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For questions about Transmission Control Protocol (TCP), a transport protocol used to encapsulate data across a network for reliable communication.

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How to calculate a window size if you have SEQ and ACK number

I made something in Cisco Packet tracer and I saw that when I sent first message the SEQ=1 and ACK=1 and window size is 65535 so that is maximum number, but when other server answer then SEQ=1 and ACK=...
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can teach how to calculate ack seq pls [on hold]

Suppose a client sent a web page request to a web server after TCP connection established. The size of the web page request is 2000 bytes, and the size of the requested web page is 4000 bytes. After ...
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2answers
187 views

How does the Transport Layer construct the Pseudo-Header for TCP checksum?

THE TCP Psuedo Header needs sender and destination IP Address and protocol type. All of this informations is present in the network layer/IP header. Since the transport layer cannot access the data ...
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14 views

Unexpected TCP throughput performance over 802.11ac wifi with different TCP streams and different antenna numbers [on hold]

I have seen similar questions like mine. However, none of the solutions have fixed my issue. The question is as follows: I have 2 different devices under test (DUT). One has 3x3 antenna configuration,...
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2answers
29 views

How could a response be sent to the requestor without requestor's address?

I'm reading this talking about the differences between two fire-and-forget message (for example, under UDP) and a request-response communication (for example, under TCP). I came across this: The ...
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35 views

Processing received SACK information in case of reordering

I would like to understand how TCP receiver in established state should treat SACK information of out-of-order and fully within receive window segments, where rcv_nxt < seq_no < rvc_nxt + ...
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18 views

TCP Retransmission requests from IPTV Server and TCP Dup Ack Requests from Client [on hold]

Server address ( 208.240.190.100) and client ( 210.220.160.48). We are having some problem in the IPTV traffic. It stucks sometimes and sometimes there is a delay in video . Below mentioned is the tcp ...
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20 views

Receiving Acknowledgements of transmitted packets in ns3

I want to implement sliding window protocol (go-back-N) in ns3. For that I need a way to receive acknowlegments for the current window packets. How can I do it? I know TCP in principle has ...
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1answer
33 views

How many TCP connections are required to download a file though ftp?

Regardless of which mode is used (active or passive mode), the initial connection is done on port 21 (command port). Then a second channel starts (data port) for exchanging the files/data. Each of ...
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1answer
24 views

Random intercontinental TCP streams are slow

I have a home server in New Zealand and a remote server in Amsterdam of the following configuration: I have a simple test script: #!/bin/bash for i in `seq 1 20`; do scp root@remoteserver:~/...
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3answers
202 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 ...
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21 views

How web sockets avoid creating congestion? [duplicate]

My idea about web socket connection is that when a handshaking is complete between a client and the server, the connection is not released and kept open(accross all the hops in between?) for ...
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2answers
40 views

Is it possible for my own application to use port 20 and 21 but not for FTP purposes?

Basically, my question is that for these official ports, can I still let my own application use these ports for other data exchange purposes? What could be the downsides if I choose to do so?
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1answer
1k 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. ...
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1answer
50 views

Questions about TCP packets

I am currently in college learning about networks, and I just wanted to make sure that I understood part of the TCP correctly. The question is "What does TCP use to reassemble packets in the correct ...
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0answers
30 views

What could block two simultaneous connections on one device to the same IP/port? [closed]

My company develops and sells a system where one or more client devices are deployed in the customer's network, and they establish two websocket (TCP) connections on port 443 to the cloud server. ...
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1answer
70 views

TCP connection question

Let’s say I have 4 ethernet interfaces getting IP addresses via DHCP. I make a TCP connection to a TCP server via one of the IP addresses on a certain ethernet interface. After the connection is ...
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1answer
38 views

Load-balancing one VPN-connection over multiple WANs

My internet connection will be provided by 4 different WANs (each 250 Mbit down, 100 Mbit up), which should be load-balanced to one 1 Gbit connection (full duplex, most likely ethernet (should be ...
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0answers
19 views

The amount of new data to send during Fast Recovery

The step 5 of Fast Retransmit/Fast Recovery algorithm in RFC 5681 says the following: When previously unsent data is available and the new value of cwnd and the receiver's advertised window allow, a ...
2
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1answer
52 views

If we can calculate RTT using timestamps in TCP options then why do we use the value of the backed off timer to compute next RTT in karn's algo?

I am new to learning networking concepts. This might be stupid question but please resolve this doubt. Thanks in advance.
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1answer
21 views

Are TCP 'ACK's sent per hop or per complete source-destination traversal?

Looking briefly at a TCP transmission-related youtube video: https://www.youtube.com/watch?v=GfpThGUvbrM, I see that 'ACK's are sent per hop? Is this the case of all TCP transmissions? Are there ...
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1answer
30 views

Whether every TCP packet have a Ack Reply?

The TCP Acknowledgements you see in the diagram's green arrows, have ACK numbers separated by 3000(two 1500 bytes). I have a question, why the Ack number is separated by two packets? Or is it just ...
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1answer
108 views

What is the relationship between throughput and latency

Looking at the structure of a TCP packet, such as discussed here: What is the internal structure of a mobile phone call packet/datagram?, this indicates that a TCP packet size is 192 bytes excluding ...
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1answer
22 views

Client drops packet from server when SNAT is not enabled at Load Balancer

I understand that one reason we use SNAT on a load balancer for incoming requests is so that the response packet from server will go through the load balancer, where the source IP of returning packet ...
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1answer
41 views

How TCP and firewall handle security?

I'm a newbie in networking, still don't quite understand about security. Let's say a person A uses TCP to establish a TCP connection with a server. And there is a hacker B who is sniffing, so B ...
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1answer
76 views

Can I force a higher TCP segment size with netcat?

I'm using netcat to send random data from A to B, both Linux machines on Ethernet networks, with a router in the middle. For pedagogic purposes I'd like to force IP fragmentation on the router (Cisco ...
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1answer
158 views

Linux TCP stack repeatedly sends “TCP window update” without acknowledging any data

My company is developing its own TCP stack for low-latency purposes and one of the tests involves running 128 instances of ncat on Linux 4.11 to listen to ports 55000 through 55127 and sending data in ...
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1answer
90 views

How IP datagram know its upper layer protocol?

Hi I'm a newbie in networking, I just want to know how IP datagram know its upper layer protocol is TCP or UDP? I know there is protocol field inside the IP datagram header that can tell the layer ...
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2answers
128 views

What are the differences between TCP iRTT and ICMP Ping?

I’m attempting to estimate latency between my PC and any servers/clients it interacts with. I don’t want to use Ping for various reasons (requires both ends to allow it, would require additional ...
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3answers
317 views

difference between ip checksum and tcp checksum

If an error on a packet occurs on a router, who does detect the error, IP checksum or TCP checksum? I have understood that the ipv4 checksum detects errors only inside the ip header and the tcp ...
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2answers
311 views

How to determine whether files are downloaded serially or in parallel using Wireshark?

In the http-ethereal-trace provided in the link below there are three HTTP GET request.The 2nd and 3rd request downloads a GIF and JPG format image recpectively.How can we determine wether the two ...
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0answers
25 views

Setting up a GPS TCP server [closed]

I am working on a project where we are using a GSM modem with built in GPS system. The modem has setting to send GPS signal NMEA format to a remote TCP server. Can someone consult on where should i ...
6
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1answer
129 views

Is a FIN only packet legal?

It would be convenient to mark TCP packets with just the FIN flag set, as an intrusion (without tracking the reply). I have always assumed that a FIN without an ACK, while rude and rare, is legal, ...
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38 views

Wireshark editcap create a tcp.payload file

I want a file of just the payloads from a 5min. tcp exchange between two hosts. I believe I can use Wireshark to just capture those packets which contain a tcp.payload. But after that, I believe I ...
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2answers
53 views

What are the resources that the server allocates to a client when it receives a TCP SYN request before receiving the ACK? [closed]

So lets say someone sends a lot of SYN requests to a server by spoofing IP, before receiving the ack from the client, does the server reserves the connection's Window size in its memory? if not, then ...
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1answer
62 views

Can TCP session be closed by the server depending on the packet content?

I am analyzing a pcap of command-and-control traffic caught during execution of a malicious file. First, a DNS request for a malicious domain was sent and after response is received and TCP connection ...
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3answers
96 views

Do OSI and TCP/IP models use the same protocols?

OSI is known for using hundreds of protocols to do its job. Both OSI and TCP/IP have Transport and Network(Internet) layers where TCP and IP protocols work respectively. It is clear that TCP/IP model ...
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2answers
170 views

If TCP is a reliable data transfer method, then how come its checksum is not 100% reliable?

So in the networking book by Kurose, we define UDP as a unreliable method because it might not detect errors and therefore transfer a corrupted packet or transfer the data without the order so its ...
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1answer
16 views

IP packets get queued in intermediate routers and can delay their delivery to the destination?

TCP segment go inside IP packets,there are many problems IP packets get queued in intermediate routers and can delay their delivery to the destination?
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1answer
32 views

IP packets can get dropped with TCP payloads?

TCP segment encapsulate it IP payload,if some way ip packet is lost in transmission. some time IP packet will be fragmented, i ask if this one fragment part will be lost in transmission.how can fix ...
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3answers
65 views

How does any program identify the protocol header next from TCP?

I need to know how does wireshark or any other program knows the protocol next from TCP. I mean, for instance: The Ethernet layer has a field named Type which carry the IPv04 The Internet protocol ...
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1answer
34 views

tcpreplay packet flooding?

I have limited networking knowledge so bear with me here on this explanation... In my companies datacenter we have some devices that run tcpreplay traffic and usually, there are no issues as the ...
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1answer
57 views

Is there anything inside the application layer in the three way handshake phase?

So is the application layer of TCP handshake packets empty no matter what the protocol is? and when the first packet of TCP handshake(phase 1) arrives at the server, which process does the server ...
3
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1answer
75 views

Is the first segment which is sent by the client in the 3 way handshake counted in the tcp congestion control?

So lets say we want to make a TCP connection with a server since in TCP we double the sending segments(the number of segments we send or window) after receiving the acks because of tcp congestion ...
2
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1answer
140 views

End-to-End delay

I’m working through questions from computer networking top down approach and was hoping to get some clarity on the end-to-end delay calculation. At this stage we are not considering processing, ...
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3answers
82 views

Do TCP implementations retransmit bytes or segments?

The sequence number and acknowledgement number in the TCP header is specified to contain byte counts. However, a lot of resources, including RFCs, say that "lost segments are retransmitted" instead ...
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1answer
109 views

Wireshark capture only TCP packets with the RST flag set

I'm quite new to networking and I got stuck while reading "Practical Packet Analysis: Using Wireshark to Solve...". On page 61 it is written: A common scenario is to capture only TCP packets ...
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21 views

Is there a retransmission timer for each segment of TCP? if not, why? [duplicate]

So if there is only timer for all of the segments of our connection, in this case lets assume timeout timer is 1.01 sec, and we send 10 packets at the same time then if we have only 1 timer and that ...
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1answer
162 views

Is there any TCP segment that both of its SYN bit and ACK bit are 0?

So i read this somewhere that there is no such TCP segment and 0 for both of SYN and ACK is not possible, and i wanted to check whether its true or not if the segment is not the first segment of the ...
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1answer
118 views

Is this a normal TCP retransmission pattern?

Our organisation's desktop computers have been performing not satisfactorily during their accessing of network resources. Out of suspicion, I perform a TCP retransmission statistics. Below picture is ...