Main Content


PCAP file writer of protocol packets


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

    You can write these packet types to a PCAP file:

    • Generated and recovered 5G NR protocol packets

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

    • Generated and recovered Bluetooth® low energy (BLE) link layer (LL) packets (requires Communications Toolbox™ Library for the Bluetooth Protocol)



    pcapObj = pcapWriter creates a default PCAP file writer object.


    pcapObj = pcapWriter(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.


    expand all


    The pcapWriter object does not overwrite the existing PCAP file. During each call of this object, specify a unique PCAP file name.

    Name of the PCAP 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

    Object Functions

    expand all

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


    collapse all

    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.


    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.



    [1] Group, The Tcpdump. “Tcpdump/Libpcap Public Repository.” Accessed May 20, 2020.

    [2] “Development/LibpcapFileFormat - The Wireshark Wiki.” Accessed May 20, 2020.

    Extended Capabilities

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

    See Also


    Introduced in R2020b