Abstract:
A small form-factor transceiver module performs protocol translation, in addition to the conventional electrical and/or optical transmission media conversion. Such protocol conversion may enable transport of traffic from limited-range primary networks over long-range secondary networks, such as extension of Ethernet networks over low-rate TDM links. Additionally, such protocol conversion may enable interworking between different networks of differing technologies, such as transport of ATM traffic over Ethernet networks. The transceiver module may be a Small Form Factor transceiver (SFF), Small Form Factor pluggable module (SFP), Gigabit Interface Converter (GBIC) or any similar small form-factor module consisting of a housing, internal electronic circuitry and optionally optical components, and associated electrical or optical connectors. The transceiver module performs protocol translation by means of an integral protocol translation unit that performs standards-based or proprietary conversion between network protocols.

Description:
RELATED APPLICATIONS  
       [0001]     None  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the field of digital communications networks such as Ethernet, ATM, SONET/SDH, IP, MPLS, and low-rate TDM networks, in particular to the facilitating of interconnection of such networks. More specifically, the invention consists of a small form-factor device that enables standards-based or proprietary interworking between different network types, such as the transport of Ethernet frames, IP packets or ATM cells over TDM links, or the transport of ATM or TDM traffic over Ethernet, IP or MPLS networks.  
       BACKGROUND OF THE INVENTION  
       [0003]     With the explosive increase in data rates of backbone networks, edge switches need to feed increasing numbers of tributary networks, and hence need more and more ports. For example, 10 Mbit/s Ethernet hubs commonly had only 4 or 8 ports, while Gigabit Ethernet (GbE—IEEE 802.3z) switches often have 48 or 60 ports. For this reason the physical interfaces, including electrical and/or optical circuitry and connectors, need to be miniaturized.  
         [0004]     Small form-factor modules have become extremely popular interface devices due to their small physical dimensions and low power consumption. Several such modules types have been standardized by the industry, including Small Form Factor (SFF), Small Form Factor Pluggable (SFP), and Gigabit Interface Converter (GBIC) modules. These all consist of a housing, internal electronic circuitry and optionally optical components, along with associated electrical or optical connectors.  
         [0005]     In addition to not requiring additional shelf space, such transceiver modules have the additional advantage of having very low power consumption, and of obtaining their power from the switch to which they connect. This alleviates power delivery wiring complications.  
         [0006]     When such modules are used to provide bidirectional interconnection between different  5  network technologies, they are called transceiver modules. Electrical transceiver modules interconnect two electrical networks, while when one of the network is based on fiber-optics the converter is usually called an electro-optical transceiver module.  
         [0007]     SFF and SFP modules are finger-sized (about half the width of the earlier GBIC technology modules), and conform to an industry Multi-Source Agreement (MSA). The physical size of SFF/SFP modules facilitates maximal port density consistent with conventional connectors. The difference between the SFF and SFP lies in the SFF being permanently connected to the switch, while the SFP is a pluggable, hot-swappable, interface that may be replaced or exchanged as required.  
         [0008]     The SFF and SFP devices that have been widely deployed allow interconnection of a high-rate primary network (e.g. Gigabit Ethernet) with a secondary network or link of the same or lower rate (e.g. 100 Mbit/s Ethernet). The SFF or SFP is located in a switch at the edge of the primary network, and its electrical or optical connector feeds the secondary network or link. Large numbers of tributaries may be connected to a high-rate network by densely packing SFF or SFP modules on the switch front panel. Each SFF or SFP module performs physical layer format conversion, converting between the electrical format of the primary network and the electrical or optical format of the secondary networks or links.  
         [0009]     Small form-factor devices may be found on Ethernet switches, IP or MPLS routers, ATM switches, and SONET/SDH devices such as add and drop multiplexers (ADMs). As such the lower layers of the primary network may consist of Ethernet, ATM or Optical networks such as OC-3 (155 Mbit/s)/OC-12(622 Mbit/s). Similarly, the lower layers of the secondary network or link are typically TDM, Ethernet or ATM.  
         [0010]     Ethernet networks, having been originally designed as Local Area Networks (LANs), are severely limited in physical extent. Traditional Ethernet was limited to 100-meter spans, and while later extensions, such as Ethernet in the First Mile (EFM), have increased this limit, Ethernet is still most frequently used as a LAN technology, with other technologies providing the wide area network (WAN) components.  
         [0011]     When Ethernet LANs are physically remote from each other they can be interconnected by transporting Ethernet frames over long-range transport technologies, such as TDM networks. For example, to support high data rates, Ethernet frames may be carried over SONET/SDH infrastructure by using the Generic Framing Procedure (GFP—ITU-T Recommendation G.7041/Y.1303), and greater flexibility and bandwidth efficiency is attained when augmenting this approach with Virtual Concatenation (VC—ITU-T Recommendation G.707). In addition, Ethernet frames may be carried over SONET/SDH links using the Packet Over SONET (POS) encapsulation, specified in IETF RF 2615.  
         [0012]     When lower data rates are sufficient for the traffic to be transported, Ethernet frames may be transported over T 1  (1.544 Mbit/s), E 1  (2.048 Mbit/s), T 3  (44.736 Mbit/s) or E 3  (34.368 Mbit/s) links. This can be accomplished by encoding the Ethernet frames using the High-level Datalink Control Protocol (HDLC—ISO/IEC 3309, IETF RFC 1662), Ethernet over Link Access Protocol—SDH (LAPS—ITU-T Recommendation X.86/Y.1323), or GFP. Despite its name, X.86/Y.1323 is directly applicable as it describes the mapping of an Ethernet frame into a continuous stream of octets, but does not describe the mapping of this bit-stream into SDH. Recent ITU-T Recommendation G.7043/Y.1343 describes the virtual concatenation of low-rate TDM signals and G.8040/Y.1340 describes the mapping of GFP frames into such virtually concatenated TDM signals.  
         [0013]     The present invention addresses this need, and specifies small form-factor modules that enable transport of Ethernet frames over low-rate TDM links where it would be difficult or expensive to do so by conventional means.  
         [0014]      FIG. 1  illustrates physical configuration of the small form-factor transceiver module  100 . The module consists of a housing  101 , an internal connector  102  for connection to the primary network, a printed circuit board (PCB)  103  containing all the required protocol and transmission medium conversion circuitry, and an external connector  104  for connection to the secondary network or link.  
         [0015]      FIG. 2  depicts a simplified block diagram of the small form-factor transceiver module  200  for transport of Ethernet traffic over a TDM link. The main blocks are the internal connector  202 , and external connector  203 , the Ethernet PHY  210  with its crystal oscillator  211 , the protocol translation logic  220 , the TDM PHY  230  with its TDM crystal oscillator  231  and TDM protection circuitry. The internal connector  202  connects to the primary Ethernet network, while the external connector  203  connects to the secondary TDM network or link.  
         [0016]      FIG. 3   a  illustrates protocol translation for the case of packet- or frame-based traffic transported by a serial protocol link, such as TDM. When there are no packets the serial oriented protocol consists of idle indicator  301 . When a data packet arrives, the protocol translator outputs a start flag  302  followed by the content of the data packet  303 . This content may first be adapted for example by, removing un-needed headers or replacing occurrences of data patterns that may be mis-interpreted as idle indicators with another data pattern.  
         [0017]     The scope of the applicability of the present invention is not limited to transport of Ethernet frames over low-rate TDM links. One versed in the art will readily appreciate that this invention can be extended to any limited-range network over any link or network with the desired physical range. Indeed it is not even required for the primary packet-oriented network to be extended over the secondary serial/TDM link; rather it may be the case that the TDM link is required to be extended over the primary packet-oriented network.  
         [0018]      FIG. 3   b  illustrates the protocol translation for the case wherein serial traffic such as TDM  310  is to be transported by a packet or frame oriented protocol. The TDM bit stream is first segmented and then the resulting segments  312  are encapsulated by prepending packet headers  311 . The TDM segments  312  may first be adapted in order to aid in recovery of the source TDM clock frequency, and to help conceal the effects of packet loss.  
         [0019]     Protocol translation is useful in contexts other than extension of limited-range networks. For historical reasons a large number of different data communications technologies presently exist and are widely deployed. Technology disparities limit a user&#39;s choice of transport means and present barriers to communications between users served by network of dissimilar technologies.  
         [0020]     In order to overcome these two constraints, two generic forms of “interworking”, that is interconnection between networks of disparate technologies, have been developed. Network interworking (also known as client-server interworking) enables tunneling of traffic of one technology through a transport network of a second technology. When the transport network is packet-switched network, this can be accomplished by encapsulating the entire protocol content of the first network (payload data and protocol overhead) in packets of the second network. At the other end of the transport network the packet is decapsulated, revealing the original protocol content. When such a tunnel is so used to emulate a native technology it is often called a pseudowire (PW), since from the points of view of the end-users the tunnel seems to be a bare wire.  
         [0021]     Service interworking (also known as peer-to-peer interworking) enables interchange of data between end networks of disparate technologies. In such cases the first network protocol is terminated, that is the protocol overhead removed and the payload data then encapsulated in packets of the second network protocol by adding new protocol overhead.  
         [0022]      FIG. 3   c  illustrates network interworking (client-server interworking) between two packet-oriented protocols. The entire packet of the client protocol, consisting of the packet headers  312  and payload  322 , becomes the payload  324  for the server protocol that encapsulates it by adding its own packet headers  323 .  
         [0023]      FIG. 3   d  illustrates service interworking (peer-peer interworking) between two packet oriented protocols. The packet headers  325  of one protocol are replaced by those of second protocol  327 , while the payload  326  is carried intact.  
         [0024]     Both network interworking and service interworking can be implemented by appropriate protocol translation logic in a small form-factor module. Service interworking entails a small form-factor module with protocol translation unit that terminates the secondary network protocol and transfers the payload data to the format of the primary network protocol, and vice versa.  
         [0025]     Network interworking can be realized by two network elements, such as Ethernet or ATM switches, on the same primary network. Each of these network elements contains small form-factor modules that interface to the same secondary protocol. The small form-factor modules encapsulate the entire protocol content of the secondary networks and enable tunneling of this content across the primary network infrastructure.  
         [0026]     A number of pseudowire protocols have been standardized by the IETF and ITU-T. For instance, the ITU-T has standardized tunneling over MPLS networks of ATM (Y.1411 and Y.1412), of frame-relay (X.84), of low-rate TDM (Y.1413), and of Ethernet (Y.1415).  
         [0027]     The scope of the applicability of the present invention is not limited to transport of ATM, frame-relay, low-rate TDM and Ethernet over MPLS networks. One versed in the art could readily extend this invention to the transport over Ethernet, IP, ATM or SDH primary networks, and to the transport of other protocols over MPLS or these aforementioned networks.  
         [0028]     As will subsequently become apparent, the essential defining feature of the present invention is the capability of performing protocol format translation in a small form-factor module.  
         [0029]     U.S. Pat. No. 6,179,627 to Daly et al. describes a small form-factor pluggable high-speed interface converter module for converting data signals from a first transmission medium to a second transmission medium. It teaches the physical and electrical aspects of such a device, including details of the housing, connectors, releasable latch, and guide tabs. It further teaches how to prevent spurious electromagnetic emissions by appropriate shielding. However, Daly et al does not teach the use of such interface modules for low-rate TDM links, rather they specifically limit the scope of their invention to high rate networks, such as GbE. Furthermore, Daly et al does not teach protocol translation in such a device.  
         [0030]     U.S. Pat. No. 6,731,510 to Hwang et al. describes a small form-factor pluggable with an RJ connector. It teaches the provision of an RJ connector for use with an SFP module, and the use of a reinforced structure that strengthens the connection between said RJ connector and the rest of the SFP module. As RJ connectors are frequently used for low-rate TDM (as well as 10BaseT Ethernet), this invention would be complementary to an invention enabling the interconnection of low-rate TDM with high-rate networks via SFP modules. However, Hwang et al is silent as to the use of the RJ connector it proposes, and in particular does not specify its use for low-rate TDM. Furthermore, Hwang et al does not teach protocol translation in such a device.  
         [0031]     U.S. Pat. Nos. 6,705,879 to Engel et al. describes a small form-factor transceiver module that may be plugged into a switch or other network device. The transceiver consists of transceiver electronics implemented on a printed circuit board sized to fit within the switch port cage, and an RJ connector that extends outside of the port cage. Engel et al teaches the implementation of a small form-factor transceiver for interconnection of networks using electronic and magnetic circuitry. However, Engel et al does not teach the use of such transceiver modules for low-rate TDM links. Furthermore, Engel et al does not teach protocol translation in such a device.  
         [0032]     Whatever the precise merits, features and advantages of the above inventions, they do not achieve or fulfill the purposes of the present invention.  
       SUMMARY OF THE INVENTION  
       [0033]     The present invention is a small form-factor transceiver module that provides protocol translation in addition to conventional conversion between electrical and/or optical transmission media. Such protocol conversion may enable transport of traffic from limited-range primary networks over long-range secondary networks, such as extension of Ethernet networks over low-rate TDM links. Additionally, such protocol conversion may enable network and service interworking between different networks of differing technologies, such as transport of ATM or frame-relay traffic over MPLS networks.  
         [0034]     The small form-factor transceiver module consists of a housing, internal electronic circuitry and optionally optical components, along with associated electrical or optical connectors, and will usually conform to industry standards, e.g. SFF, SFP or GBIC modules. The protocol translation may be standards-based or proprietary.  
         [0035]     In particular, the present invention enables transport of Ethernet frames over n*64K serial links, T 1 , E 1 , fractional T 1 , fractional E 1 , T 3 , E 3 , and 155/622 Mbit/s SONET/SDH or ATM links; the transport of TDM over Ethernet, IP, MPLS and ATM networks; and ATM or frame-relay over Ethernet or MPLS networks. Furthermore, the present invention enables transport of Ethernet over MPLS networks and supports the building of Virtual Private LAN Services.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]      FIG. 1  illustrates physical configuration of the small form-factor transceiver module implementing protocol translation.  
         [0037]      FIG. 2  depicts a simplified block diagram of the transceiver module for the first embodiment wherein Ethernet traffic is transported over a TDM link.  
         [0038]      FIG. 3   a  illustrates protocol translation for the case of packet- or frame-based traffic transported by a serial protocol link, such as TDM.  
         [0039]      FIG. 3   b  illustrates the protocol translation for the opposite case, wherein serial traffic such as TDM is to be transported by a packet or frame oriented protocol.  
         [0040]      FIG. 3   c  illustrates network interworking (client-server interworking) between two packet-oriented protocols.  
         [0041]      FIG. 3   d  illustrates service interworking (peer-peer interworking) between two packet oriented protocols.  
         [0042]      FIG. 4   a  depicts the use of a small form-factor module with protocol translation to extend Ethernet over a TDM link.  
         [0043]      FIG. 4   b  depicts the use of a small form-factor module with protocol translation to transport TDM over an Ethernet network.  
         [0044]      FIG. 4   c  depicts the use of a small form-factor module with protocol translation for the transport of ATM over an MPLS network (ATM pseudowire).  
         [0045]      FIG. 4   d  depicts the use of a small form-factor module with protocol translation for the transport of Ethernet over a TDM network.  
         [0046]      FIG. 4   e  depicts the use of a small form-factor module with protocol translation for transport of Ethernet over an ATM network (service interworking).  
         [0047]      FIG. 4   f  depicts the use of a small form-factor module with protocol translation for transport of TDM over an ATM network.  
         [0048]      FIG. 4   g  depicts the use of a small form-factor module with protocol translation for transport of Ethernet over an MPLS network (Ethernet pseudowire).  
         [0049]      FIG. 4   h  depicts a Virtual Private LAN Service (VPLS) supported by small form-factor modules.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0050]     As has been previous stated, the invention may be instantiated in any small form-factor module, such as SFF, SFP, GBIC, etc. The high-rate network will usually be Ethernet at 100 Mbit/s or 1 Gbit/s, SONET/SDH at 155 or 622, or ATM at these same rates, but may be at other rates or may consist of any high-rate packet-oriented or frame-oriented network. The low-rate TDM link will usually be T 1 , E 1 , T 3  or E 3 , but may be any synchronous serial digital network of appropriate rate.  
         [0051]     In a first embodiment Ethernet frames are transported for long distances over a TDM link or network. A small form-factor transceiver module is connected to a suitable port of a standard Ethernet (such as 10 Mbit/s, 100 Mbit/s, or 1 Gbit/s Ethernet) switch connected to a first Ethernet network. Inside the small form-factor module the Ethernet frames are encoded using HDLC, Ethernet over LAPS, or GFP into a framed or unframed T 1  or E 1  bit-stream. This bit-stream is then encoded using an appropriate line code (e.g. AMI, B8ZS, HDB3) to produce a TDM physical layer signal that is applied to twisted-pair or coaxial cable via an appropriate connector on the exposed side of the small form-factor module. The twisted-pair or coaxial cable connected to the connector on the small form-factor module forms the secondary link. This cable may run for a long distance (e.g. 3000 feet for AMI) and may be extended further by employing repeaters or DSL modems. At its other end, the cable connects to a second small form-factor transceiver module is connected to a switch connected to a second Ethernet network. By exploiting standard Ethernet switch functionality, the two Ethernet networks have been interconnected, subject only to the bandwidth restriction imposed by the secondary low-rate TDM link.  
         [0052]      FIG. 4   a  depicts the use of a small form-factor module with protocol translation to extend Ethernet over a TDM link. A first Ethernet switch  402  is connected to a first Ethernet network  401 . A small form factor module  403  in Ethernet switch  402  interconnects Ethernet network  401  and TDM link  404 . At the far end of TDM link  404  a second small form-factor module  406  in Ethernet switch  405  interconnects the TDM link  404  with a second Ethernet network  407 .  
         [0053]     In a variation of this embodiment, the T 1  or E 1  signals may themselves be transported using higher rate PDH or SONET/SDH infrastructures, thus eliminating all distance restrictions without need for T 1 /E 1  repeaters. In this case the PDH or SONET/SDH networks function as a secondary network, enabling interconnection of two primary Ethernet networks. By exploiting the Public Switched Telephony Network (PSTN) the two Ethernet networks being connected may then be located anywhere in the world.  
         [0054]     In yet another variation of the first embodiment, the first and second small form-factor modules may be equipped with coaxial cable connectors, and encode the Ethernet frames over unframed T 3  or E 3  digital signals. This enables utilization of the larger data-rates supported by these PDH signals.  
         [0055]     In yet another variation of the first embodiment, the small form-factor modules may be electro-optical transceivers. They then have fiber-optic connectors (e.g. LC, ST, SC or FC-type) and connect to fiber-optic cables. This can potentially significantly extend the range of the low-rate TDM, e.g. to 100 km.  
         [0056]     In a second embodiment T 1  or E 1  TDM traffic is transported across an Ethernet network, which may additionally have IP or MPLS higher layers. A first small form-factor transceiver module is plugged into a suitable port of a first Ethernet switch connected to a primary Ethernet network, and a second small form-factor transceiver module is plugged into a suitable port of a second Ethernet switch Ethernet switch connected to the same primary Ethernet network. The small form-factor modules are equipped with RJ or BNC connectors to which T 1  or E 1  TDM signals are applied. Accordingly, both small form-factor modules encapsulate TDM signals into Ethernet frames, e.g. according to ITU-T Recommendation Y.1413 for MPLS, or according to one of the IETF methods Structure Agnostic TDM over Packet (SAToP), TDM over IP (TDMoIP) or Circuit Emulation Service over Packet Switched Network (CESoPSN) for UDP/IP, or according to Metro Ethernet Forum (MEF) Implementation Agreement  8  for raw layer  2  Ethernet. Similarly, both small form-factor modules decapsulate Ethernet frames and reconstitute TDM signals according to the aforementioned standards. In this fashion T 1  or E 1  TDM traffic may be transported over an Ethernet, IP or MPLS packet switched network.  
         [0057]      FIG. 4b  depicts the use of a small form-factor module with protocol translation to transport TDM over an Ethernet network. A first small form-factor module  413  in Ethernet switch  412  is connected to a first TDM link  414 . At the other end of the primary Ethernet network  411  is a second Ethernet switch  415  in which is a second small form factor module  416  feeding a second TDM link  417 .  
         [0058]     In a variation of the second embodiment, the TDM signals may be T 3  or E 3  signals PDH signals applied to BNC connectors on the small form-factor modules. These modules encapsulate and decapsulate the PDH signals using the aforementioned standards in order to enable their transport over a packet switched network.  
         [0059]     In yet another variation of the second embodiment, the TDM signals may be SONET/SDH signals applied to fiber-optic connectors on the small form-factor modules. These modules encapsulate and decapsulate the SONET/SDH signals according to Circuit Emulation over Packet (CEP), as defined by the IETF.  
         [0060]     In a third embodiment ATM traffic is transported across an MPLS network. A first small form-factor transceiver module is plugged into a suitable port of a first MPLS Label Switched Router (LSR) connected to an MPLS network, and a second small form-factor transceiver module is plugged into a suitable port of a second LSR connected to the same MPLS network. Both small form-factor modules receive ATM traffic in any of the physical formats in which ATM may be delivered (including fiber-optic, copper, or ATM carried over TDM links). The ATM cells are extracted from whatever physical layer over which they are provided, and encapsulated according to either of ITU-T Recommendations Y.1411 or Y.1412 or similar ATM pseudowire specifications for tunneling across the MPLS network.  
         [0061]      FIG. 4   c  depicts the use of a small form-factor module with protocol translation for the transport of ATM over an MPLS network (ATM pseudowire). A first small form-factor module  423  in a first MPLS Label Switched Router (LSR)  422  encapsulates ATM cells from a first ATM link  424  and tunnels them across MPLS network  412 . At a second LSR  425  a second small form-factor module  426  decapsulates the MPLS packet, retrieving ATM cells that are sent to a second ATM link  427 .  
         [0062]     In a variation of the third embodiment, instead of ATM links we may have frame-relay ones. The frames are then extracted from whatever physical layer over which they are provided, and encapsulated according to ITU-T Recommendations X.84 or similar frame-relay pseudowire specifications for tunneling across the MPLS network.  
         [0063]     In a fourth embodiment Ethernet frames are transported for long distances over a TDM network, as in the first embodiment, only here the TDM network is the primary network and the Ethernet is the secondary link. A first small form-factor transceiver module is connected to a tributary port of a first TDM add and drop multiplexer (ADM), and a second small form-factor transceiver module is connected to a tributary port of a second ADM on the same TDM network. The modules have either RJ or fiber-optic (LC, ST, SC or FC-type) external connectors for connection of Ethernet (e.g. 10 Mbps or 100 Mbps Ethernet) cables. The protocol conversion may be as in the first embodiment into a T 1  or E 1  bit stream that may then be placed in a suitable virtual container for transport over SONET/SDH, or may be using Ethernet over SONET (EoS) according to ITU-T Recommendation X.86/Y.1323. In this fashion two Ethernet local area networks (LANs) may be connected over the TDM network.  
         [0064]      FIG. 4   d  depicts the use of a small form-factor module with protocol translation for the transport of Ethernet over a TDM network. A first small form-factor module  433  in a first TDM device, e.g. a SONET/SDH Add and Drop Multiplexer (ADM)  432  receives Ethernet frames from a first Ethernet link  434  and forwards them across TDM network  431 . At a second ADM  435  a second small form-factor module  436 , retrieves Ethernet frames that are sent to a second Ethernet link  437 .  
         [0065]     In a fifth embodiment Ethernet frames are transported for long distances over an ATM network. A first small form-factor transceiver module is connected to a port of a first ATM switch, and a second small form-factor transceiver module is connected to a port of a second ATM switch. The modules have either RJ or fiber-optic (LC, ST, SC or FC-type) external connectors for connection of a 10 Mbit/s, 100 Mbit/s, or Gbit/s Ethernet cables. The protocol conversion is according to ATM Adaptation Layer Type 5 (AAL5) as described in ITU-T Recommendation I.363.5. This embodiment will probably be constrained in some way due to memory requirements of such an implementation.  
         [0066]      FIG. 4   e  depicts the use of a small form-factor module with protocol translation for transport of Ethernet over an ATM network (service interworking). A first small form-factor module  443  in a first ATM switch  442  receives Ethernet frames from a first Ethernet link  444 , terminates the Ethernet layer, uses AAL type 5 to adapts the payload into ATM cells that are forwarded across ATM network  441 . At a second ATM switch  445  a second small form-factor module  446  terminates the ATM layer and reconstitutes Ethernet frames that are sent to a second Ethernet link  447 .  
         [0067]     In a sixth embodiment TDM traffic is carried over an ATM network. A first small form-factor transceiver module is connected to a port of a first ATM switch, and a second small form-factor transceiver module is connected to a port of a second ATM switch. The modules have either RJ or BNC external connectors for connection of T 1 , E 1 , T 3  or E 3  TDM signals. The protocol conversion may be according to ATM Adaptation Layer Type 1 (AAL1) as described in ITU-T Recommendation I.363.1. For channelized T 1  or E 1  the protocol conversion may alternatively be according to ATM Adaptation Layer Type 2 (AAL2) as described in ITU-T Recommendation 1.363.2.  
         [0068]      FIG. 4   f  depicts the use of a small form-factor module with protocol translation for transport of TDM over an ATM network. A first small form-factor module  453  in a first ATM switch  452  receives a TDM bit-stream from a first TDM link  454 , uses AAL type 1 or 2 to adapts the payload into ATM cells that are forwarded across ATM network  451 . At a second ATM switch  455  a second small form-factor module  456  terminates the ATM layer and reconstitutes the TDM bit-stream that is sent to a second TDM link  457 .  
         [0069]     In a seventh embodiment, Ethernet traffic is transported across an MPLS network. A first small form-factor transceiver module is plugged into a suitable port of a first MPLS Label Switched Router (LSR) connected to an MPLS network, and a second small form-factor transceiver module is plugged into a suitable port of a second LSR connected to the same MPLS network. Both small form-factor receive Ethernet traffic in any of the physical formats in which Ethernet may be delivered (including 10 Mbit/s, 100 Mbit/s, 1 Gbit/s, fiber-optic or copper links). The Ethernet frames are extracted from whatever physical layer over which they are provided, and encapsulated according to ITU-T Recommendation Y.1415 or similar Ethernet pseudowire specifications for tunneling across the MPLS network.  
         [0070]      FIG. 4   g  depicts the use of a small form-factor module with protocol translation for transport of Ethernet over an MPLS network (Ethernet pseudowire). A first small form-factor module  463  in a first MPLS LSR  462  encapsulates Ethernet frames from a first Ethernet link  464  and tunnels them across MPLS network  462 . At a second LSR  465  a second small form-factor module  466  decapsulates the MPLS packet, retrieving Ethernet frames that are sent to a second Ethernet link  467 .  
         [0071]     In a variation of the seventh embodiment, multiple LSRs on the same MPLS network all feed small form-factor modules of the type described. By adding bridging functionality at each LSR, a Virtual Private Network (VPN) implementing Virtual Private LAN Service (VPLS) may be formed.  
         [0072]      FIG. 4h  depicts a Virtual Private LAN Service (VPLS) supported by small form-factor modules that interconnect Ethernet links  472 ,  473 ,  474 , and  475  through the use of MPLS network  471 .  
         [0073]     It will be clear to those versed in the art that other embodiments consisting of different input and/or output formats are possible, and that the embodiments herein specified are only for exemplification of the principles involved and are not intended to limit the scope of the invention to the specific embodiments given.