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Claims  |
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What is claimed is:
1. A method of using a network system having a plurality of access points
and a plurality of stations, each of said plurality of stations
selectively couplable to each of said plurality of access points, said
network system transmitting data among said stations according to routing
information stored in said plurality of access points, said method
comprising the steps of:
(a) coupling a station to a first one of said plurality of access points;
(b) storing, in said station, a list of at least one of said plurality of
access points to which said station has been coupled, said list including
data corresponding to said first one of said plurality of access points;
(c) decoupling said station from said first one of said plurality of access
points;
(d) coupling said station to a second one of said plurality of access
points;
(e) transmitting at least a portion of said list from said station to said
second one of said plurality of access points; and
(f) updating the muting information as a function of said portion of said
list, whereby data destined for said station but received by said first
one of said plurality of access points can be routed by said first one of
said plurality of access points to said second one of said plurality of
access points.
2. The method of claim 1, wherein said step (f) includes the step of
storing said updated routing information at said first one of said
plurality of access points.
3. The method of claim 1, wherein said network system is an SR-LAN.
4. The method of claim 3, wherein said first one and said second one of
said plurality of access points are SR-TB bridges.
5. The method of claim 4, wherein said station can be coupled to said first
one and said second one of staid plurality of access points via a wireless
TB-LAN.
6. The method of claim 1, further comprising a step (g) wherein said second
one of said plurality of access points sends the routing information for
said station to said first one of said plurality of access points.
7. The method of claim 6, further comprising a step (h) wherein said first
one of said plurality of access points, upon receiving data destined for
said station, mutes said data to said second one of said plurality of
access points according to the routing information.
8. A method of using a network system having a plurality of access points
and a plurality of stations, each of said plurality of stations
selectively couplable to each of said plurality of access points, said
network system transmitting data among said stations according to routing
information stored in said plurality of access points, said method
comprising the steps of:
(a) coupling a first one of said plurality of stations to a first one of
said plurality of access points;
(b) storing, in said first one of said plurality of stations, a list of at
least one of said plurality of access points to which said first one of
said plurality of stations has been coupled, said list including data
corresponding to said first one of said plurality of access points;
(c) finding the routing information for said first one of said plurality of
stations from said first one of said plurality of access points to a
second one of said plurality of stations;
(d) inserting, at said first one of said plurality of access points, the
routing information into the data to be transmitted from said first one of
said plurality of stations to said second one of said plurality of
stations;
(e) receiving, at said second station, said data including the routing
information;
(f) inserting the routing information, in reverse order, to data to be
transmitted from said second one of said plurality of stations to said
first one of said plurality of stations;
(g) decoupling said first one of said plurality of stations from said first
one of said plurality of access points;
(h) coupling said first one of said plurality of stations to said second
one of said plurality of access points;
(I) transmitting at least a portion of said list from said first one of
said plurality of stations to said second one of said plurality of access
points; and
(j) updating the routing information as a function of said portion of said
list, whereby data destined for said first one of said plurality of
stations but received by said first one of said plurality of access points
can be routed by said first one of said plurality of access points to said
second one of said plurality of access points.
9. The method of claim 8, wherein said network system is an SR-LAN.
10. The method of claim 9, wherein said first one and said second one of
said plurality of access points are SR-TB bridges.
11. A method of using a network system having a plurality of access points
and a plurality of stations, each of said plurality of stations
selectively couplable to each of said plurality of access points, said
network system transmitting data among said stations according to routing
information stored in said plurality of access points, said method
comprising the steps of:
(a) coupling a first one of said plurality of stations to a first one of
said plurality of access points;
(b) finding the routing information for said first one of said plurality of
stations from said first one of said plurality of access points to a
second one of said plurality of stations;
(c) storing, in said first one of said plurality of stations, a list of at
least one of said plurality of access points to which said first one of
said plurality of stations has been coupled, said list including data
corresponding to said first one of said plurality of access points;
(d) decoupling said first one of said plurality of stations from said first
one of said plurality of access points;
(e) coupling said first one of said plurality of stations to a second one
of said plurality of access points;
(f) transmitting at least a portion of said list from said first one of
said plurality of stations to said second one of said plurality of access
points; and
(g) updating the routing information as a function of said portion of said
list, whereby data destined for said first one of said plurality of
stations but received by said first one of said plurality of access points
can be routed by said first one of said plurality of access points to said
second one of said plurality of access points.
12. The method of claim 11, wherein said network system is an SR-LAN.
13. The method of claim 12, wherein said first one and said second one of
said plurality of access points are SR-TB bridges.
14. A method of using a network system having a plurality of access points
and a plurality of stations, each of said stations selectively couplable
to each of said plurality of access points, said network system
transmitting data among said stations according to routing information
stored in said plurality of access points, said method comprising the
steps of:
(a) coupling a first one of said plurality of stations to a first one of
said plurality of access points;
(b) finding the routing information for said first one of said plurality of
stations from said first one of said plurality of access points to a
second one of said plurality of stations;
(c) storing, in said first one of said plurality of stations, a list of at
least one of said plurality of access points to which said first one of
said plurality of stations has been coupled, said list including data
corresponding to said first one of said plurality of access points;
(d) decoupling said first one of said plurality of stations from said first
one of said plurality of access points;
(e) coupling said first one of said plurality of stations to any other one
of said plurality of access points;
(f) transmitting at least a portion of said list from said first one of
said plurality of stations to said any other one of said plurality of
access points; and
(g) updating the routing information as a function of said portion of said
list, whereby data destined for said first one of said plurality of
stations but received by said first one of said plurality of access points
can be routed by said first one of said plurality of access points to said
any other one of said plurality of access points to which said first one
of said plurality of stations is currently coupled.
15. The method of claim 14, wherein said network system is an SR-LAN.
16. The method of claim 15, wherein each of said plurality of access points
are SR-TB bridges. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates to data communication networks in general,
and more particularly, to data communication networks that use source
routing and source-transparent routing protocols.
BACKGROUND OF THE INVENTION
It is known that a typical Local Area Network (LAN) can use routing bridges
to route data among stations connected to the LAN. The routing bridges
receive and transmit data packet-by-packet at data link layer level. There
are several protocols to define data routing at data link layer,
including: source routing defined by IEEE 802.5, transparent routing
defined by IEEE 802.1D, and source-transparent routing which is a are
facto industry protocol.
Bridges build according to source routing, transparent routing and
source-transparent routing are referred as source routing bridge
(SR-bridge), transparent routing bridge (TB-bridge) and source-transparent
bridge (SR-TB-bridge), respectively. Analogously, LANs using source
routing and transparent routing are referred as source routing bridged LAN
(SR-LAN) (e.g., a Token-Ring LAN) and transparent routing bridged LAN
(TB-LAN), respectively.
Source muting requires each of the packets to be transmitted to contain
route information inserted by a source end station. An SR-bridge uses the
routing information to determine whether it should forward the packets,
and to what LAN-segment the packets should be sent. A LAN-segment is a
part of a LAN where end stations can communicate directly with each other
via the LAN media, without the need for an intermediate link, such as a
bridge or a router. For example, in a Token-Ring LAN, a LAN-segment is a
ring. In an Ethernet LAN, a LAN-segment is a cable including components
like "repeaters" or hubs.
According to source routing protocol, a source end station initially
invokes a route determination procedure to "find" a route to a destination
end station. The source end station transmits copies of a special kind of
packet and sends a copy to each possible path. Each copy collects route
information while it is being transmitted over LAN-segments and bridges.
When a source end station finds a route to a destination end station, it
keeps the routing information so that the information can be inserted for
subsequent packets to the same destination end station.
FIG. 1 depicts a typical configuration for an SR-LAN, where stations A and
B are connected with each other through SR-bridges 1-2 and SR-segments
1-3. By transmitting copies of a special kind of packet and sending a copy
to each possible path, station A finds the route to station B as being:
SR-segment 1, SR-bridge 1, SR-segment 2, SR-bridge 2, SR-segment 3, and
station B. When station A wants to deliver packets to station B, it
inserts this routing information into the packets designated for station
B.
When station B responds to a message from to station A, station B inserts
the same routing information, as it reads from the packet(s) from station
A, in reverse order. Whether station B takes this routing information from
only the first packet sent by station A, or it continuously updates the
routing information from all packets from station A is implementation
dependent. In contrast to source routing, transparent routing does not
need the route information as required by source routing.
To accommodate the packets with and without the routing information, an
SR-TB-bridge is used to connect an SR-LAN to a TB-LAN. Because the packets
on a TB-LAN do not contain the muting information required for source
routing, an SR-TB-bridge should perform be capable of: (1) responding to
any route determination procedure initiated by a station on the SR-LAN, to
find routing information for a station on the TB LAN, (2) maintaining the
routing information to end stations on the SR-LAN in its location data
base, (3) adding the routing information to the packets transmitted by end
stations on the TB-LAN and destined for end stations on the SR-LAN based
on its location data base, and (4) removing the routing information from
the packets transmitted by the end stations on the SR-LAN and destined for
the end stations on the TB-LAN.
Conceptually, this process can be regarded as if the SR-TB-bridge handles
the source routing procedures on behalf of the stations on the TB-LAN.
A well known commercially available SR-TB-bridge is IBM 8209 LAN Bridge.
FIG. 2 depicts a typical configuration where an SR-LAN is connected to a
TB-LAN through an SR-TB-bridge. In FIG. 2, stations A and B are connected
with each other through SR-bridges 1-2, SR-TB-bridge 3, SR-segments 1-3,
and TB-segment 4.
In FIG. 2, if mobile station A transmits the packet destined for station B,
this packet is received by SR-TB-bridge 3 on TB-segment 4. If SR-TB-bridge
3 has the routing information to station B stored in its location data
base, it will insert this routing information in the packet and forward
the packet to station B via the SR-LAN. If the route information to
station B is not in its location data base, SR-TB-bridge 3 will invoke a
route determination procedure to generate the routing information. The
routing information in this example is: SR-segment 1, SR-bridge 1,
SR-segment 2, SR-bridge 2, and SR-segment 3.
The problem for a conventional SR-LAN is that it can not properly transmit
data in a roaming environment, where a station that is roaming dynamically
changes access points on the SR-LAN. The primary reason for this problem
is that the muting information is "semi-static" and kept in the
correspondent stations the roaming station is communicating with.
"Semi-static" means that the information is not constantly, dynamically;
updated. It is determined at a certain point in time, and used for some
period of time, depending on situations, higher level procedures,
implementation, and usage.
U.S. Pat. No. 5,371,738 entitled WIRELESS LOCAL AREA NETWORK SYSTEM WITH
MOBILE STATION HANDOVER by H. Moelard et al. discloses a method of
handling station roaming in a TB-LAN.
SUMMARY OF THE INVENTION
An illustrative embodiment of the present invention provides a method in a
network system, which has a plurality of access points including a first
access point and a second access point and a plurality of stations
including a first station and a second station. The network system
transmits data among the stations according to routing information. The
method comprises the steps of: connecting the first station to the first
access point; finding the routing information for the first station from
the first access point to said second station; removing the first station
from the first access point and connecting the first station to the second
access point; and updating the routing information from the first access
point to the second access point for the first access point, so that data
destined for the first station but received by the first access point can
be re-transmitted to the second access point.
BRIEF DESCRIPTION OF THE FIGURES
The advantages of the present invention will become apparent to those
skilled in the art to which the invention relates from the subsequent
description of the preferred embodiments and the appended claims, in
conjunction with the accompanying drawing in which:
FIG. 1 depicts a typical configuration for an SR-LAN;
FIG. 2 depicts a typical configuration in which an SR-LAN is connected to a
TB-LAN through an SR-TB-bridge;
FIG. 3 depicts a network configuration in accordance with one embodiment of
the present invention;
FIG. 4 depicts a network configuration in accordance with another
embodiment of the present invention;
FIGS. 5A and 5B depicts flowcharts showing a hand-off procedure at a new
access point and a previous access point, respectively, in accordance with
the present invention; and
FIG. 6 depicts a flowchart showing the operation at an access point when
receiving a packet for a mobile station, in accordance with the present
invention.
DETAILED DESCRIPTION
FIG. 3 depicts an illustrative network configuration including SR-LAN 302,
wireless TB-LAN 304, SR-TB-bridges 4 and 5, mobile station A, and station
B. SR-LAN 302 includes SR-segments 1, 2 and 3, and SR-bridges 1 and 2.
Wireless LAN 304 includes wireless TB-segments 4 and 5. Mobile station A
is preferably wirelessly connected with wireless TB-segment 4 or wireless
TB-segment 5. Thus, it can use either SR-TB-bridge 4 or SR-TB-bridge 5 as
the access point to SR-LAN 302. Some embodiments of the present invention
can update routing information when mobile station A dynamically changes
access points between SR-TB-bridge 4 and SR-TB-bridge 5.
When mobile station A is wirelessly connected with wireless TB-segment 4
and wants to communicate with station B, it uses SR-TB-bridge 4 as the
access point to SR-LAN 302. SR-TB-bridge 4 receives the packets from
mobile station A and inserts the routing information, as being SR-segment
2, SR-bridge 2 and SR-segment 3, into the packets.
When station B sends packets to mobile station A, it inserts the reversed
routing information, as being SR-segment 3, SR-bridge 2 and SR-segment 2,
into the packets. After the packets have been delivered to SR-TB-bridge 4,
it relays the packets to mobile station A via wireless TB-segment 4.
Whether station B takes this routing information from only the first
packet sent by mobile station A, or it continuously updates this
information from all packets sent by mobile station A is implementation
dependent.
When mobile station A moves to and is connected with wireless TB-segment 5,
it changes the access point to SR-LAN 302 from SR-TB-bridge 4 to
SR-TB-bridge 5. The access point change can be executed by WaveLAN
procedure, which has been described in the patent application entitled
HANDOVER METHOD FOR MOBILE WIRELESS STATION, with Ser. No. 08/065,328 (our
docket No. 5577), by Loeke Brederveld et al. Applicant hereby incorporates
this patent application by reference.
In response to the change of the access point, SR-TB-bridge 5 now handles
the source routing on behalf of mobile station A, and inserts appropriate
routing information into the packets transmitted from mobile station A to
station B.
In FIG. 3, as to the routing information in the packets transmitted from
station B to mobile station A, there are two situations.
In the first situation, station B updates its routing information whenever
it receives a packet from a station (mobile station A in this case) it
communicates with. SR-TB-bridge 5 inserts the new routing information when
mobile station A sends a packet to station B.
Alternatively, to expedite the update of routing information in station B,
SR-TB-bridge can send a dummy frame with new routing information to
station B on behalf of station A. To do so, mobile station A has to inform
SR-TB-bridge 5 that mobile station A is in communication with station B as
soon as it switches to SR-TB-bridge 5 as the access point.
When station B uses the new routing information, packets destined for
mobile station A will be delivered to SR-TB-bridge 5 for further transfer
to station A via wireless TB-segment 5.
In the second situation, station B does not update its routing information
when it receives a packet. It continuously uses the routing information
that it determined when the connection with mobile station A was
established.
In the both situations, before receiving the new routing information from
mobile station A, station B will still insert the old routing information,
as being SR-segment 3, SR-bridge 2, SR-segment 2 and SR-TB-bridge 4, into
the packets for mobile station A. Therefore, to re-route the packets to
the changed access point, a hand-off procedure is executed between
SR-TB-bridges 4 and 5 as soon as mobile station A switches access points.
The hand-off procedure finds the routing information from SR-TB-bridge 4 to
SR-TB-bridge 5 as being SR-segment 2, SR-bridge 1, SR-segment 1 and
SR-TB-bridge 5. SR-TB-bridge 4 keeps the routing information to identify
that mobile station A is now connected with SR-TB-bridge 5. After
receiving a packet delivered for station A, SR-TB-bridge 4 will insert the
routing information into the packet and re-route it to SR-TB-bridge 5 for
delivery to station A.
When a new connection is being established between mobile station A and
station B via SR-TB-bridge 5, the right routing information to station B
via SR-TB-bridge 5 is determined.
It should be noted that without updating the routing information, the
packet for mobile station A arriving at SR-TB-bridge 4 would be sent to
TB-segment 4 and be lost at mobile station A. As a result, station B will
(probably after a retry) consider the logical connection to mobile station
A as lost.
After loosing a logical connection, a process will be initiated to
re-establish the logical connection, usually by higher layer protocols
(higher than the data link layer protocol).
In contrast, embodiments of the present invention preferably maintain the
logical connection to a mobile station by dynamically updating the routing
information.
It should be appreciated that "dynamically updating the routing
information" is typically more time efficient than "re-establishment of
the logical connection." This is so because the reestablishment of the
logical connection is initiated by the event that no response is received
from the other station. It takes time to find out that a logical
connection has been lost, involving: time-out, retry, time-out again,
sending control frames, time-out, . . . ). In addition, the
reestablishment of the logical connection requires a route determination
procedure, which also takes some time. Furthermore, the initiation of the
re-establishment of the logical connection is implementation dependent; it
may not be done automatically, but may require user intervention.
Advantageously, updating the routing information as soon as the mobile
station changes access points prevents these time consuming processes. The
updating process can take place while there is no active communication
between the stations.
FIG. 4 depicts an illustrative network configuration including SR-LAN 402,
wireless TB-LAN 404, SR-TB-bridges 4, 5 and 6, mobile station A, and
station B. SR-LAN 402 includes SR-segments 1, 2, 3 and 4, and SR-bridges
1, 2, 3 and 4. Wireless LAN 304 includes wireless TB-segments 4, 5 and 6.
When mobile station A roams from Wireless TB-segment 4 to wireless
TB-segment 5, and further roams to wireless TB-segment 6, the access point
will be changed from SR-TB-bridge 4 to SR-TB-bridge 5, then to
SR-TB-bridge 6.
In FIG. 4, as to the routing information in the packets transmitted from
station B to mobile station A, there are two potential situations.
In the first situation, station B has updated its routing information to
SR-TB-bridge 5 after mobile station A roams from wireless TB-segment 4 to
TB-segment 5. Under this situation, the hand-off procedure will find the
routing information from SR-TB-bridge 5 to SR-TB-bridge 6 as being
SR-segment 1, SR-bridge 4, SR-segment 4 and SR-TB-bridge 6. SR-TB-bridge 5
keeps the routing information to identify that mobile station A is now
connected with SR-TB-bridge 6. After receiving a packet delivered for
mobile station A, SR-TB-bridge 5 will insert the routing information into
the packet and re-route it to SR-TB-bridge 6 for delivery to station A.
In the second situation, station B has not updated new routing information
after mobile station A roams first from wireless TB-segment 4 to
TB-segment 5, and then from TB-segment 5 to TB-segment 6. Under this
situation, the hand-off procedure should find the routing information for
both SR-TB-bridge 4 and SR-TB-bridge 5, so that the packets destined to
mobile station A can be re-routed to SR-TB-bridge 6. This means that the
hand-off procedure must involve all access points that once supported
mobile station A (SR-TB-bridges 4 and 5 in the example shown in FIG. 4).
One method to update re-routing information for all access
points(SR-TB-bridges 4 and 5 in the example shown in FIG. 4) is to send a
multicast protocol packet. In Token-Ring terms, the multiple protocol
packet is a packet with a Functional Group MAC (Media Access Control)
address.
As defined by IEEE standard 802(-1990), every station has a unique MAC
address at the sublayer of the OSI data link layer. A destination MAC
address can be an individual address (unique for each station), or a
multicast address that addresses a group of stations (e.g. all bridges in
a LAN can be addressed by a specific multicast MAC address). A special
case of multicast address is the "all stations" address, popularly
referred to as the "broadcast address."
As an alternative, mobile station A maintains a list of information about
all access points it has once used and provide this information to the new
access point. During the hand-off procedure, the new access point can then
inform all those access points individually. In the example shown in FIG.
4, the list of re-routing information at SR-TB-bridge 6 contains: (1) for
SR-TB-bridge 4 as being: SR-segment 2, SR-bridge I, SR-segment 1,
SR-bridge 4, SR-segment 4; and (2) for SR-TB-bridge 5 as being: SR-segment
1, SR-bridge 4, SR-segment 4.
As another alternative, mobile station A only provides the address of its
previous access point to the new access point. During the hand-off
procedure, after the new access point gets a location update, every access
point can then update re-routing information for the previous access
point. In this example, SR-TB-bridge 6 updates the rerouting information
for SR-TB-bridge 5, and SR-TB-bridge 5 updates the rerouting information
for SR-TB-bridge 4.
The information about what mobile stations are attached to what access
point is maintained at all access points. In FIG. 4, after the hand-off to
SR-TB-bridge 6 has taken place, SR-TB-bridge 4 knows that mobile station A
is connected to SR-TB-bridge 6, and the routing information to
SR-TB-bridge 6 as being: SR-segment 2, SR-bridge 1, SR-segment 1,
SR-bridge 4, SR-segment 4; and SR-TB-bridge 5 knows that mobile station A
is connected to SR-TB-bridge 6, and the routing information to
SR-TB-bridge 6 as being: SR-segment 1, SR-bridge 4, SR-segment 4.
FIG. 5A depicts a flowchart showing the preferred hand-off procedure at a
new access point. After a mobile station (MS) has been connected to a new
access point, in step 504 the new access point acknowledges the new
connection of the mobile station. In step 506, the new access point
registers the MS as its "own" station. In step 508, the new access point
sends "hand-off" packet to all previous access point(s), possibly by using
multicast address.
The function of the "hand-off" packet is to inform the previous access
point(s) that mobile station A is now connected to the new access point.
The exact format of the "hand-off" packet is dependent on the type of LAN
the source routed LAN is, but it generally contains the following
information:(1) Destination Address: the multicast address, or the address
of the previous access point, the "hand-off" packet is sent to;(2) Source
Address: the address of the new access point that sends the "hand-off"
packet; and(3) Mobile Station Address: the MAC address of the mobile
station this hand-off is for.
The "hand-off" packet will be identified as a "route explorer" packet,
which causes, (on its route(s) to the previous access point(s)) the
routing information to the new access point will be added by the
SR-bridges.
FIG. 5B depicts a flowchart showing the preferred hand-off procedure at a
previous access point. In step 512, the previous access point receives the
"hand-off" packet from the new access point (AP). In step 514, based on
the information in the "hand-off" packet, the previous access point
identifies the mobile station and the routing information to the new
access point (AP). In step 516, the previous access point registers the
mobile station (MS) as from "new AP" and the routing information to the
"new AP."
FIG. 6 depicts a flowchart showing the operation at an access point (which
can be a new access point or a previous access point) when receiving a
packet for the mobile station. In step 604, the access point receives a
packet for a mobile station (MS). In step 606, the access point checks the
ownership of this mobile station. If the access point owns this mobile
station, in step 614, the access point sends the packet to this mobile
station via its own wireless TB-segment. If the access point does not own
the mobile station, in step 608 the access point inserts the routing
information to the access point (AP) that owns this mobile station. In
step 610, the access point send the packet to the access point (AP) that
owns this mobile station via SR-LAN.
While the particular embodiments of the present invention have been
described in detail, it should be understood that the invention may be
implemented through alternative embodiments. Thus, the scope of the
invention is not intended to be limited to the embodiments described
above, but is to be defined by the appended claims.
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