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Add PCAP analysis to successful calls (#413) 

* Adopt tutorial format to dockerized VoLTE lab

* Fixed several lines according to Supreeth's feedback

* add PCAP analysis to successful calls
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miaoski 2020-04-18 21:13:17 +08:00 committed by GitHub
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@ -191,6 +191,49 @@ The successful calls were made with a commercial eNB (in his case a Casa
smallcell), while srsENB the ACK takes a very long time to reach the UE,
resulting in disconnected calls.
**UE registration**
![UE registration with IPSec](https://raw.githubusercontent.com/miaoski/docker_open5gs/gh-pages/screenshots/ue-ipsec.png)
From the screenshot, we see a UE that supports IPSec got a response from
S-CSCF, indicating that ipsec-3gpp is supported, protocol is ESP (ethernet
proto 50, IPSec). Client port (port-c) is 5100 and server port (port-s) 6100.
Refer to [IMS/SIP - Basic Procedures](https://www.sharetechnote.com/html/IMS_SIP_Procedure_Reg_Auth_IPSec.html) if you want to know more.
Also, notice that packets after 401 Unauthorized are transmitted over ESP.
If a UE does not support IPSec, you don't see the "security-server", as shown below:
![UE registration without IPSec](https://raw.githubusercontent.com/miaoski/docker_open5gs/gh-pages/screenshots/ue-noipsec.png)
**VoLTE calls**
![ipsec to ipsec call](https://raw.githubusercontent.com/miaoski/docker_open5gs/gh-pages/screenshots/ipsec-to-ipsec%20calls.png)
The Wireshark above shows that after several IPSec (ESP) packets, S-CSCF is
sending a SIP INVITE for UE 03 to UE 04. To be more precise,
```
Request-Line: INVITE sip:0398765432100;phone-context=0498765432100@0498765432100;user=phone SIP/2.0
...
Record-Route URI: sip:mo@10.4.128.21:6101;lr=on;ftag=7b3fae13;rm=8;did=078.654
```
The SIP port of the caller (`contact`) will also be passed to the callee,
```
Contact URI: sip:0498765432100@192.168.101.3:6400;alias=192.168.101.3~6401~1
```
After S-CSCF forwarded the INVITE to P-CSCF, it returns a 100 Trying, and contacts with the callee via IPSec:
![ipsec callee](https://raw.githubusercontent.com/miaoski/docker_open5gs/gh-pages/screenshots/ipsec-to-ipsec%20callee.png)
This can be contrasted when the callee does not support IPSec. After 100
Trying, a UE that does not support IPSec is sent a SIP INVITE in clear text:
![non-ipsec callee](https://raw.githubusercontent.com/miaoski/docker_open5gs/gh-pages/screenshots/ipsec-to-noipsec.png)
#### 7. Known issues