Essential understaning of MAN

Deployments in DWDM have stimulated huge capaciti level in long haul backbones nad large scale ethernet in LAN applications bandwidth.The subsequent bandwidth bottlenecks in MAS (Metropolitan Area Network) and AN (access network) have become increasly problematic.IP based voice and video service usch as NGN and IPTV have placed higher demand on MAN and AN functions and perfomance,rendering the condition of these two networks a significant concern to carriers

The concenpt of MAN initially describes a computer network concept corresponding to LAN and now it has been applied intelecom networks as a publice multiservice bearer network that provides broadband data and multimedia services in cities or suburbs with no strict definition.According to the NGN hierarchical architeture recommended by ETSI and ITU-T,NGN comprises two basic strata:service and transport.The transport layer refers to the service-supporting bearer network

A bearer network can be devided into three horizontal constituent parts:backbone netwrok,MAN and AN.The key factor in selecting bearer netwrok techonolies is the features of the services to the borne and these should be reflected in the technical developments of MAN.MAN services can be currently characterized as follows:

1.Compicated services.In additionto traditional TDM and internet, MAN has to bear nascent service usch as IPTV,NGN,3G,P2P and internet broadband applicaiton

2.Mainstream IP services.Essential to a new-type MAN construction is efficeint IP service bearing capability and suitably high QoS and security features.

3. Service inovations.New innovation rich services have been rapidly hitting the market, meaning that it is more adn more difficulty to cater the user demands since MAN require to possess sufficient flexibility,expandability and responsiveness in order to adapt to constantly changing requirements

4.Bandwidht hungry services.THe number of service necessitating high bandwidth coupled with increased users has placed upon MAN considerable badwidth and service management pressures

5.P2P applicaiotions.Large scale P2P applicaitons have changed traditional network traffic structure

6.Traditional service.Including TDM,FR and ATM these still occupy a place in the market.PSTN servie will exist long term and NGN and 3G service developments still rely on certain TDM circuits.The financial adn political sectors have special QoS and securiy demands and currently stick to traditional dedicated line services since doubts remain about the integrity of IP networks

7.Cost.MAN features a short service transport distance compared with the backbones, so cost is of great importance.Carrier can adopt low cost phisical layer technologies to enable short distance transport including ethernet direct connection and CWDM

Traditional networking concept comprises relively independent transport and data networks that provide different functions and so different applications are not carried over the sam network.Traditional carrier's MAN network include metro SDH,metro IP and occasionally ATM,FR and DDN which are siin to be replaced

SDH previously supported PSTN and PLMN and offered physical layer circuits to data networks.The metro IP networks was mainly used to provide internet service but the increase incarrie class IP application requires MAN to offer high quality IP bearing services.SDH networks have consequently developed into MSTP (multi service transport platform) that offer ethernet service and an IP bearing functions.The metro IP netwrok has also been developed into a carrier class by using MPLS and optimized ethernet technologies.For additonal carriers most MAN network will soon include metro MSTP and metro IP network.These two type of network are mmuttualy compelemtary but do compere with each other.They should be deployed in different area according to the conditions of subsequent phases with varied services domains.The gradual decrease in TDM services and the rapid growth of IP services means that the SDH based MSTP will offer fewer functions,while metro IP networks and ethernet will offer more