Enterprise FMC and the T-Mobile HotSpot@Home service
In recent years the features of dual-mode devices (cellular voice and data clients with additional Wi-Fi
radios) have grown increasingly sophisticated. The burgeoning capabilities of these devices have attracted
the attention of IT staff at enterprises and universities with campus environments because of potential
synergies with already installed wireless LANs. More specifically, the potential exists for a user to carry a
single device that leverages Wi-Fi coverage where cellular reception is poor, thereby lowering telecom
expenses and improving the user browsing experience because of Wi-Fi’s higher data rates.
Analysts such as ABI Research see a bright future for dual-mode Wi-Fi/cellular technology (see right). As
volumes increase and the cost of adding Wi-Fi to a cellphone falls, increasing numbers of handset
manufacturers are supporting Wi-Fi on a wide range of devices.
The T-Mobile HotSpot@Home service supports a range of dual-mode client devices that implement the
Unlicensed Mobile Access (UMA) protocol, an ITU/3GPP standard. UMA is a form of fixed-mobile
convergence (FMC) in which the phone has a single number for both cellular and Wi-Fi networks, and
automatically hands over to Wi-Fi when it detects good reception from a suitable access point, returning to
cellular when the device loses a usable Wi-Fi signal. UMA is one of many forms of FMC, and due to lack of
integration with the PBX, is most suitable for organizations that do not rely on PBX-based 4- or 5-digit
numbering plans. A companion paper, Fixed-Mobile Convergence with UMA for Enterprises, discusses
different FMC architectures and their suitability for different organizations.
No other national cellular operator in the U.S. offers a comparable service, putting T-Mobile in a unique
position to benefit students, schools and enterprises alike.
In this guide we discuss features required by a network engineer in order to develop reliable support for the
HotSpot@Home service using an Aruba wireless LAN. Key technical considerations discussed include:
. Authentication requirements;
. Advertising a suitable SSID;
. Implementing firewall rules;
. End- to-end quality of service;
. Bandwidth requirements and call admissions control;
. Emergency call handling.
Before diving into the technical details, let’s examine why enterprises, and universities in particular, would
find this service of interest.
Students, faculty and staff save on their personal cellular bills
Students were traditionally significant customers of universities’ telecoms groups because everyone needed
fixed lines to their dorm rooms and long-distance plans. Today students favor cellphones over fixed lines,
and Skype or other free VoIP services over traditional long distance services. This change represents a loss
of significant revenue for universities’ telecoms groups.
A service such as HotSpot@Home offers a cost-reduction path from which students, faculty, and staff who
pay their own cellular bills will benefit. Users that purchase a suitable phone and subscribe to the
HotSpot@Home service for $10/month can make free local and national calls over Wi-Fi (including home
access points and T-Mobile hotspots). Since these calls do not accrue towards monthly air-time minutes, this
plan can yield considerable savings for garrulous users.
While the increase in voice traffic over a university’s WLAN does not directly benefit the school, it may be
possible for the university to negotiate incentives with the carrier.
University employees and faculty trim the university’s budget
The section above targeted students, but all members of the university community who work on-campus but
pay their own cellular bills would benefit in the same way. As noted, the benefits to the user are direct, while
the university’s are indirect.
Conversely, any user whose cellular bill is paid or reimbursed by the university represents an immediate
opportunity for cost savings by the telecom department. By converting that user from a standard cellphone
contract to HotSpot@Home, the university can ensure that calls made and received on-campus, at a TMobile
hotspot or at home near a HotSpot@Home-configured Wi-Fi access point are free, and do not count
in the monthly usage contract.
Samsung Katalyst
802.11b/g
WPA2 -personal
WMM QoS
WMM power save
Samsung t409
802.11b/g
WPA2 -personal
WMM QoS
WMM power save
BlackBerry 8820
802.11a/b/g
WPA2 -enterprise
WMM QoS
WMM power save
BlackBerry Curve
802.11 b/g
WPA2 -enterprise
WMM QoS
WMM power save
A selection of HotSpot@Home handsets
Aruba Networks T-Mobile HotSpot@Home UMA Service on a University or Enterprise WLAN 3
International roaming represents a most promising opportunity for savings. If a faculty member travels
internationally to another university served by a HotSpot@Home-enabled WLAN, all calls made and
received when on Wi-Fi will be free, instead of incurring international roaming charges. The calls will be
delivered over Wi-Fi and VoIP via the Internet to the T-Mobile UMA gateway.
Improved coverage
Beyond cost savings, an additional benefit of the HotSpot@Home service is that a university can add voice
coverage in areas where cellular signals are weak, a common issue on large campuses. Previously this
problem was addressed by installing additional cellular base stations, a very expensive proposition. With
HotSpot@Home, coverage holes can be filled by the university’s telecom/datacom group as part of the
normal WLAN build-out.
Note that it is possible to use HotSpot@Home with a standard T-Mobile SIM card installed in a
HotSpot@Home handset, without subscribing to the extra $10/month HotSpot@Home ‘talk forever’ service.
In this case minutes used are deducted from the subscriber’s plan in the usual way, but there is no
supplementary monthly charge. This may be attractive where the desired benefit of the Wi-Fi service is
improved coverage rather than cost savings.