PDH to SDH Evolution Strategy

Because the SDH transmission format is designed to overcome the limitations of PDH, then all the telecom companies are challenged to introduce into the SDH transmission network, PDH networks they already get up first. Important issue is the question of balance between the advantages offered by SDH and cost barriers in network investment. This requires a strategy on network evolution from PDH to SDH.
There are three main alternatives, each of which has its advantages and disadvantages. Telecommunications company may need to adopt a mixed strategy as the best answer for each of the environmental conditions.
Three alternatives are:

    * Top-down (the method level or layer)
    Bottom-up (method of islands or branch)
    * Parallel (overlay method)
Coating methods particularly relevant to the company's telecommunications services are still introduced at the level of digitalization of its network trunk or for those who need to support new services in layers over top of the inter-urban networks (as an example for the connection MAN-MAN )
The main aim is cost savings for large transport capacity in dealing with the growth of communications traffic. In the introduction to this strategy begins at the level of SDH backbone / supernode level with a few nodes are connected with systems of STM-16 or SDH STM-4. Interconnection to a PDH network is a gateway (gate contact), generally at the cross connect ports and the supply port cross-connect ports adequate to support all the functionality required PDH and SDH. This is an important aspect of network planning.
The following step is to change the layers of the lower subsequent to the SDH, and move its gateway to the point where the advantages of SDH most can be guaranteed. Thus, SDH provides full advantage of the layers of higher and selectively in layers lower.
Strategy with the island method is to install the SDH network nodes at the middle level and lower level, namely providing SDH islands for a particular community (for example, centers of trade and financial). With a layer approach, it takes a gateway-gateway for PDH networks.
At this level, some of the main cross-connect products will be broadband (wideband), menginterkoneksi systems STM-1 transport through interfaces of 155 Mbps (or 140 Mbps via a gateway interface), with channeling and combining facilities in VC level 1, 2 and 3 are carried in a speed of 2 Mbps or 1.5 Mbps.
Through the parallel method, SDH installed in an overlay network (which is overlaid) in addition to its PDH network in a few knots. The goal is to implement certain new services (such as videoconferencing and LAN interconnection / LAN) as well as benefit from all functions of SDH as soon as possible, and provide improvements in terms of quality.
Gateway for PDH networks are still needed, although there is segregation (separation) between the services between the old and new facilities SDH and PDH. It is also important that all the equipment necessary to provide full functionality in SDH SDH is overlaid is already installed.
This strategy is attractive to telecom companies with a traffic growth of rapid communication, and for those who wish to add functionality SDH (for example, to offer premium services; the caller / caller being charged pulses with special rates, which are usually applied to services information) as they increase their network capacity