Questions tagged [layer4]
For questions about OSI Layer 4 (transport layer).
168
questions
0
votes
1
answer
42
views
HTTP and TCP relationship
I always wondered how HTTP knows when it has enough TCP segments in order to process a request or response.
Can someone give me more information about the process?
Thanks.
- 7
0
votes
2
answers
81
views
UDP supports multicasting and broadcasting in transport layer or application layer?
We know that UDP does supports multicasting and broadcasting. My question is which layer "UDP supports multicasting and broadcasting"? Is it transport layer or application layer? We know ...
- 346
1
vote
1
answer
269
views
What is difference between socket connection and TCP connection?
We know TCP socket is port numbers and IP addresses. Is TCP socket connection is 3-way handshake:the SYN packet, the SYN-ACK packet, and the ACK packet?
Is TCP socket connection follows TCP stack?
And ...
- 346
0
votes
0
answers
7
views
How IP packet's payload bigger than the whole former PDU (segment)? [duplicate]
As far as I know:
File is too big ---> Fourth layer (TCP or UDP) divide it to a multiple segments ---> Then each segment encapsulated separately into a packet.
What means if I have 10 segments, ...
- 1
1
vote
1
answer
99
views
How n level come to know the n+1 level contents?
Suppose in application layer is running some application. And application has respective source port number and destination port number. And know that n layer has no authentication to know about n+1 ...
- 346
1
vote
1
answer
66
views
Router could get packet of size more than 1500 bytes?
Suppose transport layer get the segment 4000 bytes from application layer at sender site. But we know maximum MTU in layer2(Ethernet) is 1500 bytes.
My question is so fragmentation is happening at ...
- 346
0
votes
1
answer
78
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 ...
- 346
0
votes
3
answers
116
views
How NAT router use layer4 contents in layer3?
I followed from this question and @PeterGreen's Answer , and come to know that NAT router working in layer3, but using layer4 contents(layer4 port number,layer4 checksum). My question is when layer3 ...
- 346
0
votes
2
answers
172
views
Acknowledgement, retransmission of layer2 is actually belongs to layer4?
I followed from this question understand that only transport layer responsible for acknowledgement. But I have read on book stop and wait, GBN, SR protocols uses acknowledgement, retransmission in ...
- 346
0
votes
2
answers
125
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 ...
- 346
2
votes
1
answer
979
views
Which one is right, UDP has 508 or 512 bytes payload limits?
We know the size guarantees the datagram won't be fragmented in IPv4 is maximum 576 bytes. But the size when use UDP header 8 bytes and if we take UDP payload 512 bytes and choose maximum header size ...
- 346
0
votes
1
answer
63
views
Why loss of first Syn + Ack from the server will not establish a connection? [duplicate]
In TCP 3-way handshake, 3 segments will be sent (SYN, SYN ACK, ACK). What if loss of syn+ack from the server will not establish a connection? What if the third segment(ACK) is lost? Is the sender ...
user80113
-1
votes
1
answer
160
views
Why sender window or congestion window size becomes 2^n mss after nRTT in slow start mechanism?
I seen everywhere in slow start mechanism if initial sender size denoted by cwnd= 1mss , then after 1 RTT cwnd becomes = 2 mss, and after 2 RTT cwnd becomes = 4 mss and so on. My question is why ...
- 346
0
votes
1
answer
165
views
Is really TCP takes 3*RTT time to make a connection?
TCP takes 3 RTT time I have read from one stack overflow answer to make a connection with server. We know that TCP takes triple (Syn, Syn/Ack, Ack) to make a connection by 3-way handshake with server....
- 346
0
votes
2
answers
111
views
Why client will send a RESET when it is closed state?
Suppose I have an TCP state transition diagram. And assume that the last ACK is lost. Then, B will think that A did not receive the FIN and will retransmit the FIN. From B point of view this is the ...
- 346
-1
votes
1
answer
127
views
Why the pseudo-header is not transmitted with the UDP datagram?
I have read from E. Comer - Internetworking with TCP/IP 4th edition that "The purpose of using a pseudo-header is to verify that the UDP datagram has reached its correct destination. The key to ...
- 346
0
votes
1
answer
277
views
UDP checksum calculation for checksum results in the value zero
I read UDP checksum from Wikipedia that "If the checksum calculation results in the value zero (all 16 bits 0) it should be sent as the one's complement (all 1s) as a zero-value checksum ...
- 346
0
votes
1
answer
192
views
Why UDP checksum is optional for IPv4?
We know that IPv4 header has checksum for header not for data .Therefore for checking data error we need checksum in transport layer. Suppose we're using UDP in layer 4. So if I remove the checksum ...
- 346
0
votes
1
answer
90
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 ...
- 346
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 ...
- 346
1
vote
1
answer
105
views
What happens to the packets in the sender buffer when "eventually a timeout would be reached" for a **delayed ACK** in a AIMD TCP connection?
In a AIMD TCP connection, What happens to the packets in the sender buffer when "eventually a timeout would be reached" for a delayed ACK for a specific packet at the sender side?
Suppose ...
- 113
0
votes
3
answers
317
views
What would happen if TCP flow control is turned off hypothetically? [closed]
I understand that TCP flow control provides a way for the receiver to backpressure the sender. But what if we eliminated this from the protocol. Of course, the receiver would still ACK everything ...
- 133
1
vote
1
answer
39
views
Nature of TCP Timeouts
Are timeouts in TCPs inherently part of sequence numbers, or is it an entirely different component of a TCP packet?
I understand that timeouts provide some level of reliabilty to a data stream, in ...
10
votes
5
answers
3k
views
Does the destination port change during TCP three-way handshake?
I'm learning networking programming in C and there is a question bothers me a lot, does the destination port change during TCP three-way handshake? Let's say I have a cilent application running on ...
- 261
1
vote
1
answer
139
views
Does the first TCP FIN packet (active close) goes with just only FIN bit set?
Suppose we have established TCP connection. The active close process assumes the FIN packet been sent to trigger TCP connection closing.
But I can't figure out, is this first (active close) FIN packet ...
- 113
1
vote
1
answer
82
views
Is there any other network protocol than tcp/udp that works with ports?
Do you know at least one protocol (any OSI layer) that, like tcp and udp, works with ports ?
Thank you
- 13
2
votes
2
answers
196
views
Why is delayed segment prevention (TIME_WAIT) in TCP only done for one side?
One of the reasons for TIME_WAIT is to prevent old packets/duplicates, coming in late, to screw up subsequent connections on the same (src ip, src port, dst ip, dst port) quadruplet.
That makes sense, ...
44
votes
7
answers
15k
views
Does UDP do anything at all?
It's my understanding that TCP has logic for ensuring reliable communication, but UDP just naively sends information along the channel set up for it using IP and things in lower layers.
Does UDP ...
- 559
2
votes
2
answers
641
views
What will happen if a server receives a duplicate SYN for an existing connection?
If a server receives a fresh SYN packet for a connection that is already established, what should it do?
I have already seen What will happen at server side if it received 2 SYN packet from the same ...
- 138
1
vote
2
answers
220
views
Is this UDP diagram wrong?
I was just wondering if anyone can tell me why all UDP diagrams I have seen list a request from the server to the client as the first point of communication? Take a look at the following diagram for ...
-1
votes
2
answers
529
views
What is the window size of TCP pipelined sending?
We know that instead of sending a packet and waiting a RTT then sending another (stop and wait), TCP uses pipelined sending as picture below shows:
So, my question is, what's the maximum number of ...
- 119
2
votes
1
answer
322
views
Do both sides need to agree on MSS value?
By definition, The TCP Maximum Segment Size (MSS) is the maximum amount of data that a host is willing to accept in a single TCP/IPv4 datagram. And MSS is one of the parameters which is negotiated ...
- 35
0
votes
2
answers
81
views
Diffie helman Agreement on Prime Number and Generator
So, to start DH, the two parties need to agree upon a prime number and Generator, correct? How do they do do that without someone listening in?
Where does the loop end/start?
Also, Does it matter if a ...
- 25
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 ...
0
votes
1
answer
722
views
TCP Checksum Calculation
I recently started with networking and tcp/ip.
The RFC 793 document tells the checksum is made of:
pseudo header+tcp header+tcp payload+zeroes(if not divisible by 16).
So I have to take 16bit ...
- 113
4
votes
1
answer
246
views
Which exact bytes are transmitted while TCP zero window probing?
I read the post about TCP zero window probe and it seems that such a probing segments transmit some payload.
But I can't figure out which exactly bytes are sent in probing segments? Is it one (or more)...
- 207
1
vote
2
answers
154
views
Can TCP stand for "Transport Control Protocol"
I know it might sound like a silly question, but afaik TCP stands for transmission control protocol. However I found a couple of websites using the term Transport Control Protocol.
So I was wondering ...
- 113
1
vote
1
answer
221
views
How does triple handshake avoid establishing connection for duplicate packets(coming later down the line)
The idea behind triple handshake seems to be for duplicates to not cause issues.
The way I understand it host sends a sequence x to server. Server acknowledges it and sends it's own sequence y. Host ...
- 89
1
vote
1
answer
244
views
Do sequence and acknowledgment numbers treat 3-Way Handshake differently?
1- Just as the message ID that is assigned to each message in PAR, the "sequence number" is a means of providing reliability in a transfer of a byte stream. So sequence numbers are assigned to every ...
- 149
5
votes
2
answers
612
views
Is a datagram from an upper network layer converted 1:1 to one of the lower layer?
I know datagrams from upper layers are converted to those of lower layers by adding metadata, but I cannot seem to find this information anywhere. Which one of the below is correct?
A single TCP ...
- 401
1
vote
2
answers
1k
views
Sequence numbers of segments in three way handshakes of TCP connection establishment or termination
I was trying to understand TCP connection establishment and termination steps from Forouzan's book.
In third step of three way handshake of connection establishment, it says following
The client ...
- 179
1
vote
1
answer
86
views
Is TCP aware of MAC adress
lets say I would like to make connection between client and server on port 80. Is 3 way handshake aware of server MAC address? I mean: client send SYN data packet to specific IP:port and MAC. In ...
- 13
3
votes
1
answer
2k
views
When TCP sender window shrinks?
I was learning TCP from Forouzan's book. It explains sender side window as follows:
In that it defines size of receiver window as follows:
rwnd = receiver buffer size - number of bytes waiting to ...
- 179
1
vote
1
answer
116
views
ports and security
I'm thinking about how the "port" operates for the network connections and tried reading the CCNA cert. guide to understand the details, however, I need to clarify doubts:
does occupying all the TCP/...
- 123
1
vote
1
answer
84
views
Finding MSS for a remote connection that uses tunnelling
I'm working on a codebase where we're trying to test network health by verifying if we can ping the remote site having payload = MSS without any packet fragmentation (using -df flag).
Typically, for ...
- 113
0
votes
0
answers
22
views
how OSI and TCP/IP layers work? [duplicate]
I am really confused by how the layers these model work. I'm not asking about what are their functions. I read that transport layer provides end-to-end of all packet delivery, and networking also ...
- 101
0
votes
1
answer
1k
views
How does browser decide which destination port to use?
Suppose I have a Vanilla machine and this is the first time I am connecting it to Internet. There is no Cache at any level. I access a website through browser by typing example.com (no http//: or ...
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)
...
user60007
1
vote
1
answer
950
views
Why server cannot send data in TCP three-way handshaking?
In the three-way handshaking, only from the ACK packet we can send data.
Why cannot the server send data with SYN-ACK packet? I understated why a client cannot send data to a server (preventing, for ...
- 119
2
votes
3
answers
1k
views
What's the use of an acknowledgement number without the ACK flag set?
Isn't it redundant if the ACK flag in the header isn't also on?
Do you ever mix an acknowledgement with a normal message - send data and acknowledge a message in the same TCP segment?
I feel like ...
- 213