Why am I getting SIP response 400: Bad Session Description?

I dumped The following SIP INVITE datagram from Linphone to a file with CR-LF line breaks, using wireshark:

INVITE sip:1002@172.16.76.21 SIP/2.0 
Via: SIP/2.0/UDP 172.16.76.21:5060;rport;branch=z9hG4bK1936726928 
From: <sip:1555@172.16.76.21>;tag=1350138383 
To: <sip:1002@172.16.76.21> 
Call-ID: 1393698667 
CSeq: 20 INVITE 
Contact: <sip:1555@172.16.76.20> 
Content-Type: application/sdp 
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO 
Max-Forwards: 70 
User-Agent: Linphone/3.5.2 (eXosip2/3.6.0) 
Subject: Phone call 
Content-Length:   205 

v=0 
o=1555 1125 1125 IN IP4 172.16.76.21 
s=Talk 
c=IN IP4 172.16.76.21
t=0 0 
m=audio 7078 RTP/AVP 8 0 101 
a=rtpmap:8 PCMA/8000 
a=rtpmap:0 PCMU/8000 
a=rtpmap:101 telephone-event/8000 
a=fmtp:101 0-11

I wrote a simple Python script that reads the file binary, puts in a UDP datagram and sends through a a socket bound to port 5060. When I send this to a client running user agent, I get 200 OK. When I try to send it to our SIP proxy, FreeSwitch, I get 400 Bad Session Description.

FreeSwitch responded with 200 OK when this message was originally sent by Linphone.

Solution

Apparently FreeSwitch does not tolerate them.

It's not an issue of FreeSwitch. As suggested by @Stanislav in his comment, your "Content-Length" value is wrong. It must be "Content-Length: 213" for your Session Description.