Patent Publication Number: US-2003235214-A1

Title: Service channel over the Ethernet inter-frame gap

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This application claims priority from and is related to the following prior application: “Service Channel Over The Ethernet Inter-Frame Gap,” U.S. Provisional Application No. 60/378,291, filed May 7, 2002. This prior application, including the entire written description and drawing figures, is hereby incorporated into the present application by reference. 
    
    
     
       FIELD  
       [0002] The technology described in this patent application relates generally to the field of Ethernet systems. More particularly, the application describes a system and method for providing a service channel over the Ethernet inter-frame gap.  
       BACKGROUND  
       [0003] A standard Ethernet physical line transports Ethernet frames that are each separated by a minimum delay, referred to as the inter-frame gap. Standard Ethernet does not support an in-band or out-band service channel. By utilizing a service channel frame inserted within the inter-frame gap, however, additional services and functionality may be implemented that are typically not available at the Ethernet physical layer.  
       SUMMARY  
       [0004] An interface for transmitting and receiving service channel frames over an Ethernet includes an Ethernet physical layer and a physical service channel. The Ethernet physical layer is configured to transmit and receive Ethernet frames over an Ethernet physical medium. The physical service channel is configured to transmit and receive service channel frames over the Ethernet physical medium. In operation, the physical service channel transmits the service channel frames within inter-frame gaps defined by the Ethernet frames so as not to interfere with the transmission or receipt of the Ethernet frames. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0005]FIG. 1 is a diagram illustrating the transmission of Ethernet frames over an Ethernet physical medium;  
     [0006]FIG. 2 depicts a service channel frame inserted in the inter-frame gap defined by two Ethernet frames;  
     [0007]FIG. 3 depicts a plurality of service channel frames transmitted over an Ethernet physical medium at a pre-defined rate;  
     [0008]FIG. 4 shows the physical layers of a standard Ethernet stack model, as illustrated in IEEE Std 802.3 for use with a 100 Mbps baseband network;  
     [0009]FIG. 5 is an Ethernet stack model having a physical service channel;  
     [0010]FIG. 6 is a block diagram of an example Gigabit Ethernet interface having a physical service channel;  
     [0011] FIGS.  7 A- 7 C depict an example service channel frame protocol; and  
     [0012]FIG. 8 is a system diagram illustrating an example SONET/SDH transport network utilizing a service channel equipped Ethernet.  
    
    
     DETAILED DESCRIPTION  
     [0013] With reference now to the drawing figures, FIG. 1 is a diagram illustrating the transmission of Ethernet frames  12  over an Ethernet physical medium  13 , such as a fiber optic or copper cable. In accordance with industry standards, Ethernet frames  12  transmitted over an Ethernet physical medium  13  are each separated by a minimum delay, referred to as the inter-frame gap (IFG)  14 . One industry standard governing Ethernet communication is set forth in IEEE Standard 802.3, 2000 Edition (IEEE Std 802.3). In accordance with IEEE Std 802.3, the minimum inter-frame gap  14  may vary from 9.6 μs for a 10 Mbps baseband network to 0.096 μs for a 1000 Mbps baseband network. In each case (e.g., 10 Mbps, 100 Mbps, 1000 Mbps Ethernet, etc.), an inter-frame gap  14  defined by two adjacent Ethernet frames  12  should be large enough to transport at least twelve (12) octets of information. That is, the standard inter-frame gap  14  provides the necessary space for transporting of up to twelve (12) octets of information, independent of the transmission speed.  
     [0014]FIG. 2 depicts a service channel frame  22  inserted in the inter-frame gap  14  defined by two Ethernet frames  12 . The service channel frame  22  should be limited in size (12 octets for IEEE Std 802.3 Ethernet) such that the service channel frame  22  can be transmitted within the inter-frame gap  14  without interfering with Ethernet frame  12  traffic. IEEE Std. 802.3 does not support an in-band or out-band service channel. However, by utilizing a service channel frame  22 , specific actions and services that are typically not available at the Ethernet physical layer can be implemented. For example, the service channel frame  22  may be utilized in a point-to-point Ethernet transmission to provide monitoring and service functions. For instance, the service channel frame  22  may be used for line quality monitoring; an Operation, Administration, Maintenance and Provisioning (OAM&amp;P) channel; remote monitoring; measuring Service Level Agreement over an Ethernet line between two customers; providing additional Ethernet line protection against failure and Ethernet line switching; providing line monitoring for maintenance purposes; service billing; fault localization and maintenance; far-end Ethernet equipment (or customer equipment) management; and other types of monitoring and services.  
     [0015] It should be understood that a standard function of the inter-frame gap  14  is to enable collision detection in an Ethernet system operating in half-duplex mode. Therefore, service channel frames  22  should preferably be employed in a full-duplex mode of operation.  
     [0016]FIG. 3 depicts a plurality of service channel frames  22  transmitted over an Ethernet physical medium  13  at a pre-defined rate  32 . If there is no Ethernet frame  12  traffic, or if there is sufficient space in the inter-frame gap  14 , then a plurality of service channel frames  22  may be transmitted over the Ethernet physical line  13  at a fixed rate  32  without the occurrence of an Ethernet frame  22 . If an Ethernet frame  22  is transmitted while service channel frames  22  are being transmitted at a fixed rate  32 , then the corresponding service channel frame  22  is delayed until the next inter-frame gap, as illustrated, so as not to interfere with the transmission of Ethernet frame  22 .  
     [0017] The service channel frames  22  may, for example, be transmitted at a fixed rate  32  in order to maintain an active service channel without regard to Ethernet frame  12  traffic. For example, service channel frames  22  may be transmitted at a fixed rate  32  to continuously monitor the integrity of the Ethernet physical line  13 , or to perform other continuously-active service or monitoring functions.  
     [0018]FIG. 4 shows the physical layers of a standard Ethernet stack model  40 , as illustrated in IEEE Std 802.3 for use with a 100 Mbps baseband network. The standard 100 Mbps Ethernet stack  40  includes a medium dependent interface (MDI)  44 , a physical medium dependent sublayer (PMD)  46 , a physical medium attachment sublayer (PMA)  48 , a physical coding sublayer (PCS)  50 , and a media independent interface (MII)  52 . The PMD  46 , PMA  48  and PCS  50  are referred to collectively as the Ethernet physical layer. Also illustrated is the Ethernet physical medium  13 .  
     [0019] The Ethernet physical layer collectively transmits, receives, and manages the encoded signals that are impressed on and recovered from the physical medium  13 . The PCS  50  is typically responsible for coding and decoding data octets, generating carrier sense and collision detection indications, and managing the auto-negotiation process. The PMA  48  typically serializes and deserializes the data. The PMD  46  typically functions as an interface specific to the particular type of Ethernet physical medium  13 , such as single-mode optical fiber, multi-mode optical fiber, and copper cabling. The MII  52  (or GMII in the case of Gigabit Ethernet) provides a transparent signal interface between the Ethernet physical layer and an OSI data link layer, such as a media access control (MAC) layer. The MDI  44  is a physical connector that couples the PMD  46  with the Ethernet physical medium  13 . A more detailed description of the Ethernet stack model  40 , along with other standard Ethernet stacks, is set forth in IEEE Std 802.3.  
     [0020]FIG. 5 is an Ethernet stack model  60  having a physical service channel  62 . As illustrated, the physical service channel  62  may be coupled between the physical coding sublayer (PCS)  50  and the physical medium attachment (PMA) sublayer  48  in a standard Ethernet stack model  40 . The physical service channel  62  is configured to transmit and receive service channel frames  22  over the Ethernet physical medium  13 . Also illustrated is a central processing unit (CPU) bus for coupling the physical service channel  62  to a processing device. A more detailed description of the physical service channel  62  is provided below with reference to FIG. 6.  
     [0021] It should be understood that the physical service channel may be similarly incorporated in other Ethernet stack models. For example, a standard Ethernet stack model for 1000 Mbps Ethernet (i.e., a Gigabit Ethernet stack model) is similar to the Ethernet stack model  40  of FIG. 4, except that the MII  52  is replaced with a Gigabit Media Independent Interface (GMII) (see, e.g., FIG. 5).  
     [0022]FIG. 6 is a block diagram of an example Gigabit Ethernet interface  70  having a physical service channel  62 . Similar to the 100 Mbps Ethernet stack model shown in FIG. 5, this Gigabit Ethernet stack  70  includes a PMD  46 , a PMA  48 , a PCS  50  and a physical service channel  62 . Also illustrated are the Ethernet physical medium  13  and a Gigabit media independent interface (GMII)  71 . The components of the Gigabit Ethernet stack  70  may, for example, be included on a single Ethernet card, but could also be implemented as separate components. Also, a plurality of Gigabit Ethernet stacks  70  could be included on the same Ethernet card.  
     [0023] The Ethernet stack  70  is configured for a full-duplex Ethernet system, and can, therefore, both transmit and receive data from an Ethernet physical medium  13 . With reference first to the receipt of information, all Ethernet data, including Ethernet frames  12  and service channel frames  22 , broadcast over the physical medium  13  are received and deserialized by the PMD  46  and PMA  48 , respectively. The deserialized data is transferred to the physical service channel  62 , which extracts the service channel frames  22 . The physical service channel  62  may, for example, include a line quality monitoring module  72  that monitors the service channel frames  22  for signal degradation, and a service channel protocol extraction module  74  that removes the service channel frames from the inter-frame gap  14 . The line quality monitoring module  72  and the service channel protocol extraction module  74  may be implemented as software modules, hardware modules, or a combination of both. In one embodiment, for instance, the line quality monitoring module  72  may inspect a cyclic redundancy check byte within the service channel frame (see, e.g., FIG. 7A) to identify data transmission errors indicative of quality problems in the Ethernet physical medium  13 . In addition, the extracted service channel frame  22  may be transmitted to a processing device via the CPU bus  64  to further process other embedded service or monitoring data included within the service channel frame  22 . An example service channel frame protocol  100  is described in detail below with reference to FIGS.  7 A- 7 C.  
     [0024] As described above with reference to FIG. 3, service channel frames  22  may be broadcast over the Ethernet physical medium  13  with or without Ethernet frames  22 . If received Ethernet data includes Ethernet frames  13 , the service channel frames  22  are extracted, and the remaining Ethernet frames  12  are transferred from the physical service channel  62  to the PCS  50 . The PCS  50  decodes the Ethernet frames  22  for use by the OSI data link layer (e.g., the MAC layer), and may also use the received Ethernet frames  22  to perform synchronization, auto-negotiation, and carrier sense functions, as described in more detail in IEEE Std. 802.3. The decoded data from the Ethernet frames  12  is then transferred via the GMII  71  (or MII  52  in the case of 100 Mbps Ethernet) to the OSI data link layer.  
     [0025] With reference now to data transmission, data sent from the OSI data link layer (e.g., MAC layer) via the GMII  71  (or MII  52 ) is encoded and encapsulated into Ethernet frames  12  by the PCS  50 . The Ethernet frames  12  are then transferred to the physical service channel  62 , which includes a service channel protocol insertion module  76  to insert service channel frames  22  within the inter-frame gaps  14 , as described above with reference to FIGS. 2 and 3. The service channel protocol insertion module  76  may be implemented as a software module, a hardware module, or a combination of both. The Ethernet transmission data, including both the Ethernet frames  12  and the service channel frames  22 , is then serialized and broadcast over the Ethernet physical medium  13  by the PMA  48  and PMD  46 , respectively. Also, as described above, the physical service channel  74  may broadcast service channel frames  22  via the PMA  48  and PMD  46  at a fixed rate  32  without the occurrence of an Ethernet frame  22 .  
     [0026]FIG. 7A depicts an example service channel frame protocol  100 . The service channel frame protocol  100  includes a start segment  102 , a header  104 , a flags segment  106 , a payload data unit (PDU)  110 , and a CRC byte  112 . The start segment  102  may include a pre-defined series of bits that is used by an Ethernet stack  70  to identify the beginning of a service channel frame  22 . An example header  104  is shown in FIG. 7B, and may include a PDU type segment  114  to identify the type of data contained in the payload data unit  110  and a sequence number  116  to distinguish the service channel frame  22  from other service channel frames broadcast from the same host. An example flags segment  106  is illustrated in FIG. 7C, and may include flags indicating the presence of a local or a remote fault. The payload data unit (PDU)  110  may, for example, include status or configuration information, one or more commands, statistical data, event data, or other monitoring or service information. The CRC  112  is a checksum that may, for example, be used to verify the integrity of the service channel data.  
     [0027] In one embodiment, the CRC  112  portion of the service channel protocol  100  may be used by the physical service channel  62  to monitor line quality of the Ethernet physical medium  13 . For example, the physical service channel  62  in a remote host unit may continuously broadcast service channel frames  22  at a pre-determined rate  32 , each including a CRC  112 . The physical service channel  62  in a local host may then monitor the service channel frames  22  for errors in the CRCs  112 , indicating a possible quality problem in the Ethernet physical medium  13 .  
     [0028]FIG. 8 is a system diagram  120  illustrating an example SONET/SDH transport network  122  utilizing a service channel equipped Ethernet. The illustrated SONET/SDH network  122  includes a plurality of nodes  124 - 126 , each of which provides Ethernet connections to a plurality of local clients  128 ,  130 . Example systems for transmitting Ethernet data over a SONET/SDH network  122  are described in detail in the following co-owned application, which are hereby incorporated into the present application by reference: U.S. patent application Ser. No. 09/378,844, entitled “System And Method For Packet Transport In A Ring Network”; U.S. patent application Ser. No. 09/817,982, entitled “Virtual Ethernet Ports With Automated Router Port Extension”; U.S. patent application Ser. No. 10/163,828, entitled “Ethernet Protection System” and U.S. patent application Ser. No. 10/164,180, entitled “System And Method For Transporting Channelized Ethernet Over SONET/SDH.” In the illustrated system  120 , however, at least one of the Ethernet connections includes a service channel, as described above.  
     [0029] The service channel equipped Ethernet is shown between node  126  and local client  130 , and is illustrated in more detail in block  132 . The network architecture detailed in block  132  illustrates the service channel equipped Ethernet stacks  60  at both the SONET/SDH node  126  and the local client  130 . Also illustrated in block  132  are OSI data link layer interconnection devices and sublayers, including the MAC layers  134  that are responsible for transferring data to and from the physical layers  40 ,  60 , a bridge  136  that links the service channel equipped Ethernet  60  to a standard Ethernet  40  at the local client  130 , and a mapper  138  that is responsible for transmitting and receiving data via the SONET/SDH network  122 .  
     [0030] This written description uses examples to disclose the invention, including the best mode, and also to enable a person skilled in the art to make and use the invention. The patentable scope of the invention may include other examples that occur to those skilled in the art.