Avaya Configuring LLC Services Uživatelský manuál stáhnout pdf (Strana 31)

Logical Link Control Overview

117357-A Rev. A 1-13

SAP addresses can be

• Individual -- Designates a single SAP. The individual address is usable as both

an SSAP and a DSAP. The individual SAP has an Address Designation bit

value of 0.

• Group -- Designates a group of DSAPs. The group DSAP has an Address

Designation bit value of 1.

• Global -- Designates a group consisting of all DSAPs that the underlying

MAC SAP addresses actively service. The global DSAP has a value of all 1s.

• Null -- Designates the SAP of the underlying MAC sublayer and does not

identify any SAP to the network layer or any SAP to an associated layer

management function. The Null address is usable as both an SSAP and a

DSAP. The Null SAP has a value of all 0s.

Control Field

The Control ﬁeld consists of one or two octets that designate command and

response functions. It also contains sequence numbers when required.

The format of the Control ﬁeld of the LLC PDU deﬁnes the type of operation

(Type 1 versus Type 2):

• Information (an I format PDU)

• Supervisory (an S format PDU)

• Unnumbered (a U format PDU)

igure 1-7 shows the three Control ﬁeld formats.

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 81 82

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Avaya Configuring LLC Services Uživatelský manuál Strana 31