Network switch with panic mode

Details Network switch with panic mode Network switch with panic mode

1998-01-13

2001-10-09

Ngyeun, Chau (Department: 2663)

Multiplex communications

Fault recovery

Bypass an inoperative channel

C370S245000, C370S401000

Reexamination Certificate

active

06301224

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to communications network switches and more particularly to network switches having a panic mode of operation for facilitating communication on a redundant communication path.
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 operate 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.
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.
It is often beneficial in bridged LAN's and other types of communication systems or networks for redundant communication paths to be provided. Referring again to
FIG. 1
, a switch
37
in bridged LAN
200
provides a redundant communication path between LAN
50
and LAN
60
.
Prior art
FIG. 2
depicts another communication system having redundant communications paths. As shown, the system includes LAN's
305
-
330
. LAN
305
is connected to LAN
310
by switch
340
. LAN
310
is connected to LAN
315
by a switch
350
. This provides a primary communication path between LAN's
305
and
315
. Accordingly, during normal operations communications between users X and Y are directed through switches
340
and
350
along the communication path
410
. A redundant path
420
is also shown connecting LAN's
305
and
315
. This path is under the control of switch
360
which also connects LAN
305
with LAN's
320
-
330
. Conventional switch
360
includes a switch controller which implements forward processing and spanning tree processing, the latter in accordance with a spanning tree protocol.
Each of the switches periodically exchange hello messages, typically at a frequency of once per second. It will be recognized by those skilled in the art that data communications are being received by switch
360
at a substantially higher frequency and that tens of thousands, if not hundreds of thousands of data communications packets may be received by the switch
360
every second. Based upon the spanning tree protocol implemented by the switch
360
, data traffic between users X and Y is prohibited by switch
360
from transmission via the redundant communication path
420
as long as the hello messages are periodically received.
If a succession of hello messages are not received from either of switch
340
or switch
350
, for example, fifteen successive hello messages are missed, the switch
360
, in accordance with the spanning tree protocol, opens the redundant communication path and allows communications between users X and Y to be transmitted via the redundant link
420
. This is intended to ensure that the redundant communication path is only available for transmitting communications between LAN's
305
and
315
when the primary communication path
410
has failed. As those skilled in the art will recognize, if both communication paths
410
and
420
are simultaneously open to traffic, a network loop will be formed which will result in an extreme overloading of the system which is, in turn, likely to bring the network down.
Conventional switches
340
-
360
may have a threshold capacity over which the switch is unable to forward received traffic. Accordingly, each switch is configured such that when the amount of received traffic exceeds the threshold capacity or limit, the excess traffic may be simply dropped. However, this dropping of traffic may also result in anomalies in the switch
360
monitoring of the hello messages. More particularly, if hello messages are dropped along with excess data communications, the switch
360
will erroneously conclude that the primary communication path
410
is inoperable and therefore open the redundant communication path
420
unnecessarily, thereby causing a network loop which will overload and bring down the system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a communications switch which controls a redundant communication link in an enhanced manner.
It is another object of the present invention to provide a communications switch which routes data traffic over a redundant communications link in such a way that network communications loops are avoided.
It is a further object of the present invention to provide a communication switch which does not unnecessarily route data traffic over a redundant communications link.
Additional objects, advantages, novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.
In accordance with the present invention, a communications switch is provided for use in transmitting traffic from a first user to a second user in cases where the first and the second users are interconnected by primary and redundant communications paths. The switch includes a first port configured to receive periodic hello communications indicative of a proper operation of the primary communications path. During normal operations, a switch control monitors the receipt of hello communications, and directs the forwarding of the received data communications up to a threshold capacity or limit. The hello communications typically are received at a first frequency, e.g., once per second, and the data communications are received at a second frequency, e.g., tens of thous

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