IEEE 802.12

Description Glossary RFCs Publications Obsolete RFCs

Description:

Protocol suite:IEEE 802.12. 100 VG - AnyLAN.
Type:Physical and Data Link Layer protocols.
SNMP MIBs:

The IEEE 802.x specifications are a group of network standards defined by ISO. IEEE 802.12 deals with the low level - Data Link Layer.

The Data Link Layer is divided into two sublayers:

The IEEE 802.12 100 VG - AnyLAN is a high-speed network with a data rate of 100 megabits per second (Mb/s) which can be transmitted over several types of twisted pair cable including single or multiple mode fiber optic cable. The 100VG-AnyLAN data packets can be encapsulated by IEEE 802.5 Token Ring or IEEE 802.3 Ethernet frames. The packets can also be routed across FDDI, ATM, and wide area networks. For media access, a packet is formatted with a training frame that is initially utilized by the IEEE 802.12 interface. This initialization determines whether the packet is normal or high priority (for example, multimedia video or audio data) according to the Demand Priority Access Method media protocol (DPAM).


IEEE 802.12 Frame:

Start Frame IEEE 802.12 packet FCS

Start Frame.
Indicates that the frame is about to begin.


IEEE 802.12 Packet Training Frame format.

0001020304050607 0809101112131415 1617181920212223 2425262728293031
Destination Address
Destination Address Source Address
Source Address
Requested Configuration
Allowed Configuration
Data :::

Destination Address. 6 bytes.
Contains a null destination address.

Source Address. 6 bytes.
To pass training, an end node must use its source address in the source address field of the training frame. A repeater may use a non-null source address if it has one, or it may use a null source address.

Requested Configuration. 16 bits.
The requested configuration field allows the slave mode device to inform the master mode device about itself and to request configuration options. The training response frame from the master mode device contains the slave mode device's requested configuration from the training request frame. The currently defined format of the requested configuration field as defined in the IEEE Standard 802.12-1995 standard is shown below. Please refer to the most current version of the IEEE document for a more up to date description of this field. In particular, the reserved bits may be used in later versions of the standard.

First Byte Second Byte
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
v v v r r r r r r r r F F P P R

 

Description

vvv: The version of the 802.12 training protocol with which the training initiator is compliant. The current version is 100. Note that because of the different bit ordering used in IEEE and IETF documents this value corresponds to version 1.
r: Reserved bits (set to zero)
FF: 00 = frameType88023.
  01 = frameType88025.
  10 = reserved.
  11 = frameTypeEither.
PP: 00 = singleAddressMode.
  01 = promiscuousMode.
  10 = reserved.
  11 = reserved.
R: 0  = training initiator is an end node.
  1 = the training initiator is a repeater.

Allowed Configuration. 16 bits.
The allowed configuration field allows the master mode device to respond with the allowed configuration. The slave mode device sets the contents of this field to all zero bits. The master mode device sets the allowed configuration field as follows:

First Byte Second Byte
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
v v v D C N r r r r r F F P P R

Description

vvv: The version of the 802.12 training protocol with which the training responder is compliant. The current version is 100. Note that because of the different bit ordering used in IEEE and IETF documents this value corresponds to version 1.
D: 0 = No duplicate address has been detected.
1 = Duplicate address has been detected.
C: 0 = The requested configuration is compatible with the network.
1 = The requested configuration is not compatible with the network and/or the attached port. In this case, the FF, PP, and R bits indicate a configuration that would be allowed.
N: 0 = Access will be allowed, providing the configuration is compatible (C = 0).
1 = Access is not granted because of security restrictions
r: Reserved bits (set to zero).
FF: 00 = frameType88023 will be used.
  01 = frameType88025 will be used.
  10 = reserved.
  11 = reserved.
PP: 00 = singleAddressMode.
  01 = promiscuousMode.
  10 = reserved.
  11 = reserved.
R: 0 = Requested access as an end node is allowed.
 1 = Requested access as a repeater is allowed.

Data. 594 - 675 bytes.
The data field is filled in by the training initiator.

FCS, Frame Check Sequence. 4 bytes.
Cyclic redundancy check (CRC) value.


Glossary:

DPAM, Demand Priority Access Method.
(RFC 2266, page 8) An IEEE 802.12 repeater can be configured to operate in either Ethernet or Token Ring framing mode. This only affects the frame format and address bit order of the frames on the wire. An 802.12 network does not use the media access protocol for either Ethernet or Token Ring. Instead, IEEE 802.12 defines its own media access protocol, the Demand Priority Access Method (DPAM). There is an existing standards-track MIB module for instrumenting IEEE 802.3 repeaters [RFC 2108]. That MIB module is designed to instrument the operation of the repeater in a network implementing the 802.3 media access protocol. Therefore, much of that MIB does not apply to 802.12 repeaters. However, the 802.3 Repeater MIB also contains a collection of objects that may be used to map the topology of a network. These objects are contained in a separable OBJECT-GROUP, are not 802.3-specific, and are considered useful for 802.12 repeaters. In addition, the layer management clause of the IEEE 802.12 specification includes similar functionality. Therefore, vendors of agents for 802.12 repeaters are encouraged to implement the snmpRptrGrpRptrAddrSearch OBJECT-GROUP defined in the 802.3 Repeater MIB.

Master Mode Operation.
(RFC 2020, page 9, RFC 2266, page 4) In an IEEE 802.12 network, "master" devices act as network controllers to decide when to grant requesting end-nodes permission to transmit. These master devices may be repeaters, or other active controller devices such as switches. Devices which do not act as network controllers, such as end-nodes or passive switches, are considered to be operating in "slave" mode.

Training Frame.
(RFC 2020, page 10, RFC 2266, page 4) Training frames are special MAC frames that are used only during link initialization. Training frames are initially constructed by the device at the lower end of a link, which is the slave mode device for the link...Training frames are always sent with a null destination address. To pass training, an end node must use its source address in the source address field of the training frame. A repeater may use a non-null source address if it has one, or it may use a null source address.


RFCs:

[RFC 2020] IEEE 802.12 Interface MIB.

[RFC 2266] Definitions of Managed Objects for IEEE 802.12 Repeater Devices.


Description Glossary RFCs Publications Obsolete RFCs