October 1999
Balancing Voice And Quality On The LAN
BY KEN DUMONT
Today many vendors, including well-established vendors and startups, are introducing
LAN-PBX solutions. These products do not measure up to the voice quality and reliability
standards offered by current PBX-based telephone systems. Customers need to understand the
limitations when implementing a telephone system based on current LAN-PBX technology.
The bar for acceptable voice system performance has been established, and enterprises
will not expect anything less from a LAN-PBX solution. Moving to a LAN-PBX architecture
should not force customers to compromise on what they have today. As a result, there are
several key issues that need to be addressed before solutions can meet and exceed the
expectations set by existing products, including reliability, voice quality,
interoperability, usability, and management.
HOW CAN A LAN-PBX BE MADE RELIABLE?
Businesses understand that a LAN-based telephone solution needs to be as reliable
as their current installed PBX solution. For most enterprises, telephony represents the
original mission critical application, implemented long before other data
applications became critical.
One way to achieve high reliability is to install redundant and fault-tolerant system
components. Redundancy provides fault tolerance because if a component fails, the hot
spare will take over without any loss of service. Further, fault tolerance can be achieved
through the use of hot-swappable components. Even if a component fails, a truly reliable
product will allow the technician to replace the faulty unit without powering down the
entire system. These types of fault tolerant and redundant equipment techniques are
expected in todays PBXs, but are not necessarily included in PC servers, including
any PC-based server that runs call server software in a LAN-PBX architecture. While many
of the servers components can be made redundant, this reliability comes at a cost
that many small and medium-sized businesses may not be able to afford.
Also, PC servers that run multiple applications will be exposed to more failures due to
the misbehavior of other applications. It is typically recommended that the
organization run the call server software on a dedicated hardware server, at least for the
near term.
In addition to hardware failure, server downtime can also be attributed to power loss.
There are several Uninterruptible Power Supply (UPS) products on the market that will keep
PC servers running for a limited amount of time. Unfortunately, most of these products are
not designed for high server availability in the event of a significant power failure, but
are only meant to allow users to save their current data and allow the administrator to
gracefully shut down the server. This is not acceptable for a telephone system, so
administrators will have to implement a battery backup system for all LAN PBX components
a system that can maintain power to the call server, network connectivity devices
(such as Ethernet switches and routers), and Ethernet phones in the event of a power
outage. All of this adds to the cost and complexity of the voice and data network.
CAN TOLL QUALITY VOICE MEASURE UP?
A common belief is that most LANs have enough excess capacity to handle the
relatively small amount of traffic generated by voice applications. However, traffic loads
are dynamic on a LAN, and only the use of specialized and sophisticated bandwidth
allocation techniques can guarantee available bandwidth at all times of operation. These
factors, coupled with the lower bandwidth of WAN connections, mean that LAN-PBX systems
must be prepared to deal with varying bandwidths without sacrificing quality.
The bane of any packetized voice stream is delay. Once a packet takes longer than
100200 ms to travel to its location, voice quality starts to become unacceptable.
Human factors research has shown that most people greatly dislike long transmission
delays in telephone calls. Subjectively, too much latency makes it difficult to carry on
an interactive dialog, which is typically the case in voice communications. This is
particularly apparent when people try to interject comments or questions while someone
else is talking. One party hears that the other has stopped speaking and begins to talk,
only to find that the second party merely paused before continuing to say more. As latency
increases, people tend to step all over each other in the conversation, not
unlike collisions on an Ethernet LAN.
Other factors that affect voice quality in a LAN-PBX system are echo and packet loss.
Echo becomes a problem in most voice-over-packet networks be-cause the round-trip delay
through the network is almost always greater than 50 ms the threshold of human
perception. These systems must address the need for echo control, and may need to
implement some means of echo cancellation.
INVESTMENT PROTECTION AND LEGACY MIGRATION
To protect your current investment in legacy voice systems, a LAN-PBX needs to be
compatible with the existing infrastructure. To date, vendors are not selling their
products to companies with existing PBXs, but to smaller companies that have no PBX and
have outgrown their key systems or Centrex service.
First, if the PBX has adequate capacity, and users and administrators know how to
program it, why settle for a voice and data solution that has fewer features, and
different implementations of these features? Second, switching to a LAN-PBX system may
represent a fork-lift upgrade that requires all new phones and some re-wiring.
Third, the average life span of a telephone system is shrinking, but still typically five
to 10 years (compared to 18 months to three years for a PC). Finally, companies have a
significant soft investment in training users and administrators on how to
utilize and administer it. The thought of training users on a new system with new desktop
interfaces, new ways of implementing features, or even doing without the key functionality
to which theyve become accustomed, is not particularly appealing.
Thus, any organization considering an implementation of LAN-PBX systems will need to
consider asset protection for its pre-existing systems (and people). Ideally, a LAN-PBX
system should work in a hybrid implementation along with existing legacy
proprietary systems to protect both hard and soft voice investments. Examples are branch
offices that are networked to the head office, or departmental adjuncts within larger
organizations. Hybrid implementations need to deliver seamless integration, feature and
functionality transparency between the IP and traditional systems, common telephone set
interfaces, etc. Also, vendors need to demonstrate a clear migration path between legacy
voice equipment and next-generation platforms. This will define the product roadmap, which
products will migrate forward (and which will not), and how legacy systems will
interoperate with new platforms.
MANAGING A LAN-PBX
PBX telephone systems are typically managed by a physical port each port
can be assigned a phone number, name, location, and calling access and restrictions. This
management and configuration is performed using a graphical interface that communicates
directly to the telephone system hardware.
With a LAN-PBX system, there is no concept of a PBX port. Instead, administration will
need to be associated with a particular user name or some other differentiation, such as
the MAC or IP address of an Ethernet phone.
Ideally, a LAN-PBX system would be managed based on uniquely defined user names. With
such a system, a user would have the same telephone number and access rights even if
he/she was using a different Ethernet phone. By tying this information into a directory
service potentially based on Directory Enabled Networks (DEN) or Lightweight
Directory Access Protocol (LDAP) the administrator would be able to globally manage
every Ethernet phone in the entire enterprise from a central location.
Another issue that is unique to a LAN-PBX system is policy-based management
maintenance of access control lists and quality-of-service settings per user or Ethernet
phone. As phones move onto the data network, the same management techniques that are used
for controlling PCs and users will need to be implemented for LAN-PBX components and
users.
CHALLENGES
The network and telecommunications equipment industry faces significant
challenges in driving widespread adoption of LAN-PBX solutions, but the momentum towards
IP-based network convergence is inevitable. Proof of the value of voice/data convergence
in the wide area will eventually cause it to happen in the enterprise. Its a matter
of when, not if LAN-PBXs will become popular.
In order for LAN-PBX solutions to compete on an equal footing with traditional PBXs,
and be accepted by the mainstream market, they must address the practical challenges,
including reliability, voice quality, interoperability, and management. c
Ken Dumont is vice president of marketing for Mitel Corporation. Mitels
product portfolio has evolved from world leading business communications systems and
desktop peripherals to include networked voice and data systems, a portfolio of call
center solutions, messaging products, computer telephony (CT) applications and enabling
platforms, network access products, remote access products, and public switching products.
For additional information, visit Mitels Web site at www.mitel.com.
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