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Traffic flow in GPON FTTH network

Traffic flow in GPON FTTH network : Some friends often ask how traffic flow occurs in FTTH networks? I have tried to write about traffic flow in FTTH network, maybe you all like it. In the traffic flow of GPON FTTH network data is transmitted in downstream from OLT to ONT as a broadcast manner and in upstream as a Time Division Multiplexing (TDM).

The wavelength of the downstream data is 1490 nm, the voice and data services from the core network transported to the optical network reach the OLT and are delivered to the ONT via the FTTH network via power division. Each home receives the packet through its ONT. Upstream represents data transmission from ONT to OLT.
Traffic flow in FTTH


GPON FTTH Traffic Flow 

How the traffic flow occurs upstream and downstream in the FTTH network is mentioned above. The wavelength is 1310 nm. If signals from different ONTs come to the splitter input at the same time and at the same wavelength 1310nm, this results in the superposition of different ONT signals when it reaches the OLT.

Therefore TDMA is adopted to avoid interference of signals from ONT. During traffic flow in TDMA time slots will be provided to each subscriber on demand for transmission of their packets. Optical splitter packets arrive in sequence and are combined and transmitted to the OLT.

Type B protection is used in the design of  GPON FTTH access network which is also mentioned in this article. This type of protection  provides redundancy against both feeder and GPON port failures. In this type of protection, each fiber trapped in the feeder cable is connected to two GPON ports in the OLT.
Traffic flow in FTTH

One ports is configured as active and the other for the standby. Above figure indicates the general direction of traffic, once the fiber strand has failed, the OLT automatically activates the standby GPON port to transmit a copy of the downstream traffic to feed the FDT, which is beyond the failure point from the other direction as shown in the right side figure.

This standby GPON port will also receive upstream traffic of a separate feeder part. Figure below failure indicates a state of being near the active GPON port, in which case the OLT automatically turns the optical signal to the security line via the standby GPON port.
Type B protection in GPON FTTH

Important design points of GPON FTTH

The design of FTTH access networks is challenging; It needs to compromise various factors including size, cost and scalability. There is no standard FTTH access network model because the feasibility of an access network strongly depends on consumer density and settlement structures, thus modeling has to depend on a concrete settlement structure, a given country, and the results obtained on that country. Depend on it.

To design an outdoor plant OSP, desk top planning does not work, each route is physically surveyed and then planned using knowledge and experience. International standards cannot be applied because each country has its own unique underground factors.

The ground thermal line or freeze line should be considered to identify the point where the surrounding soil temperature in the underground is constant (neither freezing nor overheating) thus allowing a constant temperature for the FO cable.

Another important factor that must be addressed is to decide the depth and type of backfill material required to minimize ground vibration effects. OLT at CO is used as an access platform. Some types of OLT supports the 8-port GPON of 16 slots cards. Two levels of division are used to provide a total division ratio of 64.

This means that total numbers of 64 users can serve from each GPON port. A lower vertex approach is used to determine the required number of GPON ports. By simple arithmetic, we can see that 16 GPON ports with 64 partition ratios are sufficient to serve 1000 users.

This statement is true for FTTH networks where locations are geographically located close to each other and the number of users is evenly distributed between locations, which is not our case.

Due to our network constraints, the number of required ports will be calculated based on the number of FATs. As per the 64 partition ratio, total of 4 FATs can serve by each GPON port because each FAT has a 1:16 splitter, then 48 GPON ports are needed to service 185 FATs.

Another bunch of redundant 48 GPON ports are used to provide Type-B protection. As per the technical view the total number of OLT GPON cards used by the design will be 12, with 6 cards in each direction. 6 FDTs are used to hold Level-1 splitters with each FDT holding 8 splitters.

As a result each FDT will be connected to one OLT card using a backup card using 8 fibers from one direction and 8 fibers from the other direction. In FTTH network design two feeder rings are used, the 12 fibers for the first feeder, 8 of which are connected to 8 level-1 splitters inside the FDT.

Last Word

Very special and important information has been given about the traffic flow in FTTH network, perhaps you will not find such information in another article. Above topic "Important design points of FTTH" also very important. How did you like this article "Traffic flow in GPON FTTH network", tell me by commenting, also share it with your telecom friends.

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