Download Introduction to Wireless Technology

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Copyright © 2002 Concord Communications, Inc. Network Health is a registered trademark of Concord Communications,
Inc. Concord, the Concord logo, eHealth, eHealth Suite, Application Health, System Health, and Live Health are
trademarks of Concord Communications, Inc. Other trademarks are the property of their respective owners.
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I.
Executive Summary ........................................................................................ 2
II.
Wireless Technology....................................................................................... 2
III.
Mobile Wireless .............................................................................................. 3
IV.
Wireless LANs ................................................................................................ 8
V.
Wireless Broadband ...................................................................................... 10
VI.
Managing Wireless with eHealth 5.0............................................................ 11
VII. References ..................................................................................................... 16
VIII. Glossary......................................................................................................... 17
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This document presents an overview of the wireless technologies that are currently of interest to
Concord’s service provider and enterprise customers. We distinguish among the three basic
wireless technologies, offer a discussion of each, and describe how eHealth can be used to
support them.
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The term wireless is applied to three different technologies:
•
Mobile wireless refers to support for hand-held devices using cellular frequencies over
airwaves. The cellular devices communicate via base stations attached to a wired
infrastructure that offers connectivity with traditional telephone and data networks.
•
Wireless local area networks (LANs) are local area networks which communicate over
airwaves rather than over traditional LAN media such as shared coaxial cable, twisted
pair, or fiber.
•
Wireless broadband provides access to central offices over airwaves using a licensed
spectrum and offers a wireless alternative to access technologies such as digital
subscriber lines (DSL) and cable.
In the next three sections we address each in turn.
Concord Communications – Introduction to Wireless Technology
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Mobile wireless technology supports hand-held telephones, laptop computers, and other mobile
personal devices, connecting them to various services and to each other via cellular
communication over airwaves. It is currently moving from a generation dominated by analog
cellular (1G) through one featuring low-speed digital cellular (2G), and looks to a future of high
speed digital cellular (3G).
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Cellular technologies exploit the concept of reuse of frequencies. The same frequency can be
used to support multiple conversations provided they are sufficiently separated in space. Cellular
communication takes place on reusable frequencies within a network of hexagonal cells. Since a
signal cannot be guaranteed to drop off to zero at the boundary of a cell, the cells have to be
configured so that two adjacent cells do not share a frequency. To this end, the available
frequencies are divided into seven sets and the sets allocated to cells as shown in Figure 1.
Concord Communications – Introduction to Wireless Technology
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3
4
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Figure 1. Hexagonal Cell Layout
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The following three cellular technologies (illustrated in Figure 2) permit a mobile device to
access a cellular infrastructure.
•
Frequency Division Multiple Access (FDMA) allocates a frequency within a cell to a
single call and modulates an analog signal. This approach, known as Frequency Division
Multiple Access (FDMA), consumes an entire frequency for the duration of a connection.
Of all the cellular access methods, it is the least efficient in terms of utilization of the
available frequencies.
•
Time Division Multiple Access (TDMA) assigns a time slot within a frequency channel to
a connection. Strictly speaking this access method is TDMA superimposed on FDMA
and it represents a clear improvement over simple FDMA in terms of effective use of
bandwidth.
•
Code Division Multiple Access (CDMA) is a spread-spectrum technology that assigns a
distinct digital code to a connection and supports all calls on a range of frequencies. A
transmitter effectively encrypts the signal and a receiver effectively decrypts it based on
shared knowledge of the same digital code. CDMA has considerable advantages over
TDMA and FDMA in terms of effective use of the spectrum and security. Spreadspectrum was originally developed for military use, which favored a signal spread out
Concord Communications – Introduction to Wireless Technology
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over a wide range of frequencies because it is harder to detect and decode than one
confined to a narrow range.
frequency
FDMA
call 1
call 2
call 3
frequency
time
TDMA/FDMA
call 1a call 1b call 1c
call 1d
call 2a call 2b call 2c
call 3a call 3b call 3c
call 2d
call 3d
frequency
time
CDMA
all calls
time
Figure 2. Mobile Wireless Access Methods
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Following is a summary of the three generations of mobile cellular technology:
•
1G is based on FDMA and analog signaling. Its most common variants are (or were)
Advanced Mobile Phone System (AMPS) in the United States and variations on Total
Access Communication Systems (TACS) in Europe. It was designed for voice
communication and can be made to handle data only incidentally.
•
2G is usually based on TDMA superimposed over FDMA, although some
implementations utilize CDMA. Unlike 1G, it is a digital technology which supports
both voice and low speed data. The data features are suitable for fax and and short
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messages, but not such data intensive services as Web browsing. The most popular 2G
technology is General System for Mobile Communication (GSM). The European Union
standardized on GSM early, with commercial networks in operation by 1991. As a result,
Europe has taken an early lead in market penetration of mobile wireless devices. The
terms 2G+ or 2.5G are used for services based on a 2G infrastructure that allow higher
speed data of the order of fractional T1 speeds. Probably the most well-known 2G+
service is General Packet Radio Service (GPRS), an IP-based value-added service
superimposed on a GSM network.
•
3G emphasizes data-oriented services and is expected to offer data rates of up to 2 Mbps
based primarily on CDMA.
To POTS, Internet
wired infrastructure
(routers, switches, LAN/WAN media)
mobile infrastructure
(cells, base stations)
wireless devices
Figure 3. Mobile Wireless Infrastructure
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A G2 or G3 wireless infrastructure consists of mobile part and a wired part, as illustrated in
Figure 3. The mobile wireless infrastructure consists of the hand-held devices utilizing cellular
communication over airwaves. Each cell has a fixed base station. The base stations are
interlinked via a wired infrastructure. The wired infrastructure provides communication among
Concord Communications – Introduction to Wireless Technology
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the various base stations as well as connectivity between the base stations and global networks of
interest, including POTS and the Internet.
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General Packet Radio Service (GPRS) is an IP packet service based on GSM. Figure 4 illustrates
the two types of server that are central to its operation: a Serving GPRS Support Node (SGSN)
and a Gateway GPRS Support Node (GGSN). The former permits mobile stations to
communicate with remote services. It does this by exchanging information with the GGSNs. The
GGSNs are gateways to networks and services external to the wireless network. Critical to the
operation of such network is the GPRS Tunnel Protocol (GTP) which tunnels traffic through the
IP infrastructure. GTP requires the underlying services of TCP/IP.
Wired
Infrastructure
SGSN
Mobile
Infrastructure
GTP
GPRS
SGSN
GGSN
GTP
GGSN
Internet
General Packet Radio Service
Serving GPRS Support Node
Gateway GPRS Support Node
GPRS Tunnel Protocol
wireless
devices
Figure 4. GPRS and GTP
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The Wireless Application Protocol (WAP) represents a set of standards designed to facilitate the
presentation of information on wireless phones and other wireless devices with small display
screens. WAP, with its own protocol stack, is implemented via a WAP Gateway, illustrated in
Figure 5. The WAP Gateway translates between conventional HTML-based server formats and
the Wireless Markup Language (WML) more appropriate to hand-held devices.
Concord Communications – Introduction to Wireless Technology
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wired infrastructure
internet
WEB
server
WAP
gateway
WAP Protocol
mobile infrastructure
wireless devices
Figure 5. Wireless Application Protocol
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Wireless LANs, as their name implies, support short-range communication among multiple
devices over airwaves. Broadly speaking, they can be divided into two categories: the more
powerful wireless LANs, designed primarily for corporate use, and Personal Area Networks
(PANs), for more limited distance personal and home use.
The dominant corporate wireless LAN standard is IEEE 802.11, which supports an Ethernet-like
protocol and offers wireless devices access to each other or to a fixed network. Unlike Ethernet,
IEEE 802.11 utilizes a collision avoidance mechanism rather than collision detection, since
airwave delays are too large to guarantee that a station can hear any other station when
transmitting. IEEE 802.11 uses RTS/CTS (request-to-send/clear-to-send) and acknowledgment
mechanisms as well. An alternative to IEEE 802.11 is HiperLAN 2 which uses a TDMA
mechanism in place of collision avoidance.
Two common flavors of IEEE 802.11 are available. IEEE 802.11b operates in the unlicensed 2.4
GHz frequency band, supports speeds up to 11 Mbps and has a range of 100-300 meters,
depending upon the environment. IEEE 802.11a operates in the 5 GHz frequency band and
supports speeds up to 54 Mbit/sec. Both standards support the same datalink layer protocol, but
they differ in the way they use the underlying physical medium, that is, the airwaves.
IEEE 802.11b utilizes two different spread-spectrum technologies, which transmit over a broad
range of frequencies and are robust to noise and interference. Frequency Hopping Spread
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Spectrum (FHSS) sends data over a set of different frequencies in a predefined pattern and is
limited to a 2 Mbps data rate. Direct Sequence Spread Spectrum (DSSS) combines the data with
a spreading signal, in a fashion similar to CDMA, but with a single code, and transmits at rates up
to 11 Mbps.
IEEE 802.11a utilizes Orthogonal Frequency Division Multiplexing (OFDM) which sends data
simultaneously over multiple carrier frequencies and achieves speeds as high as 54 Mbps.
HiperLAN 2 utilizes OFDM as well.
The dominant PAN standard is Bluetooth (named after the king who united Denmark in the tenth
century). It supports speeds in the vicinity of 1 Mbps, a range of 10-100 meters, and is designed
for inexpensive communication among personal devices, for example, laptops, cell phones, and
other personal items. A typical application might link a mouse, keyboard, and printer to a single
personal computer and free the user from the inconvenience of cabling. Like 802.11b, Bluetooth
utilizes FHSS technology in the 2.4 GHz band.
Topologically, the 802.11 and Bluetooth technologies are more alike than different. Both support
infrastructure mode where there is at least one access point connected to a wired network and ad
hoc mode where a set of wireless devices communicate with each other independently, as shown
in Figure 6.
Ad Hoc
Infrastructure
Figure 6. Wireless LAN Topologies
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Wireless broadband offers point-to-point or multipoint links between fixed sites or between fixed
sites and points of presence. It can be used for local loop bypass or serve as a wireless WAN
where obstructions, bodies of water, rights of way, regulatory authorities, or cost preclude wired
alternatives.
Wireless broadband configurations include customer premise network termination devices
supporting end user ports (for example, T1/E1, Ethernet, and ATM). The termination devices are
connected to a remote base station via airwaves. The base station is, in turn, connected to
backbone networks via a set of fixed wired interfaces, as illustrated in Figure 7.
Wireless broadband utilizes a high-frequency licensed spectrum and a cellular technology, albeit
one designed for fixed, rather than mobile communication. It is a line-of-sight technology
permitting data rates of tens of megabits per second. Two wireless point-to-multipoint broadband
services have been licensed by the regulatory authorities. Multichannel Multipoint Distribution
Service (MMDS) has relatively large cells requiring a single transmitter for a radius of 24-30
miles. Local Multipoint Distribution Service (LMDS) utilizes smaller cells than MMDS, with
ranges up to 5 miles.
Concord Communications – Introduction to Wireless Technology
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To POTS, Internet
base
station
airwaves
customer premise
network
termination
T1/E1
Ethernet
ATM
Figure 7. Wireless Broadband
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The following sections describe some of the problems that Concord customers have encountered
in the wireless space and how eHealth can address them.
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Digital mobile wireless is in its infancy. Service providers are ramping up offerings and planning
to transition from G2 to G3 over the next three to five years. For the moment, wireless network
capacity is adequate to handle today’s speeds, transaction sizes, and numbers of subscribers. The
major concerns now are the systems and the applications that use the network. As the wireless
networks become more heavily utilized, we can expect more interest in monitoring the fixed and
mobile wireless infrastructures. Indeed, even at present, interest is evident in monitoring
SGSN/GGSN activity in a GPRS environment.
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Mobile wireless service providers face the following three basic problems:
•
Guaranteeing the availability and performance of the servers and associated applications
that use the network,
•
Maintaining the integrity of the fixed wireless support infrastructure, and
•
Maintaining the integrity of the mobile wireless support infrastructures.
The first problem is of more immediate concern than the latter, but they are expected to grow in
importance very quickly and should not be ignored.
eHealth system and application monitoring products address the first problem. System Health
can monitor the servers that support mobile wireless applications, and Application Health, along
with associated eHealth SystemEdge Agents and plug-ins, permits monitoring of the various
applications of interest. eHealth supports SystemEdge plug-ins for IIS, Apache, Exchange,
Oracle, SQL Server, and Checkpoint Firewall-1.
Solving the second problem requires routine monitoring of a service network. Our old standby
products Router/Switch Health and LAN/WAN Health provide support for the fixed wireless
infrastructure.
The only missing piece is a solution to the third problem, explicit monitoring of the mobile
wireless infrastructure. Support for this feature is currently under discussion.
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Enterprise customers today are implementing wireless LANs and require the same level of
network performance monitoring as for their traditional wired LANs. In addition to this, the
implementation of wireless LANs brings with it new issues related to the performance of the
underlying physical layer over airwaves, including congestion at the access point and signal
attenuation.
eHealth can manage wireless LANs in much the same fashion as wired LANs, that is, as a
variation of the same basic LAN element. Figure 8 is a wireless LAN At-a-Glance report. It
contains many of the same panels as wired LAN At-a-Glance reports, as well as new panels
which specifically address wireless LAN features, for example, RTS failures, retry statistics, and
duplicate frames.
We expect network operators and network managers to be particularly interested in monitoring
availability and bandwidth utilization. The former identifies network outages while the latter
emphasizes over-utilized bandwidth which leads to delay and response time problems. Studying
historic trends will enable managers with Live Health to establish alarm thresholds to permit them
to fix network outages before they occur, and to ignore intermittent problems and concentrate on
real ones. eHealth Live Exceptions permits alarming when the value of a variable of interest is
above or below a threshold for a significant period of time. For example, eHealth generates a live
Concord Communications – Introduction to Wireless Technology
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exception when the number of errors on a Wireless LAN rises to an unacceptable value and
remains there long enough to indicate a real problem.
At-a-Glance Report
Wireless LAN Element Mortimer-Seg-1
BW: 11.0 Mbps
Bandwidth Utilization
15%
Errors (errors/sec)
0.02 incoming
10%
0
5%
0.02 outgoing
0%
Frames (frames/sec)
500 incoming
0
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0
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0.001
0
0
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20
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Successful Retries (/sec)
0.003
0.002
0
20
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outgoing
0
0
Latency (msec)
30
Duplicate Frames (/sec)
0.003
20
0.002
10
0.001
0
0
Availability
100%
Maxed Out on Retries (/sec)
0.003
0.002
50%
0.001
0%
0
Time
Time
Figure
2. 8.
Wireless
LAN
Report Report
Figure
Wireless
LANAAG
At-a-Glance
Concord Communications – Introduction to Wireless Technology
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Service providers and enterprise customers are implementing fixed wireless services today. They
need to integrate these devices into their networks and monitor them in the same fashion as other
local loop broadband devices. Wireless broadband reports are of interest to the following
personnel:
•
Service provider and enterprise capacity planners need to predict and detect proactively
when a fixed wireless infrastructure will start to degrade. They need to recommend
service upgrades and implement infrastructure improvements before users become aware
of any problems.
•
Service provider account managers are interested in trend analysis as it relates to airwave
bandwidth utilization. Sales personnel want to be able to go to the customer, report in
hand, and pitch upgrades.
•
Service provider and enterprise NOC personnel monitor the LMDS/MMDS digital base
stations and network terminations and need to isolate and correct problems in real time.
eHealth is able to support these devices by certifiying key wireless broadband elements,
specifically:
(a) network termination end user ports
(b) airwave links between the network termination device and the base station
(c) base station interfaces to a fixed infrastructure
(d) base stations
(e) network termination devices
For items (a) through (c), we can use our existing LAN/WAN models. For items (d) and (e) we
can make use of Router/Switch models. A base station can be viewed as a switch with interfaces
(b) and (c); similarly a network termination device can be viewed as a switch with interfaces (a)
and (b).
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[1] AU-System Radio AB, WAP White Paper, © AU-System Radio, February 1999
[2] Judy Berck, A Brief History of PCS (Digital Cellular) Technology Development in the United
States, © 1999 Intel Corporation, http://www.mdi-ng.org/es53060/history.htm#Introduction
[3] Bell Mobility, Overview of CDMA Data And Security, Version 1.0, March 3, 1999, © 1999,
http://www.bellmobility.ca/digitaldata/developer/cdmaoverview.asp
[4] Tom Farley, Mobile Telephone History, http://www.privateline.com/PCS/history.htm
Concord Communications – Introduction to Wireless Technology
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[5] Trillium Digital Systems, Inc., Third Generation (3G) Wireless White Paper, March 2000,
http://www.trillium.com/whats-new/wp_3g.pdf
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1G. The earliest mobile wireless generation, featuring analog voice communication over cellular
frequencies.
2G. The current mobile wireless generation dominated by digital cellular communication for
voice and low-speed data. 2G offers cellular communication utilizing TDMA superimposed over
FDMA or occasionally CDMA.
2G+. See 2.5G.
2.5G. This term represents data services based on a 2G infrastructure that permit higher data
speeds -- of the order of hundreds of kilobits/second -- than basic 2G. The most well-known
2.5G service is General Packet Radio Service (GPRS), an IP-based value-added service
superimposed on GSM.
3G. The upcoming mobile wireless generation featuring high-speed digital cellular
communication, up to 2 Mbps, based on CDMA.
Advanced Mobile Phone System (AMPS). A 1G service based on FDMA and analog signalling,
used in the United States.
Bluetooth. The dominant PAN standard, named after the king who united Denmark in the tenth
century. It was designed for inexpensive communication among personal devices such as
laptops, cell phones and other personal items.
Code Division Multiple Access (CDMA). A mechanism for sharing cellular bandwidth based on a
spread-spectrum technology that assigns a distinct digital code to each user and supports all users
on a range of frequencies.
Concord Communications – Introduction to Wireless Technology
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Direct Sequence Spread Spectrum (DSSS). A wireless modulation technique, used by IEEE
802.11b, which combines the data with a spreading signal and transmits at rates up to 11 Mbps.
Frequency Division Multiple Access (FDMA). A mechanism for sharing cellular bandwidth which
assigns an entire frequency channel to each connection.
Frequency Hopping Spread Spectrum (FHSS). A wireless modulation technique, used by IEEE
802.11b, which sends data over different frequencies in a predefined pattern. FHSS can achieve a
2 Mbps data rate.
Gateway GPRS Support Node (GGSN). A gateway from a fixed GPRS infrastructure to an
external network.
General Packet Radio Service (GPRS). An IP packet service based on GSM.
Global System for Mobile Communications (GSM). The most popular 2G technology,
standardized by the European Union.
GPRS Tunnel Protocol (GTP). A protocol which exchanges information between SGSNs and
GGSNs by tunnelling through an IP infrastructure.
HiperLAN 2. A corporate wireless LAN standard that uses TDMA over OFDM. HiperLAN 2 is
an alternative to IEEE 802.11.
IEEE 802.11. The dominant corporate wireless LAN standard. IEEE 802.11 supports an
Ethernet-like protocol and provides wireless devices access to each other or to a fixed network. It
utilizes a collision avoidance mechanism, RTS/CTS (request-to-send/clear-to-send) exchanges,
and acknowledgment mechanisms. Two flavors of IEEE 802.11 are available: IEEE 802.11a and
IEEE 802.11b. They offer the same layer 2 protocol, but differ in the way they use the
underlying physical medium, that is, the airwaves.
Local Multipoint Distribution Service (LMDS). A licensed, cellular, point-to-multipoint
broadband service which utilizes relatively small cells with a range of up to five miles.
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Mobile Wireless. A technology that supports hand-held devices using cellular technology over
airwaves. Mobile wireless utilizes base stations and a fixed infrastructure to permit connectivity
with traditional telephone and data networks.
Multichannel Multipoint Distribution Service (MMDS). A licensed, cellular, point-to-multipoint
broadband service which has relatively large cells with a 24 to 30 mile radius.
Orthogonal Frequency Division Multiplexing (OFDM). A wireless modulation technique, used
by IEEE 802.11a and HiperLAN 2, which sends data simultaneously over multiple carrier
frequencies and achieves speeds as high as 54 Mbps.
Personal Area Network (PAN). A wireless LAN technology designed for personal and home use,
featuring low-cost, relatively low bandwidths, and short ranges.
Serving GPRS Support Node (SGSN). A device in a fixed GPRS infrastructure that permits
mobile stations to communicate with remote services.
Time Division Multiple Access (TDMA). A mechanism for sharing cellular bandwidth which
assigns a time slot within a frequency channel to each connection.
Total Access Communication Systems (TACS). A 1G serivce based on FDMA and analog
signalling, formerly used in Europe.
Wireless Access Protocol (WAP). A set of standards designed to facilitate the presentation of
information on wireless devices with small display screens.
Wireless Broadband. An access technology that provides connectivity to central offices using
licensed spectrum over airwaves. Wireless Broadband is a wireless alternative to wired access
technologies such as DSL and cable.
Wireless LAN. A local area network which communicates via airwaves rather than traditional
wired media
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