🧩 Overview
| Layer | Technology | Type | Core Function |
|---|
| Packet Layer (L2–L2.5) | PTN | Packet-based | Efficiently transport and manage packet (Ethernet/IP/MPLS) traffic |
| Digital Optical Layer (L1.5) | OTN | Digital frame-based | Encapsulate client signals (Ethernet, SDH, Fibre Channel, etc.) into standardized optical containers |
| Physical Optical Layer (L1) | WDM | Optical | Multiplex many optical wavelengths over one fiber pair for massive capacity |
⚙️ Detailed Comparison
| Feature | PTN (Packet Transport Network) | OTN (Optical Transport Network) | WDM (Wavelength Division Multiplexing) |
|---|
| Layer | 2 / 2.5 | 1.5 (digital optical) | 1 (physical optical) |
| Technology Base | Ethernet / MPLS-TP | ITU-T G.709 | Optical multiplexing (DWDM/CWDM) |
| Transmission Unit | Packets | Optical channel data unit (ODU) | Light wavelengths (λ) |
| Switching Type | Packet-based | Circuit-based (time slot or ODU-level switching) | Optical wavelength-based |
| Traffic Type | IP, Ethernet, mobile backhaul | Aggregated, mixed client traffic | Any optical signal |
| QoS / OAM | Excellent (per packet) | Good (per ODU) | Minimal (handled above) |
| Latency | Low–medium | Very low | Negligible |
| Bandwidth Scalability | Moderate (Gbps–10s of Gbps) | High (10G–400G+ per wavelength) | Extremely high (many wavelengths × 400G+) |
| Use Case | Metro networks, aggregation, access | Core transport, service multiplexing | Long-haul, core transmission |
| Resiliency | Protection at packet layer | Protection via ODUk path/signal | Protection via optical path |
🔄 Relationship Between Them
They form a layered hierarchy — each layer adds intelligence and abstraction above the previous one:
[Service Layer]
(IP/MPLS, 5G, Enterprise Ethernet)
↓
[PTN Layer] – packet transport, QoS, OAM, aggregation
↓
[OTN Layer] – digital encapsulation, multiplexing, error correction
↓
[WDM Layer] – optical transmission (multiple wavelengths)
↓
[Fiber Optic Cable]
🧠 Example in Practice
- WDM: provides raw optical “highways” (e.g., 80 × 400 Gb/s channels).
- OTN: acts like “lanes” within those highways, organizing traffic into digital containers (ODUk).
- PTN: runs services like mobile backhaul, Ethernet VPNs, or IP aggregation over those containers.
🧭 In Short
| Aspect | PTN | OTN | WDM |
|---|
| Purpose | Packet switching and QoS | Digital multiplexing & framing | Optical multiplexing |
| Main Domain | Metro / aggregation | Core / backbone | Core / long-haul |
| Typical Vendor Gear | Huawei PTN9xxx, Nokia 7750 | Huawei OptiX OSN, Infinera, Ciena 6500 | Ciena Waveserver, Infinera Groove |
| Complementary Roles | Service intelligence | Transport grooming | Transmission capacity |
✅ Summary:
- WDM = Physical layer (many light channels)
- OTN = Digital framing layer (organizes and protects data)
- PTN = Packet-aware transport layer (intelligent switching and service management)
