The top-level domain for Laos is .la. Transport in Laos  This article concerns the systems of transportation in Laos. Laos is a country in Asia, which possesses a number of modern transportation systems, including several highways and a number of airports. As a landlocked country, Laos possesses no ports or harbours on the sea, and the difficulty of navigation on the Mekong means that this is also not a significant transport route. Because of its mountainous topography and lack of development, Laos has few reliable transportation routes. This inaccessibility has historically limited the ability of any government to maintain a presence in areas distant from the national or provincial capitals and has limited interchange and communication among villages and ethnic groups. The Mekong and Nam Ou are the only natural channels suitable for large-draft boat transportation, and from December through May low water limits the size of the draft that may be used over many routes. Laotians in lowland villages located on the banks of smaller rivers have traditionally traveled in pirogues for fishing, trading, and visiting up and down the river for limited distances. Otherwise, travel is by ox-cart over level terrain or by foot. The steep mountains and lack of roads have caused upland ethnic groups to rely entirely on pack baskets and horse packing for transportation. The road system is not extensive. A rudimentary network begun under French colonial rule and continued from the 1950s has provided an important means of increased intervillage communication, movement of market goods, and a focus for new settlements. As of mid-1994, travel in most areas was difficult and expensive, and most Laotians traveled only limited distances, if at all. As a result of ongoing improvements in the road system started during the early 1990s, it is expected that in the future villagers will more easily be able to seek medical care, send children to schools at district centers, and work outside the village. Rail transport does not play a significant part in Laos's transport sector, since the country largely lacks the required infrastructure. A short portage railway, the Don Det – Don Khon narrow gauge railway, was built by the French while Laos was a part of French Indochina. The railway crossed over the islands of Don Det and Don Khon, enabling vessels, freight and passengers to travel along the Mekong River. The railway was abandoned and fell into disrepair, although some of the infrastructure is still in place. In the late 1920s, work began on the Thakhek–Tan Ap railway, that would have run between Thakhek, Khammouane Province and Tân Ấp Railway Station, Quảng Bình Province, Vietnam through the Mụ Giạ Pass.