Local area network of serial intelligent cells

Details Local area network of serial intelligent cells Local area network of serial intelligent cells

1998-07-28

2002-11-12

Patel, Ajit (Department: 2664)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via time channels

C340S315000, C370S276000

Reexamination Certificate

active

06480510

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to local area networks and, more particularly, to local area network topologies based on serial intelligent cells.
Bus Topology
Most prior art local area networks (LAN) use a bus topology as shown by example in
FIG. 1. A
communication medium
102
is based on two conductors (usually twisted pair or coaxial cable), to which data terminal equipment (DTE) units
104
,
106
,
108
,
110
, and
112
are connected, via respective network adapters
114
,
116
,
118
,
120
, and
122
. A network adapter can be stand-alone or housed within the respective DTE.
This prior art bus topology suffers from the following drawbacks:
1. From the point of view of data communication, the medium can vary significantly from one installation to another, and hence proper adaptation to the medium cannot always be obtained.
2. The bus topology is not optimal for communication, and hence:
a) the maximum length of the medium is limited;
b) the maximum number of units which may be connected to the bus is limited;
c) complex circuitry is involved in the transceiver in the network adapter;
d) the data rate is limited.
3. Terminators are usually required at the ends of the medium, thus complicating the installation.
4. Only one DTE can transmit at any given time on the bus, and all other are restricted to be listeners.
5. Complex arbitration techniques are needed to determine which DTE is able to transmit on the bus.
6. In case of short circuit in the bus, the whole bus malfunctions, and it is hard to locate the short circuit.
7. Addresses should be associated independently with any network adapter, and this is difficult to attain with bus topology.
Star Topology
A number of prior art network devices and interconnections summarized below utilize star topology.
The multiplexer is a common item of equipment used in communication, both for local area networks and wide-area networks (WAN's). It is used in order to provide access to a data communications backbone, or in order to allow sharing of bandwidth between multiple stations. As shown in
FIG. 2
, one side of a multiplexer
202
is usually connected to a single high data rate connection
204
(“highway”), but several such connections can also be used. The other side of multiplexer
202
has multiple low data rate connections
206
,
208
,
210
,
212
, and
214
. The ellipsis indicates that additional connections can be made. Each low data rate connection uses art of the bandwidth offered by the high data rate connection. These low data rate connections can be of the same type or different types, and can have different or identical data rates. The multiplexing technique most commonly used is time-domain multiplexing (TDM). However, frequency-domain multiplexing (FDM) is also used.
A popular multiplexer in use is the voice multiplexer, shown in
FIG. 3. A
pulse-code modulation (PCM) bus
304
handling 2.048 megabits per second, containing
30
channels of 64 kilobits per second is connected to one side of a PABX/PBX
302
, and up to 30 telephone interfaces
308
,
312
, and
316
are connected to the other side via connections
306
,
310
, and
314
. The ellipsis . . . indicates that additional connections can be made. In this configuration, each channel in the PCM bus can be switched or be permanently dedicated to a specific telephone line. An example of such system is disclosed in U.S. Pat. No. 3,924,077 to Blakeslee.
Similarly a small private branch exchange (PABX/PBX), as shown in
FIG. 4
, is widely used (usually in an office or business environment) where several outside lines
403
,
404
, and
405
are connected to one side of a PABX/PBX
402
, and multiple telephones
408
,
412
, and
416
are connected to the other side via lines
406
,
410
, and
414
, respectively. The ellipsis . . . indicates that additional connections can be made. The PABX/PBX connects an outside line to a requesting or requested telephone, and allows connection between telephones in the premises.
In the configurations described above, star topology is used in order to connect to the units to the multiplexer, which functions as the network hub. The disadvantages of star topology include the following:
1. A connection between each unit and the network hub is required, and the wiring required for this connection can involve a lengthy run. Thus, when adding new unit, an additional, possibly lengthy, connection between the new unit and the network hub must be added.
2. No fault protection is provided: Any short circuit or open circuit will disrupt service to the affected units.
3. The multiplexer can impose extensive space and power requirements.
Computer Interfaces
Various interface standards have been established in order to allow interoperability between the PC (personal computer) or workstation and its various connected elements. These standards usually relate to both mechanical and electrical interfaces, and include industry standard architecture (ISA), extended industry standard architecture (EISA), Personal Computer Memory Card Industry Association (PCMCIA), intelligent drive electronics (IDE), small computer system interface (SCSI), and others. Each added hardware unit usually utilizes a specific software driver for interoperability with the specific platform. These protocols are applicable to small distances only, and allow units to be housed within or nearby the PC or workstation enclosures. For example, equipping a PC for video capture could involve a plug-in ISA card housed within the PC on the motherboard, a video camera connected to the card, and a software driver. This configuration does not allow remote video monitoring.
Relevant Prior Art
The use of the same wire pair or pairs for both power and data communication is well known, and is widely used in telecommunications, from “Plain Old Telephone Service” (“POTS”) to Integrated Services Digital Network (ISDN) and broadband services in the local-loop including other Digital Subscriber Line (xDSL) technologies. Such a concept is described, for example, in U.S. Pat. No. 4,825,349 to Marcel, describing using two pairs for such a scheme. A DC-to-DC converter for such DC feeding is described, for example, in U.S. Pat. No. 4,507,721 to Yamano et al.
The concept of power line communication (PLC) is also widely known. However, in most cases the connection is similar to a LAN environment, in which a single transmitter occupies the entire medium. Examples of such techniques include X-10 and the consumer electronics bus (CEBus, described in the EIA-600 standard). Much of this technology uses complex spread-spectrum techniques in order to accommodate problematic media (characterized by high amounts of noise and interference). Even with such improved technologies, however, the data rate obtained is relatively low.
Prior art in this field includes U.S. Pat. No. 5,684,826 to Ratner, U.S. Pat. No. 5,491,463 to Sargeant et.al U.S. Pat. No. 5,504,454 to Daggett et al., U.S. Pat. No. 5,351,272 to Abraham, U.S. Pat. No. 5,404,127 to Lee et al., U.S. Pat. No. 5,065,133 to Howard, U.S. Pat. No. 5,581,801 to Spriester et al., U.S. Pat. No. 4,772,870 to Reyes, and U.S. Pat. No. 4,782,322 to Lechner et al. Other patents can be found in U.S. Class 340/310 (sub-classes A/R and others) and International Class H04M 11/04.
The concept of using existing telephone wiring also for data communication is first disclosed in U.S. Pat. No. 5,010,399 to Goodman et al., where video signals superimposed over the telephone signals are used. However, the scheme used is of the bus type and has the drawbacks of that topology. Similarly, the idea of data transmission over a public switched telephone network (PSTN) using the higher frequency band is widely used in the xDSL systems, as is disclosed in U.S. Pat. No. 5,247,347 to Litteral et al. The patent discloses an asymmetric digital subscriber line (ADSL) system. However, only a single point-to-point transmission is described over the local-loop, and existing in-house wiring is not discussed, and thus this prior art does not discl

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