High Variability in Service Demand
Capacity planning in a metro environment has always been a challenge. However the recent increases in service demand across metro networks has driven a dramatic increase in the range of services offered, bandwidth required and most importantly, the variability of service demand across the network. Clearly higher bandwidth transport is necessary. However to respond to these challenges new metro systems must also provide highly flexible methods of accommodating new services in addition to increased capacity.
Xtera’s “Agile Optical Networks (AON)” solution makes it possible to accept Ethernet and legacy SDH/SONET services at any rate and efficiently groom or switch these services onto the most cost effective transmission link available.
The Xtera solution – The 7200 Optical Switching Platform (OSP)
The Xtera 7200 Optical Switching Platform (OSP) is a key element of the Agile Optical Network solution. It has been designed to meet the metro network’s needs for cost effective deployment of high capacity while also providing system flexibility by incorporating 3 types of switching fabrics (at Layers 0, 1 and 2) on the 7200 Optical Switching platform (figure 1). Each fabric type provides the most flexible and cost effective means of deploying a specific range of services. They can be independently installed as and when required to optimise the deployment of an operator’s metro DWDM network. The 3 switch fabrics include:
Layer 0: Wavelength Switching
The 7200 OSP delivers wavelength switching in 2 ways (figure 2):
All Optical (OOO) using a WSS based Remote Optical Add/Drop Multiplexor (ROADM). This allows any wavelength from an incoming fiber to be either dropped locally or passed through to an outgoing fiber. All wavelengths dropped and passed through are automatically power balanced to simplify operations and reduce costs. Up to 4 degrees are possible.
Optical-Electrical-Optical (OEO) using the 7200 320Gig switch fabric. OEO switching of a full wavelength is more expensive than all optical switching but it provides the same functionality plus a number of incremental features such as the ability to translate the wavelength (change colour) to enable any to any grid interconnect, up to 32 degrees of switching and SDH like resiliency and protection.
Layer 1: Sub Wavelength Switching (SWS)
The 7200 OSP delivers Sub Wavelength Switching using the 320G switch fabric (figure 3). Sub Wavelength Switching manages the bandwidth within a 2.5G or 10G wave to make it possible to :
- Switch any incoming SDH/SONET (in VCAT groups) and Ethernet data streams within a wavelength from / to any other wavelength terminating on the switch. (granularity is VC4 (150 Mbps))
- Aggregate Gigabit Ethernet interfaces into WDM wavelengths
2 x GE on 2.5G waves
9 x GE on 10G waves
- Size VCAT groups according to demand
Using LCAS (G.7042) can dynamically increase the size of the VCAT group and size it according to the traffic demand across the network.
The power of SWS is especially useful for Ethernet services. This is explained further in the SWS solutions paper.
Layer 2: Ethernet Tunnel Switching
The 7200 OSP delivers Ethernet Tunnel Switching using Intelligent Ethernet Gateway (IEG) blades. These blades can be installed as required in units of 40 GB/s. Once installed the IEG can support:
Layer 2: Ethernet Switching
- Mapping of Ethernet traffic into PBB-TE tunnels
- Traffic management across the network according to traffic contract and QoS
- Traffic policing of the traffic onto the network based on parameters such as CIR
- Shaping the traffic through the network according to traffic engineering rules
- Granularity of traffic can be engineered down to Mbps level
The result of the switching fabric flexibility of the 7200 is that a network operator can install the correct mix of equipment to meet the initial network requirements, secure in the knowledge that additional functionality can be installed when required. The flexibility in choosing the appropriate fabrics provides the most cost effective and operationally efficient service deployment.
Deployment
The 7200 OSP is placed at strategic points in metro rings and works together with access multiplexers such as the 3300 Optical Services Multiplexor (OSM), the 2610/40 Ethernet Access Switches (EAS) or 3rd party MSPP’s. In a typical network the 7200 would be placed as a hub point of a metro ring connecting to one or more metro rings (figures 5&6).
The incoming services would be managed by the switch fabric best suited to the application. For instance full 10G waves coming in on the access ring would be optically switched directly to the core of the metro network minimising the service handling and cost. On the other hand partially full 10G waves can be combined together with other partially full 10G waves to fill the 10G waves transported into the core network. Where the service would benefit from L2 management for aggregation, QOS, policing, PBB-TE or MPLS-TP processing etc, the service can be directed to the Ethernet Tunnel switch.
Figure 1. 7200 OSP switching fabrics
Figure 2. Wavelength switching
Figure 3. Sub wavelength switching
Figure 4. Ethernet tunnel switching
Figure 5. Typical access ring
Figure 6. Metro network
