pcapWriter

PCAP file writer of protocol packets

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.

Properties

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.

FileName — Name of the PCAP file

'capture' (default) | character row vector | string scalar

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

ByteOrder — Byte order

'little-endian' (default) | 'big-endian'

This property is read-only after object creation.

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

Data Types: char | string

PipeName — Name of FIFO pipe file

'' (default) | character vector | string scalar

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

Specific to This Object

write	Write protocol packet data to PCAP or PCAPNG file
writeGlobalHeader	Write global header to PCAP file

Examples

Write 5G NR Packet to PCAP File

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);

Write WLAN Packet to PCAP File

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);

Write Bluetooth LE Link Layer Packet to PCAP File

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

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

R2026a: pcapWriter moves to Wireless Network Toolbox from WLAN Toolbox and Bluetooth Toolbox

In R2026a, the pcapWriter object and associated object functions move to the Wireless Network Toolbox™ product from the WLAN Toolbox™ and Bluetooth^® Toolbox products. Starting in R2026a, writing WLAN or Bluetooth packets to a PCAP file requires Wireless Network Toolbox. In releases R2025b and before, these functionalities require the WLAN Toolbox or Bluetooth Toolbox products, respectively.

R2026a: pcapWriter adds support for pipe interface

The pcapWriter object now enables you to specify a FIFO pipe file through the PipeName property.