   path from AS 2 to AS 1 seems to be a cheaper link than the other.
   Thus, oracle-based approaches are exposed to a fairness issue among
   multiple autonomous domains.

   In summary, inter-AS policies are so complex that ASes cooperate with
   each other in fairly regulating policies of distinct ASes in terms of
   cross-domain cost configuration.

2.2.2.  Asymmetric economic policies

   There is a difficulty in regulating the asymmetric economic policies
   between transit customers and providers.  One of the causes of this
   difficulty is same as that of the issue on the unfair policy
   configuration; i.e., because each AS configures its own desired
   policy.  Another cause of this difficulty is that the policies on the
   transit links are asymmetric.  So, one party's policy does not match
   the other's.  The same asymmetric nature is also found in BGP
   routing.  However, the asymmetric policy regulation on transit links
   becomes more complex in the overlay routing than BGP routing.  This
   is because overlay network nodes that have the same functionality or

Asai, et al.              Expires June 3, 2012                  [Page 9]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   contents possibly exist in multiple ASes although the functionality
   (i.e., connectivity to the destination) of BGP routing is mapped to a
   single AS.  Moreover, BGP path-vector routing is performed under the
   control of the layer 3 network providers by route import and export
   policies.  Consequently, the computed paths in BGP routing are based
   on the benefit principle with avoiding free-riding.

                                    +------+
                                    | AS 1 |
                           provider +------+
                                     5 | transit
                                    30 v
                           customer +------+
                                    | AS 2 |
                           provider +------+
                                     5 | transit
                                    30 v
                           customer +------+
                                    | AS 3 |
                                    +------+

   Each number in this figure represents cost.  Note that cost for each
   type of AS relationships is already regulated here; 5 for provider to
      customer and 30 for customer to provider.  This asymmetric cost
      configuration is also found in the typical import policy in BGP
                     routing (i.e., local preference).

           Figure 4: An example of asymmetric cost configuration

   For example, suppose the cost of each inter-AS link configured as
   shown in Figure 4 is egress cost, then the end-to-end cost from AS 1
   to AS 2 becomes smaller than that from AS 3 to AS 2.  On the other
   hand, suppose the cost of each inter-AS link configured as shown in
   Figure 4 is ingress cost, then the end-to-end cost from AS 1 to AS 2
   becomes larger than that from AS 3 to AS 2.  This means that the path
   from AS 3 to AS 2 is preferred than the other from the viewpoint of
   AS 2 but the path from AS 1 to AS 2 is preferred than the other from
   the viewpoint of AS 1 and AS 3.  Unlike BGP routing, overlay networks
   may have the same functionality or contents at their nodes both in
   AS 1 and AS 3, and consequently, it is required to consider the
   conflicts of asymmetric economic policies on transit links between
   multiple ASes.

   Although the conflicts of asymmetric economic policies on transit
   links may develop, the AS-level application-layer traffic
   optimization can be performed by looking at the ALTO servers operated
   by the local AS without any regulation.  However, the global view
   with regulation possibly optimizes the cross-domain traffic in terms

Asai, et al.              Expires June 3, 2012                 [Page 10]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   of transit charge more than the local view based one as shown in
   Appendix A.  Moreover, Appendix A points out the problem that the
   local view based application-layer traffic optimization increases
   transit traffic to providers for some transit customers.

Asai, et al.              Expires June 3, 2012                 [Page 11]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

3.  Solution Approaches

   This section discusses the conceivable approaches to solve the
   problems and considerations described in Section 2.  We assume that
   the cost or policy information is provided via ALTO servers defined
   in [RFC5693].  The solution approaches are listed as follows.

   o  Inference-based Global Policy Map

   o  End-to-End Cost Map Exchange

   o  Accumulated Cost Map with Path-Vector Policy Advertisement

   The details of each solution approach are given in the following
   sections.

3.1.  Inference-based Global Policy Map

   Since the underlying problem inducing the considerations on the
   policy conflicts between distinct ASes is that the economic policies
   between interconnected ASes cannot be disclosed by each network
   provider due to commercial contracts, AS relationships inference can
   be one of the solution approaches to disclose the economic policies.
   AS relationships inference algorithms have been proposed in the
   research field, such as [Asai10-2], [Dimitropoulos07], and [Gao01].
   The end-to-end (AS-to-AS) cost can be computed from the AS
   relationships inferred by these algorithms although this document
   does not define the cost computation algorithm.  By providing the
   computed cost to applications through ALTO servers, overlay networks
   can be aware of the inter-AS economics.  This approach is based on
   the better-than-random principle because the inferred AS
   relationships for some links may not be accurate.  Note that the
   inaccurate inference can be overwritten by combining other solution
   approaches.  The advantage of this approach is that this approach can
   be deployed at third-party ALTO servers because this does not require
   the information provided by network providers.

   This approach solves the problems and considerations described in
   Section 2 as follows.

   o  Unawareness of the layer 3 network economics: Overlay networks can
      be aware of the layer 3 network economics by providing the end-to-
      end cost computed from the inferred AS relationships to
      applications through ALTO servers.

   o  AS-level traffic detouring: In this approach, ALTO servers have
      the information on the inferred AS relationships, so the ALTO
      servers can provide the information to check whether the detoured

Asai, et al.              Expires June 3, 2012                 [Page 12]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

      path is acceptable to network providers as well as the end-to-end
      cost.  Note that the inferred AS relationships may not exactly
      match the policies and preference of network providers.

   o  Unfair policy configuration: The end-to-end cost is fairly
      computed from the inferred AS relationships at a centralized
      server.  Note that there still exists an issue that the same type
      of AS relationships may not present the same economic policy in
      terms of transit charge.

   o  Asymmetric economic policies: The cost computation servers can
      regulate the asymmetric policies when they compute end-to-end
      cost.  Note that the symmetric policies may not always match the
      preference of network providers.

3.2.  End-to-End Cost Map Exchange

   A simple solution approach is to establish a cost exchange regulation
   for inter-AS economic policies among ALTO servers of other ASes
   (i.e., the cost exchange regulation will be established by creating
   full mesh).  ALTO servers exchange the inter-AS cost (perhaps the
   cost is aggregated per-prefix or per-AS) to other ALTO servers, while
   regulating the cost by a certain algorithm.  Note that this document
   does not define the cost regulation algorithm.  ALTO servers in each
   AS provide the end-to-end cost according to the computed end-to-end
   cost map.  This approach is simple but does not solve the problem
   with AS-level traffic detouring.  Moreover, there is an issue that
   ALTO servers are required to establish the cost exchange regulation
   with the other ASes' ALTO servers to exchange the inter-AS cost
   although this approach works better-than-random if only a part of
   ALTO servers establishes the cost exchange regulation.

   This approach solves the problems and considerations described in
   Section 2 as follows.

   o  Unawareness of the layer 3 network economics: ALTO servers can
      provide the end-to-end cost to applications, then overlay networks
      can be aware of the layer 3 network economics.

   o  AS-level traffic detouring: This problem is not solved by this
      approach because the end-to-end cost does not contain the policies
      of the paths that are disallowed by ASes.

   o  Unfair policy configuration: Since ALTO servers among multiple
      ASes establish a regulation for the exchanged inter-AS economic
      policies, the issue on unfair policy configuration is solved.

Asai, et al.              Expires June 3, 2012                 [Page 13]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   o  Asymmetric economic policies: The regulation between ALTO servers
      also solves the issue on asymmetric economic policies.

3.3.  Path-Vector Policy Advertisement

   The cost-based approaches have limitations to reflect the inter-AS
   policies in BGP routing because BGP is a path-vector routing protocol
   that is one of the policy-based routing protocols.  A solution
   approach to achieve the inter-AS application-layer traffic
   optimization while following the BGP routing policies is to introduce
   path-vector policy advertisement like BGP routing.  According to a
   path-vector protocol for the inter-AS application-layer traffic
   optimization, the ALTO servers operated by an AS establish
   interconnections with the ALTO servers operated by other ASes such as
   BGP neighbors, and exchange inter-AS policies over the
   interconnections; perhaps the path-vectors are aggregated per-prefix
   or per-AS.  In this way, each ALTO server obtains the path-vectors
   with inter-AS policies.  Here, note that this document does not
   specify the protocol to exchange inter-AS policies over the
   interconnections nor the algorithm to convert the path-vectors with
   inter-AS policies into the information (e.g., cost) that is provided
   from ALTO servers to applications.

   The advantage of this approach is that it can emulate BGP routing
   policies between interconnected ASes, and consequently, ALTO servers
   can provide the preference of the layer 3 network providers to
   applications.  In addition to the BGP emulation (i.e., advertising
   the best paths), ALTO servers can also exchange and advertise n-th
   best paths or negative paths (not preferred or disallowed in BGP)
   that are also informative in converting the received path-vectors to
   preference of end-to-end paths.  However, this approach requires to
   interconnect ALTO servers operated by multiple ASes, and they
   propagate the policies to the ALTO servers operated by other ASes.
   Therefore, a protocol specification and a policy regulation algorithm
   are essential for this approach.

   This approach solves the problems and considerations described in
   Section 2 as follows.

   o  Unawareness of the layer 3 network economics: ALTO servers can
      provide the layer 3 network information converted from the
      received path-vectors to applications, then overlay networks can
      be aware of the layer 3 network economics.

   o  AS-level traffic detouring: When ALTO servers advertise n-th best
      paths and negative paths, they can provide the preference
      information on detoured paths whether the detoured paths are
      acceptable for network providers (i.e., n-th best paths) or not

Asai, et al.              Expires June 3, 2012                 [Page 14]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

      (i.e., negative paths).

   o  Unfair policy configuration: Since neighboring ALTO servers
      establish a regulation for the exchanged inter-AS economic
      policies, the issue on unfair policy configuration is regressed.
      However, since ALTO servers exchange path-vectors with policies
      through hop-by-hop, a common regulation algorithm is required to
      be defined and used at every ALTO server.

   o  Asymmetric economic policies: The regulation algorithm shared
      among ALTO servers also solves the issue on asymmetric economic
      policies.

Asai, et al.              Expires June 3, 2012                 [Page 15]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

4.  IANA Considerations

   No need to describe any request regarding number assignment.

Asai, et al.              Expires June 3, 2012                 [Page 16]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

5.  Security Considerations

   This document is neither a requirements document nor a protocol
   specification.  However, since the solution approaches exchange the
   inter-AS economic policies with ALTO servers operated by other ASes
   (i.e., external network domains), two security considerations are
   discussed as follows.

   o  The ALTO servers operated by other ASes may falsify the received
      cost map or policies.  The protocol specifications of the solution
      approaches should include anti-falsification and verification
      mechanisms (e.g., signing) for the exchanged cost map or policies.

   o  The exchanged cost map or policies may contain the non-disclosure
      inter-AS information.  The protocol specifications of the solution
      approaches should consider the schemes to aggregate and filter the
      exchanged cost map or policies in order not to reveal the non-
      disclosure information.

Asai, et al.              Expires June 3, 2012                 [Page 17]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

6.  Acknowledgements

   Moritz Steiner (Bell-Labs), Piotr Wydrych (AGH University of Science
   and Technology), Russ White (Cisco Systems), Stefano Previdi (Cisco
   Systems), Volker Hilt (Alcatel-Lucent Bell-Labs), and many others
   provided informative discussions and valuable comments.

Asai, et al.              Expires June 3, 2012                 [Page 18]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

7.  Informative References

   [RFC4277]  McPherson, D. and K. Patel, "Experience with the BGP-4
              Protocol", RFC 4277, January 2006.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-10 (work in progress),
              October 2011.

   [Aggarwal07]
              Aggarwal, V., Feldmann, A., and C. Scheideler, "Can ISPs
              and P2P users cooperate for improved performance?",
               SIGCOMM Comput. Commun. Rev., vol. 37, no. 3, pp. 29-40,
              2007.

   [Asai10-1]
              Asai, H. and H. Esaki, "Towards Interdomain Transit
              Traffic Reduction in Peer-assisted Content Delivery
              Networks",  14th International Telecommunications Network
              Strategy and Planning Symposium, pp. 95-100, 2010.

   [Asai10-2]
              Asai, H. and H. Esaki, "Estimating AS Relationships for
              Application-Layer Traffic Optimization",  3rd Workshop on
              Economic Traffic Management, LNCS Vol. 6236, pp. 51-63,
              2010.

   [Dimitropoulos07]
              Dimitropoulos, X., Krioukov, D., Fomenkov, M., Huffaker,
              B., Hyun, Y., claffy, k., and G. Riley, "AS Relationships:
              Inference and Validation",  ACM SIGCOMM Comput. Commun.
              Rev., Vol. 37, No. 1, pp. 29-40, 2001.

   [Gao01]    Gao, L., "On inferring autonomous system relationships in
              the Internet",  IEEE/ACM Transactions on Networking,
              Vol. 9, No. 6, pp. 733-745, 2001.

   [Ho09]     Ho, Haddow, T., Ledlie, J., Draief, D., and P. Pietzuch,
              "Deconstructing internet paths: an approach for AS-level
              detour route discovery",  Proceedings of the 8th
              international conference on Peer-to-peer systems, p. 6,
              2009.

Asai, et al.              Expires June 3, 2012                 [Page 19]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   [Wang03]   Wang, F. and L. Gao, "On Inferring and Characterizing
              Internet Routing Policies",  IMC '03: Proceedings of the
              3rd ACM SIGCOMM conference on Internet measurement,
              pp. 15-26, 2003.

   [Xie08]    Xie, H., Yang, Krishnamurthy, A., Liu, and A.
              Silberschatz, "P4P: provider portal for applications",
               SIGCOMM '08: Proceedings of the ACM SIGCOMM 2008
              conference on Data communication, pp. 351-362, 2008.

Asai, et al.              Expires June 3, 2012                 [Page 20]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

Appendix A.  The Impact of Cross-domain Policy Conflicts

   To illustrate the impact of cross-domain policy conflicts for the AS-
   level application-layer traffic optimization, we evaluate the cross-
   domain traffic of a P2P CDN with trace-driven simulation.

   For the peer distribution, we had collected lists of peers from a
   tracker (http://bttracker.debian.org:6969/announce) every minute from
   31/10/2009 to 30/11/2009 (JST) for the content: Debian Linux DVD
   image; debian-503-i386-DVD-1.iso (4.4GB).  The collected lists
   contain sets of peer's IP address and port number.  The number of
   unique IP addresses of the collected peers is 48844, and these peers
   are distributed to 2569 ASes which has a power law distribution.
   From this peer distribution, we generated a trace for the trace-
   driven simulation according to the method described in [Asai10-1].
   By using this trace and a trace-driven simulator used in [Asai10-1],
   we computed the exchanged cross-domain traffic volume of ASes
   providing the Internet connectivity to peers.  Note that the piece
   size was set to 4.4GB (i.e., whole file) in this simulation and other
   parameters follow [Asai10-1].

   We evaluated five oracle-based peer selection algorithms in the P2P
   CDN; 1) Random, 2) AS hops, 3) Local view, 4) Remote view, and 5)
   Global view. ``Random'' and ``AS hops'' are algorithms to randomly
   select a peer and to select a peer minimizing AS hops between source
   and destination, respectively. ``Local view'' is an algorithm to
   select a peer minimizing expense of ASes accommodating local peers
   downloading the file from other peers; i.e., ``intra-domain'' is the
   highest priority, followed by ``from customer'', ``from peer'' and
   ``from provider''. ``Remote view'' is an algorithm to select a peer
   maximizing profit of ASes accommodating remote peers transferring the
   file to local peers; i.e., ``intra-domain'' is the highest priority,
   followed by ``to customer'', ``to peer'' and ``to provider''.
   ``Global view'' is the intermediate between ``Local view'' and
   ``Remote view''; i.e., to select a peer minimizing the summation of
   cost of both local and remote sides where the cost values of intra-
   domain, from/to provider, from/to peer, and from/to customer are 0,
   3, 2, 1, respectively.

Asai, et al.              Expires June 3, 2012                 [Page 21]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

      +-------------+----------------+----------------+------------+
      | Algorithm   | From providers | From customers | From peers |
      +-------------+----------------+----------------+------------+
      | Random      |          96.8% |           0.4% |       2.7% |
      |             |                |                |            |
      | AS hops     |          90.2% |           4.9% |       4.9% |
      |             |                |                |            |
      | Local view  |          89.3% |           8.8% |       1.9% |
      |             |                |                |            |
      | Remote view |          96.5% |           0.0% |       3.4% |
      |             |                |                |            |
      | Global view |          88.9% |           5.6% |       5.5% |
      +-------------+----------------+----------------+------------+

     Table 1: Simulation Results: Breakdown of total exchanged cross-
     domain traffic volume of ASes accommodating peers by types of AS
                     relationships (incoming traffic)

         +-------------+--------------+--------------+----------+
         | Algorithm   | To providers | To customers | To peers |
         +-------------+--------------+--------------+----------+
         | Random      |        61.0% |        24.8% |    14.2% |
         |             |              |              |          |
         | AS hops     |        62.0% |        19.7% |    18.3% |
         |             |              |              |          |
         | Local view  |        63.6% |        12.8% |    23.6% |
         |             |              |              |          |
         | Remote view |         7.4% |        83.2% |     9.4% |
         |             |              |              |          |
         | Global view |        11.4% |        79.4% |     9.3% |
         +-------------+--------------+--------------+----------+

     Table 2: Simulation Results: Breakdown of total exchanged cross-
     domain traffic volume of ASes accommodating peers by types of AS
                     relationships (outgoing traffic)

   Table 1 and Table 2 show the breakdown of total exchanged cross-
   domain traffic volume of ASes accommodating peers by types of AS
   relationships.  These results show that each algorithm did not
   achieve to reduce incoming transit traffic from providers much.  On
   the other hand, for outgoing traffic, ``Remote view'' and ``Global
   view'' algorithms significantly reduced outgoing transit traffic to
   providers.  The reason why the impact on the incoming transit traffic
   from providers is small is that the ASes accommodating local peers
   are generally transit customers, and consequently, the number of the
   paths that these ASes become transit providers or peering ASes are
   small.  On the contrary, the impact on the outgoing transit traffic
   to providers is larger than the incoming transit traffic because the

Asai, et al.              Expires June 3, 2012                 [Page 22]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

   number of the paths that the ASes accommodating remote peers become
   transit providers or peering ASes are not small.  The breakdown of
   the edge types of AS relationships for possible delivery paths is
   discussed in [Asai10-1].

   Moreover, this simulation points out the problem that ``Local view''
   algorithm increases transit traffic to providers for some transit
   customers.  In this simulation, when ``Local view'' algorithm is
   used, transit traffic to providers was increased for 23% of ASes
   accommodating peers while it was decreased for 13% of them, compared
   to ``AS hop'' algorithm.  This exhibits the policy conflicts have
   developed between local and remote ASes at ``Local view'' algorithm.

   Note that these simulation results intend to indicate that the AS-
   level application-layer traffic optimization based on local view
   increases transit traffic to providers for some transit customers,
   and the global view based one with the policy regulation among
   multiple ASes can reduce high-cost transit traffic.  For other traces
   and applications, further evaluation should be performed.

Asai, et al.              Expires June 3, 2012                 [Page 23]
Internet-Draft       Considerations on AS-Level ALTO            Dec 2011

Authors' Addresses

   Hirochika Asai
   The University of Tokyo
   7-3-1 Hongo
   Bunkyo-ku, Tokyo  113-8656
   JP

   Phone: +81 3 5841 6748
   Email: panda@hongo.wide.ad.jp

   Hiroshi Esaki
   The University of Tokyo
   7-3-1 Hongo
   Bunkyo-ku, Tokyo  113-8656
   JP

   Phone: +81 3 5841 6748
   Email: hiroshi@wide.ad.jp

   Tsuyoshi Momose
   Cisco Systems G.K.
   2-1-1 Nishi-Shinjuku
   Shinjuku-ku, Tokyo  163-0409
   JP

   Phone: +81 3 5324 4154
   Email: tmomose@cisco.com

Asai, et al.              Expires June 3, 2012                 [Page 24]