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Communications Programming Concepts
DLCTOKEN Device Manager Nodes
The token-ring data link control (DLCTOKEN) device manager operates between
two or more nodes on the token-ring local area network (LAN) using IEEE 802.2
procedures and control information as defined in the Token-Ring
Network Architecture Reference. Protocol support includes:
- Asynchronous disconnected mode (ADM) and asynchronous balanced mode extended
(ABME)
- Two-way simultaneous (full-duplex) data flow
- Multiple point-to-point logical attachments on the LAN using network and
service access point addresses
- Peer-to-peer relationship with remote station
- Both name-discovery and address-resolve services
- Source-routing generation for up to eight bridge hops.
DLCTOKEN provides full-duplex, peer-data transfer capabilities over a token-ring
LAN. The token-ring LAN must use the token-ring IEEE 802.5 medium access control
(MAC) procedure and a superset of the IEEE 802.2 logical link control (LLC)
protocol, as described in the Token-Ring Network Architecture
Reference.
Multiple token-ring adapters are supported with a maximum of 254 service
access point (SAP) users per adapter. A total of 255 link stations (LS) per
adapter are supported and are distributed among active SAP users. Multiple
ring segments can be accessed using token-ring network bridge facilities,
with up to eight consecutive ring segments supported between any two nodes.
LLC refers to the manager, access-channel, and LS subcomponents of a generic
data link control (GDLC) component, such as DLCTOKEN device manager, as illustrated
in the DLC[TOKEN, 8032, ETHER, or FDDI] Component Structure (Figure 4)
figure.
Figure 4. DLC[TOKEN, 8032, ETHER, or FDDI] Component Structure. This
diagram shows the component structure of the following four DLC device managers:
DLCTOKEN, DLC8032, DLCETHER, and DLC FDDI. Each device manager has the same
component structure with one exception: the DLC Component is named for the
device manager it illustrates. The diagram has two parts: the components outside
the DCL[TOKEN, 8032, ETHER, or FDDI] Component, and the components inside
of it. Outside, the User Physical Unit Services connects to the DLC Manager
on the inside and to the User Data Services on the outside. The diagram shows multiple
(numbered from one to k) User Data Services, with the first connecting to
the last. Each User Data Service connects to a corresponding Link Station,
which connects to the DLC Manager. The diagram shows multiple (numbered from
one to n) Link Stations, with the first connecting to the last. Each Link
Station connects to a single Access Channel Control, which connects to the
DLC Manager. The connection for Access Channel Control crosses the line from
LLC to MAC to connect with two Medium Access Controls. The two Medium Access Controls
connect with each other, then with the DLC Manager.
Each LS controls the transfer of data on a single logical link. The access
channel performs multiplexing and demultiplexing for message units flowing
from each LS and manager to the MAC. The DLC manager performs the following
actions:
- Establishes and stops connections
- Creates and deletes an LS
- Routes commands to the proper station
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