NOSintro – TCP/IP over Packet Radio

An Introduction to the KA9Q Network Operating System

by Ian Wade, G3NRW



This book contains many abbreviations and acronyms, and a lot of networking and computer jargon. Many of these terms mean different things to different people, and even the experts use the same words in quite different ways. So to pull everything together, this chapter presents a unified description of these words and abbreviations, explaining how they are used in the book. Having defined the terminology and the ground rules here, the rest of the book should then be much easier to read.


Abbreviations and Acronyms

PC:   Personal Computer, in the widest sense, not just an IBM PC running DOS. Although this book specifically describes the IBM PC environment for NOS, most of what you see is equally applicable to the other popular machines such as Apple Macintosh, Amiga, Atari, and so on.

DOS:   Disk Operating System. This means Digital Research’s DR-DOS, Microsoft’s MS-DOS or IBM’s PC-DOS, or any of the many vendor-specific work-alikes.

NOS:   Network Operating System. This is the basic TCP/IP software package and the subject of this book. Earlier PC versions were known as NET, and some versions for other platforms are still known as NET. The examples in this book are based on PA0GRI’s NOS version 2.0m released in Summer 1992, which is in turn based on KA9Q’s version of 29 December 1991. Other currently available DOS versions of NOS include WNOS and JNOS.

NET/ROM:   This is the networking software for switching nodes from Software 2000, or work-alike packages such as TheNet.


Networking Protocols

The world of data communications is overflowing with abbreviations, acronyms and protocols. Here is a checklist of the protocols used in NOS:

AMPRnet:   Amateur TCP/IP Packet Radio Network.

ARP:   Address Resolution Protocol. Handles the association between IP hostnames and AX.25 callsigns or Ethernet adapter addresses.

AX.25:   Amateur X.25 Link Layer Protocol. Handles level 2 frame transfer between stations.

AXIP:  AX.25 over IP protocol. Used for encapsulating AX.25 packet frames for transmission through an IP "wormhole".

BOOTP:   Boot Protocol. Used for bootstrapping NOS.

FINGER:   Finger Protocol. Allows users to find out about other users.

FTP:   File Transfer Protocol. The principal protocol for transferring ASCII and binary files between stations.

ICMP:   Internet Control Message Protocol. Handles IP transmission errors.

IP:   Internet Protocol. The workhorse network protocol in the TCP/IP combination.

KISS:   "Keep It Simple, Stupid!" Protocol. Handles data transfer between the host computer and the tnc.

NET/ROM:   Handles Transport Layer data transfer.

NNTP:   Network News Transfer Protocol. Handles distribution of news files.

NRS:   NET/ROM control protocol for managing an external (non-NOS) NET/ROM node.

PING:   Packet Internet Groper protocol. Used for checking the availability of other stations.

POP, POP2, POP3:   Post Office Protocols. Handle reverse forwarding of SMTP mail.

PPP:   Point-to-Point Protocol. Handles serial link data transfers.

RIP:   Routing Information Protocol. Handles IP routing table broadcasts.

RLOGIN:   Remote login. Allows login to remote computers.

RSPF:   Radio Shortest Path First protocol. Another protocol for handling IP routing table broadcasts.

SLIP:   Serial Link Internet Protocol. Another point-to-point serial link protocol.

SLFP:   Serial Link Frame Protocol. Handles serial link compression.

SMTP:   Simple Mail Transfer Protocol. Handles the forwarding and reception of mail.

TCP:   Transmission Control Protocol. Handles reliable virtual circuits between stations, flow control and error recovery (e.g. duplicate or missing packets).

TELNET:   Remote login. In NOS systems, handles login to the NOS BBS.

TIP:   Terminal Interface Protocol. Handles direct communication with a serial port, character-by-character, with no additional protocol overhead. Can be used for initialising a tnc or modem.

TTYLINK:   Chat Protocol. Handles interactive character-by-character conversations.

UDP:   User Datagram Protocol. Handles one-shot data transfers (which may get lost en-route).

UUENCODE:   Encodes binary files into ASCII prior to transmission.

UUDECODE:   Decodes uuencoded files from ASCII back to binary.



NOS is based on software which has been around for a long time in the UNIX world. This means that many of the UNIX conventions apply.

NOS commands are case-sensitive. That is, they consist entirely of lower-case letters; for example, NOS understands the command session but doesn’t understand SESSION or Session or SeSsIoN, or any other variation containing capital letters.

Unlike UNIX or DOS, NOS understands abbreviated commands. You can abbreviate most commands down to one or two letters, provided the abbreviation is still unique. For example, NOS understands sess or ses or even se to mean session, but s by itself is ambiguous, as there are several other commands beginning with the letter s.

In this book, command names are given in full for clarity.

NOS file paths use forward slashes (/), not backslashes (\) like DOS. Thus you will see NOS filenames written like /spool/mail/sysop.txt, not \spool\mail\sysop.txt. Also, NOS filenames are in shown in lower-case.

All NOS directories are rooted on DOS drive letter N: — thus the NOS file /spool/mail/sysop.txt corresponds to the DOS file N:\SPOOL\MAIL\SYSOP.TXT. In this book, we define the NOS root with the command:


and so the NOS file /spool/mail/sysop.txt is really the DOS file C:\NOS\SPOOL\MAIL\SYSOP.TXT.

For the few DOS-specific files described in this book, the usual DOS conventions apply. That is, they are written in upper-case and with backslashes; e.g. C:\DOS\ANSI.SYS.


Station Identification

To run NOS you will need to choose an IP hostname. This is the name of your system by which other TCP/IP stations will know you, and will normally be your callsign. In this book, IP hostnames are in lower-case; e.g. ns9bob.

To distinguish between IP hostnames and AX.25 callsigns, the latter are in upper-case; e.g. NS9BOB-5.


Almost all callsigns in this book are fictitious. The following prefixes apply to make it easier to distinguish between different types of station:

ns9... NOS (TCP/IP) station

NR9... NET/ROM node

AX9... AX.25 end-user station

BB7... AX.25 PBBS station


NET/ROM aliases in this book are of the form #<suffix>. For example, ns9bob has the alias #BOB. (In reality, the choice of alias is largely a matter of personal preference, but usually it begins with # or the letters IP or TCP, to distinguish it from ordinary NET/ROM aliases).


Keyboard Characters

The following abbreviations apply:

CR carriage-return (enter)

\r carriage-return (enter)

LF line-feed (newline)

^ the CTRL key (e.g. ^Z means control-Z)

CTRL the CTRL key


ALT the ALT key

ESC the ESCAPE key

Fn Function Key n


Mail and Bulletin Boards

The generic word mail encompasses personal messages and public bulletins.

PBBS:   The PBBS is the traditional packet bulletin board system, featuring the familiar AX.25 mailer (using commands like SP to send mail, R to read it, and so on).

NOS BBS:   The NOS BBS is the bulletin board system built into NOS. This handles AX.25 mail in the same way as a PBBS, and also handles SMTP mail for AMPRnet/Internet.

External mailers (such as PCElm, ELM and BM) are alternative programs to handle SMTP mail. You can run these programs completely separately from NOS, or you call them from within NOS with the mail command.

PMS:   A PMS is the Personal Messaging System built in to conventional tncs.


The Terminal Node Controller

The tnc operates in three basic modes:

Native Mode is the normal mode for which the tnc was originally designed. That is, it lets you access the packet network directly from the keyboard, by giving commands in response to the familiar cmd: prompt. The tnc controls everything to do with sending and receiving AX.25 packets, and does not even need a host computer (all that is required is a dumb terminal).

Host Mode requires the use of a host computer with the tnc. The host computer takes over virtually all of the functionality of the tnc, allowing a much greater degree of control, but is still restricted to sending and receiving AX.25 packets.

KISS (Keep it Simple, Stupid!) Mode is a variation of host mode. The host computer runs almost all of the network software, and communicates with the tnc using the KISS protocol. In KISS mode, the tnc can handle all the protocols supported by AMPRnet, Internet, NET/ROM and AX.25.


Origin/Target and Source/Destination

When sending information via intermediate stations, it is important to understand the distinction between terms like origin, source, destination and target. In this book, these terms are used as follows (see Fig 3-1):

Fig 3-1: Origin and Target refer to the extreme end-points of communication. Source and Destination refer immediate neighbours.

Origin:   is the station originating the information. If you are sending a message to somebody else, your station is the origin.

Target:   is the final intended recipient of your information.

Source:   is the station transmitting the information at this point.

Destination:   is the station receiving the information at this point.

Thus, referring to Fig 3-1, station A is the origin of the information, and station D is the final target. For the path between A and B, A is the source and B is the destination, and for the path between B and C, B is the source and C is the destination, and so on.

We’ll see that the situation can get quite complicated when considering a multi-layer path between NOS stations, where the end-to-end path may take in IP gateways, NET/ROM nodes and AX.25 digipeaters. In this situation it’s very important to keep a clear head when referring to source and destination, as these terms may refer to different stations at the different network layers.


Routers and Gateways

TCP/IP has been around for several years, and a whole vocabulary has grown up around it. More recently, the International Standards Organisation (ISO) has formulated the Open Systems Interconnection (OSI) model — the so-called 7-layer model — to describe network communications, and this too has its own vocabulary and jargon.

It turns out that there is some commonality between the TCP/IP and OSI models, but there is also a lot of overlap and conflict, with the same terms having quite different meanings in the two models. Predictably, this can cause a lot of confusion. This is not the place to compare the two models; instead we will say here that the TCP/IP terminology will be used throughout most of this book, with just occasional references to the OSI model for comparison.

The main candidate for confusion is the word gateway. In the TCP/IP world it is referred to as an IP gateway, which corresponds roughly to an OSI Router (and is nothing to do with an OSI gateway).



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[Copyright 1992-2009 Dowermain Ltd. All Rights Reserved. This page last modified: 21 May 2009]