Abstract:
An interface for a networking device. A network interface module existing within a networking device monitors certain contacts of a network connection to identify a protocol of the networking system to which it is connected. Based on the detected protocol, the network interface module selects a set of configuration information with which to configure the networking device.

Description:
BACKGROUND 
   (1) Field of the Invention 
   The invention relates to networking. More specifically, the invention relates to coordination of networking protocols between two networking devices. 
   (2) Background 
   Certain communication protocols have been popularized in existing networking systems. In North America, the predominant protocol is T1 which transmits information at 1.544 megabits per second. T1 typically carries DS1 frames which are composed of 24 bytes plus a framing bit in a 125 microsecond frame. T1 provides twenty-four data channels as a trunk interface. The information is contained in the timing of the signals and not their polarity. A T1 transmission uses a bipolar return to zero alternate mark inversion line coding scheme to keep the DC carrier component from saturating the line. 
   The other predominant communication protocol is E1, referring to the European framing specification. The protocol is widely used in Europe and Asia. E1 conducts transmission of thirty DS0 data streams at a transmission rate of 2.048 megabits per second. E1 has two subprotocols, balanced and unbalanced, which refers to certain characteristics of the transmission line. Issues arise when a network device executing an E1 protocol is connected to a networking device executing a T1 protocol. Such communication is unlikely to result in any valid data transmission. Some existing systems are designed to have internal switches which permit the user to open the box and manually/mechanically switch from an E1 protocol to a T1 protocol, or vice versa. Then based on the switch position, software loads the appropriate configuration information for the protocol selected. However, this involves opening the box with its attendant inconveniences. Repeated opening of the box may result in damage to sensitive internal components, particularly if exposed to dust or other contaminants. Moreover, user selected configuration assumes knowledge by the user which may not be present. 
   BRIEF SUMMARY OF THE INVENTION 
   An interface for a networking device is disclosed. A network interface module existing within a networking device monitors certain contacts of a network connection to identify a protocol of the networking system to which it is connected. Based on the detected protocol, the network interface module selects a set of configuration information with which to configure the networking device. Other features and advantages of the present invention will be apparent from the accompanying drawings and detailed description that follows below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements and in which: 
       FIG. 1  is a block diagram of a system of one embodiment of the invention. 
       FIGS. 2   a - 2   c  show three possible cable connectors which may be used to select between different protocols. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a block diagram of a system of one embodiment of the invention. A first networking device  10  has a processor  12  coupled to a memory  14 , the processor  12  controlling operation of the networking device. The processor  12  is coupled to a framer  15 . The framer  15  is responsible for placing outgoing data into an appropriate frame structure for the protocol in use. With respect to incoming data, the framer  15  performs decoding and clock recovery functions and distributes the data to a user. The first networking device  10  is coupled by a cable  28  having connectors  22  and  24  at opposing ends to a networking device  20 . Connectors  22  and  24  are male connectors that connect to corresponding female connectors  26  and  30  in networking devices  20  and  10 , respectively. In an alternative embodiment of the invention the connector of the cable may be female and the connector of the networking device may be male. 
   For networking devices operating under a T1 or E1 balanced protocol RJ-48, connectors are commonly used. RJ-48 connectors are an industry standard eight pin connectors. E1 unbalanced systems use a BNC connector for coaxial cable. However, T1 and E1 networking cables use only four signal lines  42 . Two signal lines are used for transmit and two for receive. This implies that four contacts of an eight pin connector are unused. Here, the plurality of contacts  40  are unused. As used herein, an “unused contact” is a contact in a connector which is not connected to a signal line of a cable when a pair of networking devices are coupled together by the cable. 
   An interface module  16  is provided in networking device  10  to identify based on the cable connected which protocol networking device  20  is using. Unused contact  50  within networking device  10  is grounded. Similarly, unused contacts  52  and  54  are connected through resistors  32  to a power supply voltage V DD . Detectors  34  are coupled between a selection device  36  and contacts  52  and  54 . Detectors  34  detect the presence of a voltage at the contacts  52  and  54 . 
   If contacts  52  and  54  are merely terminated inside the connector, the voltage seen by the detectors will be V DD . Conversely, if the contacts  52  or  54  are coupled to contact  50  within connector  22 , a current will flow through the corresponding resistor  32  and the voltage seen by the detectors  34  will be the ground voltage. Suitable resistance values are on the order of 10K. 
   The detectors  34  can provide a high or low voltage indication to buffer  36 . In this manner, the buffer  36  can be read by the processor  12  and can identify which of a plurality of different sets of configuration information should be used. In one embodiment, the buffer  36  indicates which of T1, E1 balanced, and E1 unbalanced configuration information should be used. The buffer  36  indicates to the processor an appropriate configuration. The processor  12  then configures the framer  15  to operate within the desired protocol. This permits networking device  10  to automatically self-configure based on the cable connected. 
     FIGS. 2   a - 2   c  show three possible cable connectors which may be used to select between different protocols. Cable connector  22  has no interconnection between any of the unused contacts. Thus, contacts  50 ,  52 ,  54  all merely terminate within connector  22 . This will result in detection by both detectors  34  of V DD . 
   Connector  62  has contact  54  coupled to contact  50 . Contact  52  terminates within connector  62 . Thus, the detector  34  coupled to contact  54  will detect ground, while the detector  34  coupled to contact  52  will detect V DD . Connector  72  has contact  52  shorted to contact  50 , while contact  54  is terminated within connector  72 . This will result in a detection of ground by the detector  34  connected to contact  52  and a detection of V DD  by the detector  34  coupled to contact  54 . 
   These three connector configurations permit interface module  16  to identify the protocol in use. Thus, the manufacturer, by shipping an appropriate cable with the networking device for the environment to which it will be networked, ensures that the networking device will be properly configured as a result of the cable detection in the interface module. 
   As noted above, while both T1 and E1 balanced typically use RJ-48 connectors, E1 unbalanced commonly uses BNC connectors. Accordingly, in one embodiment, a generic networking device employing the invention will have an RJ-48 connector, and the cable will provide adaption to BNC at the opposing end when the networking device is to be inserted in an E1 unbalanced system. 
   The present embodiment permits a generic networking device with three sets of configuration information to be inserted into any of the predominant networking protocols. The only change required is shipment of the appropriate cable. This provides additional benefits because the manufacturer of the networking device need only service and support a single product rather than three separate products, one corresponding to each protocol. Manufacturing costs are also expected to be reduced by having a single generic hardware arrangement that is independent of protocol. Moreover, if the networking device is moved from one system to another, merely a change of cable will automatically accomplish any required reconfiguration without ever opening the box. 
   In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.