address: 6038 NE 78th Court DS0 = The first (and perhaps only) digital telephone switch at that location The item to note in the above example is that Portland is usually abbreviated as "PTLD", but because of the relatively small number of possible combinations available in the two-character location code, the city abbreviation must occasionally be modified for locations added later, usually by incrementing the fourth character in the code. DLLSTXRNDS1 DLLS = Dallas TX = Texas RN = The Richardson office DS1 = The second digital telephone switch at that location Note that this location is actually in Richardson, Texas, not Dallas. Apparently, the organizational structure of Southwestern Bell Telephone at the time considered Richardson to be within its own Dallas organization, although the cities themselves have always been legally separate. SWASONXTSG1 SWAS = Swastika, a 1908 mining village on the Ontario Northland Railway at the edge of Kirkland Lake ON = Ontario XT = X indicated a nominally independent telephone company, in this instance Timmins-area Northern Telephone Ltd. SG1 = a Western Electric step-by-step exchange NorthernTel's +1-705-642 exchange at 5 Cameron Avenue, Swastika was a throwback to a simpler era in which mechanical stepping switches rotated in response to dial pulses from rotary dial telephones. As a step-by-step exchange offers none of the calling features of an electronic or digital switch, these are becoming increasingly rare as mechanical switching equipment is displaced by electronics. This one held out a little longer than most as it was a small community in formerly independent telco territory, but was ultimately replaced by a digital remote station SWASONXTRSA controlled from Timmins TMNSONXTCG0. OTWAON080MD OTWA = Ottawa ON = Ontario 08 = A Bell Canada co-location site on Iona Street in Ottawa 0 = Identifies a specific local exchange at the site (this one is Rogers Wireless) MD = A mobile phone exchange or competitor's point of interconnection (POI) to an incumbent landline network. Rogers is not a landline incumbent but a rival mobile telephone carrier with a block of 220000 Ottawa numbers. The Iona Street office (OTWAON08) is a co-location facility which hosts a landline exchange (incumbent Bell Canada's OTWAON08 -CG0) and three rival mobile switches (-0MD is Rogers, -3MD is Telus, -AMD is Bell Mobility), one for each major wireless carrier. Similar naming conventions apply for CLEC exchanges at a point of interconnection to incumbent carrier networks. The suffix -MD nominally