South Korea is a crowded country, with 50.3 million people in 18.8 million households. 47% of the total households live in condominiums or apartment buildings while 40% live in single homes. Different types of housings require different types of Internet access network topologies as seen in the figure below.

For a user living in a single home, an optical fiber cable from an OLT at the operator's CO (central office) is split once by a splitter installed under a manhole in the street, and then again by another splitter installed on a pole near the user's home. Next, one of the split cables is connected to an ONT in his home, and then on to his PC via a UTP LAN port (100 Mbps). For a user living in a condominium or apartment building, the access network topology to be used slightly vary depending on the wiring system installed in the building: fiber, UTP and twisted pair. (1) Optic fiber: An optical fiber cable from the OLT is split by a splitter installed in MDF of the building. Then, one of the split cables is connected to an ONT in the PC. (2) UTP: Previously, each building had one L3 switch installed in its MDF, and multiple L2 switches installed floors away from one another (e.g. on 5th, 10th and 15th in a 20-story building). The L3 switch was connected to the L2 switches on different floors. This type of topology requires L3 switches be located outside of (and far away from) the operator's CO, leading to higher OPEX. Now, L3 Switches are replaced by splitters, and L2 switches are replaced by ONUs, allowing splitters to be connected to an OLT at CO. (3) Twisted pair: Previously, each building had one L3 switch in its MDF, and multiple VDSL DSLAMs installed floors away from one another. Again, this type of topology requires L3 switches be located outside of (and far away from) the operator's CO, leading to higher OPEX. Now, L3 switches are replaced by splitters, and L2 switches are replaced by ONUs (VDSLs), allowing splitters to be connected to an OLT at CO. KT’s broadband access network illustrated above is quite similar to that of SK Broadband and LG U+, except KT and LG U+ use E-PON while SK Broadband uses G-PON. All three operators support 100 Mbps in both UL and DL, and take care of the Internet, IPTV and VoIP traffic through this one single cable (Triple Play Service). KT will Launch GiGA Internet (1Gbps DL & UL) and GiGA Wire (300 Mbps DL & 100 Mbps UL) services in the second half of this year. See 1) Korea Communication Review, July 2014, and 2) What's GiGAtopia envisioned by Chairman Chang-gyu Hwang of KT?, for more details. Broadband Access Network Architecture in Korea OLT L3 SW Splitter (1:4) Splitter (1:8) ONT UTP FTTH Dimensioning • 32 ONTs per PON port • 20 PON ports per OLT • 640 ONTs per OLT (5,000 ONT per OLT ~ planned) 100M bps ONT Splitter (32 ONTs) Splitter (1:8) Pole Manhole BRAS Backbone Central Office Edge GE GE Gbps Gbps Gbps Gbps VDSL DSLAMs L3 SW Twisted pair 100M bps GE Central Office Central Office L2 SWs L3 SW UTP 100M bps GE Splitter (1:4) ONUs UTP 100M bps Gbps Gbps Splitter (1:4) ONUs (VDSL) Twisted pair 100M bps Gbps fiber fiber Gbps 100M bps Migration Migration E-PON ❶ Fiber to the home ❷ UTP to the home ❸ Twisted pair to the home Single Homes Apartments Home Fiber to the home nxGE E-PON: Ethernet Passive Optical Network G-PON: Gigabit Passive Optical Network OLT: Optical Line Terminal ONU: Optical Network Unit ONT: Optical Network Terminal L3 SW: Layer 3 Switch GE: Gigabit Ethernet