Experience: Implications of Roaming in Europe

ABSTRACT

“Roam like Home” is the initiative of the European Commission (EC) to end the levy of extra charges when roaming within the European region. As a result, people are able to use data services more freely across Europe. However, the implications roaming solutions have on performance have not been carefully examined. This paper provides an in-depth characterization of the implications of international data roaming within Europe. We build a unique roaming measurement platform using 16 different mobile networks deployed in six countries across Europe. Using this platform, we measure different aspects of international roaming in 3G and 4G networks, including mobile network configuration, performance characteristics, and content discrimination. We find that operators adopt common approaches to implementing roaming, resulting in additional latency penalties of ∼60 ms or more, depending on geographical distance. Considering content accessibility, roaming poses additional constraints that leads to only minimal deviations when accessing content in the original country. However, geographical restrictions in the visited country make the picture more complicated and less intuitive.

“漫游如在家”（Roam like Home）是欧盟委员会（EC）旨在取消欧洲区域内漫游时额外费用征收的一项倡议。因此，人们得以在欧洲各地更自由地使用数据服务。

然而，漫游解决方案对性能的影响尚未得到周详的考察。本论文对欧洲境内国际数据漫游的影响进行了深入的特性表征。我们利用部署在欧洲六个国家的16个不同移动网络，构建了一个独特的漫游测量平台。通过此平台，我们测量了3G和4G网络中国际漫游的不同方面，包括移动网络配置、性能特征和内容歧视。

我们发现，运营商在实施漫游时普遍采用通用方法，这导致了约60毫秒或更高的额外时延，具体取决于地理距离。在内容可访问性方面，漫游带来了额外的限制：

1. 在访问“归属国”内容时，由此导致的偏差极小
2. 然而，“到访国”的地理限制使得情况更为复杂且不那么直观

INTRODUCTION

International roaming allows mobile users to use their voice and data services when they are abroad. The European Commission (EC), in an effort to create a single digital market across the European Union (EU), has recently (as of June 2017) introduced a set of regulatory decisions [1] as part of the “Roam like Home” initiative. This initiative abolishes additional charges for users when they use voice and data services while roaming in EU. In this setting, Mobile Network Operator (MNO) are expected to deliver services with Quality of Service (QoS) properties similar to the ones a user experiences when at home.

国际漫游服务允许移动用户在境外使用其语音和数据业务。欧盟委员会（EC）为在欧盟（EU）范围内打造单一数字市场，近期（截至2017年6月）推行了“漫游如在家”（Roam like Home）倡议，并为此出台了一系列监管决策[1]。该倡议旨在取消用户在欧盟境内漫游时使用语音和数据服务所需支付的额外费用。在此背景下，移动网络运营商（MNO）被期望提供与用户在归属地网络所体验到的服务质量（QoS）相当的服务。

To support roaming, MNOs commonly connect with each other through an IP Packet Exchange (IPX) network. An IPX [2, 3] can be described as a hub that interconnects MNOs over a private IP backbone network and is possibly run by a third party IPX provider. An IPX provider has connections to multiple network operators and thus enables each MNO to connect to other operators via a single point of contact. In Fig. 1, we present a set of topology architectures that can be used for roaming in a mobile network, namely, home-routed roaming (HR), local breakout (LBO) and IPX hub breakout (IHBO). When a mobile node is at home (left, see Fig. 1), the home user’s traffic will take a short path inside the network to reach a suitable Packet Data Network Gateway (PGW) to the Internet. The traffic of a roaming user (right, see Fig. 1) is directed to an egress PGW whose location depends on the roaming architecture. In the case of HR, the mobile node receives the IP address from its home MNO and the roaming user’s traffic is first routed towards a PGW in the home network (red path). With LBO, the mobile node receives its IP address from the visited network and the traffic is routed towards a local PGW in the visited network (purple path). When using IHBO, the mobile node obtains its IP address from the IPX networks and the traffic is routed through a PGW in the IPX network (green path). The topology can have a potential impact on the communication performance. For instance, when the node accesses services inside the visited network, the performance is likely to be worse in the HR case, because all packets travel twice between the visited and the home country; less so when the communication peer is in a third country and is minimal when accessing services in the home country.

为支持漫游，移动网络运营商（MNO）通常通过IP包交换（IPX）网络实现互联。IPX网络[2, 3]可被描述为一个通过私有IP骨干网互联各MNO的枢纽，并可能由第三方IPX提供商运营。IPX提供商与多家网络运营商连接，从而使每个MNO都能通过单一连接点与其他运营商建立联系。我们在图1中展示了一组可用于移动网络漫游的拓扑架构，即归属路由漫游（Home-Routed roaming, HR）、本地疏导（Local Breakout, LBO）和IPX枢纽疏导（IPX Hub Breakout, IHBO）

1. 当 移动节点位于归属网络 时（如图1左侧所示），其用户流量将通过网络内部的短路径到达合适的分组数据网络网关（Packet Data Network Gateway, PGW），进而接入互联网
2. 漫游用户的流量 （如图1右侧所示）则被导向一个出口PGW，其位置取决于所采用的漫游架构
   1. 在 HR模式 下，移动节点从其归属MNO获取IP地址，漫游用户的流量首先被路由至归属网络中的PGW（红色路径）
   2. 采用 LBO模式 时，移动节点从到访网络获取IP地址，流量则被路由至到访网络中的本地PGW（紫色路径）
   3. 当使用 IHBO模式 时，移动节点从IPX网络获取IP地址，流量通过IPX网络中的PGW进行路由（绿色路径）

这种拓扑结构可能对通信性能产生潜在影响。例如，当节点访问到访网络内的服务时，HR模式下的性能可能会较差，因为所有数据包都需要在到访国和归属国之间往返传输两次；当通信对端位于第三国时，此影响有所减轻；而当访问归属国服务时，影响则最小

In this paper, we perform an extensive large-scale measurement study 1 to understand the roaming ecosystem in Europe after the “Roam like Home” initiative. More specifically, we investigate: (i) Which technical solutions are actually being deployed and used today? and (ii) What are the implications of roaming on the service experienced by the roaming user?

在本文中，我们进行了一项广泛的大规模测量研究，旨在深入理解“漫游如在家”倡议实施后欧洲的漫游生态系统。具体而言，我们研究以下问题：（i）当前实际部署并使用的是哪些技术解决方案？以及（ii）漫游对用户所体验到的服务会产生何种影响？

To address these questions, we built a unique measurement platform, MONROE-Roaming, to assess roaming and its performance implications. The platform integrates dedicated measurement hardware that we deployed in six different countries (see Fig. 2 and § 2 for details) across Europe, covering a total of 16 MNOs. We purchased Subscriber Identity Modules (SIMs) that support roaming for these MNOs and distribute them across the six countries. We characterize roaming operation and network performance (§ 3) and evaluate the impact on VoIP and web applications (§ 4) while roaming. We find that all observed MNOs use HR, which yields noticeable latency increases. We do not observe traffic differentiation policies for VoIP or web, but we do find evidence of content discrimination for roaming users. We review the existing work in § 6 and conclude the paper in § 7.

为解答这些问题，我们构建了一个独特的测量平台——MONROE-Roaming，用以评估漫游及其性能影响。该平台集成了我们部署于欧洲六个不同国家（详情参见图2及第2节）的专用测量硬件，共覆盖16个移动网络运营商（MNO）。我们为这些MNO购买了支持漫游的用户身份模块（SIM卡），并将它们分布部署在这六个国家。我们对漫游操作和网络性能（第3节）进行了表征，并评估了漫游状态下其对VoIP和Web应用的影响（第4节）。我们发现所有观察到的MNO均采用归属路由（HR）方式，这导致了显著的时延增加。我们未观察到针对VoIP或Web应用的流量差异化策略，但确实发现了针对漫游用户的内容歧视证据。我们将在第6节回顾相关工作，并在第7节对本文进行总结。