Abstract:
An optical network includes a first optical network for carrying a plurality of optical channels in an optical fiber, wherein each of the plurality of optical channels comprise a discrete wavelength in a first range of wavelengths. A second optical network coupled to the first optical network by a first tunable filter. A first customer location coupled to the second optical network by a second tunable filter. The first tunable filter is configured to pass a first set of optical channels from the first optical network to the second optical network. The first set of optical channels includes a subset of the plurality optical channels within a second range of wavelengths less than the first range of wavelengths. The second tunable filter is configured to pass a particular channel within the first set of optical channels from the second optical network to the first customer location.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/611,008 filed Dec. 14, 2006, the entirety of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     With the explosion in communication via the Internet in recent years, there has been a corresponding increase in demand for high bandwidth networks, such as networks incorporating optical fibers. One type of network architecture includes several different classes or types of networks coupled together to enable users to communicate with each other. Enterprise or access level networks provide bandwidth to individual customers and typically connect to larger metropolitan level networks. The metropolitan level networks, in turn, typically connect to even larger long haul or backbone level networks. In one type of network topology, each network is configured as a ring, with each ring having a number of nodes configured to add or drop traffic to or from the parent network. 
     In conventional metropolitan level ring networks (often referred to as metropolitan area networks or MANs), carrier level switching facilities receive traffic from the long haul network and distribute the traffic among a number of carrier aggregation facilities using Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) frames delivered via time domain multiplexing (TDM) technologies. Each aggregation facility connects to an access level network for delivering the SONET/SDH frames to customer premises. 
     Unfortunately, TDM aggregation and processing equipment is costly and difficult to maintain. Each aggregation point on a traditional SONET over TDM network requires significant infrastructure development. Additionally, switching systems associated with SONET frames delivered via TDM require costly traffic grooming and other equipment at the enterprise or local network level. Lastly, the optical-to-digital and digital-to-optical conversions required to process TDM signals introduce additional cost and potential errors at the aggregation facilities and customer premises locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of the invention and, together with the description, explain the invention. In the drawings, 
         FIG. 1  is a block diagram illustrating an exemplary communications system  100  in which systems and methods described herein may be implemented; 
         FIG. 2  is another block diagram illustrating an exemplary communications system  200  in which systems and methods described herein may be implemented; and 
         FIG. 3  is a block diagram illustrating one exemplary configuration of a customer premises connection to an access network as depicted in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following detailed description of implementations consistent with the present invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents. 
     Systems and methods described herein provide cost-effective deployment of metropolitan to enterprise access level optical networks. In one implementation, a first set of tunable optical filters may be used to direct ranges or bands of long reach wavelength division multiplexing (WDM) channels through a metropolitan network to a number of enterprise level access networks. A second set of tunable optical filters located on each access network may be used to direct individual WDM channels to customer premises locations. 
       FIG. 1  is a block diagram illustrating an exemplary communications system  100  in which systems and methods described herein may be implemented. Communications system  100  may include multiple networks including a long haul network  102 , a metropolitan (“metro”) ring network  104 , and a number of enterprise access (“access) rings  106 . Metro ring  104  may be coupled to long haul network  102  at a carrier switch facility  108 . Access rings  106  may be coupled to metro ring  104  at a number of nodes  110 . A number of customer premise locations  112  may be coupled to each access ring  106 . 
     Traffic to and from high bandwidth long haul network  102  may be switched on to and off of metro ring  104  by carrier switch  108 . Traffic on metro ring  104  may be further directed to access rings  106  at each node  110 . The traffic may then be routed or delivered from the access rings  106  to respective customer premises locations  112 . As will be described in additional detail below, systems described herein may enable efficient and low cost delivery of optical signals from carrier switch  108  to customer premises locations  112  without requiring expensive aggregation or optical to digital conversions. 
       FIG. 2  is a block diagram illustrating one exemplary communications system  200  implementation of a metro ring and access ring configuration. System  200  may include a metro ring  204 , a number of access rings  206   a ,  206   b , and  206   c , and a number of customer premises locations  208   a ,  208   b ,  208   c ,  208   d , and  208   e . As illustrated, metro ring  204  may be coupled to long haul networks  202   a  and  202   b  by a carrier switching facility  210 . Additionally, access rings  206   a - 206   c  may be coupled to metro ring  204  by a number of banded optical filters  212   a ,  212   b , and  212   c , respectively. Customer premises locations  208   a - 208   e  may be coupled to access rings  206   a - 206   c  by a number of channelized optical filters  214   a ,  214   b ,  214   c ,  214   d , and  314   e.    
     In an exemplary implementation, switching facility  210  may provide traffic to and from long haul network  202  to metro ring  204  using wavelength division multiplexing (WDM) technologies. As is known, WDM is a more recent optical transmission technology that enables a number of discrete optical wavelengths to be multiplexed or simultaneously transmitted on a single optical fiber. A variant of WDM known as dense WDM or DWDM enables between 80 and 100 or even more discrete optical channels to travel within a single fiber. 
     In one implementation, carrier switching facility  210  may include a number of add/drop multiplexers  216  (ADMs) configured to connect switching equipment to long haul networks  202   a  and  202   b  or, alternatively, to adjacent metro rings, thereby facilitating the transfer of traffic between the networks. In one implementation, long haul networks  202   a  and  202   b  and/or adjacent metro rings may include OC-192 four fiber bi-directional line switching rings (BLSR/4F) configured to cover distances as long as 600 kilometers (km). As is known, OC-192 supports speeds of approximately 10 gigabits per second. Additionally, a BLSF/4F configuration includes a ring topology in which two fibers are provided as working fibers and two fibers are provided as protection fibers. In one embodiment, ADMs  216  may divide received OC-192 signals into four OC-48 signals each capable of speeds up to 2.5 gigabits per second. 
     In one exemplary embodiment, carrier switching facility  210  may also include a layer 2 IP switch  218  as well as a broadband digital cross connect (BBDXC)  220  configured to perform multiservice switching between long haul network  202   a  or  202   b  and metro ring  204 . Carrier switching facility  210  may include an optical transmitter  222  capable of multiplexing and transmitting a number of DWDM channels covering wavelengths λ 1 -λ z  over distances of at least about 80 km, where z is an integer representing a last wavelength channel. Unlike conventional traffic aggregation and regeneration facilities required by SONET/SDH via TDM metropolitan networks, traffic forwarded by optical transmitter  222  may be capable of reaching customer premises locations  208   a - 208   e  entirely within the optical domain. In this manner, the aggregation facilities may be bypassed, resulting in significant cost and maintenance savings. 
     Banded optical filters  212   a ,  212   b , and  212   c  may include tunable passive filters configured to direct only predetermined DWDM channels to the associated access rings  206   a ,  206   b , and  206   c . For example, as illustrated in  FIG. 2 , banded optical filter  212   a  may be configured to pass channels associated with wavelengths λ 1 -λ i  to access ring  206   a , filter  212   b  may be configured to pass channels associated with wavelengths λ i+1 -λ p  to access ring  206   b , and filter  212   c  may be configured to pass channels associated with wavelengths λ p+1 -λ z  to access ring  206   c . As described above with respect to variable z, variables i and p are likewise integers representing selected wavelength channels along metro ring  204 . It should be noted that the number of access rings  206  shown is merely exemplary and that any suitable number of access rings may be provided, depending on the bandwidth requirements for associated customers premises locations  208   a - 208   e  and the number of discrete channels transmitted on metro ring  204  by optical transmitter  222 . 
     Unlike conventional SONET/SDH via TDM metro rings, by configuring metro ring  204  to carry DWDM channels, costly signal aggregation and TDM switching facilities may be replaced with inexpensive passive filters  212   a - 212   c.    
     Channelized optical filters  214   a - 214   e  may include tunable passive filters configured to pass only specific channels from access rings  206   a - 206   c  to each respective customer premises location  208   a - 208   e . For example, one of filters  214  may be configured to pass a single channel to a single customer premises location  208 . Alternatively, a filter  214  may be configured to pass multiple discrete channels to multiple customer premises  208 , ensuring that each customer premises  208  receives a dedicated channel. 
     As illustrated in  FIG. 2 , optical filter  214   a  may be configured to pass channel associated with a wavelength λ i+1  to customer premises location  208   a , optical filter  214   b  may be configured to pass a channel associated with a wavelength λ i+2  to a first access point  209   a  at customer premises location  208   b  and a channel associated with a wavelength λ m  to a second access point  209   b  at customer premises location  208   b , optical filter  214   c  may be configured to pass a channel associated with a wavelength λ m+1  to customer premises location  208   c , optical filter  214   d  may be configured to pass a channel associated with a wavelength λ p−1  to customer premises location  208   d , and optical filter  214   e  may be configured to pass a channel associated with a wavelength λ p  to customer premises location  208   e . Variable m is an integer representing a selected wavelength channel along access ring  206   b.    
       FIG. 3  is a block diagram illustrating one exemplary configuration of an access ring  300  and a customer premises location  302 . In a manner similar to that described above, customer premises location  302  may be coupled to access ring  300  by a channelized filter  304  configured to pass a predetermined bandwidth from access ring  300  to a feeder fiber  306  associated with customer premises location  302 . 
     A customer premises location initially configured to support SONET/SDH via TDM (e.g., customer premises location  302 ) may be served by a single fiber  306  coupled to access ring  300 . This fiber may be referred to as a “feeder fiber”. In a typical configuration, feeder fiber  306  may be incapable of supporting bidirectional traffic of DWDM and WDM channels. In one embodiment described herein, a pair of circulators  308  may be coupled on either ends of feeder fiber  306  to facilitate bidirectional support and enable DWDM traffic to be transmitted both to and from customer premises location  302 . 
     By enabling an all-optical distribution of traffic from a carrier switching facility to each customer premises location, systems consistent with principles described herein may substantially increase the efficiency of network operations while simultaneously significantly reducing costs associated with delivering high bandwidth traffic to access networks and eventually individual customers. 
     CONCLUSION 
     Implementations described herein provide for all-optical delivery of network traffic through a metropolitan level network, and an access level network to enterprise or customer level locations. In one implementation, tunable filters may be used to deliver targeted wavelengths from the metropolitan network to each associated access network. Additional filters may be used to pass specific traffic channels from the access networks to customers associated with the access networks. 
     The foregoing description of exemplary embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. 
     It will be apparent to one of ordinary skill in the art that the features described above, may be implemented in many different forms of hardware, software, or firmware in the implementations illustrated in the figures. The actual hardware or control software used to implement the described features is not limiting of the invention. Thus, the operation and behavior of these features were described without reference to specific hardware or control software—it being understood that one of ordinary skill in the art would be able to design hardware and software to implement the features based on the description herein. 
     No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. The scope of the invention is defined by the claims and their equivalents.