Multiplex communications – Channel assignment techniques – Using a separate control line or bus for access control
Reexamination Certificate
1998-04-13
2002-04-09
Marcelo, Melvin (Department: 2737)
Multiplex communications
Channel assignment techniques
Using a separate control line or bus for access control
C370S489000, C370S496000
Reexamination Certificate
active
06370153
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communication networks, such as hybrid fiber coaxial (HFC) cable networks, wireless communication networks, satellite networks, etc., in which multiple subscriber stations transmit messages on one or more unidirectional multiple access communication channels. In particular, the present invention relates to enabling each subscriber station to reserve a portion of one or more multiple access unidirectional communication channels for contention free access. This enables the cable network to be used for point-to-point and multicast communication in addition to conventional broadcast TV.
BACKGROUND OF THE INVENTION
It is desirable to provide ubiquitous, integrated high speed and high capacity digital communication services (such as video, data and voice) to homes, schools, governments, and businesses. One such network, the telephone network, could be upgraded to provide such services. However, the century-old copper telephone network, primarily designed for telephony, has a usable bandwidth of only about 1 MHZ. Therefore, it is quite difficult and expensive to provide multi-channel digital video, along with data and voice on the telephone network. On the other hand, the coaxial drop line of a cable network to each home has a high usable bandwidth of about 1 GHz, providing ample speed and capacity to the integrated broadband services listed above, in addition to delivering traditional broadcast analog video programs. These traditional coaxial cable networks can be readily upgraded to bidirectional hybrid fiber-coaxial cable networks (HFC networks) to enable bidirectional high speed and high capacity communications. The HFC network is inherently a shared medium technology. Nevertheless, providing efficient, high speed, high capacity shared access to the upstream transmission has been a challenge to the communication industries.
FIG. 1
shows a conventional bidirectional hybrid fiber coaxial (HFC) cable network
10
having a head end
12
. The head end
12
has a head end controller
28
that can communicate with one or more other networks
30
, such as the Internet and local area networks. Downstream directed signals are transmitted from, and upstream directed signals are received at, the head end controller
28
via a coaxial link
34
connected to a diplexer
32
. The diplexer
32
splits the downstream directed signals from the other signal carried on the link
34
and outputs them to a laser transmitter
36
. The laser transmitter
36
modulates the downstream directed signals onto an optical signal that is transmitted via a downstream optical fiber trunk
14
. Likewise, upstream directed signals modulated on a signal carried via an upstream optical fiber trunk
14
′ may be demodulated at an optical receiver
38
. The diplexer
32
combines such upstream directed signals with the other signals carried on the link
34
for receipt at the head end controller
28
.
The upstream and downstream optical trunks
14
,
14
′ connect the head end
12
to an optical node
16
. The head end
12
and optical node
16
may be separated by up to about 80 kilometers. Like the head end
12
, the optical node
16
has a laser transmitter
40
, an optical receiver
42
and a diplexer
44
. The laser transmitter
40
is for modulating upstream directed signals received via the diplexer
44
onto an optical signal for transmission on the upstream directed optical trunk
14
′. The optical receiver
42
is for demodulating downstream directed signals from the optical signal carried on downstream optical trunk
14
and transferring the demodulated downstream directed signal to the diplexer
44
.
The diplexer
44
outputs onto coaxial trunk
18
the downstream directed signals that are demodulated by the optical receiver. Likewise, the diplexer
44
receives from the coaxial trunk
18
upstream directed signals for modulation by the laser transmitter
40
. The individual links of the coaxial trunk
18
are interconnected by bidirectional amplifiers
20
and taps
22
. Taps
22
are also provided for connecting coaxial drop lines
22
to the coaxial trunk
18
. The coaxial drop lines
22
connect the subscriber locations
26
to the coaxial trunk
18
for upstream and downstream directed communication.
The optical trunks
14
,
14
′, coaxial trunks
18
, taps
20
and coaxial drop lines
22
define a shared communications medium over which communicated signals are transmitted or received by all connected network devices, such as subscriber stations at the subscriber locations
26
and the head end
12
. The cable network
10
is specifically designed to deliver information in the downstream direction from the head end
12
to the subscriber locations
26
. For downstream directed communication, frequency division multiplexed communication channels are defined which have mutually unique carrier frequencies and non-overlapping bands (6 MHZ bands in North America and other NTSC cable TV systems, 8 MHZ bands in Europe and other PAL and SECAM cable TV systems) in the band from 54 MHZ up to the upper cut-off frequency of the coaxial trunks
18
and drop lines
22
(typically, 500-750 MHZ). This is also known as sub-split cable network. Each 6 MHZ downstream channel can carry either traditional analog NTSC composite video signals or digitally encoded data appropriately modulated by a RF carrier. Each traditional broadcast video programs are each transmitted in a separate communication channel by modulating an NTSC signal onto a predetermined carrier signal having an assigned carrier frequency and transmitting the signal from the head end controller
28
.
Although the cable network
10
has a large amount of bandwidth, the cable network
10
presents certain challenges for providing high speed and high capacity upstream transmission from a large number (typically a few hundred) of subscriber locations
26
. Most notably, the subscriber locations
26
may be distributed over a large geographic area. The signal path (i.e., sum of the lengths of the coaxial drop lines
22
, coaxial trunk links
18
and optical trunk links
14
) between individual subscriber locations
26
or subscriber locations
26
and the cable head end
12
can be on the order of tens of kilometers. Such long signal paths introduce noticeable delays in the transmission of signals which tend to be about 5 &mgr;s/kilometer.
Recognizing such challenges, several standard bodies and industry consortiums, such as IEEE 802.14, SCTE, MCNS and DAVIC have proposed similar communication schemes as follows. Two channels are defined for communication, namely, an upstream directed channel (UC) and a downstream directed channel (DC). Subscriber stations (SSs)
50
(FIG.
2
), such as cable modems, set top boxes or data terminals, at subscriber locations
26
can transmit on the upstream directed channel UC but can only receive on the downstream directed channel DC. The head end
12
can only receive on the upstream directed channel UC and only transmit on the downstream directed channel DC. In other words, the upstream channel UC is a multi-point to point channel whereas the downstream channel DC is a point to multi-point channel. These channels UC and DC are said to be multiple access channels, meaning that multiple network devices (SSs
50
, head end
12
, etc.) are permitted to access each channel UC or DC. As such, although the physical topology of the cable network
10
is a tree and branch configuration, the communication channels UC and DC may be illustrated as a logical bus network as shown in FIG.
2
.
Each channel UC and DC is assigned a different frequency band and center frequency, such as is shown in FIG.
3
. As shown, the upstream channel UC may be assigned a band in the 5-42 MHZ band not already used for control message communication. The downstream channel DC may be assigned one of the unused 6 MHZ bands, i.e., not currently used for communicating traditional broadcast video programming. The DC channel is divided into time slots and the UC channel is divided time
Marcelo Melvin
Proskauer Rose LLP
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