Note: Descriptions are shown in the official language in which they were submitted.
CA 02381467 2002-02-06
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PRIVATE LINES TRAVERSING A PACKET NETWORK AND RE-
ARRANGEMENT OF CHANNELS AMONG PACKET NETWORK
CONNECTIONS
BACKGROUND
The invention relates to private lines traversing a packet network and re-
arrangement of channels among packet network connections.
A traditional telephone exchange configuration provides circuit connections
between remote locations. Many of the telecommunications networks currently
used
are synchronous digital networks. Digitized voice communications are
transmitted
synchronously over the networks at a fixed rate. Discrete time periods (time
slots)
can be packed with the digital information for a particular call, and digital
information
for multiple calls can be packed sequentially to form a time division
multiplexed
(TDM) data stream.
Private lines, which are dedicated, non-switchable links from one or more
customer-specified locations to other customer-specified locations, offer
highly
available connectivity because they are dedicated to the use of a single
entity such as
an organization. Private lines can provide a cost-effective alternative to
usage-
sensitive, switched services.
Traffic from private lines can traverse high-capacity, transmission
facilities,
including packet-domain network architectures. Asynchronous transfer mode
(ATM)
networks, for example, use fixed-size packets of data, known as cells, that
are
transferred between low-overhead packet switches and that provide virtual
circuits
between the end points of a network. The virtual circuits may be provisioned
to
provide a permanent virtual circuit between the end points.
One difficulty encountered in providing private line service over a packet
network is that the packet network tends to induce additional delays during
transmission of the private line traffic. Long delays may be unacceptable and
can
exacerbate echoes that interfere with the voice or other signals. Although
echo
cancellation techniques are available, they tend to be costly.
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SUMMARY
According to one aspect, a method of providing communication services
includes provisioning a packet network connection that has packet channels,
each of
which is independently capable of carrying narrowband signals so as to emulate
a
private line circuit. A narrowband private line that traverses the packet
network
connection using a particular one of the packet channels is established.
In various implementations, one or more of the following features may be
present. A dedicated narrowband circuit can be associated with the particular
packet
channel. A dedicated narrowband circuit connection can be provided to a port
of a
gateway associated with the packet network connection, where the gateway is
configured to perform adaptations between circuit-switched bearers and packet-
switched bearers. Furthermore, additional nan owband private lines that
traverse the
packet network connection using other packet channels can be established
without
adversely affecting the existing lines.
In a related aspect, a method of providing communication services includes
setting up multiple private narrowband lines associated with different
entities. The
private lines traverse a single virtual circuit in a packet network. Dedicated
narrowband circuits can be associated with respective channels in the virtual
circuit.
Private lines traversing the virtual circuit can be removed without adversely
affecting
the remaining lines.
A communication system also is disclosed and includes gateways configured
to perform adaptations between circuit-switched bearers and packet-switched
bearers.
A packet network includes a virtual circuit connection between a pair of the
gateways,
and the virtual circuit connection includes channels each of which is
independently
capable of carrying narrowband signals so as to emulate a private line
circuit.
In some implementations, a dedicate narrowband circuit can be coupled to a
port on one of the gateways in the pair to form a private line circuit
traversing one of
the channels in the virtual circuit connection. The system can include
dedicated
narrowband circuits associated with different entities and associated with
different
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ones of the channels to form multiple private line circuits traversing a
single virtual
circuit connection.
In another aspect, a method of providing narrowband communication services
includes rolling over a narrowband communication line that traverses a channel
in a
first virtual circuit connection in a packet network to a channel in a second
virtual
circuit connection in the packet network. The technique can be applied to
private
lines, although it is not limited to such applications. In some
implementations, the
method includes broadcasting traffic from a narrowband circuit that forms part
of a
private line. The traffic is broadcast over the channels in the first and
second virtual
circuit connections. Packets at a receiving end of the channel in the second
virtual
circuit connection are detected. Subsequently a path is established from the
receiving
end of the channel in the second virtual circuit connection to the narrowband
circuit.
Resources associated with the path from the receiving end of the narrowband
circuit
to the channel in the first virtual circuit connection then can be released.
In various implementations, one or more of the following advantages may be
present. For example, private lines can more easily be adapted to packet
networks.
Delays that might otherwise be introduced on a private line as a result of
packetizing
the narrowband signals can be reduced by carrying the signals over a packet
connection having multiple channels. Similarly, the need to employ echo
cancellation
techniques can be reduced. Furthermore, private lines can be added or removed
from
channels in the packet connection independently of one another.
Narrowband circuits within a packet network can be re-arranged without end-
users perceiving transmission difficulties. The re-arrangement of packet
channels can
be applied to real-time traffic traversing packet networks, as well as private
line
services.
Other features and advantages will be readily apparent from the following
detailed description, the accompanying drawings and the claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a telephone connection through a hybrid ATM
network and an associated signaling network.
FIG. 2 is a simplified block diagram of an exemplary media gateway.
FIGS. 3A through 3D illustrate a technique for re-arranging channels among
packet network connections.
DETAILED DESCRIPTION
A large number of individual telephone circuits, such as DSO circuits, can be
carried, for example, on fiber optic carriers 10 using time-division
multiplexing
(TDM) according to the Telcordia Synchronous Optical Network (SONET)
standards.
The narrowband traffic associated with the DSO circuits can include, for
example,
voice, modulated digital data from a modem, or facsimile machine data. The
carriers
10 are coupled to access ports 16 in media gateways 14 (see FIG. 2).
The media gateways 14 adapt the narrowband telephone line signals to packet-
based signals and vice-versa. Each gateway 14 can separate incoming TDM
signals
into individual DSO signal streams. In one implementation, shown in FIG. 2,
each
gateway 14 includes a TDM switching matrix 17 that provides full switching
capabilities. The switching matrices 17 permit the DSO circuits to be
interconnected
flexibly with nan owband channels appearing on the media gateways 14. Echo
cancellation and other digital signal processing functions can be performed in
a digital
signal processing portion 18 of each gateway. The DSO streams are adapted by
an
ATM adaptation layer 20 into ATM cells. The ATM adaptation layer 20 combines
incoming DSO signals from a particular TDM carrier 10 into payloads for ATM
cells.
Each ATM cell is inserted through the ATM ports 21 into an ATM cell stream
that
traverses an ATM network 25. Each gateway 14 includes a control section 19
that
controls overall operation of the gateway. In one implementation, the gateways
100A, 100B are implemented as Salix 7720 Class-Independent Switches available
from Tellabs Operations, Inc.
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As illustrated in FIG. 1, each gateway 14 is connected to an ATM end point
switch 22. The connection between a gateway and an ATM end point switch 22 and
the connection between the ATM end point switch and the ATM network 25 are
user-
network interfaces (LJNIs). Within the ATM network 25, there are a number of
ATM
switches 26 which are inter-connected by network-node interfaces (NNIs).
As described in greater detail below, a single packet network connection has
multiple channels each of which can emulate a private line circuit to help
reduce the
delay that otherwise might be associated with each circuit. The various packet
channels can be associated with narrowband circuits independently of one
another to
allow private lines to be added or removed without impacting the integrity of
the
circuits already assigned to the packet network connection.
When a customer request is received for private line service between two
locations, the service provider can install, for example, a T1 line carrying
twenty-four
DSO circuits at each location. Gateways 14 having connections to the customer
locations are provisioned to establish a virtual packet circuit with multiple
channels
through the ATM network 24. For example, in one implementation, the gateways
14
are provisioned to establish a virtual circuit with twenty-four independently
assignable channels. The gateways 14 assign resources to handle the ATM cell
stream. Each channel in the packet network connection is provisioned to be
capable
of carrying a TDM-based signal through the packet network 25 so as to emulate
a
private line circuit.
Once the packet-domain resources are assigned, dedicated circuit connections
are provided between the customer locations through the gateways 14. The DSO
circuits are permanently assigned to an available gateway port 16 associated
with the
virtual circuit. Particular channels in the virtual circuit are assigned to
the DSO
circuits to establish one or more narrowband private line connections between
the
customer locations through the packet network 25.
Additional private line circuits can be provided over the packet circuit at
any
time. To add another private line between customer locations, an available DSO
circuit would be assigned permanently to an available gateway port 16
associated with
the virtual circuit in the ATM network 25. An available channel in the virtual
circuit
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is assigned to the DSO circuit to allow the new private line to traverse the
packet
network 25. In general, the channels in the virtual circuit can be provisioned
to
emulate private line circuits independently of one another, thereby permitting
private
lines from multiple customers to traverse a single virtual circuit in the
packet network
25 without adversely affecting the existing connections. Similarly, one or
more
private lines traversing the virtual circuit can be removed without adversely
impacting
the integrity of the remaining DSO circuits assigned to the virtual circuit.
From the service provider's perspective, individual private lines from
multiple
customers can be bundled for transport through the core packet network, and
changes
in one customer's line arrangement can be made without affecting service to
other
customer's sharing the bundle. Furthermore, by making a single packet
connection
available for multiple DSO circuits, the additional delay (if any) resulting
from the
packet connection is distributed over the various channels in the virtual
circuit.
Therefore, from the user's perspective, private lines incur minimal additional
transmission delays even though they are packetized for transmission over the
service
provider's core network. Additionally, where voice circuits are carried on the
lines,
the techniques can reduce or eliminate the need to deploy echo cancellers on
ATM-
adapted private lines because the delay characteristics of the lines are not
appreciably
changed.
In some implementations, a single private line may comprise multiple DSO
circuits. In that case, a narrowband private line circuit can be established
that
traverses the packet network connection using multiple packet channels. For
example, if a private line includes six DSO circuits, then six channels in the
packet
network connection would be used to provide the corresponding DSO circuit
emulation.
Situations may arise where it is desirable to rearrange channels among the
circuits in the packet network dynamically. In particular, it may be desirable
to
rearrange the channels so that one or more private lines traverse a different
virtual
circuit in the packet network. For example, assume that there are two virtual
circuit
connections between the gateways 14 through the ATM network 25 and that each
virtual circuit connection includes twenty-four independently assignable
channels.
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Assume further that all twenty-four channels in one of the virtual circuit
connections
form respective private line circuits, but that only one of the channels in
the second
virtual circuit is being used. At some later time, there may be a request to
disconnect
one of the DSO circuits associated with a channel in the first virtual circuit
in the
packet network. In order to free up the unused bandwidth in the ATM network,
it is
desirable to rearrange the packet channels so that the private line traversing
the
channel in the second virtual circuit traverses the free channel in the first
packet
circuit instead. That allows the second virtual circuit to be released.
FIGS. 3A through 3D illustrate the rearrangement of a private line circuit.
The private line starts on a DSO circuit (A) and traverses a channel in the
virtual
circuit (B). As described below, the channels can be rearranged so that the
private
line circuit traverses an available channel in the virtual circuit (C).
Although the
technique is described with respect to a single gateway 14, the gateways on
both sides
of the virtual circuit connection (B) typically would be requested to perform
the
rollover from the virtual circuit (B) to the virtual circuit (C) substantially
simultaneously. The gateways 14, however, may perform the rollover
asynchronously.
As shown in FIG. 3A, it is assumed that a private line narrowband circuit has
been provisioned over the virtual circuit (B) and that the second virtual
circuit (C)
also exists. Each circuit includes incoming and outgoing paths with respect to
the
gateway 14. Upon receiving a request to reassign the DSO circuit (A) to a
channel in
the virtual circuit (C), the gateway 14 bi-casts the traffic from the DSO
circuit (A)
over both virtual circuits (B) and (C), as illustrated in FIG. 3B. The gateway
14 waits
until it detects the presence of packets arriving at the receiving end of the
specified
channel in the virtual circuit (C). Once the gateway 14 detects the presence
of packets
arriving on the receiving end of the specified channel in the virtual circuit
(C), the
gateway reconfigures its resources to establish an incoming path from the
particular
channel in the virtual circuit (C) to the receiving side of the DSO circuit
(A), as shown
in FIG. 3C. The gateway 14 also releases the resources that formed the
incoming path
from the channel in the virtual circuit (B) to the receiving end of the DSO
circuit (A).
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In some cases, it may be desirable to send "out of service" patterns on unused
packet channels. In that case, the gateway 14 would try to detect the arrival
of
packets having different patterns on the receiving end of the specified
channel in the
virtual circuit (C). Once the gateway 14 detects packets having patterns other
than
"out of service" patterns, it would reconfigure its resources to establish an
incoming
path from the particular channel in the virtual circuit (C) to the receiving
side of the
DSO circuit (A).
The transition from the connection arrangement of FIG. 3B to that of FIG. 3C
should occur quickly to reduce the possibility of interference on the private
line that is
detectable by the line-terminating equipment on the customer premises or by
end-
users themselves. Transition times on the order of fifty milliseconds are
preferred.
Such times are consistent with SONET protection switching times which are well-
known in the art and avoid inducing customer-detectable problems. The gateway
14
then reconfigures its resources to remove the outgoing path from the DSO
circuit (A)
I S to the channel in the virtual circuit (B).
During the rearrangement of channels in the packet circuits, other commands
should not be executed with respect to the particular DSO circuit that forms
part of the
private line until the rearrangement is completed. For example, a request to
disconnect the DSO circuit should be denied or delayed until after the
channels have
been rearranged.
The foregoing technique can be used to rearrange channels in packet circuits
dynamically so as to maximize available bandwidth. Moreover, the technique can
be
performed transparently to users. The technique can be used, for example, to
ensure
efficient use of ATM Adaptation Layer I (AALI) resources in a network of
gateways
14. The technique can be particularly advantageous with respect to constant
bit rate
and real-time variable bit rate connections. Various types of packet networks
can be
used, including ATM, Internet Protocol (IP), frame relay and Ethernet.
Although the rearranging of channels in packet circuits has been described in
the context of private lines that traverse packet networks, the technique can
be applied
to switched traffic as well.
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The techniques can be used in systems employing "robbed" bit supervisory
signaling as well as clear channel operation.
The foregoing techniques may include manual and/or automated provisioning
of the various circuits. Various features of the system can be implemented in
hardware, software, or a combination of hardware and software. For example,
some
aspects of the system can be implemented in computer programs executing on
programmable computers. Each program can be implemented in a high level
procedural or object-oriented programming language to communicate with a
computer system. Furthermore, each such computer program can be stored on a
storage medium, such as read-only-memory (ROM) readable by a general or
special
purpose programmable computer, for configuring and operating the computer when
the storage medium is read by the computer to perform the functions described
above.
Other implementations are within the scope of the claims.
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