# Research on Key Technologies of Elastic Satellite Optical Network Based on Optical Service Unit
## 3 Analysis and Discussion
### Performance Comparison Between OISL-OSU and OISL-MPLS  
The performance of OISL-OSU and OISL-MPLS was evaluated based on the Internet Engineering Task Force (IETF) request for comments 2544 (RFC2544) standard under a packet loss rate of 0% (26). The test results were measured by using an Ethernet tester (MTS 5800, VIAVI Solutions Inc., Chandler, AZ, USA) for throughput, loop delay, packet jitter, and back-to-back performance, as shown in Figure 10, Figure 11, Figure 12, and Figure 13, respectively. The hierarchical evaluation framework in RFC2544 throughput testing exhibits distinct operational characteristics across Open Systems Interconnection (OSI) layers, as systematically demonstrated through controlled experimentation (27). At Layer 1 (L1, i.e., the physical layer), raw bit rate quantification excludes protocol overhead through the computational model as follows:  
\[L1=N_{frames}\times B_{frame}, \tag{11}\]  
where \(N_{frames}\) denotes frames per second and \(B_{frame}\) represents bits per frame. Electrical signal synchronization was rigorously maintained using precision clock recovery circuits (0.1 ppm stability) during measurement. At layer 2 (L2, i.e., the data link layer), constituting the RFC2544 baseline implementation, frame forwarding efficiency is demonstrated as follows:  
\[L2=N_{frames}\times(S_{frame}+20\text{B}), \tag{12}\]  
which incorporates inter-packet gap compensation as defined in Institute of Electrical and Electronics Engineers (IEEE) 802.3 specifications (28). Our experimental configuration maintained 68B to 1522B VLAN frame sizes with \(\pm 0.01\%\) measurement tolerance. Layer 3 (L3, i.e., the network layer) evaluation necessitated IP stack parameter optimization, particularly maximum transmission unit (MTU) configuration, with throughput calculated as  
\[L3=N_{packets}\times S_{MTU}, \tag{13}\]  
where \(N_{packets}\) denotes packets per second and \(S_{MTU}\) is empirically determined through path MTU discovery algorithms. Layer 4 (L4, i.e., the transport layer) analysis implemented transmission control protocol (TCP) window scaling (RFC7323) and selective acknowledgment (RFC2018) mechanisms, measuring application-layer data unit transmission efficiency under varied congestion control regimes (29;30). Firstly, Figure 10 demonstrates that OISL-OSU facilitates flexible bandwidth distribution, ranging from 2 Mbps to 1000 Mbps, and can dynamically adapt to operational demands. Both OISL-OSU and OISL-MPLS achieve high bandwidth utilization (with L1 rates ranging from 999.96 Mbps to 999.97 Mbps and 999.99 Mbps to 1000.00 Mbps, respectively). Notably, OISL-OSU outperforms OISL-MPLS in terms of bandwidth utilization when car  
Figure 9: OISL-OTU-FEC frame. rying small-packet services (frame lengths ranging from 68B to 132B). The throughput of OISL-MPLS depends on the network's bandwidth configuration and traffic management strategy, constrained by packet switching efficiency and network congestion. On the other hand, Figure 11 illustrates the loop delay performance. OISL-OSU adopts a flexible time-slot multiplexing mechanism, which eliminates the necessity for fixed data caching at intermediate nodes, thereby substantially reducing single-node delay. By optimizing the encapsulation layer, OISL-OSU significantly decreases both encapsulation and cross-processing latencies. Compared with OISL-MPLS, OISL-OSU reduces single-node delay by 44.72%, 46.26%, 48.78%, 52.11%, 56.29%, and 58.58% for frame lengths ranging from 68B to 1522B, respectively. These results demonstrate that OISL-OSU is well-suited for time-sensitive business scenarios. Figure 10: Throughput test results. Furthermore, Figure 12 shows the packet jitter performance. OISL-OSU provides a hard channel with predictable delays, effectively reducing packet jitter and making it suitable for delay-sensitive services. Packet jitter in OISL-MPLS is influenced by network congestion and traffic scheduling.