Bus services in Dublin are operated for the most part by state owned Dublin Bus but a number of peripheral bus routes are provided by Go-Ahead Ireland a private operator who operate a number of peripheral bus routes on behalf of the NTA. There is an extensive bus network of 110 radial, cross-city and peripheral routes in the Greater Dublin Area, which constitutes the bulk of the area's public transport system. Daytime routes are identified by number and sometimes suffixed with a letter (e.g. 25, 25a, 25b) and 18 "Nitelink" overnight services which run on Friday and Saturday nights are identified by a number suffixed with "N" (e.g. 41n). There are two 24-hour services for which there is no N equivalent and daytime fares are charged all day.