E.1. Considerations when buying second-hand terminal
servers
Internet Service Providers have been large users of terminal
servers in the past. Each modem would be connected to a terminal
server port and incoming users would be permitted to send
IP packets anywhere, not just to some predefined
minicomputer. Manufacturers renamed the equipment to "access
servers" or "modem servers" to reflect this new
use.
These access servers have been superseded by a new generation
which allows telephone trunks to be plugged directly into the
ISP's router. There are no discrete modems; the
modem tones are decoded by digital signal processing chips within
the router. As a result terminal servers are currently readily
available on the second-hand market.
When purchasing a second-hand terminal server ensure that you
are also buying the rights to the software. Some companies license
their software and have contract terms which state that the license
cannot be resold, but has to be repurchased from the company if the
terminal server changes hands.
Many vendors require a current maintenance contract to obtain
software updates. These maintenance agreements can be expensive, a
common figure is 15% per annum of the manufacturer's retail price.
You may be able to source a cheaper software updates from a
third-party maintenance supplier.
Many older terminal servers are no longer sold or supported
by their vendors. Search the vendor's web site for "end of
life".
Vendor support can be a particular issue when the
most-recently available software does not fit within the
RAM or flash memory contraints of the terminal
server you have purchased. You should check this before purchasing
a seond-hand terminal server. Upgrading flash memory can be
particularly difficult, as the ROM on the
motherboard may also need to be replaced with one aware of the new
flash memory's characteristics.
Third-party parts suppliers such as Kingston or MemoryX can usually provide
dynamic RAM and flash memory. They cannot
usually supply ROMs or static
RAM.
Most old terminal servers will not support
Secure Shell. In this is the case
accessing the terminal server by its ethernet port is a poor idea:
when you login to the console you password will travel across the
Internet in clear text. Either dial in to the terminal server or
use a one-time password system such as the
RADIUS protocol with
S/KEY authentication.
An alternative to using a terminal server is to use a
multiport serial card in another Linux system.