Metro Transport network

MSTP is based on SDH,can enjoy existing SDH network resource and provides various interface to support data service such as ethernet and ATM.Through the analysis of SDH network operational,maintenance and management experience,MSTP is fully compatible with existing TDM service and can integrate multiple service transport and access to meet upward spiraling data service commands.

Fro traditional carriers with mature SDH network offering a huge quantity of TDM service,MSTP is the most direct and efficient metro transport network solution.

MSTP has been widely applied and most new metro SDH networks are MSTP.To efficienly process and transmit data service,it utilize some key technologies including GFP,VC (virtual connection) and LCAS (Link capacity adjustment scheme).As MSTP is TDM based,the service mode it suits is the provision of traditional TDM service while partially supporting IP and ATM service.

MSTP can be located on the convergence adn access layers of a metro transport network and can integrate service networks into both

The existing network environment bears traditional TDM services, whereas MSTP can reliably bear new,high capaity services such as ethernet leased line,point to multipoint and ring services.Integrated access with convergence from DSLAM to BRAS can be offered to large scale customers and it can also transmit NGN and 3G services

MSTP mainly exist as a layer 1 network and is not suitable for large scale layer 2 and layer 2 services.Ehen introducing MSTP,carriers should ensure that existing networks can coordinate and coorporate.MSTP can mainly offer existing metro network and ATM networks access and convergence functions, and it can be used to expand the ethernet and ATM service coverage.Its data processing function effeciently handles data services but it can not wholly replace data service networks

MSTP related rechnologies have been constantly developed adn optimized.To further improve its perfomance in transmitting ethernet services and balance nodes, some MSTPs adopt embedded RPR (Resilence packet ring),which enables highly efficent data service transport.Given RPR only supports ring network topologies,some MSTPs adopt built in MPLS (multi protocol lable switching) to process inter ring services

As MAN bandwidth demands have been soaring,it is increasingly difficult for SDH based MSTP to cater to MAN developments. A trend for solving the MAN bandwidth bottleneck is to gradually introduce WDM into MAN.WDM represents a mainstream technology in terms of long haul transport, but it has only been recently applied to MAN.Metro WDM embodies another type of driving force and characteristic that are different to those of long haul WDM.When used in long haul transport,WDM can save on expensive long haul optical fiber resources.

In the MAN network with its mostly short transport distance, costs on optical fibers will be much lower than in long haul backbones.Node equipment normally incurs high costs in each metro transport network and while it is beneficial to save optical fibers in some MAN,however service flexibility,manageability and cost effetiveness are more important for MAN applications.

The metro WDM network must support multiple services on the same platform and should be transparent to rates and protocols.Equipment ought to be low in price and the network should feature good expandibility in order to adapt to various metro service demands.Wavelength management capabilities must be strong to facilitate rapid wavelength service deployment.

A solid network self healing capacity that matches SDH network is necessary to offer different levels of protection according to services demands.As transmisiion distances in the MAN are alwasys short, there is no unreasonable demand on network capacity, and some cheaper components can be employed to reduce DWDM equipment cost.Alternatively,the network can adopt CWDM,which enable large inter channel distance.Point to point WDM cannot meet the demands of MAN applications so, as ROADM (reconfigurable optical add drop multiplexer) matures, ROADM can enable optical layer networking and introduce the control plane so that WDM plays greater role in MAN networks

Metro optical networks can provide strong bandwidth support for metro IP networks and ethernet.Compared with pure,direct optical fiber connections,this is network is more flexible,secure and resource efficient.The WDM networkcan deploy some new service such as BoD (bandwidth od demand),wavelength wholesale,wavelength lending,OVPN (optical VPN) and optical multicast.As the SDH network on the electronic layer is gradually replaced by IP/ethernet,future metro transport network will adopt the optocal layer metro WDM network