Transport Layer-Self doubt

Question

Here A,B,C are 3 networks and a packet sends from A to C . When packet 180 B sends from A to B it is connected with 20B IP header as well as 20 B TCP header. In network B we are segmenting data packet as 100 B and we are removing IP header of A and it never comes back again for calculation. right?

But then we can see TCP header is never removed and it is calculated as part of header send to destination C. 

My question is if IP header are different for network A, B,C then how TCP header will be same for network A,B,C?

Comments

at network layer fragmentation is done not segmentation ,fragmentation done at router before entering in any network.at network layer when packet come then header of transport layer considered as part of payload of packet of network layer.thats why during fragmentation TCP header is never removed.

---

but see the picture
A too B application layer transfering 180 B only , not 200 B
derive more

---

When massage comes from application layer,every layer add header because it is require to reach at destination without header how do we know what is destination address,what is port no. Of process,what type of required etc . When application layer can send any amount of data,but data link layer can accept upto 1500 Bytes packet .that's why fragmentation is done at network layer .headers are overhead but these are required.when packet comes at network layer from transport layer it became part of payload means data nd additional network add his header.

---

@Prateek I mean which one header should include and which one should exclude

https://gateoverflow.in/3731/gate2004-it-87

here it has that discussion

Not we only include or exclude header but also but also check if it is divide by 8 or not

right?