Automatic isolation in loops

Details Automatic isolation in loops Automatic isolation in loops

1998-05-01

2001-02-13

Rao, Seema S. (Department: 2732)

Multiplex communications

Fault recovery

Bypass an inoperative station

C370S225000, C370S245000, C370S463000, C370S522000, C714S004110, C340S870030

Reexamination Certificate

active

06188668

ABSTRACT:

TECHNICAL FIELD
The present invention relates to electronic network communications systems, and more specifically to automatic isolation of a node or loop segment in a loop network where a data channel transmitting data from a hub port to the node or loop segment has failed.
BACKGROUND OF THE INVENTION
Electronic data systems are frequently interconnected using network communication systems. Area-wide networks and channels are two approaches that have been developed for computer network architectures. Traditional networks (e.g., LAN's and WAN's) offer a great deal of flexibility and relatively large distance capabilities. Channels, such as the Enterprise System Connection (ESCON) and the Small Computer System Interface (SCSI), have been developed for high performance and reliability. Channels typically use dedicated short-distance connections between computers or between computers and peripherals.
Features of both channels and networks have been incorporated into a new network standard known as “Fibre Channel”. Fibre Channel systems combine the speed and reliability of channels with the flexibility and connectivity of networks. Fibre Channel products currently can run at very high data rates, such as 266 Mbps or 1062 Mbps. These speeds are sufficient to handle quite demanding applications, such as uncompressed, full motion, high-quality video. ANSI specifications, such as X3.230-1994, define the Fibre Channel network. This specification distributes Fibre Channel functions among five layers. The five functional layers of the Fibre Channel are: FC-0—the physical media layer; FC-1—the coding and encoding layer; FC-2—the actual transport mechanism, including the framing protocol and flow control between nodes; FC-3—the common services layer; and FC-4—the upper layer protocol.
There are generally three ways to deploy a Fibre Channel network: simple point-to-point connections; arbitrated loops; and switched fabrics. The simplest topology is the point-to-point configuration, which simply connects any two Fibre Channel systems directly. Arbitrated loops are Fibre Channel ring connections that provide shared access to bandwidth via arbitration. Switched Fibre Channel networks, called “fabrics”, are a form of cross-point switching.
Conventional Fibre Channel Arbitrated Loop (“FC-AL”) protocols provide for loop functionality in the interconnection of devices or loop segments through node ports. However, direct interconnection of node ports is problematic in that a failure at one node port in a loop typically causes the failure of the entire loop. This difficulty is overcome in conventional Fibre Channel technology through the use of hubs. Hubs include a number of hub ports interconnected in a loop topology. Node ports are connected to hub ports, forming a star topology with the hub at the center. Hub ports which are not connected to node ports or which are connected to failed node ports are bypassed. In this way, the loop is maintained despite removal or failure of node ports.
More particularly, an FC-AL network is typically composed of two or more node ports linked together in a loop configuration forming a single data path. Such a configuration is shown in FIG.
1
A. In
FIG. 1A
, six node ports
102
,
104
,
106
,
108
,
110
,
112
are linked together by data channels
114
,
116
,
118
,
120
,
122
,
124
. In this way, a loop is created with a datapath from node port
102
to node port
104
through data channel
114
then from node port
104
to node port
106
through data channel
116
, and so on to node port
102
through data channel
124
.
When there is a failure at any point in the loop, the loop datapath is broken and all communication on the loop halts.
FIG. 1B
shows an example of a failure in the loop illustrated in FIG.
1
A. Data channel
116
connecting node port
104
to node port
106
has a failure
125
before entering node port
106
. The failure
125
could be caused by a problem such as a physical break in the wire or electromagnetic interference causing significant data corruption or loss at that point. Node port
106
no longer receives data or valid data from node port
104
across data channel
116
. At this point, loop
100
has been broken. Data no longer flows in a circular path and the node ports are no longer connected to one another. For example, node port
104
cannot transmit data to node port
108
because data from node port
104
does not pass node port
106
. The loop has, in effect, become a unidirectional linked list of node ports.
In a conventional FC-AL system, recovery proceeds according to a standard. Accordingly, when node port
106
detects that it is no longer receiving valid data across data channel
116
, node port
106
begins to generate loop initialization primitive (“LIP”) ordered sets, typically LIP (F8, AL_PS) or LIP (F8, F7) (“LIP F8”) ordered sets. “AL_PS” is the arbitrated loop address of the node port which is issuing the LIP F8 ordered sets, in this case, node port
106
. The LIP F8 ordered sets propagate around the loop. Each node receiving a LIP F8 primitive sequence stops generating data or other signals and sends a minimum of
12
LIP F8 ordered sets. A sequence of three consecutive LIP F8 ordered sets forms a LIP F8 primitive sequence. At this point, the LIP F8 primitive sequences and ordered sets composing primitive sequences propagate through the broken loop
100
shown in FIG.
1
B. Loop
100
typically does not function again until the data channel
116
has been repaired or replaced, such as by physical replacement or bypass by a second wire or cable. When node port
106
receives the LIP F8 primitive sequence, node port
106
begins loop initialization.
A conventional partial solution to recovery from a broken node port-to-node port loop is provided by the introduction of a hub within a loop. A hub creates a physical configuration of node ports in a star pattern, but the virtual operation of the node ports continues in a loop pattern. The connection process (i.e., sending data between node ports) and interaction with the hubs is effectively transparent to the node ports connected to the hub which perceive the relationship as a standard FC-AL configuration.
FIG. 2A
illustrates an arbitrated loop
200
with a centrally connected hub. Similar to loop
100
illustrated in
FIG. 1A and 1B
, loop
200
includes six node ports
202
,
204
,
206
,
208
,
210
,
212
, each attached to a hub
214
. Hub
214
includes six hub ports
216
,
218
,
220
,
222
,
224
,
226
where each hub port is connected to another hub port in a loop topology by a sequence of internal hub links. In this way, node ports
202
-
212
are each connected to a corresponding hub port
216
-
226
. Thus, node ports
202
-
212
operate as though connected in a loop fashion as illustrated in FIG.
1
A.
When a failure occurs on a data channel carrying data from a node port to a hub port, the loop is maintained by bypassing the failed node port. In a conventional hub, when a hub port no longer receives data from a node port, the hub port goes into a bypass mode where, rather than passing data received on the data channel from the node port, the hub port passes data received along the internal hub link from the previous hub port. For example, data channel
234
connecting node port
206
to hub port
220
may fail, such as through physical disconnection or interference such that valid data no longer passes from node port
206
to hub port
220
. Hub port
220
detects the cessation of valid data from node port
206
and enters bypass mode. In this way, the loop integrity is maintained. Rather than breaking the loop, as was the case illustrated in
FIG. 1B
, the bypass mode of a hub port allows the loop to be preserved. As shown in
FIG. 2A
, data continues to flow around the loop even while data channel
234
has failed because hub port
220
is operating in a bypass mode and isolates node port
206
.
FIG. 2B
illustrates a different problem which is unresolved by conventional hub technology. In
FIG. 2B
, a data channel
236
carrying

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