簡介：
該系列文章主要介紹，上級域對國標平臺進行預覽/回看等流程的信令交互。
一個簡單的gb28181直播預覽流程：
-
接收下級域的註冊請求
-
發送catalog請求，查看設備信息
-
選擇設備進行預覽
註冊流程：
- 接收register請求
- 回覆401，要求帶上用戶信息
- 第二次接收register請求
- 驗證通過後，回覆200
具體信令：
注：1.下面的信令，忽略了401的流程。
2.上級域ip：192.168.30.173。域id：34020000002000000001。下級平臺ip：192.168.30.228。下級平臺id：34020000001110000001
上級域接收register請求：
REGISTER sip:34020000002000000001@3402000000 SIP/2.0
Via: SIP/2.0/UDP 192.168.30.228:5060;rport;branch=z9hG4bK2084371513
From: <sip:34020000001110000001@3402000000>;tag=1061032626
To: <sip:34020000001110000001@3402000000>
Call-ID: 408251015
CSeq: 13 REGISTER
Contact: <sip:[email protected]:5060>
Max-Forwards: 70
User-Agent: Embedded Net DVR/NVR/DVS
Expires: 86400
Content-Length: 0
上級域回覆200：
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.30.228:5060;rport=5060;received=192.168.30.228;branch=z9hG4bK2084371513
From: <sip:34020000001110000001@3402000000>;tag=1061032626
To: <sip:34020000001110000001@3402000000>
CSeq: 13 REGISTER
Call-ID: 408251015
Contact: <sip:[email protected]:5060>
User-Agent: SRS/4.0.26(Leo)
Expires: 86400
Content-Length: 0
之後，下級域會定時發送保活請求：
MESSAGE sip:34020000002000000001@3402000000 SIP/2.0
Via: SIP/2.0/UDP 192.168.30.228:5060;rport;branch=z9hG4bK800985051
From: <sip:34020000001110000001@3402000000>;tag=417964224
To: <sip:34020000002000000001@3402000000>
Call-ID: 1320623185
CSeq: 20 MESSAGE
Content-Type: Application/MANSCDP+xml
Max-Forwards: 70
User-Agent: Embedded Net DVR/NVR/DVS
Content-Length: 180
<?xml version="1.0" encoding="gb2312"?>
<Notify>
<CmdType>Keepalive</CmdType>
<SN>3632</SN>
<DeviceID>34020000001110000001</DeviceID>
<Status>OK</Status>
<Info>
</Info>
</Notify>
上級域回覆200：
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.30.228:5060;rport=5060;received=192.168.30.228;branch=z9hG4bK800985051
From: <sip:34020000001110000001@3402000000>;tag=417964224
To: <sip:34020000002000000001@3402000000>
CSeq: 20 MESSAGE
Call-ID: 1320623185
User-Agent: SRS/4.0.26(Leo)
Content-Length: 0