Transilien Paris-Nord
Transilien Paris-Nord is one of the sectors in the Paris Transilien suburban rail network. The trains on this sector depart from Gare du Nord in central Paris, and serve the north-west and north-east of Île-de-France region with Transilien lines H and K. Transilien services from Gare du Nord are part of the SNCF Gare du Nord rail network. Line H. The trains on Line H travel between Gare du Nord in Paris and the north-west of Île-de-France region, with termini in Luzarches, Pontoise, Persan–Beaumont and Creil. Services. Like  other Transilien lines, every train service consists of four letters and is called a "name of mission", "mission code" or a "name of service". These have been adopted during the Transilien service update of 2004. They are only displayed on timetables and on passenger information display systems. The first letter corresponds to the destination of the train. The second, third and fourth letters indicate the stations served by the train. A Transilien Line H train calling all stations has an O as the second or the third letter (AOLA, OPOC, POVA, SOGA). An E on the second position indicates that  a radial service does not serve nearly all stations on the route (LEMI, LEVI). If the train runs via Montsoult–Maffliers then the third letter is always an M (LOMI, POMA). Some of the service names may spell backwards when going in "down" direction, which is from Gare du Nord. This usually occurs when the fourth letter is the train's station of origin. Examples: ADDO (to Gare du Nord) spelled backwards is ODDA (to Pontoise), AREV (to Gare du Nord) spelled backwards is VERA (to Valmondois). Line K. The trains on Line K serves primarily the north-est of  Île-de-France region and travel between Gare du Nord in Paris and Crépy-en-Valois in Hauts-de-France region. Services. The four-letter codes of Line K are much simpler. Only one of the four letters have a meaning: this indicates the destination, which is the start of the code. If a four-letter code begins with a K, this means that the train runs to Crépy-en-Valois, but if a four-letter code begins with an A, this means that the train runs to Gare du Nord. Line K assigns names of services to TER services  as well for Paris-Laon services ("TERL" to Laon and "TERP" to Gare du Nord).