222:
supported by the Linux kernel to facilitate more modern setups with the actual transceivers directly placed under or in the antenna mast, creating a 'low loss', shorter RF wiring need, and replacing expensive and long and thick coax cables and amplifiers with cheap fiber (RFI (both ways)/EMP/lightning resistant) or copper
Ethernet wiring. BPQ Ethernet framing allows connecting entire stacks of TNC+transceiver pairs to any existing network of computers which then can all access all radio links offered simultaneously (transparently bridged), communicate with each other internally over AX.25, or with filtered routing select specific TNCs/radio frequencies.
61:
sent before waiting for acknowledgement. "Selective Reject" allows only the missing frames to be resent, rather than having to wastefully resend frames that have already been received successfully. Despite all these advantages, few implementations have been updated to include these improvements published more than 20 years ago. The only known complete implementation of v2.2, at this time (2020), is the Dire Wolf software TNC.
259:
only being two "endpoints" involved in the conversation. With SLIP, these were the two SLIP-connected hosts; with KISS, it is assumed that the KISS framing link is over serial with only the host computer and the TNC involved. Among other things, this makes it awkward to address multiple TNCs without having multiple (serial) data channels.
110:
encoding. HDLC specifies the syntax, but not the semantics, of the variable-length address field of the frame. AX.25 specifies that this field is subdivided into multiple addresses: a source address, zero or more repeater addresses, and a destination address, with embedded control fields for use by
60:
AX.25 v2.2 (1998) added improvements to improve efficiency, especially at higher data rates. Stations can automatically negotiate payload sizes larger than the previous limitation of 256 bytes. Extended sequence numbers (7 vs. 3 bits) allow a larger window size, the number of frames that can be
258:
The KISS framing is not part of the AX.25 protocol itself nor is it sent over the air. It merely serves to encapsulate the protocol frames in a way that can successfully pass over a serial link to the TNC. The KISS framing is derived from SLIP, and makes many of the same assumptions, such as there
221:
includes native support for AX.25. The computer connects to a transceiver via its audio interface or via a simple modem. The computers can also interconnect to other computers or be bridged or routed to TNCs and transceivers located elsewhere using BPQ over
Ethernet framing, which is also natively
437:
signal in some smart modulation needs a lot fewer resources than reception of the same signal, thus a sufficient microprocessor might cost just US$ 5 instead of US$ 30 and a system cost might stay below US$ 50, transmitter included. However, in recent years, the ability to receive as well as send
452:
It seems, however, that any new system that is not compatible with the current Bell 202 modulation is unlikely to be widely adopted. The current modulation seems to fulfill sufficient need that little motivation exists to move to a superior design, especially if the new design requires
335:
WARC2003 the radio amateur station callsign specification was amended so that the earlier maximum length of six characters was raised to seven characters. However, AX.25 has a built-in hard limit of six characters, which means a seven-character callsign cannot be used in an AX.25 network.
386:
new radio level modulations would need different radio gear than what is currently in use and the resulting system would be incompatible with the existing one – thus requiring a large initial investment in new radio
147:
from local stations. They allow multi-hop connections to be established between two stations unable to communicate directly. The digipeaters use and modify the information in the frame's address field to perform this function.
693:
410:
microprocessors with 128 bytes of RAM would not be enough, and new ones might cost US$ 30 instead of US$ 3. Phil Karn did demo decoding of this new modulation of his by running it on a
1364:
1331:
1354:
623:
ISO/IEC 3309: "Information technology. Telecommunications and information exchange between systems. High-level Data Link
Control (HDLC) procedures. Frame structure" (1984).
557:
320:, and typically 1,200 bit/s), the use of additional network layers with AX.25 is impractical due to the data overhead involved. This is not a limitation of AX.25
1104:
111:
the repeaters. To simplify compliance with amateur radio rules, these addresses derive from the station call signs of the source, destination and repeater stations.
1184:
1147:
1189:
1232:
225:
Dire Wolf is a free open-source replacement for the 1980s-style TNC. It contains DSP software modems and a complete implementation of AX25 v2.2 plus
1349:
99:. At the physical layer, AX.25 defines only a "physical layer state machine" and some timers related to transmitter and receiver switching delays.
414:
machine – some 10 years later, mid-level embedded microprocessors are capable enough to do the same with under US$ 50 system cost.
229:
forward error correction. It can function as a digital repeater, GPS tracker, and APRS Internet
Gateway (IGate) without any additional software.
697:
278:
stations, without any additional network layers. This is sufficient for keyboard-to-keyboard contacts between stations and for accessing local
948:
429:
Small gadget transmitters do not need to know what is being transmitted. There is only a need to monitor channel occupation by radio receiver
121:
AX.25 supports both virtual-circuit connected and datagram-style connectionless modes of operation. The latter is used to great effect by the
1260:
64:
AX.25 is commonly used as the data link layer for network layer such as IPv4, with TCP used on top of that. AX.25 supports a limited form of
1097:
1164:
271:
1134:
754:
1369:
1227:
1009:
1001:
838:
801:
474:
290:
122:
1159:
68:. Although it is possible to build AX.25 switches similar to the way Ethernet switches work, this has not yet been accomplished.
603:
1341:
1303:
1222:
1142:
1090:
1061:
807:
144:
642:
1242:
1066:
906:
544:
480:
423:
226:
418:
Despite these limitations, an extension to the AX.25 protocol, supporting forward error correction, has been created by the
360:
KA9Q, have argued that AX.25 is not well-suited to operation over noisy, limited-bandwidth radio links, citing its lack of
1359:
1275:
1199:
1176:
434:
115:
1071:
349:); the SSID often assumes this role. Thus there can be only one service per AX.25 station SSID address, which is often
103:
1470:
1465:
1457:
1374:
830:
793:
729:
516:
419:
456:
Most recently, a wholly new protocol with forward error correction has been created by Nino
Carillo, KK4HEJ, called
941:
327:
HDLC protocols identify each frame by an address. The AX.25 implementation of HDLC includes sender and destination
301:
672:
520:
1438:
485:
457:
1433:
986:
361:
248:
191:
887: – a web site established to be a concise repository for AX.25 layer 2 design activities
163:
1496:
1443:
399:
305:
54:
867:
1491:
1428:
1117:
1113:
934:
279:
158:
protocol, but this has seen little use outside of keyboard-to-keyboard or keyboard-to-BBS connections.
137:
331:
plus four-bit
Secondary Station Identifier (SSID) value in range 0 through 15 in the frame address. At
1412:
368:. However, a viable widely adopted successor to AX.25 has yet to emerge. Likely reasons may include:
346:
1152:
1082:
893:
880:
850:
297:
214:
46:
1407:
1379:
1321:
1125:
834:
797:
341:
175:
50:
190:
Traditionally, amateur radio operators have connected to AX.25 networks through the use of a
159:
1394:
1294:
365:
167:
750:
251:
that implements the KISS framing as a low-cost alternative to using expensive and uncommon
910:
897:
884:
871:
854:
317:
23:
433:(Received Signal Strength Indication) to know when not to send. Transmitting interleaved
316:
At the speeds commonly used to transmit packet radio data (rarely higher than 9,600
182:, which is an amateur radio TCP/IP network using AX.25 UI-frames at the datalink layer.
379:
easy availability of cheap, low-power FM transmitters, especially for the 430 MHz
195:
129:
96:
92:
80:
65:
913: – Tadd Torborg KA2DEW - Terrestrial Amateur Radio Packet Network site
1501:
1485:
724:
595:
203:
171:
155:
31:
784:
1014:
957:
634:
469:
324:, but places constraints on the sophistication of applications designed to use it.
275:
218:
35:
903:
991:
391:
207:
1402:
1035:
916:
857: – a project to construct a global, radio-based network using
411:
373:
283:
240:
133:
42:
262:
Alternatives to KISS do exist that address these limitations, such as 6PACK.
1384:
1045:
664:
545:"AX.25 Throughput: Why is 9600 bps Packet Radio only twice as fast as 1200?"
439:
357:
719:
1316:
1311:
1217:
971:
443:
403:
199:
140:
106:
frame syntax and procedures. (ISO 3309) frames are transmitted with
76:
AX.25 does not define a physical layer implementation. In practice 1200
1212:
1030:
668:
509:
179:
1250:
1207:
858:
581:
552:
446:
350:
202:. These devices allow network resources to be accessed using only a
170:
exist to provide routing between nodes. In principle, a variety of
976:
407:
83:
and 9600 baud G3RUH DFSK are almost exclusively used on
1040:
430:
252:
107:
77:
27:
1086:
930:
926:
380:
332:
88:
84:
874: – a site dedicated to packet radio on Linux
864:
669:"The KISS TNC: A simple Host-to-TNC communications protocol"
786:
AX.25 Amateur Packet-Radio Link-Layer
Protocol, Version 2.0
174:
protocols can be used with AX.25, including the ubiquitous
270:
AX.25 has most frequently been used to establish direct,
900: – Bob Bruninga's official APRS website
890:
877:
136:
is available at the datalink level. Digipeaters act as
847:
510:"AX.25 Link Access Protocol for Amateur Packet Radio"
300:
of AX.25 packets over IP, AXIP and AXUDP are used to
751:"TARPN Software Products - Protocols and Modulation"
376:
FM radios and especially existing APRS applications,
1456:
1421:
1393:
1340:
1302:
1293:
1274:
1259:
1241:
1198:
1175:
1133:
1124:
1054:
1023:
1000:
964:
151:The AX.25 specification defines a complete, albeit
95:the standard transmission mode is 300 baud
26:protocol originally derived from layer 2 of the
45:connections, transferring data encapsulated in
1098:
942:
34:operators. It is used extensively on amateur
8:
398:takes more effort than the 1,200 bit/s
118:approach with collision recovery (CSMA/CR).
41:AX.25 v2.0 is responsible for establishing
1299:
1130:
1105:
1091:
1083:
949:
935:
927:
827:Packet: Speed, More Speed and Applications
438:using cheap microcontrollers (such as the
383:band, to match existing legacy radio gear,
16:Amateur radio data communications protocol
504:
502:
198:and an implementation of the protocol in
143:, receiving, decoding and retransmitting
53:, and detecting errors introduced by the
694:"6PACK a "real time" PC to TNC protocol"
372:a large existing deployment of recycled
353:around with varying degrees of success.
498:
30:protocol suite and designed for use by
732:from the original on 22 November 2008
596:"9600 Baud Packet Radio Modem Design"
7:
213:AX.25 has also been implemented on
645:from the original on 11 March 2008
293:has become a popular application.
14:
675:from the original on 25 July 2008
563:from the original on 8 March 2021
475:Automatic Packet Reporting System
449:families) has been demonstrated.
123:Automatic Packet Reporting System
114:Media access control follows the
453:significant hardware purchases.
829:(2nd ed.). Newington, CT:
813:from the original on 2014-01-07
757:from the original on 2021-07-09
606:from the original on 2012-06-07
526:from the original on 2014-06-11
406:. Previously sufficient small
178:(IP). This approach is used by
481:FX.25 Forward Error Correction
102:At the link layer, AX.25 uses
1:
1422:Delay and disruption tolerant
116:Carrier sense multiple access
1072:Encoder receiver transmitter
919:ax25.net –
831:American Radio Relay League
794:American Radio Relay League
635:"Linux AX.25 Configuration"
517:Tucson Amateur Packet Radio
422:. This extension is called
247:AX.25 is often used with a
1518:
720:"Packet Radio Under Linux"
825:Rich Roznoy, ed. (1997).
486:Improved Layer 2 Protocol
458:Improved Layer 2 Protocol
987:Terminal node controller
396:forward error correction
362:forward error correction
339:AX.25 lacks an explicit
192:terminal node controller
633:John Ackermann (2002).
356:Some amateurs, notably
1444:Dynamic Source Routing
1114:Channel access methods
394:potentially including
280:bulletin board systems
55:communications channel
783:Terry L. Fox (1984).
718:Jeff Tranter (1997).
594:James Miller (1995).
1118:media access control
556:. 12 November 2021.
364:(FEC) and automatic
239:See full article at
217:. For example, the
22:(Amateur X.25) is a
1342:Collision avoidance
1024:TCP/IP packet radio
917:AX.25 Specification
194:, which contains a
153:point to point only
97:Bell 103 tones
81:Bell 202 tones
1304:Collision recovery
909:2021-06-21 at the
896:2021-05-06 at the
883:2006-07-07 at the
870:2008-11-20 at the
853:2001-03-31 at the
390:adoption of newer
255:controller cards.
215:personal computers
1479:
1478:
1458:Duplexing methods
1452:
1451:
1289:
1288:
1080:
1079:
792:. Newington, CT:
329:station call-sign
304:AX.25 into IP or
289:In recent years,
233:KISS-mode framing
176:Internet Protocol
1509:
1300:
1131:
1107:
1100:
1093:
1084:
951:
944:
937:
928:
861:over AX.25 links
844:
821:
819:
818:
812:
791:
766:
765:
763:
762:
747:
741:
740:
738:
737:
715:
709:
708:
706:
705:
696:. Archived from
690:
684:
683:
681:
680:
663:Mike Chepponis;
660:
654:
653:
651:
650:
630:
624:
621:
615:
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591:
585:
579:
573:
572:
570:
568:
562:
549:
541:
535:
534:
532:
531:
525:
514:
506:
435:Reed-Solomon FEC
366:data compression
132:mechanism using
1517:
1516:
1512:
1511:
1510:
1508:
1507:
1506:
1482:
1481:
1480:
1475:
1448:
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1194:
1171:
1120:
1111:
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1076:
1050:
1019:
996:
960:
955:
924:
922:
911:Wayback Machine
898:Wayback Machine
885:Wayback Machine
872:Wayback Machine
855:Wayback Machine
841:
824:
816:
814:
810:
804:
789:
782:
778:
776:Further reading
772:
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314:
268:
235:
188:
186:Implementations
74:
24:data link layer
17:
12:
11:
5:
1515:
1513:
1505:
1504:
1499:
1497:Link protocols
1494:
1484:
1483:
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1474:
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1460:
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1395:Collision-free
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888:
875:
865:Linux-AX25.org
862:
845:
839:
822:
802:
796:. p. 18.
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742:
710:
685:
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536:
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489:
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377:
313:
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274:links between
272:point-to-point
267:
264:
245:
244:
234:
231:
196:microprocessor
187:
184:
130:source routing
73:
70:
66:source routing
15:
13:
10:
9:
6:
4:
3:
2:
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1347:
1345:
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1333:
1330:
1328:
1325:
1323:
1320:
1318:
1317:Slotted ALOHA
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1313:
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1127:
1126:Channel-based
1123:
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918:
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899:
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879:
878:AX.25 Layer 2
876:
873:
869:
866:
863:
860:
856:
852:
849:
846:
842:
840:0-87259-605-2
836:
832:
828:
823:
809:
805:
803:0-87259-011-9
799:
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788:
787:
781:
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775:
773:
756:
752:
746:
743:
731:
727:
726:
725:Linux Journal
721:
714:
711:
700:on 2012-02-24
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404:Bell 202
401:
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204:dumb terminal
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156:network layer
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79:
72:Specification
71:
69:
67:
62:
58:
56:
52:
48:
44:
39:
37:
33:
32:amateur radio
29:
25:
21:
1492:Packet radio
1326:
1295:Packet-based
1015:APRS Calling
981:
958:Packet radio
923:
826:
815:. Retrieved
785:
771:
759:. Retrieved
745:
734:. Retrieved
723:
713:
702:. Retrieved
698:the original
688:
677:. Retrieved
658:
647:. Retrieved
638:
628:
619:
608:. Retrieved
599:
589:
577:
565:. Retrieved
551:
539:
528:. Retrieved
470:Packet radio
455:
451:
428:
417:
395:
392:line codings
355:
340:
338:
328:
326:
321:
315:
295:
288:
276:packet radio
269:
266:Applications
261:
257:
246:
238:
224:
219:Linux kernel
212:
189:
172:layer 3
152:
150:
127:
120:
113:
101:
75:
63:
59:
40:
36:packet radio
19:
18:
1055:Specialized
992:FBB (F6FBB)
965:Traditional
312:Limitations
302:encapsulate
284:DX clusters
208:transceiver
134:digipeaters
1486:Categories
1403:Token Ring
1036:KISS (TNC)
817:2014-01-07
761:2021-07-08
736:2009-01-01
704:2009-05-28
679:2008-08-18
649:2008-03-05
610:2012-02-03
584:github.com
530:2014-01-15
493:References
412:Pentium II
374:narrowband
241:KISS (TNC)
43:link layer
38:networks.
1408:Token bus
1385:CSMA/CARP
1067:FX.25 FEC
1046:Phil Karn
665:Phil Karn
582:Dire Wolf
440:Atmel AVR
358:Phil Karn
308:packets.
298:tunneling
141:repeaters
128:A simple
1413:MS-ALOHA
1218:TD-SCDMA
972:ALOHAnet
907:Archived
894:Archived
881:Archived
868:Archived
851:Archived
808:Archived
755:Archived
730:Archived
673:Archived
643:Archived
639:febo.com
604:Archived
558:Archived
521:Archived
519:. 1997.
464:See also
460:(IL2P).
444:Motorola
200:firmware
125:(APRS).
49:between
1365:CSMA/CA
1332:CSMA/CD
1322:R-ALOHA
1251:HC-SDMA
1233:MC-CDMA
1228:FH-CDMA
1223:DS-CDMA
1213:TD-CDMA
1185:MF-TDMA
1153:SC-FDMA
1062:Spartan
1031:AMPRNet
848:AMPRNet
488:(IL2P)
442:or the
351:kludged
180:AMPRNet
160:NET/ROM
145:packets
138:simplex
1208:W-CDMA
859:TCP/IP
837:
800:
553:GitHub
477:(APRS)
447:68HC08
322:per se
206:and a
168:TexNet
166:, and
47:frames
1434:VANET
1429:MANET
1355:MACAW
1327:AX.25
1312:ALOHA
1190:STDMA
1148:OFDMA
982:AX.25
977:PRNET
904:TARPN
811:(PDF)
790:(PDF)
600:AMSAT
567:7 May
561:(PDF)
548:(PDF)
524:(PDF)
513:(PDF)
424:FX.25
408:8-bit
387:gear,
318:bit/s
227:FX.25
91:. On
51:nodes
20:AX.25
1502:X.25
1360:CSMA
1350:MACA
1276:PAMA
1261:PDMA
1243:SDMA
1200:CDMA
1177:TDMA
1165:WDMA
1135:FDMA
1116:and
1041:KA9Q
1010:APRS
1002:APRS
891:APRS
835:ISBN
798:ISBN
569:2020
431:RSSI
420:TAPR
400:AFSK
345:(or
342:port
296:For
291:APRS
282:and
253:HDLC
164:ROSE
108:NRZI
104:HDLC
87:and
78:baud
28:X.25
1471:FDD
1466:TDD
1439:DTN
1380:HCF
1375:PCF
1370:DCF
1160:WDM
1143:FDM
402:of
381:UHF
347:SAP
333:ITU
306:UDP
249:TNC
89:UHF
85:VHF
1488::
833:.
806:.
753:.
728:.
722:.
671:.
667:.
641:.
637:.
602:.
598:.
550:.
515:.
501:^
426:.
286:.
210:.
162:,
93:HF
57:.
1106:e
1099:t
1092:v
950:e
943:t
936:v
843:.
820:.
764:.
739:.
707:.
682:.
652:.
613:.
571:.
533:.
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