📄 rfc2106.txt
字号:
1 | |
+ - - - - - - - - - - - - - - - - - +
2 | |
+ - - - - - - - - - - - - - - - - - +
3 | |
+ - - - - - - - - - - - - - - - - - +
4 | |
+ - - - - - - - - - - - - - - - - - +
5 | |
+-----------------------------------+
6 | Source SAP |
+-----------------------------------+
7 | Reserved |
+-----------------------------------+
Figure 3-4. CAN_U_REACH, I_CAN_REACH, and I_CANNOT_REACH Data
The MAC Address field carries the MAC address of the target
workstation that is being searched. This is a six-byte MAC Address
field. The same MAC Address is returned in the I_CAN_REACH and the
I_CANNOT_REACH frames.
Byte 6 is the source SAP. The destination SAP is set to zero when an
explorer frame is sent to the network.
If the sender did not receive a positive acknowledgment within a
recommended threshold value of 60 seconds, the destination is
considered not reachable.
3.4.2. START_DL, DL_STARTED, and START_DL_FAILED Frames
These frame types are used by DRAP to establish a link station
(circuit). The START_DL frame is sent directly to the server that
responds to the CAN_U_REACH frame. When the server receives this
frame, it establishes a link station with the source and destination
Chiang, et. al. Informational [Page 7]
RFC 2106 DLSRAP February 1997
addresses and saps provided in the START_DL frame. If the circuit
establishment is successful, a DL_STARTED frame is sent back as a
response. A failure will result in a START_DL_FAILED response. The
server can also send START_DL frames to clients, to establish
circuits.
+---------------+-----------------------+
| Field Name | Information |
+---------------+-----------------------+
| Message Type | 0x04, 0x05, or 0x06 |
+---------------+-----------------------+
| Packet Length | 0x18 |
+---------------+-----------------------+
Figure 3-5. START_DL, DL_STARTED, and START_DL_FAILED Header
Chiang, et. al. Informational [Page 8]
RFC 2106 DLSRAP February 1997
+-----------------------------------+
| Field Name (Each row is one byte) |
+===================================+
0 | Host MAC Address |
+ - - - - - - - - - - - - - - - - - +
1 | |
+ - - - - - - - - - - - - - - - - - +
2 | |
+ - - - - - - - - - - - - - - - - - +
3 | |
+ - - - - - - - - - - - - - - - - - +
4 | |
+ - - - - - - - - - - - - - - - - - +
5 | |
+-----------------------------------+
6 | Host SAP |
+-----------------------------------+
7 | Client SAP |
+-----------------------------------+
8 | Origin Session ID |
+-----------------------------------+
9 | |
+ - - - - - - - - - - - - - - - - - +
10| |
+ - - - - - - - - - - - - - - - - - +
11| |
+-----------------------------------+
12| Target Session ID |
+ - - - - - - - - - - - - - - - - - +
13| |
+ - - - - - - - - - - - - - - - - - +
14| |
+ - - - - - - - - - - - - - - - - - +
15| |
+-----------------------------------+
16| Largest Frame Size |
+-----------------------------------+
17| Initial Window size |
+-----------------------------------+
18| Reserved |
+ - - - - - - - - - - - - - - - - - +
19| |
+-----------------------------------+
Figure 3-6. START_DL, DL_STARTED, and START_DL_FAILED Data
The Host MAC address is the address of the target station if the
session is initiated from the client, or it is the address of the
originating station if the session is initiated from the server.
Chiang, et. al. Informational [Page 9]
RFC 2106 DLSRAP February 1997
The next two fields are the Host and Client SAPs. Each is one byte
long. The Host SAP is the SAP used by the station with the Host MAC
address. The Client SAP is the SAP used by the client.
The Origin Session ID, is the ID of the originating station that
initiates the circuit. The originating station uses this ID to
identify the newly created circuit. Before the START_DL frame is sent
to the target station, the originating station sets up a control
block for the circuit. This link station information is set because
DRAP does not use a three-way handshake for link station
establishment. In the DL_STARTED and the START_DL_FAILED messages,
the Origin Session ID is returned as received in the START_DL frame.
The Target Session ID is set by the target station and returned in
the DL_STARTED message.
The Target Session ID is not valid for the START_DL and the
START_DL_FAILED frame, and should be treated as Reserved fields. In
the DL_STARTED frame, it is the session ID that is used to set up
this circuit by the target station.
The Largest Frame Size field is used to indicate the maximum frame
size that can be used by the client. It is valid only when it is set
by the server. The Largest Frame Size field must be set to zero when
a frame is sent by the client. Both START_DL and DL_STARTED use the
Largest Frame Size field and only its rightmost 6 bits are used. The
format is defined in the IEEE 802.1D Standard, Annex C, Largest Frame
Bits (LF). Bit 3 to bit 5 are base bits. Bit 0 to bit 2 are extended
bits. The Largest Frame Size field is not used in the START_DL_FAILED
frame and must be set to zero.
bit 7 6 5 4 3 2 1 0
r r b b b e e e
Figure 3-7. Largest Frame Size
Please note that if the client is a PU 2.1 node, the client should
use the maximum I-frame size negotiated in the XID3 exchange.
The Initial window size in the START_DL frame gives the receive
window size on the originating side, and the target DRAP station
returns its receive window size in the DL_STARTED frame. The field is
reserved in the START_DL_FAILED frame. The usage of the window size
is the same as the one used in DLSw. Please refer to RFC 1795 for
details.
The last two bits are reserved for future use. They must be set to
zero by the sender and ignored by the receiver.
Chiang, et. al. Informational [Page 10]
RFC 2106 DLSRAP February 1997
If the sender of the START_DL frame did not receive a START_DL_FAILED
frame within a recommended threshold value of 60 seconds, the
connection is considered unsuccessful.
3.4.3. HALT_DL, HALT_DL_NOACK, and DL_HALTED Frames
These frame types are used by DRAP to disconnect a link station. A
HALT_DL frame is sent directly to the remote workstation to indicate
that the sender wishes to disconnect. When the receiver receives this
frame, it tears down the session that is associated with the Original
Session ID and the Target Session ID provided in the HALT_DL frame.
The receiver should respond with the DL_HALTED frame. The DL_HALTED
frame should use the same Session ID values as the received HALT_DL
message without swapping them. The HALT_DL_NOACK frame is used when
the response is not required.
+---------------+-----------------------+
| Field Name | Information |
+---------------+-----------------------+
| Message Type | 0x0C, 0x0D, or 0x0E |
+---------------+-----------------------+
| Packet Length | 0x10 |
+---------------+-----------------------+
Figure 3-8. HALT_DL, HALT_DL_NOACK, and DL_HALTED Header
Chiang, et. al. Informational [Page 11]
RFC 2106 DLSRAP February 1997
+-----------------------------------+
| Field Name (Each row is one byte) |
+===================================+
0 | Sender Session ID |
+ - - - - - - - - - - - - - - - - - +
1 | |
+ - - - - - - - - - - - - - - - - - +
2 | |
+ - - - - - - - - - - - - - - - - - +
3 | |
+-----------------------------------+
4 | Receiver Session ID |
+ - - - - - - - - - - - - - - - - - +
5 | |
+ - - - - - - - - - - - - - - - - - +
6 | |
+ - - - - - - - - - - - - - - - - - +
7 | |
+-----------------------------------+
8 | Reserved |
+ - - - - - - - - - - - - - - - - - +
9 | |
+ - - - - - - - - - - - - - - - - - +
10| |
+ - - - - - - - - - - - - - - - - - +
11| |
+-----------------------------------+
Figure 3-9. START_DL, DL_STARTED, and START_DL_FAILED Data
3.4.4. XID_FRAME, CONTACT_STN, STN_CONTACTED, INFO_FRAME, FCM_FRAME,
and DGRM_FRAME
These frame types are used to carry the end-to-end data or establish
a circuit. The Destination Session ID is the Session ID created in
the START_DL frame or the DL_STARTED frame by the receiver. The usage
of the flow control flag is the same as the one used in DLSw. Please
refer to RFC 1795 for details.
+---------------+----------------------------+
| Field Name | Information |
+---------------+----------------------------+
| Message Type | Based on Message type |
+---------------+----------------------------+
| Packet Length | 0x0C + length of user data |
+---------------+----------------------------+
Figure 3-10. Generic DRAP Header
Chiang, et. al. Informational [Page 12]
RFC 2106 DLSRAP February 1997
+-----------------------------------+
| Field Name (Each row is one byte) |
+===================================+
0 | Destination Session ID |
+ - - - - - - - - - - - - - - - - - +
1 | |
+ - - - - - - - - - - - - - - - - - +
2 | |
+ - - - - - - - - - - - - - - - - - +
3 | |
+-----------------------------------+
4 | Flow Control Flags |
+-----------------------------------+
5 | Reserved |
+ - - - - - - - - - - - - - - - - - +
6 | |
+ - - - - - - - - - - - - - - - - - +
7 | |
+-----------------------------------+
Figure 3-11. Generic DRAP Data Format
3.4.5. DATA_FRAME
This frame type is used to send connectionless SNA and NetBIOS
Datagram (UI) frames that do not have a link station associated with
the source and destination MAC/SAP pair. The difference between
DGRM_FRAME and DATA_FRAME is that DGRM_FRAME is used to send UI
frames received for stations that have a link station opened, whereas
DATA_FRAME is used for frames with no link station established.
+---------------+-----------------------------+
| Field Name | Information |
+---------------+-----------------------------+
| Message Type | 0x0A |
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -