Internet Research Task Force (IRTF) I. Rimac
Request for Comments: 6029 V. Hilt
Category: Informational M. Tomsu
ISSN: 2070-1721 V. Gurbani
Bell Labs, Alcatel-Lucent
E. Marocco
Telecom Italia
October 2010
Internet Research Task Force (IRTF) I. Rimac
Request for Comments: 6029 V. Hilt
Category: Informational M. Tomsu
ISSN: 2070-1721 V. Gurbani
Bell Labs, Alcatel-Lucent
E. Marocco
Telecom Italia
October 2010
A Survey on Research on the Application-Layer Traffic Optimization (ALTO) Problem
应用层流量优化问题研究综述
Abstract
摘要
A significant part of the Internet traffic today is generated by peer-to-peer (P2P) applications used originally for file sharing, and more recently for real-time communications and live media streaming. Such applications discover a route to each other through an overlay network with little knowledge of the underlying network topology. As a result, they may choose peers based on information deduced from empirical measurements, which can lead to suboptimal choices. This document, a product of the P2P Research Group, presents a survey of existing literature on discovering and using network topology information for Application-Layer Traffic Optimization.
今天，互联网流量的很大一部分是由最初用于文件共享的对等（P2P）应用程序产生的，最近用于实时通信和实时媒体流。此类应用程序通过覆盖网络发现彼此之间的路由，而对底层网络拓扑知之甚少。因此，他们可能会根据经验测量得出的信息选择同龄人，这可能导致次优选择。本文档是P2P研究小组的产品，介绍了关于发现和使用网络拓扑信息进行应用层流量优化的现有文献综述。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
This document is a product of the Internet Research Task Force (IRTF). The IRTF publishes the results of Internet-related research and development activities. These results might not be suitable for deployment. This RFC represents the consensus of the Peer-to-Peer Research Group of the Internet Research Task Force (IRTF). Documents approved for publication by the IRSG are not a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文件是互联网研究工作组（IRTF）的产品。IRTF发布互联网相关研究和开发活动的结果。这些结果可能不适合部署。本RFC代表了互联网研究工作组（IRTF）对等研究小组的共识。IRSG批准发布的文件不适用于任何级别的互联网标准；见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6029.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc6029.
Copyright Notice
版权公告
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2010 IETF信托基金和确定为文件作者的人员。版权所有。
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.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Survey of Existing Literature . . . . . . . . . . . . . . . . 4
2.1. Application-Level Topology Estimation . . . . . . . . . . 5
2.2. Topology Estimation through Layer Cooperation . . . . . . 8
2.2.1. P4P Architecture . . . . . . . . . . . . . . . . . . . 9
2.2.2. Oracle-Based ISP-P2P Collaboration . . . . . . . . . . 9
2.2.3. ISP-Driven Informed Path Selection (IDIPS) Service . . 10
3. Application-Level Topology Estimation and the ALTO Problem . . 10
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Coordinate Estimation or Path Latencies? . . . . . . . . . 12
4.2. Malicious Nodes . . . . . . . . . . . . . . . . . . . . . 12
4.3. Information Integrity . . . . . . . . . . . . . . . . . . 12
4.4. Richness of Topological Information . . . . . . . . . . . 13
4.5. Hybrid Solutions . . . . . . . . . . . . . . . . . . . . . 13
4.6. Negative Impact of Over-Localization . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
7. Informative References . . . . . . . . . . . . . . . . . . . . 14
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Survey of Existing Literature . . . . . . . . . . . . . . . . 4
2.1. Application-Level Topology Estimation . . . . . . . . . . 5
2.2. Topology Estimation through Layer Cooperation . . . . . . 8
2.2.1. P4P Architecture . . . . . . . . . . . . . . . . . . . 9
2.2.2. Oracle-Based ISP-P2P Collaboration . . . . . . . . . . 9
2.2.3. ISP-Driven Informed Path Selection (IDIPS) Service . . 10
3. Application-Level Topology Estimation and the ALTO Problem . . 10
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Coordinate Estimation or Path Latencies? . . . . . . . . . 12
4.2. Malicious Nodes . . . . . . . . . . . . . . . . . . . . . 12
4.3. Information Integrity . . . . . . . . . . . . . . . . . . 12
4.4. Richness of Topological Information . . . . . . . . . . . 13
4.5. Hybrid Solutions . . . . . . . . . . . . . . . . . . . . . 13
4.6. Negative Impact of Over-Localization . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
7. Informative References . . . . . . . . . . . . . . . . . . . . 14
A significant part of today's Internet traffic is generated by peer-to-peer (P2P) applications, used originally for file sharing, and more recently for real-time multimedia communications and live media streaming. P2P applications pose serious challenges to the Internet infrastructure; by some estimates, P2P systems are so popular that they make up anywhere between 40% and 85% of the entire Internet traffic [Karagiannis], [LightReading], [LinuxReviews], [Parker], [Glasner].
当今互联网流量的很大一部分是由对等（P2P）应用程序产生的，最初用于文件共享，最近用于实时多媒体通信和实时媒体流。P2P应用对互联网基础设施构成严重挑战；据估计，P2P系统非常流行，它们占整个互联网流量的40%到85%，[Karagiannis]，[LightReading]，[LinuxReviews]，[Parker]，[Glasner]。
P2P systems ensure that popular content is replicated at multiple instances in the overlay. But perhaps ironically, a peer searching for that content may ignore the topology of the latent overlay network and instead select among available instances based on information it deduces from empirical measurements, which in some particular situations may lead to suboptimal choices. For example, a shorter round-trip time estimation is not indicative of the bandwidth and reliability of the underlying links, which have more of an influence than delay for large file transfer P2P applications.
P2P系统确保在覆盖中的多个实例上复制流行内容。但也许具有讽刺意味的是，对等搜索该内容可能会忽略潜在覆盖网络的拓扑结构，而是根据从经验测量中推断的信息在可用实例中进行选择，这在某些特定情况下可能导致次优选择。例如，较短的往返时间估计并不表示底层链路的带宽和可靠性，这对大型文件传输P2P应用程序的影响大于延迟。
Most Distributed Hash Tables (DHT) -- the data structures that impose a specific ordering for P2P overlays -- use greedy forwarding algorithms to reach their destination, making locally optimal decisions that may not turn out to be globally optimized [Gummadi]. This naturally leads to the Application-Layer Traffic Optimization (ALTO) problem [RFC5693]: how to best provide the topology of the underlying network while at the same time allowing the requesting node to use such information to effectively reach the node on which the content resides. Thus, it would appear that P2P networks with their application-layer routing strategies based on overlay topologies are in direct competition against the Internet routing and topology.
大多数分布式哈希表（DHT）——为P2P覆盖施加特定顺序的数据结构——使用贪婪转发算法到达目的地，做出局部最优的决策，但结果可能不是全局优化的[Gummadi]。这自然会导致应用层流量优化（ALTO）问题[RFC5693]：如何最好地提供底层网络的拓扑，同时允许请求节点使用此类信息有效地到达内容所在的节点。因此，P2P网络及其基于覆盖拓扑的应用层路由策略似乎与Internet路由和拓扑直接竞争。
One way to solve the ALTO problem is to build distributed application-level services for location and path selection [Francis], [Ng], [Dabek], [Costa], [Wong], [Madhyastha] in order to enable peers to estimate their position in the network and to efficiently select their neighbors. Similar solutions have been embedded into P2P applications such as Vuze [Vuze]. A slightly different approach is to have the Internet service provider (ISP) take a proactive role in the routing of P2P application traffic; the means by which this can be achieved have been proposed [Aggarwal], [Xie], [Saucez]. There is an intrinsic struggle between the layers -- P2P overlay and network underlay -- when performing the same service (routing); however, there are strategies to mitigate this dichotomy [Seetharaman].
解决ALTO问题的一种方法是为位置和路径选择[Francis]、[Ng]、[Dabek]、[Costa]、[Wong]、[Madhyastha]构建分布式应用程序级服务，以使对等方能够估计其在网络中的位置并有效地选择其邻居。类似的解决方案已经嵌入到P2P应用程序中，如Vuze[Vuze]。一种稍微不同的方法是让互联网服务提供商（ISP）在P2P应用程序流量的路由中扮演主动角色；已经提出了实现这一目标的方法[Aggarwal]、[Xie]、[Saucez]。当执行相同的服务（路由）时，层之间存在着内在的斗争——P2P覆盖和网络底层；然而，有一些策略可以缓解这种二分法[Seetharaman]。
This document, initially intended as a complement to RFC 5693 [RFC5693] and discussed during the creation of the IETF ALTO Working Group, has been completed and refined in the IRTF P2P Research Group. Its goal is to summarize the contemporary research activities on the Application-Layer Traffic Optimization problem as input to the ALTO working group protocol designers.
本文件最初旨在作为RFC 5693[RFC5693]的补充，并在IETF ALTO工作组创建期间进行了讨论，已在IRTF P2P研究小组中完成并完善。其目的是总结应用层流量优化问题的当代研究活动，作为ALTO工作组协议设计者的输入。
Terminology adopted in this document includes terms such as "ring geometry", "tree structure", and "butterfly network", borrowed from P2P scientific literature. [RFC4981] provides an exhaustive definition of such terminology.
本文件采用的术语包括借用自P2P科学文献的“环形几何”、“树结构”和“蝴蝶网络”等术语。[RFC4981]提供了此类术语的详尽定义。
Certain security-related terms are to be understood in the sense defined in [RFC4949]; such terms include, but are not limited to, "attack", "authentication", "confidentiality", "encryption", "identity", and "integrity". Other security-related terms (for example, "denial of service") are to be understood in the sense defined in the referenced specifications.
某些安全相关术语应理解为[RFC4949]中定义的含义；这些术语包括但不限于“攻击”、“身份验证”、“机密性”、“加密”、“身份”和“完整性”。其他安全相关术语（例如，“拒绝服务”）应理解为参考规范中定义的含义。
Gummadi et al. [Gummadi] compare popular DHT algorithms, and besides analyzing their resilience, provide an accurate evaluation of how well the logical overlay topology maps on the physical network layer. In their paper, relying only on measurements independently performed by overlay nodes without the support of additional location information provided by external entities, they demonstrate that the most efficient algorithms in terms of resilience and proximity performance are those based on the simplest geometric concept (i.e., the ring geometry, rather than tree structures, butterfly networks, and hybrid geometries).
Gummadi等人[Gummadi]比较了流行的DHT算法，除了分析它们的恢复能力外，还提供了对物理网络层上逻辑覆盖拓扑映射的准确评估。在他们的论文中，他们仅依赖覆盖节点独立执行的测量，而不支持外部实体提供的附加位置信息，证明了弹性和接近性能方面最有效的算法是基于最简单几何概念的算法（即环形几何体，而不是树结构、蝴蝶网络和混合几何体）。
Regardless of the geometrical properties of the distributed data structures involved, interactions between application-layer overlays and the underlying networks are a rich area of investigation. The available literature in this field can be divided into two categories (Figure 1): using application-level techniques to estimate topology, and using some kind of layer cooperation to estimate topology.
不管所涉及的分布式数据结构的几何特性如何，应用层覆盖和底层网络之间的交互都是一个丰富的研究领域。该领域的现有文献可分为两类（图1）：使用应用程序级技术来估计拓扑，以及使用某种层协作来估计拓扑。
Application-layer traffic optimization
|
+--> Application-level topology estimation
| |
| +--> Coordinates-based systems
| | |
| | +--> GNP
| | |
| | +--> Vivaldi
| | |
| | +--> PIC
| |
| +--> Path selection services
| | |
| | +--> IDMaps
| | |
| | +--> Meridian
| | |
| | +--> Ono
| |
| +--> Link-layer Internet maps
| |
| +--> iPlane
|
+--> Topology estimation through layer cooperation
|
+--> P4P: Provider portal for applications
|
+--> Oracle-based ISPs and P2P cooperation
|
+--> ISP-driven informed path selection
Application-layer traffic optimization
|
+--> Application-level topology estimation
| |
| +--> Coordinates-based systems
| | |
| | +--> GNP
| | |
| | +--> Vivaldi
| | |
| | +--> PIC
| |
| +--> Path selection services
| | |
| | +--> IDMaps
| | |
| | +--> Meridian
| | |
| | +--> Ono
| |
| +--> Link-layer Internet maps
| |
| +--> iPlane
|
+--> Topology estimation through layer cooperation
|
+--> P4P: Provider portal for applications
|
+--> Oracle-based ISPs and P2P cooperation
|
+--> ISP-driven informed path selection
Figure 1: Taxonomy of Solutions for the Application-Layer Traffic Optimization Problem
图1：应用层流量优化问题解决方案的分类
Estimating network topology information on the application layer has been an area of active research. Early systems used triangulation techniques to bound the distance between two hosts using a common landmark host. In such a technique, given a cost function C, a set of vertexes V and their corresponding edges, the triangle inequality holds if for any triple {a, b, c} in V, C(a, c) is always less than or equal to C(a, g) + C(b, c). The cost function C could be expressed in terms of desirable metrics such as bandwidth or latency.
在应用层估计网络拓扑信息一直是一个活跃的研究领域。早期的系统使用三角测量技术，使用公共地标主机来限制两台主机之间的距离。在这种技术中，给定一个代价函数C，一组顶点V及其相应的边，如果V中的任何三元{a，b，C}，C（a，C）总是小于或等于C（a，g）+C（b，C），则三角形不等式成立。成本函数C可以用期望的度量（例如带宽或延迟）表示。
We note that the techniques presented in this section are only representative of the sizable research in this area. Rather than
我们注意到，本节中介绍的技术仅代表该领域的大规模研究。而不是
trying to enumerate an exhaustive list, we have chosen certain techniques because they represent an advance in the area that further led to derivative works.
为了列举一个详尽的列表，我们选择了某些技术，因为它们代表了该领域的进步，进而导致衍生作品的出现。
Francis et al. proposed IDMaps [Francis], a system where one or more special hosts called tracers are deployed near an autonomous system. The distance measured in round-trip time (RTT) between hosts A and B is estimated as the cumulative distance between A and its nearest tracer Ta, plus the distance between B and its nearest tracer Tb, plus the shortest distance from Ta to Tb. To aid in scalability beyond that provided by the client-server design of IDMaps, Ng et al. proposed a P2P-based Global Network Positioning (GNP) architecture [Ng]. GNP was a network coordinate system based on absolute coordinates computed from modeling the Internet as a geometric space. It proposed a two-part architecture: in the first part, a small set of finite distributed hosts called landmarks compute their own coordinates in a fixed geometric space. In the second part, a host wishing to participate computes its own coordinates relative to those of the landmark hosts. Thus, armed with the computed coordinates, hosts can then determine interhost distance as soon as they discover each other.
Francis等人提出了IDMaps[Francis]，一种在自治系统附近部署一个或多个称为跟踪器的特殊主机的系统。主机A和B之间以往返时间（RTT）测量的距离估计为A与其最近的示踪剂Ta之间的累积距离，加上B与其最近的示踪剂Tb之间的距离，再加上Ta与Tb之间的最短距离。为了在IDMaps的客户机-服务器设计之外提供可扩展性，Ng等人提出了一种基于P2P的全球网络定位（GNP）体系结构[Ng]。GNP是一个基于绝对坐标的网络坐标系统，绝对坐标是通过将互联网建模为一个几何空间计算出来的。它提出了一个由两部分组成的体系结构：第一部分，一组称为landmarks的有限分布式主机在固定的几何空间中计算自己的坐标。在第二部分中，希望参与的主机计算其自身相对于地标主机的坐标。这样，通过计算出的坐标，主机一旦发现彼此，就可以确定主机间的距离。
Both IDMaps and GNP require fixed network infrastructure support in the form of tracers or landmark hosts; this often introduces a single point of failure and inhibits scalability. To combat this, new techniques were developed that embedded the network topology in a low-dimensional coordinate space to enable network distance estimation through vector analysis. Costa et al. introduced Practical Internet Coordinates (PIC) [Costa]. While PIC used the notion of landmark hosts, it did not require explicit network support to designate specific landmark hosts. Any node whose coordinates have been computed could act as a landmark host. When a node joined the system, it probed the network distance to some landmark hosts. Then, it obtained the coordinates of each landmark host and computed its own coordinates relative to each landmark host, subject to the constraint of minimizing the error in the predicted distance and computed distance.
IDMaps和GNP都需要以跟踪程序或地标主机的形式提供固定网络基础设施支持；这通常会导致单点故障，并抑制可扩展性。为了解决这一问题，开发了新技术，将网络拓扑嵌入到低维坐标空间中，通过矢量分析实现网络距离估计。Costa等人介绍了实用互联网坐标（PIC）[Costa]。虽然PIC使用了landmark主机的概念，但它不需要明确的网络支持来指定特定的landmark主机。任何已计算坐标的节点都可以作为地标主机。当一个节点加入系统时，它探测到一些地标主机的网络距离。然后，在预测距离和计算距离误差最小的约束下，获得每个地标主体的坐标并计算其相对于每个地标主体的坐标。
Like PIC, Vivaldi [Dabek] proposed a fully distributed network coordinate system without any distinguished hosts. Whenever a node A communicates with another node B, it measures the RTT to that node and learns that node's current coordinates. Node A subsequently adjusts its coordinates such that it is closer to, or further from, B by computing new coordinates that minimize the squared error. A Vivaldi node is thus constantly adjusting its position based on a simulation of interconnected mass springs. Vivaldi is now being used in the popular P2P application Vuze, and studies indicate that it scales well to very large networks [Ledlie].
与PIC一样，Vivaldi[Dabek]提出了一个完全分布式的网络坐标系统，没有任何可分辨的主机。每当一个节点a与另一个节点B通信时，它测量到该节点的RTT并学习该节点的当前坐标。节点A随后通过计算使平方误差最小化的新坐标来调整其坐标，使其更接近或更远离B。因此，Vivaldi节点根据相互连接的质量弹簧的模拟不断调整其位置。Vivaldi现在正在流行的P2P应用程序Vuze中使用，研究表明它可以很好地扩展到非常大的网络[Ledlie]。
Network coordinate systems require the embedding of the Internet topology into a coordinate system. This is not always possible without errors, which impacts the accuracy of distance estimations. In particular, it has proved to be difficult to embed the triangular inequalities found in Internet path distances [Ledlie]. Thus, Meridian [Wong] abandons the generality of network coordinate systems and provides specific distance evaluation services. In Meridian, each node keeps track of a small fixed number of neighbors and organizes them in concentric rings, ordered by distance from the node. Meridian locates the closest node by performing a multi-hop search where each hop exponentially reduces the distance to the target. Although less general than virtual coordinates, Meridian incurs significantly less error for closest node discovery.
网络坐标系要求将Internet拓扑嵌入坐标系中。如果没有误差，这并不总是可能的，因为误差会影响距离估计的准确性。特别是，事实证明很难嵌入互联网路径距离中的三角不等式[Ledlie]。因此，Meridian[Wong]放弃了网络坐标系的通用性，提供了特定的距离评估服务。在Meridian中，每个节点跟踪少量固定数量的邻居，并将它们组织成同心环，按与节点的距离排序。Meridian通过执行多跳搜索来定位最近的节点，其中每一跳都以指数方式减少到目标的距离。尽管与虚拟坐标相比，Meridian的通用性较差，但其发现最近节点的误差要小得多。
The Ono project [Ono] takes a different approach and uses network measurements from Content Distribution Networks (CDNs) such as Akamai to find nearby peers. Used as a plugin to the Vuze bittorrent client, Ono provides 31% average download rate improvement [Su].
Ono项目[Ono]采用不同的方法，使用来自Akamai等内容分发网络（CDN）的网络测量来查找附近的对等方。作为Vuze bittorrent客户端的插件，Ono提供了31%的平均下载速率提升[Su]。
Comparison of application-level topology estimation techniques, as reported in literature. Results in terms of number of (D)imensions and (L)andmarks, 90th percentile relative error.
应用级拓扑估计技术的比较，如文献所述。结果在（D）尺寸和（L）和分数方面，第90百分位相对误差。
+----------------+---------------+----------------+-----------------+
| GNP vs. | PIC(b) vs. | Vivaldi vs. | Meridian vs. |
| IDMaps(a) (7D, | GNP (8D, 16L) | GNP (2D, 32L) | GNP (8D, 15L) |
| 15L) | | | |
+----------------+---------------+----------------+-----------------+
| GNP: 0.50, | PIC: 0.38, | Vivaldi: 0.65, | Meridian: 0.78, |
| IDMaps: 0.97 | GNP: 0.37 | GNP: 0.65 | GNP: 1.18 |
+----------------+---------------+----------------+-----------------+
+----------------+---------------+----------------+-----------------+
| GNP vs. | PIC(b) vs. | Vivaldi vs. | Meridian vs. |
| IDMaps(a) (7D, | GNP (8D, 16L) | GNP (2D, 32L) | GNP (8D, 15L) |
| 15L) | | | |
+----------------+---------------+----------------+-----------------+
| GNP: 0.50, | PIC: 0.38, | Vivaldi: 0.65, | Meridian: 0.78, |
| IDMaps: 0.97 | GNP: 0.37 | GNP: 0.65 | GNP: 1.18 |
+----------------+---------------+----------------+-----------------+
(a) Does not use dimensions or landmarks. (b) Uses results from the hybrid strategy for PIC.
（a） 不使用尺寸标注或地标。（b） 使用PIC混合策略的结果。
Table 1
表1
Table 1 summarizes the application-level topology estimation techniques. The salient performance metric is the relative error. While all approaches define this metric a bit differently, it can be generalized as how close a predicted distance comes to the corresponding measured distance. A value of zero implies perfect prediction, and a value of 1 implies that the predicted distance is in error by a factor of two. PIC, Vivaldi, and Meridian compare their results with that of GNP, while GNP itself compares its results with a precursor technique, IDMaps. Because each of the techniques uses a different Internet topology and a varying number of landmarks and dimensions to interpret the data set, it is impossible to
表1总结了应用程序级拓扑估计技术。突出的性能指标是相对误差。虽然所有方法对该度量的定义略有不同，但它可以概括为预测距离与相应测量距离的接近程度。值为零表示预测完美，值为1表示预测距离的误差为2倍。PIC、Vivaldi和Meridian将其结果与GNP进行比较，而GNP本身将其结果与前体技术IDMaps进行比较。由于每种技术都使用不同的互联网拓扑和不同数量的地标和维度来解释数据集，因此不可能
normalize the relative error across all techniques uniformly. Thus, we present the relative error data in pairs, as reported in the literature describing the specific technique. Readers are urged to compare the relative error performance in each column on its own and not draw any conclusions by comparing the data across columns.
统一标准化所有技术的相对误差。因此，如描述特定技术的文献中所述，我们成对提供相对误差数据。敦促读者单独比较每一列的相对错误性能，不要通过跨列比较数据得出任何结论。
Most of the work on estimating topology information focuses on predicting network distance in terms of latency and does not provide estimates for other metrics such as throughput or packet loss rate. However, for many P2P applications latency is not the most important performance metric, and these applications could benefit from a richer information plane. Sophisticated methods of active network probing and passive traffic monitoring are generally very powerful and can generate network statistics indirectly related to performance measures of interest, such as delay and loss rate on link-level granularity. Extraction of these hidden attributes can be achieved by applying statistical inference techniques developed in the field of inferential network monitoring or network tomography subsequent to sampling of the network state. Thus, network tomography enables the extraction of a richer set of topology information, but at the same time inherently increases complexity of a potential information plane and introduces estimation errors. For both active and passive methods, statistical models for the measurement process need to be developed, and the spatial and temporal dependence of the measurements should be assessed. Moreover, measurement methodology and statistical inference strategy must be considered jointly. For a deeper discussion of network tomography and recent developments in the field, we refer the reader to [Coates].
关于估计拓扑信息的大多数工作侧重于根据延迟预测网络距离，而不提供吞吐量或丢包率等其他指标的估计。然而，对于许多P2P应用程序来说，延迟并不是最重要的性能指标，这些应用程序可以从更丰富的信息平面中获益。主动网络探测和被动流量监测的复杂方法通常非常强大，可以生成与性能指标（如链路级粒度上的延迟和丢失率）间接相关的网络统计数据。这些隐藏属性的提取可以通过在网络状态采样之后应用推理网络监测或网络层析成像领域开发的统计推断技术来实现。因此，网络层析成像能够提取更丰富的拓扑信息集，但同时固有地增加潜在信息平面的复杂性并引入估计误差。对于主动法和被动法，都需要建立测量过程的统计模型，并评估测量的空间和时间依赖性。此外，测量方法和统计推断策略必须联合考虑。关于网络层析成像和该领域最新发展的深入讨论，请参考[Coates]。
One system providing such a service is iPlane [Madhyastha], which aims at creating an annotated atlas of the Internet that contains information about latency, bandwidth, capacity, and loss rate. To determine features of the Internet topology, iPlane bridges and builds upon different ideas, such as active probing based on packet dispersion techniques to infer available bandwidth along path segments. These ideas are drawn from different fields, including network measurement as described by Dovrolis et al. in [Dovrolis] and network tomography [Coates].
提供这种服务的一个系统是iPlane[Madhyastha]，它旨在创建一个有注释的互联网地图册，其中包含有关延迟、带宽、容量和丢失率的信息。为了确定Internet拓扑结构的特征，iPlane桥接并建立在不同的思想之上，例如基于分组分散技术的主动探测，以推断路径段上的可用带宽。这些想法来自不同的领域，包括Dovrolis等人在[Dovrolis]和网络层析成像[Coates]中描述的网络测量。
Instead of estimating topology information on the application level through distributed measurements, this information could be provided by the entities running the physical networks -- usually ISPs or network operators. In fact, they have full knowledge of the topology of the networks they administer and, in order to avoid congestion on critical links, are interested in helping applications to optimize the traffic they generate. The remainder of this section briefly
这些信息可以由运行物理网络的实体（通常是ISP或网络运营商）提供，而不是通过分布式测量在应用程序级别估计拓扑信息。事实上，他们完全了解所管理网络的拓扑结构，为了避免关键链路上的拥塞，他们有兴趣帮助应用程序优化其生成的流量。本节的其余部分将简要介绍
describes three recently proposed solutions that follow such an approach to address the ALTO problem.
描述了三个最近提出的解决方案，它们遵循这种方法来解决ALTO问题。
The architecture proposed by Xie et al. [Xie] has been adopted by the Distributed Computing Industry Association (DCIA) P4P working group [P4P], an open group established by ISPs, P2P software distributors, and technology researchers, with the dual goal of defining mechanisms to (1) accelerate content distribution and (2) optimize utilization of network resources.
Xie等人[Xie]提出的体系结构已被分布式计算行业协会（DCIA）P4P工作组[P4P]采用，该工作组是由ISP、P2P软件分销商和技术研究人员成立的一个开放小组，其双重目标是定义（1）加速内容分发和（2）的机制优化网络资源的利用。
The main role in the P4P architecture is played by servers called "iTrackers", deployed by network providers and accessed by P2P applications (or, in general, by elements of the P2P system) in order to make optimal decisions when selecting a peer to which the element will connect. An iTracker may offer three interfaces:
P4P体系结构中的主要角色由称为“iTracker”的服务器扮演，这些服务器由网络提供商部署，并由P2P应用程序（或通常由P2P系统的元素）访问，以便在选择元素将连接到的对等方时做出最佳决策。iTracker可以提供三个接口：
1. Info: Allows P2P elements (e.g., peers or trackers) to get opaque information associated to an IP address. Such information is kept opaque to hide the actual network topology, but can be used to compute the network distance between IP addresses.
1. 信息：允许P2P元素（例如对等点或跟踪器）获取与IP地址相关的不透明信息。这些信息保持不透明以隐藏实际的网络拓扑，但可用于计算IP地址之间的网络距离。
2. Policy: Allows P2P elements to obtain policies and guidelines of the network, which specify how a network provider would like its networks to be utilized at a high level, regardless of P2P applications.
2. 策略：允许P2P元素获取网络的策略和指导原则，这些策略和指导原则指定网络提供商希望其网络在高级别上得到利用的方式，而不考虑P2P应用程序。
3. Capability: Allows P2P elements to request network providers' capabilities.
3. 功能：允许P2P元素请求网络提供商的功能。
The P4P architecture is under evaluation with simulations, experiments on the PlanetLab distributed testbed, and in field tests with real users. Initial simulations and PlanetLab experiment results [P4P] indicate that improvements in BitTorrent download completion time and link utilization in the range of 50-70% are possible. Results observed on Comcast's network during a field test trial conducted with a modified version of the software used by the Pando content delivery network (documented in RFC 5632 [RFC5632]) show average improvements in download rate in different scenarios varying between 57% and 85%, and a 34% to 80% drop in the cross-domain traffic generated by such an application.
P4P体系结构正在通过仿真、PlanetLab分布式试验台上的实验以及与实际用户的现场测试进行评估。初始模拟和PlanetLab实验结果[P4P]表明，BitTorrent下载完成时间和链路利用率在50-70%范围内的改善是可能的。在使用Pando内容交付网络（RFC 5632[RFC5632]中记录）所用软件的修改版本进行现场测试期间，在康卡斯特网络上观察到的结果表明，在不同的场景中，下载率的平均提高在57%到85%之间，这样一个应用程序产生的跨域流量下降了34%到80%。
In the general solution proposed by Aggarwal et al. [Aggarwal], network providers offer host servers, called "oracles", that help P2P users choose optimal neighbors.
在Aggarwal等人[Aggarwal]提出的一般解决方案中，网络提供商提供称为“oracles”的主机服务器，帮助P2P用户选择最佳邻居。
The oracle concept uses the following mechanism: a P2P client sends the list of potential peers to the oracle hosted by its ISP and receives a re-arranged peer list, ordered according to the ISP's local routing policies and preferences. For instance, to keep the traffic local, the ISP may prefer peers within its network, or it may pick links with higher bandwidth or peers that are geographically closer to improve application performance. Once the client has obtained this ordered list, it has enough information to perform better-than-random initial peer selection.
oracle概念使用以下机制：P2P客户端向其ISP托管的oracle发送潜在对等方列表，并接收重新排列的对等方列表，该列表根据ISP的本地路由策略和首选项排序。例如，为了使流量保持本地，ISP可能更喜欢其网络中的对等点，或者它可能选择具有更高带宽的链路或地理位置更近的对等点以提高应用程序性能。一旦客户机获得了这个有序列表，它就有足够的信息来执行比随机初始对等选择更好的操作。
Such a solution has been evaluated with simulations and experiments run on the PlanetLab testbed, and the results show both improvements in content download time and a reduction of overall P2P traffic, even when only a subset of the applications actually query the oracle to make their decisions.
这种解决方案已经在PlanetLab测试台上进行了模拟和实验评估，结果表明内容下载时间得到了改善，总体P2P流量也有所减少，即使只有一部分应用程序实际查询oracle以做出决策。
The solution proposed by Saucez et al. [Saucez] is essentially a modified version of the oracle-based approach described in Section 2.2.2, intended to provide a network-layer service for finding the best source and destination addresses when establishing a connection between two endpoints in multi-homed environments (which are common in IPv6 networking). Peer selection optimization in P2P systems -- the ALTO problem in today's Internet -- can be addressed by the IDIPS solution as a specific sub-case where the options for the destination address consist of all the peers sharing a desired resource, while the choice of the source address is fixed. An evaluation performed on IDIPS shows that costs for both providing and accessing the service are negligible.
Saucez等人提出的解决方案。[Saucez]本质上是第2.2.2节中描述的基于oracle的方法的修改版本，旨在提供网络层服务，以便在多宿环境中建立两个端点之间的连接时查找最佳源地址和目标地址（在IPv6网络中很常见）。P2P系统中的对等点选择优化——当今互联网中的ALTO问题——可以通过IDIPS解决方案作为一个特定的子案例来解决，其中目标地址的选项由共享所需资源的所有对等点组成，而源地址的选择是固定的。对IDIPS进行的评估表明，成本为或者提供和访问服务都可以忽略不计。
The application-level techniques described in Section 2.1 provide tools for peer-to-peer applications to estimate parameters of the underlying network topology. Although these techniques can improve application performance, there are limitations of what can be achieved by operating only on the application level.
第2.1节中描述的应用程序级技术为对等应用程序提供了估算底层网络拓扑参数的工具。尽管这些技术可以提高应用程序的性能，但仅在应用程序级别上操作所能实现的功能仍有局限性。
Topology estimation techniques use abstractions of the network topology, which often hide features that would be of interest to the application. Network coordinate systems, for example, are unable to detect overlay paths shorter than the direct path in the Internet topology. However, these paths frequently exist in the Internet [Wang]. Similarly, application-level techniques may not accurately estimate topologies with multipath routing.
拓扑估计技术使用网络拓扑的抽象，通常隐藏应用程序感兴趣的特征。例如，网络坐标系无法检测到比Internet拓扑中的直接路径短的重叠路径。然而，这些路径经常存在于互联网[Wang]。类似地，应用级技术可能无法准确估计具有多路径路由的拓扑。
When using network coordinates to estimate topology information, the underlying assumption is that distance in terms of latency determines performance. However, for file sharing and content distribution applications, there is more to performance than just the network latency between nodes. The utility of a long-lived data transfer is determined by the throughput of the underlying TCP protocol, which depends on the round-trip time as well as the loss rate experienced on the corresponding path [Padhye]. Hence, these applications benefit from a richer set of topology information that goes beyond latency, including loss rate, capacity, and available bandwidth.
当使用网络坐标估计拓扑信息时，基本假设是延迟方面的距离决定性能。但是，对于文件共享和内容分发应用程序，性能不仅仅取决于节点之间的网络延迟。长寿命数据传输的效用由底层TCP协议的吞吐量决定，它取决于往返时间以及相应路径上经历的丢失率[Padhye]。因此，这些应用程序受益于一组更丰富的拓扑信息，这些信息超越了延迟，包括丢失率、容量和可用带宽。
Some of the topology estimation techniques used by P2P applications need time to converge to a result. For example, current BitTorrent clients implement local, passive traffic measurements and a tit-for-tat bandwidth reciprocity mechanism to optimize peer selection at a local level. Peers eventually settle on a set of neighbors that maximizes their download rate, but because peers cannot reason about the value of neighbors without actively exchanging data with them, and because the number of concurrent data transfers is limited (typically to 5-7), convergence is delayed and easily can be sub-optimal.
P2P应用程序使用的一些拓扑估计技术需要时间才能收敛到结果。例如，当前BitTorrent客户端实现本地被动流量测量和针锋相对的带宽互惠机制，以优化本地级别的对等选择。对等方最终会选择一组邻居，以最大化其下载速率，但由于对等方无法在不主动与他们交换数据的情况下对邻居的价值进行推理，并且由于并发数据传输的数量有限（通常为5-7），收敛会延迟，并且很容易达到次优。
Skype's P2P Voice over IP (VoIP) application chooses a relay node in cases where two peers are behind NATs and cannot connect directly. Measurements taken by Ren et al. [Ren] showed that the relay selection mechanism of Skype (1) is not able to discover the best possible relay nodes in terms of minimum RTT, (2) requires a long setup and stabilization time, which degrades the end user experience, and (3) is creating a non-negligible amount of overhead traffic due to probing a large number of nodes. They further showed that the quality of the relay paths could be improved when the underlying network Autonomous System (AS) topology is considered.
Skype的P2P IP语音（VoIP）应用程序在两个对等方位于NAT后面且无法直接连接的情况下选择中继节点。Ren等人[Ren]进行的测量表明，Skype的中继选择机制（1）无法发现最小RTT的最佳中继节点，（2）需要较长的设置和稳定时间，这会降低最终用户体验，以及（3）由于探测大量节点，正在创建不可忽略的开销通信量。他们进一步表明，当考虑底层网络自治系统（AS）拓扑时，中继路径的质量可以得到改善。
Some features of the network topology are hard to infer through application-level techniques, and it may not be possible to infer them at all, e.g., service-provider policies and preferences such as the state and cost associated with interdomain peering and transit links. Another example is the traffic engineering policy of a service provider, which may counteract the routing objective of the overlay network, leading to a poor overall performance [Seetharaman].
网络拓扑的一些特征很难通过应用级技术推断，并且可能根本无法推断它们，例如，服务提供商策略和偏好，例如与域间对等和传输链路相关的状态和成本。另一个例子是服务提供商的流量工程策略，这可能会抵消覆盖网络的路由目标，导致整体性能不佳[Seetharaman]。
Finally, application-level techniques often require applications to perform measurements on the topology. These measurements create traffic overhead, in particular, if measurements are performed individually by all applications interested in estimating topology.
最后，应用程序级技术通常要求应用程序对拓扑进行测量。这些测量会产生流量开销，特别是当所有对拓扑估计感兴趣的应用程序都单独执行测量时。
Beyond a significant amount of research work on the topic, we believe that there are sizable open issues to address in an infrastructure-based approach to traffic optimization. The following is not an exhaustive list, but a representative sample of the pertinent issues.
除了大量关于该主题的研究工作外，我们认为，在基于基础设施的交通优化方法中，还存在大量有待解决的问题。以下不是详尽的清单，而是相关问题的代表性样本。
Despite the many solutions that have been proposed for providing applications with topology information in a fully distributed manner, there is currently an ongoing debate in the research community whether such solutions should focus on estimating nodes' coordinates or path latencies. Such a debate has recently been fed by studies showing that the triangle inequality on which coordinate systems are based is often proved false in the Internet [Ledlie]. Proposed systems following both approaches -- in particular, Vivaldi [Dabek] and PIC [Costa] following the former, and Meridian [Wong] and iPlane [Madhyastha] the latter -- have been simulated, implemented, and studied in real-world trials, each one showing different points of strength and weaknesses. Concentrated work will be needed to determine which of the two solutions will be conducive to the ALTO problem.
尽管已经提出了许多以完全分布式的方式为应用程序提供拓扑信息的解决方案，但研究界目前仍在争论此类解决方案是否应侧重于估计节点坐标或路径延迟。最近有研究表明，坐标系所基于的三角不等式在互联网上经常被证明是错误的，这引发了这样的争论[Ledlie]。采用这两种方法的拟议系统——特别是采用前一种方法的Vivaldi[Dabek]和PIC[Costa]，以及采用后一种方法的Meridian[Wong]和iPlane[Madhyastha]已经在现实世界中进行了模拟、实施和研究，每种方法都显示出不同的优缺点。需要集中精力确定两种解决方案中的哪一种将有助于解决ALTO问题。
Another open issue common in most distributed environments consisting of a large number of peers is the resistance against malicious nodes. Security mechanisms to identify misbehavior are based on triangle inequality checks [Costa], which, however, tend to fail and thus return false positives in the presence of measurement inaccuracies induced, for example, by traffic fluctuations that occur quite often in large networks [Ledlie]. Beyond the issue of using triangle inequality checks, authoritatively authenticating the identity of an oracle, and preventing an oracle from attacks are also important. Existing techniques -- such as Public Key Infrastructure (PKI) [RFC5280] or identity-based encryption [Boneh] for authenticating the identity and the use of secure multi-party computation techniques to prevent an oracle from collusion attacks -- need to be explored and studied for judicious use in ALTO-type solutions.
在大多数由大量对等节点组成的分布式环境中，另一个常见的开放问题是对恶意节点的抵抗。识别不当行为的安全机制基于三角不平等检查[Costa]，然而，在存在测量不准确时，三角不平等检查往往会失败，从而返回误报，例如，大型网络中经常发生的流量波动[Ledlie]。除了使用三角形不平等检查的问题外，权威性地验证oracle的身份以及防止oracle受到攻击也很重要。需要探索和研究现有技术，如用于身份验证的公钥基础设施（PKI）[RFC5280]或基于身份的加密[Boneh]，以及使用安全多方计算技术防止oracle受到共谋攻击，以便在ALTO类型的解决方案中明智地使用。
Similarly, even in controlled architectures deployed by network operators where system elements may be authenticated [Xie], [Aggarwal],[Saucez], it is still possible that the information returned to applications is deliberately altered, for example, assigning higher priority to financially inexpensive links instead of
类似地，即使在网络运营商部署的受控体系结构中，系统元素可能经过身份验证[Xie]、[Aggarwal]、[Saucez]，返回给应用程序的信息仍有可能被故意更改，例如，将更高的优先级分配给经济上便宜的链接，而不是
neutrally applying proximity criteria. What are the effects of such deliberate alterations if multiple peers collude to determine a different route to the target, one that is not provided by an oracle? Similarly, what are the consequences if an oracle targets a particular node in another AS by redirecting an inordinate number of querying peers to it causing, essentially, a Distributed Denial-of-Service (DDoS) [RFC4732] attack on the node? Furthermore, does an oracle broadcast or multicast a response to a query? If so, techniques to protect the confidentiality of the multicast stream will need to be investigated to thwart "free riding" peers.
中立地应用接近标准。如果多个对等方串通确定到目标的不同路线（oracle不提供的路线），这种蓄意更改会产生什么影响？类似地，如果oracle将另一个AS中的特定节点作为目标，将过多的查询对等点重定向到该节点，从而在该节点上造成分布式拒绝服务（DDoS）[RFC4732]攻击，会产生什么后果？此外，oracle是否广播或多播对查询的响应？如果是这样，则需要研究保护多播流机密性的技术，以阻止“搭便车”对等方。
Many systems already use RTT to account for delay when establishing connections with peers (e.g., Content-Addressable Network (CAN) [Ratnasamy], Bamboo [Rhea]). An operator can provide not only the delay metric but other metrics that the peer cannot figure out on its own. These metrics may include the characteristics of the access links to other peers, bandwidth available to peers (based on operators' engineering of the network), network policies, preferences such as state and cost associated with intradomain peering links, and so on. Exactly what kinds of metrics an operator can provide to stabilize the network throughput will also need to be investigated.
许多系统已经使用RTT来解释与对等方建立连接时的延迟（例如，内容寻址网络（CAN）[Ratnasamy]，Bambol[Rhea]）。操作员不仅可以提供延迟度量，还可以提供对等方无法自行确定的其他度量。这些度量可以包括到其他对等方的接入链路的特征、对等方可用的带宽（基于运营商的网络工程）、网络策略、诸如与域内对等链路相关联的状态和成本等偏好。此外，还需要研究运营商能够提供何种指标来稳定网络吞吐量。
It is conceivable that P2P users may not be comfortable with operator intervention to provide topology information. To eliminate this intervention, alternative schemes to estimate topological distance can be used. For instance, Ono uses client redirections generated by Akamai CDN servers as an approximation for estimating distance to peers; Vivaldi, GNP, and PIC use synthetic coordinate systems. A neutral third party can make available a hybrid layer-cooperation service -- without the active participation of the ISP -- that uses alternative techniques discussed in Section 2.1 to create a topological map. This map can be subsequently used by a subset of users who may not trust the ISP.
可以想象，P2P用户可能不习惯于操作员干预以提供拓扑信息。为了消除这种干扰，可以使用其他方案来估计拓扑距离。例如，Ono使用Akamai CDN服务器生成的客户端重定向作为估计到对等方距离的近似值；维瓦尔第、GNP和PIC使用合成坐标系。中立的第三方可以提供混合层合作服务（无需ISP的积极参与），该服务使用第2.1节中讨论的替代技术创建拓扑图。此映射随后可供不信任ISP的部分用户使用。
The literature presented in Section 2 shows that a certain level of locality-awareness in the peer selection process of P2P algorithms is usually beneficial to application performance. However, an excessive localization of the traffic might cause partitioning in the overlay interconnecting these peers, which will negatively affect the performance experienced by the peers themselves.
第2节中的文献表明，在P2P算法的对等选择过程中，一定程度的局部性意识通常有利于应用程序的性能。但是，流量的过度本地化可能会导致互连这些对等点的覆盖中出现分区，这将对对等点自身的性能产生负面影响。
Finding the right balance between localization and randomness in peer selection is an open issue. At the time of writing, it seems that different applications have different levels of tolerance and should be addressed separately. Le Blond et al. [LeBlond] have studied the specific case of BitTorrent, proposing a simple mechanism to prevent partitioning in the overlay, yet reach a high level of cross-domain traffic reduction without adversely impacting peers.
在同伴选择中找到本地化和随机性之间的正确平衡是一个悬而未决的问题。在撰写本文时，似乎不同的应用程序具有不同的容忍度，应分别予以解决。Le Blond等人[LeBlond]研究了BitTorrent的具体情况，提出了一种简单的机制来防止覆盖中的分区，同时在不影响对等方的情况下实现高水平的跨域流量减少。
This document is a survey of existing literature on topology estimation. As such, it does not introduce any new security considerations to be taken into account beyond what is already discussed in each paper surveyed.
本文是对现有拓扑估计文献的综述。因此，除了在所调查的每一篇论文中已经讨论的内容之外，它没有引入任何新的安全考虑因素。
Insofar as topology estimation is used to provide a solution to the ALTO problem, the issues in Sections 4.2 and 4.3 deserve special attention. There are efforts underway in the IETF ALTO working group to design a protocol that protects the privacy of the peer-to-peer users as well as the service providers. [Chen] provides an overview of ALTO security issues, Section 11 of [Alimi] is an exhaustive overview of ALTO security, and Section 6 of RFC 5693 [RFC5693] also lists the privacy and confidentiality aspects of an ALTO solution.
就拓扑估计用于解决ALTO问题而言，第4.2节和第4.3节中的问题值得特别注意。IETF ALTO工作组正在努力设计一种保护点对点用户和服务提供商隐私的协议。[Chen]概述了ALTO安全问题，[Alimi]的第11节详细介绍了ALTO安全问题，RFC 5693[RFC5693]的第6节也列出了ALTO解决方案的隐私和保密方面。
The following references provide a starting point for general peer-to-peer security issues: [Wallach], [Sit], [Douceur], [Castro], and [Friedman].
以下参考文献提供了一般对等安全问题的起点：[Wallach]、[Sit]、[Douceur]、[Castro]和[Friedman]。
This document is a derivative work of a position paper submitted at the IETF RAI area/MIT workshop held on May 28th, 2008 on the topic of Peer-to-Peer Infrastructure (P2Pi) [RFC5594]. The article on a similar topic, also written by the authors of this document and published in IEEE Communications [Gurbani], was also partially derived from the same position paper. The authors thank profusely Arnaud Legout, Richard Yang, Richard Woundy, Stefano Previdi, and the many people that have participated in discussions and provided insightful feedback at any stage of this work.
本文件是在2008年5月28日举行的IETF RAI地区/麻省理工学院研讨会上提交的关于对等基础设施（P2Pi）[RFC5594]主题的立场文件的衍生作品。同样由本文件作者撰写并发表在IEEE Communications[Gurbani]上的关于类似主题的文章也部分源自同一立场文件。作者非常感谢Arnaud Legout、Richard Yang、Richard Woundy、Stefano Previdi以及在本研究的任何阶段参与讨论并提供深刻反馈的许多人。
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Authors' Addresses
作者地址
Ivica Rimac Bell Labs, Alcatel-Lucent EMail: rimac@bell-labs.com
Ivica Rimac Bell实验室，阿尔卡特朗讯电子邮件：rimac@bell-实验室网站
Volker Hilt Bell Labs, Alcatel-Lucent EMail: volkerh@bell-labs.com
沃尔克希尔特贝尔实验室，阿尔卡特朗讯电子邮件：volkerh@bell-实验室网站
Marco Tomsu Bell Labs, Alcatel-Lucent EMail: marco.tomsu@alcatel-lucent.com
Marco Tomsu Bell实验室，阿尔卡特朗讯电子邮件：Marco。tomsu@alcatel-朗讯网
Vijay K. Gurbani Bell Labs, Alcatel-Lucent EMail: vkg@bell-labs.com
Vijay K.Gurbani Bell实验室，阿尔卡特朗讯电子邮件：vkg@bell-实验室网站
Enrico Marocco Telecom Italia EMail: enrico.marocco@telecomitalia.it
Enrico Marocco Telecom Italia电子邮件：Enrico。marocco@telecomitalia.it