Network #

Network Architecture #

The diagram below illustrates the network types in the system library along with the corresponding network layers.

Network Architecture

Transport Layer #

The transport layer includes two fundamental protocols for sending and receiving data: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). The TCP protocol is connection-oriented, used wherever there’s a need for a guarantee that data will arrive in its entirety and in the correct order. The UDP protocol does not require establishing a connection and does not guarantee data delivery, but it supports broadcasting. It’s used where speed is more important than reliability, such as in video streaming or voice calls.

UDP and TCP allow for data transmission, but they do not define the messages that can be sent with them or any fixed order of their exchange. When using these protocols directly, we must take care of things like authentication or encryption ourselves.

Application Layer #

The application layer defines higher-level protocols—how applications communicate with each other and exchange data. Application layer protocols, such as HTTP, FTP, SMTP, or DNS, specify the message format and the rules of interaction between a client and a server. Unlike transport protocols (TCP/UDP), which deal with byte transmission, application protocols focus on the semantics of the data and operations specific to a given service.

Many of the protocols in the application layer are most often TCP/UDP protocols wrapped in message exchange semantics. HTTP up to version 2, SMTP, and FTP use TCP; HTTP version 3, VoIP (Voice over IP), BitTorrent, and DNS use UDP. In .NET, the HttpClient class is the primary way to interact with HTTP-based services.

Addresses and Ports #

For communication between devices and computers on a network, we need addresses. There are two standards for writing addresses: the 32-bit IPv4 (e.g., 192.168.8.1) and the 128-bit IPv6 (e.g., DEAD:BEEF:2137:6967:0420:0B4D:ADD4:E550). The IPAddress class from the System.Net namespace can represent both types of addresses.

IPAddress ipv4 = IPAddress.Parse("192.168.0.100");
Console.WriteLine($"{ipv4}, addr family: {ipv4.AddressFamily}");
IPAddress ipv6 = IPAddress.Parse("2001:0db8:85a3:0000:0000:8a2e:0370:7334");
Console.WriteLine($"{ipv6}, addr family: {ipv6.AddressFamily}");
// 192.168.0.100, addr family: InterNetwork
// 2001:db8:85a3::8a2e:370:7334, addr family: InterNetworkV6

TCP and UDP protocols divide each IP address into 65536 ports (0-65535), allowing a computer with a single IP address to run multiple applications, each on a separate port. An IP address along with a port is represented by the IPEndPoint class.

IPAddress ipv4 = IPAddress.Parse("192.168.0.100");
IPEndPoint ipv4Ep = new IPEndPoint(ipv4, 5000); // Port 5000
Console.WriteLine(ipv4Ep);
// 192.168.0.100:5000

DNS #

DNS is a service that allows for the conversion between IP addresses and human-friendly domain names (e.g., csharp.mini.pw.edu.pl).

The Dns class allows for two-way conversion:

foreach (IPAddress address in await Dns.GetHostAddressesAsync("pw.edu.pl"))
    Console.WriteLine(address);
// 194.29.151.9

IPHostEntry entry = await Dns.GetHostEntryAsync("194.29.151.9");
Console.WriteLine(entry.HostName);
// www-virt6.ci.pw.edu.pl