SAS ITIdentify the Symptom First
Different quality problems have different root causes. Treating them generically wastes time.
| Symptom | Most Likely Cause |
|---|---|
| Choppy or robotic audio | Jitter or high latency |
| Words cutting out | Packet loss |
| One-way audio | NAT traversal and firewall |
| Echo | Acoustic echo cancellation issue |
| Call drops after 30 seconds | SIP timeout and ALG enabled |
Step 1: Measure Before You Fix
Run a VoIP quality test from the affected device or network segment. Target values:
| Metric | Good | Acceptable | Problem |
|---|---|---|---|
| Latency | under 50ms | 50 to 150ms | over 150ms |
| Jitter | under 10ms | 10 to 30ms | over 30ms |
| Packet loss | 0% | under 0.5% | over 1% |
Fix: Jitter
- Enable QoS on firewall and all switches
- Mark VoIP traffic as DSCP EF (Expedited Forwarding)
- Prioritise VLAN 50 (or equivalent voice VLAN) in switch config
- Increase jitter buffer on soft PBX if available
Fix: Packet Loss
- Check switch port error counters for CRC and frame errors
- Replace bad patch cable — always test before blaming software
- Check for interface duplex mismatch
- Check ISP stats for upstream packet loss
Fix: One-Way Audio
- Disable SIP ALG on router and firewall (most common cause)
- Open required RTP UDP port range in firewall
- Configure correct external IP on PBX if behind NAT
Fix: Calls Dropping After 30 Seconds
This is almost always SIP ALG rewriting SIP headers. Disable SIP ALG on your firewall first.
Fix: Echo
- Enable echo cancellation on PBX
- Reduce handset speaker volume slightly
- Confirm correct codec (G.711 preferred over G.729 for LAN)
Related: IP Telephony Dubai | Networking and Security Dubai
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About the Author
Reviewed by Mustafa Husain, Founder of SAS IT Services, with 10+ years of experience in IT infrastructure, networking, and security — alongside the same engineers who design, install, and support the work described on this site. SAS IT Services was founded on 22 February 2020 in Dubai and has since delivered 500+ projects for businesses across the UAE.
We specialize in Fortinet, Cisco, and Microsoft, among 17 vendor product lines we regularly install, configure, and support across networking, cybersecurity, CCTV, and cloud infrastructure — hands-on experience that informs the technical guidance in our articles.
Our work is independently rated 5.0 out of 5 from 17 verified Google Reviews. Every article is reviewed internally for technical accuracy before publishing and reflects practices we apply on real client deployments in Dubai and the UAE.
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