Field trials of high density DWDM router interfaces
May 27, 2016
Our customers have been carrying out field trials and deployments of our latest 100GE DWDM coherent interfaces. In this new generation, a CFP2-ACO  module containing the tunable coherent optics plugs into an MX MIC or a PTX PIC containing the DSP, framer/deframer and FEC encoder/decoder. This results in a higher density and lower power consumption than the previous generation, while maintaining the same impressive performance (2000 km+ reach). For example, on the PTX5000, this results in 5 x 100GE DWDM ports per PIC (i.e. 10 ports per slot), compared to 4 ports per slot in the previous generation. Having pluggable coherent optics avoids having to buy all the optics upfront if not all the ports on the PIC are needed on day one.
The traditional way of connecting routers over a DWDM system is to have grey optics on the routers connecting to a transponder shelf on the DWDM system. However, the advantages of the IP over DWDM approach are as follows:
1/ Reduced CAPEX by eliminating four grey optic modules per bidirectional router-to-router link
2/ Increased reliability and easier trouble-shooting, as a result of having fewer components in the end to end path
3/ Reduced power consumption and rack space, as a result of eliminating the DWDM transponder shelf
4/ Improved signal integrity: the entire end-to-end link, from router port to router port, benefits from Soft Decision Forward Error Correction (FEC). In contrast, in conventional deployments, the grey client-side tails between the DWDM transponder shelf and the router ports don't benefit from this.
5/ Ability to take pre-emptive action if the pre-FEC BER exceeds a configured threshold, such as taking down the port and cutting the traffic over seamlessly onto other links.
PTX5000 with 5-port 100GE DWDM PICs (outlined in red) during one of the field trials
In one of the trials, our latest generation PTX DWDM PICs were tested over a production DWDM network. This was over a distance of 820 km, via a path containing 11 ROADMs and 2 in-line amplifiers. As expected, the system ran completely error-free post-FEC. The chart below shows the average pre-FEC BER as a function of time during the course of an overnight soak test. This type of performance monitoring information is easy to access via the CLI or via the Black Links MIB. As can be seen in the chart below, the pre-FEC BER is just below 2E-4, which implies a healthy system margin of about 4.3 dB.
Pre-FEC BER as a function of time during an overnight soak test over a production DWDM system
Several of our customers have commented that when they deployed the IP over DWDM scheme, they found it remarkably straight-forward to use, and have never looked back!