Method and means for leader choosing on a token ring system

In a token ring transmission system, token loss causes selection of a leader terminal, which issues a new token. The leader terminal is chosen by selecting and storing a leadership selection reference value and then generating a succession of terminal identification signals and transferring them on the token ring transmission system. Each terminal receives the succession of signals and iteratively compares the terminal identification signals sequentially with the leadership reference signal. Each time a terminal identification signal exceeds the magnitude of the leadership reference signal, the leadership reference value is replaced with the value of the terminal identification signal. The first terminal detecting equality of a terminal identification signal with its leadership selection reference signal assumes leadership and issues a token.

BACKGROUND OF THE INVENTION 
The invention is in the field of token ring systems, in which a token ring 
transmission network uni-directionally transmits data between terminals 
attached to the network by passing a data signal, termed a "token", which 
symbolizes authority to place data on the transmission network. 
This invention particularly relates to a method and means for responding to 
loss of a token in a token ring network by choosing a leader terminal 
having the responsibility for regenerating the token and placing it on the 
transmission network. 
Token ring systems are well understood in the art, and involve the use of a 
looped, uni-directional transmission system which connects a plurality of 
terminals for data exchange. A prior art token ring network is illustrated 
in FIG. 1 and consists of a set of receive/send (R/S) units 10, 12, 14, 
and 16, interconnected by uni-directional transmission links 10, 12; 12, 
14; 14, 16; and 16, 10. The system is looped in that each send unit 
uni-directionally transmits over a respective link to the receive unit of 
one adjacent terminal. The receive unit's terminal has provision for 
providing the received information to the terminal's send unit so that the 
information is forwarded to the next adjacent terminal, and so on, until 
the information is eventually propagated around the ring, back to the 
receive unit of the originating terminal. 
The prior art token ring system of FIG. 1 includes four terminals 
identified as a, d, s, and n, wherein the alphabetic character associated 
with each terminal also represents a unique identification code having a 
value with a magnitude which is relative to the magnitudes of the other 
terminals. In this regard, the identification code magnitudes of the prior 
art terminals of FIG. 1 have the relationship a&lt;d&lt;n&lt;s. 
The system of FIG. 1 is a "token passing" system in that any one of the 
terminals a, d, n, s is enabled to place data on the token ring network 
when it obtains a signal having a unique bit pattern called a "token". In 
FIG. 1, the token is continuously circulated in a clockwise direction in 
the token ring network. When the token is received at a terminal having 
data available for transmission, the terminal inserts the data into the 
token, changes the token's configuration to indicate that it is 
unavailable, identifies itself and the terminal which is to receive the 
data, and retransmits the altered token on the token ring network. 
The token is circulated on the token ring network until it arrives at the 
designated receiving terminal, where the data is read, and the token, once 
again, is forwarded. When the token arrives back at the sending terminal, 
the data is removed, and the token is altered to an available state and 
retransmitted on the ring. 
Token passing protocols may vary, to some extent, from the procedure 
outlined above. However, all share the common characteristics of 
uni-directional transmission in a closed-looped transmission system to 
which access is obtained according to a protocol based upon a circulating 
token. 
In token ring systems, a problem commonly arises when terminal failure or 
system noise obliterates or alters a circulating token. To recover 
synchronicity and reimplement the data transfer protocol, a new token must 
be generated to replace the lost or altered one. This can be done by 
designation of a master terminal having primary responsibility for token 
generation, system synchronization, and protocol oversight. Of course, if 
such a master terminal fails, the system will either fail totally or 
recover in a reduced-capacity state by transfer of master terminal duties 
to a subservient terminal. 
In other token ring systems, system oversight and control is transferrable, 
with responsibility for token regeneration allocated according to a 
democratic procedure. In such systems, an algorithm or procedure is 
invoked to designate a "leader" terminal having responsibility for 
maintenance of a circulating token, and for regeneration of a lost or 
altered token. 
Since a token ring network is intended to provide a high degree of 
communications availability, a token regeneration scheme must provide fast 
recovery from loss of a token in the form of speedy token regeneration. 
Preferably, token regeneration is preceded by selection of a leader 
terminal, following which the selected leader generates a new token. 
Implicit in this process is that leader selection be rapid, unambiguous, 
and as simple as possible. 
The prior art procedures for token regeneration are based upon circulation 
of terminal identification codes in the event of token loss. In one 
procedure, all healthy terminals place their own identification codes on 
the token ring and forward all received identification codes. The first 
terminal to recognize its own code interrupts the procedure and generates 
the token. In another procedure, each terminal retransmits only 
identification codes having a predetermined magnitude relationship with 
its own identification code. Thus, for example, each terminal will 
retransmit only an identification code having a greater magnitude than its 
own. In this scheme, the first terminal receiving its identification code 
becomes the leader. 
SUMMARY OF THE INVENTION 
In the specific embodiment of this invention, loss or non-conventional 
alteration of a token stimulates a leadership selection procedure in which 
any terminal sensing token loss immediately places a leadership selection 
frame on the ring which contains its own identification. During the 
procedure, each terminal receiving a leadership selection frame inspects 
the terminal identification and compares it against a stored leadership 
reference value. If the terminal identification in the leadership choosing 
frame equals the leadership reference value, the leadership mantle falls 
upon that terminal. If the terminal identification in the leadership 
choosing frame has a magnitude greater than the leadership reference 
value, the leadership reference value in the terminal is changed to equal 
the terminal identification value. Thus, each terminal maintains or 
increases its stored leadership reference value in response to a 
succession of terminal identification codes which are circulated on the 
ring, until a leadership reference/terminal identification code match 
occurs. 
This procedure does not wait until a terminal recognizes its own 
identification code. Therefore, it is faster than the prior art leadership 
selection protocols based upon terminal self-recognition. The procedure is 
flexible in that it allows leadership to be transferred in the event of 
system malfunction. Moreover, the change in the leadership reference value 
in response to a magnitude difference ensures that the protocol will 
unambiguously select a single leader. 
Of course, it is not intended that the invention be limited to an 
increasing magnitude response. Indeed, the leadership choosing protocol of 
this invention is validly practiced by changing the leadership reference 
value in response to a lower magnitude terminal identification code. 
The invention is practiced in a token ring system for interconnecting a 
plurality of terminals and concerns a method for leadership selection. The 
method of the invention involves, first, at a first terminal in the 
system, identifying an event which initiates the procedure, and then 
generating and transmitting in the token ring system a succession of 
signals to select a system leader. Each of these signals in the succession 
has a terminal identification characteristic which identifies a respective 
one of the system terminals. The succession of signals is received at the 
first terminal and the following sequence is performed in response to 
identification of the starting event: 
(a) leadership selection reference signal is stored; 
(b) a signal from the succession of signals is received; 
(c) the terminal identification characteristic of the received signal is 
compared with the leadership selection reference signal; 
(d) if the terminal identification characteristic of the received signal 
matches the leadership selection reference signal, a token is generated at 
the first terminal and circulated in the system; otherwise, 
(e) steps (a)-(d) are performed. 
The procedure of the invention further includes the step of, after step 
(d), and before step (e),: 
(d.sub.i) if the terminal identification characteristic of the received 
signal has a particular magnitude relationship with the leadership 
selection reference signal, the leadership selection reference signal is 
changed to equal the value of the terminal identification signal. 
This method further includes inspection of the signal obtained in step (b), 
and if the characteristics include token characteristics, the sequence is 
terminated. Otherwise, the sequence is continued. 
It is, therefore, the primary objective of the invention to choose a leader 
terminal in a token ring system in which the token has been lost. 
A further objective is to have the identified leader regenerate the token 
and transmit it on the system. 
A significant feature of the system is that leadership is conferred on the 
first terminal to detect a second occurrence of the same terminal 
identification in a sequence of signals transferred in the token ring 
system to select a system leader. 
Other objectives, significant advantages, and important features of this 
invention will become evident upon a reading of the detailed description 
of this invention with reference to the below-described drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In this application, it is assumed that token ring technology is 
well-developed, and that an in depth lexicography of token ring terms has 
developed. In this regard, reference is given particularly to the 
DICTIONARY OF COMPUTING, copyright 1987, International Business Machines 
Corporation, for the terms "token", "token access control", "token 
passing", "token passing procedure", and "token ring network". See also 
definitions for "master node control", "event", "time-out", and "time-out 
control". 
Reference is also made to U.S. Pat. No. 4,539,679 entitled "SYNCHRONIZATION 
IN A COMMUNICATION NETWORK OF INTERCONNECTED RINGS", assigned to the 
assignee of this application, and incorporated herein by reference. In the 
incorporated patent, FIG. 2 illustrates a data format used for token ring 
information exchange. The prior art also has provision for token ring data 
formatting logic which interprets and constructs data structures employed 
in a token ring system for inter-terminal transmission of data on a token 
ring network. 
In understanding the practice of this invention, structures and procedures 
are known for making failed or non-functional terminals "transparent" and 
for reconfiguring a transmission ring upon the failure of a ring 
component. 
TABLE I 
______________________________________ 
Leader-Choosing Protocol 
______________________________________ 
197 IF awake by TIME-OUT /* No leader*/ 
198 THEN Name-ID: = my name 
/* initial value is 
my name*/ 
199 ELSE Name-ID: = name received 
/* initial value is 
name in 
message 
received*/ 
201 Your-Temp-ID := Name-ID 
/* initial value*/ 
SEND Name-ID /* along the ring 
to your 
neighbor*/ 
203 RECEIVE Name-ID /* your 
predecessor's 
name*/ 
204 IF Name-ID is a token /* there is a new 
leader*/ 
205 THEN BEGIN 
206 Resend the token /* return to 
normal 
operation*/ 
207 exit the protocol 
208 IF Name-ID = Your-Temp-ID 
/* your previous 
value*/ 
209 THEN BEGIN /* you are the new 
leader*/ 
210 Become a leader 
211 Create and send a token 
/* return to 
normal 
operation*/ 
212 exit the protocol 
213 ELSE 
214 IF Name-ID&gt;Your-Temp-ID 
/* replace your 
value*/ 
215 Then 
Your-Temp-ID :=Name-ID 
216 GOTO 202 
______________________________________ 
In Table I, the leader-choosing protocol of the invention is presented in a 
pseudo-code form. Those skilled in the art of computer programming will 
appreciate that this pseudo-code representation can be embodied in a 
variety of language- and system-specific structures. 
For an understanding of the invention as embodied in Table I, refer first 
to FIG. 2 in which two message frame formats are illustrated. A first 
message frame format is a standard one for a token frame, and is indicated 
by reference numeral 23. For the standard token frame, reference is given 
to the example illustrated in FIG. 2 of the incorporated U.S. patent. The 
header of the token frame 23 includes start delimiter bytes S and a 
transport control field TC, which includes the token. Following the 
transport control field is an identification field ID in which destination 
and originating addresses are placed. For the purposes of this invention, 
a terminal's address is considered to be equivalent to its identification, 
and the numerical representation of the address is the terminal's 
identification code. 
A leadership choosing protocol (LCP) frame is indicated in FIG. 2 by 
reference numeral 25. This frame includes a unique header field LCPH and a 
field for containing the terminal identification (TID) code of a 
respective terminal on the system. 
The frame formats of FIG. 2 include unique characteristics in the form of 
the TC, and NID fields of the frames 23 and 25. In the invention, a 
terminal will begin the leadership choosing protocol upon detection of an 
LCP frame 25, and will operate according to the protocol in response to 
the magnitude value in the NID field. A terminal will exit the protocol of 
the invention upon detecting the token frame 23 of FIG. 2. 
In Table I, it is assumed that a programmed terminal processor can 
distinguish between an LCP frame and a token frame. During the 
leader-choosing protocol of Table I, the processor of terminal a receives 
LCP frames which include terminal identification codes (names) from its 
predecessor on the ring, terminal n, and sends names in LCP frames to its 
successor on the ring, terminal d. The macro commands RECEIVE and SEND 
perform these actions. During execution of the protocol, a terminal 
processor can send messages only to its successor and receive messages 
only from its predecessor, since there is no token. When a token is 
generated and transmitted in the token ring system, it will "clean up" the 
ring by successively resetting the terminals to normal operation. 
Table I represents the leadership protocol programming which is present in 
the processor of each terminal. The protocol is initiated by one of two 
events. The first event occurs when the terminal detects that a maximum 
token transmission time has been exceeded. Relatedly, it is assumed that 
loss of a token will be indicated by elapse of an arbitrary time, the 
magnitude of which is sufficient to permit the slowest possible 
circulation of the token through the ring. This time is measured by 
conventional time-out procedures. Thus, if the terminal is awake when its 
time-out period expires, then the procedure is entered in step 197 of 
Table I with the terminal assuming that the previous leader has been lost, 
as indicated by loss of token. 
The alternative event for initiating the procedure of Table I is receipt by 
the terminal of an LCP frame having the format illustrated in FIG. 2. 
Thus, if the terminal's time-out period is exceeded in step 197, then the 
terminal will generate an LCP frame with its own identification in the NID 
field. The terminal prepares for this by entering its identification (my 
name) into a storage location, Name-ID, where the NID value for an LCP 
frame is stored. This is step 198. 
Otherwise, if the procedure is initiated in step 199 by receipt of an LCP 
frame, the terminal stores at Name-ID the terminal identification code in 
the NID field of the received frame. 
Initially in the protocol, in step 201, the terminal stores a leadership 
selection reference value as a temporary identification in a location 
TEMP-ID. In step 201, the leadership selection reference value is, 
initially, the terminal's identification (if step 198 is executed), or the 
terminal identification code contained in the NID field of the first LCP 
frame received (in step 199). 
Following storage of the leadership selection reference value in TEMP-ID, 
the terminal generates and transmits on the ring an LCP frame to the next 
downstream terminal. The terminal identification code in the NID field of 
the LCP frame is the value stored at Name-ID. 
Once the leadership choosing protocol of Table I is invoked, the terminal 
prepares to receive a succession of frames, which may be LCP or token 
frames. In either case, the second field of the received frame is 
inspected in step 203. If the second field is a token, a new leader has 
been selected and the terminal exits the protocol by first resending the 
token in a return to normal operation, and then terminating protocol 
execution in step 207. 
Alternatively, if the received frame is a LCP frame, the terminal 
identification code in the NID field of the frame is compared against the 
leadership selection reference value stored in TEMP-ID. If the magnitudes 
are equal, the terminal accepts leadership in steps 209 and 210, and 
undertakes its first act as leader by creating and sending a token frame 
in step 211. Once the terminal accepts the leadership role, it exits the 
protocol in step 212. 
Alternatively, in steps 213-215, if the received LCP frame contains a 
terminal identification code in the NID field greater than the magnitude 
of the leadership selection reference value stored in TEMP-ID, the 
leadership reference value is changed by storing the terminal 
identification code contained in the ID field of the received LCP frame in 
TEMP-ID as the new leadership reference value. The procedure is then 
looped back to step 202 by way of step 216. 
Of course, in step 214, the magnitude comparison could be reversed, 
resulting in replacement of the leadership reference value by a lower 
magnitude terminal identification code in the NID field of a received LCP 
frame. 
The protocol of Table I is illustrated in conventional computer flow 
diagram form in FIG. 3. In FIG. 3, the protocol initiates, and in step 20 
monitors both the time-out function and the format of incoming frames to 
determine whether an event for initiating the leadership choosing protocol 
has occurred. The two events, of course, are expiration of the time-out or 
detection of LCP frame. For so long as neither event is detected, the 
negative exit is taken from the decision 21 and the monitoring is 
continued in step 20. 
When one of the events is detected, the protocol exits the decision 23 
based upon whether the event was expiration of the time-out (TO) or 
detection of an LCP frame. If TO, the positive exit is taken from the 
decision 23 and the terminal's identification code (my name) is entered 
into the Name-ID storage location. Otherwise, the negative exit is taken 
from decision 23, in which case the terminal identification code in the 
NID field of the received LCP frame is entered into Name-ID. In step 27, 
the leadership reference value is established by entry into Temp-ID from 
the Name-ID location. Then, the terminal sends a LCP frame with the value 
in Name-ID field entered into the NID field. In step 29, the next frame is 
received, if it contains a token, the positive exit is taken from decision 
31, the token frame is forwarded in step 32, and the terminal exits the 
leadership protocol in step 34. 
If the received frame is not a token frame, the terminal identification 
code in the NID field of the received LCP frame is stored at Name-ID and 
the value is compared with the leadership reference value. If the values 
are equal, the protocol exits from comparison 36 through step 38 in which 
a leadership latch (L) is set, indicating that the terminal has assumed 
the leadership role, a token frame is generated with a token in it, and 
sent in step 32 and the protocol is exited in step 34. 
In comparison 36, when the value in the Name-ID field is greater than the 
leadership reference value in the TEMP-ID location, the protocol loops 
through step 27, if the value is less than the leadership reference value, 
the loop out of the comparison 36 is through step 28. 
FIG. 4 illustrates a terminal mechanism which executes the leadership 
protocol illustrated in Table I and FIG. 3. In FIG. 4, the mechanism is 
illustrated as residing in terminal a, it being understood that the 
mechanism is identical in all other terminals of the token ring system of 
FIG. 1. In FIG. 4, a frame is received on 16, 10 through the receiver 
mechanism (R) 10b. Initially, prior to commencement of the 
leadership-choosing protocol, and assuming that the terminal is not 
currently the leader, the latches 40, 42, and 44 are all reset. The 
latches 40 and 42 control a register pipeline comprising registers 45 and 
46. Register 45 stores the second field of a received frame which can be 
either a terminal identification code, if the frame is LCP, or a token, 
otherwise. During execution of the protocol, the register 45 contains the 
Name-ID value. The leadership selection reference value is stored in the 
register 46, whose address is that for the Temp-ID location. 
Initially, the inverted output of the latch 40 is active, providing an 
active gating signal to AND circuits 50 and 51. The AND circuit 52 is 
initially deactivated by the positive output of the latch 40 P.sub.1, 
which is reset. Since the latch 42 is reset, its inverse output positively 
gates the AND circuit 54, while its positive output disables the AND 
circuit 56. 
Thus initialized, the leadership choosing mechanism of FIG. 4 is in a state 
which is prepared to respond to one of the two events which initiates the 
leadership choosing protocol. Assume, first, that the time-out expires. In 
this event, the time-out (TO) circuit 58 activates a time-out signal which 
is fed to an OR gate 60 and to the AND gate 50. In this case, the AND gate 
feeds the terminal identification code for this terminal (my ID) from a 
register 62 through OR gate 63 into the register 45. This initializes the 
Name-ID value to the terminal's own identification code. Concurrently, the 
OR gate 60 provides the active signal from the circuit 58 to the data (D) 
port of the latch 40, causing the latch to change state on the first clock 
cycle following time-out. This sets the latch 40, thereby deactivating the 
AND circuits 50 and 51. Simultaneously, the AND circuit 52 is gated by 
activation of the P.sub.1 signal from the latch 40. The my ID value in 
register 45 is entered also in register 46 through AND circuit 54 and OR 
gate 46. This initializes the leadership reference value to MY-ID. 
Activation of the latch signal P.sub.1 causes the latch 42 to set on the 
following clock cycle, thereby activating the P.sub.2 signal. This removes 
the gating signal from the AND circuit 54 and positively gates the AND 
circuit 56. 
Now, the second field of each frame registered at 40 is passed through the 
AND circuit 52 and the OR gate 63 to the register 45. The contents of the 
register 45 are compared with those of the register 46 in a conventional 
digital comparator (C) 47. If the magnitude of the value stored in 
register 45 exceeds the magnitude of the leadership reference value in 
register 46, the output N&gt;T is activated by the comparator 47, causing the 
contents of the register 45 to be moved on the transfer path 56, 57 into 
the register 46. 
The comparator 47 is constrained from operating until after receipt of the 
first frame following setting of the latches 40, 42. This suppresses a 
false=output resulting from the initial loading of the registers 45 and 
46. The constraint is by way of a latch 47a which clocks the output of the 
latch 42 to a gate circuit 47b in response to a clock signal RCLK which 
synchronizes circuit activity to receipt of a frame by the receiver 10b. 
When the output of the latch 47a is positive, the contents of registers 45 
and 46 are provided to the comparator 47. 
If the register contents are equal, the =output of the comparator 47 is 
activated. In this case, the OR gate 58 provides the activated signal to 
the asynchronous reset (R) terminals of the latches 40 and 42, resetting 
the latches, and deactivating the pipeline consisting of the registers 45 
and 46. Activation of this output is also fed to the data (D) port of the 
leadership latch 44, resulting in setting the latch to indicate that the 
terminal is now the leader. The OR gate 5a collects the positive output of 
the leadership latch 44 and the =output of the comparator 47 to activate a 
token generator 70, whose output is fed to a multiplexer 72. While the 
terminal is acting as a leader, the output of the OR gate configures the 
multiplexer 72 to select the token generated by the circuit 70. For so 
long as the terminal has not been selected as leader, the multiplexer 72 
receives the output of the register 45. 
Assume now that another terminal has timed out and generated an LCP frame 
before the time-out circuit 58 activates its output. In this case, the LCP 
frame is received in the register 40 and provided to a LCP frame decoding 
circuit 75. The circuit 75 provides a positive output to the AND circuit 
51 in response to the LCP frame in the decoder. This positive output is 
fed through the OR gate 60, resulting in the sequential activation of 
latches 40 and 42. In addition, the contents of the NID field of the LCP 
frame in the register 40 are fed through the AND gate 51 into the register 
45. These contents are also fed from the register 45 through the AND gate 
54 to the register 46. Thus, the leadership-choosing protocol will have 
been initiated by response to an LCP frame by entry of the terminal ID 
code in the received frame into the Name-ID register 45 and the Temp-ID 
register 46 in keeping with the protocol. Inspection of FIG. 4 will assure 
the skilled artisan that, for each LCP subsequently received, the value in 
its NID will be fed to the register 45 and compared with the leadership 
reference value in the register 46. If the magnitude of the contents of 
the register 45 exceeds the magnitude of the contents of register 46, the 
leadership reference value will be changed by entry of the contents of the 
register 45 into the register 46. 
Assume now that a previous terminal has accepted leadership and sent a 
token frame. In this case, the frame is entered into the register 40, and 
entered into the register 45 through the gate path 52, 63. In the circuit 
of FIG. 4, the contents of the register 45 are decoded by a token decoding 
circuit 80. If the register 45 contains a token extracted from a token 
frame, the token decoding circuit 80 activates an output on signal line 
81, which is fed to the OR gate 58, causing asynchronous resetting of the 
latches 40 and 42. This terminates the leadership choosing protocol in the 
same manner as detection of equal values in the registers 45 and 46. For 
transmission of LCP and token frames in protocol of this invention, an 
encoding circuit 84 operates conventionally to receive the output of the 
multiplexer 72, and encode it into a frame format in response to an OR 
gate 85. Until the terminal is selected as the leader, the input to the 
encoder circuit 84 is always the contents of the register 45, which may 
contain a terminal identification code or a token. For so long as the 
leadership choosing protocol is being conducted and the register 45 
contains no token, the output of the OR gate 85 will be inactive. For so 
long as the output of this gate is inactive, the encode circuit 84 encodes 
the contents of the register 45 into a frame having the LCP format of FIG. 
2. Assume now that the terminal mechanism of FIG. 4 has received a token 
frame. In this case, the register 45 contains the token and the token 
decoding circuit 80 provides an active output. The active output is fed by 
the OR gate 85 to the encoder 84. In response to the activation of the 
output of gate 85, the encode circuit places the token in the register 45 
into a frame having the token format of FIG. 2. 
Similarly, when the mechanism of FIG. 4 indicates that the terminal has 
been selected as the leader, the active output of the OR gate 59 is fed by 
the OR gate 85 to the encoder circuit 84 at the same time that the 
multiplexer 72 is configured to select the token generated by the circuit 
70. Now the encoder 84 receives a token from the circuit 70 and encodes it 
into the token frame format of FIG. 2. 
Conventionally, the SEND circuit (S) 10a transmits the frames generated by 
the encode circuit 84 to the next terminal downstream from terminal a on 
the link 10,12. 
Although the mechanism for leadership selection is presented in FIG. 4 in a 
structure including discrete logical elements, those skilled in the art 
will realize that the protocol can be as easily embodied in programmable 
circuitry in the form illustrated and explained above in reference to 
Table I and FIG. 3. 
Although the examples and embodiments described above implement a 
leader-choosing protocol based upon the highest-magnitude identification 
code, this constitutes only one example of the practice of the invention, 
and other methods can be used, such as a minimal identification code 
recognition. No matter which significance characteristics are chosen, the 
invention permits token-ring terminals to dynamically assume leadership 
once the current leader fails to take charge, without waiting for a 
system-wide time-out to occur. This provides a major savings in time over 
the prior art methods. 
While I have described a preferred embodiment of my invention, it should be 
understood that modifications and adapations thereof will occur to persons 
skilled in the art. Therefore, the protection afforded my invention should 
only be limited in accordance with the scope of the following claims.