'Surely Korea is No. 1 in the world?' — It has fallen to 22nd, behind Vietnam

South Korea's internet speeds, once among the fastest in the world, have fallen behind those of Vietnam and Thailand, according to new data — though experts caution that results can vary depending on measurement methods and network conditions, making it difficult to draw firm conclusions from any single survey.

According to Ookla's Speedtest Global Index, released Wednesday, South Korea ranked 22nd globally in fixed broadband download speeds as of August, clocking in at 251.33 Mbps.

Vietnam came in eighth at 301.48 Mbps and Thailand ninth at 298.92 Mbps — roughly 20 percent and 19 percent faster than South Korea, respectively. Singapore topped the rankings at 462.50 Mbps, while the United States also outpaced South Korea, placing seventh.

In mobile internet download speeds, South Korea ranked sixth worldwide at 250.56 Mbps. The UAE led at 675.51 Mbps, followed by Qatar at 535.94 Mbps and Kuwait at 399.92 Mbps. South Korea's mobile speeds fell short of half the UAE's figure.

The figures stand in stark contrast to 2017, when a survey by US market research firm Akamai ranked South Korea first in the world for internet speed, ahead of Hong Kong, Singapore and others. Korea was the only country with an average speed exceeding 25 Mbps at the time, outpacing Norway at 23.5 Mbps and Sweden at 22.5 Mbps.

Some observers question the reliability of such rankings, noting that methodology and measurement criteria are not always transparent. With high-speed broadband, speeds can vary depending on a subscriber's service plan, and it is unclear how such differences are factored into the surveys.

Rankings have differed significantly across research firms. South Korea placed first in Akamai's 2017 survey, fifth in Ookla's 2018 survey and 16th in a separate 2018 measurement by Cable.co.uk. The discrepancies stem in part from differing methodologies — Akamai aggregates average speeds, while Ookla uses median values.

Measurement conditions can also affect results. Experts note that speeds can vary based on a user's internet service plan, network infrastructure, test server location and connection routing path.