Cisco Precision Time Protocol for NCS 2000 Network

Chapter 1: Overview of PTP Solution

Overview of PTP

Challenges

In today's fast-growing network traffic, network operators are adding new nodes to ensure smooth traffic flow in data centers and networks. The addition of new nodes increases latency over the networks, posing a significant challenge. To avoid delays in synchronizing time signals and network latency, the need for precise timing synchronization is increasing. Precision Time Protocol (PTP) offers a high-precision timing synchronization solution across networks.

Solution

Cisco has developed a PTP solution for NCS 2000 networks to help avoid latency and ensure timing synchronization. The NCS 2000 platform provides the operational capacity to meet increasing network demands. PTP for NCS 2000 networks combines the functionality of NCS 2000 with precise PTP synchronization to enhance network efficiency. This solution can be implemented over existing NCS 2000 optical networks using NCS 5500 and NCS 540 routers.

The NCS 5500 and NCS 540 routers provide PTP support to NCS 2000 networks, leveraging PTP signals to establish transparent clock synchronization over the NCS 2000 network. Previously, NCS 2000 networks used an in-band channel for PTP signals, limiting bandwidth utilization. The PTP filter introduces an out-of-band OSC signal at 1518 nm to propagate PTP signals, keeping in-band channels free for traffic and allowing full utilization of NCS 2000 network channels.

In a typical setup, a Grandmaster (GM) clock feeds PTP signals to an NCS 5500 router (First Router) via a primary clock (TBC). The ONS-SC-PTP-1510 pluggable installed in the NCS 55xx router enables timing signal synchronization over the NCS 2000 DWDM cloud.

PTP Filter

Figure 1: PTP Solution for NCS 2000 DWDM Cloud Using NCS 5500 and NCS 540 Routers depicts a network architecture where an external clock connects to a TBC (First Router), which then interfaces with an NCS 2000 DWDM Cloud via an ONS-SC-PTP-1510 pluggable. The DWDM cloud connects to NCS 5500 and NCS 540 routers, also using ONS-SC-PTP-1510 pluggables, to other TBCs and external clocks.

On the NCS 55xx router, the PTP optical clock signal is generated by an external clock acting as the GM clock. This GM clock synchronizes PTP signals with Boundary Clocks (BC), both primary and secondary, distributed across the network. Primary clocks establish PTP sessions with downstream secondary clocks to reduce network hops and packet delays. The ONS-SC-PTP-1510 and ONS-SC-PTP-1514 pluggable optics support NCS 55xx routers in propagating PTP clock signals over the NCS 2000 DWDM cloud.

The PTP solution utilizes SFP pluggable optics and a PTP filter. The filter combines and splits PTP and OSC signals within the NCS 2000 network. Pluggable optics are inserted into NCS 5500 and NCS 540 routers to transmit PTP signals. The following table lists the required hardware:

The PTP filter enables multiplexing and demultiplexing of OSC and PTP signals over NCS 2000 networks. It transmits the PTP signal over an Out-of-Band (OOB) OSC channel. The filter receives the PTP signal from NCS 5500 or 540 and the OSC signal from NCS 2000 controller cards, combining them for transmission over a line card OSC channel. An SFP in the NCS 5500 or 540 router sends the PTP signal (1510 or 1514 nm) to the filter, while the controller card sends the OSC signal (1518 nm). The filter then sends the combined signal through an NCS 2000 line card's OSC channel, connecting to routers and cards on both east and west sides for PTP transmission.

PTP Pluggable Optics

PTP pluggable optics facilitate PTP signal transmission to NCS 2000 DWDM networks. These SFPs are hosted on routers like NCS 540 or NCS 55xx, which support sending and receiving PTP signals. The optics are available in variants for 1510 nm and 1514 nm, both supporting DWDM transmission at 1 Gbps. They are designed bidirectionally to minimize latency associated with full-duplex communication over separate fibers.

The ONS-SC-PTP-1510 pluggable transmits PTP signals at 1510 nm and receives 1514 nm signals. The ONS-SC-PTP-1514 pluggable transmits at 1514 nm and receives at 1510 nm.

Note: For intra-lab connectivity using these pluggable optics, an attenuator (15 or 20 dB) must be added to the connection.

Bring Up of PTP Over OSC Link Workflow

The following workflow outlines the steps to establish a PTP over OSC link for NCS 2000 networks:

1. Install the Cisco ONS 15216 OSC PTP Filter Module on NCS 2000 networks. Refer to the "Installation" section in the Installing the Cisco ONS 15216 DWDM and CWDM Passive Optical Modules book.
2. Ground the PTP module and clean its ports. Refer to the "Ground Description" section in the same book.
3. Connect cables. Refer to "PTP Module Port Connections" on page 3.
4. Configure the PTP Clock Signal. Refer to "Configuration of PTP Clock Signal" on page 4.

PTP Module Port Connections

Figure 2: PTP Filter Port Connections Block Diagram illustrates the PTP filter port connections with NCS 5500 / NCS 540 and TNCS-2O in NCS 2000. It shows an NCS 5500/540 Router connected via an ONS-SC-PTP-1510 pluggable to a PTP Filter. The filter has PTP-10-E-TX/RX and COM-10-E-TX/RX ports. It also connects to an NCS 2000 Chassis via an ONS-SC-OSC-18.0 pluggable, featuring OSC-E-TX/RX and PTP-10-E-TX/RX ports, and a TNCO Card.

Chapter 2: Use Cases and Limitations

Use Case

The PTP solution for NCS 2000 enables the utilization of PTP signals from NCS 5500 and NCS 540 routers over NCS 2000 networks.

NCS 2000 Network Configuration for PTP over OSC Link

The PTP solution for NCS 2000 networks is supported across the following NCS 2000 flex spectrum network configurations:

The following table details the reach of the PTP over OSC link in NCS 2000 networks, with and without RAMAN amplifiers:

Note: To keep RX power below the allowed maximum (-7 dBm), attenuators must be used with PTP SFPs.

PTP over OSC Link with OTDR using PTP Filter

This solution involves placing a PTP filter between the TNCS-2O card and the GM clock in the router. The filter multiplexes the PTP signal from the GM clock and the OSC signal from the NCS 2000 TNSC-2O card. The combined signal is sent over the NCS 2000 network via the near-end ROADM, which propagates it through its OSC channel to the far end. At the next PTP filter, the combined signal is demultiplexed to send the PTP signal to NCS 55xx/540 and the OSC signal to the TNSC-2O card. This multiplexing and demultiplexing process for PTP and OSC signals continues on both sides of the CDC ROADM throughout the NCS 2000 network.

Figure 3: PTP over OSC Link with OTDR Signal Flow using PTP Filter illustrates the signal flow of the PTP over OSC link using a PTP filter. For port connection details, refer to "PTP Module Port Connections" on page 3.

Use Case 1: PTP over OSC Link with OTDR, without RAMAN Amplifier

The following hardware is required for this use case:

• Pluggable optics: ONS-SC-OSC-18.0, ONS-SC-PTP-1514, and ONS-SC-PTP-1510
• Filter: 15216-OSC-PTP

Use Case 2: PTP over OSC Link with OTDR, RAMAN Amplifier

The following hardware is required for this use case:

• Pluggable optics: ONS-SC-OSC-18.0, ONS-SC-PTP-1514, and ONS-SC-PTP-1510
• Filter: 15216-OSC-PTP
• Amplifier: OPT-EDFA-24, 15454-M-RAMAN-CTP
• ROADM: SMR9 (NCS2K-9-SMRxxFS / NCS2K-9-SMRxxFS-L)

The 15216-OSC-PTP filter combines the OSC signal from the TNCS card and the PTP clock signal from the ONS-SC-PTP-1510 pluggable in NCS 55xx (east direction). It sends the combined signal to the OSC RX port of the EDFA-24 amplifier card via the COM-E-TX port. EDFA-24 then sends the signal, via RAMAN-CTP amplifier on Side A and B, to the SMR9 ROADM card. The SMR card routes the signal to the COM-W-RX port of the 15216-OSC-PTP filter. The filter splits the signal via the OSC-W-RX port, sending the PTP signal to the boundary clock and the OSC signal to the TNCS card.

The following table shows the COM port connections for the PTP Filter Module for this scenario:

Figure 4: PTP over OSC with OTDR, Without RAMAN Amplifier depicts the signal flow and connections for this configuration.

The following table shows the COM port connections for the PTP Filter Module when using RAMAN Amplifier:

Figure 5: Sending PTP over OSC Link with OTDR and RAMAN Amplifier illustrates the signal flow and connections for this scenario.

Limitations in PTP for NCS 2000 Networks

The PTP solution has certain limitations across its supported use cases. The following sections detail these limitations.

NCS 2000 Network with PTP Filter

The table below outlines limitations found in NCS 2000 networks equipped with PTP filters:

NCS 5500 Router

The table below lists limitations specific to the NCS 5500 router:

Appendix A

Cisco ONS 15216 OSC PTP Filter Module

The Cisco ONS 15216-OSC-PTP Filter module is used in the NCS 2000 network to multiplex and demultiplex optical signals provided by DWDM SFPs. It carries PTP signals at 1510 and 1514 nm, and the standard OSC signal at 1518 nm.

The module's operations include:

• Separating 1510- and 1518-nm wavelengths from the composite signal entering the COM-W-RX port and routing them to the PTP-14-W-TX and OSC-W-TX ports, respectively.
• Receiving the 1514-nm wavelength from the PTP-14-W-RX port and combining it towards the COM-W-RX port.
• In the opposite direction, receiving 1518- and 1510-nm wavelengths from the OSC-E-RX and PTP-10-E-RX ports, respectively, and combining them towards the COM-E-TX port.
• Separating the 1514-nm wavelength entering the COM-E-TX port and routing it to the PTP-10-E-TX port.
• The path from OSC-W-RX to COM-W-TX is a simple bypass path (no filtering), as is the path from COM-E-RX to OSC-E-TX.

Features

Figure 6: 15216-OSC-PTP Filter Module Optical Block Diagram shows the module's optical ports and internal connections.

Note: The filter propagates 1510 and 1514-nm signals on the same optical fiber between adjacent nodes in opposite directions.

Figure 7: OSC + PTP Signal Transmission Block Diagram illustrates the signal transmission between terminal W, a Line Amplifier Site, and another terminal W, showing the flow of OSC/OTDR (1518 nm) and PTP (1510 nm/1514 nm) signals.

The Cisco ONS 15216-OSC-PTP Filter module offers the following features:

• Thin-film DWDM 100GHz-spaced filters for multiplexing and demultiplexing optical transmission channels, modulated up to 100 Gbits.
• Passive device with athermal design (no active temperature control).
• Optical connectivity using LC-UPC connectors and 900 micrometer fiber.
• Integrated tap coupler (PLC or fused fiber).

Port Label Description

The following table details the connection ports, their descriptions, and connector types. All ports are on the module faceplate and use optical LC adapters.

Port Identification Label

Figure 8: Cisco 15216-OSC-PTP Filter Module Label shows the port identification label on the module's faceplate, indicating port names (OSC-E, OSC-W, PTP-10-E, PTP-14-W, COM-E, COM-W) and their TX/RX indicators.

Optical Specifications

The following table provides the optical specifications for the Cisco 15216-OSC-PTP Filter module:

The following table provides the optical path specification for each path in the ONS-15216-OSC-PTP Filter module:

Safety Information

Before installing, operating, or servicing this product, read the Regulatory Compliance and Safety Information for Cisco Optical Transport Products document for important safety information and warning translations.

This product complies with GR 1089, UL60950 / CSA 22.2 No. 60950-00, and IEC 60950 standards.

Laser Radiation Emission Restrictions

A Class 1M Laser safety and warning label is affixed to this product. It indicates that the product should not be used or installed in an optical network with emissions higher than Class 1M.

⚠️ Warning: Class 1M laser radiation when open. Do not view directly with optical instruments. Statement 281

⚠️ Warning: Invisible laser radiation may be emitted from disconnected fibers or connectors. Do not stare into beams or view directly with optical instruments. Statement 1051

Laser Safety During Operation

⚠️ Warning: Invisible laser radiation may be emitted from disconnected fibers or connectors. Do not stare into beams or view directly with optical instruments. Statement 1051

Electrical Safety

This product is optically and electrically passive, requiring no electrical connections. No electrostatic discharge (ESD) or other electrical safety considerations apply.