SIP INFO PBX接口规范-CSTA问题

[skyymrj]

向交换机里发送：
REGISTER sip:192.168.91.212:5060 SIP/2.0
Via:SIP/2.0/UDP 192.168.91.212:5701;branch=z9hG4bK78b5493d-cb3c-4ad6-a435-1808b74a268d;rport
To:8000<sip:8000192.168.91.212:5060>
From: 8000<sip:8000@192.168.91.212:5060>;tag=hetfgeeb
Call-ID: gdhisemewofqcjxysiwjjnrtfdwsfcmykvspmdxfnpllcrdsyi
CSeq: 1 REGISTER
Contact: <sip:8000@192.168.91.212:5780>
Expires: 3600
Supported: 100rel
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE
Max-Forwards: 70
Content-Length: 0
Authorization: Digest username=" + myUserName + @", realm="asterisk", nonce="" , response="", uri="sip:192.168.91.2125060, algorithm=MD5"
交换机返回200 OK

当然我根据交换机厂家提供的接口，发起INVITE请求程序就死在那边了，报文如下：
INVITE sip:192.168.91.212:5060 SIP/2.0
Via:SIP/2.0/UDP 192.168.91.212:5701;branch=z9hG4bK78b5493d-cb3c-4ad6-a435-1808b74a268d;rport
Max-Forwards: 70
To:8000<sip:8000192.168.91.212:5060>
From: 8000<sip:8000@192.168.91.212:5060>;tag=hetfgeeb
CSeq: 1 INVITE
Contact: <sip:8000@192.168.91.212:5780>
Session-Expires: 300
Content-Type:application/csta+xml
Content-Disposition:signal;handling=requierd
Content-Length: 1000
Content-Length: nnn
<?xml version="1.0" encoding="UTF-8"?>
<RequestSystemStatus xmlns="http://www.ecma-international.org/standards/ecma-323/csta/ed3"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>

小弟刚刚学这东西，望高手指定，分不多，谢谢！！