# Evaluation of Modern Internet Transport Protocols over GEO Satellite Links
## 1 Introduction  
Satellite networks have become an important component of the Internet due to their wide coverage, high bandwidth and broadcasting capabilities. However, satellite communication links suffer from several limitations. The first primary limitation is the large propagation delay which is especially notable in geostationary (GEO) satellites that are located around 36,000 km above earth. The second limitation is the high bit error rate (BER) which is caused by the significant path loss in the satellite propagation channel. In modern satellite systems employing Adaptive Modulation and Coding (AMC), the link bit rate, and hence the frame size, varies with the channel conditions resulting in excessive segmentation and reassembly at higher layers. Another problem is the bandwidth asymmetry that exists between the hub gateway and satellite terminals which is caused by the nature of the shared return channel [1]. These problems at the link level greatly affect the performance of many Internet services running over satellite networks.  
Over the years, there have been continuous efforts to overcome these problems at different layers of the Internet protocol stack which is illustrated in Figure 1.  
At the transport layer, various TCP congestion control algorithms were designed to address the high latency problem of satellite links [2]. Also, performance enhancement proxies (PEPs) were widely used to improve TCP connection throughput using various, mostly proprietary solutions. At the application layer, newer forms of Internet protocols such as HTTP/2 over TCP and HTTP/3 over Quick UDP Internet Connection (QUIC) have been designed to address many of the shortcomings of legacy HTTP and TCP protocols [3].  
Since satellite networks are usually deployed for long-term service often spanning many years, it is important to provide a cost-effective means for evaluating new and evolving Internet protocols over these networks. In this research work, we investigated the behavior of the modern HTTP variants such as HTTP/2 over TCP and HTTP/3 over QUIC running in modern satellite networks using a realistic emulation testbed. The testbed was built using state-of-the-art web browsers and web servers to mimic the true behavior of Internet protocols. The testbed can be used for optimizing the performance of these protocols as well as devising new algorithms to enhance their performance. Also, it will provide guidelines for different configurations of the protocol stacks and congestion control algorithms that could be used to improve Internet performance over future satellite networks.  
In this paper, we present the findings of a detailed investigation of HTTP/3 over QUIC and HTTP/2 over TCP in GEO satellite links with modern congestion control algorithms and various web page structures. Specifically, the paper provides the following contributions:  
* A testbed for GEO satellite links, with full DVB-S2/RCS emulation, running state of the art web servers and clients with complex web page structures that are otherwise extremely difficult to achieve via simulation;
* A performance comparison of HTTP/2 and HTTP/3 over GEO satellite links when using modern congestion algorithms such as Cubic and BBR;
* A web-level performance comparison of HTTP/2 and HTTP/3 when using complex web page structures with varying objects sizes and distribution. Here we employ First Contentful Paint (FCP) and Largest Contentful Paint (LCP) in addition to the page load time (Time) as our web-level user-perceived performance metrics.  
The rest of the paper is organized as follows. A literature review of related work on evaluating Internet protocols in satellite networks is presented in Section 2. Next, Section 3 explains the details of the modern Internet protocols such as QUIC and HTTP/2. The evaluation testbed with its hardware and software components is described in Section 4. The evaluation scenarios and the results are presented in Sections 5 and 6, respectively. Finally, we summarize our main findings and conclusions at the end of the paper.