At least 49 hotlines have been established between the two Koreas to arrange diplomatic talks, deconflict military operations, coordinate air and sea traffic, hold humanitarian discussions, and cooperate on economic issues
North Korea has said it is cutting communication hotlines with South Korea, a tactic the isolated country has used repeatedly during periods of rising tension.
At least 49 hotlines have been established between the two Koreas to arrange diplomatic talks, deconflict military operations, coordinate air and sea traffic, hold humanitarian discussions, and cooperate on economic issues.
Most of all, the South sees the lines as an important way to prevent misunderstandings in the event of a crisis.
Sometimes the lines fall into disuse when relations sour, as they have when multilateral talks stalled over North Korea's nuclear weapons programme and strict international sanctions imposed on it.
Lines of communication were last cut in 2016 and restored in 2018, when North Korean leader Kim Jong Un launched a diplomatic offensive after two years of intensive ballistic missile and nuclear tests, and a heated war of words with US President Donald Trump.
When North Korea has stopped communicating, South Korean officials still typically try to call every day at the same time, even if there is no answer.
South Korean officials have sometimes used a bullhorn to shout messages across the border at the Joint Security Area (JSA) in Panmunjom, the only spot along the heavily fortified demilitarized zone (DMZ) where troops from both sides stand face to face.
In January 2018, when North and South Korea arranged the first official talks in more than two years, liaison officials spoke using desktop telephone consoles, each the size of a small refrigerator.
That hotline dates to the 1970s, though newer systems were installed in 2009.
All of the hotlines operated by the South's Unification Ministry, which handles civilian inter-Korean affairs, use similar equipment, according to the ministry.
The system features a computer screen, disk drives, and USB ports, as well as two colour-coded telephone handsets.
A red phone is for incoming calls from North Korea and South Korea uses a green phone to make outgoing calls to the North.
No other numbers can be called - the phones only connect to a counterpart on the other side. The two sides also use fax machines to send documents.
Photos of the equipment used by the South Korean military show a series of small, olive-drab desktop phones labelled "two-sided inter-Korean hotline."
It is not known what the equipment looks like on the North's side.
The spurt of inter-Korean talks that followed those January phone calls led to the opening of more hotlines, including - for the first time - a direct connection between the offices of South Korean President Moon Jae-in and North Korean leader Kim Jong Un.
In 2019, South Korea's prime minister revealed that the presidential hotline had never been used, and local media report it has not been used since.
The two Koreas also opened a liaison office in Kaesong, North Korea, where officials from both sides worked daily.
In January, that office was "temporarily" closed because of coronavirus worries, though the two sides had continued to hold daily phone calls from Seoul and Pyongyang.