Retention of authorship notice would not be inappropriate
WARNING - EXPERIMENTERS ONLY!
Host mode on TNC-2 and derivative TNCs at this time remains experimental. Obvious features received a quick "going over" and rather cursory debug, but discovery of the remaining inevitable bugs and critical programming oversights awaits the adventurous reader/developer. Please direct discoveries and criticisms:
via slow boat : to Howard Goldstein
5201-23rd Ave. N.
St. Petersburg, FL 33710 USA
via compuserv : to 75006,702
via ham packet: to N2WX @ W4DPH.FL
1 Introduction
This document describes the data-link control protocol (DLC) used by the TNC-2 terminal node controller on its RS-232 line.
1.1 Where it fits in
DLC provides a bidirectional error-protected two-way queue, for BLP (the binary interface protocol). DLC uses the underlying QAFT physical layer driver as its transmission medium.
SOURCE : Physical address of the sending (SOURCE) and sinking (DESTINATION) DLC devices for this DLC packet. <Optional in TNC-2>
CTRL : type of packet
The high nibble of the control byte contains the DLC packet type. Values in the low nibble are sequence numbers.
hex
---
10 RESET - Link restart (request)
20 RESET_ACK - Link restarted (response)
4x DATA - Sequenced data (request)
(x := mod 16 sequence # of data)
5x DACK - Sequenced data acknowledgement (response)
(x := mod 16 acknowledges up through seq # x-1)
2 Defining DLC
DLC is a balanced protocol. Since there are no master-slave relationships, any one DLC device can communicate with any other electrically connected DLC device. (for ex., one computer-one TNC, or two computers and no TNCs, or two TNCs back-to-back). Note however that the current TNC-2 implementation does not specify source/destination addressing, therefore only one DLC link may take place across the physical medium.
DLC is described and was implemented as an event-driven finite-state machine.
2.1 DLC Objects
Each DLC link uses these variables and objects:
DLSTATE: One of n states. (see section on DLC states, below)
DQUEUE: FIFO queue of packets as yet unacknowledged by the peer DLC device.
2.2 DLC States
Four states and seven events are defined. See the appendix for the state tables.
2.2.1 States
2.2.1.1 DLIDLE
The DLC link is now inactive and awaits either (1) receipt of a link reset (RESET) packet; or (2) local command to initiate an outgoing call from the upper-level BLP driver.
If the DLC machine receives RESET, the DLC driver shall respond with a reset-acknowledged (RESET_ACK) packet and reset all of its upper level BLP links.
2.2.1.2 DLRESET
The DLC machine enters this state when a local event occurs (ex: upper-level BLP attempts to place a call, or a datagram is received). When the BTIMER-expired event occurs, the machine in this state sends a RESET packet to the peer.
The DLC machine leaves this state and is ready for data transfer when a reset-acknowledged (RESET_ACK) or another RESETindication is received.
2.2.1.3 DLDATA
Document dedicated to the public domain by N2WX
Retention of authorship notice would not be inappropriate
WARNING - EXPERIMENTERS ONLY!
Host mode on TNC-2 and derivative TNCs at this time remains experimental. Obvious features received a quick "going over" and rather cursory debug, but discovery of the remaining inevitable bugs and critical programming oversights awaits the adventurous reader/developer. Please direct discoveries and criticisms:
via slow boat : to Howard Goldstein
5201-23rd Ave. N.
St. Petersburg, FL 33710 USA
via compuserv : to 75006,702
via ham packet: to N2WX @ W4DPH.FL
1 Introduction
This document describes the data-link control protocol (DLC) used by the TNC-2 terminal node controller on its RS-232 line.
1.1 Where it fits in
DLC provides a bidirectional error-protected two-way queue, for BLP (the binary interface protocol). DLC uses the underlying QAFT physical layer driver as its transmission medium.
SOURCE : Physical address of the sending (SOURCE) and sinking (DESTINATION) DLC devices for this DLC packet. <Optional in TNC-2>
CTRL : type of packet
The high nibble of the control byte contains the DLC packet type. Values in the low nibble are sequence numbers.
hex
---
10 RESET - Link restart (request)
20 RESET_ACK - Link restarted (response)
4x DATA - Sequenced data (request)
(x := mod 16 sequence # of data)
5x DACK - Sequenced data acknowledgement (response)
(x := mod 16 acknowledges up through seq # x-1)
2 Defining DLC
DLC is a balanced protocol. Since there are no master-slave relationships, any one DLC device can communicate with any other electrically connected DLC device. (for ex., one computer-one TNC, or two computers and no TNCs, or two TNCs back-to-back). Note however that the current TNC-2 implementation does not specify source/destination addressing, therefore only one DLC link may take place across the physical medium.
DLC is described and was implemented as an event-driven finite-state machine.
2.1 DLC Objects
Each DLC link uses these variables and objects:
DLSTATE: One of n states. (see section on DLC states, below)
DQUEUE: FIFO queue of packets as yet unacknowledged by the peer DLC device.
2.2 DLC States
Four states and seven events are defined. See the appendix for the state tables.
2.2.1 States
2.2.1.1 DLIDLE
The DLC link is now inactive and awaits either (1) receipt of a link reset (RESET) packet; or (2) local command to initiate an outgoing call from the upper-level BLP driver.
If the DLC machine receives RESET, the DLC driver shall respond with a reset-acknowledged (RESET_ACK) packet and reset all of its upper level BLP links.
2.2.1.2 DLRESET
The DLC machine enters this state when a local event occurs (ex: upper-level BLP attempts to place a call, or a datagram is received). When the BTIMER-expired event occurs, the machine in this state sends a RESET packet to the peer.
The DLC machine leaves this state and is ready for data transfer when a reset-acknowledged (RESET_ACK) or another RESETindication is received.
2.2.1.3 DLDATA
Local and peer DLCs are ready to transact. The state changes to DWAIT when new outgoing sequenced data packets are enqueued. DDATA state is reentered once all outstanding packets are acknowledged.
2.2.1.4 DLDWAIT
The DLC machine has data outstanding for the remote DLC, and is awaiting a response. If a BTIMER-expired event occurs, the data packet(s) is (are) retransmitted. If a DACK packet acknowledging all outstanding packets is received, the state changes to DDATA.
2.3 DLC packet types
2.3.1 RESET - Call setup
format:
|DESTINATION|SOURCE|10|
^^^^^^^^^^^^^^^
(optional)
If the DLC link is idle, one side will transmit a RESET packet to fix both sides of the link to a known (DLDATA) state.
When a device receives a RESET packet it shall reply with a RESET_ACK packet and reset all of the BLP circuits its associated with.
2.3.2 RESET_ACK - DLC resetted
format:
|DESTINATION|SOURCE|LCN|20|
^^^^^^^^^^^^^^^
(optional)
Receipt of the RESET_ACK packet indicates that the DLC link is successfully opened and BLP may begin using the link.
2.3.3 DLDATA - Sequenced data command packet
format:
|DESTINATION|SOURCE|4x|[data0...datan]|
^^^^^^^^^^^^^^^
(optional)
x :: sequence number, mod 16
2.3.3.1 DACK - Sequenced data acknowledgement
format:
|DESTINATION|SOURCE|5x|
^^^^^^^^^^^^^^^
(optional)
x :: sequence number, mod 16
Acknowledges packets through sequence number 'x'
DLC State table
rx DACK, all
| rx RESET |rx RESET_ACK |rx DATA | acknowledged | timer xpd |new data queued | Local start
(.txt)