Custom Search

Entrepreneurial Capitalism and Innovation:
A History of Computer Communications 1968-1988
By James Pelkey

Home Page
Table of Contents
Market Sectors
Supporting Documents
Computer History Museum

CHM Home Page
Oral History Archive


Entrepreneurial Capitalism & Innovation:
History of Computer Communications
1968 -1988
By James Pelkey

This history is organized by three co-evolving market sectors and also standards making.
An overview of the schema is presented in the Introduction.

Ch. 1: Emergence
Ch. 3: Competition
Ch. 5: Market Order
Ch. 11: Adaptation

Ch. 2: Vision
Ch. 4: Arpanet
Ch. 6: Diffusion
Ch. 7: Emergence
Ch 8: Completion
Ch. 10: Market Order

Ch. 9: Creation

Ch. 12: Emergence



Chapter 12
Internetworking: LANs and WANs 1985-1988
Local Area Networks and Wide Area Networks


12.3    Repeaters - Physical Layer: Solutions to Extend a Network

If a customer only had Ethernet (CSMA/CD) LANs, and not too many devices connected to them, then the most straightforward solution was repeaters. Repeaters are amplifiers able to boost a decaying LAN signal so it can travel the length of connected LAN(s). Neither complicated nor expensive, repeaters function entirely on the Physical Layer of the OSI Reference Model. (See Exhibit 12.1 The Ethernet Repeater) Their simplicity also gives rise to a fundamental limitation: they boost every signal as if locked in broadcast mode. Thus, all the traffic on one LAN continues onto the next, cumulatively, quickly degrading the performance of the interconnected LANs.

Exhibit 12.1 -- The Ethernet Repeater


Incremental innovation yielded modest repeater improvements, e.g. the ability to detect faults in a connected LAN and isolating the offending LAN. Repeaters, however, could never overcome the limitations inherent in not knowing the source and destination addresses of connected devices. Nor could repeaters ever interconnect different types of LANs, such as Ethernet and token ring. These limitations combined with the compelling economic advantages of interconnecting networks, motivated vendors to take on the more complex, hence expensive, task of innovating the first real product of Internetworking: bridges. [1]


[1] I was reminded by John Day that the products of Internetworking were not innovated sequentially because they had known from the beginning. What caused the trajectory was the need to master software engineering, and possibly the propensity to pick “low hanging fruit” – my language.