DISCUSSION

On Measurements Limitations

The MONROE-Roaming platform integrates measurement nodes located in six different EU countries and a measurement responder per country. Although this allows us to capture at an unprecedented scale the performance of international roaming in Europe, it is still a limited view in terms of spatial sample distribution within each country (we only use two hardware devices per country, in the same location). Similarly, the findings in this paper refer to just one snapshot – and the community should repeat these experiments over time to identify and investigate changes. The high cost of mounting such an experimental study is a major restricting factor for the density of sampling geo-locations. We instead focus on characterizing multiple MNOs by taking advantage of the SIM farm we built using MONROE-Roaming. For each MNO, we purchased a similar data plan (10GB/month) enabling us to capture similar number of samples per MNO and country. Furthermore, using the same equipment type throughout the measurement platform and in all locations eliminates potential device bias we might observe in the measurement samples.

Our measurement study focuses mainly on network performance and content implications of the roaming solutions in Europe. We leave for future work the exploration of potential performance penalties (see Section 3.1) on actual end-user Quality of Experience (QoE).

MONROE-Roaming平台集成了部署于六个不同欧盟国家的测量节点以及每个国家一个测量响应器。尽管这使我们能够以前所未有的规模捕获欧洲国际漫游的性能，但就各国内部的空间样本分布而言，这仍然是一个有限的视角（我们在每个国家仅使用两台位于同一地点的硬件设备）。类似地，本文的发现仅涉及一个时间快照——学术界应随时间推移重复这些实验，以识别和调查变化。开展此类实验研究的高昂成本是限制地理位置采样密度的主要因素。我们转而利用通过MONROE-Roaming构建的SIM卡池，专注于表征多个移动网络运营商（MNO）。针对每个MNO，我们购买了相似的数据套餐（10GB/月），这使我们能够为每个MNO和每个国家捕获相似数量的样本。此外，在整个测量平台和所有地点使用相同类型的设备，消除了我们在测量样本中可能观察到的潜在设备偏差。

我们的测量研究主要关注欧洲漫游解决方案在网络性能和内容方面的影响。我们将对最终用户实际体验质量（QoE）的潜在性能代价（参见第3.1节）的探索留待未来工作。

TL;DR

1. 我们做了: 漫游的三个解决方案(HR/IPX/LBO)在网络层面和内容的影响
2. 期待有人: QoE for Client-Side && Performance Cost
3. 局部弊端: 最好是高密度架设设备进行仿真，但目前受到成本的限制

On Roaming Configurations

LBO appears a natural choice for an IP-based service and could offer lower operational cost as well as cheaper data tariffs. At the same time, we have shown that this can eliminate delay and potentially increase capacity for some traffic (depending on the destination). Although, LBO relies on access to local infrastructure, offering this could act as a product differentiator for the MNOs that provide this service first. In contrast, HR provides the home MNOs with all the accounting and billing information. This has been verified to be the major problem with MNOs that need to have near real-time view of the customer traffic for accounting reasons.

对于基于IP的服务而言，LBO（本地疏导）似乎是一种自然选择，并且可能提供更低的运营成本以及更便宜的数据资费。同时，我们已经表明，这可以消除延迟，并可能增加某些流量的容量（取决于目的地）。尽管LBO依赖于对本地基础设施的访问，但率先提供此服务的MNO可以将其作为一种产品差异化因素。相比之下，HR（归属路由）为归属MNO提供所有的账户和计费信息。对于那些出于账户管理原因需要近乎实时地掌握客户流量视图的MNO而言，这已被证实是其面临的主要问题。

Whereas Session Initiation Protocol (SIP) signalling could be used to derive billing information for voice (and VoLTE) calls, an MNO typically uses records to issue bills. Breakout at different points complicates this accounting, with possible abuse from customers (e.g, the delay in billing might allow excessive amount of data traffic when roaming). Within the cellular network, classes of traffic can be differentiated using the Access Point Name (APN) and QoS Class Identifier (QCI). This could be used, for instance, by MNOs to implement HR for data, but LBO for VoLTE [16]. This raises the question of whether the roaming agreement could be updated using the same principle to break out some/all data traffic.

尽管会话发起协议（SIP）信令可用于获取语音（和VoLTE）通话的计费信息，但MNO通常使用记录来开具账单。在不同点进行疏导会使这种账户管理复杂化，并可能导致客户滥用（例如，计费延迟可能允许漫游时产生过量的数据流量）。在蜂窝网络中，可以使用接入点名称（APN）和QoS等级标识符（QCI）来区分不同类别的流量。例如，MNO可以利用这一点对数据业务实施HR，但对VoLTE实施LBO [16]。这就提出了一个问题：漫游协议是否可以基于相同原则进行更新，以疏导部分或全部数据流量。

Any additional complexity from LBO can add to the operational cost of supporting users of the network (e.g., debugging issues, tracking faults, and predicting traffic). And if a service fails, it is not obvious who is responsible for finding the fault and fixing this. An IPX can help mitigate these impacts. Some solutions introduce additional proxy elects [2], responsible for routing traffic towards the correct network, and the associated control functions to coordinate.

LBO带来的任何额外复杂性都会增加支持网络用户（例如，调试问题、跟踪故障和预测流量）的运营成本。而且，如果一项服务失败，由谁负责发现并修复故障并不明确。IPX（IP包交换网络）可以帮助减轻这些影响。一些解决方案引入了额外的代理实体[2]（proxy elects），负责将流量路由到正确的网络，以及相关的控制功能以进行协调。

LBO在技术上看起来能规避HR的弊端, 为什么还没被推广?

1. LBO引入额外的复杂性, 增加运营成本
2. 但凡出错, 由谁负责发现并修复故障并不明确

Additionally, there are filtering rules, Digital Rights Management (DRM), language preference and personal content that depend upon the location (country) in which the content is viewed. Lawful intercept further complicates the picture. Here, the home network has full visibility of the necessary data, but the visited network may not. Lawful intercept may be further complicated because of variations in regulatory requirements depending on the geographic location of equipment. In a nutshell, enforcing and accounting for multiple policies for different content in different locations can become complex. Home routing simplifies this by letting the original operator see and manage all the traffic.

此外，还存在过滤规则、数字版权管理（DRM）、语言偏好和个人内容等问题，这些都取决于内容被查看的地点（国家）。合法监听进一步使情况复杂化。在此情况下，归属网络对必要数据有完全的可见性，但到访网络可能没有。由于设备地理位置不同导致的监管要求的差异，合法监听可能进一步复杂化。 简而言之，在不同地点为不同内容执行和管理多种策略可能变得非常复杂。归属路由通过让原始运营商查看和管理所有流量来简化了这一点。

HR在技术上看起来很低能, 为什么还被推广?

因为，在不同地点为不同内容执行和管理多种策略可能变得非常复杂

归属路由 (HR) 通过让原始运营商查看和管理所有流量来简化了这一点

Lastly, access to content served by Content Delivery Networks (CDN) needs to be carefully optimized to avoid cases where a roaming user is redirected to local replica that is spatially close, but whose network path is unnecessarily long (due to breakout constraints).

最后，对内容分发网络（CDN）提供的内容的访问需要仔细优化，以避免漫游用户被重定向到空间上接近但由于疏导限制导致网络路径不必要地过长的本地副本的情况。

The choice of which form of roaming is used therefore is a function of the roaming agreement and capabilities of the visited network. These are constrained by many technical and legal requirements. Therefore, different breakout options can affect performance of application in different ways.

因此，使用何种漫游形式取决于漫游协议和到访网络的能力。这些因素受到许多技术和法律要求的约束。因此，不同的疏导选项会以不同方式影响应用程序的性能。