What is TCP over Amateur Packet Radio?

INTRODUCTION

If you have been thinking of trying TCP/IP on packet radio, but been put off by all the jargon, then this page should help to remove some of the mysteries surrounding TCP/IP.

It introduces you to one of the fastest growing areas in amateur packet radio today. It explains briefly what TCP/IP is and what you can do with it and also deals with some things you will need to know to get started.

WHAT IS TCP/IP?

TCP/IP literally means the 'Transmission Control Protocol/Internet Protocol' but is usually simply called the 'Internet Protocol'. It was developed as a standard protocol to allow different types of computers to exchange electronic mail and other files over a network. The network using this protocol is known as "The Internet" and has grown from it's beginnings when it linked military and educational sites in the USA to become a rapidly expanding world-wide network where users gain access via the telephone and a modem.

TCP/IP on Amateur Radio provides those same functions of electronic mail and file transfer between different computers.

HOW DOES TCP/IP DIFFER FROM AX25?

In many ways TCP/IP is very similar to AX25, although at first sight it may not appear to be. This is mainly due to the different terminology used to describe the various functions, operations and services.

TCP/IP however carries out transfers in a more integrated way than is possible by logging onto your local Mailbox using AX25 and most traffic is handled automatically. For example, you do not have to log onto a Mailbox to collect your Mail. Your local Hub will send it direct without any action from you. Also, you do not have to work out a string of other stations to ensure your message reaches its destination. You simply send it to your local Hub and the network does the work.

One big advantage of TCP/IP is it's ability to make better use of faster baud rates which are coming into use and make the transfer of large files much quicker than with AX25 due to the latter's inherent inability to handle large packet sizes at high speed. Already a lot of TCP/IP traffic is sent at 9600 baud and experiments are under way for transmissions at 19200 baud and higher.

TCP/IP software also improves data throughput on busy channels by using 'back off' techniques. TCP/IP senses when a frequency gets busy and waits longer before sending packets of data. As the channel activity dies down your station automatically starts sending more quickly. This reduces collisions and retries and gets everyone's packets moving more smoothly

The software also permits multi-tasking within the programme and you can have several connections and modes in operation at the same time

The system has a huge potential and may well supplant AX25 in time. At present development is concentrated in local areas (LAN's..Local Area Networks). For the time being most trunk traffic is still handled by the AX25 system via Hubs which provide TCP/IP to AX25 Gateways. This means you are not cut off from the rest of the amateur packet radio world.

ARE THERE ANY DRAWBACKS?

When you start using TCP/IP you join a Network which operates 24 hours a day in which most traffic is handled automatically without the intervention of the operator.

This means that, ideally, your station should be left running although you can turn off the monitor to conserve power. In this way traffic is spread throughout the whole day and the best use made of the frequency.

This, however, is not essential and connection with the network can be re-established easily when you again switch on. The POP facility for collecting mail and which is described later is particularly useful for those who do not operate on a 24 hour basis.

If you do wish to leave your station on 24 hours a day you should refer to Section 2 of your Licence Conditions (BR68) relating to unattended operations.

WHAT IS NEEDED TO USE TCP/IP?

If you are already on Packet Radio, the only additional thing you will need is the software to run TCP/IP and an IP address. Software is available for most machines/operating systems. Although some offer more of the facilities than others do, they all cover most of the important features such as mail handling (SMTP) and file transfers (FTP).

WHAT IS AN IP ADDRESS?

An IP address is another form of identification for your station in addition to your Callsign. It is a block of four numbers in the form 44.131.ABC.XYZ . The 44 defines it as Amateur Radio. The 131 refers to the United Kingdom The ABC is the number of the region where your station is sited (drawn up on RF boundaries rather than on a County basis) and the XYZ is your unique number within that region.

HOW TO GET AN IP ADDRESS

IP addresses are issued by local IP address co-ordinators.

The local co-ordinators keep the National IP address co-ordinator fully up to date with the list of addresses they have issued, to ensure no duplicate addresses or host names are issued.

WHAT IS A HOST NAME?

A host name is the name given to a Computer Terminal and is the station Callsign followed by ampr.org e.g. g3abc.ampr.org where the placing of the full stops is important. Your computer is the Local Host and the computer with whom you are in contact is called the Remote Host.

WHAT IS A HUB?

In the United Kingdom the TCP/IP Network is being developed using the Hub system. Hubs are suitably sited stations, which handle traffic generally at low power with local users in their service area but also have links to other Hubs to pass traffic for more distant destinations. Hubs are specially licensed by the Radiocommunications Agency under a procedure known as a Notice of Variation (NoV) and are issued with a GB7 callsign

The local users use the Hub's local user ports, which are generally on 2 metres at the 1200 baud rate although some Hubs also have local user ports available at either 1200 baud or 9600 baud on a 70 cms frequency.

Traffic on the links between Hubs is usually done at 9600 baud on 70 cms and local users are discouraged from using these frequencies.

Hubs make use of advanced forms of the TCP/IP software known as the Server versions and provide various services, which are described elsewhere in this page

Hubs can be compared with Mailbox's in the AX25 network.

The planning and development of inter hub links to provide a TCP/IP national packet radio network is a continuing process.

©1998 Steve Morton G8SFR
Produced here with kind permission.



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