Telephonic communications – Subscriber line or transmission line interface – Network interface device
Reexamination Certificate
2000-02-23
2004-05-18
Tieu, Binh (Department: 2643)
Telephonic communications
Subscriber line or transmission line interface
Network interface device
C379S093090, C379S413040, C361S785000, C361S791000, C361S823000, C361S824000, C361S827000
Reexamination Certificate
active
06738474
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to POTS splitter devices that are mounted externally to digital subscriber loop access multiplexers in remote terminal and central office equipment racks.
BACKGROUND OF THE INVENTION
Providing high rate digital transmissions over the local subscriber loops of telephone companies is advantageous since the infrastructure for such local subscriber loops is currently in existence. High-rate digital subscriber loop (DSL) data services have been implemented using transmission technologies such as asynchronous DSL (ADSL), synchronous DSL (SDSL), high-speed DSL (HDSL), and very high-speed DSL (VDSL), which are generally referred to as xDSL.
High-speed digital transmissions available via xDSL share the same DSL with analog telephony (i.e., plain old telephone service (POTS)). POTS and xDSL are transmitted on the same analog telephone lines using frequency division multiplexing. For example, POTS transmissions generally occur in a frequency range
12
of 0 Hertz (Hz) to 4 kiloHertz (kHz). xDSL transmissions use higher frequencies such as 20 kHz to 1.1 MegaHertz (MHz). With reference to
FIG. 1
, xDSL frequencies
14
use higher frequency bands that do not overlap with the analog voice or POTS frequency range. This allows for the use of high-pass filters (HPFs) and low-pass filters (LPFs) to separate the POTS and xDSL signals at both ends of the DSL transmission line. Separate frequency bands can also be allocated for upstream xDSL transmissions toward the network (e.g., a central office (CO) or local exchange (LE)) and downstream xDSL transmissions toward customer premises. Thus, xDSL permits data transfer on existing telephone lines in both directions simultaneously, and does not interfere with analog telephone transmissions.
To provide DSLs to customer premises, customer premises xDSL equipment is needed, as well as POTS equipment for voice calls. As shown in
FIG. 2
, telephone company equipment (e.g., a remote terminal (RT) or CO) which accommodates xDSL data transmissions is also needed. The customer premises
18
can comprise, for example, a network interface device (NID)
20
connected to an analog telephone line
22
. The NID
20
comprises a LPF or POTS splitter
24
that filters high frequency xDSL signals and passes low frequency POTS signals to POTS equipment such as telephones
26
. xDSL modems use a HPF to attenuate POTS signals to recover the data signals in the higher frequency bands.
With reference to
FIG. 3
, the RT or CO
30
receives signals from and provides signals to the telephone line
22
which can have POTS signaling, as well as xDSL data transmissions. The RT or CO
30
generally comprises channel banks (CBs)
32
or other voice termination equipment for processing voice calls, and a DSL access multiplexer
34
hereinafter referred to as a DLSAM for processing xDSL transmissions. Different types of DSLAMs include, but are not limited to, a central office DSLAM, a remote DSLAM and remote ADSL multiplexers.
The RT
30
is generally contained in a cabinet containing the RT termination equipment (e.g., channel banks), an auxiliary power source and protection devices to protect telephony devices against unwanted voltage and current. The cabinet is located remotely with respect to the CO. The CO comprises termination and switching equipment, much of which is mounted in equipment racks. The amount of rack space available for accommodating equipment such as DSLAM to provide new services is limited and must be used efficiently.
With continued reference to
FIG. 3
, DSLAMs
34
are typically provided with circuitry
38
for passing POTS signals to voice call processing circuits such as CBs
32
, and for passing xDSL data to xDSL processing circuits. A LPF can be used to filter xDSL data signals from incoming telephone lines and pass POTS-only signals to the channel bank or telephone. HPFs are provided on-site at the customer premises and at the CO or RT to filter out POTS signals and pass only the xDSL signals to the appropriate processing circuits. In existing systems, POTS splitters are used in the on-site NID
20
and in a DSLAM or POTS splitter rack at a CO or RT to filter POTS signals.
The processing of POTS and xDSL signals at an RT or CO will now be described in further detail with respect to FIG.
4
.
FIG. 4
illustrates a portion of an exemplary DSLAM
34
located within an RT or CO
30
. The RT or CO
30
is provided with a protection panel
40
comprising at least one surge plug
42
. A telephone line
22
from a subscriber's premises
18
comprises POTS and xDSL signaling. The telephone line
22
enters the RT or CO
30
and through the protection panel
40
to an xDSL modem circuit
44
. A POTS filter
46
(e.g., a high pass filter) can pass the xDSL transmission to the xDSL modem circuit
44
for processing. The xDSL modem converts the signal to data packets or asynchronous transfer mode (ATM) cells which are forwarded to a data switch, router or multiplexer. The line
48
from the protection panel
40
also provides the POTS and xDSL signaling from the subscriber's premises to POTS-only circuits. A POTS splitter
38
passes the POTS signals which are then sent through the protection panel, as indicated by the line
50
to a CB
32
.
Existing DSLAMs
34
incorporating internal POTS splitters
38
have several disadvantages and therefore present a number of drawbacks to implementing xDSL transmissions in subscriber loops. POTS splitters are generally passive devices comprising an inductive coil. The coil is generally large with respect to printed circuit board (PCB) area on which the POTS splitter and other POTS circuitry is provided. Optimization of PCB area is important to minimize the volume or space within the chassis of the termination equipment enclosing the PCB.
The size of the chassis of a DSLAM
34
or RAM is a concern of vendors for telecommunications equipment since their customers (e.g., telephone service providers) have a limited amount of rack space at their COs and in their RTs, as stated previously. In other words, the larger the profile of the DSLAM chassis, for example, the more rack space that is required at the CO or RT to accommodate DSL service using that vendor's DSLAM, and the more likely that the smaller DSLAMs of competing vendors will be chosen. For example, a POTS splitter can require on the order of 2.5 cubic inches of PCB area. Reducing size of the coil in the POTS splitter is not a desirable option since the effectiveness of a POTS splitter can be compromised. A high inductance with a high quality or Q factor is desirable for a coil in a POTS splitter.
In addition to consuming valuable space within a DSLAM
34
, internal POTS splitters
30
are problematic because the filtering of high frequency signals (e.g., xDSL signals) inside a DSLAM can present electromagnetic interference problems with xDSL circuitry
44
in close proximity to the POTS splitters
38
. Also, POTS signals routed through the DLSAM
34
are lightning-exposed. Thus, POTS splitters require large clearances, in addition to the PCB area and DSLAM internal volume taken by virtue of their size. POTS splitters therefore preclude the use of fine-pitch front panel connectors to reduce the consumption of front panel space (e.g., the face plate of the DSLAM when rack mounted) and PCB area. Accordingly, a need exists for DSL equipment such as a DSLAM or RAM that economizes space at an RT and CO.
An existing central office POTS splitter that is externally mounted with respect to a DSLAM is commercially available. The POTS splitter is provided with other POTS splitters in a rack mountable chassis. A chassis that supports as many as 72 tip and ring pairs is on the order of nine inches high and therefore consumes considerable rack space. Thus, a need exists for POTS splitters that are externally mounted with respect to both the DSLAM and the racks in an RT or CO.
In addition to the size and space considerations of using internal or external, rack-mounted, POTS splitters, existing DSLAMs
34
are characterized b
ECI Telecom Ltd.
Nath & Associates PLLC
Novick Harold L.
Tieu Binh
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