Availability due to power outages
During a typical power outage, VoIP becomes unavailable because VoIP devices (computers,
routers, adapters) usually rely on a power source to function. Traditional phone lines are usually
still available during such an outage, which is a major advantage in an emergency. Ultimately, it
may be necessary to use an uninterruptible power supply (UPS) with a VoIP installation if
connectivity is desired during a power outage or some other kind of emergency.
Availability due to bandwidth
VoIP communication nearly always requires a high-speed (broadband) internet connection for
reliable functionality. Even given typical broadband connection speeds, though, service
interruptions or degradation of quality is possible due to high internet traffic. For example, if you
are trying to place a VoIP call while other people are using a lot of bandwidth on the same
internet connection, the sound quality of your VoIP call or general VoIP availability may be
affected.
911 services
911 services are not guaranteed with a basic (VoIP to VoIP) setup. However, it is available with
many of the interconnected services that extend VoIP connectivity to traditional landlines. You
should not assume that 911 services are present and working (even with interconnected VoIP
services) but should consult with the terms of your service agreement. The FCC has described
some of the challenges of VoIP services and has provided tips for VoIP subscribers. For more
information, visit: http://www.fcc.gov/cgb/consumerfacts/voip911.html.
Threats / Risks
Many of the threats associated with VoIP are similar to the threats inherent to any internet
application. Internet users are already familiar with the nuisance of email abuse in the form of
spam and phishing attempts. VoIP opens yet another pathway for these annoyances, which can
lead to spam over internet telephony (SPIT), spoofing, and identity theft. Additionally, the
confidentiality of VoIP conversations themselves has come into question, depending on service
type or VoIP configuration.
Spam over internet telephony (SPIT)
As VoIP usage increases, so will the pesky marketing strategies associated with it. Perennial
annoyances like telemarketing and spam have been plaguing consumers and internet users for
years. A new sort of hybrid of these two concepts is SPIT, or spam over internet telephony. Like
email spamming, sending commercial messages via VoIP is fast and cheap. Unlike traditional
telemarketing, though, VoIP offers the potential for large volumes of unsolicited calls, due to the
wide array of tools already available to attackers on the internet. Telemarketers could easily send
Produced 2006; updated 2008, by US-CERT, a government organization. 3