1-way audio

[RL5901]

CUCM version 11.0*

Gateways (MGCP) two Cisco 3845 ISR* providing a connection through PRIs, located at the main site

Conditions: 

• Called Party = internal number
• Calling Party = external number
• 1-way audio condition = internal Called Party is unable to hear external Calling Party
• Occurs intermittently (example 1 in 10 calls or so)
• across multiple locations (at remote sites and at the main site) 
• occurs over either Cisco 3845 ISRs

Details: 

Our locations (main and remote) are minimally staffed due to the pandemic. The problem may be more widespread than we know because of the limited number of end-users at the sites. 

Our IT started receiving reports 2 weeks ago that calls from external calling parties sometimes could not be heard. External calling parties could hear the internal called party (1-way audio). We have run a pcap from a phone at one of the remote sites when we thought it was isolated there but have received new reports from other sites, including the main site, since that time. 

*Note - because of a budget crisis we have not had funds to upgrade our CUCM nor replace our ISRs and have no TAC support. We are hoping to have the budget in the upcoming fiscal year. So we are very aware that our voice infrastructure is out of support. 

[Nithin Eluvathingal]

Could you share the output of show controller E1 or T1, to verify if there is any errors.

i hope you have verified the network reachability. Most common reason for one audio is network reachability  issue.

Make sure that your gateway can ping all you phone subnet and vice Versa.

have you configured network clock and network participate Commands on gateway ?

[RL5901]

I am able to ping the phone we tested with from both gateways. I've attached the information you asked for. 

There have been no configuration changes to either gateway (verified via Prime). There have been no audio problems until quite recently (actually started about 1.5 weeks ago). 

[Nithin Eluvathingal]

When checking reachability , you need to ping both ways. From phone to gateway and gateway to phone.

is there a firewall in between the gateway and phone subnet ?

From the attachment, i don't see any errors on your PRI, if you are sure that your gateway and phone can talk eachother. I will suggest to open a ticket with your TSP.

[RL5901]

I would think that a firewall would block all of the time, not intermittently. But we do not have a firewall between the gateway and the phone subnet. 

In the pcap, the CUCM sets up the call and hands off the RTP stream to the gateway and the phone. But no audio comes in from the gateway side. 

I'm waiting on the next call example from one of the 3 sites that are minimally staffed that reported the problem. Then I will open a ticket with the carrier and provide the call example. They may push back, as they always do. 

[Adam Pawlowski]

Check if there’s some firewall between the gateway and the UCM which is mangling your traffic to the gateway , assuming the firewall has an ALG for your trunk protocol. 

[RL5901]

Curious. The problem was intermittent but was reliably affecting around 4 to 6 calls out of many throughout the day for 3 sites. The day before I posted this problem I tried to run debugs on one of the gateways and it became unresponsive (hung). It had to be manually powered down and back up again. It had been up for over two and a half years. I've reached out to the groups of people who reported the 1-way audio problem and they said they have had no 1-way calls since. 

[RL5901]

Update.  The problem turned out to be on the carrier end (their "facility" which they repaired).