pcapWriter

PCAP file writer of protocol packets

Description

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 (LE) link layer (LL) packets (requires Bluetooth^® Toolbox)

Creation

Syntax

pcapObj = pcapWriter

pcapObj = pcapWriter(Name,Value)

Description

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.

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

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'

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

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);

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™.

Version History

Introduced in R2020b