I pointed the ATA186 directly to the AS5300 without proxy server, the same problem happened. So I drew a conclusion that the problem was on the Gateway side. After changing the T1 port on the AS5300, it worked well. ----- Original Message ----- From: Bo To: serusers(a)lists.iptel.org Sent: Sunday, March 16, 2003 11:30 PM Subject: [Serusers] 503 service unavailable I am doing some tests between Cisco ATA186 and AS5300 by using SER as the proxy server. AS5300 sent back 503 (service unavailable). Anyone has any clue on this? Thanks