Interactive video distribution systems – Video distribution system with upstream communication – Remote testing of cable system
Reexamination Certificate
1999-05-28
2004-06-29
Faile, Andrew (Department: 2611)
Interactive video distribution systems
Video distribution system with upstream communication
Remote testing of cable system
C725S111000
Reexamination Certificate
active
06757908
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates to the field of data communication and data-over-cable systems. More particularly, the invention relates to a method of graphically representing conditions in such a system (such as signal to noise ratio, noise floor levels, or other types of conditions, which may or may not indicate an impairment in the system) in a convenient manner such that the source of the impairment to the system is easy to comprehend by a technician or human operator.
B. Description of Related Art
Cable modem systems for wide area network access, e.g., Internet access, are now being rolled out in selected metropolitan areas of the United States. Basically, these systems provide high-speed data communications over a cable television infrastructure. 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. 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 and a switch or router
20
. A cable system head-end 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 digital data into analog form and supplies analog signals to a fiber network
22
, which is connected to a plurality of 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 promises equipment
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 or CMTS
30
. This device provides a network side interface to a wide area network, indicated at
32
, and an 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 CMTS
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 CMTS
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
in.
FIG. 1
) and a 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, 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 as 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 two-way cable system without telephony return, the cable modem termination system
30
can continuously collect information about the level of impairments or other conditions, such as noise floor level, on the upstream RF path of a cable plant, i.e., the portion of the network between the demodulation circuit in the CMTS
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. However, in order for the collected data to be useful, there must be a method of correlating impairments with upstream channels, cable modems, and impairment levels in order for the user (e.g., technician or cable system operator) to ascertain what the cause of the particular impairment is. This problem of correlation is further complicated if there are intermittent, or multiple, impairments on a given upstream path, or across multiple upstream channels.
Unfortunately, the collected impairment data does not lend itself well to plotting on standard format graphs. A tabular presentation of impairment data can involve a significant amount of work by the user to interpret results, and do so in an expeditious manner. Thus, there has been a need in the art for a new method of presenting the impairment data that will allow the user to quickly analyze the data and determine what the cause or causes of the impairments are. The standard way of presenting impairment data or other conditions in a data over cable transmission path is to show the RF spectrum in the channel being monitored with a spectrum analyzer. There are several drawbacks with this approach. First, the method is costly, as in order to get the resolution that is required a separate device is used for data collection. In many cases, the data collection device is limited in how many channels it can monitor. Secondly, the method gives the provider or user no information on active cable modems that may be the cause of the problem. Thirdly, it does not sufficiently narrow down the problem to enable quick troubleshooting of the cause of the impairment. The present invention overcomes these problems.
SUMMARY OF THE INVENTION
A method of presenting impairment data in a cable modem system in a useable, easy to understand graphical form is described herein. I have adopted the term “impairment circle” to refer to the graphical representation of the impairment data
3Com Corporation
Faile Andrew
Koenig Andrew Y
McDonnell & Boehnen Hulbert & Berghoff
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