MO can't hear MT but MT can hear MO

Hello Experts,

Kindly elaborate.

In an IP based network on 2G, there is a situation where:

  • MO can’t hear MT
  • MT can hear MO

What causes this configuration wise?
What isn’t defined?

(Nokia BTS and BSC)

Admin note: this post was updated with image below.

Check Vlan IP.

Compare IPs defined in BTS with other sites,some IPs are missing in problematic site.

Audit IP configuration from BSC on ETPA.

Mean holding time can help you to find problematic sites, because users facing this issue will hang up the call sooner than normal.

Samples script to add missing ones:



First ZEFO:BCF:; to find ETGGID

And replace it in second command, here ETGGID was 3.

Inside the BCF group same VLAN id is used for the TRXSIG and CS/PS u-planes.

In this, is service IP, right?

Yes i think, just compare with normal sites to make sure.