User Tools

Site Tools


ch10_handbook:ethernet_data

Export page to Open Document format

ETHERNET DATA

Type 0x68, Ethernet Data, Format 0

Ethernet Data, Format 0 packets are used to record Ethernet data frames from an Ethernet network. In general, an Ethernet data packet will contain multiple captured Ethernet data frames.

The layout of the CSDW is shown in Figure 6-52. The iNumFrames field indicates the number of Ethernet frames included in this data packet. The iFormat field indicates the format of the captured Ethernet frames. Format type 0x00 is described in Chapter 10 as “Ethernet Physical Layer” but in practice is better described as “Ethernet Data Link Layer” because support for physical layer features such as frame sync preamble and collision events are not described in the Chapter 10 standard.

struct SuEthernetF0_ChanSpec 
    { 
    uint32_t    uNumFrames  : 16;   // Number of frames 
    uint32_t    Reserved1   : 12; 
    uint32_t    uFormat     :  4;   // Format of frames 
    }; 

Type 0x68 Ethernet Data Format 0 CSDW

Individual Ethernet data messages follow the CSDW. The format of the intra-packet data header is shown in Figure 6-53. The suIntrPckTime value is an eight byte representation of time in either 48-bit relative time format derived from the RTC (format shown in Figure 6-5) , or as absolute time. If this time is absolute time, it is in either Chapter 4 weighted 48-bit time (format shown in Figure 6-6) or IEEE 1588 time format (format shown in Figure 6-7). The uDataLen field is the length of the Ethernet data in bytes. The uNetID field is used to uniquely identify the physical network attachment point. The uSpeed field indicates the bit rate at which the frame was captured by the recorder. Early coaxial cable based Ethernet networks (10BASE5 and 10BASE2) required all network participants to operate at the same bit rate since they were sharing the same physical channel. Most modern Ethernet network topologies (10BASE-T, 100BASE-TX, etc.) are a star configuration with a single point to point link between the networked device and a network hub. In this case, the network bit rate is the bit rate negotiated between the device (e.g. the recorder) and the network hub. In this star topology, different devices can operate at different bit rates on the same Ethernet network. The uSpeed field only indicates the bit rate of the link the data recorder has with the network hub. It does not imply the speed of any other devices on the network. The uContent field indicates the type of data payload. The Media Access Control (MAC) content type (0x00) indicates Ethernet Data Link Layer frames, including the destination address, source address, type (in the case of Ethernet II) or length (in the case of IEEE 802.3), data, and frame check sequence. The data link frame preamble is not included, nor are other features of the physical layer such as collisions or auto-negotiations. The bFrameError flag indicates an unspecified error has occurred in the reception of the Ethernet frame.

struct SuEthernetF0_Header 
    { 
    uint64_t    suIntraPckTime;         // Reference time 
    uint32_t    uDataLen        : 14;   // Data length 
    uint32_t    Reserved1       :  2;   // 
    uint32_t    uNetID          :  8;   // Network identifier 
    uint32_t    uSpeed          :  4;   // Ethernet speed 
    uint32_t    uContent        :  2;   // Captured data content 
    uint32_t    bFrameError     :  1;   // Frame error 
    uint32_t    Reserved2       :  1;   // 
    }; 

Type 0x68 Ethernet Data Format 0 intra-packet data header


Type 0x69 - 0x6F, Ethernet Data, Format 1 - Format 7

Reserved for future use.

ch10_handbook/ethernet_data.txt · Last modified: 2014/05/29 14:42 by bob