.
`
`AX.2S AMATEUR PACKET·RADIO
`LINK·LAYER PROTOCOL
`""
`
`W~~®D@~ ~D@
`@©u@~~~ u@®~
`
`CISCO Exhibit 1012, pg. 1
`
`

`
`,
`"
`
`AMERICAN RADIO RELAY LEAGUE, INC.
`NEWINGTON, CT USA 06111
`
`CISCO Exhibit 1012, pg. 2
`
`

`
`AX.25 Amateur Packet-Radio
`Link-Layer Protocol
`
`Version 2.0
`October 1984
`
`By
`
`Terry L. Fox, WB4JFI
`
`American Radio Relay League, Inc.
`Newington, CT USA 06111
`
`CISCO Exhibit 1012, pg. 3
`
`

`
`This protocol is intended as a guide to aid in the design and use of
`amateur packet-radio systems, in order to ensure link-layer compatibility
`between stations. The existence of this protocol does not preclude anyone
`from designing, marketing or using products, processes or procedures not
`conforming to the protocol. This protocol is subject to periodic review, and
`users are encouraged to use the latest edition.
`
`Copyright (c) 1984 by
`
`The American Radio Relay League, Inc.
`
`Copyright secured under the Pan-American Convention
`
`International Copyright secured
`
`This work is publication No. 56 of the Radio Amateur ' s Li brary, published by
`the League. Blanket permission to copy this pub lic a t i on by end users for
`noncommercial purposes is hereby granted. No part of this work may be
`reproduced in any form where such copy is of f ered in exchang e for any payment
`unless written permission has first been sec ured from the publisher.
`
`Printed in USA
`
`Quedan reservados todos los derechos
`
`Library of Congress Catalog Card Number:
`
`84-72853
`
`ISBN:
`
`0-87259-011-9
`
`$8.00 in USA
`$9.00 Canada and elsewhere
`
`ii
`
`CISCO Exhibit 1012, pg. 4
`
`

`
`AX.2S Amateur Packet-Radio Link-Layer Protocol
`
`Contents
`
`Page
`
`2. AX.25 Link-Layer Protocol Specification
`
`2.1 Scope and Field of Operation
`
`2.2 Frame
`2.2.1
`2.2.2
`2.2.3
`2.2.4
`2.2.5
`2.2.6
`2.2.7
`2.2.8
`2.2.9
`2.2.10
`2.2.11
`2.2.12
`2.2.13
`
`Structure
`Flag Field • •
`Address Fie ld
`Contro 1 · Fie ld
`PID Field
`Information Field • • • • •
`Bit Stuffing • • • •
`Frame-Check Sequence
`• • • • •
`Order of Bit Transmission
`Invalid Frames • • • • • • • • • • • • • •
`Fr ame Abor t
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`Interframe Time Fill
`• • • • • • • •
`Link Channel States • • • • • • • • • • • • • • • •
`Address-Field Encoding • • • • •
`• •••
`2.2.13.1 Nonrepeater Address-Field Encoding.
`• ••
`2.2.13.1.1 Destination Subfield Encoding.
`2.2.13.2 Level 2 Repeater-Address Encoding.
`2.2.13.3 Multiple Repeater Operation
`• • • •
`
`.
`
`.
`
`1
`
`1
`
`2
`2
`2
`3
`3
`3
`4
`4
`4
`4
`4
`4
`4
`5
`5
`7
`8
`9
`
`2.3 Elements of Procedure • • • • . • • • • • • • • • • • • • • • • • 10
`2.3.2 Control-Field Formats and State Variables
`• • • • • 10
`2.3.2.1 Control-Field Formats • • • • •
`• ••• 10
`2.3.2.1.1
`Information-Transfer Format • • • • • 11
`2.3.2.1.2 Supervisory Format.
`• • 11
`2.3.2.1.3 Unnumbered Format
`• • • • • • • • 11
`2.3.2.2 Control-Field Parameters
`•• 12
`2.3.2.3 Sequence Numbers • • • • • • • • • • • • • • • • 12
`2.3.2.4 Frame Variables and Sequence Numbers • • • • • • 12
`2.3.2.4.1 Send State Variable V(S) • • • • • • • 12
`2.3.2.4.2 Send Sequence Number W(S) • • • • • • 12
`2.3.2.4.3 Receive State Variable VCR)
`12
`2.3.2.4.4 Received Sequence Number N(R).
`• • 12
`2.3.3 Functions of Poll/Final (P/F) Bit • • • • • • • • • • • • 12
`
`ix
`
`CISCO Exhibit 1012, pg. 5
`
`

`
`AX.25 Amateur Packet-Rad~o L~nK-~aye~ CLV~V~v~
`
`Contents
`
`Page
`
`2.3.4 Control
`2.3.4.1
`2.3.4.2
`
`2.3.4.3
`
`2.3.4.2.2
`
`2.3.4.2.3
`Unnumbered
`2.3.4.3.1
`
`2.3.4.3.2
`2.3.4.3.3
`2.3.4.3.4
`
`.
`
`.
`
`. • 12
`.
`• • • 13
`• 13
`
`15
`• 15
`• 16
`
`Field Coding for Commands and Responses
`Information Command Frame Control Field
`Supervisory Frame Control Field ••••
`2.3.4.2.1 Receive Ready (RR) Command and
`Response • • • • • • • • • • • • • • 13
`Receive Not Ready (RNR) Command
`and Response • ••
`• • • • • • • 14
`Reject (REJ) Command and Response •• 14
`Frame Control Fields • • • • • • • • • 14
`Set Asynchronous Balanced Mode
`(SASH) Command • • • • • • •
`Disconnect (DISC) Command
`Frame Reject (FRMR) Response • •
`Unnumbered Acknowledge (UA)
`• •••• 17
`Response • • • • • •
`2.3.4.3.5 Disconnected Mode (DM) Response
`18
`2.3.4.3.6 Unnumbered Information (UI) Frame •• 18
`2.3.5 Link Error Reporting and Recovery
`•• 18
`2.3.5.1 DXE Busy Condition • • • • • • • • • • • • • • • 18
`2.3.5.2 Send Sequence Number Error •••
`• •••• 18
`2.3.5.3 Reject (REJ) Recovery • • • • • • • • • • • • • • 19
`2.3.5.4 Time-out Error Recovery. •
`• •••• 19
`2.3.5.4.1 Tl Timer Recovery
`•• 19
`2.3.5.4.2 Timer T3 Recovery
`•• 19
`Invalid Frame or FCS Error • • • • • • • • • • • 19
`2.3.5.5
`2.3.5.6 Frame Rejection Condition • • • • •
`• 19
`
`• 20
`•• • • • • •
`2.4 Description ofAX.25 Procedures
`• •••• 20
`• • • • • • •
`2.4.1 Address Field Operation
`• • 20
`2.4.1.1 Address Information.
`• • • •
`• • 20
`2.4.1.2 Command/Response Procedure
`• • • •
`2.4.2 pIF Bit Procedures • • • • • • • • • •
`• • • • • 21
`• • • • 21
`2.4.3 Procedures For Link Set-Up and Disconnection •
`•• 21
`2.4.3.1 LAPB Link Connection Establishment
`2.4.3.2
`Information-Transfer Phase
`• • • • • • • • • 22
`2.4.3.3 Link Disconnection
`• • • •
`• • • • • • 22
`2.4.3.4 Disconnected State • • • • • • • • • • • • • • • 22
`2.4.3.5 Collision Recovery • • • • • •
`• •••• 23
`2.4.3.5.1 Collisions in a Half-Duplex
`Environment • • • • •
`Collisions of Unnumbered
`Commands
`SASH
`Collision of a DK with a
`or DISC
`Connect ion less Operation
`
`2.4.3.5.2
`2.4.3.5.3
`
`2.4.3.6
`
`• 23
`• • 23
`
`• • 23
`• • 23
`
`x
`
`CISCO Exhibit 1012, pg. 6
`
`

`
`AX.25 Amateur Packet-Radio Link-Layer Protocol
`
`Contents
`
`2.4.4
`
`2.4.5
`2.4.6
`2.4.7
`
`Page
`
`• 24
`Procedures for Information Transfer
`• • • • • • 24
`2.4.4.1 Sending I Frames • • • • •
`2.4.4.2 Receiving I Frames • • • • • • • • • • • • • • • 24
`2.4.4.3 Reception of Out of Sequence Frames • • • • • • • 25
`2.4.4.4 Reception of Incorrect Frames • • • • • • • • • • 25
`2.4.4.5 Receiving Acknowledgement •
`• • •
`• 25
`2.4.4.6 Receiving Reject • • . •
`• • • • • • • • • • 26
`2.4.4.7 Receiving a RNR Frame. • • • • • •
`• •••• 26
`2.4.4.8 Sending a Busy Indication
`••• 26
`2.4.4.9 Waiting Acknowledgement.
`• 27
`Frame Rejection Conditions • • • •
`• • • • • • 27
`Resetting Procedure •• • • • • •
`• • • • • • •• 27
`List of System Defined Parameters • • • • • • • • • • • • 28
`2.4.7.1 Timers • • • • • • • • •
`• • ••
`28
`2.4.7.1.1 Acknowledgement Timer T1 •
`• 28
`2.4.7.1.2 Response Delay Timer T2 • • • • • • • 29
`2.4.7.1.3
`Inactive Link Timer T3 • • • • • • • • 29
`2.4.7.2 Maximum Number of Retries (N2) • • • • • • • • • 29
`2.4.7.3 Maximum Number of Octets in an I Field (NI) ••• 29
`2.4.7.4 Maximum Number of I Frames Outstanding (k) ••• 29
`
`••• •
`
`Appendix A Glossary •
`
`Appendix B References . . . . .
`
`Appendix C Implementation Notes
`
`Appendix D State Tables • . . . .
`
`. . . . . . . . .
`
`. • . • . • 31
`
`. . • • 34
`
`. .
`
`• • 35
`
`• • • 36
`
`xi
`
`CISCO Exhibit 1012, pg. 7
`
`

`
`AX.25 Amateur Packet-Radio Link-Layer Protocol
`
`2.4.4.6 Receiving Reject
`
`Upon receiving a REJ frame, the transmitting DXE will set its send
`state variable to the same value as the REJ frame's received sequence number
`in the control field. The DXE will then retransmit any I frame(s) outstanding
`at the next available opportunity conforming to the following:
`
`1. If the DXE is not transmitting at the time, and the channel is open.
`the device may commence to retransmit the I frame(s) immediately.
`
`2.
`
`3.
`
`If the DXE is operating on a full-duplex channel transmitting a UI or
`S frame when it receives a REJ frame, it may finish sending the UI or
`1
`S frame and then retransmit the I frame(s).
`
`If the DXE is operating in a full-duplex channel transmitting another
`I frame when it receives a REJ frame, it may abort the I frame it was
`sending and start retransmission of the requested I frames
`immediately.
`
`4. The DXE may send just the one I frame outstanding, or it may send
`more than the one indicated if more I frames followed the first one
`not acknowledged, provided the total to be sent does not exceed the
`flow-control window (7 frames).
`
`If the DXE recives a REJ frame with the poll bit set, it should
`respond with either a RR or RNR frame with the final bit set before
`retransmitting the outstanding I frame(s).
`
`2.4.4.7 Receiving a RNR Frame
`
`Whenever a DXE receives a RNR frame, it shall stop transmission of I
`frames until the busy condition has been cleared.
`If timer Tl runs out after
`the RNR was received, the waiting acknowledgement procedure listed in 2.4.4.9.
`below. should be performed. The poll bit may be used in conjunction. with S
`1
`frames to test for a change in the condition of the busied-out DXE.
`2.4.4.8 Sending a Busy Indication
`
`Whenever a DXE enters a busy condition. it will indicate this by
`sending a RNR response at the next opportunity. While the DXE is in the busy
`condition. it may receive and process S frames, and if a received S frame has
`the P bit set to one, the DXE should send a RNR frame with the F bit set to
`one at the next possible opportunity. To clear the busy condition, the DXE
`should send either a RR or REJ frame with the received sequence number equal
`to the current receive state variable, depending on whether the last received
`I frame was properly received or not.
`
`26
`
`CISCO Exhibit 1012, pg. 8