Since G.709 standards do NOT include GbE interfaces, an OTN layer will always need a sub-layer to aggregate the GbE to a higher rate interfaces (as STM64, STM16), is that right?
Short answer is yes, sort of. But let me try to add some clarity.
G.709 today is being implemented primarily at two speeds. OTU1 is defined at 2.7 Gbps and OTU2 is defined at 10.7 Gbps. Both are fully capable of carrying multiple types of traffic streams as payload, just like SONET/SDH. So, for example, an OTU1 frame can transparently carry OC48/STM16 a 2.4 Gbps signal, such that the SONET/SDH overhead is protected while still offering OAM&P for OTU1.
This same frame can carry 2 Gigabit Ethernet circuits and a few other circuit types all the way up to the full ~2.4Gbps payload. Our implementation of OTU1 and OTU2 utilize OC3/STM1 frame sizes for aggregation. So a GigE circuit would require 7x155Mbps or 1.085Gbps to carry a GigE.
What about the lack of OA&M tools for Ethernet over Optics? (OAM&P stuff, the equivalent to AIS SDH that let routers to start rerouting over a link failure) Has this issue has been solved?
This is a relatively simple answer for Ciena because we come from the perspective of transport where OAM&P are absolutely critical. Leveraging this experience, we offer Optical Ethernet solutions that are fully managed with the ability to carry any type of data across a wavelength with full transparency. That is to say the integrity of the optical network is standards based with OAM&P tools that the industry is familiar with.
Higher layer services carried across this network are carried transparently and are left to utilize their own restoration techniques, such as using internal and external routing protocols, MPLS fast reroute, link aggregation, etc. techniques to restore traffic.
This way, optical networks always work just like we expect them to, and the higher layer devices work just like we expect them to. For Ciena Ethernet transport devices, such as the CN 4350 we are essentially are offering the benefits of an Ethernet interface with the familiar OAM&P of optical transport.
For the cost savings using ROADMs, what is relative opex/capex savings ratio
Great question with a complex answer.
In general, ROADMs offer OPEX savings in terms of their ability to simplify planning and/or best optimize network resource utilization (i.e., allow better use of the WDM network). However, OPEX savings will be dictated by the products, the ROADM technology deployed and the scalability and flexibility offered.
Third-generation ROADMs (aka dynamic wavelength routers- DWR) can offer the ultimate in flexibility by allowing any circuit to be provisioned anywhere on the network. They provide the flexibility to be changed at any time and the scalability to support the adding, dropping and grooming of several wavelengths at every location. This can be done with the use of a wavelength selective switch. In terms of CAPEX savings, we believe this technology also offers lower cost points than previous generations of ROADMs, which have not proven economically attractive in metro networks.
Do you see ROADM and GMPLS as being competing architectures, or complementary?
Actually, they are very complementary technologies and often offer similar results in terms of reducing networking OPEX costs. ROADM technology is hardware based, while GMPLS is a draft standard for network control, and is software based. They are both elements of an optical network architecture.
ROADM was created in an effort to ease the planning and provisioning process of circuits on a WDM ring. This replaced what was once a very manual process with little room for error with flexibility to make changes on the fly, thus leaving room for network re-configuration as networks and customer requirements changed. Some ROADM technologies can even be extended beyond use in rings, and can be applied to mesh networks. The distinguishing feature of the ROADM is that switching is done in the optical domain, without converting the signal back to an electronic form.
GMPLS on the other hand was designed to automate the provisioning and traffic management across optical networks, somewhat similar to what MPLS offered to data networks. In the case of GMPLS, the standards are being defined by the IETF (Internet Engineering Task Force). The ITU (International Telecommunications Union) has extended these concepts in formulating the G.ASON standards, taking into account additional requirements important to service providers. The Optical Internetworking Forum (OIF) formulates interoperability agreements based primarily on the G.ASON standards. Most recently the OIF User to Network Interface 2.0 (OIF UNI 2.0) has been demonstrated at Supercomm to automatically provision Ethernet circuits across a multi-vendor optical network..
GMPLS and G.ASON, although applicable in principle to ROADM-based networks, are now practically limited to networks where switching is done electrically. The problem of choosing a route in an all-optical network can be a complex optical engineering task, a problem that the standards groups have not yet tackled. In this case a UNI approach is ideal, as it can be used for interoperable automated provisioning while leaving the tough routing decision to a technology-aware software module in the optical network.
