C / C++ / MFC

19-Jan-09 23:46

As per google, MTU(Maximum transmission unit) can have maximum value of 1500 bytes but I am sending more then 1500 bytes data over socket from one application to other(on differnet m/c).It is going fine. I have tried up to 3500 bytes.
Please tell that what is the maximum size of MTU and how can I find out?

Thanks in advance.

Regards,
Vishal Soni

Maximilien20-Jan-09 0:46

Maximilien

20-Jan-09 0:46

what's MTU ?

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Vishal Kumar Soni20-Jan-09 0:50

20-Jan-09 0:50

Maximum transmission unit

Code-o-mat20-Jan-09 2:15

Code-o-mat

20-Jan-09 2:15

The MTU effects only packet size. You can use send specifying bigger buffers as the MTU, but -i belive it's TCP's job- TCP will cut your data into ~MTU sized packets, send that over, and the receiver side will put the fragments together to "recreate" your data. Or am i missing the point here?

> The problem with computers is that they do what you tell them to do and not what you want them to do. <

Vishal Kumar Soni20-Jan-09 2:41

20-Jan-09 2:41

I am trying to send 3500 byts.On the receiver side,I have not implemented the code to take care of fragmented packets.So both client and server application have not functionality to deal with fragmented packets.
Without this,I am able to send and receive more then 1500bytes but as per MTU,it should not get more then 1500 bytes.
So there is lot of confustion related to MTU? In which case it is linked to TCP/IP send/receive size.

Thanks and Regards,
Vishal Soni

CPallini20-Jan-09 3:05

CPallini

20-Jan-09 3:05

Vishal Kumar Soni wrote:
So both client and server application have not functionality to deal with fragmented packets.

That's fine, since TCP/IP does it for you.

Vishal Kumar Soni wrote:
Without this,I am able to send and receive more then 1500bytes but as per MTU,it should not get more then 1500 bytes.
So there is lot of confustion related to MTU? In which case it is linked to TCP/IP send/receive size.

Possibly packet fragmentation is an internal detail, hidden to the application layer.
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Stuart Dootson20-Jan-09 3:10

Stuart Dootson

20-Jan-09 3:10

Vishal Kumar Soni wrote:
So both client and server application have not functionality to deal with fragmented packets.

Your code doesn't, but the code **you call** does. I bet your code doesn't perform checksums on the data you send either - doesn't mean that doesn't happen (the ethernet layer will do that). I bet your code doesn't work out which computers your data should go through to get between client and server either - again, that doesn't mean that it doesn't happen.

Vishal Kumar Soni wrote:
So there is lot of confustion related to MTU?

Not really. Look at Wikipedia's page on MTU[^] - it quite clearly says that the MTU is the maximum size of data packet that can be transmitted by a layer of a communication protocol. Looking at the table of MTUs on that page, you can see that the MTU size depends on the transport you're using. Imagine you have this link to your server:

Client <-- <small>Wireless (802.11)</small> --> Gateway <-- <small>Ethernet</small> --> Gateway <-- <small>FDDI</small> --> Server

There are three different transports with three different MTUs (802.11=2272 bytes, Ethernet = ~1500, FDDI = 4500). Without an underlying layer that automatically adjusts for those different MTUs, your code would have to handle it all.

As ever with networking questions, I would recommend you download and become familiar with the IBM Networking Redbook[^].

Code-o-mat20-Jan-09 3:14

Code-o-mat

20-Jan-09 3:14

As ^CPallini said, you don't need to fiddle with fragmentation. You just need to Send and Recv, fragmentation is done by the TCP/IP layer, also it ensures you that you get your data in the same order you sent it, so don't worry about "puttinng your fragments together in the right order" on any side.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> Life: great graphics, but the gameplay sux. <

Vishal Kumar Soni20-Jan-09 6:00

20-Jan-09 6:00

Thanks for reply.
This problem started from live system at customer side.Sender application is sending 1800 bytes on socket but reciever side is receiving only 1460 bytes.Then one of my senior colleague asked me that it MTU problem so we need to change our implemataion.

Randor 20-Jan-09 7:09

Randor

20-Jan-09 7:09

Vishal Kumar Soni wrote:
Then one of my senior colleague asked me that it MTU problem so we need to change our implemataion

Hi Vishal,

I have read the other responses and mostly agree with them for 99.9% of engineers. However there are valid reasons why some network engineers choose to enable a Large MTU Network[^]. By reducing SYN/ACK cross-talk you can significantly reduces network overhead and consequently increase network throughput. There are essentially two ways to improve TCP performance... one is by increasing the MTU and the other is enabling RFC-1323[^] known as the TCP window scale option.[^]

The answer to your question is that the MTU is generally "Auto-Discovered[^]" by default. You can disable this option and enforce a specific maximum transmission packet-size, however... if there is ONE router which cannot handle the oversized packet, it will send back an ICMP error message and cause the packet to resent in smaller chunks... this is known as packet fragmentation and is very harmful for throughput.

Best Wishes,
-David Delaune

Vishal Kumar Soni20-Jan-09 8:17

20-Jan-09 8:17

Hi David,

Thanks for information.
According to previous discussion, we can send more then 1500 bytes over TCP/IP socket connection without caring the MTU size.At application level we don't need to implement fragmenation and defragmentaion.
So I can continue with this?

Regards,
Vishal Soni

Randor 20-Jan-09 8:50

Randor

20-Jan-09 8:50

Vishal Kumar Soni wrote:

we can send more then 1500 bytes over TCP/IP socket connection without caring the MTU size.At application level we don't need to implement fragmenation and defragmentaion.
So I can continue with this?

Yes, the application level should generally be designed to fuction with disregard to packet size.

Best Wishes,
-David Delaune

Vishal Kumar Soni20-Jan-09 9:11

20-Jan-09 9:11

Thanks David!

Regards,
Vishal

Vishal Kumar Soni23-Jan-09 10:32

String displayed distorted in RTL view

23-Jan-09 10:32

An update to this problem.
As we discussed in this thread that if we send data more then MTU size then it is supposed to handle by TCP/IP protocol.At application level,we don't need to anything.

I think lot of things depends upon network adapter setting.

So I tried to find out that why it is not working on two m/c where both client and server applications are running.Both m/c having windows 2003 server and having broadcom network adapter.
In broadcom network adapter there is proprty "LSO & Jumbo frame off". By default this property has value "LSO enabled and jumbo frame off". By changing this property to "LSO disabled & jumbo frame 3000",applications are able to send/receive the data more then 1500 bytes. but some times it is still failing.Sometimes it is able to send/receive ony 536 bytes.
Could you please tell the reason?

Thanks and Regards,
Vishal Soni

Alex@9C19-Jan-09 23:42

Alex@9C

19-Jan-09 23:42

I have displayed a messagebox with MB_RTLREADING flag.
The string that i tried to display is some thing like: "Name(First Name)"
However I am getting the display of "(Name ( First Name"

The syntex used for the messagebox was as follows:
MessageBox(NULL,"Name (FULL NAME)","good",MB_RTLREADING );

Please suggest what setting i am missing?

CPallini20-Jan-09 0:35

CPallini

20-Jan-09 0:35

Possibly you're missing this part of the documentation [^]

MB_RTLREADING
Displays message and caption text using right-to-left reading order on Hebrew and Arabic systems.

Alex@9C20-Jan-09 0:49

Alex@9C

20-Jan-09 0:49

Hi
It is treating closing bracket as the line terminatior.
This can be understood by this example.
Source string: Name (First Name).
Displayed in the RTLREADING: .(Name (First Name

However

Source string: Name (First Name) is Ok.
Displayed in the RTLREADING: .Name (First Name) is OK

What i want is
Source string: Name (First Name).
Displayed in the RTLREADING: .(ame (First Name)

I need suggestion for displayed text in the above stated format.

David Crow20-Jan-09 8:27

David Crow

20-Jan-09 8:27

piyush kumar tewari wrote:
I have displayed a messagebox with MB_RTLREADING flag.

Which is not the same as having right-justified text.

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Alex@9C22-Jan-09 18:09

Alex@9C

22-Jan-09 18:09

If you mean to say that the MB_RTLREADING is not the appropriate flag to use, then what can be the other options to try in this situation?