Abstract:
Communications apparatus, including client interface units (CIUs) coupled to network service lines for sending and receiving data carried by the service lines in accordance with respective communication protocols. The CIUs include at least first and second CIUs that communicate with respective first and second channels of the data operating in accordance with different, respective first and second protocols. The apparatus includes optical interface units (OIUs), coupled to a passive optical network (PON) and modulating optical radiation responsive to the data so as to convey the data over the PON. 
     The apparatus further includes a connectivity unit which conveys the data between the CIUs and the OIUs, while mapping the channels to the OIUs so that data from the first and second channels is carried in alternation by one of the OIUs to first and second users of the PON communicating respectively according to the first and second protocols.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to data transfer, and specifically to multi-channel data being transferred via a plurality of wavelengths in an optical network. 
     BACKGROUND OF THE INVENTION 
     A point-to-multi-point passive optical network (PON) operates as a communication system by broadcasting optical signals downstream from a central unit, herein termed an optical line termination (OLT), to optical network terminations (ONTs). The signals are transferred from the OLT to the ONTs via fibre optic cables and passive optical splitters, which comprise the physical fabric of the network. For upstream communication, each ONT must be able to transmit signals which are not interfered with by other ONTs. 
     One of the methods known in the art for performing such upstream and downstream transmissions is by using time division multiple access (TDMA), wherein each ONT is allocated a window when only it can transmit, and where the OLT also has windows for transmission to specific ONTs. Other methods for avoiding interference include transmitting signals at different wavelengths, using wavelength division multiple access (WDMA). Combinations of TDMA and WDMA are also known in the art. Signals are typically transmitted within the PON according to an protocol based on these methods. Upstream of the OLT, signals are typically transferred via an industry-standard data transmission protocol, such as an Ethernet protocol. 
     As demand on transmission networks increases, the need for improving the flexibility of the networks also increases. One way in which network flexibility may be increased is by enabling elements of the network to convey data via more than one protocol. 
     SUMMARY OF THE INVENTION 
     It is an object of some aspects of the present invention to provide apparatus and a method for distributing data channels transmitted according to a plurality of protocols via a passive optical network (PON). 
     In a preferred embodiment of the present invention, an optical line termination (OLT) communicates at its upstream side with data service lines, each line operating according to a respective industry-standard protocol. Each line is able to transfer a set of data channels, and is coupled to the OLT via one of a first plurality of channel interface (CIF) cards comprised in the OLT. 
     At its downstream side the OLT communicates with the PON via a second plurality of optical interface (OIF) cards, each of which conveys one or more of the data channels between the PON and the OIF card by modulation of optical radiation. The OIF cards are able to convey the data channels regardless of the protocol of the channels. For each OIF card, one of a pair of wavelengths is used for downstream transmission, the other wavelength of the pair being used for upstream transmission. 
     A connectivity unit in the OLT couples the CIF cards and the OIF cards. The connectivity unit is implemented so that any CIF card and any OIF card may be coupled, so as to transfer one or more data channels between the CIF and OIF cards. The implementation is preferably performed by a main central processor (MCP) in the OLT, and may be performed in a dynamic manner, irrespective of the protocol of the data channels. Enabling variable routing of data channels between any CIF card and any OIF card, regardless of the protocol, allows extremely flexible channel assignment configurations, and enables high bandwidth levels for transmitted channels. 
     In order to transfer downstream data from different channels via the connectivity unit, the data from each CIF card is buffered by channel in a respective memory as it enters the connectivity unit, and its destination OIF card is also identified in the respective memory. The MCP performs a series of steps wherein data from each CIF card is read, in units of a size set by management software controlling the data transfer. The data is routed through the connectivity unit to an OIF memory for the OIF card assigned to the channel, then stored in the OIF memory for subsequent downstream transmission. During the routing and storage, channel boundaries are inserted and then removed as necessary, as the data is transferred. 
     A similar process is performed by the MCP in transferring upstream data from a specific OIF card to a CIF card assigned to the channel. 
     The connectivity unit is also implemented to enable local “cross-connection” of channels within the PON via the OIF cards. Thus, an upstream channel signal received by one OIF card may be “looped-back” by the connectivity unit to a downstream channel, via a different OIF card. The ability to cross-connect channels by looping signals back allows flexibly defined virtual local area networks (VLANs) to be implemented between the ONTs coupled to the PON. 
     There is therefore provided, according to a preferred embodiment of the present invention, communications apparatus, including:
         a first plurality of client interface units, adapted to be coupled to network service lines so as to send and receive data carried by the service lines in accordance with respective communication protocols, the client interface units including at least first and second client interface units that are adapted to communicate with respective first and second channels of the data operating in accordance with different, respective first and second protocols;   a second plurality of optical interface units, adapted to be coupled to a passive optical network (PON) and to modulate optical radiation responsive to the data so as to convey the data over the PON; and   a connectivity unit, coupled to convey the data between the client interface units and the optical interface units, while mapping the channels to the optical interface units so that data from the first and second channels is carried in alternation by one of the optical interface units to first and second users of the passive optical network communicating respectively in accordance with the first and second protocols.       

     Preferably, each of the optical interface units is adapted to convey the data from the first and the second channels from the first and the second users of the passive optical network, and the connectivity unit is adapted to map the first channel to the first client interface unit and the second channel to the second client interface unit. 
     Preferably, each of the communication protocols comprises a respective industry-standard communication protocol. 
     Preferably, the data is transferred in the PON via a time division multiplexed method. 
     Preferably, each of the optical interface units conveys the data via a respective pair of wavelengths, so that the data is transferred in the PON by a wavelength division multiplexed method. 
     Preferably, the connectivity unit includes a first plurality of memories which are adapted to store routing information for channels of the data sent and received by respective client interface units. 
     Further preferably, each of the first plurality of memories includes a downstream label memory adapted to store the routing information indicative of the optical interface unit, included in the second plurality of units, to which downstream data included in the channels of the data is to be sent. 
     Preferably, the connectivity unit includes a second plurality of memories which are adapted to store routing information for channels of the data sent and received by respective optical interface units. 
     Further preferably, each of the second plurality of memories includes an upstream label memory adapted to store the routing information indicative of the client interface unit, included in the first plurality of units, to which upstream data included in the channels of the data is to be sent. 
     Preferably, the connectivity unit includes a memory including management software, wherein the management software is adapted to convey the data between the client interface units and the optical interface units in data-units having a predetermined minimum size. 
     Further preferably, the management software is adapted to insert channel boundaries in the conveyed data and to remove the channel boundaries after the data has been conveyed. 
     Preferably, the second plurality of optical interface units includes a first optical interface unit and a second optical interface unit, and the connectivity unit is coupled to convey upstream data included in the data from the first optical interface unit as downstream data to the second interface unit, and the upstream and downstream data are included in an identical channel. 
     There is further provided, according to a preferred embodiment of the present invention, a method for transferring data, including:
         providing a first plurality of client interface units, adapted to be coupled to network service lines so as to send and receive the data carried by the service lines in accordance with respective communication protocols, the client interface units including at least first and second client interface units that are adapted to communicate with respective first and second channels of the data operating in accordance with different, respective first and second protocols;   providing a second plurality of optical interface units, adapted to be coupled to a passive optical network (PON) and to modulate optical radiation responsive to the data so as to convey the data over the PON;   coupling a connectivity unit between the client interface units and the optical interface units so as to convey the data therebetween; and   mapping the channels to the optical interface units so that data from the first and second channels is carried, via the connectivity unit, in alternation by one of the optical interface units to first and second users of the passive optical network communicating respectively in accordance with the first and second protocols.       

     Preferably, each of the optical interface units is adapted to convey the data from the first and the second channels from the first and the second users of the passive optical network, and the connectivity unit is adapted to map the first channel to the first client interface unit and the second channel to the second client interface unit. 
     Preferably, each of the communication protocols includes a respective industry-standard communication protocol. 
     Preferably, the method includes transferring the data in the PON via a time division multiplexed method. 
     Preferably, each of the optical interface units conveys the data via a respective pair of wavelengths, and the method includes transferring the data in the PON by a wavelength division multiplexed method. 
     Preferably, the connectivity unit includes a first plurality of memories, and the method includes comprising storing routing information for channels of the data sent and received by client interface units in the respective memories. 
     Further preferably, each of the first plurality of memories includes a downstream label memory adapted to store the routing information indicative of the optical interface unit, included in the second plurality of units, to which downstream data included in the channels of the data is to be sent. 
     Preferably, the connectivity unit includes a second plurality of memories, and the method includes storing routing information for channels of the data sent and received by optical interface units in the respective memories. 
     Further preferably, each of the second plurality of memories includes an upstream label memory adapted to store the routing information indicative of the client interface unit, included in the first plurality of units, to which upstream data included in the channels of the data is to be sent. 
     Preferably, the connectivity unit includes a memory comprising management software, and the method includes conveying the data between the client interface units and the optical interface units in data-units having a minimum size determined by the management software. 
     Further preferably, the method includes the management software inserting channel boundaries in the conveyed data and removing the channel boundaries after the data has been conveyed. 
     Preferably, the second plurality of optical interface units includes a first optical interface unit and a second optical interface unit, and the method includes conveying, via the connectivity unit, upstream data included in the data from the first optical interface unit as downstream data to the second interface unit, wherein the upstream and downstream data are included in an identical channel. 
     There is further provided, according to a preferred embodiment of the present invention, communications apparatus, including: 
     a first plurality of client interface units, adapted to be coupled to network service lines so as to send and receive data carried by the service lines in accordance with respective communication protocols, the client interface units including at least first and second client interface units that are adapted to communicate with respective first and second channels of the data operating in accordance with different, respective first and second protocols; 
     a second plurality of network interface units, adapted to be coupled to a data transfer network and to convey the data over the network; and 
     a connectivity unit, coupled to convey the data between the client interface units and the network interface units, while mapping the channels to the network interface units so that data from the first and second channels is carried in alternation by one of the network interface units to first and second users of the data transfer network communicating respectively in accordance with the first and second protocols. 
     There is further provided, according to a preferred embodiment of the present invention, a method for transferring data, including: 
     providing a first plurality of client interface units, adapted to be coupled to network service lines so as to send and receive the data carried by the service lines in accordance with respective communication protocols, the client interface units including at least first and second client interface units that are adapted to communicate with respective first and second channels of the data operating in accordance with different, respective first and second protocols; 
     providing a second plurality of network interface units, adapted to be coupled to a data transfer network and to convey the data over the network;
         coupling a connectivity unit between the client interface units and the network interface units so as to convey the data therebetween; and       

     mapping the channels to the network interface units so that data from the first and second channels is carried, via the connectivity unit, in alternation by one of the network interface units to first and second users of the data transfer network communicating respectively in accordance with the first and second protocols. 
     The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a layout of an optical distribution system, according to a preferred embodiment of the present invention; 
         FIG. 2  is a schematic diagram showing structure of a section of an optical line termination (OLT) in the system of  FIG. 1 , according to a preferred embodiment of the present invention; 
         FIG. 3  is a flowchart showing how data is transferred in an upstream direction from optical interface (OIF) cards in the OLT to client interface (CIF) cards in the OLT, according to a preferred embodiment of the present invention; 
         FIG. 4  is a flowchart showing how data is transferred in a downstream direction from CIF cards to OIF cards, according to a preferred embodiment of the present invention; and 
         FIG. 5  is a schematic block diagram illustrating elements of the optical distribution system of  FIG. 1  used for local routing of upstream data, according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to  FIG. 1 , which is a schematic diagram illustrating a layout of an optical distribution system  10 , according to a preferred embodiment of the present invention. System  10  comprises generally similar service lines  12 , each of the service lines being able to transfer data according to an industry-standard protocol. For example, a first service line  12  may comprise a coaxial cable adapted to transfer Ethernet data-frames at 10 Mbit/s or higher rates; a second service line  12  may comprise a twisted wire pair adapted to transfer data-frames at rates of the order of 1 Gbit/s; and a third service line  12  may comprise an optical fiber transmitting data-frames according to a Synchronous Optical Network (SONET) standard. Other types of lines and other methods for transferring data will be familiar to those skilled in the art; all such types and methods are considered to be within the scope of the present invention. 
     Service lines  12  are coupled to an optical line termination (OLT)  14  which is able to receive downstream data from service lines  12 , and which is able to transmit upstream data to the service lines. OLT  14  conveys downstream data received from service lines  12  to a passive optical network (PON)  16 , and conveys upstream data received from PON  16  to the service lines. The OLT acts as a central transmission point and an overall controlling device for system  10 . Data is conveyed between OLT  14  and PON  16  by one or more fiber optic lines using a plurality of discrete wavelength groups [λ 1 ], [λ 2 ], [λ 3 ], [λ 4 ], . . . . Each wavelength group comprises a first wavelength at which OLT  14  transmits the downstream data for the group and a second wavelength at which the OLT receives the upstream data for the group. Thus, data is transferred within PON  16  by a wavelength division multiplexed method. PON  16  is terminated at its downstream side by generally similar optical network terminations (ONTs)  18  acting as respective receiving end points, each ONT  18  operating at one of the wavelength groups. Each ONT  18  then distributes received data to one or more end users, each end user receiving the data according to one of the protocols transmitted by service line  12 . Each ONT  18  preferably also acts as a collection point for data transmitted upstream by respective end users of the ONT. 
     Most preferably, for each wavelength group, data transfers between OLT  14  and ONTs  18  by a dynamically varying time division multiplexed (TDM) method. A detailed description of such a method is given in U.S. patent application Ser. No. 10/016,584, which is assigned to the assignee of the present application and which is incorporated herein by reference. Alternatively, data for each wavelength group transfers between OLT  14  and ONTs  18  by another TDM method known in the art. 
     OLT  14  comprises a first plurality of generally similar client interface (CIF) units  20 , each unit being coupled to one or more service lines  12  via one or more ports. Typically, each port comprises a different physical connection. By way of example in system  10 , four service lines  12  are coupled by four ports to a first CIF unit  20 , two service lines  12  are coupled by two ports to a second CIF unit  20 , and one service line  12  is coupled to a third CIF unit  20 . It will be appreciated that each CIF unit  20  may be coupled to virtually any number of service lines. Each CIF unit  20  operates to transfer data between its respective service lines and OLT  14 , and is preferably implemented as a printed circuit card. It will be appreciated that each CIF unit  20  may be implemented by other means known in the art, such as one or more application specific integrated circuits. Hereinbelow, CIF units  20  are also referred to as CIF cards  20 . 
     OLT  14  also comprises a second plurality of generally similar optical interface (OIF) units  24 , each OIF unit  24  transferring data between OLT  14  and network  16  for one of the wavelength groups [λ 1 ] [λ 2 ], [λ 3 ], [λ 4 ], . . . . Preferably, each OIF unit  24  transfers its wavelength group to and from network  16  using one fiber optic. Alternatively, each OIF unit  24  transfers its wavelength group to and from network  16  using two separate fiber optics. As for the CIF units, each OIF unit  24  is preferably implemented as a printed circuit card, or alternatively by other means known in the art, such as one or more application specific integrated circuits. Hereinbelow, OIF units  24  are also referred to as OIF cards  24 . 
     Each CIF card  20  is implemented to operate in the industry-standard formats of the service lines to which the card is connected, examples of which are given above. Each CIF card  20  acts as a data buffer, both for upstream and downstream data. Each CIF card  20  also acts as a data transducer between its one or more service lines and the OLT. Similarly, each OIF card  24  acts as a data buffer for upstream and downstream data. Each OIF card  24  also acts as a transducer converting between optical and electronic signals. For upstream data flow each OIF card  24  functions as a first element in directing data for a specific channel upstream to one of CIF cards  20 , each CIF card  20  acting as a receiver of the upstream data before transmitting the data on its coupled service line(s)  12 . For downstream data flow, each CIF card  20  functions as a first element in directing data for a specific channel downstream to one of OIF cards  24 , each OIF card  24  acting as a receiver of the downstream data before transmitting the data on its respective downstream wavelength. Data is transferred between CIF cards  20  and OIF cards  24  via a connectivity unit  22  in OLT  14 . Connectivity unit  22  is preferably implemented as a printed circuit card. Alternatively, connectivity unit  22  may be implemented by any other means known in the art. Further details of the operation of CIF cards  20  and OIF cards  24  and of connectivity unit  22  are described below. OLT  14  most preferably comprises a main central processor (MCP)  26 , which acts as an overall controller for transfer of data between CIF cards  20  and OIF cards  24 . 
       FIG. 2  is a schematic diagram showing structure of a section of OLT  14 , according to a preferred embodiment of the present invention. For clarity, only one CIF card  20  and sets of elements used by the CIF card are shown in  FIG. 2 , and the one CIF card  20  is assumed to be coupled to one service line  12 . Similarly, only one OIF card  24  and sets of elements used by the OIF card are shown. It will be appreciated that OLT  14  comprises substantially similar sets of elements for each CIF card  20  and each OIF card  24  comprised in OLT  14 . Each CIF card  20  and each OIF card  24  is coupled to a bus  50  comprised in connectivity unit  22 . MCP  26  is also coupled to bus  50 . 
     For each CIF card  20  there is an upstream data memory (DM)  40  in unit  22 , DM  40  being sub-divided into zones  40 A,  40 B,  40 C, and  40 D which are dedicated to wavelength groups [λ 1 ], [λ 2 ], [λ 3 ], [λ 4 ] respectively. Unit  22  also comprises, for each CIF card  20 , an upstream channel memory (CM)  42 , a downstream DM  44 , a downstream label memory  60 , and a downstream CM  46 . Upstream CM  42  is sub-divided into zones  42 A,  42 B,  42 C, and  42 D, and downstream CM  46  is sub-divided into zones  46 A,  46 B,  46 C, and  46 D, the zones corresponding to the wavelength groups [λ 1 ], [λ 2 ], [λ 3 ], [λ 4 ] respectively. Each CIF card  20  comprises an upstream first-in first-out (FIFO) memory  69  for upstream data storage, and upstream serializer-deserializer (SERDES) logic  65  for transferring the data. Each CIF card  20  also comprises a downstream FIFO memory  68  and downstream SERDES logic  64  for transferring downstream data. Unit  22  comprises an upstream SERDES logic  63  and a downstream SERDES logic  62  for each CIF card  20 . Each SERDES logic  63  communicates with its corresponding SERDES logic  65 , and each SERDES logic  64  communicates with its corresponding SERDES logic  62 . 
     For each OIF card  24  there is an upstream label memory  54  in unit  22 . Unit  22  also comprises an upstream SERDES logic  76  and a downstream SERDES logic  77  for each OIF card  24 . Each OIF card  24  comprises an upstream FIFO memory  74  and upstream SERDES logic  72 . Each OIF card  24  also comprises a downstream FIFO memory  75  and downstream SERDES logic  73 . Each SERDES logic  72  communicates with its corresponding SERDES logic  76 , and each SERDES logic  77  communicates with its corresponding SERDES logic  73 . 
     It will be appreciated that methods, other than methods using SERDES logic units described herein, may be used for transferring data. For example, data may be transferred substantially directly, with no translation between serial and parallel and vice versa. All such methods are considered to be comprised within the scope of the present invention. 
     OLT  14  uses its CIF cards  20 , OIF cards  24 , and connectivity unit  22  to route channels between any service line  12  and any OIF card  24 , i.e., any wavelength group. The routing of each channel is implemented according to a service level agreement between a provider of data of the channel and an operator of system  10 , when the channel is initially set up for transmission within the system. The routing may be changed by the operator at a later time. The operator stores the routing in each upstream label memory  54  and each downstream label memory  60 , using management software  58  comprised in a memory  59  of connectivity unit  22 . The stored routing enables any channel to be routed between any CIF card  20  and any OIF card  24 . 
       FIG. 3  is a flowchart showing how data is transferred in an upstream direction from OIF cards  24  to CIF cards  20 , according to a preferred embodiment of the present invention. In an initial step  100  the operator of system  10  sets up a routing for each channel using software  58 , so that MCP  26  will be aware of which CIF card  20  and which OIF card  24  is to be used for each channel. For each OIF card  24  the routing is entered into respective upstream label memory  54 , which stores a label for each channel transmitted by the wavelength group of the card, and a mapping between the channels and their CIF card  20   s . The label is attached to data of a specific channel when data for that channel is transmitted (from downstream ONTs  18 ), and is used as an identifier of the channel. Also, labels for each channel transmitted by each CIF card  20  are stored in respective memories  30  of the cards. 
     In a second step  102 , upstream data arriving at each OIF card  24  is entered into the respective upstream FIFO memory  74  for the card. The upstream data is identified by channel according to the label attached to the data. The upstream data is then transferred out of each memory  74  by respective SERDES logic  72  in card  24 , via the corresponding SERDES logic  76 , to bus  50 , boundaries being inserted between channels. 
     In a third step  104 , connectivity unit  22  reads the transferred upstream data from each OIF card  24  and writes the data to its mapped CIF card, according to the label on the data and according to the mapping that was stored in each respective label memory  54 . The data is written into the appropriate section of each CIF upstream data memory  40 , e.g., for data read from OIF card  24  corresponding to wavelength group [λ 2 ], the data is written into zone  40 B of memory  40  of the specific CIF card  20  determined by label memory  54 . Unit  22  reads the data from each OIF card  24  in units having a predetermined minimum size, preferably four bytes, the size being set by software  58 , although software  58  may be used to set any other convenient unit size. 
     Substantially in parallel with writing into each data memory  40 , connectivity unit  22  writes start and end addresses for the data into the appropriate zone in each channel memory  42 . Thus, for the example described above, start and end addresses in data memory  40  are written into zone  42 B. 
     In a fourth step  106 , unit  22  reads data sequentially from data memory  40  for a specific CIF card  20 , until all data memory  40  is cleared. 
     In a fifth step  108 , data read from the specific data memory  40  is sent to the corresponding CIF card  20 , using SERDES logic  63  to convert the data to a serial form and then transfer the data. Boundaries between the channels read from data memory  40  are inserted into the serial data, and the channel data is also sent with its corresponding channel label. 
     In a final step  110 , each CIF card  20  receives its serial data. The data is converted in SERDES logic  65 , the channel boundaries are removed, and labels are recovered from the converted parallel data. Each recovered channel label is compared with labels stored in a memory  30  of the specific CIF card  20 , and when the labels correspond, the data is written, according to channel, into the upstream FIFO memory  69  comprised in the card. 
       FIG. 4  is a flowchart showing how data is transferred in a downstream direction from CIF cards  20  to OIF cards  24 , according to a preferred embodiment of the present invention. In an initial step  120 , downstream routing and a label for each channel transmitted via each CIF card  20  is stored in downstream label memory  60  of the respective card, using software  58 . The routing stored in each memory  60  indicates the OIF card  24  to which each channel from the CIF card is to be sent. Software  58  also provides the labels to each respective CIF card  20 . 
     In a second step  122 , downstream data arriving at each CIF card  20  is entered into the respective downstream FIFO  68  for the card. A label, chosen from those provided by software  58  to the specific CIF card  20 , is attached to each channel of the downstream data. The downstream data is then transferred out of each memory  68  by the respective SERDES logic  64  in card  20 , via SERDES logic  62 , to bus  50 . 
     In a third step  124 , unit  22  writes the transferred data to the respective downstream data memory  44  of the CIF card. Substantially as the downstream data is written, unit  22  writes start and end addresses of each channel into one of zones  46 A,  46 B,  46 C, or  46 D of downstream channel memory  46 . The zone is determined from label memory  60 . 
     In a fourth step  126 , data for a specific OIF card  24  is read from the appropriate zone of each data memory  44  of each CIF card  20  until all data for the zone has been read. The data is then placed on bus  50 , for subsequent transfer to the OIF card  24  corresponding to the zone. 
     In a final step  128 , downstream data directed to a specific OIF card  24  is transferred from bus  50  via the respective SERDES logics  76 , and the SERDES logic  72  of the OIF card. Channel boundaries are introduced and removed by the SERDES logics, substantially as described above for step  110 . 
     It will be appreciated that initial steps  100  and  120 , for the flowcharts of  FIGS. 3 and 4 , may be performed at substantially any time during operation of system  10 , for example, in the case of the system operator needing to update routing of one or more channels, introduce new channels to the system, or delete existing channels from the system. It will further be appreciated that downstream data from a particular CIF card  20  may be multicast to more than one OIF card  24 , by the system operator making appropriate entries in channel memory  46  and/or label memory  60 . 
     It will be understood that system  10  enables a data channel to be transferred between any CIF card  20  supporting the protocol of the data channel and any OIF card  24  and its corresponding wavelength group. Since the OIF card may be chosen independent of the protocol of the data channel, system  10  enables implementation of highly flexible channel allocation over the wavelength groups of the system, and thus enables efficient use of wavelength group bandwidth. 
       FIG. 5  is a schematic block diagram illustrating elements of system  10  used for local routing of upstream data, according to a preferred embodiment of the present invention.  FIG. 5  is generally similar to  FIG. 2 , but for clarity, elements not involved in locally routing upstream data are not shown in FIG.  5 . In addition to transferring upstream and downstream data as described above with respect to  FIGS. 3 and 4 , system  10  enables one or more upstream data channels from a first OIF card  24 , herein termed OIF card  24 A, to be locally routed as respective downstream data channels to a second OIF card  24 , herein termed OIF card  24 B. The local routing may be performed as well as, or in place of, routing to a specific CIF card  20 , herein termed CIF card  20 M. In the following description, suffixes A, B, and M are appended to identifiers of elements associated respectively with card  24 A, card  24 B, and card  20 M. 
     To transfer an upstream channel of data from OIF card  24 A to become a downstream channel into OIF card  24 B, software  58  sets upstream label memory  54 A for card  24 A to store the upstream channel data in downstream data memory  44 M for CIF card  20 M. Data is written into memory  44 M using channel memory  46 M. The data is then written, using management software  58 , from memory  44 M into FIFO  75 B via SERDES logics  77 B and  73 B, substantially as described above in steps  126  and  128  with reference to FIG.  4 . OIF card  24 B is then able to transmit the data from FIFO  75 B as downstream data, substantially as described above with reference to FIG.  2 . It will be appreciated that in order for the data to be written into FIFO  75 B, software  58  requires read access to data memory  44 M. The read access may be provided by any means known in the art. 
     It will be understood that by enabling local routing of upstream data to downstream data, ONTs  18  in system  10  may be effectively configured in the form of virtual local area networks (VLANs), the configuration of the VLANs being controlled by the local routing set by software  58 . 
     It will be further understood that preferred embodiments of the present invention may be implemented in a data transfer network other than a passive optical network such as PON  16 , such as data transfer networks which are implemented at least partly using a transmission medium such as conductive cabling, and/or transmission over-the-air. All such data networks are included within the scope of the present invention. 
     It will be appreciated that the preferred embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.