Networking Protocols

A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer.

Layered Software and the OSI Model

Computers communicate using a layered set of protocols, the primay example of which is the Open Systems Interconnection (OSI) reference model.  This is a model that was propsed as a set of standard layers and protocols for communication between different computers around the world and has been in use since 1983.  Although not universally adopted, much of this model is considered the standard and in heavy use.  This protocol is different from TCP/IP which will discussed later.

Layers provide a division of the work done by a network.  Networks are set up with a protocol hierarchy that divides the communication task into several layers.  A protocol is a set of rules for communication within a layer.  A service is what the layer provides to the layer above it through an interface.  Protocols at one layer are unaware of issues at another layer.

The OSI Layers

The OSI reference model organizes a network into seven layers (a protocol stack).  These layers define how networking hardware and software are to hand data and transfer it across a network.  Interoperability, the purpose for defining a standard protocol model, exists when there is compatibility between the protocol stack of one workstation or peripheral device and that of another.  Each layer is able to communicate with the corresponding layer of a receiving station.
 
 

Application Layer
Application Layer
Presentation Layer
Presentation Layer
Session Layer
Session Layer
Transport Layer
Transport Layer
Network Layer
Network Layer
Data Link Layer
Data Link Layer
Physical Layer
Physical Layer

 

The OSI model related to both IPX/SPX (Novell Netware) and TCP/IP (WindowsNT & UNIX) Protocol Models
 


IPX/SPX (Novell Netware)
 
 
 
 

Netware Lower-Layer Protocols

Netware normally runs over standard lower-layer protocols, such as Ethernet (IEEE 802.3).  The lower-layer protocol briefly discussed here, MLID, is a proprietary standard for network interface card drivers.

MLID (Multiple Link Interface Driver) - operates at the Medium Access Sublayer of the Data-Link Layer of the OSI model.  MLID is a standard for NIC cards and takes on the form of a driver for the NIC card.

NetWare Middle-Layer Protocols:


Netware Upper-Layer Protocols
 

TCP/IP (MicrosoftNT and UNIX)
 



Internet Protocols (TCP/IP)

The Internet Protocol suite is unique in that it is made up of non-proprietary protocols.  This means that they do not belong to any one company and that the technology is available for anyone to use them.  The above diagram only roughly maps the comparison of the two models.  As you may notice, the Internet model does not cover the two layers of the OSI model.  This means that TCP/IP is hardware independent.  Since TCP/IP does not include lower level protocols, we'll start with the middle level protocols.

Internet Middle-Layer Protocols

OSI model's network and transport layers are concerned with transporting packets across the internetwork.  TCP/IP and other Internet protocols use three types of addresses for network addressing:
 

IP (Internet Protocol) - works at the network layer.  It handles addressing, packet-switching, route selection and error control for communication.

TCP (Transmission Control Protocol) - the Internet protocol's main transport layer protocol.  It also provides addressing services at the network layer.

DNS (Domain Name System) - a distributed database system that works at the transport layer to provide name-to-address mapping for client applications.  DNS servers maintain databases that consist of hierarchical name structures of the various domains in order to use logical names for device identification.

Internet Upper-Layer Protocols

FTP (File Transfer Protocol) - used for file transfer between internetwork nodes.  It also allows users to initiate processes on a remote host.  It funtions at the top three layers of the OSI model:  at the session layer, FTP provides session adminisrtation; at the presentation layer, FTP is concerned with translation using machine independent file translation; and at the application layer, FTP supplies network services such as file services.  FTP is a peer-to-peer protocol.

Telnet - used for remote terminal emulation.  It enables users to access host-based applications by emulating one of the host's terminals.  Telnet provides connectivity between dissimilar operating systems.  At the session layer, it provides dialog control; at the presentation layer, telnet provides translation using byte order and character codes; and at the application layer, telnet provides the services for remote operations.

SMPT (Simple Mail Transfer Protocol) - a protocol for routing email messages.  It works at the application layer to provide message service.


Miscellaneous Protocols

Serial Line Internet Protocol - SLIP -Used with dial up connections to the Internet.  Works exclusively at the Physical Layer of the OSI model.  An older protocol that was improved upon with PPP.

Point-to-Point Protocol - PPP - Provides dial up connectivity to the Internet.  Operates at the Physical and Data-Link Layer of the OSI model.  It provides physical device addressing and error control.

Integrated Services Digital Network - ISDN - a set of standards to provide voice, video and data transmission over digital telephone lines.  ISDN operates at the Physical, Data-Link, Network and Transport layers of the OSI model.