Sun Microsystems SunLink SNA 9.1 PU2.1, Руководство по настройке

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IBM Token Ring Concepts D-7
D
Figure D-4 LLC Address Format
Each LLC PDU consists of one destination SAP and one source SAP. Bits 0
through 5 consist of the actual address bits. Bit 6 identifies whether the SAP
address is user-defined (set to 0) or defined by the IEEE (set to 1). Bit 7
identifies whether the SAP is an individual SAP (set to 0) or a group SAP (set
to 1).
Like group MAC addresses, group SAP addresses must occur in the DSAP of
the LLC frame format. Bit 7 in the SSAP field distinguishes an LLC command
from an LLC response. Since this is controlled internally, you must specify a
value of 0 for bit 7 when specifying a local SAP.
Sun Token Ring products allow you to set DSAPs, SSAPs, and group SAPs
with which the local SAP is associated. The value of
X'FF'
is the default group
SAP for the local SAP and its value cannot be disabled. The value of
X'00'
,
called the Null SAP, is used for ring station identification purposes and must
not be used in configuration definitions. Many products have default SAP
values. For example, Internetwork Protocol (IP) uses a default SAP value of
X'AA'
, SNA uses a default SAP value of
X'04'
and a group SAP value of
X'05'
, and ISO uses a default SAP value of
X'FE'
.
D.3 Source Routing and Multiple-Ring Operation
Rather than have all stations on an IBM Token Ring network located on the
same physical ring, the IBM Token Ring architecture allows for interconnection
of multiple rings using Token Ring bridges. A Token Ring bridge is a specially
configured ring station that is connected to two physical Token Ring networks.
A ring station that has a frame to transmit decides whether to transmit the
frame on the local (or source) ring or to all rings. The decision to execute a
multiple-ring transmission depends on the higher-level protocols that exist on