Virtual network for personal computers

A network for personal computers includes a network arbiter (10) disposed centrally with respect to a plurality of network stations (12), (14), (16), and (18). Each of the network stations (12-18) includes a personal computer (20), a network peripheral (24) and an interface (22). Each of the interfaces (22) interfaces with the arbiter (10) through a communication link. Each of the network stations has associated therewith a network program (82) that is operable to be executed by a central processing unit (56) in the background to an application program (80). Each of the network programs (82) has associated therewith at the network station a network status memory (86). When information is generated that is to be sent to a network peripheral, an interrupt program (92) interrupts output data from the application program (80) and controls the central processing unit (56) to output the data on a line (94) to the network interface (22). This data is then routed to the arbiter (10) along the line (98).

TECHNICAL FIELD OF THE INVENTION 
This invention pertains in general to networks, and more particularly, to a 
virtual network for use with personal computers. 
BACKGROUND OF THE INVENTION 
Networking of data processing systems has seen ever increasing use in 
recent years. Initially, networks involved centralized file servers, 
memory banks and printer stations which were interconnected through "dumb" 
terminals. The purpose of these networks was to allow a large number of 
users to access a common data-base. Additionally, these networks also 
allow relatively high density memories and a high speed central processing 
unit to be utilized, which in past years were very expensive. As memory 
and processing prices have plummeted, this need has gone away. 
The price of a personal computer has made it possible for relatively 
mundane tasks to be accomplished on relatively small machines with 
localized mass storage, powerful processing capabilities and the ability 
to support peripheral devices such as modems. This has made it possible to 
utilize stand-alone systems for such dedicated tasks as word processing, 
although the total power of a personal computer is not realized in such 
applications. The price of the hardware has made it possible to adapt the 
personal computers to such uses. 
In the small office environment, the personal computer is typically much 
less expensive than the peripherals that it supports, such as printers, 
modems, facsimile cards, etc. Therefore, while it is economical to provide 
a very powerful personal computer at a given number of stations, it is 
still not economical to provide the peripherals at each station. Networks 
provide a much needed support function in this area. 
Due to the proliferation of personal computers in the work environment, a 
need has arisen to interconnect the personal computers for the purposes of 
sharing peripheral devices to minimize the total number of peripheral 
devices needed for a group of stand-alone systems, and also to allow 
transfer of data therebetween in the form of documents, electronic mail 
and accounting data. Typically, these networks require some type of 
centralized operating system with a centralized processor. The centralized 
processor interfaces with the various personal computers on the network 
through parallel or serial data links, which data links require separate 
wiring to be provided in an office. Further, these networks require some 
modification of the personal computer hardware. 
In situations where it is only desirable to utilize some of the peripherals 
on an occasional basis, existing networks tend to be too expensive and the 
capabilities of these networks are not fully needed. This occurs 
especially in the case of secretarial use, such as where one personal 
computer station has a very heavy word processing load and another 
personal computer station has a relatively light load. Further, one 
personal computer station may have multiple jobs and only one printer 
associated therewith. It is therefore desirable to provide a network that 
would allow access to the peripherals at another station without requiring 
the expense of modifying the personal computer, utilizing a relatively 
expensive central processor, or incurring the costs of purchasing and 
installing a high-speed data link. 
SUMMARY OF THE INVENTION 
The present invention disclosed and claimed herein comprises a network for 
interfacing a plurality of personal computers, each of the personal 
computers disposed at a remote network node. Each of the personal 
computers includes a central processing unit that is operable to execute 
application programs and an operating system for allowing the central 
processing unit to interface with a user and input/output device. A 
plurality of network devices are defined and disposed at select ones of 
the network nodes and associated with the personal computer at that 
associated network node An arbiter is provided having a plurality of node 
ports, each of the node ports being associated with one of the network 
nodes. The arbiter is operable to receive network data having destination 
information associated therewith and transmit the received network data to 
one of the network nodes associated with the destination information. A 
data link is provided between the arbiter and each of the network nodes. 
Interface circuitry is provided in each of the personal computers for 
interfacing between the associated network node and the associated data 
link in the arbiter. The interface circuitry includes a memory for storing 
network status at each of the network nodes for defining at which of the 
network nodes each of the peripheral devices is disposed. An input/output 
instruction set is provided that is operated by the central processing 
unit to define the one of the network peripheral devices that is to be 
accessed by the application program during operation thereof. This is 
defined by the network status information. A set of network instructions 
is executed by the central processing unit in parallel with the 
application program. The network instructions when processed by the 
central processing unit cause data that is to be output from the central 
processing unit running the application program to be converted to network 
data for routing to the defined network peripheral.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, there is illustrated a block diagram of the 
network of the present invention. The network is comprised of a centrally 
disposed arbiter 10 which is interconnected to, in the present example, 
four network stations 12, 14, 16 and 18. Each of the network stations 
12-18 are comprised of a personal computer 20, a network interface 22 and 
a network peripheral 24. The arbiter 10 is interconnected to the interface 
22 of network station 12 through a serial data link 26. In a similar 
manner, arbiter 10 is connected to network stations 14, 16 and 18 through 
serial data links 28, 30 and 32, respectively. 
In the preferred embodiment, the arbiter 10 is operable to route packets of 
information received on any of the data links 26-32 to any of the data 
links 26, 32. Each packet that is received is buffered and a unique 
identification code analyzed to determine which port of the arbiter 10 the 
packet is to be transferred to. The arbiter 10 does nothing more than 
route information received on one port to an output on any of the ports of 
the arbiter 10. The arbiter 10 could, in fact, route the information back 
out the same port it was received on. 
Each of the network stations 12-18 is essentially a stand-alone system with 
the personal computer 20 having its own memory, its own operating system, 
and its own application programs. Therefore, the personal computer 20 is 
operable to execute its application programs at the location of the 
network station, but input of data to the personal computer for use by the 
application program and the personal computer 20 can be obtained from 
anywhere in the network, and data can be output to any network peripheral 
24 in the network, as will be described hereinbelow. 
Each personal computer 20 has its own operating system, which, in the 
preferred embodiment, is in part comprised of a disk operating system 
(DOS). The operating system also includes a Basic Input Output System 
(BIOS). DOS and BIOS are programs which control every part of the computer 
system and not only make it possible for other application programs to 
work, but also provide complete control over what the computer does and 
how it does it. They are a link between the user and the computer. It 
essentially is the operating system that manages the hardware and allows 
the other application programs to interface with the hardware. The 
operating system is invisible to the user and merely provides the 
background function of storing and retrieving files on a disc or printing 
to a printer, etc. Although only one operating system is described, it 
should be understood that any operating system can be accommodated by the 
network of the present invention. 
In the network of the present invention, each of the personal computers 20 
has its own operating system which is independent of the other operating 
systems in the network, i.e., they are distributed. When information is 
transferred from one personal computer 20 to another personal computer 20 
in the network, it is unimportant for the operating systems of the two 
computers to interrelate. However, the network of the present invention 
makes this invisible to the user of the personal computer 20. The network 
makes each of the network's peripherals 24 appear as if it is attached 
locally to the personal computer 20 and is controlled by its disk 
operating system as opposed to being controlled by the disk operating 
system on another computer. 
For example, if the personal computer 20 at network station 12 has a job 
that needs to be output on the network peripheral 24 at network station 
18, status information in personal computer 20 at network station 12 is 
changed to indicate that the output will go to the network peripheral 24 
at network station 18. Once the status information has been changed, the 
application program and the user operate as if the network peripheral 24 
at network station 18 were attached to network station 12; that is, the 
application program outputs data to an output port that would normally be 
associated with the personal computer 20 at that network station. The 
network software which is stored in each of the personal computers 20 at 
all of the network stations 12-18 intercepts the output data and routes it 
along the network through arbiter 10. 
As a more specific example, consider that the network peripheral 24 at 
network station 18 is a printer. The personal computer 20 at the network 
station 12 will run an application program that will have the possibility 
of outputting printer data to three ports which are designated LPT1, LPT2, 
and LPT3 in accordance with the internal commands in the operating system. 
Whenever one of these ports is selected, the network defines which of the 
network peripherals 24 at the network stations 12-18 are associated with 
this command. Therefore, if the network peripheral 24 were designated as 
the LPT1 port for the personal computer 20 at network station 12, any 
application program which selected the output port as LPT1 would have the 
output data intercepted and routed through arbiter 10 to personal computer 
20. The background network program in the personal computer 20 would then 
receive this information and output it to the network peripheral 24 
associated with the network station 18. However, if the network peripheral 
24 associated with the network station 12 were designated as the 
peripheral associated with the LPT1 output command, the personal computer 
20 would route the data to network peripheral 24 in the normal manner, not 
utilizing the background network program. 
As a further example, assume that the network peripheral 24 at network 
station 12 is designated in the hardware as LPT1. Therefore, any time an 
application program running in personal computer 20 designates the output 
port as LPT1 and the status information in the network program at station 
12 also designates the network peripheral 24 associated with network 
station 12 as the LPT1 port, any output data from the application program 
in personal computer 20 at network station 12 will be routed to the 
associated network peripheral 24. Assume also, that network peripheral 24 
in network station 18 is designated as the LPT2 output. Therefore, any 
application programs that were running in personal computer 20 at network 
station 12 that designated LPT2 as the output port would be intercepted by 
the background network program and routed through the arbiter 10 to the 
personal computer 20 at the network station 18. Status information in the 
personal computer 20 at network station 18 recognizes that the information 
is being routed to the associated network peripheral 24, regardless of 
which network peripheral 24 it is connected to. If it is assumed that 
network peripheral 24 of network station 18 is connected to the LPT1 port, 
the background program interfaces with the operating system of personal 
computer 20 associated therewith and routes this information to the LPT1 
port therein, thus outputting it to the network peripheral 24 at station 
18. Therefore, the network program in the personal computer 12 recognizes 
an application program outputting data to the LPT2 output, intercepts it 
and routes it to personal computer 20 at network station 18. The network 
program at network station 18 then receives the data and routes it to the 
LPT1 output of the associated personal computer 20, thus outputting the 
data to the associated network peripheral 24. 
When setting up the network status on the personal computer 20 at any of 
the network stations 12-18, a "hot key" is provided. This hot key allows 
each associated personal computer 20 to define which network peripheral is 
associated with which of the operating system outputs. As will be 
described hereinbelow, the hot key is accessible during the operation of 
any of the application programs. Therefore, the network routing can be 
defined without exiting the application program and routing does not 
require any alteration of the application program. The application program 
operates completely independent of the network. 
The hot key, as will be described hereinbelow, allows the user to redirect 
the output of a particular program without changing the settings in the 
application program itself. For example, if a particular application 
program is set up to output to the LPT1 port, the network merely changes 
the routing of all LPT1 output from the associated personal computer 20. 
Under normal operation, the LPT1 output on an application program would 
relate to the network peripheral connected directly from the personal 
computer to the first parallel port. This is a hardware-defined 
interconnection and the operating system recognizes the LPT1 command and 
automatically outputs an LPT1 output to that parallel port. However, when 
routing to another peripheral in the network that is local, the LPT1 
command being output by the application program is recognized and the 
output data placed in an internal buffer and then routed through the 
arbiter 10 to another one of the peripherals 24 in the network. The 
destination of the data is determined at the associated personal computer 
20 and then routed to the arbiter 10. It is therefore an important aspect 
of the present invention that the status information for the entire 
network be resident in each of the personal computers 20 at each of the 
network stations 12-18. However, the status information only determines 
where the peripherals 24 are located in the network, but does not contain 
routing information for outbound data from another network station. 
Referring now to FIG. 2, there is illustrated a detailed block diagram of 
the network station 12, each of the remaining network stations 14-18 being 
essentially identical. The personal computer 20 has associated therewith a 
display 34 and a keyboard 36. The keyboard 36 allows data to be input to 
the personal computer 20 and the display 34 provides one form of an 
output. The network peripheral 24 is illustrated in FIG. 2 as being 
comprised of a printer 38, a modem 40, and a hard-disk drive 42. It should 
be understood that other types of peripheral devices can be interfaced 
with the personal computer 20 and be considered a network peripheral 
device. 
The printer 38 is connected through the network interface 22, the network 
interface 22 being inserted in series with the connection to the printer 
38. A parallel bus 44 is provided for interconnecting between the personal 
computer 20 and the interface 22 and a parallel bus 46 is provided between 
the network interface 22 and the printer 38. The modem 40 is operable to 
be interfaced with the personal computer 20 through a parallel bus 48 and 
also with a standard telephone company line connection 50. The hard-disk 
drive 42 is interconnected with the personal computer through a parallel 
bus 52. The hard-disk drive 42 is operable to provide non-volatile storage 
for the personal computer 20. 
In the network station 12, illustrated in FIG. 2, the operating system, the 
printer 38 and the hard-disk drive 42. In addition, the modem 40 is also 
controlled by the operating system. Therefore, the network allows the 
personal computer 20 to directly access the hard-disk drive 42 and the 
printer 38 through its own operating system or to use the network and the 
operating system of another personal computer 20 on the network to access 
the peripheral device thereon. 
Referring now to FIG. 3, there is illustrated a block diagram of the 
internal modules for the personal computer 20. In general, data is routed 
internal to the personal computer 20 through address and data buses, as 
represented by a single bus 54. The central processing unit (CPU) is 
illustrated by a block 56 which is interfaced through a bi-directional bus 
58 to the address/data bus 54. In addition, volatile memory 60 in the form 
of random access memory (RAM) is interfaced with the address/data bus 
through a bi-directional bus 62. In a similar manner, non-volatile memory 
in the form of read only memory (ROM) 64 is interfaced with the 
address/data bus 54 through the bus 66. In addition to the CPU 56, the RAM 
60 and the ROM 64, a plurality of I/O modules 68 are interfaced with the 
address/data bus 54 through a bus 70. It is to be understood that the 
buses 50, 62, 66 and 70 represent both address, data and control lines. 
The I/O module 68 provides the interface between the address/data bus 54 
and the printer 38, modem 40, hard disk drive 42, display 34 and keyboard 
36 and any other input/output devices that may be connected to the 
personal computer 20. 
In general, an application program can be loaded from the hard-disk drive 
42 into the RAM 60 and then a set of instructions executed in a sequence 
according to the particular application program. When a particular 
instruction requires data to be transferred through the I/O modules 68 to 
either the display 34, the printer 38 or the modem 40 or even the 
hard-disk drive 42, it is necessary to execute a particular set of 
instructions to interface with the input/output devices. These 
instructions are embedded in the operating system which is also stored in 
the RAM 60 in the form of an executable program. 
In order to communicate with the network, it is also necessary to provide 
an output to the interface 22 and to also receive input from the interface 
22. Therefore, the network background program is also stored in RAM 60 and 
comprises a set of executable instruction steps which are operable to 
effect communication with the interface 22 in accordance with those 
instruction steps. Since the interface is an input/output device, the 
personal computer operating system stored in RAM 60 is utilized to effect 
this communication. This will be described in more detail hereinbelow. 
Referring now to FIG. 4, there is illustrated a logical block diagram of 
one of the network stations 12-18. The CPU 56 provides the central 
processing capability for the network station. Since the network station 
of FIG. 4 is illustrated in a logical format, the CPU 56 is illustrated as 
being interfaced with an application program 80 and network program 82. 
The application program 80 is generally loaded into Random Access Memory 
(RAM) and comprises a series of executable instructions which are executed 
in a predetermined order. The portion of the memory in the network station 
that is associated with the application program is referred to as the 
application memory 84, which application memory 84 is interfaced with the 
application program 80. During execution, the application program 80 is 
run by the CPU 56 and accesses data stored in the application memory 84 as 
needed. Typically, the application memory 84 is comprised in part of RAM 
and in part of nonvolatile memory, such as that found in the hard-disk 
drive 42. 
The network program 82 interfaces with the network status memory 86. The 
network status memory 86 is similar to the application memory 84 in that 
it is comprised partially of RAM and partially of nonvolatile memory in 
the form of the hard-disk drive 42. The network program 82 utilizes the 
network status memory 86 to store status information therein. The status 
information is comprised of two forms of status, local status and network 
status. The network status informs the network station and the associated 
network program 82 as to the peripheral units that exist in the network 
and on which system port they are located. As described above, the arbiter 
10 has defined input/output ports associated therewith. Each of these 
ports has a defined network station associated therewith. By having 
knowledge of which network port a particular peripheral unit is associated 
with, a data packet can be generated with this address and sent out to the 
arbiter 10, as will be described in more detail hereinbelow. Further, this 
status information also determines the availability of a particular 
network peripheral, i.e., whether it is already in use. 
The second type of status information contained in the network status 
memory 86 is local routing information. For example, if the LPT1 output 
port designates a particular peripheral on another network station, this 
information is contained in the network status memory 86. However, this 
routing information is not available to other network stations, since this 
data would be of no use to the other network stations. It is only 
necessary for the network program 82 at the associated network station, to 
allow determination of where information is to be output under the control 
of the CPU 56 and the network program 82. 
The network program 82 is a background program which operates on an 
interactive basis. In general, the program is normally idle when 
information is not being routed to the network but it continues to operate 
in an interleaved fashion with the application program 80. This background 
operation "steals" a number of cycles from the operating cycle of the CPU 
56 during which the instruction steps in the network program 82 are 
executed. When one program is being executed, the other program is halted 
at the previous execution instruction and then the execution of the one 
program resumes in the normal sequence. When the network program 82 is 
active and is required to assemble packets of data and transmit them to 
the arbiter 10, the percentage of an operating cycle of the CPU 56 that is 
required for the network program 82 to operate increases. 
The CPU 56 operates with a network peripheral 24 through a BIOS 88, the 
BIOS 88 providing the general input/output interface. Commands can be 
routed to the operating system 90 which can be a DOS system, it being 
understood that both the BIOS 88 and the operating system 90 all comprise 
the overall operating system of the network station. The CPU 56 can also 
communicate directly with the BIOS 88 to access the peripherals 24, which 
is the normal operating mode for accessing printers and the such. This 
access is in the form of standard commands which are output to the BIOS 88 
and these are handshakes that are received back from the BIOS 88. These 
handshakes are in the form of commands such as Printer Ready, etc. 
An interrupt program 92, which is an integral part of the network program 
82, is operable to an interface between the CPU 56 and the BIOS 88 and 
functions to determine whether a particular instruction is to be 
intercepted by the network program 82. As an example, assume that network 
status memory 86 had the routing information therein set such that the 
LPT1 output is designated as being on another network station. Assume 
further that the application program 80 during its execution outputs data 
to the LPT1 output. The interrupt program 92 would recognize this 
situation and would send this information to the network program 82 which 
would then begin to retrieve and assemble the data into packets. These 
packets of data are then transferred by the CPU 56 to the network 
interface 22 on a line 94. The line 94 comprises select ones of the 
input/output lines between the CPU 56 and the associated peripherals 24. 
The network interface 22 is inserted such that the output of the network 
interface 22 passes these lines through the peripherals 24 via line 96 and 
also interfaces with the arbiter 10 through a line 98, line 98 
corresponding to the lines 26-32 of FIG. 1. 
In operation, it is only necessary for the network program 82 to assemble 
the packets of data and, through the CPU 56, transfer the data to an 
input/output port. Although the network interface 22 of the present 
invention is illustrated as being in series with already existing 
input/output lines, a separate input/output port could be defined as a 
dedicated port. However, one aspect of the present invention is that the 
network interface 22 can be incorporated external to the personal computer 
20 without requiring a dedicated port or the circuitry to interface with 
the CPU 56. 
When data designated for a local peripheral is intercepted by the interrupt 
program 92, it is necessary for the application program 82 to receive 
handshake information from the BIOS 88 indicating that data has been 
transferred to the LPT1 port. Assume, by way of example, that the 
information is to be output to a printer, with no printer being associated 
with the local network station. The application program 80 would expect to 
receive a Printer Ready signal back from the BIOS 88. To account for this, 
an adaptation program 100 is provided that operates in conjunction with 
the interrupt program 92 and the BIOS 88. The adaptation program 100 
generates signals such that the application program 80 receives the 
appropriate handshake, even though the handshake was not directly 
generated by the BIOS 88. In this manner, no modification need be made to 
the application program 80 or to the operating software in order to effect 
network transfer. 
Referring now to FIG. 5, there is illustrated a perspective view of the 
network interface 22, as utilized in the preferred embodiment. The 
interface 22 is comprised of a housing which is operable at one end to be 
connected to a parallel printer port 104 on the back of the personal 
computer 20. The parallel printer port 104 is the port to which the 
printer 38 is normally connected through the cable 46. At the end of the 
cable 46 is disposed a port connector 106 that interfaces with the other 
end of the housing 22. Housing 22 is designed such that it receives the 
line 26 in the form of a four wire telephone jack 108. Therefore, the line 
26 that interfaces between the network interface 22 and the arbiter 10 is 
comprised of a four wire conductor. By utilizing the telephone jack 108, 
conventional wiring can be utilized in an office environment. No special 
cabling is required other than the running of the conventional telephone 
wire. This is relatively inexpensive and can be easily facilitated in 
either an initial build out of an office or in a rewiring scheme. 
Referring now to FIG. 6, there is illustrated a block diagram of the 
network interface 22 at its interconnection with the printer 38. The 
network interface 22, although illustrated in FIG. 5 as being directly 
connected to the parallel port, can be connected anywhere along the 
printer cable 46. The internal wiring for the network interface 22 allows 
the line 44 and the data transferred thereon to be connected to the data 
link 26. The specific interface is illustrated in FIG. 6a. 
In FIG. 6a, select ones of the parallel lines on the port 104 are routed to 
the data link 26, which is described above as a four wire data link. The 
four wires comprise a data line 110, a supply line 112, a clock line 114 
and a ground line 116. The ground line 116 is connected to the ground line 
from the personal computer 20 and the associated port 104. However, the 
clock line 114 and positive supply line 119 are connected to two of the 
data lines, a line 118 which constitutes the DB3 data line and a line 
which constitutes the DB2 data line. The data line 110 is connected to two 
lines, a line 120 and a line 122, which are detached from the output of 
interface 22 such that they do not pass through to the printer 38. The two 
lines 120 and 122 comprise the Paper Empty (PE) line and the Auto-Feed 
(AF) line respectively. The PE line 120 is a receive input and the AF line 
122 is a transmit output. Therefore, the data line 110 comprises a 
bidirectional data line. Although the PE line 120 and the AF line 122 are 
disconnected from the printer 38, they are generally utilized by the 
printer and are available. However, if the printer 38 does need the use of 
these lines, they will not be available with the configuration of FIG. 6a. 
The network program 80 in conjunction with the interrupt program 92 and the 
adaptation program 100 revolve around an array of tasks, or processes, the 
method of communication between a processes and the method of executing 
the various processes. All communications between processes are performed 
in units called packets. Packets are built of smaller units called 
messages, the smallest unit of data transferrable over the communications 
channel. In the preferred embodiment, a message consists of eight bytes. 
Each packet consists of a packet header message followed by the actual 
data. The first three bytes of each packet header are defined as the 
Packet Type byte, the Source/Destination byte, and the Packet Length byte. 
The other five bytes of the packet header message vary depending on the 
type of process that sent the packet. 
Communications are performed by two background tasks, a Write Next Message 
and a Read Next Message. The Write Next Message task is responsible for 
finding the next message to be sent over the communications channel. The 
Read Next Message task is responsible for taking messages from the 
communications channel and placing them in the correct process buffers. 
These tasks are performed independently of the data in the packets. 
When an output process is created on one of the personal computers 20 and 
generates a packet to be transferred, it sets the Packet Type byte in the 
packet header message to a value depending on the type of process that 
sent the packet. When the packet header is received at the destination 
computer, the Packet Type and Source/Destination bytes are checked to 
determine if the destination process for this packet exists. If not, a 
destination process for the packet is created and the appropriate function 
pointers for the process are set to handle the appropriate buffer 
conditions. After the first message has been transferred and the 
destination process has been created, the sending computer sends the next 
message of data to the destination process which was created when the 
packet header message was received, as will be described hereinbelow. When 
the last message of the packet is read in, a buffer full flag for the 
process that received the packet is set. 
If the Write Next Message task is not currently writing a packet, it looks 
in a round-robin fashion for processes with packets to be sent. Processes 
with packets to be sent are identified by the type of process and certain 
combinations of bits in a flag field in the process. Output processes or 
input processes with the flag set to a full condition are processes with 
data to be sent over the communications channel. When flags corresponding 
to a write and a Ready-to-Send condition are set, the Write Next Message 
task will begin sending the packet. After the packet header message is 
written to the communications channel, these bits are cleared to indicate 
that the buffer is no longer full. When the last message of the packet is 
written, the appropriate Empty bit will be set in the flags field. 
The Read Next Message task is responsible for reading in the messages off 
of the communications channel and building the packets in the destination 
processes' buffers. The packet is placed in the input buffer of the 
process indicated in the low order nibble of the Source/Destination byte 
in the packet header message. The Packet Length byte is used to determine 
the number of messages in the packet. 
The network program 82 continuously looks for processes that need some sort 
of action to be performed. When the proper bits are set in the packet, 
certain routines must be performed. For example, in an output process, 
this function would generate more data to be sent. A secondary function, 
indicated by a different bit, would indicate that data has been received 
and this process must perform some action to interpret that data. For an 
input process, the primary condition would signal that data had been 
received and the process must remove it from the buffer so that more data 
may be received. A secondary function in an input process indicates that 
the data has been transmitted to the output process on another personal 
computer 20 corresponding to this process. 
Each process has a Type field, the value of which indicates either 
inactive, input or output. Inactive processes are ignored by the network 
program 82. The type of process determines where data will be placed when 
transferred over the communication channels. For input processes, read 
data will be placed in a primary buffer and data sent from this process 
will be sent from a secondary buffer. For output processes, data will be 
sent from a primary buffer. Data address to an output process will be 
placed in the secondary buffer. Data is passed between complimentary pairs 
of processes. The only destination for an output process is an input 
process. 
The pair of processes running and the associated functions to support those 
processes can be divided into process types. There are five process types 
in the preferred embodiment: Introduction, Chat, Printer connection, File 
transfer, and Modem sharing. The network program allows multiple instances 
of the same process type to be executing on the same computer at the same 
time. That is, there can be several output introduction processes 
executing on the same computer at the same time. 
The primary buffer size sets the upper limit on the amount of data that can 
be passed between processes at one time before the next process with 
waiting data has control of the communication channel. The normal flow of 
data between processes is from the primary buffer of an output process to 
the primary buffer of an input process. The secondary buffer allows 
bidirectional flow of data between processes. Data will be transferred 
from the secondary buffer of an input process to the secondary buffer of 
an output process. This feature allows status information to be returned 
to an output process. The information that can be returned to an output 
process. In the preferred embodiment this secondary buffer size is set to 
eight bytes. 
Referring now to FIG. 7, there is illustrated a flow diagram for the 
process whereby data packets are received by the network program 82. In 
the program flow, the first block is a decision block 124 which determines 
whether data has been received. If it has not been received, the program 
flows along the "N" path back to the input of the decision block 124. In 
this mode, the network program is idle and is merely looking for data. 
When data is received, the program flows along the "Y" path to a function 
block 126 wherein the message is read, which message is eight bytes long. 
The program then flows to a function block 128 wherein the message is 
placed in a buffer. The program then flows to function block 130 wherein 
the buffered sixteen messages long. These messages, although in a single 
packet, can be from different sources. For example, there may be two 
printers at a particular network station which are being accessed. The 
network of the present invention allows both printers to be accessed 
simultaneously with information assembled in the packet being routed at a 
later time to the respective printers. 
After the packet has been assembled, the packet is placed in a packet 
buffer, as indicated by function block 132. The program then flows to 
decision block 134 to determine if all data has been received. If not, the 
program flows back to the input to the decision block 124 to assemble 
another packet and place it in the packet buffer. Once complete, the 
program flows from the decision 134 along a "Y" path to a return block 
136. 
Referring now to FIG. 8, there is illustrated a flow diagram for the 
operation for transmitting data to the arbiter 10. The program is 
initiated at the input of a decision block 138, where it is determined 
whether data is to be transmitted. When no data is ready to be 
transmitted, the program flows along "N" path back to the input of the 
decision block 138. In this mode, the process is idle and continues to 
look for either receive data to be transmitted. When data is to be 
transmitted, the program flows along the "Y" path to a function block 140 
wherein the messages are put in a queue. The messages are then transmitted 
from the queue in accordance with the order in which they were placed in 
the queue, as indicated by function block 142. The program then flows to a 
decision block 144 to determine if all the messages have been transmitted. 
If not, the program flows along the "N" path back to the input of the 
decision block 138. Once all the messages have been transmitted, the 
program flows along the "Y" path to a return block 146. 
Referring now to FIG. 9, there is illustrated a flow diagram for the 
classification procedure of received packets of data. Once packets have 
been received and placed in the packet buffer, the program flows to a 
decision block 148 to determine if packets are present in the packet 
buffer, if not the program flows along an "N" path back to the input of 
the decision block 148. When packets are in the buffer, the program flows 
along the "Y" path to a function block 150 wherein packets are classified 
in various classes. In the present embodiment the packets are either 
designated for a printer, a file, modem, a "chat" mode and/or for an 
"introduction" mode. 
The program flows from the function block 152 to a decision block 152 to 
determine if the packet is a printer packet. If so, the program flows 
along the "Y" path to a function block 154 indicating the operation 
wherein the packet is processed through the local operating system for a 
print operation. If it is not a printer packet, the program flows along 
the "N" path to the input of a decision block 156 to determine if the 
packet is a file packet. If the packet is a file packet, the program flows 
along the "Y" path to a function block 158 wherein the file is written to 
the appropriate location via the local operating system. 
If the packet is not a file packet, the program flows along the "N" path 
from the decision block 156 to the input of a decision block 160 to 
determine the if the program operates in the "Chat" mode. In the "Chat" 
mode, the operator of one computer can access the display in another 
computer while operating in the application program. However, once the 
network has been placed in the "Chat" mode, the operation of the 
application program at either the receiving or transmitting network 
station is interrupted and a gateway opened between the two network 
stations. Therefore, when the packet is being designated for the "Chat" 
mode, the program flows along the "N" path from the decision block 160 to 
the input of a decision block 164 to determine if the packet is an 
Introduction packet. 
An Introduction packet is the method by which status information is 
maintained on the network. In the preferred embodiment, periodic updates 
are provided by the network program 82 operating in the background to 
determine if a particular network station is still on the network and if 
the peripherals for that network are still designated as network 
peripherals. Initially, when a network station comes on-line it updates 
the status in the network status memory 86 by sending Introduction packets 
to each of the ports on the arbiter 10. This Introduction packet 
identifies the port on the arbiter to which the network station is 
interfaced and also the peripherals that are associated therewith. These 
peripherals now become network peripherals in the network status memory 86 
of each of the network stations 12-16. This is indicated by function block 
166 connected to the "Y" path of the decision block 164. If the packet is 
not an Introduction packet, the program flows to a return block 168. 
The arbiter 10 is manufactured by Dallas Semiconductor, Part no. DS9050 
which is comprised of a four way junction circuit, Part no. DS9030, and a 
port adapter, DS1256. The port adapter was described with reference to 
FIG. 5 and reference numeral 22. The four way junction box DS9030 utilizes 
a Quad-port Serial RAM, Part no. DS2015, manufactured by Dallas 
Semiconductor. The Quad-port Serial RAM provides an arbitration function 
which is handled by protocol and a message center which forces discipline 
and prevents collisions. Each port has access to all other ports for 
reading information and can write information only in its own memory area. 
The memory space for each port is 64 bits. Access to and from each port 
takes place over a three wire serial bus. The serial bus keeps the pin 
count low while providing sufficient bandwidth to accommodate 
communication. Each port also provides a message flag which can be 
utilized to warn of message ready conditions. The operation of the 
Quad-port Serial RAM is described in a preliminary data sheet for the 
DS2015, pages 92-102, which is incorporated herein by reference. 
The introduction processes as described above provide a means of passing 
status information between the various personal computers 20 on the 
network. The flow of events is illustrated in Table 1 between the two 
computers. 
TABLE 1 
______________________________________ 
INTRODUCTION PROCESS 
Computer 1: Computer 2: 
______________________________________ 
Create Introduction output 
and Introduction packet. 
Send packet. 
Read packet and create 
input process. 
Change process type to 
input. 
Build reply packet. 
Change process type to 
output. 
Send ACK. 
Receive ACK. 
Send ACK. 
Receive ACK. 
Send reply data packet. 
Receive data packet. 
Kill process. Kill process. 
______________________________________ 
In the introduction process, the introduction output process is created in 
addition to the Introduction packet. This packet is sent from computer 1 
to computer 2 wherein it is read. Computer 1 then changes the process type 
to an input process. A reply packet is built by computer 2 and an 
acknowledgement sent back to computer 1 from computer 2. The process type 
of computer 2 is then changed to an output process prior to sending the 
acknowledgement packet. Computer 1, which has the process type set to an 
input process, receives the acknowledgement and then sends back an 
acknowledgement. Computer 2 receives the acknowledgement and then sends 
the reply data packet which is received by computer 1. 
The "Chat" mode allows "Chat" connection between two computers which take 
up two processes. One pair of processes is utilized for each direction of 
data, allowing maximum throughput. The flow of events is illustrated in 
Table 2. 
TABLE 2 
______________________________________ 
CHAT MODE 
Computer 1: Computer 2: 
______________________________________ 
Create Chat output process 
and Begin Chat packet. 
Send packet. 
Read packet and create 
input process. 
If an error occurs return 
data packet explaining 
why and kill process. 
Create Continue Chat 
output process and 
packet. 
Send packet. 
Receive packet. 
Send ACK. 
Receive ACK. 
Open Chat Window. 
Send ACK. 
Receive ACK. 
Open Chat Window. 
(Each user enters chat information. Each 
line typed is sent out the appropriate output 
process. The input process displays to the 
screen until one user presses the .ltoreq.Esc.gtoreq. key. 
Assume it is user 1). 
Send data packet with the 
first byte PR-END-CHAT. 
Close Chat Window. 
Kill process. Receive Data packet. 
Close Chat Window. 
Display "Chat connection 
closed by --------". 
Kill process. 
______________________________________ 
In the "Chat" mode, the first computer creates the "Chat" output process 
and then begins to accumulate the "Chat" packet. The packet is sent and 
read by computer 2 which then creates an input process. Computer 2 creates 
a continued "Chat" output process and packet, and then sends a packet back 
to computer 1. The packet is received by computer 1 and acknowledgement 
sent to computer 2 which then opens a "Chat" window. An acknowledge is 
then sent from computer 2 to computer 1 and computer 1 then opens a "Chat" 
window. The data packet is then sent from computer 1 to computer 2 and 
then the "Chat" window closed, this data packet received by computer 2. 
When accessing a printer, a printer output process must be implemented. 
This allows the network station to share printers over the network. The 
flow of events in the printer output process is illustrated in Table 3. 
TABLE 3 
______________________________________ 
PRINTER OUTPUT PROCESS 
Computer 1: Computer 2: 
______________________________________ 
User generates 1st character 
of output and connection 
not established. 
Create Printer output process 
and Request Printer packet. 
Send packet. (Waits for ACK) 
Read packet and create 
input process. 
If error, return data 
packet explaining why 
and kill process. 
Send ACK. 
Receive ACK. Buffers 
up data. 
(User 1 buffers up data. When LPT.sub.-- BUFF.sub.-- SIZE 
(128) reached send packet and set spoollng 
available flag to FALSE (0). On next 
character wait for acknowledge or time out). 
Send data packet with 
printer data. 
Receive printer data 
packet. 
Print out data to 
printer. 
Send ACK when done. 
Receive ACK. 
Set spooling available 
flag to TRUE(1). 
(When "Release After" time 
elapsed). 
Send data packet with LPT.sub.-- CLOSE. 
Kill process. 
Set connection established 
to FALSE. 
Display "Connection Closed". 
Receive packet. 
Print data to printer 
Kill process. 
Set printer status to 
idle. 
______________________________________ 
In the printer process, the first user generally creates the printer output 
process and also creates a Request Printer packet. This packet is sent and 
then computer 1 waits for an acknowledgement. This packet is read by 
computer 2 and then an acknowledgement signal sent back to computer 1. 
Upon receipt of the acknowledgement signal, computer 1 buffers up data. 
This data packet is sent with printer data which is received by computer 2 
and data sent out to the printer associated therewith, this operation 
occurring in the background of the application program, as described 
above. Acknowledgement is then sent back to computer 1, which, upon 
receipt results in a data packet being sent to close the printer output 
process. A data packet indicating the close operation is sent to computer 
2 which then kills its input process and sends the remaining data out to 
the printer. During this process, computer 2 sets its printer status to 
busy, after which it sets its status to idle. When it is desirable to 
transfer files between two network stations, it is necessary to view the 
directory or library of files in a remote network station. It is therefore 
necessary to transfer the directory between the two network stations. This 
is referred to as a directory output process. The flow of events for this 
process is illustrated in Table 4. 
TABLE 4 
______________________________________ 
DIRECTORY TRANSFER 
Computer 1: Computer 2: 
______________________________________ 
Create Get Directory output 
process and Get Directory 
packet. 
Send packet. 
Read packet and create 
input process. 
Change process type to input. 
Build directory packet. 
Change process type to 
output. 
Send ACK. 
Receive ACK. 
Send ACK. 
(The computer with the directory repeats the 
following step, building the directory 
listing and sending to the requesting 
computer). 
Receive ACK. 
Send directory data 
packet. 
Receive data packet. 
Send ACK. 
(When the lat entry has been sent). 
Kill process. 
Receive ACK. 
Kill process. 
______________________________________ 
In the directory output process, computer 1 first creates a Get Directory 
output process and then creates a Get Directory packet. This packet is 
sent to computer 2 which, upon reading the packet, creates an input 
process. The directory packet is built up in computer 2 and then the 
process type therein changed to an output process. Acknowledgements are 
sent between computer 1 and computer 2 to determine if computer 1 is ready 
to receive the directory. Upon proper transfer of acknowledgement signals, 
the directory packet is sent to computer 1. After receipt of the directory 
data packet, the acknowledgement is sent back to computer 2 and the 
process killed. 
After the directories have been received, it is desirable to transfer a 
file from computer 1 to computer 2. This is referred to as the Put File 
process. The flow of events is illustrated in Table 5. 
TABLE 5 
______________________________________ 
PUT FILE PROCESS 
Computer 1: Computer 1: 
______________________________________ 
Create Put File output 
process and Put File packet. 
Send packet. 
Read packet and create 
input process. 
Open file. Send ACK if 
OK or NACK if error 
occurred. 
Receive ACK/NACK. 
If last part of file, 
close the file. 
If closed ok. Send ACK 
else send NACK. 
Kill process. 
Receive ACK/NACK. 
Kill process. 
______________________________________ 
In the Put File output process, the output process is created and then a 
Put File packet is also created. This packet is sent to computer 2 which 
reads the packet and then opens a file. An acknowledgement is sent from 
computer 2 to computer 1 indicating the open file and then the file block 
is read in computer 1 and packets assembled and transferred to computer 2. 
These packets are read by computer 2 and written to disk and then an 
acknowledgement sent to computer 1 if the file has written OK. This is 
received by computer 1 whereby computer 1 continues to assemble and 
transfer parts of the file. Another acknowledgement sent by computer 2 if 
the last part of the file was received. This acknowledgement is received 
by computer 1 and then the processes terminated. 
Where a file is transferred from computer 2 to computer 1 under the control 
of computer 2, the Get File process is executed. The flow of events is 
illustrated in Table 6. 
TABLE 6 
______________________________________ 
GET FILE PROCESS 
Computer 1: Computer 2: 
______________________________________ 
Create Get File output process 
and Get File packet. 
Send packet. 
Read packet and create 
input process. 
Change process type to input. 
Build reply packet. 
Change process type to 
output. 
Open file. Send ACK if 
OK or Nack of error 
occurred. 
Receive ACK/NACK 
Send ACK if ok. 
Receive ACK. 
(The following is repeated until the file is 
completely transferred). 
Read file from disk. 
Send file data packet. 
Receive file data packet. 
Write file packet to disk. 
Send ACK if written ok. 
Send NACK if error. 
Receive ACK/NACK 
If last part of file, 
close the file. 
Kill process. 
Close file. 
Kill process. 
______________________________________ 
Whenever a file is transferred from computer 2 to computer 1, the Get File 
process is created on computer 1 in addition to a Get File packet. This 
packet is sent to computer 2 which reads the packet and then creates an 
input process. Computer 1 changes its process type to an input process and 
then awaits a reply packet. This reply packet is built up in computer 2, 
the process type on computer 2 changed to an output process and then a 
file opened. Acknowledgements are exchanged by the two computers to 
determine when computer 1 is ready to receive the file and then computer 2 
reads the file from disk, assembles it into a data packet and forwards the 
data packet to computer 1. Computer 1 receives the data packet and writes 
it to disk and then sends an acknowledgement to computer 2. Computer 2 
continues to read and send packets of parts of the file. When the last 
part of the file has been received by Computer 1 the file is closed and 
sends an acknowledgement to Computer 2, which upon receipt thereof, closes 
the file and terminates the process. 
Whenever it is desirable to change routing information in the network 
status memory, an update can be accomplished at any point in the execution 
of the application program by depressing a "hot key." Typically, this is a 
predefined key or keys such as the Control and Shift keys on a standard 
keyboard. Once depressed, this interrupts the application program and 
opens a "window" into the network program to either redefine the routing 
information or to open a "chat" window to another computer. 
In summary, there has been provided a network that is distributed about an 
arbitration circuit. The arbitration circuit is operable to allow 
simultaneous communication between all of the ports in the network by 
transferring data in packets. Each of the network stations has a personal 
computer associated therewith that is self contained and has its own 
operating system. Peripheral devices on each of the network stations are 
designated as network peripherals and the status of each of the network 
peripherals is stored at each of the network stations, such that each of 
the network stations is aware of the port locations on the network of each 
of the peripherals. The peripherals are accessed in the background of an 
application program running on the computer at the particular network 
station. 
Although the preferred embodiment has been described in detail, it should 
be understood that various changes, substitutions and alterations can be 
made therein without departing from the spirit and scope of the invention 
as defined by the appended claims.