Understanding Network Protocols

This article provides an overview of the following network protocols and technologies: PPP, TCP/IP, IPX/SPX, netBEUI, FTP, HTTP, NFS, SMTP, ICMP, Telnet and SSH.

Network design has advanced as computer technology has expanded and grown more powerful. Networks allow linked computers to share data. This basic functionality belies a complex interaction of a multiplicity of different rules, hardware, programs and connection standards. The most foundational aspects of networks are protocols. Network protocols define the conventions for communication between network devices such as a computer and a router. Multiple protocols exist, and each one came about because of improvements in basic design or as innovations in response to intractable problems.

Point-to-Point Protocol (PPP)

This is more properly described as a protocol suite than as a single protocol. Though considered to be part of Transfer Control Protocol/Internet Protocol (TCP/IP), PPP can be thought of as a protocol suite within the suite of TCP/IP. PPP facilitates IP transmission between network devices sharing a direct link. Through a series of link phases, a secure connection is established over which data may be transmitted. PPP actually works as an intermediate-level packet structure. It enables the transmission of higher-level protocols, such as TCP/IP, across a diversity of link environments. PPP is most commonly used for dial-up networking between modems.


TCP Connection State Diagram.
TCP Connection State Diagram. Photo Credit: Niklas Gustavsson
Transfer Control Protocol and Internet Protocol are actually two separate protocols. They are described in one phrase because they are widely used together. TCP/IP can be better understood by referring to the Open Systems Interconnection Model (OSI Model). TCP represents the third layer, Network, while IP represents the fourth layer, Transport. Thus, TCP/IP refers to situations were TCP is used to transmit information across IP networks. IP moves data from node to node, and TCP moves data from client to server. TCP also provides redundancy in that it detects errors or lost data. TCP will retransmit data until a successful transmission is completed.



Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) is the legacy networking protocol for Novell NetWare. However, it has evolved and is now used in Microsoft NT, Lotus Notes, Vista and Microsoft XP environments. IPX/SPX was eventually replaced with the more popular TCP/IP for NetWare, although IPX/SPX enjoys broad usage in other network environments. IPX is easy to configure and works well with small networks. It enables datagram services in packet-switched internetworks. Similar to IP, it has several key differences. SPX facilitates transport-layer services in conjunction with IPX’s routing capabilities. IPX addresses are hexadecimal numbers consisting of a network address and a hardwired node address.


Network BIOS Extended User Interface (netBEUI) was developed from Microsoft’s Network Basic Input Output System (netBIOS). netBIOS, in turn, was created based on Disk Operating System (DOS) BIOS, which extended the basic system with local area network (LAN) capabilities. netBEUI extends the networking features of netBIOS by formalizing the frame format for arranging information in data transmission. netBEUI works very well when limited to a single LAN. To connect to an external network with TCP/IP, the server providing the connection must be equipped with both TCP/IP and netBEUI. The server can then be programmed to choose between TCP/IP for external connections and netBEUI for internal LAN transmission.


File Transfer Protocol (FTP) is the single best protocol for transmitting files over the Internet. It sets the standard for other protocols. FTP uses TCP/IP to transmit data, making it compatible with virtually every network system in existence. FTP downloads files from servers and uploads files to servers from personal computers. FTP is commonly used for compuer to computer file transmission. Since it uses TCP/IP, anyone can download FTP and start transmitting files if they know the network address of the destination.


HyperText Transfer Protocol (HTTP) is the most widely used protocol to transfer audio, visual, graphics, text and other multimedia files over the Internet. HTTP runs over TCP/IP. Whenever a user starts a Web browser, it automatically uses HTTP to pull information from a server with TCP/IP. Hypertext is any text displayed on a webpage with a blue underlined link to another page. A user clicks on a hypertext link and the HTTP daemon, which is a part of all servers, detects and redirects the user to the new link. HTTP makes the Internet possible; TCP/IP merely fleshes it out.


Network File System (NFS) is a Unix protocol developed by Sun Microsystems. It treats remote files as if they were local files on a hard disk, allowing users to manipulate them. Importantly, users can access files across different types of computers. Using Virtual File System (VFS), which lies on top of TCP/IP, NFS lets computers act as clients when accessing remote files and also lets computers act as servers when another user is accessing their files. NFS obviously operates within a client/server framework. The advantage of NFS is letting users treat remote files as local files, which makes file sharing much easier.


Simple Mail Transfer Protocol (SMTP) is another ubiquitous Internet protocol like HTTP. SMTP facilitates the transfer of electronic mail or e-mail from computer to computer across the Internet. SMTP is used to send and receive messages between a mail client, usually an email application on the user’s computer and a mail server. SMTP interacts with Post Office Protocol (POP) or Internet Mail Access Protocol (IMAP) to retrieve e-mail from a mail server. Users need to configure both the POP or IMAP server and the SMTP server when installing and setting up an email application on their computer.


Internet Control Message Protocol (ICMP) is one of the major protocols of the IP suite. ICMP is an error detection and diagnostic protocol, essential for any IP set-up. ICMP can support packets containing error messages, which alert users to problems with network connections. A ping command, for instance, uses ICMP to test an IP address’s availability. ICMP messages usually report problems with the integrity of datagrams. To prevent infinite regression, no ICMP messages are ever sent about ICMP messages. ICMP is architecturally layered on top of IP. Error control is critical when dealing with the Network OSI layer.


Address Resolution Protocol (ARP) is rarely noticed by network administrators due to its simplicity. It operates at the second layer of the OSI model, translating IP addresses into physical hardware addresses. It does this to map an IP address to a link layer address whenever it is demanded. ARP links the IP and Ethernet network layers to facilitate data transmission. It is one of the most critical protocols for a network to use, and its simple operation and interface makes problems rare. ARP enables Ethernet adapters to transmit data between network devices by synchronizing different OSI layers to the same address.

Telnet and SSH

Telnet is a protocol that enables a user to connect to a remote computer. Most computer users have used telnet to connect to another computer. Command-line telnets exist on most computers; they are standard on nearly every Unix platform, Linux distro, and on Macs. Even Windows includes the program telnet.exe which can be accessed via the DOS command prompt interface. Another protocol that accomplishes the same task is Secure Shell (SSH). SSH uses much stronger cryptography than telnet to protect users against hackers and eavesdroppers. Telnet is older than SSH and uses minimal security to send and receive commands, making it more vulnerable. SSH is almost automatic, and telnet allows the user to pass some features onto the remote server itself.