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I claim:
1. A system for bridging local area networks comprising:
a plurality of local area networks, each comprising at least one station;
a backbone network divided into a plurality of broadband channels; and
a plurality of bridges, each bridge connected between one of the local area
networks and the backbone network, each bridge comprising, a network
interface means connected to one of the local area networks for
transmitting and receiving messages to and from the local area network to
which the network interface means is connected, a plurality of backbone
network interface means connected to the backbone network, each of said
plurality of backbone network interface means for transmitting and
receiving messages to and from said backbone network over an assigned
channel, said assigned channel being one of said plurality of broadband
channels, a memory means connected to the interface means and the
plurality of backbone network interface means, for storing a bridge
identification address, a table of addresses, and for temporarily storing
said messages, and a logic means connected to the network interface means,
the plurality of backbone network interface means, and the memory means,
for transferring messages between the network interface means and one of
the backbone network interface means and for selecting one of said
plurality of broadband channels over which to send said messages.
2. The system of claim 1 wherein,
said table of addresses associates each of said stations with its
respective bridge and associates each bridge with its assigned channels.
3. The system of claim 1 wherein,
said logic means further includes means for comparing a message originating
with the local area network to which the network interface means of that
bridge is connected with said table of addresses and if said message is
addressed to one of said stations in a second local area network of the
plurality of local area networks, said second local network is not
connected to the network interface means of that bridge, then
encapsulating said message in a message addressed to a second bridge which
is associated with said second local area network.
4. The system of claim 1 wherein,
said logic means includes means for selecting one of said plurality of
broadband channels by monitoring the message traffic over each of said
plurality of broadband channels and selecting the channel with the least
amount of message traffic.
5. The system of claim 1 wherein,
said logic means includes means for selecting one of said plurality of
broadband channels by comparing an address of a local area network message
with said table of addresses and if said address is associated with one of
said plurality of broadband channels which has been designated as a
priority channel, then selecting said priority channel.
6. A system for bridging local area networks comprising:
a plurality of local area networks, each comprising at least one station;
a backbone network divided into a plurality of broadband channels;
a plurality of bridge means, each connected between the backbone network
and one of the local area networks, for allowing messages from a station
in one local area network to be transmitted to one or more stations in one
or more of the other local area networks, each of said bridge means
comprising, a network interface means for transmitting and receiving local
area network messages to and from said local area network, a plurality of
backbone network interface means for transmitting and receiving backbone
network messages to and from said backbone network, each of said plurality
of backbone network interface means associated with one of said plurality
of broadband channels, address table means for associating each station
with a bridge means and for associating each bridge means with at least
one of said broadband channels, encapsulation means for encapsulating a
local area network message within a backbone network message for
transmission over said backbone network as a backbone network message; and
channel selector means for selecting one of said plurality of broadband
channels for transmission of a backbone network message.
7. The system of claim 6 wherein,
said bridge means further includes learning means for constructing said
table of addresses.
8. The system of claim 6 wherein,
said channel selector means has means for selecting one of said plurality
of broadband channels by monitoring the message traffic on said plurality
of broadband channels and selecting the channel with the least amount of
traffic.
9. The system of claim 6 wherein,
said address table means further comprises means for associating certain
station addresses with certain of said broadband channels; and
said channel selector means has means for selecting one of said plurality
of broadband channels by comparing a station address within a message with
said address table and selecting one of said broadband channels with which
said station address is associated.
10. A method for bridging local area networks comprising the steps of:
connecting a plurality of local area networks to a plurality of bridges,
with each local area network connected to one bridge, and each bridge
having at least one station;
connecting each of said plurality of bridges to a backbone network, said
backbone network divided into a plurality of broadband channels;
determining the location of each station relative to its associated bridge;
determining the broadband channels on the backbone network with which each
bridge may communicate;
reading the address of a local area network message on the local area
network connected to a bridge and if said local area network message is
addressed to a destination station within said local area network, then
disregarding said message, and if said local area network message is
addressed to a destination station in a second local area network of the
plurality of local area networks, then encapsulating said local area
network message within a backbone network message addressed to a
destination bridge which is associated with said destination station; and
selecting one of said broadband channels which is associated with said
destination bridge for transmission of said backbone network message
containing the encapsulated local area network message over said backbone
network.
11. The method of claim 10 wherein,
the step of selecting one of said broadband channels includes monitoring
the message traffic on each of said plurality of broadband channels and
selecting the broadband channel having the least message traffic.
12. The method of claim 10 wherein,
the step of selecting one of said broadband channels includes associating
certain station combinations of the stations connected to said bridges
with one of said channels, reading the addresses of local area network
messages to determine an origin station and a destination station and if
said origin station and destination station represent a station
combination, then selecting the channel with which said station
combination is associated.
13. A bridge for interconnecting local area networks comprising:
a network interface means for connection to a local area network for
transmitting and receiving messages to and from said local area network;
a plurality of backbone network interface means for connection to a
backbone network, each of said plurality of backbone network interface
means for transmitting and receiving messages to and from said backbone
network over an assigned channel, said assigned channel being one of a
plurality of broadband channels;
a memory means connected to the network interface means and the plurality
of backbone network interface means, for storing a bridge identification
address, a table of addresses, and for temporarily storing said messages;
and
a logic means connected to the network interface means, and plurality of
backbone network interface means and the memory means for transferring
messages between the network interface means and the plurality of backbone
interface means and for selecting one of said plurality of broadband
channels over which to send said message.
14. The system of claim 13 wherein,
said table of addresses associates a plurality of station addresses with a
plurality of bridge addresses and associates each of said plurality of
bridge addresses with at least one of said plurality of broadband
channels.
15. The system of claim 13 wherein,
said logic means further includes means for comparing a message originating
with the local area network to which the network interface means of that
bridge is connected with said table of addresses and if said message is
addressed to a station in a second local area network which is not
connected to the network interface means of that bridge, then
encapsulating said message in a message addressed to a second bridge which
is associated with said second local area network.
16. The system of claim 13 wherein,
said logic means includes means for selecting one of said plurality of
broadband channels by monitoring the message traffic over each of said
plurality of broadband channels and selecting the channel with the least
amount of message traffic.
17. The system of claim 13 wherein,
said logic means includes means for selecting one of said plurality of
broadband channels by comparing an address of a local area network message
with said table of addresses and if said address is associated with a one
of said plurality of broadband channels which has been designated as a
priority channel, then selecting said priority channel.
18. The system of claim 13 wherein,
said backbone network is a token-bus network; and
said logic means includes means for selecting one of said plurality of
broadband channels by calculating the average token rotation time for each
of said broadband channels and selecting the broadband channel with the
smallest average token rotation time.
19. The system of claim 13 wherein,
said logic means includes means for selecting one of said plurality of
broadband channels by periodically sampling the number of messages sent
over each backbone channel in a given time frame and selecting the channel
with the least amount of messages sent during that time frame. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to interconnecting local area networks and
more specifically to interconnecting local area networks using concurrent
broadband channels on a backbone network.
2. Description of the Prior Art
Local area networks (LANs) are stand alone networks which connect a
plurality of computers and other equipment. Messages are transmitted in
packets along the network. Each packet contains information identifying
the source computer and the computer to which the message is intended.
Each computer on the network typically has a filter which screens out
messages which are not intended for it. One type of network commonly used
as a local area network is the ethernet network.
Various means of interconnecting or bridging the LANs have been developed.
These include U.S. Pat. No. 4,539,679, by W. Bux, et al; U.S. Pat. No.
4,706,081, by J. Hart, et al; U.S. Pat. No. 4,627,052, by D. Hoare, et al;
U.S. Pat. No. 4,597,078, by M. Kempf; and U.S. Pat. No. 4,549,291, by R.
Renoulin, et al.
One way to interconnect LANs involves the use of a single LAN as a backbone
network in order to connect all LANs in a single system together. Messages
between the LANs travel across the backbone network. This type of system
is limited by the capacity of the backbone network. A need exists to
increase the capacity of the backbone network in order to accommodate a
greater message flow between the LANs.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a system for
interconnecting LANs by means of a backbone network having increased
capacity.
It is another object of the present invention to provide increased
reliability by providing redundant channels between networks.
Briefly, in a preferred embodiment, the present invention comprises a token
bus network which is used as a backbone network. The backbone network is
divided into three broadband channels. A number of ethernet networks are
each connected to the backbone network through a bridge device. Each
bridge contains between one and three modems corresponding to the three
backbone channels.
In operation, messages originating from one network which are intended for
another network are received by the bridge. The bridge envelopes the
message for transmission over the backbone network. The bridge monitors
the message traffic over the broadband channels and selects the channel
with the least amount of traffic. The message is then sent over the
appropriate channel and the receiving bridge de-envelopes the message and
transmits it to the destination ethernet network.
An advantage of the present invention is that it provides a system for
interconnecting LANs using a backbone network having increased message
capacity.
Another advantage of the present invention is that it provides increased
reliability by providing redundant channels between networks.
These and other objects and advantages of the present invention will no
doubt become obvious to those of ordinary skill in the art after having
read the following detailed description of the preferred embodiments which
are illustrated in the various drawing figures.
IN THE DRAWINGS
FIG. 1 is a block diagram of a system of the present invention;
FIG. 2 is a diagram of the medium access control headers for the ethernet
and token bus network;
FIG. 3 is a diagram of the backbone network packet of the present
invention; and
FIG. 4 is a block diagram of the bridge of the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
FIG. 1 shows a block diagram of one embodiment of the system of the present
invention and is designated by the general reference number 10. System 10
comprises a plurality of ethernet local area networks 12, 14, 16 and 18.
Network 12 has a plurality of stations 20 and 22. Network 14 has a
plurality of stations 24 and 26. Network 16 has a plurality of stations 28
and 30. Network 18 has a plurality of stations 32 and 34. Though each
network is illustrated with two stations, there may be any number of
stations associated with each local area network.
A broadband token bus network 40 is used as a backbone network for system
10. A plurality of bridges 42, 44, 46 and 48 connect networks 12, 14, 16
and 18, respectively, to backbone network 40. Backbone network 40 is four
hundred megahertz wide and is divided into a plurality of channels. For
purposes of illustration, FIG. 1 shows network 40 having three standard
channels "A", "B" and "C". Each bridge has at least one modem which
corresponds to one of these channels. Bridge 42 has an "A" channel modem
50, a "B" channel modem 52 and a "C" channel modem 54. Bridge 44 has an
"A" channel modem 56 and a "B" channel modem 58. Bridge 46 has an "A"
channel modem 60 and a "C" channel modem 62. Bridge 48 has only a single
"A" channel modem.
FIG. 2 shows a diagram of the structure of the packet headers in the medium
access control protocol layer and is designated by the general reference
number 100. An IEEE 802.3 reference network header 102 is shown. A
destination field 104 provides information on the address to which the
packet is directed. A source field 106 provides information of the party
who sent the packet. A length field 108 defines the length of the packet.
A data field 110 provides the high protocol layer information. A pad field
112 provides additional characters needed to achieve a minimum packet
size. An FCS field 114 provides the frame check sequence. The FCS is a
number which is calculated using an algorithm which uses the information
in the other fields. This number is then recalculated at the destination
to verify that the information in the packet is correct.
In commercial applications today, the ethernet network is commonly used.
The header packet of the ethernet is the same as the IEEE 802.3 header
except that the length field of the IEEE 802.3 header is deleted and the
ethernet network uses field 108 to contain information on the protocol
type. In this way, two different protocol systems could work on the same
ethernet network.
An IEEE 802.4 reference header 120 is also shown. Token bus networks use
the IEEE 802.4 standard. A frame control field 122 identifies the frame
type. A destination field 124 identifies the address to which the packet
is being sent. A source field 126 identifies the address of the party
sending the packet. The data field 130 contains the higher protocol layer
information. An FCS field 132 provides the frame check sequence. The data
field 130 is further divided into a header 140 and a data area 142. Header
140 is an IEEE 802.2 LLC1 type one header which describes the data in data
area 142. Data area 142 actually contains the higher protocol layer
information.
It is apparent that translation is required between the ethernet header 102
and the token bus header 120. Some fields must be eliminated and others
added. Due to this fact, the FCS number must be recalculated based on the
new frame. If an error was made in translating some of the data, the new
FCS number would be calculated using the erroneous data. When the packet
reaches the final destination and the FCS is checked, the error in
translation would not be detected.
FIG. 3 shows a diagram of the IEEE 802.4 header as used in the present
invention and is designated by the general reference number 150. The IEEE
802.4 reference is used in the token bus networks. The present invention
avoids the problems of translating the ethernet header by enveloping the
entire ethernet header inside the 802.4 data field. Header 150 contains a
frame control field 152. A bridge destination field 154 designates the
particular bridge address to which the message is addressed. A bridge
source field 156 designates the bridge from which the packet originated. A
field 157 comprises the data field 130 from the token bus 120. A header
field 158 contains the header 140 from the token bus frame 120. Field 160
comprises the data area 142 of the token bus frame 120 and comprises the
entire ethernet frame 102 including an ethernet destination field 162, an
ethernet source field 164, a protocol type field 166, an ethernet data
field 168, an ethernet pad field 169 and an ethernet FCS field 170. An
802.4 FCS field 172 follows the data field 157.
Returning now to FIG. 1, when system 10 is first put into operation, each
bridge constructs a bridge table which identifies each bridge with the
channel(s) over which it can be reached. Each bridge sends out a message
over each of its channels asking for a response. The other bridges answer
over their channels and the first bridge stores the information
associating each bridge and its channels in a bridge table.
After the bridge table is constructed, each bridge starts to construct a
station address table. For example, suppose station 20 puts out a packet
on network 12 for station 22. Bridge 42 would receive the message and look
at the ethernet source field (106 in FIG. 2). Bridge 42 would then store
station 20 with a number, 12 for example, which would designate station 20
as being in network 12. At this point, bridge 42 would not have an address
for station 22 stored. So, bridge 42 would envelope the ethernet header
inside the token bus header as shown in FIG. 3. The bridge of destination
is unknown to bridge 42 and the bridge destination field 154 in FIG. 3
would have a multicast address to all other bridges, 44, 46 and 48, in
this case. The bridge source field 156 would contain the address of bridge
42 on the backbone network 40. The FCS field 172 would then be calculated
using the entire token bus header 150. This multicast message would then
be transmitted over all three channels of backbone network 40.
Bridge 44 would receive the token bus frame from bridge 42 over the token
bus backbone network 40. Bridge 44 would note the bridge source field 156
and the ethernet source field 164 of the packet. Bridge 44 would store
information associating station 20 with bridge 42. Next, bridge 44 will
de-envelope the ethernet frame by removing the field 160 from the token
bus frame 150. The ethernet message is then placed on network 14. Since
the ethernet address is for station 22, all stations on network 14 would
disregard the message. The same procedure would occur in bridges 46 and 48
because they would also receive the multicast message.
After an initial start up period, each of bridges 42, 44, 46 and 48 will
have stored information which associates every station with its particular
bridge. Now when bridge 42 receives a message on network 12 from station
20 to station 22, bridge 42 would ignore the message. If station 20 sends
a message for station 28, then bridge 42 would envelope the message and
address it only to bridge 46. Bridge 42 would then consult the bridge
address table to determine that bridge 46 can be reached by either channel
"A" or "C". Bridge 42 would then select the appropriate channel using a
channel selection method which is explained in more detail below. In this
case, suppose channel "A" is chosen. Bridge 46 would receive the packet on
channel "A" and de-envelope the packet and send it over network 16 to
station 28. Bridge 44 and 48 would ignore the message because it is not
addressed to them and networks 14 and 18 would not be disturbed.
The channel selection method can be implemented in a number of different
ways. In the preferred embodiment, the method would select the channel
based upon the average token rotation time. In the token bus backbone
network 40, a token is passed from bridge-to-bridge. Only the bridge with
the token is allowed to transmit messages. The token rotation time, i.e.,
the amount of time it takes the token to return to the same bridge,
depends upon the number of bridges and the number of messages which each
bridge has to send. Therefore, the token rotation time is a good measure
of the traffic load of each channel. Each bridge constantly calculates an
average token rotation time for each channel. When a message may be
transmitted by more than one channel, the bridge selects the channel with
the smallest average token rotation time. This insures an equal
distribution of messages across all the channels and optimizes the total
message capacity of the backbone network 40 and system 10.
Another embodiment of the channel selection method might determine traffic
load directly. For example, each bridge might periodically sample the
number of packets going over each channel in a given time frame. The
bridge would then select the channel with the least amount of traffic.
Still other embodiments of the channel selection method are possible. The
method might monitor the number of messages cued in the bridge for each
channel. The next message would then be added to the channel with the
shortest list. The bridge could even select the channel based upon a round
robin approach by assigning the packet to the channel that has not been
used as recently as the others. Even a random selection of channels may be
used as the method.
All of the channel selection methods thus far discussed have as their
purpose to increase the overall capacity of the system. However, the
channel selection method could also be set up to prioritize messages. For
example, certain messages between predetermined stations or bridges may be
considered high priority and it may be desirable to transmit these
messages faster than others. One of the channels could be specifically
dedicated as a priority channel. The channel selection method would look
at the message origin and destination addresses and assign the priority
channel if the correct combination was shown. In this way, high priority
traffic would always get through faster.
FIG. 4 shows a block diagram of the bridges 42, 44, 46, 48 and is
designated by the general reference number 200. Bridge 200 has a
microprocessor 210 which is connected to a bus 212. The microprocessor 210
is an Intel 80186 or equivalent. A dynamic RAM 214, an EPROM 216, a boot
PROM 218, an identification EEPROM 220 and a non-volatile RAM 222 are all
connected to bus 212. An interface coprocessor 224 and modem 226 are
connected between an ethernet network, e.g. 12, 14, 16 or 18 and bus 212.
Coprocessor 224 is an Intel 82586 microprocessor or equivalent. An "A"
channel interface coprocessor 230 is connected to bus 212. An "A" channel
modem 232 is connected between coprocessor 230 and a token bus network. A
"B" channel interface coprocessor 234 and a "B" channel modem 236 are
connected between bus 212 and the token bus network. A "C" channel
interface coprocessor 238 and a "C" channel modem 240 are connected
between bus 212 and the token bus network. Coprocessors 230, 234 and 238
are Motorola 68824 microprocessors or equivalent. Modems 232, 236 and 240
are dual binary AMPSK modems, conforming to the IEEE 802.4 standard, each
assigned to one of the three standard channel frequency bands.
The boot PROM 218 is used to run test programs on the bridge components
when the system is first turned on. This is much the same as in a personal
computer boot PROM. When a message packet arrives from the ethernet
network, e.g. network 12, the interface coprocessor 224 determines if it
is a valid message. If it is a valid message, then the message is stored
in the dynamic RAM 214 and the microprocessor 210 is interrupted. The
microprocessor 210 uses the software in the EPROM 216 to evaluate the
message and if needed, select a proper channel and envelope the message
for transmission to the appropriate interface coprocessor. The software in
the EPROM 216 instructs the microprocessor 210 to store the bridge address
and station address tables in the dynamic RAM 214 and the nonvolatile RAM
222. If the bridge 200 experiences a power outage, then on power up, the
bridge 200 will still have addresses in the nonvolatile RAM 222 and there
is no need to relearn all the addresses.
The identification EEPROM 220 contains a code address which is unique to
each particular bridge. On power up, this bridge address is stored in the
interface coprocessor 230, 234 and 238. When a packet is received from the
token bus backbone network 40, the interface coprocessor verifies the code
address. If the message has a bridge destination different from that in
the identification EEPROM 220 or a multicast address, the message is
ignored. If the bridge destination is the same as this particular bridge
or its multicast address, the coprocessor stores the message in dynamic
RAM 214 and interrupts the microprocessor 210. The microprocessor 210 then
uses software in EPROM 216 to de-envelope the message and output it on the
ethernet network. The multicast address is also stored in the EPROM 216.
The present invention thus provides an effective way to increase the
capacity of the backbone network 40. The typical token bus backbone
network has a maximum capacity of ten megabits per second. By creating
three channels on the backbone network, the present invention has tripled
the traffic capacity to thirty megabits per second.
Other embodiments of the present invention are possible. Other types of
networks could be substituted for the ethernet and token bus networks of
the presently preferred embodiment. For example, a fiber optic ring could
be used as the backbone network.
Although the present invention has been described in terms of the presently
preferred embodiments, it is to be understood that such disclosure is not
to be interpreted as limiting. Various alterations and modifications will
no doubt become apparant to those skilled in the art after having read the
above disclosure. Accordingly, it is intended that the appended claims be
interpreted as covering all alterations and modifications as fall within
the true spirit and scope of the invention.
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Description |
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