pcapWriter

PCAP file writer of protocol packets

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    Description

    The pcapWriter object writes generated and recovered protocol packets to a packet capture (PCAP) file (.pcap).

    Creation

    Syntax

    pcapObj = pcapWriter
    pcapObj = pcapWriter(PropertyName=Value)

    Description

    pcapObj = pcapWriter creates a default PCAP file writer object.

    pcapObj = pcapWriter(PropertyName=Value) sets properties using one or more name-value arguments. Enclose each property name in quotes. For example, ByteOrder="big-endian" specifies the byte order as big-endian.

    example

    Properties

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    Note

    The pcapWriter object does not overwrite the existing PCAP or PCAPNG file. Each time when you create this object, specify a unique PCAP or PCAPNG file name.

    This property is read-only after object creation.

    Name of the PCAP file, specified as a character row vector or a string scalar.

    Data Types: char | string

    This property is read-only after object creation.

    Byte order, specified as 'little-endian' or 'big-endian'.

    Data Types: char | string

    Since R2026a

    This property is read-only after object creation.

    Name of the first-in first-out (FIFO) pipe file (also known as a named pipe), specified as a character row vector or string scalar. This value is an absolute or relative path to a pipe that you create outside MATLAB.

    Dependencies

    To enable this property, do not specify FileName.

    Data Types: char | string

    Object Functions

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    writeWrite protocol packet data to PCAP or PCAPNG file
    writeGlobalHeaderWrite global header to PCAP file

    Examples

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    This example uses:

    Open Live Script

    Create a PCAP file writer object, specifying the name of the PCAP file. 5G NR packets do not have a valid link type. As per Tcpdump, if a valid link type is not present, specify the link type of SLL packet.

    pcapObj = pcapWriter('FileName','sample');
linkType = 113;                                         % Link type of SLL packet
timestamp = 300;                                        % Timestamp

    Write a global header to the PCAP file.

    writeGlobalHeader(pcapObj,linkType);

    The 5G New Radio (NR) packets are not directly supported by Wireshark. To enable Wireshark to parse 5G NR packets, add encapsulation and metadata to the 5G NR packet.

    payload = [59; 205];                                    % MAC subPDU (contains truncated buffer status report (BSR) control element)
radioType = 1;                                          % Frequency division duplexing
linkDir = 0;                                            % Uplink packet
rntiType = 3;                                           % Cell-RNTI
startString = [109; 97; 99; 45; 110; 114];              % Tag to indicate the start of NR MAC signature
payloadTag = 1;                                         % Payload tag for NR packets
signature = [startString; radioType; linkDir; rntiType];
macNRInfoPacket = [signature; payloadTag; payload];

    Construct a user datagram protocol (UDP) header.

    udpPacketLength = 8 + length(macNRInfoPacket);          % Length of header (8 bytes) and payload
udpHeader = [163; 76;                                   % Source port number
    39; 15;                                             % Destination port number
    fix(udpPacketLength/256); mod(udpPacketLength,256); % Total length of UDP packet
    0; 0];                                              % Checksum

    Construct an IPv4 header.

    ipPacketLength = 20 + udpPacketLength;                  % Length of header (20 bytes) and payload
ipHeader = [69;                                         % Version of IP protocol and priority or traffic Class
    0;                                                  % Type of service
    fix(ipPacketLength/256); mod(ipPacketLength,256);   % Total length of the IPv4 packet
    0; 1;                                               % Identification
    0; 0;                                               % Flags and fragmentation offset
    64;                                                 % Time to live in seconds
    17;                                                 % UDP protocol number
    0; 0;                                               % Header checksum
    127; 0; 0; 1;                                       % Source IP address
    127; 0; 0; 1];                                      % Destination IP address

    Construct an SLL header.

    sllHeader = [0; 0;                                      % Packet type
    3; 4;                                               % Address resolution protocol hardware (ARPHRD) type
    0; 0;                                               % Link layer address length
    0; 0; 0; 0; 0; 0; 0; 0;                             % Link layer address
    8; 0];                                              % Protocol type

    Construct 5G NR packet by adding encapsulation and metadata.

    packet = [sllHeader; ipHeader; udpHeader; macNRInfoPacket];

    Write the 5G NR packet to the PCAP file.

    write(pcapObj,packet,timestamp);

    This example uses:

    Open Live Script

    Create a PCAP file writer object, specifying the name of the PCAP file. Specify the link type for WLAN packet.

    pcapObj = pcapWriter('FileName','writeWLANpacketdata2');
wlanLinkType = 105;

    Write a global header to the PCAP file.

    writeGlobalHeader(pcapObj,wlanLinkType);

    Specify a WLAN packet.

    mpdu = 'B4000000FFFFFFFFFFFF00123456789BA79A5B28';

    Write the WLAN packet to the PCAP file.

    timestamp = 124800; % Number of microseconds
write(pcapObj,mpdu,timestamp);

    This example uses:

    Open Live Script

    Create a PCAP file writer object, specifying the name of the PCAP file. Specify the Bluetooth LE link type.

    pcapObj = pcapWriter('FileName','writeBluetoothLE');
bleLinkType = 251;

    Write a global header to the PCAP file.

    writeGlobalHeader(pcapObj,bleLinkType);

    Specify a Bluetooth LE LL packet.

    llpacket = '42BC13E206120E00050014010A001F0040001700170000007D47C0';

    Write the Bluetooth LE LL packet to the PCAP file.

    timestamp = 129100;                % Packet arrival time in POSIX® microseconds elapsed since 1/1/1970
write(pcapObj,llpacket,timestamp);

    References

    [1] Group, The Tcpdump. “Tcpdump/Libpcap Public Repository.” Accessed May 20, 2020. https://www.tcpdump.org.

    [2] “Development/LibpcapFileFormat - The Wireshark Wiki.” Accessed May 20, 2020. https://www.wireshark.org.

    Extended Capabilities

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    C/C++ Code Generation
    Generate C and C++ code using MATLAB® Coder™.

    GPU Code Generation
    Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

    Version History

    Introduced in R2020b

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    See Also

    Objects