Q. How much bandwidth will I need to support VPIM?
A. This depends on many variables. Below are a set of assumptions and the bandwidth required based on these assumptions. Note that these assumptions may be high for many users who do not send many messages outside of the company, or for users in different time-zones and who will not have the same traffic peak, or for users who can wait a bit before delivering the message.
Traffic assumptions:
- 2 messages per day per subscriber.
- 20 second average message length.
- 20% (.2) of messages go to VPIM gateway to off system subscribers.
- 20% (.2) peak hour messages per subscriber.
VPIM assumptions:
- - VPIM uses 32Kbps G.726 voice encoding
- - MIME base64 encoding adds 33% to message size, giving 43Kbps (MIME with ESMTP would not add the 33%.)
- - MIME header adds about 1Kbyte per message (typically <0.05Kbps)
- - An average VPIM SMTP message (20 seconds) is about 108 Kbytes in size
In English these assumptions mean that the average subscriber sends two messages of twenty seconds in a day. Twenty percent of these messages go to subscribers not on the mail server via VPIM generating 108Kbytes of traffic. Twenty percent of the total system message traffic is generated during the peak hour.
Bandwidth requirements:
Based on the above assumptions -
- 1,000 subscribers = 80 VPIM messages per hour = 19.2Kbaud bandwidth during peak hour.
- 10,000 subscribers = 800 VPIM messages per hour = 192 bits per second (3 T1s).
Q. The VPIM specification contains some 'MUST HAVE' ESMTP commands that are not currently supported with regular e-mail servers available off-the-shelf. What is the name of a purchasable e-mail server that is fully VPIM compliant ?
A. The latest version of Sendmail is VPIM transport compliant. While it not support the optional binary transport mode, nor the pipelining, it does support the DSN, Extended Status codes, and SIZE which are the "MUST HAVE" parts of the VPIM specification. The mandatory ESTMP commands are necessary to provide the same level of service as is available in existing voice mail networks. Voice mail vendors should support the full set of REQUIRED extensions. In that mode, voice servers can pass messages between themselves with full functionality. When used with non-compliant transport services, obviously features will be lost.
