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Design Overview

Based on the above discussion, the essence of the circuitous routing problem in mobile satellite networks lies in the reliance on a fixed anchor point per PDU session and the difficulty of deploying the anchor point on satellites. This reliance directly leads to the issue where the anchor point is often not on the fastest path from the base station to the user’s target server, resulting in additional latency. To address this, a natural approach is to expand the number of available anchor points in a single session and select different anchor points based on the actual target of the user’s traffic to avoid detours.

基于上述讨论，移动卫星网络中 绕路路由（circuitous routing）问题 的本质在于 每个PDU会话依赖固定锚点，而由于锚点难以部署在卫星上，这一依赖导致锚点常常不在从基站到用户目标服务器的最优路径上，进而引发额外的通信延迟。为解决该问题，一种自然的思路是 在单个PDU会话中扩展可用锚点的数量，并根据用户实际流量的目的地选择不同锚点，从而规避绕路路径。

In this paper, we propose SkyOctopus, a multi-anchor mobile satellite network architecture that enables users to have multiple available anchor points distributed globally within a single PDU session. In SkyOctopus, multiple UPFs are deployed as anchor points at ground stations. On one hand, by introducing the Satellite UPF (S-UPF), user traffic can be forwarded to different anchor points based on its target IP addresses. This design keeps the anchor points on the ground while moving the traffic classifiers to the satellite, thereby avoiding the circuitous routing problem and the frequent anchor point reselection issue caused by satellite mobility. On the other hand, by redesigning the session establishment process, the S-UPF can establish connections with multiple anchor points simultaneously, avoiding the issue of prolonged session establishment times caused by the insertion-based process.

本文提出SkyOctopus，一种支持多锚点的移动卫星网络架构，使得用户在一个PDU会话中可以拥有分布于全球的多个可用锚点。在SkyOctopus中，多个用户面功能实体（UPF）被部署在地面站作为锚点。一方面，我们引入了卫星UPF（S-UPF），使得用户流量可根据目标IP地址被转发至不同锚点。该设计将锚点保留在地面，同时将流量分类功能上移至卫星，从而避免了绕路路由问题，并缓解了因卫星移动性带来的锚点频繁重选问题。另一方面，通过重新设计会话建立流程， S-UPF可同时与多个锚点建立连接 ，避免了因传统插入式建立方式带来的会话建立延迟问题。

However, there are two main challenges to applying this architecture. The first challenge is the anchor point selection problem. Although SkyOctopus allows for proactive routing selection, it is difficult to ensure reasonable anchor point selection to minimize end-to-end latency, considering the diversity of user targets and the mobility of satellites. The second challenge is the anchor point distribution problem, which involves determining the optimal locations for anchor points. Given the deployment and connection costs of UPFs, operators can hardly deploy anchor points without limitations. Therefore, it is necessary to strategically select their deployment locations given a fixed number of anchor points.

然而，应用该架构仍面临两大挑战。

第一是锚点选择问题：尽管SkyOctopus支持主动路由选择，但受限于用户目标的多样性以及卫星的动态移动，难以始终确保合理的锚点选择以最小化端到端延迟

第二是锚点部署问题：即如何确定锚点的最优部署位置。考虑到UPF的部署与连接成本，运营商无法无限制地部署锚点，因此需要在给定数量限制下战略性地选择锚点部署位置

To address the first challenge, we propose a fine-grained anchor point selection strategy. The S-UPF uses PDRs based on the mapping of IP addresses to geographical locations to determine the initially chosen anchor point for users. Additionally, the path update mechanism ensures that the S-UPF can always select the optimal anchor point for users, even when network conditions change. The mechanism evaluates both intra-network and inter-network conditions to ensure users experience end-to-end low-latency access.

To tackle the second challenge, we analyze the anchor point deployment problem and prove it is an NP-hard problem. Based on this, we propose a greedy algorithm for selecting deployment locations for a fixed number of anchor points.

为应对第一个挑战，本文提出细粒度锚点选择策略。S-UPF通过基于IP地址到地理位置的映射建立PDR规则，从而确定用户初始的锚点选择。此外，SkyOctopus还引入路径更新机制，即使在网络状态变化时，也能保证S-UPF持续选择最优锚点。该机制综合评估网络内部与外部的路径条件，以确保用户始终获得低延迟的端到端接入体验。

为解决第二个挑战，我们对锚点部署问题进行了建模，并证明其为一个NP难问题。在此基础上，本文设计了一种贪心算法，用于在锚点数量固定的前提下选择最优部署位置。

简要概括:

(1) 核心机制: 在单次PDU会话中, 可以连接多个UPF锚点, 其中有S-UPF在卫星上作为流量分类器

(2) 锚点如何选择？锚点如何部署？

  1. 如核心机制中提及，我们在单次PDU会话中，有那么多UPF锚点可以选择，应该选哪一个？

    • 初始选择: S-UPF通过基于IP地址到地理位置的映射建立PDR规则
    • 持续更新: 通过综合评估算法, 即使在网络状态变化时, 也能保证S-UPF持续选择最优锚点

  2. 考虑到UPF的部署与连接成本，我们在给定数量上限的情况下，应该如何部署UPF？

    • 本质路径规划问题, NP-Hard
    • 贪心算法: 在锚点数量固定的前提下选择最优部署位置