Today I was asked by a
prospective client what the difference between a digital phone and an IP phone
really is. This is an issue that
frequently arises as we work with companies looking for good information as
they search for the right solution for their current phone system upgrade or
office relocation project. Many of my
clients want to know what would make one type of solution a better fit for them
over the other.
I will not attempt to
raise either solution as one being the dominant choice over another. As with most things in life, if you encounter
someone advocating an absolute position about anything, there’s a good chance
they have a financial stake in being as vociferous as possible about the position
they are representing.
In reality, as in life,
the answer to the question “What’s best?” is typically circumstantial on a
variety of factors. The question shouldn’t
be “What’s best?” rather than “What’s best for me?”
Since you – and your
business - are a unique entity I highly encourage you to proceed with great
caution in engaging with any vendor that advocates any universal application to
anything as being “the best.”
With that said, below
you will find what I hope to be an unbiased representation of the differences
between digital and IP phone solutions. If
you have any questions, please don’t hesitate to contact me.
Transmission
Digital Phones:
Digital telephones are
the direct descendant of analog telephones.
Digital phones convert the analog voice signal into a digital signal (“1”’s
& “0”’s) and transport the signal across the connected line and then decode
that signal as sound at the other end. This means whatever is encoded at one
end is exactly the same as what is decoded at the far end. The digital signal
utilizes a unique communications protocol, such as DCP, to control the
transmission of the signal.
Additionally, the protocol carries programming codes to the PBX that
reference additional features available on the system. Many businesses use digital telephony,
commonly called ISDN, but few consumers do.
Most digital phones are run with proprietary encoding that
allows them to only interface with the PBX that they were manufactured to
support.
IP Phones:
IP Telephony is a type
of digital telephony that uses the IP protocol we use on the Internet. This
means that telephone calls can be sent over private data networks and the
public internet. IP phones transmit
their data as “packets” of information to their destination. This transmission requires that the packets
be “reassembled” in the order that they were sent in order to reconstruct the
voice transmission.
IP phones use Internet Protocol
(IP) in addition with a Media Access Control (MAC) address to communicate with
the central communication platform. The combination of the IP (signal) and the
MAC address (identity/location) of each device combine to allow the device to
be located and delivered the transmission signal.
You can think of
websites that load slowly and certain sections come up faster than others. While that may be okay for a website, it is
definitely not okay for a voice call.
The packets must be received and reassembled in the order they were
sent. Failure to reconstruct those
transmitted voice packets lead to voice quality issues, typically from packet
loss (not all packets made it to the destination) or due to jitter (an
inconsistent stream of data) on the sending or receiving end.
With the increase in the bandwidth availability
of providers today, these issues have been largely, though not entirely
resolved.
IP phones can be either “proprietary”
to communicate with a specific platform or provider, or open-source which allows
them to connect to a variety of IP platforms or providers. Typically proprietary IP phones will have a
greater ability for customized feature programming on the platform for which
they are designed, and often yield a higher call quality with a proprietary
system than an open-source phone would provide.
Power
Digital Phones:
Digital phones are much more power
efficient than IP phones. In fact, they
barely use any power – most of the power used to support a digital phone is
supplied over the line itself, typically supplied through a power module
installed in the PBX.
IP Phones:
IP phones consume more power than digital
phones. Typically they have a larger
graphical display than a digital phone which requires more power
consumption. As well, the system or PBX
the phones are interfacing with do not derive their power from the base unit. A separate AC plug (brick) or POE (Power over Ethernet)
switch is required to power these phones.
Due to the requirement for power delivery to each individual device the
overall power consumption of an IP system is much greater than that of a
digital system.
Cable
Digital
Phones:
Digital phones can be
run on a variety of cable types, including RJ45, Category 3, 5, 5e and now
CAT6. Although there is greater
versatility in the type of cable that a digital phone can be run over, they are
limited in that the digital phone is the only device that can utilize that
connection. Therefore, a separate cable
must be run to support a digital phone.
The cost of utilizing the lower categories of cable referenced above
often make a digital deployment attractive to businesses looking to minimize
construction costs.
IP Phones:
IP Phones must be run
over CAT5 (with AC power brick), CAT5e or CAT6 (with AC Power Brick or
POE). Although the type of cable that
supports an IP deployment is not as diverse as the flexibility of cable to run
a digital system, there are a couple of advantages from a cabling
perspective.
IP phones typically can “piggyback”
or “daisy-chain” to another device (computer) allowing a single cable
connection to support both the IP phone and the additional device. This configuration requires a segregated
Voice Local Area Network (VLAN) on an internal network to differentiate the
voice data from the traditional data of other applications such as web browsing
or sending emails, etc.
Alternatively, an IP phone deployment can be set up on separate
(dual) cable configuration to manually separate the voice and data networks, which is the
recommended deployment for most companies not employing an in-house IT
department or network administrator.
Bandwidth
Digital Phones:
Digital phones do not
require any bandwidth on the network (LAN) or on the internet. They are run across a variety of dial-tone
connections including analog lines, T1, PRI and SIP circuits. They are extremely flexible in the dial-tone
configuration they will support, provided the PBX is configured to support the
specific connection or dial-tone circuit.
IP Phones:
IP phones do utilize
internet and network bandwidth to support their operations. On active voice calls, most IP phones send a
signal varying from low resolution at about 45kbps/sec to high resolution at
about 85kbps/sec. Consequently, as more
users simultaneously make calls, the data usage will increase. Additionally, depending on other network
traffic, bandwidth can be “stolen” from the phone and could result in
deteriorated Quality of Sound (QOS).
Mobility
Digital phones are not
inherently mobile. This means that the
port on the PBX that phone is programmed to is specific to the terminated
location. In other words, if you
configure Office A as User A and assign Phone A to that location or port, that
is a “permanent” configuration in the PBX until an administrator assigns that
port/location/user to a separate location.
For example, If User A
were to be relocated to Office B, an administrator would need to reprogram the
PBX to indicate that Office B is now assigned to User A, and reprogram Office A
to support the extension/user information for the new employee in Office A.
IP Phones:
IP phones have greater
mobility than their digital cousins due to the transmitting protocols combining
IP signaling and MAC Address. An IP
phone is programmed with the user information to the device itself, rather than
assigned to a port on the system as in a digital deployment, and retains that
users information wherever the phone is deployed.
For example, if User A
were to be relocated from Office A to Office B, they would simply take their
phone with them and plug it into the cable connection in office B. The system would then search for the MAC
Address of the device on the network, and once located, would deliver the calls
to that location without any additional programming on the system.
This allows for greater
mobility for companies that have a need to frequently reassign employees to
other physical locations, have higher than average turnover, or have a need to
deploy phones to remote locations
Advantages & Disadvantages
In summary, depending on
the application of the business utilizing either a digital phone system or an
IP system, there are trade-offs to either configuration.
Digital systems are
inherently more stable as there are less points of failure introduced to the
system. With less “moving parts” the
integrity of the system as a whole is typically much greater. Additionally this type of configuration
requires less power consumption than a similar IP deployment. Internal operations are implemented in a “set
it and forget it” manner until an employee add, move or change is
required. For companies without remote
employees and who have access to separate cabling infrastructure, there are both
cost and deployment advantages to a digital phone deployment.
IP systems are by their
nature more complex than a digital platform, which is not necessarily a
disadvantage. Selecting an IP phone
deployment requires a more diligent and advanced support system to proactively
monitor system performance. IP phone
deployments require a comprehensive technical understanding of both internal
network administration as well as on-going awareness of bandwidth
utilization.
IP phones require more
energy than a comparative digital phone deployment. They provide a greater flexibility for
deployment based on the availability or limitations of single line or dual line
cabling infrastructure. The trade-off is
that for companies with decentralized operations (multiple locations, remote employees,
home based users, etc.) or with high turnover or portability needs the IP
deployment is a great solution.
Phone Systems Today
There are many choices
for a great performing phone system in today’s marketplace. Whether you are looking for IP phones or
Digital, there are many available solutions in today’s marketplace, including
hybrid solutions that can incorporate both Digital and IP devices.
Whatever you do, don’t
believe that there is no place for digital phones in today’s business climate,
or that they are in any way inferior to IP phones. Although IP phone technology is cutting edge
and offers a lot of very cool options, it is not the end-all/be-all of
telephony solutions.
I recommend that you
work with a consultant that has experience with – and access to – products from
both sides of the solution set. They can
help you to understand the advantages and disadvantages of either type of a
deployment, and help to make an appropriate recommendation that will allow you
to overcome any obstacles you may encounter on the road to effectively
implementing your new phone solution.
Brian C. Andersen
October 8th, 2014
