the role and purpose of standards in achieving connectivity (including RS232 and ISO 802.3)
The first networks were proprietary and from a single vendor. There was no need to connect to other networks as data was not exchanged between them so there was no need for a standard. These systems were known as closed systems.
However, as soon as data needed to be exchanged between networks, standards were needed. The first systems often used the Public Telephone systems. The standards were set by a variety of bodies. Such standards as the V-series, X-series and I-series were established. The need to interconnect higher-level networks led to the establishment of standards that defined the Format (syntax) and the Control of exchange of data between systems. Thus, equipment from one manufacturer could be connected to that of another so long as they both complied with the standard. This resulted in the Open Systems Interconnection (OSI) environment.
With the proliferation of networks needing to be connected in the 1970'6, a range of standards were introduced. The first was concerned with the overall structure of the complete communications systems within each computer. The International Standards Association (ISO) was responsible for this and it became known as the ISO Reference Model for Open System Interconnection (OSI). Other standards were to follow this.
(Ref: Data Communications, computer networks and OSI, Halsall F)
ISO
The OSI model is a layered approach where each layer performs a set functions that are either network oriented or application oriented.
The layers are as follows
| Application layer | User interface to a range of network information services. Eg email |
| Presentation layer | Syntax of data during transfer between the two layers |
| Session layer | Provides the means for two application layer protocols to synchronise and manage data exchange |
| Transport layer | Interface between the application oriented layers and the network oriented layers. |
| Network layer | Responsible for the establishment and clearing of network connections |
| Link layer | Builds on the physical connection to allow the physical to establish a reliable connection. Responsible for error detection and message retransmission. |
| Physical layer | Physical and electrical interface between the computer and the network itself. It provided the link to allow the link layer the ability to send a binary data stream. |
(Ref: Data Communications, computer networks and OSI, Halsall F pp205-213)
RS-232
The RS-232 was defined as a standards interface for connecting DTE's to a Modem thus allowing systems of different types to be connected via the telephone network. It has now been extended to allow the connection of many devices to the computer. These include mice, printers, scanners etc. It is intended that this interface be used to connect computer devices over a very short distance. The standard defines the electrical configuration and pin layout of the interface.
(Ref: Data Communications, computer networks and OSI, Halsall F pp29-30 )
802.3, X.21, V.24, I430/1 (802.2, NetBEUI, TCP/IP)
Standards set by the ISO, IEEE (American Institution for Electrical and Electronic Engineers) and CCITT are applied at each level of the OSI model. Generally the X, V and I standards apply to the connection of computer to the PSTN and ISDN systems while the ISO 8802.3, 8802.4 and 8802.5 relate to the connection of to the LAN. The standards mentioned in this all work at layer 1 - the Computer-LAN or the Computer-PSTN layer.
Mike Leishman