Note: Descriptions are shown in the official language in which they were submitted.
CA 02281009 2000-11-09
APPARATUS AND METHOD FOR BRIDGING A WIRED NETWORK AND
WIRELESS DEVICES
FIELD OF THE INVENTION
This invention relates to an apparatus and method for bridging a wired network
and wireless
devices, and more particularly, to a bridge apparatus and method for bridging
a wired network to a
plurality of wireless devices of different types and modalities.
BACKGROUND OF THE INVENTION
In warehouse inventory control, it is known to use handheld wireless units
communicating
with a central computer through one or more base stations. The central
computer is typically
provided in a wired Local Area Network (LAN). The base stations handle data
traffic between the
central computer and the handheld wireless units. Each base station is
provided with a radio through
which data received from the central computer is transmitted to the handheld
wireless units, and vice
versa.
The wired LAN uses a wired network protocol, such as Transmission Control
Protocol/Internet Protocol (TCP/IP) for communications between wired
communication devices.
Wireless networks have much lower capacity and higher error-rate compared to
wired networks. The
common wired protocols are very inefficient and often not suitable for
wireless networks. Thus, the
wireless devices use a wireless network protocol which is designed for use
over a wireless network.
A typical base station monitors messages on the wired network. When the base
station
recognizes that a message on the wired network is intended for one of the
wireless handheld units,
it strips all of the wired network protocol information from the message and
replaces it with wireless
network protocol information. For this reason, a base station is sometimes
called a protocol
converter.
There exist base stations for connecting a wired network and wireless devices,
such as those
connecting cellular phones and public telephone systems. However, these base
stations are very
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CA 02281009 2000-11-09
complicate and costly to manufacture. Accordingly, they are generally not
suitable for warehouse
inventory control.
In order to connect two networks, it is known to use bridges and routers. A
bridge connects
two networks which use the same protocols. The bridge reads data received 'ul
its input. It creates
a table of end-stations indicating the direction of the connection of the end
stations. The bridge
forwards the data as appropriate. However, it does not deal with connections
between two networks
which use different protocols. Further, existing bridges are designed for
connecting two wired
networks. A router can act as a protocol convertor. It alters packets to
connect two networks which
use different protocols. However, existing routers are generally designed for
connecting two wired
networks.
United States Patent No. 5,546,397 issued to Mahany on August 13, 1996
discloses an access
point which is a base station provided on a wireless local area network with
which roaming portable
or mobile computer devices can connect and communicate. Each access point uses
two wireless
adapters and a low level protocol processor. The second adapter is essentially
a backup in the event
that the first adapter fails, thus improving the reliability of the access
point and the entire network.
Otherwise, the access point of Mahany functions in the same way as a typical
base station described
above, and does not provide any other additional functionality.
Therefore, it is desirable to provide an apparatus which can bridge a wired
network and a
plurality of wireless devices of different types or modalities, without
performing protocol
2D conversion, and which is simple and suitable for warehouse inventory
control.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a novel bridge apparatus
and method
which obviates or mitigates at least one of the disadvantages of the prior
art.
A bridge apparatus is provided for interfacing or bridging between a wired
network having
wired communication devices and wireless devices. In one embod'unent, the
bridge apparatus
includes two more radios having different modalities in order to provide
different modality and/or
types of coverage to different wireless devices. In another embodiment, a
single bridge apparatus
offers different coverage areas. The bridge apparatus can include a filter
device for filtering data
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CA 02281009 2000-11-09
received from the wired network, and forwards the filtered data to a wireless
device. Thus, data can
be forwarded to the wireless devices from the wired network without a need for
protocol conversion.
In another embodiment, a bridge apparatus functions both as an access point to
filter data received
from the wired network, and as a base station to convert protocol information
included in data
received from the wired network.
In one aspect of the invention, there is provided a bridge apparatus for
bridging between a
wired network having wired communication devices, and wireless devices
including first type
wireless devices and second type wireless devices, the bridge apparatus
comprising: a wired network
interface for interfacing data communication between the bridge apparatus and
the wired
communication devices of the wired network; a first type radio for interfacing
data communication
between the bridge apparatus and the first type wireless devices; a second
type radio for interfacing
data communication between the bridge apparatus and the second type wireless
devices: and a bridge
controller for controlling data traffic between the wired network and the
first and second type
wireless devices, the bridge controller functioning in a first mode using the
first type radio when data
is transmitted from or destined for the first type wireless devices, and
functioning in a second mode
using the second type radio when data is transmitted from or destined for the
second type wireless
devices.
In accordance with another aspect of the present invention, there is provided
a bridge
apparatus for bridging between wireless communication devices and a wired
network having wired
2 0 communication devices, the bridge apparatus comprising a wired network
interface for interfacing
data communication between the bridge apparatus and the wired network having a
first capacity for
data communication; a radio for interfacing data communication between the
bridge apparatus and
the wireless communication devices, the wireless communication devices having
a second capacity
for data communication; and a bridge controller for controlling data traffic
between the wired
2:5 network and the wireless communication devices, the bridge controller
having a filter device for
filtering data received from the wired network and forwarding filtered data to
the wireless
communication devices.
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CA 02281009 2000-11-09
Other aspects and features of the present invention will be readily apparent
to those skilled
in the art from a review of the following detailed description of preferred
embodnnents in
conjunction with the accompanying drawings.
~ BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further understood from the following description of
certain exemplary
embodiments and the drawings in which:
Figure 1 is a block diagram showing an embodiment of a bridge apparatus in
accordance with
the present invention;
Figure 2 is a block diagram showing data frame formats;
Figure 3 is a block diagram showing an embodiment of a filter device shown in
Figure 1;
Figure 4 is a block diagram showing an embodiment of a radio shown in Figure
1;
Figure 5 is a block diagram showing another embodiment of a bridge apparatus
in accordance
with the present invention;
Figure 6 is a diagram showing an example of use of bridge apparatuses shown in
Figure 5;
Figure 7 is a flowchart showing an embodiment of a method for bridging data
from a wired
network to a wireless device in accordance with the present invention; and
Figure 8 is a flowchart showing another embodiment of a method for bridging
data from a
wired network to a wireless device in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1, an embodiment of a bridge apparatus 10 according to the
present
invention is described. The bridge apparatus 10 is provided between a wired
network 12 and
wireless devices 14. The wireless devices 14 can be mobile devices, such as
handheld units or
vehicle mount devices, providing remote and/or mobile computing functions. The
wireless devices
14 can be wireless access points connecting between wireless networks.
The bridge apparatus 10 transparently bridges between the wired network 12 and
the wireless
devices 14. That is, the bridge apparatus 10 operates as an access point. The
bridge apparatus 10
monitors the wired network 12 for messages or data intended for any wireless
device 14 for which
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CA 02281009 2000-11-09
the bridge apparatus 10 is servicing, and forwards the data to the wireless
device 14. The bridge
apparatus 10 also receives data from a wireless device 14 and forwards the
data to the wired network
12. In this way, a population of wireless devices 14 appear to have a standard
connection to the
wired network 12 and can interact with other services and devices on the wired
network 12 without
any need for special handling.
The bridge apparatus 10 comprises a wired network interface 16, a radio 18 and
a bridge
controller 20.
The wired network interface 16 interfaces data communication between the
bridge apparatus
and wired devices of the wired network 12. The wired network interface 16 is
selected
10 depending on the type of the wired network 12. It can be an Ethernet
interface, a Token Ring
interface or other type of interface.
The radio 18 interfaces data communication between the bridge apparatus 10 and
wireless
devices 14.
The bridge controller 20 controls data traffic between the wired network 12
and the wireless
devices 14. The wireless devices 14 has capacity which is generally lower than
that of the wired
network 12. The bridge controller 20 is provided with a filter device 22. By
using the filter device
22, the bridge controller 14 controls the data traffic so that it does not
transfer all data received from
the wired network 12 to the wireless devices 14.
As shown in Figure 7, the bridge apparatus 10 receives data from the wired
network 12 (S02).
The lilter device 22 filters the data (S04), and forwards the filtered data to
the radio 18 for
transmission to the wireless devices 14 (S06). The filter device 22 simply
forwards the data to the
wireless devices 14 or disregards the data. It does not do any protocol
conversion.
Filtering of data by the filter device 22 can be carried out based on any
characteristics of data
which correspond to characteristics of one or more wireless devices 14.
For example, each of the wireless devices 14 can be assigned with a unique
address. When
a wired communication device sends data to a wireless device 14, it includes
in the data the address
of the wireless device 14. Using the address included in data, the filter
device 22 filters the received
data.
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CA 02281009 2000-11-09
The filter device 22 can filter the received data in different ways. It can
have a list of
addresses of wireless devices 14 for whom the bridge apparatus 10 does not
transmit data, and filter
the data including an address which is listed in the list. Also, the filter
device 22 can have a list of
multicast addresses for whom the bridge apparatus 10 does not transmit data,
and filter the data
1.5 including the multicast addresses which are listed in the list.
Similarly, the filter device 22 can use lists of addresses of wireless devices
14 for whom the
bridge apparatus 10 transmits data.
Data sent by a wired device includes protocol information which indicates the
wired network
protocol that the wired device uses to send the data. The filter device 22 can
filter data based on
such protocol information included in the data. By selecting specific
protocols, the filter device 22
directs the bridge apparatus 10 to forward or discard data that contain a
selected protocol. Thus, the
bridge apparatus 10 can be selective of what type of data will be bridged over
the radio, and can limit
the amount of data on the wireless network.
When the wired network12 is an Ethernet network, data being sent is divided
into frames.
Each frame encapsulates fields indicating a wired network protocol type which
is used for sending
the frame. The filter device 22 can forward or discard the data by filtering
the protocol type fields
in the frame.
The filter device 2 can strip out, i:or example, detailed graphics in a hyper-
text mark-up
language web page, before the web page is transmitted. In this example, the
filter device 22 simply
2D watches for graphic files associated with the web page, removes the graphic
file and the removes the
reference to the graphic file from the web page.
Figure 2 shows fields of three different Ethernet frame formats: Ethernet II
frame 30, Logical
Link Control (LLC) frame 50 and Simple Network Management Protocol (SNAP)
frame 70.
The Ethernet II frame 30 is a basic Ethernet frame which complies with the
IEEE 802.3
25 standard. It comprises an Ethernet header 32, data field 40 and Frame Check
Sequence (FCS) field
42. The Ethernet header 32 consists of a six-byte destination Media Access
Control (MAC) address
field 34, followed by a six-byte source MAC address field 34, and a two-byte
protocol type field 38.
If the protocol type field 38 contains a value that is greater than or equal
to "0x0600", it is assumed
to be the protocol identifier for an Ethernet II header.
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CA 02281009 2000-11-09
The protocol type field 38 is used to determine which protocol is being used
in the frame.
The filter device 22 can use the type filed 38 to filter the received data by
selecting the number which
represents the Ethernet II protocol type to be filtered.
For example, if the bridge apparatus 10 is to forward only TCP/IP type data to
the wireless
devices 14, the filter device 22 can create two protocol filters, one to
forward IP (type 0x0800) and
the other to forward Address Resolution Protocol (ARP) (type 0x0806). The
filter device 22
disregards data using other protocol types.
Referring back to Figure 2, when the protocol type field contains a value that
is less than
"OxO5DC", then the value is interpreted as a length field 52 instead, as shown
in the LLC frame 50.
It is assumed that an IEEE802.2 LLC header 54 is to follow the length field
52. The LLC header 54
consists of a Destination Service Access Point (DSAP) field 56, Source Service
Access Point
(SSAP) field 58 and control field 60.
The filter device 22 can filter the received data based on the values of the
DSAP field 56
and/or the SSAP field 58.
If the DSAP and SSAP are both "OxAA", and the control field 60 has a value of
"0x03", the
LLC header will be followed by an extension which is a SNAP header 72, as
shown ui Standard
Network Access Protocol (SNAP) frame 70. The SNAP header 72 uicludes an
Organization Unit
Identifier (OUI) field 74 and a SNAP type field 76.
The filter device 22 can filter selected values of OUI field 74 and/or SNAP
type filed 76.
The filter device 22 can be also used to prevent broadcast/multicast storms
from spreading
throughout the network. Network storms can burden radio traffic with
unnecessary data
transmissions.
Storm filtering can be done by setting the maximum number of
broadcast/multicast frames
that should be received in a predetermined period. Every broadcast/multicast
frame received will
be discarded until it is determined that the storm is over. The broadcast
storm is determined to be
over when the number of broadcast frames received for the predetermined period
is less than or equal
to the value entered in the maximum number.
Figure 3 shows an example of the lilter device 22. The filter device 22
comprises protocol
i-ilter 81, Ethernet II filter 82, LLC filter 83 and storm filter 84. The
protocol filter 81 filters based
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CA 02281009 2000-11-09
on protocol types. The Ethernet II filter 82 filters using the Ethernet
protocol type filed 38. The LLC
filter 83 filters using DSAP/SSAP fields 56, 58. The storm filter 84 uses the
maximum number of
broadcast/multicast frames. The data 80 is filtered by any of filters 81-84
and the filtered data 85
is output.
While this example contains four filters 81-84, the filter device 22 does not
need to contain
all of four filters 81-84. Some of filters 81-84 can be disconnected. Also,
each filter 81-84 can
consist of multiple filters of different criteria. The filter device 22 can
also contain other type of
filters.
By using the filter device 22, the present invention allows connection between
the wired
network 12 and the wireless devices 14 by a bridge apparatus 10 with a simple
structure suitable for,
e.g., warehouse inventory.
Also, by filtering data received from the wired network 12, the bridge
apparatus 10 can
transparently bridge data communication between the wired network 12 and
wireless devices 14
regardless the differences in the capacity of the wired and wireless networks.
This allows use of high
performance wireless devices 14.
An example of such high performance wireless devices 14 is those complying
with the IEEE
802.11 standard. The bridge apparatus 10 can be preferably applied to a
wireless network which
uses the IEEE 802.11 standard protocol.
The IEEE 802.11 standard protocol is an Open Systems Interconnection (OSI)
standard for
Wireless Local Area Networks (WLANs). It specifies a radio and wireless
protocol intended to
allow wireless devices from different manufactures to be used in the same
system. With this
standard, any IEEE 802.11 radio can communicate with any other similarly-
equipped device.
Previously each manufacturer selected a radio and had to create a proprietary
protocol that prevented
any chance of interoperability.
IEEE 802.11 solely standardizes two communications layers: Physical (PHY) and
Medium
Access Control (MAC). These different PHY layer media are covered by 2.4 GHZ
Direct Sequence
Spread Spectrum (DSSS) radio, 2.4GHz Frequency Hopping Spread Spectrum (FHSS)
radio, and
infrared. Each station in a WLAN system has its own unique MAC address.
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CA 02281009 2000-11-09
The bridge apparatus 10 can operate as an access point device between an IEEE
802.11
wireless network and a non-IEEE 802.11 wired network 12. Using the IEEE 802.11
protocol with
the bridge controller 20, the bridge apparatus 10 provides a transparent
interface or bridge between
IEEE 802.11 wireless devices 14, and non-IEEE 802.11 wired devices, such as a
host computer 12a
or a network controller 12b that resides in the non-IEEE 802.11 wired network
12.
In a present embodiment, the radio 18 is based on the IEEE 802.11 standard in
a Personal
Computer Memory Card International Association (PCMCIA) format. The radio
module includes
a radio transmitter, an antenna and a radio interface for electrical
connection.
The high data rates available with IEEE 802.11 standard can often mask the
inefficiency of
using protocols designed for wired networks over the wireless network.
Thus, the bridge apparatus 10 enables communication between any wireless IEEE
802.11-
equipped devices and wired LAN devices operating on Ethernet, using a bridging
protocol. The
bridge apparatus 10 itself is resident on the LAN and functions as a MAC
bridge, providing
transparent integration between the stations on the wireless and wired
networks. An IEEE 802.11
system can operate on one or more channels, with terminals moving between
multiple bridge
apparatuses.
The radio 18 can comprise multiple radio modules, such as radio cards, of same
or similar
characteristics. Figure 4 shows first radio card 90 and second radio card 93.
The first and second
radio cards 90 and 93 are of similar technology. Each radio card 90, 93 has an
antenna 91, 94. The
antennae 91 and 94 have distinct coverage areas 92, 95. By using two radio
cards, the coverage
range of a single bridge apparatus 10 can be extended at reduced installation
costs per coverage area.
There is no existing one ideal radio technology for all applications. For
ulstance high
frequency radios have excellent throughput capacity but low coverage
characteristics. Low
frequency radios have excellent coverage characteristics but low throughput
capacity. It is common
to abandon the lower frequency radios to achieve the higher data throughput.
However, it is
desirable that users can select the radio technologies that best meets
requirements of their
application.
In order to allow such selections, it is preferable that a bridge apparatus
functions both as an
access point and as a base station.
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CA 02281009 2000-11-09
Figure 5 shows an embodiment of such a bridge apparatus 100. The bridge
apparatus 100
is provided between a wired network 102 and wireless devices 104.
The wired network 102 can include a host computer 102a and a network
controller 104b.
The wireless devices 104 include first type wireless devices 106 and second
type wireless
devices 108. In a present embodiment, the first type wireless devices 106 use
2.4GHz Spread
Spectrum with the IEEE 802.11 standard protocol, and the second type wireless
devices 108 use a
narrow band, 902 Spread Spectrum, 2.4GHz Spread Spectrum using a non-IEEE
802.11 wireless
protocol. The second type wireless devices 108 can include wireless base
stations connecting
between wireless networks. It will be apparent that in other embodiments,
different combinations
of first type wireless devices 106 and second type wireless devices can be
used, as desired.
In the present embodiment, the first type radio 106 and second type radio 108
are used
independently.
Each of the first type devices 106 is preferably assigned with a unique
address. The second
type devices 108 can or can not have addresses as typical in handheld units
conventionally used in
warehouse inventory.
The bridge apparatus 100 comprises a wired network interface 110, a first type
radio 116, a
second type radio 118 and a bridge controller 120.
The wired network interface 110 is si.milar to the wired network interface 16
shown in
Figure 1. For example, it can be an Ethernet interface hardware provided on a
main logic board of
the bridge apparatus 100 or a Token Ring interface on a PCMCIA card.
The first type radio 116 interfaces data communication between the bridge
apparatus 100 and
the first type wireless devices 106. The second type radio 118 interfaces data
communication
between the bridge apparatus 100 and the second type wireless devices 108.
The bridge controller 120 controls data traffic between the wired network 102
and the
2:3 wireless devices 104. It has a bridge filter 122 and a protocol convertor
124.
The bridge controller 120 functions in a first mode when data is transmitted
from or destined
for the first type wireless devices 106. In this mode, the bridge apparatus
100 acts as an access point
ul a sunilar manner to the bridge apparatus 10 shown in Figure 1. As shown in
Figure 8, when the
data is received from the wired network 102 (S 10), the bridge controller 120
checks if it is for a first
CA 02281009 2000-11-09
type device 106 (S 12). If so, the bridge controller 120 filters data using
the filter device 122 which
is similar to the filter device 22 of the bridge apparatus 10 (S 14). The
filtered data is transmitted to
the first type wireless device 106 (S 16).
The bridge controller 120 also functions in a second mode when data is
transmitted from or
destined for the second type wireless devices 108. In this mode, the bridge
apparatus 100 acts as a
base station. As shown in Figure 8, when the data received from the wired
network 102 is for a
second type device 108 (S 12), the bridge controller 120 uses the protocol
convertor 124 to convert
between a wired protocol used by the wired devices and a wireless protocol
used by the second type
wireless devices 108 (S 18). The wireless protocol is designed to allow all
wireless devices 108 to
communicate with the bridge apparatus 100 functioning as a base station by
sharing the use of a
radio channel in an efficient way. The protocol convertor 124 replaces the
wired protocol
information with the wireless protocol information when data is to be sent to
the wireless devices
108. The protocol converted data is then transmitted to the second type
wireless device 108 (S20).
Thus, when the bridge apparatus 100 functions as an access point, it can use a
first type
wireless protocol, such as the IEEE 802.11 protocol. When it functions as a
base station, it can use
a second type wireless protocol, such as a protocol used on Spread Spectrum
radio systems.
The bridge controller 120 is preferably capable of operating in both first and
second modes
simultaneously.
As electrical interfaces to the first and second type radios 116, 118, it is
preferable that the
bridge apparatus 100 uses a PCMCIA connector. PCMCIA connectors allow easy
interchanging of
radio technologies and provide an upgrade path as new radio technologies. The
PCMCIA connector
has two PCMCIA electrical interfaces for two PCMCIA-based radio modules; one
for the first type
radio 116 and the other for the second type radio 118. The PCMCIA connector
allows multiple
radio interfaces for communication between the bridge apparatus 100 and the
first and second type
2_5 wireless devices 106, 108.
When the bridge apparatus 100 acts as a base station, it uses routing
information for
forwarding received data. The bridge apparatus 100 can send out polls to
obtain routing information.
Then, it can regularly broadcast routing information indicating the available
routes back to the
network controller 102b. Wired devices of the wired network 102, wireless
devices 108 and wireless
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CA 02281009 2000-11-09
base stations receive the broadcasts, and determine the best communication
route to send their
messages. If a better route becomes available, the respective wired devices,
wireless devices and
base stations change communication paths accordingly.
It is preferable that the second type wireless protocol allows one or more
base stations to be
added to the entire system without cable connections. The system can operate
on one channel or on
multiple channels.
As described above, each of the first type wireless communication devices 106
is assigned
with an address. Data transmitted from and destined for one of the first type
wireless communication
devices 106 includes such an address. The bridge controller 112 can perform in
the first and second
modes in accordance with the address included in the data.
As previously discussed, different types of radios or wireless devices offer
different ranges
of coverages and bit-rates, and accordingly, for this and other reasons it can
be desired to provide
a plurality of coverage areas within a larger area, in order to provide
seamless coverage to radios or
wireless devices moving between the coverage areas.
In the present embodiment of the invention, coverage areas can be integrated
by providing
multiple bridge apparatuses (i.e. combinations of bridge apparatus 10 and/or
bridge apparatus 100,
as desired) in a network system. Each bridge apparatus offers its own radio
coverage. The bridge
apparatuses are preferably distributed to cover a predetermined area with
their radio coverages. This
allows wireless devices to move seamlessly between the bridge apparatuses 10,
100 in the system.
2~D It is presently pref'erred that the mobile wireless device manages the
transfer of
communication between adjacent bridges. For example, when a mobile wireless
device moves from
a first radio coverage of a first bridge apparatus to a second radio coverage
of a second bridge
apparatus, the mobile wireless device initiates communicates with the second
bridge, and upon
establishing a successful communication ulterface therewith, terminates
communications with the
2 5 first bridge apparatus, thus effecting a seamless transfer of
communication between the first and
second bridges. It will occur to those of skill in the art that other means of
effecting transfer from the
I:irst bridge to the second bridge can be implemented in other embodiments of
the ulvention, as
desired.
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CA 02281009 2000-11-09
Figure 6 shows an example of use of multiple bridge apparatuses in accordance
of the
invention in a network system 200. The network system 200 uses three bridge
apparatuses 210, 212,
214 to bridge between a wired local area network 220 and wireless devices 230-
240.
The wired network 220 includes a host computer 222 and a network controller
224. The
~ wired network 220 uses Transmission Control Protocol/Internet Protocol
(TCP/IP) on Ethernet
medium 226.
The wireless devices 230, 232 are handheld RF termuials and the device 234 is
a wireless
access point. The handheld RF terminals 232 communicate with the wireless
access point 234. The
wireless devices 230, 232, 234 comply with the IEEE 802.11 Wireless LAN
Standard, and as such
are each first type wireless devices. The devices 230, 232, 234 can use either
FHSS 2.4GHz or
DSSS 2.4 GHZ.
The wireless device 236 is a vehicle-mount RF terminal, the devices 238 are
handheld RF
terminals and the device 240 is a wireless base station. The wireless devices
234, 236 and 238 are
second type devices, and use the 902 MHz DS spread spectrum. The RF terminals
236 communicate
113 with the base station 238.
The bridge apparatus 210 is currently functioning as an access point to
communicate with
the RF terminals 230, 232 and access point 234. The bridge apparatus 210 is
connected to the
Ethernet link 226 of the wired network 220 through an Ethernet uiterface.
As an access point, the bridge apparatus 210 forms a communication link
between the local
2 0 area network 220, and the RF terminals 230 and access point 234 which form
a fiirther
communication link with the RF terminals 232. The bridge apparatus 210
communicates over an
IEEE 802.11 RF data link with the RF terminals 230 and the access points 234,
and over a cable with
the host computer 222 and the network controller 224 residing on the wired
network 220.
The bridge apparatus 212 is currently functioning as a base station to
communicate with the
2'-D vehicle-mount RF termina1236 and wireless base station 240 which in turn
coinmunicates with the
low performance handheld terminaLs 238.
As a base station, the bridge apparatus 212 provides a communication link
between the local
area network 200, and the RF terminals 236, 238 and the wireless base station
240 and their
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CA 02281009 2000-11-09
terminals 238. The bridge apparatus 212 uses a protocol for low performance
wireless
communication with the RF terminals 236, 238 and the base station 240.
The bridge apparatus 214 is currently functioning as both an access point and
a base station
to communicate with handheld RF terminals 230 and a handheld termina1238.
Each bridge apparatus 210, 212, 214 has a memory which stores boot code,
configuration
parameters and firmware. The configuration parameters can be changed, added or
deleted. They can
be reconfigured remotely via the wired network 220 using, for example, a
standard hyper-text mark-
up language (HTML) web browser.
When a RF terminal 238 moves from the radio coverage of the bridge apparatus
212 to the
radio coverage of the bridge apparatus 214, the bridge apparatus 212 hands
over the data
communication with the handheld terminal 238 to the bridge apparatus 214. The
terminal 238
communicates with bridge apparatuses and base stations which are within the
radio range of the
termuial 238. It determines which bridge apparatus or base station provides
the best communication
path to a bridge apparatus which resides on the wired network 220, using
routing information stored
in each bridge apparatus or base station. If multiple channels are used, the
terminal looks for a better
channel only if it cannot find an acceptable path back on its current channel.
When a RF termina1230 moves from the radio coverage of the bridge apparatus
210 to the
radio coverage of the bridge apparatus 214, the termina1230 manages the
transfer of communication
from bridge apparatus 210 to bridge apparatus 214.
For example, when the bridge apparatus 210 is connected to the wired Ethernet
LAN 220,
a wired device on the network 220 encapsulates the data in an Ethernet frame,
including a destination
MAC address specifying the mobile terminal 230, and sends the frame onto the
LAN 220. The
bridge apparatus 210, which has the mobile terminal 230 associated therewith,
takes the frame and
passes it over the RF link to the mobile terminal 230. Similarly, a frame from
the mobile terminal
230 is sent to the bridge apparatus 210 associated with the mobile terminal
230. The mobile terminal
230 puts a destination MAC address in the frame that specifies a hardware
address of a wired device
on the LAN 220. On the LAN 220, the frame is picked up by a wired device at
the destination
hardware address. By passing frames in this way, the bridge apparatus is
acting as a MAC bridge.
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CA 02281009 2000-11-09
When the terminal 230 moves out of range of the bridge apparatus 210, it will
associate with
another bridge apparatus, e.g. 214, which will then receive the data frames of
the termina1230. One
suitable means for selecting a bridge apparatus to be associated with
termina1230 is discussed in the
802.11 Specification. The bridge apparatus 214 passes the data onto the
Ethernet LAN 220 in
Ethernet frames. Returning frames are no longer accepted by the first bridge
apparatus 210, which
has disassociated from the mobile terminal 230. Returning frames for the
mobile terminal 230 are
now accepted by the newly-associate bridge apparatus 214 and passed over the
RF to the mobile
termina1230.
While particular embodiments of the present invention have been shown and
described,
changes and modifications can be made to such embodiments without departing
from the scope of
the invention. For example, only first and second type radios are used in the
above embodiment, but
more than two different types of radios can be used. Also, two radio cards per
each radio is disclosed
in the above embodiments, but more than two radio cards can be used.
Furthermore, they do not
have to take a form of radio cards. Any types of radios suitable for the
purposes of the bridge
apparatus can be used. The host computer can also function as a network
controller. It will also be
apparent that the present uivention encompasses combinations of the above-
described embodiments.
