Note: Descriptions are shown in the official language in which they were submitted.
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
LOOP NETWORK HUB USING LOOP INITIALIZATION INSERTION
TECHNICAL FIELD
The present invention relates to electronic network systems, and more
specifically to a loop network hub designed such that loop address conflicts
are
reduced by forcing initialization of the loop upon insertion of a new node
port into the
loop.
BACKGROUND INFORMATION
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
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-2-
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, FIG. IA illustrates a conventional loop configuration
100. Four node ports 101, 102, 104, 106 are shown joined together node port to
node
port. Each node port represents a connection to a device or to another loop.
Node
port 101 is connected to node port 102 such that data is transmitted from node
port
1 OI to node port 102. Node port 102 is in turn connected to node port 104
which is in
turn connected to node port 106. Node port 106 is connected to the first node
port,
node port 101. In this manner, a loop datapath is established; from node port
100 to
node port 102 to node port 104 to node port 106 back to node port 100.
FIG. 1 B illustrates a loop 107 where node ports 108, 110, 112, 114 are
organized in a physical star topology with a hub 116 in the center. Node port
108 is
connected to a hub port 118 in hub 116 as are node ports 110, 112 and 114 to
their
own respective hub ports 120, 122, and 124. Internal to hub 116 is a loop,
where hub
ports 118 - 124 of hub 116 form a loop datapath similar to the conventional
loop
configuration shown in FIG. 1 A.
The use of a hub as a central component to a loop network allows for
operation when one or more hub ports are not connected to node ports, or one
or more
hub ports are connected to node ports which have failed, by bypassing such hub
ports.
Each hub port typically contains circuitry which provides a bypass mode for
the hub
CA 02329950 2000-10-25
WO 99/57827 PCTNS99/08986
-3-
port. When a hub port is in bypass mode, data received by the hub port from
the
previous hub port in the loop is passed directly to the next hub port in the
loop.
An additional advantage of the use of hubs is that node ports may be hot
insertable. Hot insertable functionality allows the insertion and removal of
node ports
from a loop without powering down the entire loop or the hub and then
restarting
again. However, as a result of this hot insertability, the addresses of node
ports
attached to a loop are not always properly maintained.
Under FC-AL protocols, a loop initialization process is used to provide
each node port attached to the loop with a unique address, referred to as an
Arbitrated
Loop Physical Address ("AL PA"). Loop initialization is invoked under FC-AL
protocols by generating a sequence of Loop Initialization Primitive ("LIP")
ordered
sets. In a loop which is not hot insertable, after insertion or removal of a
node port
the entire loop is restarted and re-initialized. In a hot insertable loop, the
loop is not
always restarted and so is not necessarily re-initialized upon each insert or
removal.
1 S As a result, when a new node port is inserted into the loop a unique
address may not
necessarily be generated if the loop is not re-initialized.
In addition, a hub port may be connected to a hub port on another hub.
When hubs are linked one hub to another through hub ports, sometimes hubs do
not
properly initiate an initialization routine upon insertion, especially in the
case of
quiescent hubs (i.e., no loop traffic at the time of insertion). At this point
there is a
possibility of address conflicts between the node ports on the first hub and
the node
ports on the second hub.
Such an address conflict problem is illustrated in FIGS. 2A and 2B. As
shown in FIG. 2A, four node ports A1, B1, C1, Dl, are linked to a hub 200.
Three
node ports A2, B2, C2, are connected to a hub 202. The numbers 1 and 2 are
illustra-
tive only and in fact the addresses for each node port are still represented
by the letter
A, B, C, or D. At this point, each node port has a unique address within its
own loop.
However, when hubs 200 and 202 are joined, as shown in FIG. 2B, the addresses
for
the node ports are no longer necessarily unique. In the single loop shown in
FIG. 2B,
two node ports have address A, two node ports have address B, and two node
ports
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-4-
have address C. Upon detecting an address conflict, an error is generated
which starts
an initialization sequence, ultimately resulting in unique addresses for each
node port.
However, before that conflict is detected, messages may still continue to pass
which
are received by incorrect node ports resulting in possible data comzption.
S For example, in the situation shown in FIG. 2A, when node port B 1 sends
data to node port AI, the hub ports are adjacent and node port A1 receives the
data
from node port B I possibly without an error. As shown in FIG. 2B, the
connection
from node port B 1 to node port A 1 may begin without generating an address
conflict
because messages from B I successfully pass along the loop to node port A 1,
the
intended destination, as long as node port B2 was not arbitrating,
However, when node port A 1 attempts to send data to node port B 1, data
corruption may result. In the situation shown in FIG. 2A, the data is sent
from node
port A 1, past node port C 1, past node port D 1, and then to node port B 1,
the intended
destination. However, in the situation shown in FIG. 2B, data passes from node
port
A 1, past node port C 1, past node port D 1, through the hub ports connecting
hub 200
and hub 202, past node port C2 and is received by node port B2. As noted
above, the
numerals indicate only the difference between node ports from hub 200 and node
ports from hub 202. From node port Al's perspective, node port B2 is
indistinguish-
able from node port B 1. Node port A I sends data addressed to node port B.
Simi-
lady, node port B2 accepts data which is addressed to node port B.
Accordingly,
node port B2 receives data addressed to node port B, though node port A1
intended
the data to be received by node port B 1. Thus, "B" is not a unique address.
Neither
node port A I nor node port B2 is aware of the existence of either node port
B2 or
node port A I . As a result, depending on the nature of the transaction
entered into,
data corruption may result. At some point, a proper error may be generated
resulting
in the initialization sequence. That may be too late, however, to prevent or
recover
from unwanted data corruption.
The inventors have determined that it would be desirable to provide a loop
network hub which can provide unique addresses upon insertion of a new node
port or
a new hub into a loop by forcing the loop to initialize before data corruption
occurs.
CA 02329950 2000-10-25
WO 99/57827 PCT/US99108986
-5-
SUMMARY
A loop network huh of the preferred embodiment includes a hub port with
a loop initialization insertion mechanism. The loop initialization insertion
mechanism
causes a hub port which detects a new connection to automatically begin
generating
loop initialization data. A hub port continues to generate loop initialization
data until
that hub port receives a loop initialization sequence. The loop initialization
data
propagates around the loop of the hub, halting ordinary processing. In this
way, the
entire loop is cleared. Upon receiving a loop initialization sequence, the hub
port
originating the loop initialization data stops sending the loop initialization
data and
inserts the new node port into the loop. At this point, loop initialization
begins and
each node port in the loop network obtains a unique loop network address.
In an FC-AL implementation, a hub of the preferred embodiment includes
a hub port with a LIP insertion mechanism. The loop initialization insertion
mechanism causes a hub port which detects a new connection to automatically
begin
generating LIP (F7, F7) ordered sets. The hub port continues to generate LIP
(F7, F7)
ordered sets until that hub port receives a LIP primitive sequence, where a
LIP
primitive sequence includes three consecutive identical LIP ordered sets. The
LIP
(F7, F7) ordered sets propagate around the loop of the hub, halting ordinary
processing. In this way, the entire loop is cleared. Upon receiving a LIP
primitive
sequence, the hub port originating the LIP (F7, F7) ordered sets stops
inserting LIP
(F7, F7) ordered sets and inserts the new node port into the loop. At this
point, loop
initialization begins and each node port obtains, according to known FC-AL
proto-
cols, a unique physical address (an Arbitrated Loop Physical Address, "AL
PA").
CA 02329950 2000-10-25
WO 99/57827 PCTNS99/08986
-6-
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 A shows a prior art node port to node port loop.
FIG. 1 B shows a prior art loop including a hub.
FIG. 2A shows two separate prior art loops.
FIG. 2B shows two prior art loops connected to form a single loop.
FIG. 3 shows a loop including a hub.
FIG. 4 shows a block diagram of a hub port according to the preferred
embodiment.
FIG. SA shows a hub with two node ports.
FIG. SB shows a hub with three node ports.
FIG. 6A shows two separate loops including hubs.
FIG. 6B shows two loops including hubs connected by hub ports.
DETAILED DESCRIPTION
The preferred embodiment provides a mechanism to force loop initializa-
tion upon insertion of a node port into a loop network. The invention is
explained
below in the context of a Fibre Channel Arbitrated Loop ("FC-AL") as an
illustration
of the preferred embodiment. However, the invention may have applicability to
networks with similar characteristics as FC-AL networks.
An overview of loop operation in a loop network is described below with
reference to a configuration illustrated in FIG. 3. FIG. 3 shows a hub 300
with six
hub ports 302, 304, 306, 308, 310, and 312. Each hub port is connected to
another
hub port with a unidirectional internal hub link forming an internal hub loop.
In FIG.
3, data flows from hub port 302 to hub port 304 and so on in a counter
clockwise
manner. Alternatively hub ports may be connected such that data flows in a
clock-
wise direction so long as the loop topology is maintained.
Attached to three hub ports 302, 310, 312, are three node ports 314, 316,
318. Node port 314 is attached to hub port 302, node port 316 is attached to
hub port
312, and node port 318 is attached to hub port 310. Each node port is
preferably
attached to a hub port by two data channels: one data channel sends data from
the
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
hub port to the node port, one data channel sends data from the node port to
the hub
port. Thus, a data channel carries data from hub port 302 to node port 314 and
another data channel carries data from node port 314 to hub port 302. Data
from node
port 314 to be received by node port 316 passes from node port 314 through a
data
channel to hub port 302, then from hub port 302 to hub port 306, then to hub
port 306,
to hub port 308, to hub port 310. If node port 318 is operating in the loop,
the data
passes through a data channel to node port 318 and back through a data channel
to
hub port 310, and then passes to hub port 312. The data passes through a data
channel from hub port 312 and is received at node port 316.
In the preferred embodiment, incoming data entering a hub port from the
previous hub port in the loop is sent to the node port connected to the hub
port, if
present. If the hub port is in bypass mode, the incoming data is sent directly
from the
hub port to the next hub port in the loop without including any data from the
node
port in response to the incoming data. The preferred embodiment uses a
switching
device such as a multiplexer to accomplish this bypass, as described below
with
reference to FIG. 4. In addition, the attached node port recognizes whether
the data
received from the hub port is addressed to that node port or not and responds
appro-
priately. The bypass is accomplished in the hub port, however, not in the node
port.
Thus the loop is protected from node port failures. A hub port which has no
attached
node port, such as hub ports 304, 306 or 308 shown in FIG. 3, is always in
bypass
mode and passes any data directly to the next hub port. In this way, a signal
from hub
port 302 received by hub port 304 is passed directly to hub port 306. When a
hub
port with an attached node port, such as hub port 310, 312, or 302 as shown in
FIG. 3,
receives data from the previous hub port on the loop, the hub port passes the
data to
the attached node port. The node port responds appropriately and passes the
data back
to the hub port.
For example, data which is addressed from node port 318 to node port 314
flows from node port 3I 8 to hub port 310 then to hub port 312. Hub port 312
passes
the data to node port 316, if node port 316 is not bypassed. Node port 316
recognizes
that the data is not addressed to node port 316 and so passes the data back to
hub port
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-g_
312. Hub port 312 passes the data to hub port 302. Hub port 302 passes the
data to
node port 314, if node port 314 is not bypassed. Node port 314 recognizes the
data is
addressed to node port 314 and responds appropriately.
FIG. 4 illustrates internal components of a hub port according to the
preferred embodiment. A hub port 400 as shown in FIG. 4 is equivalent to hub
ports
302, 304, 306, 308, 310, and 312 shown in FIG. 3. An incoming internal hub
link 402
enters hub port 400 from a previous hub port in the loop (not shown). Incoming
internal hub link 402 is connected to a hub port transmit circuit 404. Thus,
data from
a previous hub port passes along internal hub link 402 into hub port 400 and
then into
hub port transmit circuit 404. Hub port transmit circuit 404 sends the data
received
through a data channel 406 out to a node port 408 after converting the data
into a
form usable by node port 408. Alternatively, data channel 406 may be connected
to a
hub port in a different hub, allowing interconnection hub to hub.
Node port 408 outputs data to hub port 400 via a data channel 410. Data
channel 410 is connected to a hub port receive circuit 412. Hub port receive
circuit
412 converts data received from node port 408 into a form usable inside the
hub. In
one implementation, hub port receive circuit 412 converts data from serial to
parallel
and decodes the data. Hub port receive circuit 412 also includes a loop
initialization
data detect circuit 414 and a hub port output control circuit 416. In an FC-AL
implementation, the loop initialization data detect circuit 414 is a LIP
detect circuit.
Hub port receive circuit 412 outputs data via a hub port output line 418. Hub
port
output control circuit 416 outputs control signals via a hub port output
control line
420. Hub port output line 418 is connected to a first input A of a switching
device
422, such as a multiplexer. Incoming internal hub link 402 is connected to a
second
input B of switching device 422. A loop initialization data generator 424
generates
loop initialization data and outputs those ordered sets to a loop
initialization data line
426. In an FC-AL implementation, loop initialization data generator 424 is a
LIP
generator and generates LIP (F7, F7) ordered sets. Loop initialization data
line 426 is
connected to a third input C of switching device 422. Hub port output control
line
420 is connected to a control input of switching device 422. In this way,
switching
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-9-
device 422 selects a single input A, B, or C to be output depending upon the
control
signal generated by hub port output control circuit 416. The output of
switching
device 422 is sent to outgoing internal hub link 428. Outgoing internal hub
link 428
passes data to the next hub port in the hub in the same manner that internal
hub link
402 passes into hub port 400, forming a loop as shown in FIG. 3.
When no device is attached to hub port 400, hub port output control circuit
416 holds hub port 400 in bypass mode. By selecting input B of switching
device 422
data received from the previous hub port on incoming internal hub link 402 is
output
to outgoing internal hub link 428. In bypass mode, data on incoming internal
hub link
402 enters input B of switching device 422 and is output unchanged onto
outgoing
internal hub link 428 to be passed to the next hub port in the loop (not
shown).
If, however, an operational device, such as an FC-AL NL Port or loop
segment, is attached to hub port 400, represented by node port 408, data
received
from node port 408 by hub port receive circuit 412 is sent to the next hub
port along
outgoing internal hub link 428. In order to pass data from hub port receive
circuit 412
to outgoing internal hub link 428, hub port output control circuit 416 selects
input A
of switching device 422 via hub port output control line 420.
In a conventional FC-AL hub port, typically upon initial attachment of an
operational device at node port 408, hub port receive circuit 412 detects the
reception
of data from node port 408 and ends bypass mode (where input B of switching
device
422 is selected). Data received from node port 408 is inserted onto the loop
by
selecting input A of switching device 422. The data received by hub port
receive
circuit 412 from node port 408 is immediately passed along to the next hub
port via
outgoing internal hub link 428. However, as discussed above, this immediate
insertion into the loop of a new device or hub may generate address conflicts
and lead
to undesirable data corruption.
In order to overcome this difficulty, the preferred embodiment provides a
loop initialization insertion mechanism. When an operational device or hub is
attached to hub port 400, hub port receive circuit 412 detects that new device
or hub
by detecting the reception of formatted data along data channel 410 where
previously
CA 02329950 2000-10-25
WO 99/57827 PC'T/US99/08986
-10-
there was no data. Rather than immediately passing along data from node port
408
through hub port output line 418 onto outgoing internal hub link 428, hub port
output
control circuit 416 selects input C of switching device 422. Loop
initialization data
generator 424 generates a constant stream of loop initialization data which
indicates
to other hub ports in the loop that a new device or hub has been attached.
Other hub
ports in the loop upon receiving a loop initialization sequence pass the
sequence
along. A loop initialization sequence is a specified combination of loop
initialization
data. In an FC-AL implementation, a LIP primitive sequence consists of three
consecutive identical LIP ordered sets of the same type. In this way, the
processing
of transactions on the loop stops and each hub port begins to pass along or
generate
loop initialization data. Loop initialization data generator 424 repeatedly
generates
loop initialization data, preferably in coordination with the frame sequence
appropri-
ate to the loop network.
Hub port output control circuit 416 continues to select input C of the hub
port switching device 422 until loop initialization data detect circuit 414
detects a
loop initialization sequence received from node port 408. Node port 408, as
described above, receives signals from incoming internal hub link 402 via hub
port
transmit circuit 404. The selection of inputs on switching device 422 does not
affect
the reception of data by node port 408 because switching device 422 controls
the
output of hub port 400 onto the loop, not the input from the loop.
In an FC-AL implementation, the loop initialization data is LIP (F7, F7)
ordered sets. These LIP (F7, F7) ordered sets are preferably in the form
(K28.5 D21.0
D23.7 D23.7), compliant with FC-AL protocols.
In this way, a loop initialization sequence generated from a previous port
in the loop (possibly this same port) enters hub port 400 on incoming internal
hub link
402 and is sent to node port 408 through hub port transmit circuit 404. Node
port 408
sends the loop initialization sequence to hub port receive circuit 412. Loop
initializa-
tion data detect circuit 414 detects the loop initialization sequence. Upon
detecting
such a loop initialization sequence, hub port output control circuit 416
switches from
selecting input C of switching device 422 to selecting input A of switching
device
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-11-
422. At this point, a loop initialization procedure begins according to
appropriate
network protocols.
A LIP detect circuit 414 generates an affirmative detection signal upon
detecting any LIP primitive sequence, not necessarily the same LIP (F7, F7)
primitive
sequence. The detected LIP primitive sequence does not need to be from the
same
hub port as originally began the LIP (F7, F7) ordered set generation from
detecting a
new device or hub.
At hub ports other than the hub port originating the loop initialization data,
when a node port receives loop initialization data from a hub port, the node
port
passes some of the loop initialization data back to the hub port. In the
preferred
embodiment the hub port passes along data from the node port (by selecting
input A
of the switching device as shown in FIG. 4)
Thus, loop initialization is forced upon attachment of a new operational
device or a new hub to an existing hub. In the preferred embodiment, the
generation
and propagation of loop initialization sequences halts ordinary loop operation
and
begins loop initialization. As described above, loop initialization is
desirable upon
connection of a new device or upon connection of a second loop to a first loop
because the loop initialization process is an assured way under network
protocols
such as FC-AL protocols to assign each device on the newly established loop a
unique
physical address.
FIG. 5A and 5B illustrate an example of inserting an operational device in
a loop according to a preferred embodiment. FIG. 5A illustrates a loop and
compo-
nents before the new device is inserted. A hub 500 has four hub ports 502,
504, 506,
508. As shown in FIG. 5A, hub 500 has only four hub ports, however, hubs may
have
more or less hub ports. The number of hub ports shown in FIG. 5A is for
illustrative
purposes only. Hub ports 502, 504, 506, 508, are connected to one another by
internal hub links to form a loop. Two node ports 510, 512 are attached to hub
ports
502, 508, respectively. Data from node port 510 to node port 512 flows through
a
data channel into hub port 502. Hub port 502 outputs the data along the
internal hub
link to hub port 504. Hub port 504 does not have an attached operational
device and
CA 02329950 2000-10-25
WO 99/57827 PCTNS99/08986
-12-
so is in bypass mode. Thus hub port 504 passes the data from hub port 502
along the
internal hub link to hub port 506. Hub port 506 is also in bypass mode and so
passes
the data along the internal hub link to hub port 508. Hub port 508 has an
operational
device attached at node port 512 and so is not in bypass mode. Similarly, data
from
node port 512 to be sent to node port 510 passes through a data channel to hub
port
508 and passes along the internal hub link to hub port 502. Hub port 502 sends
the
data along a data channel to node port S 10. In this way, hub ports 502 - 508
and hub
500 operate to maintain a loop topology.
Upon insertion of a new device attached to a node port 514, the process
described above with respect to FIG. 4 proceeds. Node port 514 is attached to
hub
port 504. Hub port 504 detects the new node port 514 from the presence of data
incoming to hub port 504 in a particular formation of data. Upon detecting
node port
514, hub port 504 does not immediately pass along data from node port S 14.
Hub
port 504 synchronizes timing and frames with data from node port 514 and
validates
1 S the proper operation of the node port S 14. As described above, hub port
504 begins
to send loop initialization data (e.g., LIP (F7, F7) ordered sets) along the
internal hub
link by selecting an input of a switching device inside of hub port 504 which
corre-
sponds to a loop initialization data generator. The loop initialization data
passes
along the internal hub link to hub port 506.
Hub port 506 is in bypass mode because no node port is attached to hub
port 506. Hence, 'the loop initialization data passes along the internal hub
link to hub
port 508.
Hub port 508 passes the loop initialization data to node port 512, if node
port S 12 is not already bypassed. The operational device attached to node
port 512
preferably responds to the loop initialization data and node port 512 passes
the loop
initialization data back to hub port 508. Because the operational device
attached to
node port 512 generates a proper response to the loop initialization data, in
the
preferred embodiment hub port 508 selects the signal received from node port
512 to
pass along the internal hub link of hub 500. A hub port such as hub port 508,
which
is attached to an operational device through a node port, passes along the
loop
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-13-
initialization data received from the node port by selecting input A of the
hub port
switching device as shown in FIG. 4. Thus, the loop initialization data is
preferably
passed along the internal hub link to the next hub port.
As shown in FIG. SB, hub port 508 passes the loop initialization data to
hub port 502. Hub port 502 follows a similar process as hub port 508 because
hub
port 502 also has an operational device attached, represented by node port S
10.
Accordingly, the loop initialization data passes from hub port 502 to hub port
504.
Hub port 504 receives the loop initialization data and transmits the loop
initialization data to node port 514, if node port 514 is not already
bypassed. Node
port S 14 passes the loop initialization data back to hub port 504, similar to
node ports
512 and 510. The loop initialization data detect circuit (414 as shown in FIG.
4) in
the hub port receive circuit of hub port 504 detects the loop initialization
data. Hub
port 504 stops outputting loop initialization data when a loop initialization
sequence
has been received. In this case, hub port 504 may have received the loop
initialization
sequence which originated at hub port 504. However, as described above, hub
port
504 ceases outputting loop initialization data upon detecting a loop
initialization
sequence from any source. In an FC-AL implementation, a hub port stops
outputting
LIP (F7, F7) ordered sets upon detecting a LIP primitive sequence of any type.
In an
alternative embodiment, the hub port transmit logic detects a loop
initialization
sequence received along the internal hub link and does not necessarily wait
for a
response from the connected node port. In either case, hub port 504 switches
from
outputting loop initialization data (through selecting input C of the
switching device
as shown in FIG. 4) to a loop initialization procedure defined by the
appropriate
network protocols.
FIG. 6A and 6B illustrate the connection of one hub loop to a second hub
loop. In general, the process is similar to that illustrated in FIG. SA and SB
for the
insertion of a new operational device to a single hub loop.
FIG. 6A shows a first hub 600 with six hub ports 602, 604, 606, 608, 610,
612. Three node ports 614, 616, and 618 are connected to hub ports 602, 604,
and
606, respectively. A second hub 620 also has six hub ports 622, 624, 626, 628,
630,
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/08986
-14-
632. Three node ports 634, 636, and 638 are connected to three hub ports 622,
624,
and 626, respectively. The hub ports of each hub are connected in a loop.
FIG. 6B illustrates the connection of hub 600 to hub 620. A pair of data
channels connect hub port 608 to hub port 632. One data channel carries data
from
S hub port 608 to hub port 632. One data channel carries data from hub port
632 to hub
port 608. In this way, the two loops contained in two separate hubs are joined
together to form a single loop. The new circular datapath among hub ports has
the
following pattern: hub port 608 to 610 to 612 to 602 to 604 to 606 back to
608, then
to hub port 632 to 622 to 624 to 626 to 628 to 630 back to 632, then back to
hub port
608, completing the circle. When data enters hub port 608 from hub port 606,
the
data passes through a transmit circuit of hub port 608 (recall FIG. 4) and
then out
through the data channel to hub port 632. The data has not yet entered a
receive
circuit of hub port 608, and does not until the data returns from hub port
632. In this
way, data flows in a circular pattern through two hubs and the two previously
physically distinct loops operate as one virtual loop.
Upon connection of one hub to another, however, the potential for address
conflicts and undesirable data corruption exists, as described above with
respect to
FIG. 2A and 2B. The loop initialization insertion mechanism provided by the
preferred embodiment overcomes this problem and forces loop initialization.
Hub
port 608 detects the connection to hub port 632 of hub 620 through the new
reception
of properly formatted data. Upon detection of hub port 632, hub port 608
follows the
procedure as defined above for detection of a new device. Hub port 608 selects
a
loop initialization data generator internal to hub port 608 and outputs loop
initializa-
tion data along the hub loop. Accordingly, loop initialization data passes
from hub
port 608 to hub port 610. Hub port 610 is in bypass mode because there is no
node
port attached to hub port 610. Hub port 610 passes the loop initialization
data along
to the next hub port, and the process continues as described above with
respect to
FIG. SB. Similarly, hub port 632 detects the connection to hub port 608 of hub
600.
Thus, hub port 632 selects a loop initialization data generator internal to
hub port 632
and outputs loop initialization data onto the hub loop of hub 620.
CA 02329950 2000-10-25
WO 99/57827 PCTNS99/08986
-15-
Accordingly, each of hub ports 608 and 632 are generating loop initializa-
tion data which is being passed along the loop. The loop initialization data
from hub
port 608 passes from hub port 608, to 610, to 612, to 602, to node port 614
(if node
port 614 is not bypassed), to hub port 602, to 604, to node port 616 (if node
port 616
is not bypassed), to hub port 604, to 606, to node port 618 (if node port 618
is not
bypassed), to hub port 606, and back to 608. However, in the preferred
embodiment,
at this point hub port 608 does not detect the loop initialization data
because the loop
initialization data detection circuit of hub port 608 is in the hub port
receiving circuit
of hub port 608. The loop initialization data received along the internal hub
link from
hub port 606 is in the hub port transmit circuit of hub port 608. Accordingly,
the loop
initialization data passes to hub port 632. Hub port 632 receives the loop
initializa-
tion data in its hub port receiving circuit and detects the loop
initialization data using
its loop initialization data detection circuit. When hub port 632 has detected
a loop
initialization sequence, in this case from the loop initialization data
generated by hub
port 608, hub port 632 changes the selection of input on the internal
switching device
of hub port 632 so that loop initialization proceeds. The bypass accomplished
internal
to hub port 632 by selecting the loop initialization data generator ends and
loop
initialization commences.
Similarly, hub port 608 receives the loop initialization data generated by
hub port 632 which passed along the internal hub link of hub 620 and
eventually from
hub port 632 to hub port 608. The loop initialization data detect circuit in
the hub
port receiving circuit of hub port 608 detects the loop initialization
sequence, ends the
bypass, and begins loop initialization processing according to standard FC-AL
protocols. Thus, both hub ports 608, 632 begin loop initialization processing.
The
handling of loop initialization is conventionally understood and defined
according to
network protocols, such as FC-AL protocols. In addition, the technique is
still .
effective if one of the interconnected hubs is a conventional hub, so long as
at least
one hub in the loop operates according to the present invention.
CA 02329950 2000-10-25
WO 99/57827 PCT/US99/0$986
-16-
Various embodiments of the invention have been described with reference
to the figures, however, the scope of the invention is not to be limited by
the descrip-
tion provided herein but rather only by the scope of the following claims.
Alternative
embodiments which fail within the scope of the claims will also be apparent to
those
of ordinary skill in the art.
