User's Manual
FIRMWARE VERSION 1.0.7.6    HT502 USER MANUAL     Page 37 of 48  
3-Way Conference 
need to dial *23 + second callee number. 
Remove OBP from 
Route Header 
Default is No. When option YES is chosen, the Out Bound Proxy will be removed from 
Route header. 
Support SIP Instance ID 
Default is Yes. If set to Yes, the contact header in REGISTER request will contain SIP 
Instance ID as defined in IETF SIP Outbound draft. 
Validate incoming SIP 
message 
Default is No. If set to yes all incoming SIP messages will be strictly validated 
according to RFC rules. If message will not pass validation process, call will be 
rejected. 
Check SIP User ID for 
incoming INVITE 
Default is No. Check the incoming SIP User ID in Request URI. If they don’t match, the 
call will be rejected. If this option is enabled, the device will not be able to make direct 
IP calls. 
SIP T1 Timeout 
T1 is an estimate of the round-trip time between the client and server transactions. 
If the network latency is high, select larger value for more reliable usage. 
SIP T2 Interval 
Maximum retransmission interval for non-INVITE requests and INVITE responses. 
DTMF Payload Type 
Sets the payload type for DTMF using RFC2833. 
Preferred DTMF method
The HT502 supports up to 3 different DTMF methods including in-audio, via RTP 
(RFC2833) and via Sip Info. The user can configure DTMF method in a priority list. 
Disable DTMF 
Negotiation 
Default is No. If set to yes, use above DTMF order without negotiation 
DTMF via RFC2833 
Send DTMF via RTP (According to RFC 2833). 
DTMF via SIP INFO 
Send DTMF via SIP INFO message. 
Send Flash Event 
Default is No. If set to yes, flash will be sent as DTMF event. 
Enable Call Features  Default is Yes. (If Yes, call features using star codes will be supported locally) 
Offhook Auto-Dial 
This parameter allows users to configure a User ID or extension number that is 
automatically dialed when off-hook. Only the user part of a SIP address needs is 
entered here. The HT502 will automatically append the “@” and the host portion of the 
corresponding SIP address. 
Offhook Auto-Dial 
Delay 
Configure the delay time for offhook auto-dial function. Range is 0-60 seconds, 
default is 0. 
Proxy-Require 
SIP Extension to notify SIP server that the unit is behind the NAT/Firewall. 
Use NAT IP 
NAT IP address used in SIP/SDP message. Default is blank. 
Use SIP User-Agent 
Header 
Used to replace SIP User-Agent Header (No Default) 
Distinctive Ring Tone 
Custom Ring Tone 1 to 3 with associate Caller ID: when selected, if Caller ID is 
configured, then the device will ONLY uses this ring tone when the incoming call is from 
the Caller ID. System Ring Tone is used for all other calls. When selected but no Caller 
ID is configured, the selected ring tone will be used for all incoming calls. Distinctive 
ring tones can be configured not only for matching a whole number, but also for 










