All CudaTel Communication Servers with remote phones beyond the local network of the CudaTel.
With using a mobile device or provisioned hard phone that is outside the local network of the CudaTel Communication Server, there are a number of outside factors that can affect quality of service. This article outlines several common problems associated with these deployments.
Note: Barracuda Networks is not responsible for call quality issues that are upstream from the CudaTel Communication Server. (i.e. audio that has call quality issues FROM the endpoint or provider TO the CudaTel). If you are a end-user who has a network managed by another party, please contact your network administrator or internet service provider for assistance.
Mobile Devices connected via carrier data:
- Signal strength/quality: Signal strength and proximity to cell tower site can have a significant effect on jitter and packet loss. Building construction and other environmental factors also play a role in signal strength.
- Type of data transmission standard employed by carrier and equipment: 2.5G, 3G or 4G data standards have varying maximum theoretical bandwidth limitations. Please consult your carrier for more information.
- Carrier Backhaul Network Topology and Enterprise Network Address Translation: Oftentimes, carriers employ enterprise NAT, Application Layer Gateways (ALG) or multiple firewalls for internet-bound traffic from your mobile device to the internet. These complex network topologies can oftentimes result in poor voice-path quality of service, failure to register, and failure to maintain a call longer than thirty seconds.
- Rate limiting, throttling, cell site congestion and network policy: It is common industry practice to see cell phone providers impose rate limiting and throttling based on data consumption per billing cycle or based on cell site congestion. These practices can have a significant effect on quality of service for VoIP/SIP calls. It is not uncommon for cell phone providers to completely block SIP traffic on their networks. It is not valid to compare the quality of circuit-switched voice calls (as these traverse the carrier's internal network) to VoIP calls to a SIP-based PBX on the public internet, such as the CudaTel Communication Server, as neither of these calls traverse the same end to end path in the carrier's network. Please consult your carrier for more information on these practices.
- Misconfiguration of soft phone: Please ensure you set up your soft phone client keeping these common mistakes in mind:
- Use of an outbound proxy: The CudaTel Communication Server does not support the use of outbound SIP proxies.
- Signalling Port: Please ensure that you use port 5065 UDP or TCP when remotely registering your device. Using port 5060 will result in a '405 Method Not Allowed' response.
- Username, Auth Username, and Password: Please ensure that you use the correct configuration as outlined on the Registration Information page for each Generic SIP device/soft phone configured.
- DTMF Method: Please use RFC2833 as the DTMF transport method
- Encryption: SIPS, SRTP, and ZRTP are not supported at this time.
- Keepalives: If you frequently encounter loss of registration, please send SIP OPTIONS packets to the Cudatel Communication Server. This will force the NAT device/firewall/gateway on the remote network to keep the NAT pinhole up longer.
- NAT Traversal and ALGs: If you are traversing a NAT firewall, please ensure that you use a method like STUN or ICE on the soft phone client so it is aware that there is NAT firewall in the path to the Cudatel. Please disable any ALG on any NAT device as well unless specifically requested by Barracuda Networks Technical Support. For more information on what an ALG is please visit this TechLibrary article: SIP ALGs and the CudaTel Communication Server
- Note: Barracuda Networks Technical Support will assist you to its best effort in configuring your soft phone client, but we cannot guarantee that all configurations and vendors are supported.
If you are connected via Wi-Fi from your mobile device or are using a provisioned hard phone connected to a consumer-grade internet connection:
Many of the same problems that affect carrier data connections like the ones listed above also affect calls via Wi-Fi. Improper access point configuration, firewalls, ALGs, and poor signal strength are most often the causes of call quality and establishment issues.
- Application Layer Gateways: Please disable any ALG on any NAT device for any kind of remote phone, whether it be a mobile device or provisioned hard phone unless specifically requested by Barracuda Networks Technical Support. For more information on what an ALG is please visit this TechLibrary article: SIP ALGs and the CudaTel Communication Server
- VPN Tunnels: VPN tunnels can affect VoIP quality of service significantly. Factors such as the amount of users connected via the tunnel or the amount of pre-existing data on link can cause jitter and packet loss. Older VPN aggregators frequently do not have the necessary throughput to handle UDP RTP traffic on the scale of a VoIP call. It is critical that when utilizing a VPN tunnel, whether it be client-to-site or site-to-site, that it is capable of a sufficiently high packet-per-second rating, the bandwidth of the tunnel is sufficient for the amount of VoIP calls traversing the link, and that QoS policies are set up to prioritize RTP/SIP traffic to/from the CudaTel Communication Server.
- Type of internet connection: Latency and factors inherent in the medium used on the remote network are important. For example, using a satellite uplink has significant latency (upwards of 500 ms on average) which can introduce jitter into the RTP stream, but not necessarily packet loss.
- For an in-depth article on how jitter and packet loss affects a voice call please review these articles:
- Bandwidth calculators and test tools:
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