Network parameters
A converged network using one or more G700 Media Gateways must meet a number of requirements to ensure voice quality. VoIP applications can yield poor results on data networks that otherwise run well.
The critical factors affecting VoIP quality are delay, jitter, and packet loss. Avaya recommends these minimum network requirements:
- Network delay: less than 50 milliseconds between endpoints.
- Network jitter: less than 20 milliseconds between endpoints.
- Network packet loss: 0.2% or less between endpoints.
Avaya also makes these general recommendations for adequate Quality of Service:
- An appropriate Class of Service (CoS) mechanism to tag voice packets and give them priority over data packets. Switched networks should use IEEE 802.1p/Q. Routed networks should use DSCP (DiffServ Code Points). Mixed networks should use both. Port priority can also be used to enhance DiffServ and IEEE 802.1p/Q.
- A fully switched network that allows full duplex and full bandwidth for every endpoint. While VoIP applications can work in a shared network with hubs or busses, switched networks ensure higher voice quality.
- The Avaya Network Assessment Services for IP Telephony Offer from Avaya, Inc. Contact an Avaya representative or authorized dealer for information on the Offer that fully reviews and evaluates your network. For more information on the Offer, see Network assessment services.
- VLAN. Placing voice packets and data packets on separate VLANs (subnets) prevents data traffic from competing for the same bandwidth as voice traffic. For more information, see VLANs.
Avaya urges caution with these network practices:
- Network Address Translation (NAT). Most implementations use VoIP endpoints behind NAT because H.323 messages (the protocol carrying voice information) may contain several instances of the same IP address and NAT may fail to locate and translate all of them. For more information, see Network address translation.
- Analog Dial-Up. Converged network upstream bandwidth is limited to a maximum of 33.6 K and in most instances is less. The result is insufficient bandwidth for analog dial-up connecting two locations, which may operate at up to 56K. Some codecs and networks may provide acceptable connections, but evaluate each connection individually.
- Virtual Private Network (VPN). Significant delay is inherent in some VPN products due to encryption, decryption, and additional data encapsulation, though some hardware-based products encrypt at near wire speed and may be used. If the VPN runs over the Internet, voice quality cannot be guaranteed unless delay, jitter, and packet loss meet the requirements above. For more information, see VPNs.
Each of these factors affecting VoIP performance and several others are discussed in more detail below.
