# Research on Key Technologies of Quantum-Safe Metro-Optimized Optical Transport Networks
## 2 Methods  
### OSU Service Mapping/Multiplexing  
The packet service architecture utilizes a standardized 2.6 Mbps OSU framework via adaptive mapping and multiplexing, facilitating dynamic network slicing and multi-service convergence [16]. As illustrated in Figure 1, the ITU-T G.709-compliant solution introduces a containerization mechanism within the optical channel payload unit (OPU) structure. This layered abstraction enables (1) physical-layer isolation through time-frequency resource partitioning; (2) deterministic latency via fixed-frame scheduling; (3) cryptographic security by employing optical channel scrambling; and (4) bandwidth elasticity, supporting adaptive adjustment from 10 Mbps to 100 Gbps. The primary requirement for OSU-hosted packet traffic is MAC-transparent transmission. The maximum bit rate of an OSU corresponds exclusively to the nominal Ethernet MAC bit rate, representing the highest assured bandwidth that an OSU can provide. An OSU is suitable for transmitting Ethernet traffic without a predetermined bit rate. The bit rate of an OSU varies with traffic fluctuations, specifically within the range of 4 to C times the PB benchmark bit rate (\(R_{\text{PB}}\)). C \(\times R_{\text{PB}}\) denotes the maximum OSU bit rate, where C represents the maximum guaranteed bandwidth allocated by the OSU connection for Ethernet services. Table 1 presents calculations of the maximum OSU bit rate for standard Ethernet services. The ODU frame structure is divided into multiple payload blocks (PBs), with each OSU filling one or more PBs. The OSU bit rate is influenced by the type of packet traffic transmitted. The client signal is first mapped to the OSU and then multiplexed into the OPU frame through the optical service branch unit (OSTU) structure. The OSTU architecture organizes \(C\) PBs within an operational period spanning \(P\) consecutive OPU PB intervals. According to ITU-T G.709 [17], the peak capacity parameter \(C\)(measured in PBs) governs the theoretical maximum OSU throughput allocable per client port, which is given by  
\[C=\frac{R_{\text{client}}\times(1+R_{\text{client\_tolerance}})\times\frac{192} {185}}{R_{\text{PB}}\times(1-R_{\text{PB\_tolerance}})} \tag{1}\]  
where \(R_{\text{client}}\), \(R_{\text{client\_tolerance}}\), \(R_{\text{PB}}\), and \(R_{\text{PB\_tolerance}}\) denote the client bit rate, client bit rate tolerance, OSU PB reference bit rate, and OSU PB reference bit rate tolerance (\(\pm\)20 ppm), respectively. The OSU maximum bit rate is calculated as follows:  
\[R_{\text{OSU}}=C\times R_{\text{PB}} \tag{2}\]  
The OSU maximum payload bit rate is calculated as follows:  
\[R_{\text{OSU\_PLD}}=C\times R_{\text{PB}}\times\frac{185}{192} \tag{3}\]  
The OSU adopts the OPU division method based on the PBs, as shown in Figure 2. For a given OPU, each transmission cycle consists of P consecutive PBs, and the PB size of each OPU is 192 bytes. Table 2 presents the corresponding \(p\) values of ODUs with different rates under the condition of 2.6 Mbps as the OSU PB benchmark bandwidth (\(R_{\text{PB}}\)), the actual PB bit rate of different OPUKs is close to the OSU PB benchmark bandwidth, and the \(p\) values can be calculated using Equation (4):  
\[p=\frac{R_{\text{OPU\_PLD}}\times(1-OPU\_PLD\_BR\_tolerance)}{R_{\text{PB}} \times(1+1000\text{ ppm})} \tag{4}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ethernet Service Rate**} & \multirow{2}{*}{\(C\)**Value**} & \multirow{2}{*}{\({}^{1}\)\(R_{\text{OSU}-\text{max}}\) (Kbps)} & \multirow{2}{*}{\({}^{2}\)\(R_{\text{OSU}\_PLD}-\text{max}\) (Kbps)} \\ \hline
10 Mbps & 4 & 10,400 & 10,020.833 \\
100 Mbps & 40 & 104,000 & 100,208.333 \\
1 Gbps & 400 & 1,040,000 & 1,002,083.333 \\
10 Gbps & 3996 & 10,381,800 & 10,003,296.875 \\ \hline \hline \end{tabular} \({}^{1}\)\(R_{\text{OSU}}=C\times R_{\text{PB}}\), \(R_{\text{PB}}=2.6\) Mbps. \({}^{2}\)\(R_{\text{OSU}\_PLD}=C\times R_{\text{PB}}\times\frac{185}{192}\), \(R_{\text{PB}}=2.6\) Mbps.  
\end{table} 
Table 1: OSU bit rate for various Ethernet service rates.