DP83261 datasheet(7/132 Pages) NSC

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30 Feature Overview (Continued)

31 FDDI MAC SUPPORT

The BMAC device implements the Standard ANSI X3T95

FDDI MAC protocol for transmitting receiving repeating

and stripping frames Many of the capabilities defined in

MAC-2 are included in the BMAC device such as bridging

end station support for setting the control indicators and

the statistic counters The BMAC device provides all of the

information necessary to implement the service primitives

defined in the standard

The BMAC device also implements many of the permitted

extensions to the FDDI-MAC standard as captured in the

FDDI MAC-2 document These include the extensions for

MAC level bridging Group Addressing support that can be

used for SMT reporting of additional events to aid the ring

management processes and enhanced versions of the state

machines

32 MAC ADDRESSING SUPPORT

Both long (48-bit) and short (16-bit) addressing are support-

ed simultaneously for both Individual and Group addresses

Up to 128 contiguous programmable group addresses and

up to 15 Fixed Group Addresses plus the universalbroad-

cast address are recognized Limited operation with null ad-

dresses is supported An interface to external address

matching logic is provided to augment the Ring Engine’s

addressing capabilities

33 MAC BRIDGING SUPPORT

Several features are provided to aid in Bridging applications

On the receive side external address matching logic can be

used to examine the PH

Indicate byte stream to decide

whether to copy a frame how to set the control indicators

and how to increment the counters

On the transmit side transparency options are provided on

the Source Address the most significant bit of the Source

Address and the FCS

In addition support for an alternate Void stripping mecha-

nism provides maximal flexibility in the generation of frames

34 MAC SERVICE CLASS SUPPORT

All of the FDDI MAC service classes are supported by the

BMAC device These include the Synchronous Asynchro-

nous

Restricted Asynchronous

and Immediate service

classes

For Synchronous transmission one or more frames are

transmitted in accordance with the station’s synchronous

bandwidth allocation

For Asynchronous transmission one programmable asyn-

chronous priority threshold is supported in addition to the

threshold at the Negotiated Target Token Rotation time

For Restricted Asynchronous transmission support is pro-

vided to begin continue and end restricted dialogues

For Immediate transmissions support is provided to send

frames from either the Data Beacon or Claim states and

either ignore or respond to the received byte stream After

an immediate transmission a token may optionally be is-

sued

35 DIAGNOSTIC COUNTERS

The BMAC device includes a number of diagnostic counters

that monitor ring and station performance

These counters allow measurement of the following

Number of frames transmitted and received by the sta-

tion

Number of frames copied as well as frames not copied

because of insufficient buffering

Frame error rate of an incoming physical connection to

the MAC

Load on the ring based on the number of tokens re-

ceived and the ring latency

Ring latency

Lost frames

The size of these counters has been selected to keep the

frequency of overflow small even under worst case operat-

ing conditions

36 MANAGEMENT SERVICES

The BMAC device provides management services to the

Host System via the Control Bus Interface This interface

allows access to internal registers to control and configure

the BMAC device

37 RING PARAMETER TUNING

The BMAC device includes settable parameters to allow

tuning of the network to increase performance over a large

range of network sizes

The BMAC device supports systems of two stations with

little cable between them to ring configurations much larger

than the 1000 physical attachments andor 200 km dis-

tance that are specified as the default values in the stan-

dard

The BMAC device also handles frames larger than the 4500

byte default maximum frame size as specified in the Stan-

dard

38 MULTI-FRAME STREAMING INTERFACE

The BMAC device provides an interface to support a multi-

frame streaming interface Multiple frames can be transmit-

ted after a token is captured within the limits of the token

timer thresholds

39 GENERATES BEACON CLAIM

AND VOID FRAMES INTERNALLY

For purposes of transient token and ring recovery no proc-

essor intervention is required The BMAC device automati-

cally generates the appropriate MAC frames

310 SELF TESTING

Because the BMAC device is full duplex loopback testing is

possible before entering the ring and during normal ring op-

eration

There are several posible loopback paths

internal to the BMAC device

through the PLAYER device(s) using the PLAYER device

configuration switch

through the CRD device

These paths allow error isolation down to the device level

The BMAC device also supports through parity

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