NCPA Downlink The Official Journal of the Northern California Packet Association Serving Amateur Radio Digital Communications in Northern California Spring, 2003 Issue number 35 $2.50 President’s Message News from the ARRL Gary Mitchell, WB6YRU From The ARRL Letter, August 8, 2003 In This Issue Here’s the Spring issue... in early LEAGUE DOCUMENTS DIGITAL President’s Message . 1 September <ahem>. Hopefully we’ll MODES ARRL News . 1 have the Summer issue out while it’s Packet Layers for the still summer. With a new Web page on digital mode specifications, ARRL hopes to make ISO/OSI and TCP/IP In the last issue, a first draft of the answering the question "Is that mode Network Models . 2 proposed “big change” to the bylaws legal?" a lot easier. DX Spotting nodes . 3 (and hence the structure of the The Layperson’s Guide organization) was published. So far, Until 1995, the only permissible digital to High Speed Amateur only one comment was made–and that modes under Part 97 rules were RTTY was only after directly requesting a and modes that used ASCII codes. On Packet Radio . 4 comment. Apparently, no one has any November 1 of that year, the Packet BBS’s . 4 FCC--acting on an ARRL strong feelings one way or the other. Is Digital Channels . 7 that really true? A major structural petition--agreed to allow the use of any change to the organization like this digital mode, providing its technical should spark at least some debate. characteristics were "publicly If you have anything to say about documented"--§97.309(a)(4)--and the HF seemed to be the best way of letting the restructuring the NCPA or the bylaws, digital mode explosion began in earnest. amateur community know that a please do so soon. In the next issue the technique is published as well as final proposed version will be published. To make finding technical specifications providing an accurate technical That’s the one you’ll be asked to vote on for existing and emerging digital modes description of what it is." at the next general meeting. more convenient, ARRL now provides Voting on the bylaws is kind of a technical documentation for many modes The documentation is adequate to big deal, we’ll need a decent turn-out for now in use on its "§97.309(a)(4) recognize the technique or protocol the vote to be valid. So, please plan on Technical Descriptions" page when observed on the air, to determine attending. <http://www.arrl.org/FandES/field/regu the call signs of stations in The next general meeting time and lations/techchar/>. communication and to read the content place hasn’t been set yet, but most likely of their transmissions. The page will once again be on Saturday at "We needed a better place to find Pacificon in October, in Concord. We currently contains technical descriptions whether a technique has been published," of CLOVER, CLOVER-2000, G-TOR, tend to get the best turn-out when said ARRL Technical Relations Manager having meetings there. PACTOR, PACTOR-II and PSK31. Paul Rinaldo, W4RI, in explaining the NCPA Volunteers are developing move to make the information more documentation for MT63, PACTOR-III, readily available. "A place on the Web MFSK-16 and Q15X25 for later The Downlink Spring, 2003 Page 1 addition. Packet Layers for the Layer 1 - Physical The ARRL invites help from designers, ISO/OSI and TCP/IP Physical layer defines the cable or manufacturers, users and user groups to physical medium itself, e.g., thinnet, fill in the gaps for additional modes. Network Models thicknet, unshielded twisted pairs Send information or inquiries to ARRL (UTP). All media are functionally equivalent. The main difference is in Technical Relations Manager Paul The ISO/OSI Network Model Rinaldo, W4RI <[email protected]>. convenience and cost of installation and maintenance. Converters from one The standard model for networking media to another operate at this level. NCPA protocols and distributed applications is the International Standard Organization's Layer 2 - Data Link Open System Interconnect (ISO/OSI) Data Link layer defines the format of model. It defines seven network layers. data on the network. A network data frame, aka packet, includes checksum, source and destination address, and data. Directors The largest packet that can be sent through a data link layer defines the Mel Gregonis (high speed, new tech.), W6BNG Maximum Transmission Unit (MTU). e-mail: [email protected] The data link layer handles the physical Howard Krawetz (Keyboard), N6HM 408-739-7936 and logical connections to the packet's home BBS: N0ARY e-mail: [email protected] destination, using a network interface. Bob Fahnestock (TCP/IP), WH6IO A host connected to an Ethernet would home BBS: WH6IO e-mail: [email protected] Bob Vallio (DXPSN), W6RGG 510-537-6704 have an Ethernet interface to handle home BBS: N0ARY e-mail: [email protected] connections to the outside world, and a Dave “Zonker” Harris (APRS), N6UOW loopback interface to send packets to home BBS: N6QMY e-mail: [email protected] itself. Gary Mitchell (BBS), WB6YRU 408-265-2336 home BBS: N0ARY e-mail: [email protected] Ethernet addresses a host using a Mike Fahmie (BBS/Keyboard), WA6ZTY unique, 48-bit address called its Ethernet home BBS: N6EEG e-mail: [email protected] address or Media Access Control (MAC) address. MAC addresses are Officers & Staff usually represented as six colon-separated pairs of hex digits, e.g., President: Gary Mitchell, WB6YRU 8:0:20:11:ac:85. This number is unique Vice-President: Secretary: Dave Harris, N6UOW and is associated with a particular Treasurer: Howard Krawetz, N6HM Ethernet device. Hosts with multiple Editor: Gary Mitchell, WB6YRU network interfaces should use the same Frequency Coordinator: Gary Mitchell, WB6YRU MAC address on each. The data link Mail: Howard Krawetz, N6HM layer's protocol-specific header specifies the MAC address of the packet's source The NCPA Downlink is published quarterly by the Northern California Packet and destination. When a packet is sent Association, P0 Box K, Sunnyvale CA 94087, for the entertainment and education of to all hosts (broadcast), a special MAC amateur Radio operators using digital modes, and those with an interest in them. A address (ff:ff:ff:ff:ff:ff) is used. one-year membership in the NCPA, including a subscription to the NCPA Downlink, is $10.00 in the U.S. and its possessions. Layer 3 - Network All original material not attributed to another source is Copyright by NCPA. NFS uses Internetwork Protocol (IP) as Excerpts may be drawn from this publication without prior permission provided the its network layer interface. IP is original contributor is credited and this publication ("The NCPA Downlink") is cited responsible for routing, directing as the source. datagrams from one network to another. The network layer may have to break The digital band plan as well as other information about the NCPA, are available on large datagrams, larger than MTU, into the Web at: http://www.n0ary.org/ncpa smaller packets and host receiving the packet will have to reassemble the The NCPA Board of Directors meets electronically in order to transact association fragmented datagram. The Internetwork business and meet with members and interested amateurs. The address for the board Protocol identifies each host with a remailer is: [email protected]. Anyone can subscribe by sending e-mail to ncpa- 32-bit IP address. IP addresses are [email protected] with the command "subscribe" (without the quotes) in the body of written as four dot-separated decimal the message. numbers between 0 and 255, e.g., Page 2 The Downlink Spring 2003 129.79.16.40. The leading 1-3 bytes of Control Protocol (TCP) and User the IP identify the network and the Datagram Protocol (UDP), sits at the Layer 6 - Presentation remaining bytes identifies the host on transport layer. Reliability and speed are External Data Representation (XDR) sits that network. The network portion of the primary difference between these two at the presentation level. It converts the IP is assigned by InterNIC protocols. TCP establishes connections local representation of data to its Registration Services, under the contract between two hosts on the network canonical form and vice versa. The to the National Science Foundation, and through 'sockets' which are determined canonical uses a standard byte ordering the host portion of the IP is assigned by by the IP address and port number. TCP and structure packing convention, the local network administrators, locally keeps track of the packet delivery order independent of the host. by [email protected]. For large sites, and the packets that must be resent. usually subnetted like ours, the first two Maintaining this information for each Layer 7 - Application bytes represents the network portion of connection makes TCP a stateful Provides network services to the the IP, and the third and fourth bytes protocol. UDP on the other hand end-users. Mail, ftp, telnet, DNS, NIS, identify the subnet and host respectively. provides a low overhead transmission NFS are examples of network Even though IP packets are addressed service, but with less error checking. applications. using IP addresses, hardware addresses NFS is built on top of UDP because of its must be used to actually transport data speed and statelessness. Statelessness from one host to another. The Address simplifies the crash recovery. The TCP/IP Network Model Resolution Protocol (ARP) is used to map the IP address to it hardware Layer 5 - Session Although the OSI model is widely used address. The session protocol defines the format and often cited as the standard, TCP/IP of the data sent over the connections.