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Network services investment guide - Gaynor M.

Gaynor M. Network services investment guide - wiley publishing , 2003. - 322 p.
ISBN 0-471-21475-2
Download (direct link): networkservicesinvestment2003.pdf
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A simplified cellular wireless network architecture is illustrated in Figure 11.2. It is very basic, containing the minimum number of components needed to understand the management structure of today's cellular networks. This figure contains the following components of a simple cellular network:
Base Station (BS). This is the radio transmitter and receiver communicating to the end user's wireless device. These stations are arranged in cells to maximize the spatial reuse.
Base Station Controller. This controls many Base Stations. It is responsible for managing the handoff of calls from one cell to another as the end user moves between cells.
Coexistence of 802.11 and 3G Cellular: Leaping the Garden Wall 195
Mobile Switching Center (MSC). This is the switch that controls many Base Station Controllers. It is similar to a standard switch in the PSTN, but it has additional functionality to handle mobility of the end user. The MSC works with the Home Location Register (HLR) to track the mobile user.
Home Location Register (HLR). The function of the HLR is to keep track of where the mobile user is. It helps manage user mobility by communicating with the MSC to always know what MSC a user is currently connected to.
One reason this structure is centralized is because the network tracks what the users are doing. The network knows what users are doing, no matter where they are. With a cellular network, servers within the network must know the location of the end device even when it is the end device initiating network communication. In effect, cellular networks impose a centralized structure on the distributed structure of the Internet access they provide.
Figure 11.2 Simple cellular network infrastructure.
196 Chapter 11
There are many advantages to this centralized management structure. The spectrum, equipment, and network resources are used efficiently. Users can have a one-stop shop where all billing is consolidated. Well-engineered cellular wireless networks are an efficient way to utilize scarce resources. As a result, there are substantial economic incentives for profit-motivated firms to undertake on the operation of such services. This efficiency, though, must be weighed against the disincentives to foster innovation.
802.11: Technology
As previously mentioned, networks based on the IEEE 802.11b standard, also know as Wi-Fi, are popping up everywhere in homes, offices, hotels, conferences, airports, and other hot spots. Individuals, loosely organized groups, and enterprises are building such networks because it is easy, it works well, and it is quite inexpensive. Anybody with an Ethernet connection to the Internet (including DSL/cable modems) can plug in an
802.11 access point to this Ethernet connection and have broadband wireless Internet connectivity. Its really that simple; I have such a wireless network in my office and my house.
In a few locations like Cambridge, Massachusetts, that have a high density of wireless access points, ad-hoc community Wi-Fi networks have evolved because individuals keep their access points open. While there is no guarantee of quality, some would venture that the proliferation of Wi-Fi is close to tipping toward widespread adoption. A viable economic model for commercial deployment, however, has yet to emerge.
The technologies of 802.11 are a group of standards specified by the IEEE and classified as a low-power, license-free spread-spectrum wireless communication system [5][6]. License-free spectrum means anybody can use it, but this spectrum must also be shared with other devices (for example, microwave ovens and X10 wireless cameras). Originally, the 802.11b standard was introduced with a 2 Mbps data rate, later being increased to 11 Mbps. It uses both frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS). Table 11.2 illustrates the 802.11 standards [3][5].
802.11 technologies are designed for hot spots, but they may turn out to work well in some wide-area applications. By increasing power or with external antennas, the range of 802.11 can extend for miles [6], which means Wi-Fi is a viable last-mile technology. Covering neighborhoods and business parks with 802.11 access points might be a cost-effective method for providing broadband wireless services in homes, offices, business parks, and public places.
Coexistence of 802.11 and 3G Cellular: Leaping the Garden Wall 197
Table 11.2 Characteristics of 802.11 Technologies
MODULATION
EMPTY SPECTRUM TECHNIQUE BANDWIDTH DISTANCE
a 5 GHz OFDM 54 Mbps 60 (feet)
b 2.4 GHz DSSS (WiFi) 11 Mbps 300 (feet)
g 2.4 GHz (b) CCK-OFDM 11, 54, (a) and 300 (feet)
5 GHz (a) (b) compatible 60 (feet)
802.11: Management Structure
802.11 is an adaptable technology allowing for flexible management structures. At one extreme, it allows a completely distributed structure where individual users at home and in the office install and manage their individual access points. Such networks can provide temporary IP addresses with a DNS/NAT where nothing within the Internet knows about this connection, which makes tracking its usage impossible. At the other extreme are large service providers that install and manage Wi-Fi networks for many different individuals or organizations, such as for wireless access in airports. At the middle ground are organizations that install and manage their own Wi-Fi infrastructure for internal use, such as college campuses and enterprise facilities. Wi-Fi networks have the flexibility to be managed either centrally or in a distributed manner.
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