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Goals and Symptoms
What happens If the Inter-Packet-Gap between the Ethernet messages is too small,
Facts and Changes
If the Inter-Packet-Gap between the Ethernet messages is too small, it could cause the connection resources to be
Causes and Fixes
According to the IEEE 802.3 standards, an Ethernet Datalink layer must allow a minimum amount of time
before another message data packet can be sent. The purpose of the inter-packet gap is to allow enough
time for the Ethernet device to recover.
Before a new Ethernet message can be received by the Datalink layer of a device (i.e., TSXETY5103),
the resources that is being used from a previous conection must be cleaned up and reallocated. If the
Inter-Packet Gap is too small, the receiving Ethernet device device may not have enough time to perform the
clean up (This is a function within the PLC that must be solved at the end of each scan of the firmware.)
When this happens, new resources are allocated for the connection. When the resources are not properly
cleaned up, they cannot be reallocated to new incoming connections and are left hanging. As this behaviour
progress over time, the resources will eventually get used up and any new incoming connection will get refused.
To resolve the problem redesign the Ethernet TCP/IP driver to allow adequate time for the Inter-Packet Gap.
References: IEEE 802.3 Part 3: Carrier sense multiple access with collision detection (CSMA/CD)
access method and physical layer speci.cations;standard., page 21, section ' ;
Published by The Institute of Electrical and Electronics Engineers, Inc,; 3 Park Avenue,
New York, NY 10016-5997, USA; 8 March 2002, Print: SH94973.
1.4.147 Inter-Packet Gap (IPG): A delay or time gap between CSMA/CD packets
intended to provide interframe recovery time for other CSMA/CD sublayers and for
the Physical Medium. (See IEEE 802.3, 220.127.116.11.1 and 18.104.22.168.2.) For example, for
10BASE-T, the IPG is 9.6 µs (96 bit times); for 100BASE-T, the IPG is 0.96 µs
(96 bit times). "
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