Virtual local area network with trunk stations

Details Virtual local area network with trunk stations Virtual local area network with trunk stations

1998-01-13

2002-10-22

Nguyen, Chau (Department: 2663)

Multiplex communications

Network configuration determination

C370S390000, C370S392000, C370S401000

Reexamination Certificate

active

06469987

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to communications networks and more particularly to virtual local area networks with trunk stations.
BACKGROUND OF THE INVENTION
Local area networks (LAN's) are used to facilitate communications between a number of users. Individual LAN's may be bridged together to allow a large number of users to communicate amongst themselves. These bridged LAN's may be further interconnected with other bridged LAN's using routers to form even larger communications networks.
Prior art
FIG. 1
depicts an exemplary interconnected bridged LAN system. The numerals
10
,
20
,
30
, etc., are used to identify individual LAN's. Bridges between LAN's are designated by the numerals
5
,
15
,
25
and
35
. A router between bridged LAN
100
and bridged LAN
200
is identified with the reference numeral
300
. In the prior art bridged LAN system depicted, a user A is able to communicate with a user B without leaving the LAN
10
. If user A desires to communicate with user C in LAN
20
or user D in LAN
30
, the communication is transmitted via bridges
5
and/or
15
.
If user A desires to communicate with user E, the communication must be routed via router
300
to bridged LAN
200
. As will be understood by those skilled in the art, bridges operated at layer
2
of the network model and transparently bridge two LAN's. It is transparent to users A and C that communications between them are ported over bridge
5
because layer
2
bridges do not modify packets, except as necessary to comply with the type of destination LAN. However, if user A wishes to communicate with user E, the communication must be ported via router
300
which operates at level
3
of the network model. Accordingly, communications over routers flow at a much slower rate than communications over a bridge, and are regulated by the routers.
Therefore, LAN network administrators generally attempt to connect together those users who frequently communicate with each other in bridged LAN's. However, if the bridged LAN becomes too large, it becomes unscalable and may experience various well-known problems. Accordingly, routers are used to interconnect bridged LAN's so that the bridged LAN's themselves can be kept to an acceptable size. This results in delays in communications between users which are transmitted via the router
300
. If, for example, in
FIG. 1
, user E and user A need to communicate frequently, it would be advantageous to interconnect LAN
10
and LAN
50
via a bridge rather than the router
300
. This would require system rewiring, which is costly and may be impracticable under many circumstances, such as, if users A and E will only need to frequently communicate for a limited period of time.
Virtual LAN's (VLAN's) have recently been developed to address the deficiencies,in interconnected bridged LAN systems of the type depicted in FIG.
1
. VLAN's allow LAN's to be bridged in virtually any desired manner independent of physical topography with switches operating at layer
2
. Hence, the switches are transparent to the user. Furthermore, the bridging of LAN's can be changed as desired without the need to rewire the network. Because members of one VLAN cannot be tranmitted to the members of another VLAN, a fire wall is established to provide security which would not be obtainable in a hardwired interconnected bridged LAN system. Accordingly, VLAN systems provide many advantages over interconnected bridged LAN's.
For example, as shown in prior art
FIG. 2
, individual LAN's
10
-
90
are interconnected by layer
2
switches
5
′-
55
′. A network management station (NMS)
290
controls the interconnection of the individual LAN's such that LAN's can be easily bridged to other LAN's on a long term or short term basis without the need to rewire the network. As depicted in
FIG. 2
, the NMS
290
has configured two VLAN's by instructing, e.g., programming, and thereby configuring the switches
5
′-
55
′ such that LAN's
10
-
60
are bridged together by switches
5
′-
45
′ and
55
′ to form VLAN
100
′ and LAN's
70
-
90
are bridged together by switches
45
′ and
55
′ to form VLAN
200
′. This is possible because, unlike the bridges
5
-
35
of
FIG. 1
which include only two ports, and accordingly are able to only transfer information from one LAN to another LAN, the switches
5
′-
55
′ are multiported and programmable by the NMS
290
such that the network can be configured and reconfigured in any desired manner by simply changing the switch instructions.
As shown in
FIG. 2
, the switch
55
′ has been instructed to transmit communications from user A of LAN
10
to user E of LAN
50
, since both users are configured within VLAN
100
′. User A, however, is not allowed to communicate with users H or F since these users are not configured within the VLAN
100
′ user group. This does not, however, prohibit users F and H, both of whom are members of VLAN
200
′, from communicating via switches
45
′ and
55
′.
If it becomes desirable to change the network configuration, this is easily accomplished by issuing commands from NMS
290
to the applicable switches
5
′-
55
′. For example, if desired, user H could be easily added to VLAN
100
′ by simply reconfiguring VLAN
100
′ at the NMS
290
to cause an instruction to be issued to switch
55
′ to allow communications to flow between users A-D and E and user H via switch
55
′, i.e., to include LAN
90
in VLAN
100
′ and remove it from VLAN
200
′.
Because the switches
5
′-
55
′ are layer
2
switches, the bridge formed by the switch is transparent to the users within the VLAN. Hence, the transmission delays normally associated with routers, such as the router
300
of
FIG. 1
, are avoided. The power of the VLAN lies in its ability to dynamically control the network configuration through software on the NMS
290
. More particularly, in accordance with its programmed instructions, the NMS
290
generates and transmits signals to instruct the switches
5
′-
55
′ to form the desired VLAN configurations.
Multicasting refers to the ability of a station on the network to simultaneously communicate a single message to a number of other stations on the network. In a typical LAN protocol, as shown in
FIG. 3
, the communication packet
400
includes a destination address
110
having six bytes, a source address
113
, and a message portion
114
. The message portion
114
typically includes the applicable LAN protocol. If the I/G (Individual/Group) bit
112
is set to zero, the packet is directed to a single specified address. However, if the I/G bit is set to one, the packet is identified as a multicast packet and is transmitted to all LAN's of the bridged LAN.
For example, referring to
FIG. 1
, if member A of bridged LAN
100
wishes to multicast to members B and C of bridged LAN
100
, the I/G bit of the destination address of the message packet would be set to one. If the I/G bit of the destination address, i.e., the multicast address designator, is at one, the bridges
5
and
15
understand that the communication is a multicast communication and direct the communication to all LAN's within the bridged LAN
100
for delivery to the members of the multicast group represented by the multicast address contained in the first 5 bytes of the MAP address. It will be noted that multicast communications are not routed by routers such as router
300
of FIG.
1
. Accordingly, in a conventional interconnected bridged LAN system, multicast communications cannot be distributed between bridged LAN's. Further, because multicast communications within a bridged LAN are distributed to all individual LAN's, e.g.
10
-
30
in
FIG. 1
, whether or not any member of a particular LAN within the bridged LAN is a member of

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