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pcapngWriter

PCAPNG file writer of protocol packets

Since R2020b

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    Description

    The pcapngWriter object writes generated and recovered protocol packets to a packet capture next generation (PCAPNG) file (.pcapng).

    You can write these packet types to a PCAPNG file:

    • Generated and recovered 5G NR protocol packets

    • Generated and recovered WLAN protocol packets (requires WLAN Toolbox™)

    • Generated and recovered Bluetooth low energy (LE) link layer (LL) packets (requires Bluetooth® Toolbox)

    Creation

    Syntax

    pcapngObj = pcapngWriter
    pcapngObj = pcapngWriter(Name,Value)

    Description

    pcapngObj = pcapngWriter creates a default PCAPNG file writer object.

    pcapngObj = pcapngWriter(Name,Value) sets properties using one or more name-value pair 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 pcapngWriter 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.

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

    Data Types: char | string

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

    Data Types: char | string

    Comment for the PCAPNG file, specified as a character vector or a string scalar.

    Data Types: char | string

    Object Functions

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    writeWrite protocol packet data to PCAP or PCAPNG file
    writeCustomBlockWrite custom block to PCAPNG file
    writeInterfaceDescriptionBlockWrite interface description block to PCAPNG file

    Examples

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    Open Live Script

    Create a PCAPNG file writer object, specifying the name of the PCAPNG file.

    pcapngObj = pcapngWriter('FileName','sample');

    Write the interface block for 5G New Radio (NR). 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.

    interface = '5GNR';                                       % Interface name
linkType = 113;                                           % Link type of SLL packet
timestamp = 300;                                          % Timestamp
interfaceID = writeInterfaceDescriptionBlock(pcapngObj,linkType,interface);

    5G 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 start of NR MAC signature
payloadTag = 1;                                           % Payload tag for NR MAC 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;                                                   % 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 an 5G NR packet by adding encapsulation and metadata.

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

    Write the 5G NR packet to the PCAPNG file.

    packetComment = 'This is NR MAC packet';                  % Packet comment
write(pcapngObj,packet,timestamp,interfaceID,'PacketComment',packetComment);

    References

    [1] Tuexen, M. “PCAP Next Generation (Pcapng) Capture File Format.” 2020. https://www.ietf.org/.

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

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

    Extended Capabilities

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

    Version History

    Introduced in R2020b

    See Also

    Objects