02 Hardware
Description
This article is from the Amiga Networking FAQ, by Richard Norman with numerous contributions by others.
02 Hardware
At the heart of a network is a shared cable often called a Backbone. In the simple case this is a PARnet cable to connect two Amigas via the parallel port. Both machines share the cable. A more complex example is an ethernet cable which without special equipment can be 1000ft in length or more with a hundred or so computers attached all interconnecting at once. This is known as a LAN or Local Area Network. A cheaper but far more limited LAN Backbone is Localtalk which Apple unleashed upon the world.
bridges, routers, and gateways Oh my!
To overcome the distance and node limitation of ethernet wiring you need at least a bridge which basically acts as a repeater. A bridge can also do a limited amount of filtering so that traffic between the LAN segments is more efficient.
There are also distance limitations with bridges, so a more complex piece of equipment is needed called a router. A router provides many more tools for controlling the flow of information between segments, and can even provide some level of security. Special security configurations of routers are know as firewalls. For really long distances leased lines or satellite links are used between the routers thus forming a Wide Area Network or WAN. These links are usually provided by common carriers or some WAN providers .
This all works great as long as the two machines are the same brand, but since there is more than one vendor there is more than one "language" called a protocol for communicating. A gateway must be used to translate between the protocols. As an alternative to a gateway, some routers are able to handle multiple protocols at the same time. Gateways are also used most heavily for converting between electronic mail formats or to go between two different physical media such as ethernet and Localtalk or ethernet and SLIP. See the Envoy specific question section for an example of an ethernet to SLIP gateway.
The gateway provides access to other parts of a network that would not otherwise be directly accessible. A router is dedicated to keeping track of routes through gateways and other routers to various domains. On large networks your default gateway will often point to a router.
The distinction between gateways, routers, and bridges is not absolute since many of the functions of each can be included in a single product. In fact some companies call their product a brouter because it performs both as a bridge and a router.
Computers use numbers, but humans use names. Therefore, another device that is used on large networks is called a _NAMESERVER_. A nameserver maintains a database of machine names and their corresponding numeric addresses. The nameserver allows the computer to look up the numeric address when you use a name. In addition to the nameserver you can maintain a HOSTS file locally which is used first by your computer when trying to translate a name into a number.
The above terminology is slanted towards the TCP/IP protocol because that is (for better or worse) what you will most likely encounter.
ethernet cable ------------------------------------
While looking through the What's New page of Mosaic, I stumbled across the Ethernet Web Page. It references an ethernet FAQ from the comp.dcom.lans.ethernet news group. So if you don't find your answer in this crude introduction then try their FAQ.
the URL for the web page is:
http://wwwhost.ots.utexas.edu/ethernet/ethernet-home.html
the gopher URL for the FAQ is:
gopher://mojo.ots.utexas.edu/11/netinfo/ethernet/ethernet-faq
An ethernet cable comes in several flavors. The maximum length of your LAN segment is determined by which flavor you choose or which flavors you intermix. There is twisted pair, thin coax and thick coax ethernet cables. Each of these are rated at 10Mbit per second.
Note that this is the TOTAL capacity (bandwidth) of the cable NOT the speed between any two nodes. The speed between nodes is determined by how many nodes are trying to communicate at any given time. Even with only two nodes communicating you will NOT get the entire bandwidth of the cable. The maximum is usually only around three Mega bits per second.
The thick coax was the first used. It ran as a backbone through a building with taps and drop cables for each node (computer).
Thin coax came into favor because of lower cost and ease of installation. Thus thin coax is often called cheaper net. It has a shorter overall maximum length than thick. It is routed in a daisy chain style using tee connectors at each node. There are adapters to go between thick and thin, but your overall length can be reduced to that of thin. There are devices called hubs which may not reduce the limit and can provide conversion between one cable type to another.
Twisted pair is the current rage because it can be used for other things as well, such as voice. You can wire an entire building with twisted pair and decide at the wiring closet what service will be provided. Ethernet over twisted pair is called 10BaseT and is most often configured as a star with an ethernet concentrator at the center usually in a wiring closet. The concentrator allows for the longer length required for a star configuration. Using a concentrator provides the LAN administrator a lot of other benefits and options such as diagnostic tools and functions for monitoring the health of the LAN segment.
Several grades of twisted pair wire exist. The best class can also carry FDDI which is a fairly new high speed token-ring style network architecture. FDDI can handle speeds of 100Mbit per second. FDDI is usually carried over fiber optic cable for long distances. There are also Gigabit per second network architectures for short distance applications such as a cluster of compute servers. As far as I know there are NO FDDI or faster adapters for the Amiga at this time.
So the same wire can carry either FDDI or Ethernet so how do they differ? Good question. It is obviously NOT just the wire. Ethernet and FDDI are also specifications for how the electrical signals will be transmitted and interpreted over the wire. The Ethernet spec was originally developed by Xerox and DEC, and is now defined by the IEEE standards committee. IEEE 802.3 is one of the main ethernet standards in use.
One reason FDDI came into being is that ethernet performance degrades rapidly as you approach the capacity of the bandwidth. This means you are limited in the number of nodes that a LAN segment can support. Depending on the activity level of the nodes you may be able to support as many as 100 nodes on a LAN segment. Beyond that and you should consider subdividing into multiple LAN segments with bridges and routers.
A new wrinkle is FAST ethernet which also runs at 100 Mbs but unlike FDDI it can coexist on the same wire as regular ethernet. They even make hybrid cards that can do both 10 and 100 Mbs depending on what the host they are talking to can support. The catch to FAST ethernet is that it has an even shorter distance limitation than regular ethernet. Also, FAST ethernet only runs over category 5 twisted pair or thick coax not the thin. Unfortunately there are no FAST ethernet cards for the Amiga yet.
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