Increasing capacity of baseband digital data communication networks

This invention provides broadband network capabilities for baseband digital collision detection transceiver equipment for communication between a plurality of data stations by affording simultaneous transmission of multiple channels over a broadband pass transmission link such as a coaxial cable. Thus, a fundamental carrier wave is transmitted on said link, received at local data stations and used to detect signals on different baseband channels for reception. For transmission the carrier wave typically is used for segregating a plurality of at least two transmission channels into typically single sideband upper and lower pass bands of baseband bandwidth capability adequately separated with guard bands to permit simple separation for receiving by means of pass band filters, etc.

This invention relates to digital data communication networks and more 
particularly it relates to increasing the data processing capability of 
baseband digital data communication systems of the type set forth in the 
U.S. Pat. No. 4,063,220 to Robert M. Metcalfe et al., issued Dec. 13, 
1977, known by the Xerox Corporation tradename "Ethernet". 
The aforesaid Metcalfe patent has led to commercialized digital data 
communication systems between two different computers, office machines, or 
the like. These systems have a restricted bandwidth of communication known 
in the trade as baseband systems. A disadvantage of these systems with the 
collision prevention technique of listening for a clear channel before 
talking not heretofore resolved is that communications are limited to a 
single narrow bandwidth communication channel. This has led to alternative 
broadband systems which are more complex and require processing of analog 
data in order to offer more channels of communication. A background on 
these alternatives is set forth in an article by Kenneth Klee et al., 
entitled "Battle of the Networks" published in Datamation, March 1982. 
Thus, the state of the art is such that there only is provided a system 
choice between a broadband network or a single channel baseband network. 
As clearly set forth in the above article, it has been heretofore deemed in 
the art inconsistent to adapt a digital baseband network with collision 
prevention means to any compatible broadband capability to process two or 
more signals simultaneously. 
It is therefore an object of this invention to improve the digital baseband 
communication network art by providing broadband multiple-channel 
communication capabilities while retaining the advantages of collision 
prevention. 
Other objects, features and advantages of the invention will be found 
throughout the following description, drawing and claims. 
DISCLOSURE OF THE INVENTION 
Thus in accordance with this invention a baseband digital communication 
network system with collision prevention means is provided for handling 
two or more communications simultaneously over a transmission link, 
thereby affording the advantages of broadband analog communication 
systems. 
In a preferred embodiment a carrier wave is transmitted over the 
transmission link and serves at a data station coupled with the link to 
segregate both transmitted and received signals into at least two separate 
bands so that at least two simultaneous signal channels may be used in the 
network while operating with the network collision prevention means. 
Thus, for example, two signal bands with appropriate guard bands 
therebetween (and between other signals transmitted on the link) may 
comprise the upper and lower single sideband transmission of the two 
respective bands. Such bands are separable by band filtering and 
demodulation by network receivers. Also transmission is readily 
accomplished by modulating and filtering to send only a single (upper or 
lower) sideband through the transmission link, which is preferably a 
coaxial cable, but also may comprise a radio link, optical link, etc. 
Accordingly, each network data station is readily convertible to 
communicate with and process a plurality of at least two data bands to 
thereby increase the data transmission capabilities of tne network as 
comparable with broadband network systems without collision prevention, 
wherein simultaneous signals may be conveyed and intercepted along the 
network.

THE PREFERRED EMBODIMENTS 
By reference to FIG. 1, it may be seen that a broadband transmission link 
15 such as a coaxial cable, radio system or optical system serves to 
connect a plurality of individual data station transceivers 16A, 16B, 17, 
18, etc. for communicating digital data therebetween in a baseband 
collision detection mode. The channel 15 bandwidth characteristic (or 
available spectrum band) is sufficient to carry simultaneously 
transmissions in a plurality of two or more (n) baseband channels between 
the data stations. 
The state of the art heretofore has required a separate transmission 
channel (coaxial cable) 15 for each baseband channel and the collision 
detection mode limits transmission on that channel to a single message. 
That is, each data station in its interface equipment 20, etc. inquires to 
see if the channel is in use before a message is communicated to another 
station along the line, as set forth in the Metcalfe patent, supra. 
As seen in the FIG. 1 system of this invention, however, the transmission 
link is afforded a mode of operation permitting more data to be processed, 
and faster access time, by simultaneous transmission of a plurality of 
baseband channels n to which the data stations 16, 17, 18, etc. have 
access. This also provides more system flexibility in the data stations, 
at the cost of some relatively simplified filtering or selection equipment 
as part of the interfacing 20 between the transceivers 16, 17, 18 and the 
transmission link 15. Thus, for example, a "busy" data station 16 may have 
two transceivers 16A, 16B each with the capacity to communicate on 
multiple channels (CH #1 and #2). Data station 17 could be a single 
channel station communicating on channel #1 only, and similarly station 18 
could communicate on channel #2. Other stations (B to L, etc.) along the 
line thus can have considerable flexibility without disturbing the system 
mode or limiting the ability to communicate single channel wise with other 
stations in the manner available to the art prior to this present 
invention. 
One specific preferred mode of operation is exemplified by the bandwidth 
graph of FIG. 2 drawn on a frequency (f) abcissa. Thus, typically a 
carrier frequency (fo) of 80 MHz is single sideband modulated with the 
baseband data of limited bandwidth to produce a properly guarded lower 
sideband first channel 21 and an upper sideband second channel 22 both 
falling within the transmission bandwidth 23 of the broadband transmission 
link. These two separate channels, CH #1 and CH #2 corresponding to 
notation of FIG. 1, provide the network capability of simultaneous 
communications not heretofore feasible with networks providing a collision 
prevention mode of transmission of digital signals. The treatment of data 
is done by state of the art modulation and multiplexing techniques, such 
as set forth in U.S. Pat. No. 3,202,762 to M. R. Aaron et al., Aug. 24, 
1965; U.S. Pat. No. 3,842,352 to W. E. Cote, Oct. 15, 1974; and U.S. Pat. 
No. 3,914,554 to H. Seidel, Oct. 21, 1975. Mixing, modulating, 
multiplexing and filtering data at required frequency bands is achieved by 
simple state of the art equipment as described for example by an article 
published in the Digest of Technical Papers of the 1973 IEEE 
International Microwave Symposium at Boulder, Colo., June 4 to 6, 1973 
entitled "A Low-Loss, Wideband Transmitter Multiplexer" by J. I. Smith and 
R. E. Fisher of Bell Laboratories. Thus, to better set forth the nature 
and spirit of this invention, the network features are set out in block 
diagram form throughout the remaining figures. 
A simplified system is attained in the two cable (15L, 15R) network of FIG. 
3. A coupler 30 is used for receiving (Rx) signals from the cables or 
transmitting (Tx) signals onto the cables from the various station units. 
Each cable 15L and 15R then may comprise a different data channel 
corresponding to the aforesaid CH #1 and CH #2. Note that a single carrier 
frequency generator 31 is coupled to a single cable 15L for use in the 
mode described in FIG. 2. 
The carrier is thus detected by receiver 32 and amplified at carrier 
amplifier 33 for local use in transmitting and receiving operations, and 
in this manner may be used for synchronous relationships (if used) in the 
system. The single transmitter 35 then receives the carrier along lead 34 
for modulation respectively of upper or lower sideband (depending upon the 
channel 15L or 15R accessibility) which is coupled to the respective cable 
by corresponding band-pass filters 36L and 36R permitting only the desired 
channel to enter the corresponding cable (as directed from the logic board 
37 along lead 38). 
Receivers 32 and 39 are coupled to the respective cables 15L, 15R in the 
manner described in the Metcalfe patent, supra and provide via logic board 
37 the respective collision signals 40 and received data 41 to digital 
processor 42 for timed release of data to be transmitted 43. Clearly the 
digital processor has access to either of two data base channels along the 
respective coaxial cables 15L, 15R, thereby to give improved access time 
and other advantages of a broadband system while retaining the significant 
advantages of the collision detection mode. 
In order to receive and segregate (demultiplex) the data from the 
respective two (or more) baseband channels (e.g. 15R, 15L), the carrier 
signal from amplifier 33 is carried by lead 45 to receivers 32, 39 and 
respectively heterodyned by state of the art techniques to detect the 
upper and lower sideband digital data transmitted over the link 15. The 
logic board 37 will then direct the selected digital data through the 
baseband pass receiving link of twisted pair 41 into digital processor 42. 
This network has advantages of simplified hardware requirements to achieve 
the broadband capabilities, essentially comprising: a second receiver 32, 
a logic board 37, a carrier amplifier 33 and filters 36 (or switching 
means) for coupling the transmitter 35 to a selected one of cables 15R or 
15L. There is no disadvantage to the two cable connection over the state 
of the art since it has only been contemplated heretofore that the 
baseband collision-detecting digital signal is sent on each communication 
link at a time. However, as shown in FIG. 4, a single cable link may be 
used at the expense of a little more complicated logic (37') and a second 
transmitter 35A. 
The conversion equipment for adapting the baseband collision detection 
network to broadband collision detection mode and capabilities is 
typically that set forth in FIGS. 5 to 8. 
The carrier amplifier circuit 33 of FIG. 5, therefore serves to derive with 
the narrow band pass filter 50 the fundamental carrier wave (fo) from the 
coaxial link 15 (15L), which is amplified (51) and limited (52) before 
processing in logic circuit 37. 
In FIG. 6, typical receiver input filter circuits are shown. In essence, 
the carrier signal is used at mixer 60 with the broadband signal from band 
pass filter 61 to derive the baseband signal filtered at narrow pass 
filter 62, e.g. a low pass filter for deriving the lower sideband of FIG. 
2. The transmitter similarly in FIG. 7 mixes the carrier signal at mixer 
70 lead 71 with the signals to be transmitted at lead 72, and derives the 
upper or lower single sideband at filter 73 for transmission. 
The logic board in FIG. 8 processes signals from the two receivers for the 
two baseband channels on lines 81, 82, through the collision detector 83 
of the Metcalfe patent, supra, to derive the collision signal 40 and to 
pass the received digital signals through OR circuit 84 to receiver line 
40. Output transmitted signals on line 85 as detected at 86 are passed to 
the carrier amplifier on line 87 for mixing as shown in FIG. 7. 
Other variations in mixing and processing signals are within the skill of 
those in the art using the present state of the art. Those novel features 
of the invention believed descriptive of the scope and spirit of the 
invention are set forth with particularity in the claims.