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6. Wi-Fi Sockets use cases

6.1 Wi-Fi TCP client

This use case configures NORA-W36 as a Wi-Fi TCP client device that initiates a TCP connection to a specified server (listener) over a Wi-Fi network. It actively seeks to establish communication by sending a connection request to the server’s IP address and port number, which the server is listening on.
The Transmission Control Protocol (TCP) is bidirectional and one socket can both send and receive data:

ATE0 turns off the AT command echo to speed up the data transmission in AT mode. The written data is not echoed back to the host, which helps to make the parsing easier.
It is possible to connect using a host name like AT+USOC=0,www.u-blox.com,80 or an IP address AT+USOC=0,75.2.60.5,80
TCP can both send and receive data between the TCP client and server

Nr	Instructions	AT command	AT event
1	Create a TCP socket	`AT+USOCR=6`	`+USOCR:0`
2	Connect using TCP port 5003	`AT+USOC=0,192.168.0.200,5003`	`+UESOC:0`
3	It is now possible to send and receive data using String or Binary mode
4	Close TCP socket	`AT+USOCL=0`	`+UESOCL:0`

6.2 Wi-Fi TCP server (listener)

This use case configures NORA-W36 as a Wi-Fi TCP server (listener) that is configured to accept incoming TCP connections over a Wi-Fi network. It “listens” on a specific IP address and port number for connection requests.

Nr	Instructions	AT command	AT event
1	Create a TCP socket	`AT+USOCR=6`	`+USOCR:0`
2	Start TCP server (listener) on port 5003	`AT+USOL=0,5003`	`+UESOC:0`
3	Incoming TCP connection, a new handle 1 to communicate with the connection		`+UESOIC:0,192.168.1.100,1`
4	It is now possible to send and receive data using String or Binary mode
5	TCP connection is closed from remote side		`+UESOCL:1`
6	Close TCP listener	`AT+USOCL=0`	`+UESOCL:0`

6.3 Wi-Fi UDP client

Unlike TCP, the User Datagram Protocol (UDP) is not bi-directional. Both an outgoing and incoming socket, AT+USOCR, are needed to send and receive data over UDP. It is possible to connect using the host name, like AT+USOC=0,www.u-blox.com,80, or the IP address AT+USOC=0,75.2.60.5,80

Nr	Instructions	AT command	AT event
1	Create a UDP socket	`AT+USOCR=17`	`+USOCR:0`
2	Connect using UDP port 5003	`AT+USOC=0,192.168.0.200,5003`	`+UESOC:0`
3	It is now possible to send data using String or Binary mode
4	Close UDP socket	`AT+USOCL=0`	`+UESOCL:0`

6.4 Wi-Fi UDP server (listener)

Nr	Instructions	AT command	AT event
1	Create a UDP socket	`AT+USOCR=17`	`+USOCR:0`
2	Start UDP server (listener) on port 5003	`AT+USOL=0,5003`	`+UESOC:0`
3	It is now possible to receive data using String or Binary mode
4	Close UDP listener	`AT+USOCL=0`	`+UESOCL:0`

6.5 Wi-Fi TCP using TLS without certificates

TLS Extensions are enabled by default but in some (mostly older) TLS servers they are not supported. See https://www.rfc-editor.org/rfc/rfc6066.html. The extensions, Server Name, Indication and Maximum Fragment Length Negotiation, are disabled with:

AT+USETE0=0 Server Name Indication, 0: Disable - 1: Enable (default)
AT+USETE1=0 Maximum Fragment Length Negotiation, 0: Disable - 1: Enable (default)
All other Extension are disabled and not supported.
It is possible to use host name like AT+USOC=0,www.u-blox.com,80 or using ip address AT+USOC=0,75.2.60.5,80 for the connections.

TCP is bidirectional and one socket can both send and receive data.

Nr	Instructions	AT command	AT event
1	Create a TCP socket	`AT+USOCR=6`	`+USOCR:0`
2	Add a TLS context to a socket	`AT+USOTLS=0,1`
3	Connect using TCP port 433	`AT+USOC=0,"www.u-blox.com",433`	`+UESOC:0`
4	It is now possible to send data using String or Binary mode
5	Close TCP socket	`AT+USOCL=0`	`+UESOCL:0`

6.6 Wi-Fi TCP using TLS with certificates

TCP is bidirectional and one socket can both send and receive data.

Nr	Instructions	AT command	AT event
1	Write a X.509 certificate and private key using Binary data	`AT+USECUB=0,"ca.pem"{sendbinarycontentof"ca.pem"}` `AT+USECUB=1,"client.pem"{sendbinarycontentof"client.pem"}` `AT+USECUB=2,"client.key"{sendbinarycontentof"client.key"}` See Binary data for more information, note that the brackets { and } should NOT be sent, they are just here in this example
2	Create a TCP socket	`AT+USOCR=6`	`+USOCR:0`
3	Add a TLS context to a socket and certificates	`AT+USOTLS=0,1,"ca.pem","client.pem","client.key"`
4	Connect using TCP on port 433	`AT+USOC=0,"www.u-blox.com",433`	`+UESOC:0`
5	It is now possible to send data using String or Binary mode
6	Close TCP socket	`AT+USOCL=0`	`+UESOCL:0`

6.7 Create own certificates using OpenSSL

Here is some example to cerate own certificates using OpenSSL https://www.openssl.org/. It shows how to use 2048 or 4096 bit keys length. Use Git Bash https://git-scm.com/download/win or a Linux environment like Ubuntu https://ubuntu.com/download to run the examples.

Create the root CA key Generate 2048 key size: opensslgenrsa-outca.key2048 or Generate 4096 key size: opensslgenrsa-outca.key4096
Create the root CA based on ca.keyopensslreq-x509-sha256-new-nodes-keyca.key-days3650-outca.pem
Create server certificate Create the server certificate signing request (CSR) for 2048 key size: opensslreq-newkeyrsa:2048-keyoutserver.key-outserver.csr-nodes or Create the server certificate signing request (CSR) for 4096 key size: opensslreq-newkeyrsa:4096-keyoutserver.key-outserver.csr-nodes
Create the server certificate using root CA and server csr, valid for 10 yearsopensslx509-req-CAca.pem-CAkeyca.key-inserver.csr-outserver.pem-days3650-CAcreateserial
Create client certificate Create the client certificate signing request (CSR) for 2048 key size: opensslreq-newkeyrsa:2048-keyoutclient.key-outclient.csr-nodes or Create the client certificate signing request (CSR) for 4096 key size: opensslreq-newkeyrsa:4096-keyoutclient.key-outclient.csr-nodes
Create the client certificate using root CA and client csr, valid for 10 yearsopensslx509-req-CAca.pem-CAkeyca.key-inclient.csr-outclient.pem-days3650-CAcreateserial
In a Windows Git Bash enviromentwinpty is a Windows software package providing an interface similar to a Unix pty-master for communicating with Windows console programs. Set up a local TLS 1.2 server (without CA validation in this case) winptyopenssls_server-CAfileca.pem-keyserver.key-certserver.pem-accept44330-tls1_2-state-Verify1
Connect to the a local TLS 1.2 server, just to try the connection (without CA validation in this case): winptyopenssls_client-connectlocalhost:44330-CAfileca.pem-keyclient.key-certclient.pem-tls1_2
In a Linux enviroment Set up a local TLS 1.2 server (without CA validation in this case)** openssls_server-CAfileca.pem-keyserver.key-certserver.pem-accept44330-tls1_2-state-Verify1
Connect to the a local TLS 1.2 server, just to try the connection (without CA validation in this case): openssls_client-connectlocalhost:44330-CAfileca.pem-keyclient.key-certclient.pem-tls1_2

Optional steps

Check the key size of the CA certificate: opensslx509-inca.pem-text-noout|grep"Public-Key"RSAPublic-Key:(4096bit)
Check the key size of the client certificate: opensslx509-inclient.pem-text-noout|grep"Public-Key"RSAPublic-Key:(4096bit)
Check the size of the client key: opensslrsa-inclient.key-text-noout|grep"Private-Key"RSAPrivate-Key:(4096bit,2primes)