API packet received are mixed up

XBee & XBee Gateway ZNet 2.5
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1

Two end devices send API data packet to a router. When they send the packet alternately, every thing is ok. But when they send simultaneously, packets that router received are mixed up and corrupt.

Packet send:
end 1： 7E 00 18 10 00 00 13 A2 00 40 66 9B 34 FF FE 00 01 11 11 11 11 11 11 11 11 11 11 1D
end 2： 7E 00 18 10 00 00 13 A2 00 40 66 9B 34 FF FE 00 01 22 22 22 22 22 22 22 22 22 22 73

The router should receive as:
7E 00 16 90 00 13 A2 00 40 78 0E 9A FF BD 41 11 11 11 11 11 11 11 11 11 11 B3
7E 00 16 90 00 13 A2 00 40 76 EC E3 C4 34 01 22 22 22 22 22 22 22 22 22 22 E8

But now the received packet mix up as:
7E 00 16 90 00 13 A2 00 40 78 0E 9A FF BD 41 11 11 11 11 11 11 11 11 11 11 B3
7E 00 16 90 00 13 A2 00 40 76 EC E3 C4 34 01 22 22 22 22 22 22 22 22 22 22 E8
7E 00 16 90 00 13 A2 00 40 78 0E 9A FF BD 41 11 11 11 11 11 11 11
7E 00 16 90 00 13
7E 00 16 90 00 13 A2 00 40 78 0E 9A FF BD 41 11 11 11 11 11 11 11
7E 00 16 90 40
7E 00 16 90 00 13 A2 00 40 78 0E 9A FF BD 41 11 11 11 11 11 11 11 11 11
7E 00 16 90
7E 00 16 90 00 13 A2 00 40 78 0E 9A FF BD 41 11 11 11 11 11 11
…
What’s the problem?

2

Not sure how you are reading API Frames but it appears that you have a receive buffer problem.

3

ZNet is a old protocol, better performance can be achieved by using ZigBee modules.
You can migrate your modules to ZigBee using the following link, http://ftp1.digi.com/support/documentation/upgradingfromznettozb.pdf