Method and apparatus for connecting a wireless LAN to a wired LAN

An internetworking node for providing internetworking services for mobile wireless nodes. Each mobile wireless node is associated with at the most one internetworking node. Each mobile wireless node selects which internetworking node it will associate with. The internetworking node will then act for all wireless nodes associated to it in relaying messages between wireless nodes or between a wired Local Area Network (LAN) and the wireless nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This patent application is related to the applications titled, ACCESS POINT 
SWITCHING FOR MOBILE WIRELESS NETWORK NODE, and ACCESS POINT TRACKING FOR 
MOBILE WIRELESS NETWORK NODE, both filed concurrently herewith, the 
disclosures of which are hereby incorporated by reference. 
FIELD OF THE INVENTION 
This invention pertains to wireless networks generally, and means for 
connecting wireless nodes or wireless LANs to wired LANs in particular. 
BACKGROUND OF THE INVENTION 
Local Area Networks (LANs) have historically consisted of nodes 
interconnected by physical telecommunications media (eg, coaxial cable, 
twisted pair wire, or fiber optics). We shall refer to such LANs as wired 
LANs. 
Recently wireless LANs, the nodes of which are not connected by means of a 
physical medium, have started to appear in the market. These wireless LANs 
communicate by means of infra-red (IR), radio or other signals. One of the 
benefits of using wireless LANs is that cabling is not required. This is a 
particularly useful feature for mobile nodes such as laptop and notebook 
computers, PDAs (personal digital assistants), and the like. If 
appropriately equipped with an appropriate wireless adapter (which 
includes a transmitter/receiver and control card), such as an IR wireless 
Adapter, the mobile nodes can move around and remain connected to the 
network, provided they do not move out of range. 
One method of implementing a wireless LAN is similar to a cellular phone 
network system. In this method wireless nodes do not communicate directly 
with each other, but rather send all signals to a central base station, 
which then redirects the signals to the destination node. 
However, in certain situations, it is advantageous to allow each wireless 
node to communicate directly with other nodes, as is the case in most 
wired LANs. In a wireless LAN which permits this, the wireless adapter and 
controlling software transmit data packets which all nodes within range 
can hear. This permits transmitting of packets which are received but 
ignored by all nodes except the one(s) to which they are addressed. This 
parallels the packet delivery systems of such wired LAN protocols as 
Ethernet. Thus, upper level network operating system software, which 
relies on a packet delivery system such as Novell Corporation's NETWARE 
(tm) can be used with such a wireless LAN. We shall refer to such a 
wireless LAN as a Peer-to-Peer Wireless LAN. 
There is an important physical characteristic in a peer-to-peer wireless 
LAN that makes it very difficult to build a reliable network compared to a 
wired LAN. In a wired LAN, every network node is physically connected to 
the network and can therefore access all of the network traffic. This is 
often not the case with wireless LANs. Each node communicates with other 
nodes by means of some form of electromagnetic signal, the range of which 
will be limited. Each node will have an area of coverage which will be 
limited by such factors as type of signal, signal strength, obstacles 
within range, etc. In the wireless LAN, it cannot be guaranteed that every 
network node, which is presumably part of the same wireless network, can 
listen to all the network traffic. For example, if nodes A, B, and C are 
connected to the same wireless network, A may be able to listen to the 
network data sent by B but not by C. In this case, C is a "hidden node" 
with respect to A. If C can listen to B but not to A, then A is a hidden 
node with respect to C. 
For proper functionality, it is desirable that a wireless LAN should also 
be able to connect to a wired LAN. In wireless LANs using a base station 
approach, the Base Station can provide such connectivity. However, there 
exists a need for system which can provide internetworking services 
between a peer-to-peer wireless LAN and a wired LAN. 
There are several problems associated with a wireless LAN which complicate 
the implementation of a simple bridge as a means for connecting a wireless 
LAN to a wired LAN. The primary function of such a device would be to 
resend overheard wireless LAN network data that is destined for a wired 
node onto the wired LAN, and vice versa. Depending on the wireless medium 
chosen, each such device would normally have a limited range. In order to 
provide adequate coverage, a plurality of devices, each having some degree 
of overlapping area is necessary. This would normally result in the 
duplication of messages received by nodes within the overlapping areas, 
and also on the wired LAN for messages originating from such nodes. 
There exists a need for a system which solves these and related problems. 
In this specification, the following terms are used: 
By internetworking services, we refer to services which allow systems to 
communicate which could not otherwise. Typical internetworking services 
include relaying messages from one wireless node to another, resending 
messages from a wired LAN to a wireless node and resending messages from a 
wireless node to a wired LAN. 
The internetworking node that provides such internetworking services is 
called an Access Point or AP. The AP is a physical device, which, in order 
to perform the full range of internetworking services has a wired network 
adapter as well as a wireless network adapter. 
The physical area that a wireless node must be within to be within range of 
the AP is called the AP's Basic Service Area (BSA). If a wireless node is 
located within the BSA of a particular AP, that wireless node will be able 
to receive transmissions sent by that AP. 
Each wireless node also has a limited range within which it can 
communicate. This range is called the Dynamic Service Area (DSA) of the 
wireless node in this specification. Other nodes within an wireless node's 
DSA will normally be able to receive transmissions from the wireless node. 
If the wireless nodes use the same adapter as the APs, then, all other 
things being equal, the wireless nodes will have the same range as the 
APs. However there can be differences between the BSA range of the AP and 
the DSA range of a wireless node. For one thing, the wireless nodes are 
usually movable. Thus their range is likely to change, depending on how 
their signals are affected by obstacles as they move. Also, access points, 
being physically connected to a wired LAN, are also connected to a supply 
of power. Thus, the transmitter used in an AP can be more powerful than 
the battery powered transmitters of the wireless nodes. If this is the 
case, the BSA range of an access point would normally be larger than the 
DSA range of a wireless node. 
In this specification, we will distinguish between the BSA of an AP and the 
DSA of a wireless node, even if the two ranges are the same. In this 
specification, one wireless node is said to be able to "hear" a second 
wireless node if it is within the DSA of the second node, so that signals 
sent by the second node can be received by it. Similarly, a wireless node 
can "hear" an AP if it is within the BSA of the AP, and an AP can "hear" a 
wireless node if the AP is within the DSA of that node. 
A "multicast" message is a form of broadcast message, sent by a wired or 
wireless node, which is addressed to other nodes having the same specific 
group address. All other wired or wireless nodes will ignore that message. 
SUMMARY OF THE INVENTION 
The invention provides a method and a means for providing internetworking 
services to wireless nodes. The invention provides for an internetworking 
node which can either directly relay a message from one wireless node to 
another wireless node, or forward such messages indirectly by first 
resending them to another such internetworking node which in turn resends 
the message to the other wireless node. The internetworking devices 
themselves can communicate through the wireless medium. Preferably, such 
internetworking devices are interconnected by means of a wired LAN. 
From a user's point of view, the invention makes such wireless nodes, as 
for example from a wireless LAN, and a wired LAN appear as a single 
logical LAN. The invention allows for integration of wireless nodes with 
existing wired LAN based network operating systems and network 
applications, by making each wireless node appear as wired network nodes 
to other wired network nodes when a wireless node sends data packets to a 
wired network node. Similarly, where a wireless node is part of a wireless 
LAN, the invention makes a wired network node appears as a wireless node 
to other wireless nodes when the wired network node sends data packets to 
the wireless node. 
The invention provides a method and means for using one or more APs as 
internetworking devices which interconnect a wired LAN and wireless nodes 
within range of each AP, and for determining when each AP should act to 
transmit data between the wired LAN and wireless nodes. 
The primary functions for each AP are, when appropriate, i) to resend data 
packets from a wireless node onto the wired LAN if the data packets cannot 
otherwise reach their destination (eg, if they are destined for a wired 
node, or are destined for a wireless node outside of the DSA of the 
sending node); and ii) to resend data packets, which are addressed to a 
wireless node, from the wired LAN to the wireless node. In the preferred 
embodiment, the wireless node is part of a wireless LAN. The AP, having 
both a wired network adapter as well as a wireless network adapter, can 
communicate using both the packet delivery system of the wired medium, as 
well as the packet delivery system of the wireless medium. Furthermore, 
the AP is able to convert a data packet from one system to the other. 
Preferably, the APs will also redirect information between two wireless 
nodes which are both within the AP's range, but are hidden to each other. 
The invention allows for this even if the AP is not connected to a wired 
LAN. 
To achieve these functions each AP has to know whether the data packets are 
for a destination within its own BSA, and whether it is responsible for 
acting. The wireless nodes use a process of association with at most one 
of the APs to carry out these functions. Each wireless node within range 
of at least one AP will associate itself with a single AP, even if it is 
within range of more than one AP. Once a wireless node associates itself 
with an AP, it will use that AP, and only that AP, to forward data to and 
from the wireless node. The AP keeps track of which nodes are associated 
with it, in order to determine whether it is responsible for acting. 
Each wireless node monitors the wireless network traffic, and keeps track 
of which nodes are within its range, ie, which other wireless nodes it has 
overheard recently. According to the invention, each wireless node uses 
this information to determine which wireless nodes, including APs, are 
within its range. 
Preferably, each AP broadcasts information about itself at regular 
intervals. In the preferred embodiment, this broadcast is in the form of a 
beacon identifying its network address. Each wireless node can determine, 
from either the AP's regular data transmissions, or from this beacon, 
whether it is within the AP's BSA. The wireless node keeps track of APs it 
has overheard. Preferably the node maintains a table of APs it has 
overheard recently. 
If the wireless node overhears data packets (either normal traffic or a 
beacon) from an AP, it can attempt to associate with the AP by sending an 
association request to the AP. If a wireless node's association request 
fails, it will preferably attempt to associate with another AP currently 
in its AP table. If the wireless node overhears more than one AP, or there 
is more than one AP in its table, the wireless node determines which AP it 
will select. In one embodiment, the mobile node selects the AP it has 
heard most recently. 
When a wireless node (the sending node) needs to send a data packet to a 
particular node (destination node), it first checks to see if it has 
recently overheard the destination node (implying the destination is 
within range). Optionally, each wireless node can emit a beacon to assist 
the other nodes in this. 
If the destination node is within range, the sending node transmits the 
data packet directly to the destination node. If the sending node has not 
recently overheard the destination node, the sending node checks to see 
whether it is associated with an AP. Assuming the sending node is 
associated with an AP, the node transmits the packet to the AP and asks 
the AP to forward the data packet to its destination. 
Once an AP has received a request from a sending node, which it is 
associated with, to forward a data packet, the AP will check to see if the 
destination node is also associated with this AP. If so, the AP will 
transmit the data packet directly to the destination node. If not, the AP 
will resend the data packet, which is still addressed to the destination 
node, onto the wired network. 
Whenever an AP overhears a directed packet on the wired LAN addressed to a 
wireless node, the AP checks to see if that node is associated with it. If 
so, the AP will forward the data packet to the node. Otherwise, the AP 
will ignore the packet. Similarly, whenever an AP overhears a broadcast 
packet on the wired LAN, it retransmits the packet to all wireless nodes 
associated with it. 
Thus, in the preferred embodiment, each wireless node actively selects 
which AP it is associated with, and determines whether it needs an AP's 
help to send messages. Each AP keeps track of which wireless nodes are 
associated with it, and automatically relays data packets addressed to 
associated nodes which the AP has received, either from the wired LAN, or 
from another associated wireless node. 
A broad aspect of the invention provides for a node for communication in a 
network, comprising wireless network adapter means for sending data by 
wireless communication to other nodes in the network and receiving data by 
wireless communication from such nodes, monitoring means for monitoring 
data which are received by said wireless adapter means, to extract from 
said data identifying information which identifies the other network nodes 
whose data are received, and storage means for storing the identifying 
information. 
Another broad aspect of the invention provides for a method for 
communication in a network, comprising sending data by wireless 
communication from a first node in the network to other nodes in the 
network and receiving data by wireless communication from such nodes, 
monitoring data which are received to extract from said data identifying 
information which identifies the other network nodes whose data are 
received, and storing the identifying information. 
These foregoing aspects of the invention, together with other aspects and 
advantages thereof will be more apparent from the following description of 
the preferred embodiments thereof, taken in conjunction with the following 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment is discussed and illustrated with respect to an 
example of its implementation using Infra-red (IR) wireless LANs and 
Ethernet wired LANs. It should be appreciated that the invention is not 
limited to IR wireless LANs or Ethernet wired LANs and could be similarly 
implemented in other wireless LANs and/or wired LANs. 
FIG. 1 and FIG. 2 each illustrate a configuration of wireless nodes A, B, 
C, D and E, a wired LAN 50, wired node X and APs AP1 and AP2. Each AP is a 
physical device that has a wired network adapter as well as a wireless 
network adapter. Each AP understands both the wired LAN and wireless LAN 
protocols. 
In the preferred embodiment, using ISO/CCITT OSI international standard 
terminology, the AP behaves as a layer 2 Data Link Layer entity that 
"bridges" between the wireless LAN and the wired LAN. It resends the data 
traffic from the wireless LAN to the wired LAN in such a way that the data 
traffic appears to nodes of the wired LAN to have come from wired network 
nodes in the wired LAN. It also resends the data traffic from the wired 
LAN to the wireless LAN in such a way that the data traffic appears to the 
wireless nodes of the wireless LAN to have come from wireless nodes in the 
wireless LAN. Thus, each AP functions as a transparent MAC-bridge (wherein 
MAC stands for Medium Access Control, as is known in the art) that 
connects the IR wireless nodes to the ethernet wired LAN. 
In the examples illustrated in drawings, the same wireless adapter is used 
for both the APs and the wireless nodes. Therefore the BSA range of the 
APs, ignoring the effect of obstacles, will be the same as the DSA ranges 
for the wireless nodes. As stated earlier, the AP, being connected 
physically to a power supply, could support a more powerful transmitter, 
with an extended BSA range. 
FIGS. 1 and 2 are the same except that FIG. 1 illustrates the DSA ranges of 
the wireless nodes while FIG. 2 illustrates the BSA ranges of the APs. In 
FIG. 1, wireless node A has a DSA 10, wireless node B has a DSA 20, 
wireless node C has a DSA 30, wireless node D has a DSA 40, and wireless 
node E has a DSA 45. 
In the IR wireless LAN, it cannot be guaranteed that every network node 
that is part of the same wireless network can listen to all the network 
traffic. In FIG. 1, wireless node E can listen to the network data sent by 
wireless node B but not by wireless node C because wireless node E is 
within B's DSA 20, but is outside C's DSA 30. In this case, C is a hidden 
node with respect to E. Similarly C is a hidden node with respect to E, 
because C is outside E's DSA 45. 
In some situations, it is possible for one IR wireless node to receive data 
sent by another wireless node but not be able to send to that node. For 
example, a first node (not shown) would be able to listen to the network 
data sent by a second node (not shown), but the second node would not be 
able to receive the data sent by the first node. This situation is known 
as asymmetry. 
To compensate for possible wireless transmission failure, wireless packet 
delivery systems usually require receiving nodes send a specific 
acknowledgement to the sending node, acknowledging the receipt of each 
data packet. For example if wireless node A sends a directed packet to 
wireless node B, B will in turn send a packet to A, acknowledging receipt 
of A's message. These acknowledgements are not normally required for 
packet delivery systems on wired LANs, due to the low failure rate of 
transmissions in such mediums. 
Turning now to FIG. 2, the BSA of AP1 is illustrated by circle 60 whereas 
AP2 is shown as having BSA 70. Wireless nodes A, B and E are within the 
BSA 60 of AP1. Wireless node B is also within the BSA 70 of AP2, as is 
wireless node D. Wireless node C is not within range of either access 
point. 
It should be noted that because node B is within range of both APs, the 
wired LAN will receive unwanted duplicated messages if both AP1 and AP2 
resend a message from B to the wired LAN, and likewise, node B will 
receive unwanted duplicated messages if both AP1 and AP2 resend a message 
from the wired LAN to B. 
To avoid such duplication the invention provides a switching mechanism for 
ensuring that no more than one AP will act for any particular wireless 
node, by ensuring that every wireless node is "associated" with no more 
than one AP. 
Each wireless node determines which AP (assuming there is more than one in 
range) it will associate with. Furthermore, each wireless node determines 
whether it can transmit a message directly to its destination node, and it 
asks an AP to deliver the message if it cannot do so directly. Each AP 
determines whether it should resend a data packet from the wired LAN to 
the wireless node to which the packet is addressed. Each AP monitors the 
wired LAN data traffic for any data packets that are destined for (ie, 
addressed to) one of the AP's associated wireless nodes. If the AP hears 
such a data packet on the wired LAN, it intercepts the data packet and 
relays it to the wireless node. 
Each wireless node must be aware of what other nodes are around it, so it 
will be able to decide whether it can send to them. Therefore, each 
wireless node monitors the wireless traffic, and maintains a table of the 
addresses of all wireless nodes it has overheard recently. We shall refer 
to this as the DSA table. If a node has overheard another node, then the 
other node's address is in its DSA table and it assumes it can transmit to 
that node (ie, it ignores asymmetry, at least initially). This table 
represents all of the other nodes within whose DSA the tracking node is. 
This is assumed (by ignoring asymmetry) to represent all nodes within the 
DSA of the tracking node. 
In the preferred embodiment, each wireless node relies on overheard 
messages emanating from nearby nodes (including all acknowledgements) to 
construct its DSA table. Optionally, each wireless node can emit a beacon, 
which would automatically be overheard by all other nodes within its DSA. 
Each wireless node also monitors the network traffic looking for data 
packets sent by an AP. To assist wireless nodes (especially nodes actually 
moving) in locating nearby APs, each AP of the preferred embodiment of the 
present invention will emit a beacon, at regular intervals, eg, every 20 
seconds, identifying the APs wireless network address. In the preferred 
embodiment, each wireless node maintains a separate table, called an AP 
table, which lists the addresses of all APs it has overheard. Preferably, 
this table also stores other information, for example which AP has been 
heard most recently, most frequently, least frequently, etc. 
Alternatively, this information could be stored as part of the DSA table. 
Preferably, the wireless node can differentiate between data packets from 
APs and packets from other wireless nodes because a bit in the control 
field of a wireless data packet indicates whether the data packet 
originates from an AP. Alternatively, each AP is assigned a unique 
wireless network address with a common prefix for its wireless LAN 
connection. For example, the network address may be "IRAP001" where IRAP 
is a common prefix for all AP wireless network addresses. No wireless 
network node other than an AP is assigned that common prefix. 
Each AP is also assigned a wired group network address for its wired LAN 
connection. The group address is used for sending "multicast" broadcasts. 
When a "multicast" message, a form of broadcast message, is sent to the AP 
group network address in the wired LAN, all APs, but only APs, receive 
that message. All other wired network nodes ignore that message. 
When a wireless node overhears an AP, it will enter this AP into its AP 
table. The node also determines which of the APs in its AP table it will 
associate with. Examples include: associate if the table is empty (ie, the 
wireless node has just powered on, or just entered the vicinity of a wired 
LAN), or maintain association with the current AP until it can no longer 
hear that AP, or associate with the AP heard most frequently, etc. 
If the procedure indicates the wireless node should associate with the AP, 
the wireless node will send an association request data packet to the AP. 
If the association request data packet is sent successfully to the AP, ie, 
acknowledged by the AP, the wireless network node considers itself 
associated with that AP. The association request includes the wireless 
network address of the wireless node. Preferably, the request also 
indicates which AP, if any, the wireless node was previously associated 
with. 
Each AP maintains a table, called its (Basic Service Set) BSS table, of all 
wireless nodes which it is associated with. After receiving the 
association request successfully from the wireless node, the AP adds the 
network node address to its BSS table. The AP can be configured so that if 
the association request indicates the wireless network node was associated 
with another AP previously, the AP sends a disassociate data packet to the 
previous AP via the wired LAN to the previously associated AP telling the 
AP to disassociate with the wireless node. Alternatively, once a wireless 
node associates with a new AP, it can instruct this AP to send such a 
disassociate request to the previous AP. 
After receiving the disassociate data packet from the new AP, the previous 
AP deletes the wireless network node address from its BSS table. 
Optionally each AP can also maintain a separate BSA table, similar to the 
DSA table maintained by each wireless node, listing the node addresses of 
all wireless nodes within its BSA, regardless of whether they are 
associated with it. 
A wireless node only accepts data packets sent by the AP it is associated 
with; it will discard all data packets sent by other APs. It will, of 
course, accept data packets that are destined for it which are sent by 
other wireless nodes. 
As stated, the selection of which AP will be associated with each wireless 
node is determined by each wireless node. Therefore, each AP accepts all 
data packets sent by any wireless node. If the AP receives a data packet 
directed to it by a wireless node that it is not associated with, the AP 
considers the data packet as an implicit association request. It adds the 
wireless node address to its BSS table and relay the data packet onto the 
wired LAN. 
If a wireless node fails to send a data packet to its associated AP 
successfully, ie, the AP fails to acknowledge receipt of the data packet, 
the wireless node considers its wireless connection with the AP broken. It 
will delete its association with that AP. It then checks its AP table to 
see if another AP is available. If there is one, it will attempt to 
establish an association with that AP. If there is more than one, the AP 
will preferably select the AP heard most recently. 
Similarly, if the AP fails to send a data packet successfully to the 
wireless node that is associated with it, it considers its wireless 
connection with the wireless node broken, and deletes the node from its 
BSS table. 
In operation, when a wireless node (the sending node) is ready to send a 
data packet to another network node (the destination node), it first 
determines whether the network node address of the destination node is in 
its DSA table. If it is, this implies that the destination node is another 
wireless node within the DSA of the sending node. The sending node 
therefore sends the data packet to the other wireless node directly. If 
the destination node is not within the DSA table, the sending node sends 
the data packet to the AP it is associated with and asks the AP to help 
deliver the data packet to the destination node. 
After receiving the data packet, the AP checks the destination of the data 
packet against its BSS. If the destination node is within its BSS (ie, if 
the destination node is also associated with the AP), the AP sends the 
data packet to the destination node directly via the wireless medium. 
Otherwise, the AP resends the data packet onto the wired LAN. If the 
destination node is a wired node, it will receive the data packet 
directly. If the destination node is on another wireless LAN which is 
attached to the same wired LAN by another AP (ie, the destination node is 
a wireless node associated with another AP), the other AP will relay the 
data packet to that destination node. 
FIG. 3 shows three examples of how the preferred embodiment works. Assume 
wireless network node A has just entered the BSA of AP1. We will assume A 
has not been associated with any AP before. When it hears AP1's beacon, or 
alteratively, hears some data traffic from AP1 to wireless network node B, 
node A sends an association request data packet to AP1. After sending the 
association request data packet successfully (ie, receiving AP1's 
acknowledgement), A considers itself associated with AP1. After receiving 
the association request data packet successfully, AP1 adds A to its BSS 
table. It also sends a disassociation data packet on the wired LAN, 
advising any previously associated AP that AP1 is now associated with node 
A and that the previous AP should disassociate. This can be done by way of 
multicast or by a directed packet to the AP A was actually associated 
with. 
Let us assume A wants to send a data packet to wired network node X. A 
first consults its DSA table to see if X is a wireless node within range. 
Since X is not in A's DSA, A sends the data packet to AP1 as is shown by 
arrow 100 in FIG. 3. AP1 then consults its BSS table to determine whether 
X is an associated wireless node within its BSA. Since X is not so listed, 
AP1 in turn resends the data packet onto the wired LAN, as is shown by 
arrow 105. 
Let us further assume that after X receives the data packet, it sends a 
response data packet back to A. AP1 monitors the wired LAN data traffic 
and overhears a data packet destined for A, which is in its BSS. AP1 
intercepts the data packet and sends it to A via the wireless medium. 
Let us now assume both nodes A and B are associated with AP1, i.e., they 
both are in AP1's BSS, and node B wants to send a data packet to A. Node B 
examines its DSA to see if A is within range. As can be seen in FIG. 1, 
node B is not within the DSA 10 of node A, nor is node A within the DSA 20 
of node B. In other words, the nodes are hidden from each other, even 
though both are within range of AP1. Direct wireless communication between 
the two nodes is not possible. Therefore, B sends the data packet to AP1 
asking it to help deliver the data packet, as is shown by arrow 120 in 
FIG. 3. AP1 examines its BSS and determines A is associated with it. 
Therefore, AP1 transmits the data packet by the wireless medium to A, as 
is shown by arrow 125. It should be noted that even though node B is also 
within the BSA of AP2, node B is associated with AP1 and therefore does 
not ask AP2 for assistance. 
Now let us assume node A wants to send a data packet to node D, which is 
associated with AP2. Since node D is not within node A's DSA, A sends the 
packet to AP1, as is shown by arrow 130. Since node D is not associated 
with AP1, AP1 resends the data packet onto the wired LAN, as is shown by 
arrow 135. AP2 overhears this data packet, determines that node D is 
associated with it, and resends the data packet directly to D, as is shown 
by arrow 140. 
Note that node B is within the BSA of both AP1 and AP2. If node B had been 
associated with AP2 (and therefore would not have been associated with 
AP1), and wireless node A sends a data packet to wireless node B, then AP1 
would not have transmitted the data packet directly to B, but rather, 
would have resent it on the wired LAN. In this circumstance, AP2 would 
intercept the data packet and resend it to B (because B would be in AP2's 
BSS table), as it would for node D. 
FIG. 4 illustrates how a roaming wireless node can move in and out of 
different APs' BSAs. When a wireless node moves between BSAs of APs, it 
disassociates with one AP and associates with another. The data packets 
sent by the wireless network node to the wired LAN are resent by different 
APs depending on where the wireless node is, and which AP the wireless 
node associates itself with. Likewise, data packets destined for the 
wireless node are resent by different APs depending on where the wireless 
node is and which AP the wireless node associates itself with. This 
procedure will now be described. 
When an node roams, it may roam out of range from all APs in its AP table. 
The wireless node is then disconnected from the wired LAN until it comes 
within range of another AP and associates itself with that AP. Of course a 
roaming node cannot associate itself with an AP until it becomes aware of 
the presence of that AP (ie, overhears either the AP's beacon or a regular 
transmission). Optionally, to shorten the time between the wireless 
network node moving into an AP's BSA and detecting the AP's existence, 
each AP can broadcast its beacon earlier when it first detects a wireless 
node. To do this, the AP maintains a BSA table, in addition to its BSS 
table, as described above. Alternatively it combines the two into an 
expanded BSA table, with an additional column identifying whether each 
wireless node listed is associated with it. If an AP overhears a wireless 
node which is not listed in its BSA table, the AP generates its beacon 
ahead of schedule. The AP detects the existence of the wireless node by 
overhearing a data packet, usually a broadcast packet, sent by the 
wireless node. This broadcast packet is usually generated in response to 
the upper layer network operating system trying to determine which other 
nodes are present in the network. The result of this broadcast packet 
emitted by a wireless network node is an early scheduled beacon emitted by 
the AP, which in turn starts the association process. 
Referring to FIG. 4 for example, assume wireless node A is originally 
located at position 200, and is associated with AP1. It therefore 
communicates with wired network node X via AP1. As A moves to an area 
which is not covered by any AP, as is illustrated as position 210, it 
cannot receive acknowledgements from AP1 for any packets which it sends 
via AP1 to X. It thus ceases to consider itself associated with AP1 as it 
cannot communicate with AP1 any more. As A moves into AP2's BSA, as shown 
at 220, it recognizes the existence of AP2 either by observing AP2's 
beacon or AP2's data traffic. It is possible AP2 would overhear node A 
before A overhears AP2. In this case, as AP2 would not have heard A at 
either position 200, or 210, AP2 can optionally recognize that A is a node 
previously unheard by it, and emit its beacon early. In any of these 
events, A initiates an association process with AP2. This reconnects A to 
the network, allowing A to communicate with X again. Assuming an entire 
area is sufficiently covered by APs, A can move around the area while 
remaining connected to the network. 
FIGS. 5 and 6 are flow charts illustrating the operating of a wireless node 
of the preferred embodiment of the present invention. FIG. 5 shows the 
message monitoring and receiving operations. As shown at step 300, a 
wireless node monitors all wireless data traffic within range. If it 
receives any messages, it extracts the identifying information contained 
within the message, as shown at step 310, in order to determine the 
network address of the source of the message. As shown at step 320 the 
wireless node evaluates whether the source node is an internetworking 
node, in which case the wireless node updates its AP table (step 330), or 
if the source is another wireless node, it updates its DSA table (step 
340). If the source is an internetworking node, the wireless node 
determines whether or not it should associate as discussed above (step 
350). If the wireless node is not currently associated with an 
internetworking node it will then associate with the internetworking node, 
(step 360). After updating the appropriate table, the wireless node 
determines whether it is the destination of the message as shown at step 
370. If it is the destination, it receives and processes the message at 
step 390. If it is not the destination, it ignores the message (step 380). 
FIG. 6 illustrates the steps taken by a wireless node in response to a 
command from the operator for the node to send data as shown by step 400. 
First, as shown at step 410, the node determines whether the destination 
is in its DSA table. If it is in its DSA table it then sends the data to 
the destination as shown at step 420. As shown at step 440 the node 
determines whether the transmission is successful (by receiving a 
confirmation from the destination node). If the transmission is not 
successful (implying that the destination is no longer within range), the 
node deletes the destination node from its DSA table as shown at step 470. 
If the destination is not in the node's DSA table, the node sends the data 
to the internetworking node (AP) associated with it, as shown at step 430, 
and relies on the associated AP to forward the message. At step 450 the 
node determines whether its transmission to the AP is successful. If not, 
it deletes the internetworking node from its AP table as shown at step 
480. If the node receives confirmation that its transmission was 
successful, then this ends the procedure, assuming that no additional 
packets of data need to be sent. 
FIGS. 7 through 9 illustrate the steps taken by an internetworking node 
according to the preferred embodiment of the present invention. FIG. 7 
illustrates the steps taken when an internetworking node receives an 
association request from a wireless node as shown at step 500. The AP adds 
the requesting node to its associated node list (eg. its BSS table) as 
shown at 510. The AP then evaluates at step 520 whether the requesting 
node was previously associated with another internetworking node. If so, 
it broadcasts at step 530 a message on the wired LAN advising the previous 
internetworking node that the wireless node has switched association. 
FIG. 8 is a flow chart illustrating the steps taken by an internetworking 
node upon receiving wireless data. The internetworking node monitors the 
wireless data traffic for any messages (step 550) periodically, it also 
issues a broadcast (step 555). Upon receipt of any wireless messages, the 
internetworking node extracts the identifying information from the message 
(step 560), and compares this identifying information with the list of 
wireless nodes it maintains in its BSA table (step 570). If the message is 
from a wireless node which is not listed in its BSA table the 
internetworking node adds the address of this wireless node (step 590). 
Optionally the internetworking node can send a broadcast message at this 
stage in order to notify the wireless node that it is now in range of the 
internetworking node. The internetworking node then determines whether the 
destination of the message is a wireless node associated with the 
internetworking node at step 600. If it is then the internetworking node 
resends the message via wireless transmission to the destination node, as 
shown at step 610. If the destination node is not associated with the 
internetworking node then the internetworking node converts the message to 
a format which can be transmitted on the wired LAN (step 620) and 
transmits the message on the wire LAN step 630. 
FIG. 9 is a flow chart illustrating the steps taken by an internetworking 
node upon receiving data from the wired LAN (step 640). The 
internetworking node then determines whether the destination of this 
message is a wireless node associated with the internetworking node (step 
650). If it is, then the internetworking node converts the message to a 
wireless format and transmits the message to the destination node as shown 
at steps 670 and 680. Otherwise the internetworking node ignores the 
message (step 660). 
FIG. 10 is a block diagram schematically illustrating the components of a 
wireless node of the preferred embodiment of the present invention and its 
associated software which carry out the above described operations. A 
wireless node 700 can take the form of a laptop computer equipped with a 
wireless adapter card 730 and a wireless transmitter/receiver 735. The 
wireless adapter card/transmitter/receiver is controlled by a CPU 710 
which in turn carries out instructions from the various software routines 
selected from those within phantom box 740 which are loaded into the 
node's memory 720. The node's memory 720 also maintains the AP table 723 
and the DSA table 725. The software routines 740 include a monitoring and 
identifying information extraction routine 745 for carrying out steps 300 
and 310; a table storage and updating routine 750 for maintaining and 
updating AP table 723 and the DSA table 725; an AP determining and 
selection routine 755 for accessing the AP table and determining the 
number of internetworking nodes for which the table contains identifying 
information, and selecting from that table an internetworking node to 
associate with; an AP association routine 760 for associating with the 
selected internetworking node; a message sending routine 765; a message 
receiving and processing routine 770; and a confirmation routine 775. 
Alternatively, suitable circuitry for carrying out similar operations can 
replace these software routines. 
FIG. 11 is a block diagram schematically illustrating the components of an 
internetworking node of the preferred embodiment of the present invention 
and its associated software which carry out the above described 
operations. An internetworking node can take the form of a desktop 
computer equipped with a wireless adapter card 830 and a wireless 
transmitter/receiver 835 along with a wired LAN adapter card 837 for 
communicating with a wired LAN 838. Both the wireless and wired adapter 
cards are controlled by a CPU 810, which in turn carries out instructions 
from the various software routines selected from those within phantom box 
840 which are loaded into the node's memory 820. The node's memory 820 
also maintains the BSS table 823 and the BSA table 825. The software 
routines 840 include a monitoring an identifying information extraction 
routine 845 which carry out steps 550 and 560; a wired LAN monitoring, 
sending and forwarding routine 850; a confirmation routine 855; a message 
sending routine 860; a received message evaluation, comparison and 
directing routine 865 for evaluating whether a message is to be forwarded 
to a specific other node and determining whether such specific other node 
is associated with the internetworking node, and if so, for resending the 
message via wireless transmission, and if not, then for resending the 
message on the wired LAN; a BSA table maintaining, comparing and actuating 
routine 870 for maintaining the BSA table of all nodes from which messages 
have been overheard within a specified interval, and adding any newly 
overheard node to the BSA table, said routine optionally causing the node 
to broadcast its beacon; a periodic broadcast generator routine 875 for 
causing the internetworking node to periodically broadcast a beacon; a 
wired/wireless forwarding routine 880 for resending wireless messages onto 
the wired LAN and vice versa; an association and BSS table maintaining 
routine for maintaining a table of all wireless nodes associated with the 
internetworking node; and a message receiving and processing routine 890. 
Alternatively, suitable circuitry for carrying out similar operations can 
replace these software routines. 
It will be apparent that many other changes may be made to the illustrative 
embodiments, while falling within the scope of the invention and it is 
intended that all such changes be covered by the claims appended hereto.