Questions tagged [layer4]

For questions about OSI Layer 4 (transport layer).

Filter by
Sorted by
Tagged with
171 votes
9 answers
102k views

Why do we need a 3-way handshake? Why not just 2-way?

The TCP 3-way handshake works like this: Client ------SYN-----> Server Client <---ACK/SYN---- Server Client ------ACK-----> Server Why not just this? Client ------SYN-----> Server ...
user avatar
  • 1,823
13 votes
1 answer
12k views

How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?

I know that TCP window sizes can be scaled to over 64KB, but looking at an ethernet packet datagram, such as this one: it looks like a layer 2 packet is limited in size to be much smaller than that. ...
user avatar
2 votes
2 answers
1k views

Why do transport layer do data chunking. If there is fragmentation in Network Layer

I just curiously wanted to know about the question regarding L4, L3 Data Chunks, IP Fragmentation : Data chunking happened at Layer 4(Transport, TCP), and Fragmentation at Layer 3(Network, ipv4) ...
user avatar
2 votes
1 answer
659 views

Of what layer is socket a concept?

In network layer, IP address is a concept. In transport layer, port is a concept. Is socket a concept of transport layer? If not, what is the corresponding concept to socket in transport layer? Of ...
user avatar
  • 1,495
0 votes
1 answer
1k views

TCP Handshaking Meaning of RST

I am trying to implement TCP handshaking but receive RST instead of ACK: No. Time Source Destination Protocol Length Info 62 24.622012890 192.168.0.147 ...
user avatar
43 votes
3 answers
125k views

What is the difference between MSS and MTU?

I'm confused as to the difference between maximum segment size and a maximum transmission unit. Can someone please explain in relation to layers 2 and 3? If I had a packet of 800 bytes in the ...
user avatar
7 votes
3 answers
4k views

How does NAT decide which connections are inbound, and which are outbound?

I'm building a P2P application that needs to be able to access nodes behind a NAT. This NAT does not allow inbound connections, therefore the nodes outside the network cannot reach out to the nodes ...
user avatar
  • 73
7 votes
5 answers
10k views

Why does NAT translate a source port?

I’m beginning to learn about nat and I was wondering why does NAT translate a source port? Doesn’t a port represent an application that’s requesting a service? So why must it be translated? Also what ...
user avatar
  • 71
3 votes
3 answers
6k views

At which layer does router operate?

I have studied from various sources that router is a layer 3 device. It does routing based on Network layer (layer 3) header, but I have a doubt. Network address translation (NAT) is a feature of ...
user avatar
  • 335
0 votes
1 answer
82 views

What is the differences between flow control and access control?

We first apply access control methods to get access to the channel link followed by the flow control methods to stop the receiver from overflowing. Suppose we are using CSMA/CD in access control ...
user avatar
19 votes
3 answers
9k views

What do TCP/UDP add to "raw ip"?

I know that both TCP and UDP are built on top of IP, and I know the differences between TCP & UDP, but I'm confused about what exactly "raw ip" is. Would it be fair to say that TCP & UDP both ...
user avatar
11 votes
3 answers
16k views

Is a TCP three-way handshake required for an HTTP POST?

I don't quite understand if i posting http form data from the browser to the server, does the protocol still need to make three-way handshake (syn-ack-data) or it only works for GET http requests?
user avatar
8 votes
4 answers
13k views

Why is a TCP Socket identified by a 4 tuple?

Newbie to networking here. I'm reading the Computer Networking (3rd edition) book, and in section 3.2 they are discussing multiplexing / demultiplexing for both UDP and TCP. In the UDP protocol, a ...
user avatar
  • 183
10 votes
4 answers
16k views

Can anyone explain to me the difference between the PSH and URG flags in TCP segment?

According to me when PSH flag is set, it indicates that data will have to be sent immediately to the wire and on receiving side the data has to be pushed to the application immediately. When URG flag ...
user avatar
13 votes
4 answers
33k views

What layer of the OSI model does NAT work?

Simple question and the answer is layer 3 of course, but can we say that PAT is working on layer 4 also because it deals with port numbers which is a layer 4 function? Or is it only a layer 3 ...
user avatar
  • 133
11 votes
4 answers
36k views

How to know whether a protocol uses TCP or UDP

Well I know that might sound a stupid question and I believe that the most proper answer will be like I will be able to tell as my experience builds up and I learn more and more about the protocols. ...
user avatar
  • 441
10 votes
2 answers
26k views

Window Size and ACK Number

Copy-pasting from my lecturer's slides: • Receiver indicates the window size is 3000 • Transfer goes ahead • Acknowledge every 3000 bytes • Receiver increases window size to 4000 • 4000 bytes ...
user avatar
  • 359
3 votes
1 answer
3k views

What is the need for transport Layer?

In 5-layer model. Why we need additional transport layer? I read these two points Users who interact with software have no control over the sub-net; Transport Service can provide a more reliable ...
user avatar
  • 515
8 votes
5 answers
665 views

Why is the IP layer aware of higher layers in the network stack?

In the IP packet header there is an 8-bit Protocol field (at offset 9) that holds the "next level protocol", with assigned numbers given in RFC 790. For example, TCP is 6. My question is, why is the ...
user avatar
2 votes
2 answers
464 views

Should all sent segments be requeued after a TCP retransmission timeout expires?

I am developing a TCP implementation and could not find a clarification to this in the relevant RFCs (793, 1122, 5681, 6298). When the retransmission timer expires, the first segment which has once ...
user avatar
1 vote
2 answers
1k views

How is UDP used in multimedia system inspite of being connectionless

We know that UDP does not care about segment (packet) in-order and their arrival on the destination.Then how on YouTube or VoIP (skype) are we able to stream videos? If a packets is lost (doesn't ...
user avatar
7 votes
1 answer
4k views

How do Endpoints in a TCP conversation determine their MSS?

I understand the MSS is the Maximum Segment Size, which is the size of the Payload TCP will send. I also understand that a "receiving" MSS value is suggested by both parties in a TCP conversation ...
user avatar
  • 14k
4 votes
3 answers
2k views

How does a router a layer 3 device translate port address in PAT, as it is a layer 3 device?

While I was reading about PAT i.e Port Address Translation.The router was configured to translate all the private IP addresses to one single public IP.Since router is a layer-3 device, it can do that ...
user avatar
3 votes
1 answer
6k views

What is the value of EstimatedRTT at first time?

Although this question might be marked as duplicated! I'm asking again because other question's answers like this couldn't help me. So please consider the case and don't mark it as duplicate and ...
user avatar
0 votes
1 answer
100 views

How UDP checksum get IP address to make pseudo header in transport layer?

We know that UDP checksum's pseudo header contains the most important parts of the IP header, that is, source and destination address, protocol number and data length. I hope that the concept of IP ...
user avatar
0 votes
2 answers
131 views

What is responsibility of different layers of OSI model and intermediate devices between sender and receiver when data packets are lost/corrupted?

Suppose sender sending some data to receiver and there are 3 routers between them. R1, R2, R3 are routers. Now sender starts sending data packet D through it's AL, TL, N/W L, DLL,PL to router R1 ...
user avatar