How Do Computer Network Protocols Work?

Assembling the physical pieces of a computer network by itself is insufficient to make it function — connected devices also require a method of communication. These communication languages are called network protocols.

Purpose of Network Protocols

Without protocols, devices would lack the ability to understand the electronic signals they send to each other over network connections. Network protocols serve these basic functions:

  • Address data to the correct recipient(s)
  • Physically transmit data from source to destination, with security protection if needed
  • Receive messages and send responses appropriately

Consider a comparison between network protocols with how a postal service handles physical paper mail. Just as the postal service manages letters from many sources and destinations, so to do network protocols keep data flowing along many paths continuously. Unlike physical mail, however, network protocols also provide some advanced capabilities like delivering a constant flow of messages to one destination (called streaming) and automatically making copies of a message and delivering it to multiple destinations at once (called broadcasting).

Common Types of Network Protocols

No one protocol exists that supports all the features every kind of computer network needs, but each serves as a key that unlocks a given network device or service. Many different kinds of network protocols have been invented over the years, each attempting to support certain kinds of network communication. Three basic characteristics that distinguish one type of protocol from another are:

1. Simplex vs. duplex. A simplex connection allows only one device to transmit on a network. Conversely, duplex network connections allow devices to both transmit and receive data across the same physical link.

2. Connection-oriented or connectionless. A connection-oriented network protocol exchanges (a process called a handshake) address information between two devices that allow them to carry on a conversation (called a session) with each other. Conversely, connection-less protocols deliver individual messages from one point to another without regard for any similar messages sent before or after (and without knowing whether messages are even successfully received).

3. Layer. Network protocols normally work together in groups (called stacks because diagrams often depict protocols as boxes stacked on top of each other). Some protocols function at lower layers closely tied to how different types of wireless or network cabling physically works. Others work at higher layers linked to how network applications work, and some work at intermediate layers in between.

The Internet Protocol Family

The most common network protocols in public use belong to the Internet Protocol family. IP is itself the basic protocol that enables home and other local networks across the internet to communicate with each other.

IP works well for moving individual messages from one network to another but does not support the concept of a conversation (a connection over which a stream of messages can travel in one or both directions). The Transmission Control Protocol (TCP) extends IP with this higher layer capability, and because point-to-point connections are so essential on the internet, the two protocols are almost always paired together and known as TCP/IP.
Both TCP and IP operate in the middle layers of a network protocol stack. Popular applications on the Internet have sometimes implemented their own protocols on top of TCP/IP. HyperText Transfer Protocol is used by web browsers and servers worldwide. TCP/IP, in turn, runs on top of lower-level network technologies like Ethernet. Other popular network protocols in the IP family include ARP, ICMP, and FTP.