History of telephone hacking
The telephone network has historically been a target of hackers. The term “phreaking”, the act
of telephone hacking, became prevalent in the 1970’s and 80’s. A subculture of telephony
hackers developed methods to illegally control telephone networks. The intent of these
intrusions varied substantially. Some simply viewed phreaking as a hobby, with no real intent to
do damage. Others gained illegal access to bypass toll charges and obtain free long distance
service. Last, the aim of certain individuals is more devious in nature. Activities such as call
diverting, rerouting, and eavesdropping are all security issues of the PSTN network.
Unfortunately, these same issues exist within VoIP telephony.
An introduction to VoIP
VoIP leverages the internet as an infrastructure for voice communications. Data packets carry
voice in the same manner as general internet traffic. This configuration is more efficient than the
PSTN network. VoIP can use one shared broadband circuit for many packet switched services;
data, voice, and even video teleconferencing. Within an office environment, VoIP
implementations often converge with the existing data network. While this consolidation
reduces costs, it also places greater performance and security demands on the network switches.
One cabling infrastructure, and one set of switches, manages network connectivity for both voice
and data services. Some networks further collapse services such as wireless and video
teleconferencing into the switch stack. Sophisticated layer three switches identify devices either
as phones, computers, or wireless access points, and then assign these devices to the appropriate
virtual local area network. Once on the correct virtual LAN, they obtain an IP assignment to the
correct network. This device categorization is important for a number of reasons. Assigning
devices to virtual networks applies security parameters distinctly based on network type, a good
security practice. Additionally, categorizing devices allows the switch to prioritize one group’s
traffic over another, a process called quality of service (QoS), which is very important in
protecting call quality in a converged system (Stredicke, 2007).





























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