Signal Distribution Within the Subscriber Premises

In the case of a single residential user, the transceiver can communicate directly with a single
computer via whatever connection the radio and the computer itself supports, be it USB, serial,
or FireWire (IEEE 1394). In the case of enterprise users or multidwelling unit (MDUs), generally
some provisions must be made for distributing the signal after it has been received over the airlink.
What this entails is the creation of an internal network for the building or compound in
question. Figure 5-7 shows an installation in an MDU. Here network operators will have to decide to what degree they want to become a building
local exchange (BLEC) and enter into the business of installing and maintaining LANs. In some
cases having this capability will mean the difference between securing an account and failing
to do so, but remember that LAN installation at its higher levels involves competencies that are
somewhat remote from those needed to set up and operate public networks, and this is especially
true if extensive new in-building wiring is required.
Internal Networks for the Enterprise User
A few words of explanation are in order regarding enterprise in-building and campus data
networks; however, taken has a whole, enterprise networks represent a vast subject area and cannot be adequately covered in a single section. Here I am primarily interested in how such
LANs interface with wide area networks (WANs) and with metro area networks (MANs), the latter
being the real province of the broadband wireless service provider.
First, an enterprise network proper—a network that would be used within an institutional
setting such as a corporation, government agency, or an educational or research institute—is a
rather different entity than a distribution system intended for an MDU. The latter ordinarily
has no switching capabilities (that is, the ability to define Ethernet subnets), though it may
have rudimentary routing abilities primarily involving dynamic Internet Protocol (IP) addressing
with perhaps some virtual private network (VPN) functionality thrown in. An enterprise
network, on the other hand, can be extremely complex and can include its own application and
content servers, special black boxes for conferencing, hardware firewalls, authentication servers,
and on and on. Normally such networks will be managed by an information technology
(IT) department, and the WAN or MAN service provider will play no direct role in respect to
what goes on within the LAN itself.
Things get more complicated still when several tenants within a single facility share the
same internal physical layer, that is, when several enterprise LANs share the same wires or
internal airlinks. At that point, the internal network looks more like a public network because
some means of ensuring fairness must be implemented, and data streams and databases associated
with individual customers must be encrypted and made inaccessible to other tenants. In
other words, the network must be actively managed. Usually this will be the responsibility
of the building owner, but in the past a number of specialized service providers, the aforementioned
BLECs, have attempted to specialize in setting up and operating these internal networks.
The MAN service provider can elect to function as a BLEC, and a number have done so.
Dedicated BLECs have generally failed in the data communications marketplace, often
because of exorbitant demands on the part of real estate owners for shares of the revenue. Consequently,
the wireless network operator who is contemplating filling such a role should give
the matter careful thought. If a large number of valued customers reside in one location, it may
be justified, but only under certain circumstances.
Generally, fulfilling a BLEC function is advisable only in the case of millimeter wave services
where a connection of minimally several hundred megabits per second serves a single
building or complex. In such a case enough bandwidth exists to provide several customers
with several tens of megabits of throughput. The internal network can be either IP or switched
Ethernet and normally would utilize either Gigabit Ethernet copper data cable or optical
fiber. Chapter 6 gives detailed information on the setup and administration of both types
of networks. MAN/LAN Integration: The Physical Layer
In any given instance, the network operator will face the choice of whether to offer a separate
wireless subscriber terminal to each subscriber in a building or attempt to serve such tenants
through an internal network spanning the last few yards. Wired connections may appear to be
the more sensible approach for the final connection—after all, cable is pretty inexpensive—
but the issue is not always as straightforward as it may appear.
First, as you have seen, the installation or modification of internal cabling thrusts the wireless
service provider into a new role that of the BLEC. At the point when the signal enters a
wired network and network operators are responsible for its delivery over that network, they
have to utilize new tools and techniques that do not obtain in the outdoor wireless environment.
In effect they have entered into a different business. Here cost is often the overriding consideration. Cable installation is fairly inexpensive in
buildings under construction, especially where the installer enjoys a good working relationship
with the general contractor. Adding new wiring to existing structures can be both
expensive and laborious, however, and simply may not be tolerated by the building owner. Determining a Business Strategy Regarding the Internal Network Most larger office buildings are
wired for data today, and some of the biggest even have internal optical fiber. Many have internal
routers or Ethernet switches as well for distributing data services to tenants. The more
elaborate the internal network, the more likely the building is to have a fiber connection.
In the case of large office buildings and complexes, the network operator’s role will
depend on many factors: the extent of the physical plant already existing in the building(s), the
posture of the real estate owner, the network operator’s own expertise, and the way that the
operator has positioned the company in the marketplace. Each installation is unique, and
there are really no invariant step-by-step procedures to guide the service provider through the
process.
If the structure to be served has no cabling or inadequate cabling, then it is probably best
to enlist the cooperation of an engineering firm specializing in such work, of which there are
many. Large office buildings can require months of installation labor to cable, and total costs
may run into the hundreds of thousands of dollars. Incidentally, traditional telecommunications
service providers have tended not to involve themselves in designing, building, or
operating internal networks.
It is of course possible to distribute signals internally via 802.11 WLANs, and constructing
such a network should be well within the capabilities of a wireless public network operator.
The problem is capacity. Specifically, 802.11 networks using direct sequence modulation can
accommodate only three users per base station simultaneously, and throughput speeds are
108Mbps best case. There are certain proprietary “Turbo” accelerators that might enable
speeds close to that but they are not part of the standard.
In the future ultrawideband radios may solve this internal distribution problem in a costeffective
manner. With throughputs in the hundreds of megabits per second, and pronounced
ability to penetrate walls, they could eliminate the need for much of the internal cabling that
festoons modern office buildings. Currently, however, the power restrictions in force in the
United States will not permit such applications.
Another option, alluded to briefly earlier, is to provide each subscriber in a building with a
separate radio and antenna. This is best attempted in the lower microwave region because of
the relatively low cost of terminals and their NLOS capabilities.
Even if new cabling is not required, new networking equipment may be, such as edge routers,
Ethernet switches, digital private branch exchanges (PBXs), firewalls, and so on. And these
in turn may require new equipment closets and, in some cases, whole data centers. Thus, it is
extremely important to determine the real market potential of each building and have firm
agreements in place with real estate owners before attempting to make any modification in an
internal network. It is equally important to develop good estimates of the cost involved in such
modifications. A network operator simply cannot afford to guess wrong in this regard. To do so
could jeopardize the whole network operation. Interfacing with Enterprise Networks
Enterprise LANs vary in size and complexity from small assemblages of a few networked
computers to sprawling networks with hundreds or even thousands of terminals. The larger
networks may include IP PBX functionality, hardware firewalls and authentication servers,
multimedia servers, internal routers and switches, IP or Ethernet network attached storage,
and so on. Dealing with such formidable entities, especially as a startup service provider, may
seem daunting, but the very complexity of the network may actually represent an opportunity
for a competitive service provider.
In reality, many telco incumbents do a poor job of serving enterprise accounts. Most traffic
over incumbent public data networks still takes place over legacy transports, including
SONET, frame relay, and ATM, and it involves complex and inefficient interfaces to the enterprise
world, which is overwhelmingly Ethernet and IP. Enterprise data managers routinely
complain that incumbent business services personnel do not really understand their networks
and are not responsive to their needs. And, up to the present, the telcos have not had to be
responsive since they enjoyed a de facto monopoly.
Generally, providing the enterprise IT manager with a fat IP pipe with self-provisionable
bandwidth will go a long way toward satisfying that individual. Ensuring QoS over longdistance
remote connections will do even more.
To achieve the latter, the wireless service provider has to enter into special relationships
with long-distance carriers that will ensure that certain stated levels of speed, latency, and
error rates will be maintained such that service level agreements with the broadband customer
can be maintained. Especially important here is minimizing the number of router hops to the
destination and assignment of special priorities to certain kinds of traffic. All this costs money
because the wireless network operator is asking for more than basic Internet service, but that
cost can be passed on to the business subscriber, and the cost will generally be justified from
the latter’s perspective if the service enables new applications that benefit the enterprise.
Such long-distance peering relationships, as they are called, are especially important if the
service offerings include videoconferencing or IP voice services. They are equally important if
highly specialized services such as links for real-time collaborative scientific computing or
massive multimedia file transfers for entertainment industry production houses are offered.
If the wireless broadband operator is offering network storage services, special provisions
will probably be necessary as well, specifically the installation at the central office of specialized
equipment to handle the service, either dedicated storage switches or multiservice
switching platforms that can handle storage transport protocols.
The network operator may also be obliged to invest in dedicated encryption hardware
when dealing with enterprise customers. The security protocols inherent in 802.16-based
equipment may not be deemed sufficient, and the customer may demand something more.
When bulk encryption of highly sensitive transmissions is required, hardware solutions are
preferred because they utilize a platform that is entirely separate from the router to perform
the computations necessary for encryption and thus do not slow it down. Chapter 7 discusses
encryption in detail.
Another specialized service offering that should be considered with respect to enterprise
customers is access to a secure Web site that will permit the subscriber to change the throughput
rate or other attributes relating to QoS. Most enterprise users have occasional needs for
large increments of bandwidth, and naturally they do not want to sign up for increased  throughput rates for periods longer than are absolutely required. Access to a self-provisioning
Web site answers such needs.
A word about legacy networks: A significant though dwindling number of enterprise networks
retain networking protocols that are currently considered legacy. These include ATM
to the desktop, token ring, Novell NetWare, AppleTalk, Banyan, and X.25, to name the best
known. While many first-generation WLAN products supported such protocols, few current
broadband wireless products do, and thus integration with such networks may represent considerable
difficulties. Accordingly, the network operator must carefully weigh the value of
potential customers demanding support for such protocols. Are they worth the operator’s
retaining staff or consultants with expertise in these areas? Internal Networks and the Residential and SOHO Subscriber
Interfacing an 802.16 subscriber premises radio with a residential data network ordinarily
poses few problems. The overwhelming majority of such networks are Ethernet or, in some
cases, small IP networks fronted by routers.
The situation is rather different when the subscriber wants a network, but the house has
not been prewired to support it. In that case the broadband wireless network operator may
want to consider offering basic installation services as a value-added service.
In such cases, putting in an 801.11 WLAN is usually the simplest option while installing
category-five data cable is the most difficult, expensive, and time consuming. Other options
that do not require running new cable are HomePNA, a sort of mini-DSL network that utilizes
the house’s existing telephone wiring, and HomePlug, a standard for running high-speed data
transmissions over the AC power lines.
In the case of MDUs where one radio may serve a number of subscribers, the installation
and management of the network can become much more difficult. The 802.11 standard,
HomePNA, and HomePlug may still suffice if the network were limited to a handful of subscribers,
but if the number is greater than that, the network operator may want to establish
subnets where contention for bandwidth is limited to the subnet. Home PNA and Home Plug
are not really designed to support Ethernet switching and the establishment of subnets, but
interestingly, 802.11 is.
As I have indicated before, MDUs do not appear to be an ideal market for wireless broadband
operators to pursue, based on return-on-investment projections. Millimeter microwave
connections are still prohibitively expensive in view of likely revenues, and lower microwave
networks generally cannot provide much capacity and are therefore at a competitive disadvantage
vis-à-vis cable and DSL. Moreover, cable and DSL service providers are relieved of the
necessity of constructing separate internal network to redistribute the signal. DSL requires no
redistribution, and in the case of coaxial cable the external network naturally lends itself to
extension within a building. Generally an MDU customer should be actively pursued only
where other broadband services are lacking and are unlikely to be offered in the near term.