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Overview of Line Protocols

1-13

Status Report Frames allow the Status Report protocol to report node conditions

and events. A condition is when a node enters a speciﬁc state (for example,

duplicate address detected). An event is an immediate occurrence (for example,

the generation of a trace). A Bay Networks station issues an SRF announcement

frame.

Parameter Management Frames allow the Parameter Management protocol to

manage an FDDI node. A management station performs operations on the MIB

attributes of a node by exchanging frames between the management station and

the FDDI node. To obtain an attribute, the management station initiates a PMF

Get Request frame. The FDDI node to which the PMF Get Request frame was

sent responds by initiating a PMF Get Response frame. A Bay Networks station

will issue a response to the sender of a PMF Get Request frame.

Wide Area Circuits

Wide area communications take place over several different types of circuits. This

section describes the T1 and E1 digital services for WAN communications.

T1 Services

T1 services use digital signals to allow two pairs of wires to carry 24 voice or data

transmissions. T

able 1-2 shows the speciﬁcation for a T1 line.

T1 Signals

T1 uses bipolar format for signals. In bipolar format, alternating positive and

negative pulses on the digital line signify the number one, and the absence of a

pulse signiﬁes zero (F

igure 1-8). A negative pulse must always follow a positive

pulse, and vice versa.

Table 1-2. Speciﬁcation for T1 Line

Attribute Value

Framing rate 8000 frames/s

Channels per frame 24

Line speed 1.544 Mb/s

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 ... 267 268

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