What is a Protocol?
- A protocol is a set of rules that governs the communications between computers on a network. In order for two computers to talk to each other, they must be speaking the same language.
- Many different types of network protocols and standards are required to ensure that your computer (no matter which operating system, network card, or application you are using) can communicate with another computer located on the next desk or half-way around the world.
- The OSI (Open Systems Interconnection) Reference Model defines seven layers of networking protocols.
|OSI Layer||Name||Common Protocols|
|7||Application||HTTP | FTP | SMTP | DNS | Telnet|
|4||Transport||TCP | SPX|
|3||Network||IP | IPX|
OSI model related to common network protocols
table illustrates how some of the major protocols would correlate to the OSI model in order to communicate via the Internet. In this model, there are four layers, including:
Ethernet (Physical/Data Link Layers)
IP/IPX (Network Layer)
TCP/SPX (Transport Layer)
HTTP, FTP, Telnet, SMTP, and DNS(combined Session/Presentation/Application Layers)
Assuming you want to send an e-mail message to someone in Italy, we will examine the layers “from the bottom up” — beginning with Ethernet (physical/data link layers).
Ethernet (Physical/Data Link Layers)
The physical layer of the network focuses on hardware elements, such as cables, repeaters, and network interface cards. By far the most common protocol used at the physical layer is Ethernet.
For example, an Ethernet network (such as 10BaseT or 100BaseTX) specifies the type of cables that can be used, the optimal topology (star vs. bus, etc.), the maximum length of cables, etc.
The data link layer of the network addresses the way that data packets are sent from one node to another. Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system where each computer listens to the cable before sending anything through the network.
Sometimes, two computers attempt to transmit at the same instant.
The original Ethernet standard was developed in 1983 and had a maximum speed of 10 Mbps over coaxial cable. The Ethernet protocol allows for bus, star, or tree topologies, depending on the type of cables used and other factors. This heavy coaxial cabling was expensive to purchase, install, and maintain, and very difficult to retrofit into existing facilities.
The current standards are now built around the use of twisted pair wire. Common twisted pair standards are 10BaseT, 100BaseT, and 1000BaseT. The number (10, 100, 1000) ands for the speed of transmission (10/100/1000 megabits per second); the “Base” stands for “baseband” meaning it has full control of the wire on a single frequency; and the “T” stands for “twisted pair” cable. Fiber cable can also be used at this level in 10BaseFL.
The Fast Ethernet protocol supports transmission up to 100 Mbps. Fast Ethernet requires the use of different, more expensive network concentrators/hubs and network interface cards. In addition, category 5 twisted pair or fiber optic cable is necessary. Fast Ethernet standards include:
- 100BaseT – 100 Mbps over 2-pair category 5 or better UTP cable.
- 100BaseFX – 100 Mbps over fiber cable.
- 100BaseSX -100 Mbps over multimode fiber cable.
- 100BaseBX – 100 Mbps over single mode fiber cable.
Gigabit Ethernet standard is a protocol that has a transmission speed of 1 Gbps (1000 Mbps). It can be used with both fiber optic cabling and copper.
1000BaseT – 1000 Mbps over 2-pair category 5 or better UTP cable.
1000BaseTX – 1000 Mbps over 2-pair category 6 or better UTP cable.
1000BaseFX – 1000 Mbps over fiber cable.
1000BaseSX -1000 Mbps over multimode fiber cable.
1000BaseBX – 1000 Mbps over single mode fiber cable.
The Ethernet standards continue to evolve. with 10 Gigabit Ethernet (10,000 Mbps) and 100 Gigabit Ethernet (100,000 Mbps)
Ethernet Protocol Summary
|Ethernet||Twisted Pair, Coaxial, Fiber||10 Mbps|
|Fast Ethernet||Twisted Pair, Fiber||100 Mbps|
|Gigabit Ethernet||Twisted Pair, Fiber||1000 Mbps|
IP and IPX (Network Layer)
The network layer is in charge of routing network messages (data) from one computer to another. The common protocols at this layer are IP (which is paired with TCP at the transport layer for Internet network) and IPX (which is paired with SPX at the transport layer for some older Macintosh, Linus, UNIX, Novell and Windows networks). Because of the growth in Internet-based networks, IP/TCP are becoming the leading protocols for most networks.
Every network device (such as network interface cards and printers) have a physical address called a MAC (Media Access Control) address. When you purchase a network card, the MAC address is fixed and cannot be changed. Networks using the IP and IPX protocols assign logical addresses (which are made up of the MAC address and the network address) to the devices on the network, This can all become quite complex — suffice it to say that the network layer takes care of assigning the correct addresses (via IP or IPX) and then uses routers to send the data packets to other networks.
TCP and SPX (Transport Layer)
The transport layer is concerned with efficient and reliable transportation of the data packets from one network to another. In most cases, a document, e-mail message or other piece of information is not sent as one unit. Instead, it is broken into small data packets, each with header information that identifies its correct sequence and document.
When the data packets are sent over a network, they may or may not take the same route — it doesn’t matter. At the receiving end, the data packets are re-assembled into the proper order. After all packets are received, a message goes back to the originating network. If a packet does not arrive, a message to “re-send” is sent back to the originating network.
TCP, paired with IP, is by far the most popular protocol at the transport level. If the IPX protocol is used at the network layer (on networks such as Novell or Microsoft), then it is paired with SPX at the transport layer.
HTTP, FTP, SMTP and DNS (Session/Presentation/Application Layers)
Several protocols overlap the session, presentation, and application layers of networks. This protocols listed below are a few of the more well-known:
DNS – Domain Name System – translates network address (such as IP addresses) into terms understood by humans (such as Domain Names) and vice-versa
DHCP – Dynamic Host Configuration Protocol – can automatically assign Internet addresses to computers and users
FTP – File Transfer Protocol – a protocol that is used to transfer and manipulate files on the Internet
HTTP – HyperText Transfer Protocol – An Internet-based protocol for sending and receiving webpages
IMAP – Internet Message Access Protocol – A protocol for e-mail messages on the Internet
IRC – Internet Relay Chat – a protocol used for Internet chat and other communications
POP3 – Post Office protocol Version 3 – a protocol used by e-mail clients to retrieve messages from remote servers
SMTP – Simple Mail Transfer Protocol – A protocol for e-mail messages on the Internet