Transport layer topology decision should be based on the guiding Principles, as well as all other decisions. All the possible options should be analysed and considered as a solution. In big project, it is a good idea to use vendors as sources of information through the Request of Proposals. All the suggestions and proposals would be analysed divided in categories in order to simplify the decision making process.

Large groups will be:

• Passive Optical Networks

• Active/Dedicated Star Ethernet and SONET

• Active PON

   

Defining criteria for analysing solutions and proposals are principles of Open and Independent standards. Another group of solutions are concentrated on industry standards focusing on G.983 standard. Smallest set of solutions included the G.984 GPON standard supporting solution.

All the solutions that are having not Ethernet based proposals can not be able to commit to interoperability. Based on the guiding Principles and Open and Independent Network solutions, Ethernet standard appeared as only applicable standard with multiple interoperable respondents.

One of the main aspects of network reliability is based on the factors that network owner could not control – cutting of the fiber line. Although, the factors for fiber cut are independent from the service provider, the impact on the network depends on the chosen topology of solution.

Reliability of the network should be considered together with the ease of maintenance factor. Although, the PON network requires less maintenance, it does not have any solution for providing connectivity in the case of fiber cut. In this case, it is critical to calculate an impact of such a cut to the network. Analysis should include the size of the affected subscribers group and frequency of cuts. It will allow to determine the impact of an inevitable fiber cut.

The cut rate/failure rate of the PON is expected to be ten times higher compared to active solution, due the approximately ten times larger amount of unprotected optical path, reducing its potential reliability.