A global bandwidth strategy

Although the explosive growth of the Internet has revolutionized the way the world communicates, it has also brought unprecedented challenges for international carriers. To cope with this uncertain new climate, carriers need capacity that will let them send traffic where and when they need it - even when requirements suddenly change.

In other words, what carriers need is globally available bandwidth-on-demand.

But providing bandwidth-on-demand - as opposed to just promising it - requires both a new business model and a new type of network architecture. The business model has to offer carriers pricing that is independent of the distance traffic travels, as well as the ability to move purchased capacity from one route to another. The network architecture must be able to support such features.

The Project Oxygen network, the first example of such an architecture for undersea networks, differs significantly from traditional cable systems; it is designed as a true multipoint-to-multipoint network. Its first phase will link 96 landing terminals in 75 countries and locations, providing connectivity to 90% of the international telecommunications market. Multiple redundant links and loops will allow traffic to be routed any number of ways to the same destination. This ensures maximum reliability through alternate routing in case of cable faults and minimizes congestion problems resulting from unpredictable shifts in traffic flows as carriers move their capacity between different routes.

Another notable difference is that the Project Oxygen network employs high-speed combined asynchronous transfer mode/synchronous digital hierarchy (SDH) switching throughout. This allows it to carry any type of voice and data traffic, and switch the routes and destinations of traffic flows.

Mesh network topology

The Project Oxygen network's 96 landing terminals will be linked in a global mesh network topology comprising individual loops. The loops will be connected at common network terminals.

Dense wave division multiplexing (DWDM) technology, with 10 Gb/s per wavelength, will increase the undersea link capacity and reduce bandwidth cost. Design features for unrepeatered submarine links include:

- 12 fiber pairs.

- 32 wavelengths per fiber.

- 10 Gb/s SDH traffic per wavelength.

- 320 Gb/s capacity per fiber pair.

- Up to 3840 Gb/s total link capacity.

Design features for long-distance submarine links include:

- Undersea optical amplifiers.

- Up to eight fiber pairs.

- 32 wavelengths per fiber.

- 10 Gb/s synchronous traffic per wavelength.

- 320 Gb/s capacity per fiber pair.

- Total link capacity of up to 2560 Gb/s.

The Project Oxygen network features fiber-routed branching unit technology. For a main trunk cable with eight fiber pairs, one pair is directed to the branch cable via the branching unit, while the other seven are passed directly through the branching unit.

The main elements of the DWDM submarine transmission system include submarine line terminating equipment, submarine optical amplifying repeaters, fiber optic cable and an associated gain degradation equalizer in the transmission path. Figure 1 shows the network's transmission equipment configuration.

Flexible service provisioning

The first layer of the Project Oxygen network is a fiber optic transport network, which is the best medium for long-haul telecom transmission applications. The second layer is the STM-64 SDH layer; the third is the ATM/STM-1 layer. The network will be able to bypass the ATM layer and access the optical layer through the SDH interface.

For international services, carriers generally access the network at the SDH layer. The Project Oxygen network offers SDH access at the STM-1 level or quadruples thereof (STM-4, STM-16, etc.). Legacy T-1/E-1 traffic is converted and carried as ATM traffic. Access at the SDH layer can be scaled up or down if demand changes because of ATM or Internet protocol developments.

Carriers can choose to send their traffic point-to-point across the Project Oxygen network, or take advantage of ATM capabilities. The ATM layer is also scalable in meeting carriers' traffic requirements. Initially, the Project Oxygen network will offer the simplest constant bit rate ATM service, but the other ATM services will be available by the time the network is complete. Figure 2 shows a conceptual view of the ATM hierarchy within the Project Oxygen network.

Carriers can route their IP traffic on the Project Oxygen network over ATM, SDH or ATM over SDH when the functions of both these layers add value to the services. An upgrade, scheduled for 2001, will give the network's bandwidth manager terminals IP routing functions so IP routing service will be available if needed.

The Project Oxygen network is partitioned into three distinct components to provide a flexible and scalable network.

The first is the submarine link with optical amplifiers for DWDM signals to maximize link capacity. It is configured as a ring to achieve the highest reliability for a transoceanic transmission system. The undersea system is designed to carry up to 2560 Gb/s.

The second component is the modular terminal equipment, which scales up the terminal plant capacity as traffic demand increases. The number of high-performance opto-electrical units in the line terminating equipment boxes will be increased as traffic demand rises, with one opto-electrical unit added for each additional wavelength used to accommodate each 10 Gb/s increase in demand.

The third part is the broadband non-blocking SDH/ATM switching fabric interfacing with the customer network on one side and the undersea plant on the other. This layer will be equipped with Lucent Technologies Wavestar bandwidth managers. The ATM/SDH switching fabric in the bandwidth manager will support a range of customer interfaces, including T-1/E-1, STM-1 and STM-4. The bandwidth manager platform will accept PDH or SDH signals that carry either ATM or non-ATM traffic.

A standard SDH channel is transmitted directly into the SDH switching fabric. Interconnection levels can be provided optically at STM-4 and STM-16 rates, and electronically at STM-1 rates. The SDH switching fabric provides STM-1 cross-connect functionality for routing traffic to its destination. The output of this level is multiplexed to the STM-64 level for transmission to the submarine line terminating equipment.

ATM input signals in SDH format will be connected to the SDH fabric for routing as point-to-point traffic or into the ATM fabric. Smaller traffic streams within the ATM signal can then be rerouted onto different STM-1 output streams of the ATM fabric, and the signal is then multiplexed in to the STM-64 level.

The bandwidth manager equipment also provides bidirectional line switched ring (BLSR) restoration capability for transoceanic system failure. The BLSR ring is kept within the STM-64 level to keep the switching time down to around 300 milliseconds. Figure 3 shows the SDH/ATM layer configuration. Figure 4 illustrates the overall design of a generic cable landing terminal, including digital distribution frames, optical distribution frames, Lucent bandwidth managers, wavelength terminating equipment and transmission line amplifiers.

One notable feature of the Project Oxygen network architecture is its switching layer, which will be controlled from network management centers on a dynamic basis, establishing traffic connectivity while providing high network reliability in case of any link or other network subsystem failure. The system availability of the Project Oxygen network for any STM-1 to STM-1 circuit in the model is expected to be 99.999%.

Management plan

The Project Oxygen network's management system provides several operational control functions for all the network equipment and services through four different layers. The various equipment and software layers will form an integrated management system for monitoring, controlling and reporting on the network.

The service management layer handles customers' operational requirements. The system in this layer is divided into three main areas of operation. Service provisioning items, such as new service orders and network provisioning requests, are processed through the order manager module. Trouble tickets for network problems and scheduled maintenance work are processed and managed through the trouble manager module. The dispatch manager processes the installation or repair work needed to deal with network problems.

The network management layer equipment provides an integrated view of the system, based on the reports of the element managers located in each of the terminal stations. The network manager controls circuit provisioning and system maintenance, and element managers act as the interface for the individual equipment items.

The element management layer equipment will be provided on a per-station basis. The element manager in each station will monitor and control all undersea plant and related terminal equipment at that station. The element managers for the SDH/ATM switch equipment are expected to manage the equipment for a number of terminal stations.

The network element layer equipment provides a direct interface to each of the network elements within the terminal stations. Separate network element equipment provides the interface to the SDH/ATM switch equipment and undersea plant equipment.

Each network element provides monitoring and control facilities for each piece of equipment to which it is connected. The network element layer also monitors power feed equipment, but for safety reasons the equipment cannot be controlled by the network element layer.

For the Project Oxygen network to operate successfully, it needs to be monitored and controlled around the clock and around the globe. Three network management centers, in the United States, United Kingdom and Singapore, will monitor and control the network continuously.

Each network management center will be capable of monitoring and controlling the entire network in case the other two centers fail. Synchronized databases located in two network management centers will have all the network information, and all three centers will operate from these databases. The database in the third center will operate on a free-run basis - asynchronous to the other two. In case of a problem in one of the two synchronized master databases, the third free-running database will be synchronized with the working master database, and the network will remain operational with fully synchronized redundant databases. When the faulty database comes back on-line, it will work asynchronously.

Because of its highly flexible and scalable architecture, the Project Oxygen network will be able to adapt the developments currently underway in the IP and ATM forums.

The final choice - whether to adopt IP, ATM or both - rests not with Project Oxygen but with international service providers. The Project Oxygen network will carry whatever services are dominant in the next century.

The benefits of designing a global optical fiber cable system as a single ubiquitous network are numerous. It provides the same advanced technology throughout the world, with automated millisecond-range restoration. It eliminates transit fees and permits direct correspondent relationships with every other carrier in the world. With an ATM/SDH backbone and high bandwidth, the network enables global variable bandwidth multimedia applications. It offers an integrated network management system on a global basis. And it makes possible network capacity prices that are orders of magnitude better than other options.