OTN Switching — Driving Networks Towards 100G and Beyond
As more and more metro enterprises are migrating from 10G to 100G and beyond, the adoption of OTN switching as an effective high transmission technology is proliferating in long haul and metro networks. This article digs deep into how OTN switching helps drive networks towards 100G and beyond, and examines the benefits of OTN switching together with its performance in common application scenarios.
What is OTN Switching?
In early 100G networks, the transponder and muxponder approach is most used to get traffic going through100G transmission interfaces at a lower cost per bit of optical transmission. In this approach, transponders and muxponders are often used along with ROADMs (Reconfigurable Optical Add & Drop Multiplexers) at the optical layer to enable DWDM multiplexing.
OTN switching is an advanced alternative to this traditional transponder and muxponder approach. It leverages Optical Transport Data Units (ODUks), digital transport containers that adhere to the G.709 OTN standard multiplexing hierarchy. ODUks vary in rate, ranging from 100Gbps (ODU4) up to 1.25Gbps (ODU0). OTN switching also uses the ROADM layer required for DWDM multiplexing with more add/drop flexibility.
With multi-chassis configurations, OTN switching makes it possible to scale the transmission rate from hundreds of Gbps to tens of Tbps. As data center operators increasingly deploy OTN switching for high-speed long haul and metro networks, the global market for this technology is seeing a boom.
Why is OTN Switching Gaining Momentum?
Behind OTN switching's rise in popularity lie a series of crucial benefits it offers. Here are key advantages of OTN switching in detail.
Lower Overall Network Cost
The traditional transponder and muxponder approach can offer the lowest cost per bit only when certain conditions are met:
A-Z wavelengths have a high fill rate.
The client interface speeds are close to the line interface speed.
Traffic patterns are fairly static and predictable.
That is not the case for an OTN switching solution since it can also have significant cost savings in long haul networks even if the above conditions are not met. OTN switching can efficiently use high-speed wavelengths by combining traffic from different client interfaces with traffic from other directions. So it requires fewer wavelengths and fewer high-speed line interfaces. The corresponding savings are likely to be much higher than the cost incurred when OTN switching is deployed.
OTN switching solutions delivers greater spectral efficiency since far fewer unique wavelengths are used in OTN switching networks. This advantage helps bring down possible wavelength blocking scenarios and make DWDM networks function for an extended period of time. In addition, it also reduces the cost of adding DWDM capacity and using new fibers in long haul 100G networks.
Operational Simplicity & Flexibility
Another key benefit of OTN switching is operational simplicity and flexibility. Unlike traditional solutions based on transponders and muxponders where new high-speed wavelengths have to be added if changes are needed in traffic, OTN switching solutions don't require adding new high-speed wavelengths. It means no need to deploy, install, and test new equipment. This is especially true when the client service speeds are relatively lower than the line interface speed.
OTN switching together with SDN can realize optical network bandwidth virtualization in ways that are impossible with traditional transponder and muxponder solutions. With OTN switching, the granularity of ODUks, from ODU0 (1.25Gbps) up to ODU4 (100Gbps), can achieve virtualized bandwidth between nodes. Moreover, the set of point-to-point connections and bandwidth between physically same end-points can be reconfigured remotely.
Fast Protection & Restoration
OTN switching also offers some significant benefits when it comes to protection and restoration. 100G long haul networks are expected to have high-quality services that are immune to multiple failures happening at the same time, such as interface and node failures. It only takes hundreds of milliseconds to complete OTN layer electrical restoration. OTN-level protection also helps 100G networks to survive multiple simultaneous failures with simple planning.
Application Scenarios Comparison
To better understand the network characteristics of the OTN switching solution and the transponder and muxponder approach, we will next examine common application scenarios to illustrate how each approach is favored in different traffic patterns.
Scenario 1: Concentrated Traffic Pattern
In a concentrated traffic pattern network scenario showed below, a high fill rate for 100G wavelengths is the result of A–Z traffic between these different locations. In this application scenario, both the traditional approach based on transponders and muxponders and the OTN switching approach use the same number of 100G interfaces and unique wavelengths. In this case, the incremental cost of the OTN switching approach will not be offset by compensatory efficiency savings on fewer 100G wavelengths. Thus, the transponder and muxponder approach will incur a lower total cost than the OTN switching solution.
Scenario 2: Distributed Traffic Pattern
In a distributed traffic pattern network scenario, two different locations share a much lower traffic volume. In this scenario, an OTN switching approach is more advantageous in terms of cost and spectral efficiency.
For example, if line interfaces are required to be 100G or higher, a point-to-point muxponder solution requires fifteen point-to-point wavelengths and thirty 100G interfaces with up to five wavelengths used on a span. By comparison, an OTN switching approach only needs seven point-to-point 100G wavelengths and fourteen 100G interfaces with only a single wavelength used on a span. This means greater spectral efficiency and much lower total cost.
OTN switching solutions make it possible to have relatively low overall cost, good spectral efficiency, simple and flexible operation, virtualized bandwidth, and fast protection and restoration in 100G transport networks. It delivers even better performance in distributed traffic pattern network scenarios. OTN switching will keep driving the evolution of 100G long haul and metro networks.