Tandem Offices and End Offices
The PSTN is made up of local exchange carriers (LECs) and interexchange carriers (IXCs) that are governed by LATA boundaries. Note that a tandem office carries traffic between end offices and does not link to the customers themselves. Also note that IXC 2 does not have POPs in LATAs 1 and 2 and must have a reselling agreement with IXC 1 in order to gain access to those areas.
Learn more about tandem office