.. index:: pair: group; MTU usage for TCP packets
.. _doxid-group__basic-mtu__tcp:

MTU usage for TCP packets
=========================

.. toctree::
	:hidden:

Check that TCP packets of full MTU size are sent and processed correctly.

Scenarios: X3-SYS04.



#. If **tx** is ``TRUE``, make sure that receive offloads are disabled on Tester interface, so that CSAP there will receive IUT packets not modified in any way.

#. If **tx** is ``FALSE``, make sure that TCP segmentation offload is disabled on Tester interface, so that CSAP sees packets there exactly as they are sent.

#. Set MTU on IUT and Tester interfaces to **mtu**.

#. Enable or disable Generic Segmentation Offload on IUT according to **gso_on**.

#. Enable or disable TCP Segmentation Offload on IUT according to **tso_on**.

#. Create a pair of connected TCP sockets on IUT and Tester.

#. Get payload size in MTU-sized packet from ``TCP_MAXSEG`` option value on IUT socket.

#. If **tx** is ``TRUE``, sender is IUT and receiver is Tester, otherwise - the other way around.

#. On the sender socket enable ``TCP_NODELAY`` option so that packets are sent as soon as possible even if they are small.

#. Create a CSAP on Tester to capture packets sent from (if **tx** is ``TRUE``) or to (if **tx** is ``FALSE``) IUT.

#. In a loop for **sends_num** times:
   
   * Send some data from sender, choosing its size randomly but according to **pkt_size**.
   
   * Check that receiver socket becomes readable.
   
   * Receive and check data on the receiver.
   
   * Obtain packets captured by CSAP, check that sizes of all the packets except the last one correspond to **mtu**.

Dmitry Izbitsky `Dmitry.Izbitsky@oktetlabs.ru <mailto:Dmitry.Izbitsky@oktetlabs.ru>`__



.. rubric:: Parameters:

.. list-table::
	:widths: 20 80

	*
		- env

		- 
		  Testing environment:
		  
		  * :ref:`env.peer2peer <doxid-group__env-peer2peer>`
		  
		  * :ref:`env.peer2peer_ipv6 <doxid-group__env-peer2peer__ipv6>`

	*
		- mtu

		- 
		  MTU to be set:
		  
		  * ``512``
		  
		  * ``1280``
		  
		  * ``1500``
		  
		  * ``1600``
		  
		  * ``9000``

	*
		- tx

		- If ``TRUE``, send from IUT to Tester, else - the other way around.

	*
		- gso_on

		- Should Generic Segmentation Offload be enabled on IUT?

	*
		- tso_on

		- Should TCP Segmentation Offload be enabled on IUT?

	*
		- pkt_size

		- 
		  Data size for **send()** call (in terms of MTUs):
		  
		  * ``less``
		  
		  * ``equal``
		  
		  * ``more``

	*
		- sends_num

		- 
		  How many times to send data:
		  
		  * ``100``