Optical communications – Multiplex – Hybrid
Reexamination Certificate
2000-05-19
2004-09-28
Pascal, Leslie (Department: 2633)
Optical communications
Multiplex
Hybrid
C398S046000, C398S047000, C398S075000, C398S082000, C398S083000, C398S115000, C398S116000, C398S069000
Reexamination Certificate
active
06798993
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical networks that use wavelength division multiplexing (WDM), and, more specifically, to internetworking of such networks with connectionless (CL) packet networks such as internet protocol (IP) networks.
BACKGROUND OF THE INVENTION
Known optical networks use wavelength division multiplexing (WDM) for point-to-point communication between nodes disposed on an optical transmission medium such as an optical fiber. Data, i.e. information bearing packets associated with a plurality of individual calls, is used to modulate a laser having a wavelength corresponding to a particular WDM channel, and the optical signal is inserted onto the transmission medium in an optical add/drop module (OADM) at one node. The optical signal is transported on the medium to a destination node, where another OADM extracts the optical signal, whereupon demodulation is performed to recover the data.
An arrangement for internetworking of optical and connectionless packet networks such as Internet Protocol (IP) networks, is described in a copending application Ser. No. 09/333406 and filed Jun. 15, 1999 and entitled “Wideband Optical Packet Ring Network”, assigned to the same assignee as the present invention, which is incorporated herein by reference. In the aforementioned application, specially equipped routers in the packet networks are arranged to have optical interfaces to OADM's in the optical network. These routers, sometimes referred to as “optical gateways” or simply “gateways”, include hardware and software that performs several functions. First, each gateway includes a packet framer and an optical transceiver that converts an “electrical” stream of packets into an optical signal that modules a laser having a particular wavelength. Second, each gateway is functionally arranged to control the OADM's in order to implement routing tables that associate specific destinations on the optical network (i.e., remote gateways connected to other OADM's) with a particular “port” on the router. The laser output, which is available at the above-mentioned particular port on the gateway, is then combined with (added to) other wavelengths on the optical transmission medium to form the WDM signal. At the destination gateway, the portion of the optical signal at the particular wavelength is then extracted (dropped) from the other wavelengths on the optical transmission medium, and the optical signal is reconverted to a stream of packets in another optical transceiver, which can then be transmitted on toward a desired destination. The path which an IP packet takes through WDM network is determined by the wavelength on which it enters the WDM network and the state of the particular ones of the OADMs through which the packet travels.
A prior art arrangement of the type just described is illustrated in
FIG. 1. A
packet network
110
includes a plurality of interconnected routers, such as conventional routers
111
and
112
, and gateways
121
and
122
, which are routers that interface both with conventional routers and also with particular OADM's in an optical WDM network designated generally at
150
. Thus, gateway
121
has a connection to OADM
151
, while gateway
122
has a connection to OADM
152
. An optical WDM transmission medium
160
with counter-clockwise optical flow, interconnects OADM
151
to OADM
153
, OADM
153
to OADM
154
, and OADM
154
to OADM
152
. OADMs
153
and
154
are, in turn, connected to gateways
133
and
134
, respectively, which may be part of packet network
110
or may be part of a different packet network.
For simplicity of description, assume that gateways
121
,
122
,
133
and
134
each have two ports, called port
1
and port
2
, each arranged as part of an electrical to optical interface at a specific wavelength &lgr;
1
and &lgr;
2
, respectively. In a real implementation (such as an implementation using AllWave™ fiber technology available from Lucent Technologies), each gateway could be arranged to simultaneously support many more WDM channels; (e.g., as many as 2000 channels) on transmission medium
160
. Each router in packet network
110
, including gateways
121
,
122
,
133
,
134
and
135
, has a routing table, which specifies which port an incoming packet (i.e., a packet received from another router in the packet network) should be applied to in order to be transported on the optical network to a particular destination gateway. Thus, for example, as shown in
FIG. 1
, the routing tables for gateways
121
and
134
may be as set forth in tables 1 and 2 below, respectively:
TABLE 1
Gateway 121 Routing Table
Destination
Port Assignment
Gateway 133
Port 1
Gateway 122
Port 2
TABLE 2
Gateway 134 Routing Table
Destination
Port Assignment
Gateway 133
Port 1
Gateway 122
Port 2
In the example of
FIG. 1
, assume that a first “connection” from gateway
121
to gateway
133
is desired. This connection can be established through the optical WDM network by applying packets received at gateway
121
(from other routers in the packet network
110
) to port
1
, which is associated in Table 1 with the desired destination (gateway
133
). The packets are used to modulate a laser having a wavelength &lgr;
1
associated with port
1
, and are inserted via OADM
151
onto transmission medium
160
, which in this case is arranged to “add” the laser output to the signals already travelling in a counterclockwise direction on transmission medium
160
. In this example, OADM
153
is arranged to extract (drop) the optical signal on transmission medium
160
at wavelength &lgr;
1
from the other *WDM signals on the transmission medium, so that the information bearing packets can be recovered by demodulation in a transceiver in gateway
133
. Also assume that a second connection from gateway
134
to gateway
122
is desired. This connection can be established through the optical WDM network by applying packets received at gateway
134
(from other routers in another packet network not shown in
FIG. 1
) to port
2
, which is -associated in Table 2 with the desired destination (gateway
122
). The packets are used to modulate a laser having wavelength &lgr;
2
associated with port
2
, and are inserted via OADM
154
onto transmission medium
160
, which in this case is arranged to “add” the laser output to the signals already travelling in a counterclockwise direction on transmission medium
160
. In this example, OADM
152
is arranged to extract (drop) the optical signal on transmission medium
160
at wavelength &lgr;
2
from the other WDM signals on the transmission medium, so that the information bearing packets can be recovered by demodulation in a transceiver in gateway
122
.
While the first and second connections just described are ongoing, it will be observed that if a connection from gateway
121
to gateway
122
is concurrently requested, the request would have to be denied. This would be true even though gateway
121
has an idle port, namely port
2
. This is because if port
2
were to be used, the incoming packets would be used to modulate a laser at wavelength &lgr;
2
. This signal would be added at OADM
151
and dropped at OADM
152
. While no interference would occur in the portion of transmission medium
160
between OADM
151
and OADM
154
, it is noted that the same wavelength, &lgr;
2
, would be used in the portion of transmission medium
160
between OADM
154
and OADM
152
, causing impermissible interference. Accordingly, the general object of the present invention is to enable efficient allocation of network resources (e.g., bandwidth) in an optical WDM network, and provide the ability to internetwork optical and packet networks so as to provide truly guaranteed connections to satisfy service requirements. A specific object is to enable intermetworking of optical WDM and packet networks in a manner in which the previously described interference is avoided.
SUMMARY OF THE INVENTION
In accordance with the present invention, a connectionless packet network and an optical WDM networ
Adams Laura Ellen
Veeraraghavan Malathi
Lucent Technologies - Inc.
Pascal Leslie
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