Stone working – Turning – Grinding-wheel dressing
Reexamination Certificate
2003-05-06
2004-08-31
Miller, John (Department: 2614)
Stone working
Turning
Grinding-wheel dressing
C725S107000, C714S025000, C714S046000, C370S242000
Reexamination Certificate
active
06782884
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
1. The present invention relates generally to methods and apparatus for transmitting data in cable television network systems. More specifically, the present invention relates to methods and apparatus for locating problematic devices in a cable television plant.
2. Discussion of Related Art
Since the late 1980's the cable TV industry has been upgrading its signal distribution and transmission infrastructure. In many cable television markets, the infrastructure and topology of cable systems now include fiber optics as part of its signal transmission component. The use of fiber optics has accelerated the pace at which the cable industry has taken advantage of the inherent two-way communication capability of cable systems. The cable industry is now poised to develop reliable and efficient two-way transmission of digital data over its cable lines at speeds orders of magnitude faster than those available through telephone lines, thereby allowing its subscribers to access digital data for uses ranging from Internet access to cable commuting. While cable TV systems have always had the ability to send data downstream, i.e. from a cable TV hub, described below, to cable modems in people's homes, cable TV systems can now send data upstream, i.e. from individual cable modems to a hub. This new upstream data transmission capability enabled cable companies to use set-top cable boxes and provided subscribers with “pay-per-view” functionality, i.e. a service allowing subscribers to send a signal to the cable system indicating that they want to see a certain program.
FIG. 1
is a block diagram of a two-way hybrid fiber-coaxial (HFC) cable system including cable modems and a network management station. The main distribution component of an HFC cable system is a primary (or secondary) hub
102
which can typically service about 40,000 subscribers or end-users. Hub
102
contains several components of which two, relevant to this discussion, are shown in FIG.
1
. One component is a cable modem termination system or, CMTS,
104
needed when transmitting data (sending it downstream to users) and receiving data (receiving upstream data originating from users) using cable modems, shown as boxes
106
,
108
,
110
, and
112
. Another component is a fiber transceiver
114
used to convert electrical signals to optical signals for transmission over a fiber optic cable
116
. Fiber optic cable
116
can typically run for as long as 100 km and is used to carry data (in one direction) for most of the distance between hub
102
to a neighborhood cable TV plant
117
. More specifically, fiber optic cable
116
is a pair of cables—each one carrying data in one direction. When the data reaches a particular neighborhood cable TV plant
117
, a fiber node
118
converts the data so that it can be transmitted as electrical signals over a conventional coaxial cable
120
, also referred to as a trunk line. Hub
102
can typically support up to 80 fiber nodes and each fiber node can support up to 500 or more subscribers. Thus, there are normally multiple fiber optic cables emanating from hub
102
to an equal number of fiber nodes. In addition, the number of subscribers as well as fiber capacity is currently increasing due to dense wave-division multiplexing technology. DWDM is a technique for transmitting on more than one wavelength of light on the same fiber.
The primary functions of CMTS
104
are (1) interfacing to a two-way data communications network; (2) providing appropriate media access control or MAC level packet headers (described below) for data on the RF interface of a cable system; and (3) modulating and demodulating the data to and from the cable system.
Cable TV (CTV) taps
122
and
124
are used to distribute a data signal to individual cable modems
106
and
110
(from CTV tap
124
) and modems
108
and
112
(from CTV tap
122
). Two-way cable TV amplifiers
126
and
128
are used to amplify signals as they are carried over coaxial cable
120
. Data can be received by the cable modems shown (each CTV tap can have output cables servicing multiple cable modems) and transmitted back to hub
102
. In cable systems, digital data is carried over radio frequency (RF) carrier signals. Cable modems are devices that modulate an RF signal to a digital signal and demodulate a digital signal to an RF signal for transmission over a coaxial cable. This modulation/demodulation is done at two points: by a cable modem at the subscriber's home and by CMTS
104
located at hub
102
. If CMTS
104
receives digital data, for example from the Internet, it converts the digital data to a modulated RF signal which is carried over the fiber and coaxial lines to the subscriber premises. A cable modem then demodulates the RF signal and feeds the digital data to a computer (not shown). On the return path, the operations are reversed. The digital data is fed to the cable modem which converts it to a modulated RF signal. Once CMTS
104
receives the RF signal, it demodulates it and transmits the digital data to an external source.
Data packets are addressed to specific modems or to a hub (if sent upstream) by a MAC layer
130
in CMTS
104
at hub
102
(there is also a MAC addressing component, not shown, in the cable modems that encapsulate data with a header containing the address of the hub when data is being sent upstream). CMTS
104
has a physical layer
134
that is responsible for keeping a list of modem addresses and encapsulating data with appropriate address of its destination. MAC layer
130
receives data packets from a Data Network Interface (not shown) in hub
102
. The main purpose of MAC layer
130
is to encapsulate a data packet within a MAC header according to the DOCSIS standard for transmission of data. This standard is currently a draft recommendation (J.isc Annex B) which has been publicly presented to Study Group 9 of the ITU in October 1997, and is known to a person in the cable modem data communication field. MAC layer
130
contains the necessary logic to encapsulate data with the appropriate MAC addresses of the cable modems on the system. Each cable modem on the system has its own MAC address. Whenever a new cable modem is installed, its address must be registered with MAC layer
130
. The MAC address is necessary to distinguish data going from the cable modems since all modems share a common upstream path, and so that CMTS
104
knows where to send data. Thus, data packets, regardless of format, must be mapped to a particular MAC address. MAC layer
130
is also responsible for sending out polling messages as part of the link protocol between the CMTS and the cable modems that is necessary to maintain a communication connection between the two.
As mentioned earlier, cable modems can be used to not only receive cable television signals but also digital data and, thus, can provide high-speed access to Internet data or to data from remote computer networks. Because of the increasing usefulness of cable modems for transmitting data over existing cable TV systems, cable modems are proliferating. As they become more prevalent, the burden of maintaining a cable TV plant having a network of cable modems increases. Specifically, the problem of tracking down and isolating a problematic device or group of devices has become increasingly difficult. In response to the increasing need to manage the growing network of cable modems, network management stations are now part of the cable TV system. As shown in
FIG. 1
, a network management station (NMS)
132
is connected to hub
102
, and more specifically to CMTS
104
. NMS
132
is located generally at a network operation center, or NOC (not shown in FIG.
1
), NMS
132
monitors the CMTS and cable modems using a data communication protocol such as SNMP (Simple Network Management Protocol) and alerts an operator in the event of a failure.
The communication link between the network management station
132
and CMTS
104
has been mostly one-way: commands going from management station
132
Chen Wei-Sing
Millet Mark E.
Naegeli Charles J.
Beliveau Scott
Beyer Weaver & Thomas LLP.
Miller John
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