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 VoIP
technology still has a few shortcomings that have led some to believe
that it is not ready for widespread deployment. However, many industry
analysts predicted that 2005 was the "Year of Inflection," where more
IP PBX ports shipped than legacy digital PBX ports.
Implementation challenges
Because IP does not provide any mechanism to ensure that data packets
are delivered in sequential order, or provide any Quality of Service
guarantees, VoIP implementations may face problems dealing with
latency (especially if satellite circuits are involved), and jitter.
They are faced with the problem of restructuring streams of received
IP packets, which can come in any order and have packets delayed or
missing, to ensure that the ensuing audio stream maintains a proper
time consistency. This problem has been addressed by Ubicom with their
StreamEngine Technology.
Another main challenge is routing VoIP traffic to traverse certain
firewalls and NAT. Intermediary devices called Session Border
Controllers (SBC) are often used to achieve this, though some
proprietary systems such as Skype traverse firewall and NAT without a
SBC by using users' computers as super node servers to route other
people's calls. Keeping packet latency acceptable can also be a
problem, due to network routing time (buffering, switching) and
transmission distances (more relevant under satellite links).
DSL Internet access
VoIP requires broadband internet access. A sizable percentage of homes
today are connected to the Internet through DSL, which requires a
traditional phone line. Having to pay for VoIP in addition to both a
basic phone line and broadband internet access reduces the potential
cost benefits of VoIP. However, some regional telephone companies now
offer DSL service without the phone, thus saving you money when you
switch to VoIP. VoIP can also be combined with cable Internet access
and there are dozens of VoIP providers to choose from.
Reliability
Conventional telephones are connected directly to telephone company
phone lines, which in the event of a power failure are kept
functioning by back-up generators or batteries located at the
telephone exchange. However, household VoIP hardware uses broadband
modems and other equipment powered by household electricity, which may
be subject to outages. In order to use VoIP during a power outage, an
uninterruptible power supply or a generator must be installed on the
premises. Early adopters of VoIP may also be users of other phone
equipment, such as PBX and cordless phone bases, that rely on power
not provided by the telephone company.
Some broadband connections may have less than desirable reliability.
Where IP packets are lost or delayed at any point in the network
between VoIP users, there will be a momentary drop-out of voice. This
is more noticeable in highly congested networks and/or where there is
long distances and/or interworking between end points.
Emergency calls
The nature of IP makes it difficult to geographically locate network
users. Emergency calls, therefore, can not easily be routed to a
nearby call center, and are impossible on some VoIP systems. Moreover,
in the event that the caller is unable to give an address, emergency
services may be unable to locate them in any other way. Following the
lead of mobile phone carriers, several VoIP carriers are already
implementing a technical work-around. The United States government had
set a deadline, requiring VoIP carriers to implement e911, however,
the deadline is being appealed by several of the leading VoIP
companies. This is a different situation with IPBX systems, where
these corporate systems often have full e911 capabilities built into
the system.
A simple solution to this problem is to store the local emergency
numbers on speed dial which is usually even faster than having to be
transferred by the 911 operator.
Integration into global telephone number system
Whilst the traditional Plain Old Telephone System (POTS) and mobile
phone networks share a common global standard (E.164) which allocates
and identifies any specific telephone line, there is no widely adopted
similar standard for VoIP networks. Some allocate an E.164 number
which can be used for VoIP as well as incoming/external calls. However,
there are often different, incompatible schemes when calling between
VoIP providers which use provider specific short codes.
Single point of calling
With commercial services such as Vonage, it is possible to connect the
VoIP router into the existing central phone box in the house and have
VoIP at every phone already connected. Other services, such as Skype &
PeerMe, typically require the use of a computer, so they are limited
to single point of calling, though handsets are now available,
allowing them to be used without a PC. Some services, such as
BroadVoice provide the ability to connect WiFi SIP phones so that
service can be extended throughout the premises, and off-site to any
location with an open hotspot.. |
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