Optical line termination

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An optical line termination (OLT), also called an optical line terminal, is a device which serves as the service provider endpoint of a passive optical network. It provides two main functions:

1. to perform conversion between the electrical signals used by the service provider's equipment and the fiber optic signals used by the passive optical network.
2. to coordinate the multiplexing between the conversion devices on the other end of that network (called either optical network terminals or optical network units).

In general, an OLT is akin to a Network Switch where each port represents one or more client ONT or a node. Each port may be attached to the boards or network/line cards via a SFP module which must be a OLT module for it to have its Tx and Rx wavelengths swapped, but not all OLTs use SFP modules as shown in the image to the left. OLTs are either found at the ISP level inside a cabinet or distribution point, or customer level for connecting ONTs locally, such as a hotel or apartments. Depending on the underlying fiber technology, an OLT can be EPON, GPON, XG-PON or WDM.

An OLT can have several ports, and each port can drive a single PON network with split ratios or splitting factors of around 1:32 or 1:64, meaning that for each port on the OLT, up to 32 or 64 ONUs at customer sites can be connected although this depends on the PON standard the OLT and the PON network supports.^[1] XGS-PON networks support split ratios of up to 1:128. An OLT with 272 ports can support up to 34,816 users assuming a split ratio of 1:128 for every port.^[2][3] It can be located in a point of presence which can be a curb-side cabinet or building, or a central office.^[4][5][6][7]