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Communications Programming Concepts
In addition to the standard IEEE
802.2 common logical link protocol (CLLP) support and the address
resolution services, IEEE 802.3 Ethernet data link control (DLC8023)
also provides a name-discovery service that allows the operator to identify
local and remote stations by name instead of by six-byte physical
addresses. Each port must have a unique name of up to 20 characters on
the network. The character set used depends on the user's
protocol. For example, systems network architecture (SNA) requires
character set A. Each new service access point (SAP) supported on a
particular port may have a unique name, if desired.
Each name is added to the network
by broadcasting a find (local name) request. After the find (local
name) request is sent the required number of times, if no response is
returned, the physical link is declared opened. The name is then
assigned to the local port and SAP. If another port on the network has
already added the name, a name-found response is sent to the station that
issued the find request, and the new attachment fails with a result code
(DLC_NAME_IN_USE). This code indicates that a different name
must be selected. Calls are established by broadcasting a find (remote
name) request to the network and waiting for a response from the port with the
specified name. Ports with attachments pending, colliding find
requests, or an attachment to the requesting remote station will answer a find
request.
Find Header
| 0-1
| Byte length of the find packet including the length field
|
| 2-3
| Key 0x0001
|
| 4-n
| Remaining control vectors
|
Target Name
| 0-1
| Vector length = 0x000F to 0x0022
|
| 2-3
| Key 0x0004
|
| 4-9
| Name structure architecture ID:
- 4-5
- Subvector length = 0x0006
- 6-7
- Key 0x4011
- 8-9
- Identifier = 0x8000 (locally administered)
- 10-m
- Object name:
- 10-11
- Subvector length = 0x0005 to 0x000C
- 12-13
- Key 0x4010
- 14-m
- Target name (1 to 20 bytes)
|
Source Name
| 0-1
| Vector length = 0x000F to 0x0022
|
| 2-3
| Key 0x000D
|
| 4-9
| Name structure architecture ID:
- 4-5
- Subvector length = 0x0006
- 6-7
- Key 0x4011
- 8-9
- Identifier = 0x8000 (locally administered)
- 10-p
- Object name:
- 10-11
- Subvector length = 0x0005 to 0x000C
- 12-13
- Key 0x4010
- 14-p
- Source name (1 to 20 bytes)
|
Correlator
| 0-1
| Vector length = 0x0008
|
| 2-3
| Key 0x4003
|
| 4-7
| Correlator value:
- Byte 4 Bit 0
- 1 represents a SAP correlator for a find (self)
- Byte 4 Bit 0
- 0 represents a link station (LS) correlator for a find (remote)
|
Source Medium Access Control (MAC)
Address
| 0-1
| Vector length = 0x000A
|
| 2-3
| Key 0x4006
|
| 4-9
| Source MAC address (6 bytes)
|
Source SAP
| 0-1
| Vector length = 0x0005
|
| 2-3
| Key 0x4007
|
| 4
| Source SAP address
|
Found Header
| 0-1
| Byte length of the found packet including the length field
|
| 2-3
| Key 0x0002
|
| 4-n
| Remaining control vectors
|
Correlator
| 0-1
| Vector length = 0x0008
|
| 2-3
| Key 0x4003
|
| 4-7
| Correlator value:
- Byte 4 Bit 0
- 1 represents a SAP correlator for a find (self)
- Byte 4 Bit 0
- 0 represents an LS correlator for a find (remote)
|
Source MAC Address
| 0-1
| Vector length = 0x000A
|
| 2-3
| Key 0x4006
|
| 4-9
| Source MAC address (6 bytes)
|
Source SAP
| 0-1
| Vector length = 0x0005
|
| 2-3
| Key 0x4007
|
| 4
| Source SAP address
|
Response Code
| 0-1
| Vector length = 0x0005
|
| 2-3
| Key 0x400B
|
| 4
| Response code:
- B'0xxx xxxx'
- Positive response
- B'0000 0001'
- Resources available
- B'1xxx xxxx'
- Negative response
- B'1000 0001'
- Insufficient resources
|
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