CONNECT_PENDING state and to send a CONTACT message to the other Data
Link Switch. Thus the target Data Link Switch has assumed the role
of the origin Data Link Switch.
4.2.2.4 CONNECT_PENDING State
Event Action(s) Next State
----- --------- ----------
Receive CONTACTED DLC_EXIT_BUSY CONNECTED
Receive HALT_DL DLC_HALT_DL HALT_PENDING
Receive DGRMFRAME DLC_DGRM
Receive DATAFRAME DLC_DGRM
DLC_RESET Send RESTART_DL (See note) CIRCUIT_RESTART
DLC_ERROR Send HALT_DL DISCONNECT_PENDING
DLC_DGRM Send DGRMFRAME
The CONNECT_PENDING state is entered by the origin Data Link Switch
when a DLC_CONTACTED signal has been received from the DLC (i.e., a
SABME command has been received). A CONTACT message is then issued.
The state is exited upon the receipt of a CONTACTED message from the
target Data Link Switch. If a DLC_RESET signal is received, the
local data link is restarted and a RESTART_DL message is sent to the
remote DLS.
Note: The IBM 6611 will also send a Test command in order to
restart the data link to the station that sent the SABME command
(i.e., a DLC_START_DL will be issued).
4.2.2.5 CIRCUIT_ESTABLISHED State
Event Action(s) Next State
----- --------- ----------
Receive CONTACT DLC_CONTACT CONTACT_PENDING
Receive HALT_DL DLC_HALT_DL HALT_PENDING
Receive XIDFRAME DLC_XID
Receive DGRMFRAME DLC_DGRM
Receive DATAFRAME DLC_DGRM
DLC_CONTACTED Send CONTACT CONNECT_PENDING
DLC_ENTER_BUSY
DLC_ERROR Send HALT_DL DISCONNECT_PENDING
DLC_DGRM Send DGRMFRAME
DLC_XID Send XIDFRAME
The CIRCUIT_ESTABLISHED state is entered by the origin Data Link
Switch from the DISCONNECTED state, and by the target Data Link
Switch from the CIRCUIT_PENDING state. The state is exited when a
connection is started (i.e., DLC receives a SABME command). The next
state is CONTACT_PENDING for the target Data Link Switch and
CONNECT_PENDING for the origin Data Link Switch.
4.2.2.6 CONTACT_PENDING State
Event Action(s) Next State
----- --------- ----------
Receive HALT_DL DLC_HALT_DL HALT_PENDING
Receive RESTART_DL DLC_HALT_DL RESTART_PENDING
Receive DGRMFRAME DLC_DGRM
Receive DATAFRAME DLC_DGRM
DLC_CONTACTED Send CONTACTED CONNECTED
DLC_ERROR Send HALT_DL DISCONNECT_PENDING
DLC_DGRM Send DGRMFRAME
The CONTACT_PENDING state is entered by the target Data Link Switch
upon the receipt of a CONTACT message. This causes the Data Link
Switch to issue a DLC_CONTACT signal to the DLC (i.e., DLC sends a
SABME command). This state is then exited upon the receipt of a
DLC_CONTACTED signal from the DLC (i.e., a UA response received).
If a RESTART_DL message is received, indicating that the remote Data
Link Switch has received a DLC_RESET signal, the local Data Link
Switch will send a DISC command frame on the adjacent LAN (i.e.,
DLC_HALT_DL signal) and enter the RESTART_PENDING state.
4.2.2.7 CONNECTED State
Event Action(s) Next State
----- --------- ----------
Receive HALT_DL DLC_HALT_DL HALT_PENDING
Receive RESTART_DL DLC_HALT_DL RESTART_PENDING
Receive DGRMFRAME DLC_DGRM
Receive INFOFRAME DLC_INFO
Receive DATAFRAME DLC_DGRM
DLC_RESET Send RESTART_DL (See note) CIRCUIT_RESTART
DLC_ERROR Send HALT_DL DISCONNECT_PENDING
DLC_DGRM Send DGRMFRAME
DLC_INFO Send INFOFRAME
The CONNECTED state is entered by the origin Data Link Switch from
the CONNECT_PENDING state upon the receipt of a CONTACTED message.
The CONNECTED state is entered by the target Data Link Switch from
the CONTACT_PENDING state upon the receipt of a DLC_CONTACTED signal.
At this time, the target Data Link Switch will return a CONTACTED
message to the origin Data Link Switch.
The CONNECTED state is exited usually under one of two conditions: a
DLC_ERROR signal received from the DLC (e.g., a DISC command received
by the local DLC), or a HALT_DL message received from the other Data
Link Switch (e.g., a DISC command received by the remote DLC).
A SABME command (i.e., a DLC_RESET signal) received by either Data
Link Switch will also cause the two Data Link Switches to leave the
CONNECTED state and eventually restart a new circuit.
Note: The IBM 6611 will also send a Test command in order to
restart the data link to the station that sent the SABME command
(i.e., a DLC_START_DL will be issued).
Following the receipt of a reset signal, the Data Link Switch will
send a RESTART_DL message to the other Data Link Switch and will
enter the CIRCUIT_RESTART state. Upon the receipt of the RESTART_DL
message, the remote Data Link Switch will send a DISC command (i.e.,
DLC_HALT_DL signal) and enter the RESTART_PENDING state.
4.2.2.8 CIRCUIT_RESTART State
Event Action(s) Next State
----- --------- ----------
Receive DL_RESTARTED If Connected: If Connected:
Send CONTACT CONNECT_PENDING,
else: CIRCUIT_ESTABLISHED
Receive DATAFRAME DLC_DGRM
DLC_ERROR Send HALT_DL DISCONNECT_PENDING
DLC_DGRM Send DATAFRAME
The CIRCUIT_RESTART state is entered if a DLC_RESET signal is
received from the local DLC. This was caused by the receipt of a
SABME command while a connection was currently active. A DM response
will be issued to the SABME command and the Data Link Switch will
attempt to restart the end-to- end circuit.
The CIRCUIT_RESTART state is exited through one of two transitions.
The next state depends upon the time the local DLC has reached the
contacted state (i.e., a DLC_CONTACTED signal is presented) relative
to the receipt of the DL_RESTARTED message. This signal is caused by
the origin station resending the SABME command that initially caused
the DATA Link Switch to enter the CIRCUIT_RESTART state. The two
cases are as follows:
1) DL_RESTARTED message received before the
DLC_CONTACTED signal- In this case, the
CIRCUIT_ESTABLISHED state is entered.
2) DL_RESTARTED message received after the
DLC_CONTACTED signal- In this case, the
CONNECT_PENDING state is entered.
4.2.2.9 DISCONNECT_PENDING State
Event Action(s) Next State
----- --------- ----------
Receive DL_HALTED DISCONNECTED
Receive HALT_DL Send DL_HALTED
Receive DATAFRAME DLC_DGRM
DLC_DGRM Send DATAFRAME
The DISCONNECT_PENDING state is entered when a DLC_ERROR signal is
received from the local DLC. Upon receipt of this signal, a HALT
message is sent. Once an DL_HALTED message is received, the state is
exited, and the Data Link Switch enters the DISCONNECTED state.
4.2.2.10 RESTART_PENDING State
Event Action(s) Next State
----- --------- ----------
Receive DATAFRAME DLC_DGRM
DLC_DL_HALTED (See note) Send DL_RESTARTED CIRCUIT_ESTABLISHED
DLC_ERROR Send HALT_DL DISCONNECT_PENDING
DLC_DGRM Send DATAFRAME
The RESTART_PENDING state is entered upon the receipt of a RESTART_DL
message from the remote DLS while the local Data Link Switch is in
either the CONTACT_PENDING state or the CONNECTED state. These cause
the local DLC to issue a DISC command. Upon the receipt of the UA
response (DLC_DL_HALTED), the data link is restarted, a DL_RESTARTED
message is returned to the remote DLS, and the CIRCUIT_ESTABLISHED
state is entered.
Note: The IBM 6611 will send a Test command in order to restart
the data link to the target station (i.e., a DLC_START_DL will be
issued) prior to sending the DL_RESTARTED message.
4.2.2.11 HALT_PENDING State
Event Action(s) Next State
----- --------- ----------
Receive DATAFRAME DLC_DGRM
DLC_DL_HALTED Send DL_HALTED DISCONNECTED
DLC_ERROR Send DL_HALTED DISCONNECTED
DLC_DGRM Send DATAFRAME
The HALT_PENDING state is entered upon the receipt of a HALT_DL
message. This causes the local DLC to issue a DISC command. Upon
the receipt of the UA response (DLC_DL_HALTED), a DL_HALTED message
is returned to the remote DLS and the DISCONNECTED state is entered.
4.3. NetBIOS Datagrams
The NetBIOS protocols use a number of UI frames for directory
services and the transmission of datagrams. Most of these frames are
directed to a group MAC address (GA) with the routing information
field indicating spanning tree explorer (STE). Two of the frames,
NB_Add_Name_Response and NB_Status_Response, are directed to a
specific MAC address with the routing information field indicating a
specifically routed frame (SRF). The handling of these frames is
summarized in the following table.
Event Action(s) Comment
----- --------- -------
DLC_DGRM (NB Group Address): Send NETBIOS_ANQ Transmitted to all
NB_Add_Name_Query remote DLS
DLC_DGRM (Specific Address): Send NETBIOS_ANR Transmitted to
NB_Add_Name_Response specific DLS
DLC_DGRM (Specific Address): Send DATAFRAME Transmitted to all
NB_Status_Response remote DLS
DLC_DGRM (NB Group Address): Send DATAFRAME Transmitted to all
NB_Name_in_Conflict, remote DLS
NB_Add_Group_Name_Query,
NB_Datagram,
NB_Datagram_Broadcast,
NB_Status_Query,
NB_Terminate_Trace
Table 5. NetBIOS DLC Frames
The above actions do not apply in the following states:
CIRCUIT_ESTABLISHED, CONTACT_PENDING, CONNECT_PENDING, CONNECTED, and
CIRCUIT_PENDING. The handling of the remaining two UI frames used by
NetBIOS systems, NB_Name_Query and NB_Name_Recognized, are documented
as part of the DLS state machine in the previous section (i.e.,
DISCONNECTED and RESOLVE_PENDING states). Furthermore, the handling
of NetBIOS datagrams (i.e., NB_Datagram) sent to a specific MAC
address is also governed by the DLS state machine.
Note: The IBM 6611 will also issue Test frames during the
exchange of the NetBIOS, NB_Name_Query and NB_Name_Recognized.
This exchange of protocol data units occurs during the start of a
data link and is used to determine the routing information. Most
other implementations of NetBIOS will use the
NB_Name_Query/NB_Name_Recognized exchange to determine routes in
conjunction with resolving the NetBIOS names. These differences
are not reflected in the SSP protocols.
The handling of the NetBIOS specific SSP messages is given in the
following table.
Event Action(s) Comment
----- --------- -------
NETBIOS_ANQ DLC_DGRM: Routed STE
NB_Add_Name_Query (NB Group Address)
NETBIOS_ANR DLC_DGRM: Routed SRF
NB_Add_Name_Response (Specific MAC Address)
NETBIOS_NQ DLC_DGRM: Routed STE
NB_Name_Query (NB Group Address)
NETBIOS_NR DLC_DGRM: Routed SRF
NB_Name_Recognized (Specific MAC Address)
DATAFRAME DLC_DGRM Routed STE
(If NB_Status_Response:
Specific MAC Address
Else: NB Group Address)
Table 6. NetBIOS SSP Messages
The above actions apply to all DLS states. The handling of NetBIOS
datagrams sent within DGRMFRAME messages is governed by the DLS state
machine. The DGRMFRAME message type is employed instead of the
DATAFRAME message type once the end-to-end circuit has been
established. At that time, the message is addressed according to the
pair of Circuit IDs in the message header instead of relying upon the
MAC address information in the token ring header.
Acknowledgments
Randall Campbell, David Miller, Gene Cox, Ravi Periasamy, and The
Ghost of Christmas Past.
References
1) ISO 8802-2/IEEE Std 802.2 International Standard,
Information Processing Systems, Local Area Networks, Part 2:
Logical Link Control, December 31, 1989
2) The NETBIOS Frames Protocol, IBM Local Area Technical
Reference, SC30-3383-03, Chapter 5, December 1990
3) ISO/IEC DIS 10038 DAM 2, MAC Bridging, Source Routing
Supplement, December 1991
Security Considerations
Security issues are not discussed in this memo.
Authors' Addresses
Roy C. Dixon
IBM Networking Systems
Department B57, Building 060
P.O. Box 12195
Research Triangle Park, NC 27709
Phone: (919) 543-3380
EMail: rcdixon@ralvmg.vnet.ibm.com
David M. Kushi
IBM Research Division
T. J. Watson Research Center
Room H0-C07
30 Saw Mill River Road
Hawthorne, NY 10532
Phone: (914) 784-7815
EMail: kushi@watson.ibm.com
Note: Any questions or comments relative to the contents of this RFC
should be sent to the following Internet address:
dlsw@ralvma.vnet.ibm.com. This address will be used to coordinate
the handling of responses.