Sierra Wireless WISMO218 User Manual download pdf (Page 54)

WA_DEV_W228_UGD_002 Rev 003 Page 54 of 78

WISMO228 TCP/IP AT Commands

Manual

 +CME ERROR:3 will be received when GPRS bearer is used

 no response is received when GSM bearer is used

To switch the WISMO

back to DATA mode, AT+WIPDATA=x,x,x should be used instead of ATO.



WISMO

is switched back to DATA mode.

Note that un-mapping a socket using the +WIPDATA command with <send size> and <wait time>



Time Out Mechanisms to Know the State of the Peer TCP Socket

In a TCP server-client connection between two remote devices, if the peer socket is closed down

abruptly (e.g. powered off) the peer TCP socket does not get any indication message. This is normal

behavior. The TCP protocol uses a timeout mechanism to check the state of the TCP sockets in a TCP

socket connection. According to this mechanism, to know the state of the peer TCP socket, the data

needs to be sent and wait for the acknowledgement within a specified time period. If the

acknowledgement is not received within the specified time out period then the data is retransmitted.

But if the time out occurs before receiving the acknowledgement then it implies that the peer TCP

socket is closed.

TCP Timeout Period = function (R, N)

Where,

R = Round trip time. This is the time for a TCP packet to go to the

remote TCP socket and the time to receive the acknowledgement

by the transmitter TCP socket. The typical round trip time is 1

second for GPRS.

N = Number of retransmissions allowed before the time out happens.

Hence, the typical timeout period is 10 minutes depending on the network and also the peer TCP

socket localization.

Data needs to be sent to know the state of the peer socket. If acknowledgement is not received within



Please note that the retransmission of the data to the peer TCP socket within the timeout period is

managed by the TCP/IP stack.

Packet Segmentation in TCP Socket

The parameters used for packet segmentation can be configured using the +WIPDATA or the

+WIPCFG command. If it is not configured using the +WIPDATA command, then the values already

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Sierra Wireless WISMO218 User Manual Page 54