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IP Telephony and QSIG Over IP
Pre-installation Guidelines
Strata CTX I&M 06/04 9-3
IP Telephony and QSIG
Over IP
Step 1: Perform a LAN Voice Readiness
Assessment
Deploying many IP telephones on a data LAN can have some unexpected pitfalls if the network
does not have the bandwidth and speed required to handle VoIP traffic. To prevent delay, jitter, and
data loss for VoIP traffic and retain the performance of your other business-critical network
applications a network Voice Readiness Assessment should be completed before installing VoIP.
Important! Voice Readiness Assessments are the responsibility of the installing TSD dealer.
Toshiba is not responsible for supporting problems which occur because the
network on which the IP telephones are installed does not meet VoIP packet
requirements.
Methods of Estimating Bandwidth Requirements
A “rule of thumb” way to translate voice packet use into worst-case LAN bandwidth requirements
is shown below. (This is no substitute for a professional Voice Readiness Assessment).
• When IP telephones use the G.711 CODEC with a packetization rate of 20 millisec. (best voice
quality), the bandwidth utilization rounds up to 115K bit/sec. per conversation.
• If the system has 100 IP telephones, multiple 25 simultaneous conversations by 115K bit/sec.
for an additional bandwidth requirement of 2.9M bit/sec. on the LAN.
Note The “25 simultaneous conversations” assume ¼ of the IP telephone users are talking at the
same time. This scenario is considered worst-case because the best quality CODEC (G.711)
is used as apposed to the G.729a which 29Kbps less bandwidth per conversation.
If installing IPTs on your LAN, Toshiba highly recommends downloading “A Handbook for
Successful VoIP Deployment: Network Testing, QoS, and More,” located at the time of this
printing at.http://www.netiq.com/products/vm/whitepapers.asp. Toshiba recommends reading this
document and making sure that you have:
• Tested Voice Over IP (VoIP) Call Quality
• Prepared your Data Network for VoIP, considering your needs for bandwidth, equipment
upgrades, network architecture, Quality of Service (QoS) and tuning, and classification of
traffic considerations.
CAUTION! If installing IP telephones remotely using cable or Digital Subscriber Lines
(DSL) Internet Service Providers (ISP) providers, Toshiba recommends
setting the telephone to use the G729a CODEC because upstream
bandwidth restrictions are usually imposed by the provider. Even if the
provider advertises an upstream rate is 128kbs, this bandwidth can still be
less depending on traffic conditions.