Source record · tier 2 current vendor documentation
Troubleshooting Guide for Cisco Unified Communications Manager Release 12.5(1) — Device Issues
- Publisher
- Cisco Systems, Inc. (www.cisco.com)
- URL
- https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/trouble/12_5_1/cucm_b_troubleshooting-guide-1251/cucm_b_troubleshooting-guide-1251_chapter_0100.html
- Published
- 2023-11-24
- Updated
- unknown
- Accessed
- 2026-09-16
- HTTP status
- 200
- License
- Cisco proprietary documentation, all rights reserved; no-redistribution; short excerpts and locators only
Source notes citing this source
- If a node will not register more than 5000 phones, the Maximum Number of Registered Devices service parameter is at its default and must be raised on each node. in context
- Phones power cycle or reset because of a TCP failure while connecting to Unified CM or a failure to receive acknowledgements to their KeepAlive messages. in context
- Unified CM Administration can show an incorrect device registration status if the Cisco RIS Data Collector service is not running or if network or DNS resolution problems prevent communication. in context
- On AS5350 and AS5400 gateways, voice-fastpath caches RTP stream information, so the logical channel is not updated after hold or transfer, causing one-way audio. The guide's fix is no voice-fastpath enable. in context
- On a Cisco IOS gateway, the backward voice path opens as soon as the RTP stream starts. in context
- Cisco's Unified CM one-way audio section is probably of limited direct use for a current SIP-trunk or SBC estate. Its remedies are IOS, H.323 and SCCP commands, while the SIP-era causes in this packet (SDP address, latching, hairpin deadlock) come from other documents. inferred in context
- The Cisco one-way audio guidance held here is in the Unified CM Release 12.5(1) troubleshooting guide, Device Issues chapter, last updated 2023-11-24. Its causes are H.323, SCCP and IOS-platform issues; none is specific to SIP trunks or SBCs. in context
- A Cisco IOS gateway does not open the forward audio path until it receives a Connect message (answer supervision) from the remote end. If answer supervision never arrives, the result is one-way audio. in context
- The same guide says the H.323 bind remedy can itself cause one-way audio on Cisco IOS 12.2(6), and gives bug ID CSCdw69681. in context
- When a Cisco IOS H.323 gateway has more than one active IP interface, the Unified CM 12.5(1) guide says to bind H.323 signalling to one source address with h323-gateway voip bind srcaddr, so the gateway always uses the same source address. in context
- Some Cisco IOS gateways, such as the VG200, have IP routing disabled by default, which the Unified CM 12.5(1) guide lists as a cause of one-way audio. The fix it gives is the global ip routing command. in context
- The guide gives minimum software for NAT to translate Skinny (SCCP) signalling for voice: Cisco IOS 12.1(5)T on IOS gateways and PIX firewall 6.0. If Skinny runs on a non-default TCP port, it also needs ip nat service skinny tcp port. in context
- Cisco's Unified CM 12.5(1) troubleshooting guide says RTP streams have no connection because they run over UDP, so traffic can get through in one direction and be lost in the other. in context
- When the gateway gets no answer supervision from the telco or switch, the guide's fix is voice rtp send-recv. It makes a Cisco IOS gateway open two-way audio as soon as the RTP channel opens, without waiting for Connect. in context
- For a softphone on VPN, the guide attributes one-way audio to the softphone choosing the wrong network adapter address. The fix is to set the VPN IP address in the softphone's Network Audio Settings. in context
- Cisco states that a Cisco IOS gateway does not cut through the audio path in the forward direction until it receives a Connect message from the remote end, that failure to receive answer supervision from the telco or switch therefore causes one-way voice, and that the voice rtp send-recv command establishes a two-way path as soon as the RTP channel opens. in context
- Cisco frames one-way audio as a call established from an IP station through a Cisco IOS voice gateway or as a toll-bypass call between 2 Cisco gateways in which only one party receives audio, and names an improperly configured Cisco IOS gateway, a firewall, and a routing or default gateway problem as possible causes. in context
- Cisco's canonical one-way audio guidance sits in the Unified Communications Manager 12.5(1) troubleshooting guide last updated 24 November 2023, and its remedies are written for H.323 signalling and Cisco IOS gateway commands. field report in context
- Cisco states that some Cisco IOS gateways such as the VG200 have IP routing disabled by default, that this leads to one-way voice problems, and directs the administrator to check for the global configuration command no ip routing before going any further. in context
- Cisco states that one-way audio, a conversation between 2 people where only one person can hear anything, does not actually represent a voice-quality issue, while covering it in the voice quality section of the troubleshooting guide. in context
- Where a Cisco IOS gateway has multiple active IP interfaces, parts of the H.323 signalling may reference different source addresses and Cisco names one-way audio among the resulting problems, with the remedy being to bind the signalling to a specific physical or loopback source address, and Cisco records a bug in IOS version 12.2(6) in which that remedy itself causes a one-way audio problem. in context
- Cisco states that because RTP streams have no connections and are transported over UDP, traffic may travel successfully in one direction but get lost in the opposite direction, which is the mechanism that makes one-way audio possible at all. in context
Cite this source record
APA
WarmTransfer. (2023, November 24). Troubleshooting Guide for Cisco Unified Communications Manager Release 12.5(1) — Device Issues. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-cucm-troubleshooting-1251-device-issues
BibTeX
@misc{warmtransfer-cisco-cucm-troubleshooting-1251-device-issues,
title = {Troubleshooting Guide for Cisco Unified Communications Manager Release 12.5(1) — Device Issues},
author = {{WarmTransfer}},
year = {2023},
url = {https://warmtransfer.net/knowledge/sources/cisco-cucm-troubleshooting-1251-device-issues},
note = {Cisco Systems, Inc. (www.cisco.com), accessed 2026-09-16}
}