It appears that in the OPTIONS ping packet, To and From fields contain only the domain name. In sofia.c: if (ping_freq) { if (ping_freq >= 5) { gateway->ping_freq = ping_freq; gateway->ping_max = ping_max; gateway->ping_min = ping_min; gateway->ping_monitoring = ping_monitoring; gateway->ping = switch_epoch_time_now(NULL) + ping_freq; gateway->options_to_uri = switch_core_sprintf(gateway->pool, "<sip:%s>", !zstr(from_domain) ? from_domain : proxy); gateway->options_from_uri = gateway->options_to_uri; } else { switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_ERROR, "ERROR: invalid ping!\n"); } } Is there a reason why To and From fields don;t contain the register username? This seems to break some other vendor gateways. thanks, stan