Issues with sending from router to coordinator in transparent mode

I have one router and one coordinator configured to communicate in transparent mode. The router’s SM (Sleep Mode) is set to 0 (No Sleep), and the coordinator is set to broadcast (i.e. destination DH/DL=0x000000000000FFFF). Both XBees belong to product family XB3-24 and are installed with firmware Zigbee 3.0 100D.

The router can send messages to coordinator all right (though there is some fraction of second in latency, the coordinator still receives the strings of letter consistently):

(1) slowly keying in words letter by letter <– OK
(2) fast keyboard stroke or holding down a key <– OK
(3) paste a long string that is over 100 characters in length <– OK

When I do the same but from coordinator to router, except for (1) where the router receives the fully strings, the router would become unresponsive, often times skipping the entire message and only resumes working after 3-5 seconds of rest (not sending anything from coordinator to router).

The router never sleeps so I’m not sure why the transmission from coordinator to router is not as smooth or stable as that from router to coordinator. Hope someone can help explain what’s happening here or how I can fix this. Thank you.

All transmissions are done in XCTU’s console.

For Broadcast transmissions, you need to have a delay to allow the packet to be propagated thru the network. In your case where there is only the two modules, I would suggest using either Unicast addressing or use the 802.15.4 firmware option.

Unicast is where you set the DL and DH of the sender to match the SL and SH of the receiver.