The High Cost of Delivering Ethernet Services
Ethernet traffic demands, triggered by services such as broadband access, enterprise networking, streaming applications and IPTV are filling legacy DWDM systems in metro fiber networks. This demand is a welcome source of revenue for network operators. However operators are struggling to cost effectively support the new Ethernet demand using legacy DWDM equipment and existing OAM processes. A new methodology for deploying and managing Ethernet services is urgently required.
Existing metro networks have many types of equipment spread across multiple network layers to support Ethernet services (figure 1). Complex processes to provision and manage the services are also required which increase the cost of delivering the services. Some analyses have shown that provisioning an Ethernet service can take 3-4 times the effort of provisioning a SONET/SDH circuit.
Packet Optical Transport (POTS) has emerged as an effective means of converging the network layers to support the new service demands with the lowest capital and operating costs. A capability of POTS is to make it possible to deliver Ethernet services as simply as with existing SONET/SDH circuits.
The Xtera packet optical transport solution
Xtera has designed a Packet Optical Transport product line and resource management system that delivers next-generation Ethernet Services with the deployment simplicity and cost of existing Transport services (figure 2).
The product line provides a range of Access Multiplexors and Optical Service Platforms that efficiently support the new Packet services as well as legacy transport. Key equipment features include:
- Support of emerging Packet Optical Transport protocols such as PBB-TE and MPLS-TP at the edge of the network to enable deterministic transport
- L0, L1 and L2 switching fabrics in the core of the network to direct the services onto the most appropriate transport pipe
- 40 channel DWDM transport
- GE, 10GE and legacy SONET/SDH transport
Operation complexity (and cost) is perhaps the largest challenge a network operator faces in the delivery of large volumes of Ethernet services. To meet this challenge the Xtera solution provides Traffic Engineering and Resource Management software operating on its NMS. This software takes advantage of the capabilities inherent in POTS to enable deterministic management of the Ethernet services. The result is an operator will be able to deploy Ethernet services using methods and procedures very similar to their existing transport systems. This dramatically reduces the cost of deployment.
Product application
The trigger to deploy Xtera’s POTS products is normally the increased demand caused by the Ethernet services, as well as the high operations cost of supporting Ethernet services on legacy DWDM networks. However the solution fits well in both “green field” and existing applications.
In existing applications an operator will often install Xtera POTS to provide the Ethernet service growth while leaving the existing DWDM system to support legacy services. If the operator wishes to remove the existing DWDM system, Xtera can support the legacy services as well.
Typical deployment
A typical deployment (Figure 3) would consist of a number of metro rings, each made up of a mix of Optical Switching Platforms (OSPs) at hub points and Access Multiplexors at the Central Offices(CO). These rings will be connected together at one or at two hub points using the OSP’s multi-degree capability (figure 4).
There are 3 sizes of Access Multiplexors available, each optimised to match a range of application sizes from a single GE to 70GB/s. They can be connected directly to each other in a daisy chain around the ring or directly to the hub using coloured 10G wavelengths (up to 40 wavelengths per fiber).
The Access Multiplexors are optimised for GE and 10GE services but will also support FE and legacy services. A key feature of the Access Multiplexors is that they will support the POTS protocols (for instance PBB-TE or MPLS-TP) at the edge of the network to enable the deterministic transport and provide the OAM features necessary to simplify the provisioning and maintenance of the Ethernet services.
The metro access rings are connected to other access rings at network hubs. Typically each ring will have one or 2 hubs but more hubs per ring are possible. The Xtera 7200 Optical Switching Platform (OSP) will be placed at hub sites to collect, aggregate and switch both legacy and Ethernet services across the metro network. It will support all of the capabilities of the Access Multiplexors but it also has a number of key capabilities to meet the special needs of a network hub in the POTs environment. These include:
Multi-degree capability
Each ring supports fibers from 2 two directions (degrees). Connecting 2 rings requires 4 degrees and if more rings converge at the same site 6 degrees or even more may be required. The 7200 OSP uses ROADM technology to support up to 4 degrees optically and its Sub-Wavelength Switching capability enables a further 16 degrees if required.
Remote optical add/drop Mux (ROADM)
The base transmission layer (Layer 0) in a DWDM system is an optical wavelength. The 7200 ROADM will be able to optically switch any incoming optical wavelength to any connected fiber to reduce the cost of switching high capacity signals.
Layer 1: Sub Wavelength Switch (SWS)
Optical wavelengths typically provide 10 GB/s of capacity and the Access Multiplexors are connected at this speed. However as the normal services provided are GE’s many access sites do not fill the incoming 10GB/s wave to capacity. In addition, the multiple GE’s originating from one site often do not terminate in the same end point. The 7200 OSP provides a 320GB/s Layer 1 switch that can groom and pack the incoming GE services into any outgoing 10GB/s wavelength. This switching can be done across all the rings connected to the hub to maximize the use of the network capacity.
Layer 2: Packet Optical Switching
As well as Layer 1 grooming the7200 also provides Layer 2 switching to aggregate across the multiple Ethernet steams coming in from the access rings. This switch can terminate as well as act as an intermediate node for CET protocols to ensure that the OAM capabilities and deterministic transport of POTS are retained. The switch also supports separation of service from transport resources, tunnel shaping, policing, service steering and all of the standard layer 2 functions.
Combining the Layer 0, 1, 2 switches in one platform ensures that the most appropriate transport for a given set of services can be selected. It also significantly reduces the number of fiber patch cords required to deliver services across the network, thus reducing the cost and speeding delivery to the customer. This is especially valuable where multiple rings connect or where a large number of services cross individual rings.
Network management
All of the network elements in these rings are managed by the Nu-Wave Network Management System (NMS) to provide traditional network management support of WDM platforms (FCAPS, Point and click provision, topology discovery, etc).
However Ethernet Services are much more complex to provision than legacy transport services. Therefore the scope of the NMS platforms must be expanded to perform Traffic Engineering and Resource Management across the network. This software simplifies the provisioning of transport tunnels across the network and makes it possible to ensure that a deterministic and predicable transport capability can be delivered end to end.
To achieve this Xtera has integrated the E-TERM (Traffic Engineering and Resource Management) software into its NMS Platform.
E-TERM enables the separation of service objects from tunnel objects, thereby creating a packet transport model similar to a SONET/SDH infrastructure. E-TERM also has a software application that uses a patented path computation algorithm to analyze QoS parameters and business rules to deliver the optimum allocation of network resources based on cost and/or traffic load balancing. E-TERM Resource management capabilities keep track of QoS characteristics and bandwidth per Class of Service (CoS) to ensure the allocation of resource per service never exceeds capabilities of the network resources.
The result is that an operator will be able to optimise the fit of Ethernet services into the available network resources and deliver these services with much lower provisioning and management costs.
Figure 1. Today’s network
Figure 2. Xtera solution
Figure 3. Typical ring
Figure 4. Typical network of interconnected rings
Figure 5. End to end network and resource management
