> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/telecom-references/transmission-and-lines/line-service.md).

# Line Service

Line service defines the payload type of a [line interface](/telecom-references/transmission-and-lines/line-interface.md) or another line service. The line service chain stops when it reach the E1/J1/T1 line service.

The E1/J1/T1 line services are also known as trunks or spans.

### Example

When configuring a DS3 [line interface](/telecom-references/transmission-and-lines/line-interface.md), it is required to add a DS3 line service then add E1/J1/T1 for that DS3 line service.

As illustrated in the picture below:

![Schematic DS3 interfaces](https://docs.telcobridges.com/w/images/6/6f/Schematic-DS3-interfaces.jpg)


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