Network Computing | ||
Issue
58 - December 2008
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The
PBX (Public Branch Exchange) phone system
that we are currently using is over 18
years old and has already reached its
end-of-life cycle. There is a great potential
risk of system breakdown due to hardware
failure which may impact the majority
of the university community. It is therefore
necessary to replace the PBX system as
soon possible. Voice
over IP (VoIP) is a digital technology
that allows voice and video calls to be
conducted over a public or private IP
network using a combination of computers
and IP phones at both ends (as opposed
to the PBX phone system using analogue
technology to carry voice-only calls over
a public or private telephone network
using a combination of telephones and
fax machines at both ends). Through the
appropriate digital gateway, the digital
IP telephony (IPT) System is able to communicate
seamlessly with an analogue PBX phone
systems over the analogue telephone network
and vice versa. Based
on the VoIP technologies, the IPT system
not only allows voice, data and video
to share the same network cable (hence
reducing cabling and support cost), but
also offers many features normally not
found or cannot be implemented under the
conventional PBX system such as broadcast
or targeted delivery of digital news in
voice, text and/or images. As such, the
university has decided to gradually phase
out the existing PBX system and adopt
the IPT technologies in all new buildings
and offices. The CityU IPT System The
CityU IP Phone project started in 2002
by replacing in Festival Walk Office (FW)
300 phone lines subscribed from the commercial
phone service provider with IP phones
and installing 450 new IP phones in Phase
I of the Student Hostel. In the Fall of
2003, another 140 phones in student rooms
of Jockey Club House and To Yuen Building
were upgraded to IP phones. Since 2004,
the coverage of IPT has been gradually
extending to new staff offices, public
phones, and Phase II of the Student Residence.
Up to now, we have more than 3200 IP phones
installed in the Student Residence, and
1500 IP phones in Main Campus and remote
offices. The IPT system is composed of a Cisco Unified Communications Manager Cluster, a Unity Voice Mail System, Voice Gateways and IP phone sets inter-connected through Cisco routers and switches. The IPT core equipments and core network are built with full redundancy and highest priority is given to voice traffic to ensure best quality and reliability. The following picture depicts the architecture of the IPT on the campus network and its linkage with the existing PBX system : Features and Advantages of IP Phones In
addition to the basic phone features, one
can enjoy more sophisticated functions and
advantages in the IPT system that are not
available in the conventional phone system.
Below lists some of the features and advantages
of the IPT: Features and functions: Advantages: Migrating to IPT System As
the IPT has been proven to be reliable and
versatile, CityU is planning to migrate
all the existing 4,000 analog devices in
the main campus such as phones, fax, etc.
on the PBX to the IPT in the near future.
The
CSC will contact each department individually
for the schedule and details of the migration.
It is expected that the migration will be
completed within 1 year. Impact to Existing
PBX Users The
University has acquired the prefix 3442
for the IPT system. Renumbering is therefore
required whenever a PBX device is migrated
to the IPT system. Unless there is a conflict,
all new phone numbers will assume the format
of <3442><last four digits of old
phone number>. For example, 2788-7658
will be changed to 3442-7658. New
Cisco IP phone sets will be provided to
users to replace the old analog phones in
the migration. For legacy devices and machines
that must run on PBX system (e.g. fax, personal
alarm system, etc.), specially designed
voice gateways are used to enabling them
to run on the IPT system transparently. To
minimize impact on the phone service during
migration, special arrangement in setting
up an inter-trunk to link up the PBX and
IPT systems is made. As a result, a user
on either phone system can make call by
just dialing the recipient’s 4-digit
extension number regardless of which phone
system the recipient’s phone number
actually belongs to. In addition, a 3-month
call forward service or playing an announcement
to inform the caller of your new phone number
will be provided by default. If you want to know more about the migration, please contact the CSC Help Desk. |
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