P E R S P E C T I V E S
WIRELESS ACCESS
ture to determine its scalability and
how well it deals with heteroge-
neous systems.
• Synchronization.Technological ad-
vancements must synchronize with
business needs.
administration,and maintenance costs
for managing such a worldwide virtual
network also need careful analysis.
Other prime issues are discovering
the called mobile unit or terminal for
completing a connection request and
maintaining the integrity of the offered
connections or calls in-progress. Sys-
For in-building wireless tele-
phony/PBX, the base station should
support the required mobility (hand-
off capabilities), QoS, and channel
capacity. Standards for wireless tele-
phony have arisen: the European CT-
2 standard (“CT” stands for cordless
telephony) supports around eight
handsets per base station, and The
Digital European CordlessTelephone
(DECT) standard supports up to 12
handsets per base station over a 100-
to 200-meter diameter.
A wireless PBX must also support
users both within and outside a loca-
tion.The wireless connection must be
secure,and the system must authenti-
cate the user before allocating a chan-
nel or circuit.
For example, consider the service-
level agreement parameters for the
PSTN. Required reliability for the
PSTN is 99.999 percent—“the five 9s.”
A user must also receive a dial tone
within three seconds 95 percent of the
time.The PSTN must support an aver-
age holding time (call length) of three
minutes or 180 seconds. The PSTN’s
connection drop rate during a call is
almost zero,because it always uses the
latest released circuit to start a new
connection. For networks to provide
PSTN-like services, they must use IP
for both signaling and media and still
For wir eles s
communica t ion
wit hin a s ingle
cor por a t e net wor k,
cons ider a n IP-ba s ed
vir t ua l net wor k.
To successfully integrate wireless
services into a network, consider
tems typically accomplish this by either
paging, broadcasting, and/or mobility
tracking or management methods. meet similar requirements.
• capacity planning to support effi-
cient operations today;
Emerging network management
strategies include
Tracking methods include
• capacity and infrastructure planning
for evolving the network to support
new applications and operations;
• support of acceptable (less than 10
percent) blocking and hand-off
from the handset to the base sta-
tion,which includes reduced block-
ing between the base station and
wireless PBX, and acceptable
blocking at the wireless PBX to
Intranet or PSTN (access-level
blocking results in redialing for ser-
vice, and in-transit blocking causes
hand-off failure); and
• location and mobility tracking data-
bases (home and visitor location
registers), such as the ones used in
the public PCS networks;
• Global Positioning System (GPS)
coordinates for tracking the loca-
tion of a terminal and then using
low-overhead mobility manage-
ment techniques for maintaining
connection continuity; and
• those for virtual private networks,
which use privately managed logi-
cal channels (or a mesh of chan-
nels) over public physical links for
enterprise network management;
• virtual network management,which
is a flavor of customer network man-
agement; and
• management of the virtual enter-
prise—that is,the entire business and
all networking processes are virtu-
ally defined.In this case,multiple lev-
els of overlay can create complexity.
• various satellite-based systems.
An advantage of an IP-based global
virtual network is that users can use
the same handset whether within a
company building or while traveling.
• backup for unexpected events,such
as facility outages.
GENs have a difficult charter
that is twofold. First, they must
ENTERPRISE NETWORK
MANAGEMENT (ENM)
Three issues need careful consider- older tested technology. Second, they
ations in implementing emerging net- must also support future technology
work management options:
N
continue to provide the reliabil-
ity and functionality now provided by
Although the initial deployment of
a wireless PBX can be expensive, it
pays off in improved employee pro-
ductivity and enhanced customer
(internal and external) satisfaction.
For wireless communications within
a single corporate network,you should
consider an IP-based virtual network
to support ubiquitous and uniform ter-
minals and services. In this environ-
ment, network segments must inter-
operate seamlessly with public and
private carriers.Additional operations,
and service evolution.Doing both well
could be a make or break competitive
• Interoperability.Vendors and orga- advantage for your company. ■
nizations are proposing a variety of
architectures,platforms,and proto- Bhumip Khasnabish is a principal
cols. The more types of networks member of technical staff at GTE
you have, the more complicated
your interoperability challenge.
• Architectures.Assess each architec- www1.acm.org/~bhumip/.
Laboratories,Waltham,Mass.Contact
him at b.khasnabish@ieee.org; http://
60 IT Pro January ❘ February 2000