FTTH access architecture revisited - what's the purpose of FWDM?

Few years ago we have been publishing some ideas for CATV over fiber, and how to integrate CATV signal in GEPON networks.
Now, looking back the article, we could see that now always FDWM element is shown. Today, we will again one more time define a main elements you will need to build a FTTH network and what's the purpose of FDWM. 

 FTTH network must be capable of providing multiple types of residential areas with video, data, and telephony services. Figure 1. illustrates small business offices/units (SBUs), multi-tenant offices/units (MTUs), multi-dwelling units (MDUs), and a mix of single-family units (SFUs).



Figure 1. FTTH access network.

The network can be divided in seven basic blocks:

• The ONUs allocated on customers premises and used for delivering home telephony, data, and video networks.
• OLT system provides connection to core transmission networks, manages the ONTs, and cross connects data traffic from multiple PONs.
• The Voice Gateway (VGW) is used to manage connection with PSTN/TDM network.
• The EDFA/CATV module is re-translating signals from a video headend and inserts local video signals.
• The Element Management Systems (EMSs) connect different parts of the network to (AD-net’s) core operation network(s).
• PON which provides connection between ONTs and OLTs.

As a good example to start for OLT system is our 2 port (for small applications) or 8 port OLT system. ONU-s - also a great selection of them are here.

You can have for example:

- ONU with Ethernet ports only:
- ONU with Ethernet and CATV ports;
- ONU with Ethernet and FXS voice ports
- Triple play ONU's with voice, ethernet and catv same time

In middle you are going to need FTTH splitters. There's a choice for PLC or FBT type splitters, and those can have different kind of casing, like ABS box type, or steel tube type.

Voice gateway, will be needed to work with a SIP ports inside the ONU. Gateway you will need connect at left side of OLT and then it's uplink for example can eb already E1 G.703 to be connected to PSTN, TDM network. But of course, in case you have IPBX, or some hybrid telephone exchanges, which are able to process SIP traffic coming from ONU's directly to OLT, then it's much easier. We have a simple test shown in video, where we connect 2 phones to FXS ONU's we have and then they are getting switched by simple Grandstream IPBX.

EDFA/CATV system get's RF signal connverted from RF to 1550 nm optical light, amplified and sent over the fiber.

And - here's where you may need FDWM device. It simply mixes 3 wavelenghts together before it get's sent into splitter (in our scheme it's 1:32). As you might know, GEPON system itself works on 1310/1490, so CATV signal here is delivered over same fiber using 1550 nm, and FDWM is a place where all this get's "mixed".

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