RADIO TCP/IP

Those who access the Internet through a normal commutated telephone line or, luckily, through a dedicated line, do not realize what happens when they connect another Internet user, operator, server or router whatever. Basically we can refer to the normal home call to understand how an Internet call works.

Every net component (terminal or server) has an own number, called IP address. It is a 32 bit number which has a hierarchic structure. It is similar to the home address (where the field nation includes the field city, which includes the field street and so on), but every field is a number. I.e. the Internet address of the main C.I.S.I. UNIX computer is 130.192.59.1

Particularly, Hams Internet addresses are formed in this way: the first number is always a 44, which stands for radio Hams or radio Ham servers; follow the number of the nation, the number of the user field, and a last personal number; such a structure is called hierarchic. I.e. the IP number or Internet address of Radio Gateway IK1XHT.AMPR.ORG is

44.134.129.100

where 100 stands for that particular Ham radio station, 129 is one of the numbers of the domain of Piedmont region , 134 is the domain Italy, 44 is the domain radio Hams.

Since, besides number 44, 24 bits remain to be used, it is possible to address 16 million users. Due to the fact that a numeric address is very difficult to remember, it is possible to use tables of correspondence or of domain, which are controlled by each computer on the net. Thus we have that

130.192.59.1

corresponds to

cisi.unito.it

As you can see, it is a hierarchic address (it = Italy, unito = University of Turin, cisi = C.I.S.I.).

Throughout the world the conversion system using correspondence tables has some differences, and it is not always true that a domain table helps in understanding an address. The last field often indicates the kind of organization corresponding to IP number. MIL indicates a military system. About radio Hams, the last two domain fields are AMPR.ORG, where AMPR stands for AMateur Packet Radio, and ORG indicates an organization different from the other coded ones.

Radio Hams are users of the air, and communicate not only using voice or telegraphy, but also digitally, and even with TCP/IP protocol! We saw that this protocol has not been the first used by radio Hams. Let's see it.

TCP/IP (Transfer Control Protocol / Internet Protocol) is a group of protocols used to share the resources of a net with many computer systems. Differently from AX25 protocol, radio Ham TCP/IP is exactly the same net protocol. The fathers of radio Ham TCP/IP are american and canadian programmers who applied the Internet protocol in packet radio. In fact to connect the Internet, a radio station uses a common TNC, a PC and a software developed by the group of KA9K, KO4KS, etc.
This software is a group of different applications: it implements the protocols IP, ICMP, TCP, UDP, ARP, RIP, RSPF, and the services FTP, TELNET, SMTP, POP, FINGER, etc.

This software is called NOS (Network Operating System) with related modifications (WNOS, JNOS, TNOS) To operate correctly, it requires for the TNC to be set to KISS mode (Keep It Simple Stupid), this means that you have to disconnect all internal functions except the transmission error control: NOS will handle it. The computer, linked to a dummy terminal, has full control on the protocol.

NOS is multitasking: it handles the protocol AX25 and the proceedings to implement net services (the same of the Internet):

Besides, NOS gives us some instruments that do not use the TCP level, but only IP level. These instruments do not carry out a real connection, they only test the possibility to reach a TCP/IP node. The foremost two are PING and HOP CHECK. The first one is like a bell on the door, it shows us if a station is answering. The second one (in UNIX it is called TRACEROUTE) shows us the route of packets to reach a specific station. Multiple sessions can be opened, and NOS is able to automatically answer to multiple calls. Display is not graphic, since with DOS RAM of 640 K it is impossible to do so. Moreover, NOS does support Ethernet interconnection, and for this reason it is ideal in implementing gateways.

THE GATEWAY

Connecting to the Internet, you have the opportunity to forward data far beyond the limits of radio. IK1XHT.AMPR.ORG gateway is made with a PC using a LINUX operating system, which has a greater flexibility and reliability than DOS. It has on one side an interface with a TNC, and on the other side an Ethernet card connecting it with the Internet through an IBM RISC 9000 950 series computer, using UNIX operating system; Linux and Unix are two similar operating systems that get on well together, unlike DOS. Packets coming from radio network can not reach the Internet in an uncontrolled way, since received datagrams are sealed into a packet with the address of UNIX computer. Sealed data are controlled for their target, and forwarded through the Internet to the destination gateway; there the packet is opened by the gateway, that identifies the Ham to which data must be forwarded. The program has a security code that doesn't permit traffic to or from users who do not have a 44 in their IP: thus are fulfilled law enforcements that allow Hams to connect only with other Hams.

digital radio modulation the TNC the protocol AX25 the protocol TCP/IP

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