ZR, ZR+, and OTN Framing

 **ZR, ZR+, and OTN Framing in Coherent Optics**  


**ZR, ZR+, and OTN** are related to high-speed optical transport, but they serve different purposes. Here’s how they compare and interact with OTN framing:


**1. ZR (400ZR & OpenZR+)**

**ZR (400ZR)** is a **coherent pluggable optics** standard (QSFP-DD, OSFP) for **400G Ethernet** over DWDM.  

**OpenZR+** extends this to support **OTN framing** (ODUflex) alongside Ethernet.  

 **Key Features:**  

   **No OTN by default (pure Ethernet)** in 400ZR.  

  **OpenZR+ adds OTN (G.709) framing** for carrier-grade transport.  

  Uses **DP-16QAM modulation** for 400G over 80km+ distances.  

  **FEC:** Uses **oFEC (Open FEC)** instead of standard OTN RS-FEC.  


### **ZR vs. OTN Framing**

| Feature       | 400ZR (Ethernet-only) | OpenZR+ (OTN-enabled) | Traditional OTN (G.709) |

|--------------|----------------------|----------------------|----------------------|

| **Framing**  | Ethernet (IEEE 802.3) | ODUflex over Ethernet | Full OTUk/ODUk/OPUk |

| **FEC**      | oFEC (Open FEC)      | oFEC or CFEC         | RS(255,239) or eFEC |

| **Use Case** | Data center interconnects (DCI) | Carrier DCI & metro | Long-haul OTN networks |


## **2. ZR+ (Enhanced ZR)**

- **ZR+** is an **extended-reach** version of ZR, supporting **higher power and longer distances** (120km+).  

- **May include OTN framing** (similar to OpenZR+).  

- Used in **metro and regional networks** where full OTN is not required.  


## **3. OTN Framing (G.709)**

- **Standard OTN** (G.709) uses **OTUk/ODUk/OPUk** hierarchy with:  

  - **Forward Error Correction (FEC):** RS(255,239) or eFEC.  

  - **Multiplexing:** ODU0/1/2/3/4/flex.  

  - **Management:** Overhead bytes for performance monitoring.  

- **OTN is mandatory in traditional transport networks** but optional in ZR/ZR+.  


### **How ZR/ZR+ and OTN Work Together?**

1. **Pure Ethernet Mode (400ZR)**  

   - No OTN, just 400GbE in a pluggable module.  

   - Used in **data center interconnects (DCI)**.  


2. **OTN-over-Ethernet Mode (OpenZR+)**  

   - Encapsulates **ODUflex inside Ethernet** (FlexO-like).  

   - Provides **OTN OAM (monitoring, FEC, multiplexing)** while keeping pluggability.  


3. **Full OTN Mode (Traditional OTN Switches/Line Systems)**  

   - Uses **full OTUk framing** (G.709) with RS-FEC.  

   - Found in **carrier-grade DWDM systems**.  


### **Conclusion**

- **ZR (400ZR)** = **Ethernet-only**, no OTN.  

- **OpenZR+** = **Adds OTN (ODUflex) over Ethernet**.  

- **ZR+** = **Extended-reach ZR, sometimes with OTN**.  

- **Traditional OTN (G.709)** = Full OTN framing, used in long-haul networks.  


Would you like details on **OTN mapping in OpenZR+** or **performance differences**?

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