ONS 15454 MSTP ROADM

The OADMs discussed in the earlier two sections are "fixed-channel" OADMs. The implementation of fixed-channel OADMs requires careful planning consideration to ensure that the appropriate wavelength channels are efficiently used at each add/drop site. To correctly design a system, a DWDM engineer must be aware of present and future wavelength channel requirements at each node within the system. Careful thought and consideration must be given to how and where banded OADM filters should be used so that future wavelength additions at a node do not require service interruptions. In addition, the DWDM engineer is required to manage an inventory of diverse fixed-channel OADM band filters and fixed-wavelength OADMs. For example, if the DWDM system is designed for full wavelength add/drop flexibility, up to 32 one-channel OADM filters would be present in the network, requiring 32 separate spare parts. Finally, as the DWDM network grows (that is, channel requirements increase), the addition of wavelengths to the system requires the manual fine-tuning of amplifiers at intermediate nodes, driving up the operations cost of ownership for DWDM networks.

To mitigate the operational complexities, network design constraints, and traffic engineering limitations posed by traditional DWDM deployment, carriers are increasingly implementing ROADM in their DWDM deployments. For the ONS 15454 MSTP solution, the ROADM consists of the 32 WSS and the 32 DMX. With the ONS 15454 MSTP ROADM solution, wavelength channel capacity can be remotely distributed to add/drop locations as service demands dictate, without the expense and time associated with re-engineering the network and manually dispatching operations personnel to fine-tune the DWDM parameters at each wavelength add/drop or amplifier site. With the ROADM architecture, the DWDM transport network is designed once, although a wide array of services across the network can be added, rearranged, or deleted infinitely, as capacity exists. This gives carriers a true "next-generation" network, whereby the services provided on the network do not depend upon the design and redesign of the transport technology. Moreover, the ROADM approach provides the flexibility to distribute wavelength channels in a ring, hub-and-spoke, or mesh patternall within the framework of a single physical design.

Figure 9-19 details a sample network using traditional DWDM versus DWDM with ROADM technology. By nature, traditional DWDM is a point-to-point technology. To interconnect DWDM systems, carriers typically deploy back-to-back terminals, whereby all the DWDM channels are dropped and ring interconnection is accomplished using transponders. This scenario requires double the normal capital expenditure outlay, in that twice the number of transponders is required for each wavelength channel. In addition, ring-to-ring interconnection requires manual intervention for transponder placement and fiber jumper routing. In contrast, the ROADM approach mechanizes wavelength channel hand-off between DWDM systems, negating the capital and operational expense requirements of the traditional DWDM approach.

Figure 9-19. Traditional DWDM versus DWDM/ROADM Ring Interconnect