Multi-channel token ring

A system for utilizing a transmission media such as a token ring having multiple, independent channels operating in parallel. The invention provides optimal use of multi-channel bandwidth to a plurality of interconnected workstations, file servers, and other devices. The workstations and devices attach to the token ring via dedicated lobe rings connected to concentrators on the token ring. Each concentrator contains the processors, memory, and logic necessary to coordinate the transmission and receipt of data over the token ring among the interconnected workstations and devices. The multi-channel token ring provides increased bandwidth and reliability to an existing token ring without requiring modifications to existing physical devices, interfaces, or protocols.

FIELD OF THE INVENTION 
This invention relates to digital communications systems including local 
area networks, and in particular, to a token ring system comprising 
multiple, independent backbone channels, that provides connected 
workstations and devices with optimal bandwidth, without requiring changes 
to higher-layer protocols or physical interfaces, while conforming to 
existing communications standards. 
BACKGROUND OF THE INVENTION 
A local area network (LAN) is characterized by its high data transmission 
rate, and the fact that, in general, the communication channel of the 
network is shared by all the workstations and devices connected to that 
particular network. There are a variety of techniques for enabling devices 
connected to a network to communicate with each other. One such technique 
is the use of a token ring, whereby a "token" is continuously circulated 
among the connected devices; messages and data to be transmitted from one 
device to another are appended to the token. The performance of a token 
ring is measured by the speed at which data is transmitted on the ring; 
standard token ring data rates are 4 Mbps (megabits per second) and 16 
Mbps. 
Users of token ring systems face the problem of how to increase performance 
without replacing their existing systems. The present invention describes 
a solution to that problem: namely, by adding a plurality of independent 
token rings or channels, operating in parallel and at the same data rate 
as the existing ring, in order to increase the capacity, or bandwidth, of 
the system. The technique described in this invention can be implemented 
without changing existing interfaces or protocols, and conforms with IEEE 
communications standards. 
Among the related prior art to local area network systems, U.S. Pat. No. 
4,766,590 describes a scheme for connecting a plurality of stations to 
form a single serial transmission loop, so as to vary the order of 
connections of the stations of the loop. The patent fails to address the 
subject of multiple backbone channels or techniques to utilize the 
capacity of multiple channels; the use of multiple channels is an integral 
part of the present invention. 
The subject matter of U.S. Pat. No. 4,468,733 is a scheme for building a 
serial bus loop system consisting of multiple serial bus loops, in order 
to increase the reliability of a single bus loop system. The patent 
involves a flat network with one channel of communication for multiple 
devices, unlike the present invention which utilizes multiple channels of 
communication for multiple devices. 
A third related patent is U.S. Pat. No. 3,748,647, which describes a scheme 
for interconnecting a plurality of shift registers into a plurality of 
rings, each ring consisting only of shift registers and logic related to 
controlling shift registers. The patent addresses only information 
contained in fixed length registers, not in variable length frames which 
are used by local area networks. The patent significantly differs from the 
present invention in that it fails to address local area networks, 
conformance to network standards, or the optimal and reliable use of 
available bandwidth. 
SUMMARY OF THE INVENTION 
In view of the shortcomings of the prior art, it is a primary object of 
this invention to provide interconnected workstations and other devices 
with optimal use of multi-channel bandwidth. Optimal use results from 
always using the first available token on any channel. 
Another object is to increase the usable bandwidth by as much as n-times 
over a conventional single channel local area network, where "n" 
represents the number of independent backbone channels in a multi-channel 
token ring. By increasing the bandwidth, there is no need to increase the 
speed or bit rate of an existing network. 
An additional object of this invention is to provide greater reliability 
than a single channel network, due to the ability to communicate over 
other channels if one is malfunctioning. 
Yet another object is to add the increased bandwidth and reliability 
without any changes to existing physical interfaces, media access control, 
or logical link control. Network management functions may be added that 
are essentially transparent to the application and protocol layers of a 
workstation. 
Finally, the invention conforms with IEEE 802.5 communication standards. 
Other objects and advantages of the present invention will be set forth in 
part in the description and the drawings which follow and, in part, will 
be obvious from the description or may be learned by practice of the 
invention. 
To achieve the foregoing objects, and in accordance with the purpose of the 
invention as broadly described herein, a communications system is provided 
comprising a transmission media having multiple channels, at least one 
access unit which interfaces with the individual channels of the 
transmission media, at least one device associated with each of the access 
units, each device employing its associated access unit to receive data 
from and transmit data to the transmission media, and means for sending 
data between the devices and the access units. Preferably, the 
transmission media is a token ring having multiple channels operating in 
parallel. Further, the sending means preferably comprises at least one 
lobe, each lobe providing communications between one of the access units 
and at least one device associated with the access unit, wherein each 
access unit includes at least one first physical interface, each 
interfacing with and corresponding to each lobe associated with the access 
unit, and second physical interfaces, one corresponding to and interfacing 
with each channel of the transmission media with which the access unit 
interfaces. Each access unit also includes means for controlling access to 
the first physical interfaces, receipt of data from and transmission of 
data to the channels of the transmission media, and access to the second 
physical interfaces. 
Each device preferably includes means for transferring data to and from its 
associated access unit via the lobe ring associated therewith. This 
transferring means includes a physical interface with the lobe ring and 
means for controlling access to its physical interface, receipt of data 
from the lobe ring and transmission of data to the lobe ring, and receipt 
of data by the device and transmission of data from the device. 
The controlling means of the transferring means communicates with the 
controlling means of its associated access unit to effect control of data 
transmission between the device and its access unit. The controlling means 
of the access unit also may include memory which includes cache memory for 
storing control data and buffers for temporarily storing data received by 
the access unit from the transmission media and from the device. The 
control means of the access unit and the control means of the device 
further cooperate so that if the buffer for receiving data from the device 
is full, the control means of the device will not send additional data to 
the control means of the access unit. Each access unit of the 
communications system preferably sends data frames received from their 
associated devices over the first available channel of the transmission 
media. 
The present invention also provides for an adapter which connects a device 
to a transmission media having multiple channels. The adapter comprises 
means for interfacing with individual channels of the transmission media, 
means for receiving data from and transmitting data to the device, and 
means for controlling the interfacing means and the receiving and 
transmitting means so that a data frame from the device is transmitted on 
the transmission media over the first available channel. Preferably, the 
controlling means further comprises means for storing control data, means 
for temporarily storing data received from the device and means for 
temporarily storing data received from the transmission media, with the 
controlling means functioning to not permit data to be sent from the 
device for transmission over the transmission media when the temporary 
device data storage means is full. Further, after the controlling means 
receives a data frame from the device, the controlling means causes the 
data frame to be transmitted over the transmission media over the first 
available channel. Further, the transmission media is preferably a token 
ring having multiple channels. 
The present invention will now be described with reference to the following 
drawings, in which like reference numbers denote the same elements 
throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the invention as applied to a token ring (IEEE 802.5 or 
FDDI) is illustrated in FIG. 1. This invention may also be applied to 
Ethernet implementations. 
A workstation 1 is connected to a concentrator or access unit 3 via a 
communication channel such as a lobe ring 2. Workstation 1 can be another 
device such as a file server, a print server, or some other peripheral, 
but will be labeled "workstation" for purposes of this description. Each 
lobe ring 2 operates as a token ring dedicated to communication with a 
concentrator 3. Each concentrator or access unit 3 is connected to one or 
more lobe rings 2, and one or more workstations 1 will be attached to each 
lobe ring 2. For discussion purposes, this specification refers to a 
concentrator connected to only one lobe ring with one attached 
workstation; FIG. 1A illustrates a probable implementation comprising a 
concentrator 3 connected to multiple lobe rings 2, each with one or more 
attached workstations 1. Returning to FIG. 1, the concentrator 3 is 
attached to a multi-channel transmission media 4 which permits 
communication between concentrator 3 and thus workstations 1 associated 
with different concentrators. The transmission media is preferably a 
multi-channel token ring 4 having n independent channels. The independent 
channels can be individual fiber or copper cables; alternatively, where 
wavelength division multiplexing technology is available, this invention 
can utilize multiple channels (wavelengths) within the same medium 
(fiber). Multiple workstation-concentrator pairs inhabit the multi-channel 
token ring 4. 
FIG. 2 illustrates the functional layers of a workstation-concentrator 
pair. In the workstation 1, an upper layer W5 includes applications, user 
interfaces, and system software. Layer W4 is the logical link control 
layer or LLC. The LLC employs communications protocol defined by IEEE 
802.2, and serves to organize and control the flow of data to and from the 
workstation 1, as well as perform error control and recovery. The next 
layer, W3, is the station media access control supervisor or SMS. The SMS, 
which is introduced by this invention, provides an interface between the 
LLC (layer W4) and the station media access control or MAC (layer W2). 
This interface duplicates the MAC interface, so that the LLC and upper 
layer W5 require no changes in order to implement this invention. The SMS 
of layer W3 also employs a protocol whereby it responds to signals from 
the concentrator MAC supervisor or CMS (to be discussed below with respect 
to layer C2) to stop transmission of data in order to prevent overflow of 
concentrator memory buffers. 
Continuing with the functional layers of the workstation 1, layer W2 
comprises the aforementioned MAC. The MAC layer is defined by IEEE 802.5, 
and controls access to the underlying physical medium layer W1. The MAC 
also appends a standard header and trailer to outgoing data, removes the 
header and trailer from incoming data, and performs error checking. Layer 
W1 is the physical interface that connects the workstation 1 to the lobe 
ring 2. Both layer W1 and lobe ring 2 conform to IEEE 802.5. 
The functional layer of the concentrator or access unit 3 that interfaces 
with lobe ring 2 is physical medium layer C1. Layer C1 corresponds to 
workstation layer W1. The next layer, C2, comprises the concentrator lobe 
MAC. This MAC controls access to physical interface layer C1, appends the 
standard IEEE 802.5 header and trailer to incoming data being transmitted 
to lobe ring 2, and removes the header and trailer from outgoing data from 
the workstation 1. Layer C3 comprises the concentrator MAC supervisor or 
CMS, which is introduced by this invention. The CMS controls a 1-to-n 
interface by transmitting data frames sent from the workstation 1 onto the 
n channels forming the multi-channel token ring 4. Conversely, the CMS 
controls an n-to-1 interface by receiving data frames sent via any of the 
n channels to the workstation 1. The CMS also monitors outbound memory 
buffers in the concentrator 3 and notifies the SMS (layer W3) in the 
workstation 1 to stop transmitting data when the buffers are full. 
A functional layer C4 comprises internal processing and memory in the 
concentrator 3. Two CPUs manage memory and coordinate the transmission of 
data frames. The memory includes inbound and outbound buffers for the 
temporary storage of data frames during transmission, and cache memory for 
use by the CPUs in coordinating data transmission. 
Layer C5 is the concentrator ring MAC layer. This layer comprises multiple 
MACs, with one MAC corresponding to each of the n channels on the 
multi-channel token ring 4. Each of the MACs in layer C5 controls access 
to an associated physical device in physical medium layer C6. The channel 
MACs encapsulate data being transmitted to the channels with the standard 
IEEE 802.5 header and trailer. The physical devices in layer C6 also 
conform to IEEE 802.5, and provide the physical connection for the 
concentrator 3 to the independent channels of the multi-channel token ring 
4. 
In FIG. 3, two workstation-concentrator pairs that inhabit the same 
multi-channel token ring are illustrated. Workstation 11 and concentrator 
12 are linked by lobe ring 20; workstation 21 and concentrator 22 are 
linked by lobe ring 30. Both of these pairs are connected to a 
multi-channel token ring that, in this embodiment, comprises three 
independent token ring channels 31, 32, 33. While only two concentrators 
(12 & 22) are shown, a plurality of devices could be connected to the 
multi-channel token ring. 
Workstation 11 includes a concentrator lobe adapter 13 with address `AAAA`. 
This adapter 13 provides the media access control (MAC) function and 
physical connection to the lobe ring 20, as described in workstation 
layers W2 and W1 in FIG. 2. Workstation 21 contains a corresponding 
concentrator lobe adapter 23 with address `BBBB`. 
Concentrator or access unit 12 is illustrated as possessing a total of four 
substantially identical adapters. A single concentrator lobe adapter 14 
having address `XXXX` is shown, although typically a concentrator will 
include one such lobe adapter for each concentrator lobe associated 
therewith. This adapter 14 provides MAC function and physical connection 
to the lobe ring 20, as described in concentrator layers C2 and C1 in FIG. 
2 (in concentrator or access unit 22, see adapter 24, which has address 
`YYYY`). The other three adapters shown in the concentrator 12 are token 
ring adapters 16, 17, which are connected, respectively, to each of the 
three independent token ring channels 31, 32, 33 of the token ring. A 
typical concentrator will include one such token ring adapter connected to 
each channel of the multi-channel token ring with which the concentrator 
interfaces. Each of these adapters 16, 17, 18 recognizes address `AAAA` in 
frames being transmitted over its associated channel of the token ring, 
and provides MAC function and a physical interface to the independent 
token ring channels 31, 32, 33, as described in concentrator layers C5 and 
C6 in FIG. 2 (in concentrator 22, see token ring adapters 26, 27, 28, each 
recognizing address `BBBB`). 
Within concentrator or access unit 12, there is a memory component that 
includes cache memory, as well as inbound buffers and outbound buffers for 
the temporary storage of data frames during communication (in concentrator 
or access unit 22, see memory component 25). The outbound buffers are used 
to hold data frames sent from workstation 11 for transmission to other 
workstations or devices on the multi-channel token ring. There is a 
separate inbound buffer in memory 15 associated with each of the token 
ring adapters 16, 17, 18, in which data frames received from workstations 
or devices on the token ring are held until they can be processed for 
transmission to the associated workstation 11. The memory 15 is managed by 
CPUs 1A and 2A (in concentrator 22, see CPUs 1B and 2B). CPU 1A manages 
the outbound buffers, while CPU 2A manages the inbound buffers. CPU 1A 
controls the protocol between the previously-discussed station media 
access control supervisor or SMS (layer W3 in FIG. 2) and concentrator 
media access control supervisor or CMS (layer C3 in FIG. 2), as well as 
the frame encapsulation protocol. The CPUs 1A 2A, in combination, perform 
traffic control for a shared data bus 19 in concentrator 12 (in 
concentrator 22, see data bus 29). The CPUs coordinate the transmission of 
queued data frames from their associated workstation to the channel on the 
multi-channel token ring having the next available token. They also 
coordinate the receipt of data frames by their associated workstation via 
the inbound buffers of the memory 15. This coordination is facilitated by 
maintaining an ordered list in the cache memory portion of memory 15 of 
the buffer locations of data frames to be transmitted or received. 
When information at a workstation is to be transmitted to another 
workstation on the multi-channel token ring or transmission media the 
logical link control or LLC (layer W4 in FIG. 2) sets up a frame 
containing the information to be transmitted, the source or "from" 
address, and the destination or "to" address. FIG. 4 illustrates how this 
frame would appear when information from workstation 11, with an adapter 
address of `AAAA` is to be transmitted to workstation 21, with an adapter 
address of `BBBB`. 
Next, the workstation MAC (layer W2 in FIG. 2) encapsulates the frame with 
a standard IEEE 802.5 header and trailer, as shown in FIG. 5. When a token 
is available on the lobe ring 20, the entire frame is transmitted onto the 
lobe ring 20. Concentrator lobe adapter 14 in concentrator 12 recognizes 
that this frame is not from concentrator 12 (i.e., source address is not 
`XXXX`), and after the concentrator lobe MAC (layer C2 in FIG. 2) removes 
the header and trailer, the frame is copied into the memory 15. Before 
transmission from the workstation 11 and to the concentrator 12 can occur, 
the CMS (layer C3 in FIG. 2) checks to see if the outbound buffers in 
memory 15 are full; no transmission will occur if the CMS notifies the SMS 
(layer W3 in FIG. 2) that the outbound buffers are full. 
When the frame is received by the concentrator lobe adapter 14, the CMS 
(layer C3 in FIG. 2) takes control of the frame and queues the frame in an 
outbound buffer of memory 15, to wait for the next available token on the 
multi-channel token ring. When the concentrator CPUs determine that a 
token on one of the channels is available, the frame is sent over the 
concentrator bus 19 to the token ring adapter corresponding to the 
available channel. For example, if the first available token is on channel 
31, the frame will pass from the outbound buffers to the token ring 
adapter 16 (if a token for channel 31 was not available, a token for 
either channel 32 or channel 33 could be utilized, if available). At token 
ring adapter 16, the concentrator ring MAC (layer C5 in FIG. 2) in the 
adapter encapsulates the frame with a standard IEEE 802.5 header and 
trailer (see FIG. 5). The encapsulated frame is then transmitted. 
Consequently, as additional tokens for other channels may become available 
prior to a token on the same line becoming available, throughput speed for 
multi-frame messages can be speeded up substantially. 
The information sent by the workstation 11 to the workstation 21 travels on 
channel 31 with its accompanying token until it reaches a token ring 
adapter in a concentrator that recognizes the destination address `BBBB` 
of the frame (e.g., token ring adapter 26 in concentrator 22). Note that 
the recognized address is the same as that of workstation 21, which is 
connected to concentrator 22 via dedicated lobe ring 30. At adapter 26, 
the concentrator ring MAC (layer C5 in FIG. 2) performs error checking and 
removes the header and trailer. The frame is moved into an inbound buffer 
of memory 25 in the concentrator 22, at which time CPU 2B is notified that 
a frame has been received, and the cache memory of memory 25 is updated 
with the location of the frame. CPU 2B signals CPU 1B via the common bus 
29 that the frame was received; in turn, CPU 1B obtains the frame location 
from the cache memory, and passes the frame to the CMS (layer C3 in FIG. 
2) of concentrator 22. 
Next, the frame proceeds to the concentrator lobe MAC (layer C2 in FIG. 2) 
in concentrator lobe adapter 24, where the frame is encapsulated with a 
standard IEEE 802.5 header and trailer (see FIG. 5). When a token is 
available on the dedicated lobe ring 30, the frame is sent to concentrator 
lobe adapter 23 at address `BBBB` in workstation 21. 
When the frame is received by adapter 23, the workstation MAC (layer W2 in 
FIG. 2) performs error checking, removes the header and trailer, and 
passes the frame to the SMS (layer W3 in FIG. 2). The SMS passes the frame 
to the LLC (layer W4 in FIG. 2), which in turn sends the information to 
the application (layer W5 in FIG. 2) running at workstation 21. Thus, 
information is sent from one workstation or device to another workstation 
or device on the same multi-channel token ring using the addressing scheme 
and components of the present invention. Because of this scheme, 
sequential data frames can be transmitted over multiple channels, which 
speeds up the data transfer as opposed to when the same channel is used, 
since it is not likely that a token will become available on the 
first-used channel until after tokens on the other channels have become 
available. 
A possible function of the SMS that is not included in the embodiment of 
the invention as described is an encapsulation procedure for transmitting 
frames from a workstation to a concentrator. This procedure could be used 
in place of the recognition by the concentrator lobe adapter that the 
source address of the frame is not that of the concentrator. In this 
alternative embodiment, the SMS (layer W3 in FIG. 2) appends additional 
source and destination address fields to the frame created by the LLC 
(layer W4 in FIG. 2), prior to sending the frame to the concentrator. As 
illustrated in FIG. 6, the source address `AAAA` is the address of adapter 
13 in the workstation 11, while the destination address `XXXX.degree. is 
that of adapter 14 in the concentrator 12. After the frame reaches the 
concentrator 12, the appended address information is removed by the CMS 
(layer C3 in FIG. 2) before the frame is queued in an outbound buffer. 
During the transmission and receipt of information, as described in this 
invention, several protocols and procedures are implemented. FIGS. 7A and 
7B illustrate the protocol between the SMS (layer W3 in FIG. 2) in a 
workstation and the CMS (layer C3 in FIG. 2) in the associated 
concentrator, whereby the CMS notifies the SMS as to whether or not the 
outbound buffer in the concentrator is full; the SMS cannot send a data 
frame if the outbound buffer is full. A recovery procedure, not shown, 
would be implemented to recover from the possibility of deadlock if the 
notification from the CMS was not received correctly by the SMS. 
In FIG. 8A, the procedure is shown by which the SMS sends a data frame to 
the CMS; FIG. 8B shows receipt of that frame by the CMS, followed by 
queuing of the frame in a concentrator outbound buffer. FIG. 9 illustrates 
the next step in the transmission process, a 1-to-n interface, whereby a 
frame that is queued in an outbound buffer is sent on the first available 
channel. FIGS. 10A and 10B illustrate the n-to-1 interface by which a 
frame coming from the multi-channel token ring is received in the 
concentrator and manipulated by the CPUs for transmission to the 
workstation. 
Finally, FIG. 11A illustrates the encapsulation procedure as used in the 
alternative embodiment of this invention, whereby the SMS encapsulates a 
data frame with the address of the concentrator lobe ring adapter and 
sends it to the CMS. FIG. 11B shows receipt of that frame by the CMS, 
followed by removal of the appended address, and queuing of the frame in a 
concentrator outbound buffer. 
It should be noted that the layers and concentrator lobe discussed herein 
may be in the form of an adaptor which enables a workstation to 
communicate over a multi-channel transmission media. 
While a preferred embodiment of the present invention has been described, 
variations and modifications in that embodiment may occur to those skilled 
in the art once they learn of the basic inventive concepts. Therefore, it 
is intended that the appended claims shall be construed to include both 
the preferred embodiment and all such variations and modifications as fall 
within the spirit and scope of the invention.