B737-800 CREW HAD AN INOP GPS IN FOREIGN AIRSPACE.

Narrative

LOSS OF GPS. WHEN SYS ANNUNCIATOR PANEL PRESSED THE IRS AND GPS LIGHTS CAME ON INDICATING LOSS OF 1 GPS. THE MEL STATES CREW PLACARDING PERMITTED AND DISPATCH NOTIFICATION REQUIRED. ADDITIONALLY; 1 GPS MAY BE INOP FOR RTES WHERE ACCURACY FOR THE RTE CAN ONLY BE MET BY GPS AND SUPPLEMENTARY MEANS OF NAV REQUIRED. I CONTACTED DISPATCH; USING OPS PERSON AS A RELAY; GIVING DETAILS AND COURSE OF ACTION. AFTER REPEATED COMMENTS; THE OPERATOR SAID DISPATCH UNDERSTOOD AND I WAS CLRED TO GO. IN FACT; THE DISPATCHER THOUGHT I HAD A GPWS PROB. ONCE AIRBORNE; I EXPLAINED THE SIT TO MIAMI ARTCC REQUESTING A315 WITH VOR NAV AS A BACKUP. ORIGINAL RTE REQUIRING BOTH GPS. SIMULTANEOUSLY; THE FO WAS CONTACTING THE DISPATCHER WITH THE SIT. MIAMI ARTCC RECOMMENDED RADAR VECTORS AS A BACKUP WITH A DIRECT TO JUNUR INTXN. DISPATCH SENT A MESSAGE STATING A COM PROB WITH HIGHLIGHTING MEL REQUIREMENTS; AND RECOMMENDING A315 ROUTING AS A BACKUP. I EXPLAINED TO MIA THE RECOMMENDATIONS OF THE DISPATCHER AND ASKED MIAMI WHAT THEY PREFERRED. THEY WANTED RADAR VECTORS PROBABLY FOR FLOW CTL. THE DISPATCHER WAS NOTIFIED OF THE DECISION TO FLY RADAR VECTORS. IN RETROSPECT; I BELIEVE SUPPLEMENTARY NAV SHOULD BE TREATED AS POTENTIAL LOST COM NECESSITATING VORS FOR THE B737-800.