Multiplex communications – Channel assignment techniques – Only active channels transmitted
Reexamination Certificate
1999-05-28
2004-08-31
Nguyen, Hanh (Department: 2662)
Multiplex communications
Channel assignment techniques
Only active channels transmitted
C370S252000, C370S395400, C725S111000, C725S103000
Reexamination Certificate
active
06785292
ABSTRACT:
FIELD OF INVENTION
The present invention relates to communications in computer networks. More specifically, it relates to a method for dynamically optimizing performance in a data-over-cable system.
BACKGROUND OF THE INVENTION
Cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications of Atlanta Ga., Tele-Communications, Inc., of Englewood Colo., Time-Warner Cable, of Marietta Ga., Continental Cablevision, Inc., of Boston Mass., and others provide cable television service to a large number of subscribers over a large geographical area. The cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial (“HFC”) cable system. The system can also provide data services having data rates of about 10 Mega-bits-per-second (“Mbps”) to 30+ Mbps per channel.
The Internet, a world-wide-network of interconnected computers, provides multi-media content including audio, video, graphics and text that requires a large bandwidth for downloading and viewing. Most Internet Service Providers (“ISPs”) allow customers to connect to the Internet via a serial telephone line from a public switched telephone network at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others that are much slower than the about 10 Mbps to 30+ Mbps available on a coaxial cable or HFC cable system on a cable television network.
With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., and others offer customers higher-speed connectivity to the Internet, an intranet, local area networks (“LANs”) and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a data rate of up to 30+ Mbps which is a much larger data rate than can be supported by a modem used over a serial telephone line.
Background information related to cable modem systems in general is described in the Data-Over-Cable Service Interface Specifications (“DOCSIS”)—Radio Frequency Interface Specifications, Interim Draft, dated Jul. 24, 1998, issued by Cable Television Laboratories, Inc. DOCSIS may be found on the World Wide Web. This document, known to persons working in the art, is incorporated by reference herein in its entirety.
The basic overall architecture of a data-over-cable system is shown in FIG.
1
. The system of
FIG. 1
provides a mechanism by which a computer
10
connected to a backbone network
12
(either directly or indirectly by intermediate networks) may communicate with another computer
14
via a cable television infrastructure indicated generally by reference numeral
16
. The cable television infrastructure
16
includes a distribution hub or “head-end”
18
that is connected to the backbone network
12
via a wide area network (“WAN”) and a switch or router
20
. A cable system head-end
18
is a central location in the cable television network that is responsible for sending cable signals in the downstream direction. The head-end
18
modulates
20
digital data into analog form and supplies analog signals to a fiber network
22
, which is connected to a plurality of optical/electronic (“O/E”) nodes
24
. The O/E nodes
24
convert optical signals in the fiber network
22
to electrical signals for transmission over a coax cable network
26
to a cable modem
28
at the customer's location. The cable modem
28
demodulates the analog signals and extracts the digital data and supplies the data to the customer premise equipment (“CPE”)
14
, which, in a typical situation, is a general purpose computer in a home environment.
The head-end
18
includes a cable modem termination system (“CMTS”)
30
. This device provides a network side interface to a wide area network, indicated at
32
, and a radio frequency (“RF”) interface between the cable modem termination system and the cable network in both the downstream and upstream directions, indicated at
34
and
36
. The term “downstream”, as used in the present document, refers to transmission in the direction from the head-end
18
or cable modem termination system
30
to the cable modem
28
at the customer premises. The term “upstream” refers to transmission in the direction from the cable modem
28
at the customer premises to the cable modem termination system
30
.
For transmission in the downstream direction, the cable modem termination system
30
supplies data from the computer
10
to a modulation circuit (“MOD”) and to a combiner
38
, where the data is combined with video signals for the cable television system. The combined signals are sent to a transmission module
40
where they are imparted onto the fiber network. In the receiving direction, data from the CPE
14
is received from the fiber network at a receive module
42
, sent to a splitter and filter bank
44
and sent to a demodulation circuit (“DEMOD”) in the cable modem termination system
30
. The data is processed by a network termination unit
46
, sent to the switch or router
20
and routed onto the WAN for transmission to the remote computer
10
.
Many cable television networks provide only uni-directional cable systems, supporting only a “downstream” cable data path. A return data path via a telephone network (i.e., a “telephony return”), such as a public switched telephone network provided by AT&T, GTE, Sprint, MCI and others, is typically used for an “upstream” data path. A cable television system with an upstream connection to a telephony network is called a “data-over-cable system with telephony return.” Such a return system is indicated at
48
where the cable modem
28
is also shown connected to the public switched telephone network (“PSTN”).
An exemplary data-over-cable system with telephony return includes customer premises equipment (e.g., a customer computer), a cable modem, a cable modem termination system, a cable television network, a public switched telephone network, a telephony remote access concentrator (“TRAC”)
49
and a backbone data network
12
(e.g., the Internet). The cable modem termination system
30
and the telephony remote access concentrator
49
together are called a “telephony return termination system.”
In a two-way cable system without telephony return, also termed a bi-directional cable system, the customer premises equipment
14
sends data packets to the cable modem
28
, which sends the data packets upstream via the cable television network
22
and
26
to the cable modem termination system
30
. Such a system is shown in FIG.
1
. The cable modem termination system
30
sends the data packets to appropriate hosts on the data network
12
. The cable modem termination system
30
sends the response data packets back to the appropriate cable modem
28
.
In a bi-directional cable system, the cable modem termination system
30
can continuously collect information about the level of impairments on the upstream RF path of a cable plant, i.e., the portion of the network between the demodulation circuit in the cable modem termination system
30
and the cable modems
28
. Further, a single O/E node
24
may serve multiple channels and cable modems. Measurements such as the noise floor level, and signal-to-noise ratio per cable modem transmission, can be made for the coax and fiber networks, along with the tracking of which cable modems are active during a given measurement interval.
The data-carrying performance of the upstream channels may vary with the conditions for radio frequency propagation on the cable network. Defective radio frequency interfaces may introduce sufficient noise into an upstream channel that the noise significantly impairs the ability of the channel to transport data packets from the cable modems to the cable modem termination system without error. Extraneous sour
3Com Corporation
McDonnell & Boehnen Hulbert & Berghoff
Nguyen Hanh
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