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ATOM DESIGN

TLDR: ATOM

ATOM是端到端流量管理系统，旨在灵活高效管理LTE与WiFi异构网络

  1. 设计1：网络中心化。ATOM在网关部署，拥全局网络视图 ，优于客户端方案(需信令交互)
  2. 设计2：可扩展性。ATOM按LTE小区独立管理，实例并行 ，易随网络扩展
  3. 设计3：无缝切换。ATOM支持流在LTE/WiFi间无缝切换，经济且适应动态
  4. 设计4：定价兼容。ATOM设计考虑多种计费模式，适应未来WiFi服务演进

ATOM实例化于接入网网关(PDN-GW)，含网络接口分配(NIA)和接口切换服务(ISS)两组件

To address the afore-mentioned drawbacks, we propose ATOM, an end-to-end traffic management system that enables operators to flexibly and efficiently manage user traffic flows across a heterogeneous network of LTE and WiFi APs. Before describing ATOM in detail, we explain our key design considerations:

为解决上述缺陷，我们提出了ATOM，一个端到端的流量管理系统，使运营商能够在其LTE和WiFi AP组成的异构网络中灵活有效地管理用户数据流。在详细描述ATOM之前，我们先阐述其关键设计考量：

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(i) Network-centric: ATOM is designed as a centralized solution that leverages a complete network view (of cell load, user QoE etc.) to determine the optimal interface selection. This gives ATOM an important advantage over client-based distributed solutions (e.g.[8]), which require proprietary signaling from the network (creating wireless link overhead and requiring change in standards) to obtain load information easily accessible by ATOM. ATOM is a gateway-level solution that can be deployed within the LTE mobile core network as opposed to being deployed within each LTE eNodeB. This design has the following benefits:

(a) Deep packet inspection (DPI) modules, policy engines etc. are already present within the LTE EPC and ATOM interfaces with these gateways to acquire appropriate information. Hence it is better to co-locate ATOM with them.

(b) Deploying ATOM in each base-stations hinders deployability as it increases the base-stations computational requirement.

(i) 网络中心化 (Network-centric)：ATOM被设计为一个 中心化解决方案，它利用完整的网络视图（小区负载、用户QoE等） 来确定最优的接口选择。

这使得ATOM相较于基于客户端的分布式解决方案（例如[8]）具有重要优势，后者需要来自网络的专有信令（产生无线链路开销并需要更改标准）才能获取ATOM可轻松访问的负载信息。ATOM是一个网关级解决方案，可以部署在LTE移动核心网内，而不是部署在每个LTE eNodeB中。此设计具有以下优点：

(a) 深度包检测（DPI）模块、策略引擎等已存在于LTE EPC中，ATOM与这些网关接口以获取适当信息。因此，将ATOM与它们共同部署更佳 (b) 将ATOM部署在每个基站会增加基站的计算需求，从而妨碍可部署性

(ii) Scalability: While maintaining a centralized view of the network, ATOM is carefully designed to scale to large deployments by treating each LTE cell (and the WiFi APs in its coverage) in isolation when deciding the network interface for users.Since traffic from an LTE cell is offloaded to the WiFi APs that are within its coverage, multiple ATOM instances run in parallel where each instance independently manages the user flows in a given LTE cell. This design choice ensures that ATOM can be scaled-up as the operator deploys more LTE base-stations and/or WiFi access points as opposed to traditional middle boxes that need to be scaled-out. This design also ensures further performance optimizations, wherein ATOM instances are instantiated only for congested cells.

(ii) 可扩展性 (Scalability)： 在保持网络中心化视图的同时，ATOM经过精心设计，能够扩展到大规模部署，其方法是在决定用户网络接口时，独立处理每个LTE小区（及其覆盖范围内的WiFi AP）。由于来自一个LTE小区的流量被分流到其覆盖范围内的WiFi AP，因此多个ATOM实例并行运行，每个实例独立管理给定LTE小区中的用户流。与需要横向扩展的传统中间设备相反，这种设计选择确保了随着运营商部署更多的LTE基站和/或WiFi接入点，ATOM可以纵向扩展。此设计还确保了进一步的性能优化，即仅为拥塞的小区实例化ATOM实例。

(iii) Seamless Switching: ATOM incorporates a mechanism to seamlessly switch user traffic flows across LTE and WiFi interfaces. This mechanism is designed such that (1) it is cost effective (2) it enables adaptive or dynamic traffic management given that wireless conditions change over time. Moreover, it is hard to estimate or define application requirements on the onset of a TCP connection from a mobile device. Hence, ATOM sets simple static policies on the mobile device, for instance all connections are initiated over the WiFi interface. With seamless switching, the appropriate decision for an application flow can be taken while the session is ongoing. This ensures operators can define more sophisticated policies, for instance based on resolution of video selected by the user.

(iii) 无缝切换 (Seamless Switching)： ATOM包含一种机制，可以 在LTE和WiFi接口之间无缝切换用户数据流。

此机制的设计目标是：(1) 经济高效；(2) 鉴于无线条件随时间变化，能够实现自适应或动态的流量管理。

此外，在移动设备发起TCP连接之初，很难估计或定义应用需求。因此，ATOM在移动设备上设置简单的静态策略，例如所有连接都通过WiFi接口发起。借助无缝切换，可以在会话进行过程中为应用流做出适当的决策。这确保了运营商可以定义更复杂的策略，例如基于用户选择的视频分辨率的策略。

(iv) Pricing: Users are generally charged based on two plans: (i) Price per byte: This is a fixed amount per KB of data (ii) Tiered data-caps: Users have a data limit (e.g., 3GB per month) paying a fixed monthly price. Moreover, operators offer WiFi free of cost to their current customers. However, such a model may change as operators offer similar carrier-grade service on their WiFi networks as they do on their LTE networks. With this in mind, we design ATOM to incorporate general pricing mechanisms to ensure that its design is applicable to either of the above pricing scenarios.

(iv) 定价 (Pricing)： 用户通常根据两种套餐付费：

(i) 按字节付费：即每KB数据固定金额；

(ii) 分级数据上限：用户有数据限制（例如，每月3GB），支付固定的月费。

此外，运营商向其现有客户免费提供WiFi。然而，随着运营商在其WiFi网络上提供与LTE网络类似的电信级服务，这种模式可能会改变。考虑到这一点，我们设计的ATOM能够整合通用的定价机制，以确保其设计适用于上述任一种定价场景。

Considering the above, ATOM is instantiated as a gateway-level solution in the operator’s access network external to the base-stations as shown in Figure 3. Since the gateway will typically handle traffic for multiple base-stations, it hosts multiple ATOM instances, each handling traffic for one LTE base-stations. ATOM’s design has two components: (i) Network Interface Assignment (NIA) component and (ii) the Interface Switching Service (ISS).

综合以上考虑，ATOM被实例化为运营商接入网络中位于基站外部的网关级解决方案，如图3所示。

由于 该网关通常会处理多个基站的流量，因此它承载多个ATOM实例，每个实例处理一个LTE基站的流量

ATOM的设计包含两个组件：(i) 网络接口分配（NIA）组件和 (ii) 接口切换服务（ISS）

ATOM
  1. ATOM实例 与 LTE基站 一一对应
  2. ATOM 部署在 PDN-GW 网关