In the below REGISTER Request, there's a mistake. Can you figure out on which header it’s present?

Interview
1

Q. In the below REGISTER Request, there’s a mistake. Can you figure out on which header it’s present?

REGISTER sip:registrar.example.net SIP/2.0  
Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bK74bf9  
Max-Forwards: 70  
From: "Alice" <sip:alice@example.com>;tag=9fxced76  
To: "Alice" <sip:alice@example.com>  
Call-ID: 3848276298220188511@pc33.example.com  
CSeq: 1 INVITE  
Contact: <sip:alice@pc33.example.com>;expires=3600  
Content-Length: 0

a) CSeq
b) Call-ID
c) Via
d) To

Check 🔎

:arrow_right: Correct answer: Letter a.

CSeq is incorrect in this REGISTER request because the method is INVITE instead of REGISTER.

Q. In the below REGISTER Request, there’s a mistake. Can you figure out on which header it’s present?

a) :white_check_mark: “CSeq”
→ Correct. The CSeq should match the request method (REGISTER), not INVITE.

b) :x: “Call-ID”
→ Incorrect. The Call-ID value is valid and unique as expected.

c) :x: “Via”
→ Incorrect. The Via header format is correct.

d) :x: “To”
→ Incorrect. The To header format is fine for this REGISTER request.