algorithm for fddi system

8/13/2019 algorithm for fddi system

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Appendix C List of Algorithms

Appendix C

Algorithm-1: wait-for-event.

Wait-for-event. This is a subroutine responsible for detecting the

events and returning the value of the detected event. Theses events are:

1. Frame-arrival. It means that a ne frame is available at the receiver

buffer.

!. TRT-expired. It means that the T"T counted up to its specified

value.

#. THT-expired. It means that the T$T counted up to its specified

value.

%. ACK-expired. It means that the AC& timer counted up to its

specified value and no ac'noledges frame as received.

(. AMP-expired. It means that the A)* timer counted up to its

specified value.

+ub Wait-for-event

Loop, if T"T.enabled false then

event T"T-expired

lse:

If mscomm. Comvent Comv"eceive then

event frame-arrival

lse:

If T$T.enabled false and to'en true then

event T$T-expired

lse:

If A)*.enabled false then

event A)*-expired lse:

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If AC&.enabled false and frame true then

event AC&-expired

nd if

nd if

nd if

nd if

nd if

Algorithm-: To-Ph!-"a!er

This procedure receives a frame/ converts its b0tes into s0mbols of %

bits/ encodes these s0mbols into ( bits s0mbols using the %-( procedure/

finall0 it puts the encoded frame onto the ring for circulating it till it arrives

the destination.

to-ph0-la0er 2s as frame / inforleng as integer 3

4im 4ata5

4im a as b0te

4ata5 cstr 2s.sd13 6 cstr 2s.sd!3

A b%-b( 2s.fc and 173

4ata5 data5 6 cstr 2A3A b%-b( 2s.fc and !%83

4ata5 data5 6 cstr 2A3

A b%-b( 2s.da1 and 173


A b%-b( 2s.da1 and !%83


A b%-b( 2s.da! and 173

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A b%-b( 2s.da! and !%83


A b%-b( 2s.sa1 and 173


A b%-b( 2s.sa1 and !%83


A b%-b( 2s.sa! and 173


A b%-b( 2s.sa! and !%83


A b%-b( 2s.LLC.dsap and 173


A b%-b( 2s. LLC.dsap and !%83


A b%-b( 2s. LLC.ssap and 1734ata5 data5 6 cstr 2A3

A b%-b( 2s. LLC.ssap and !%83


A b%-b( 2s. LLC.contro and 173


A b%-b( 2s. LLC.control and !%834ata5 data5 6 cstr 2A3

9or I8 to inforleng

A b%-b( 2s. LLC.data2I3 and 173


A b%-b( 2s. LLC.data 2I3 and !%83


ext I

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A b%-b( 2s. fcs1and 173


A b%-b( 2s. fcs1and !%83


A b%-b( 2s. fcs! and 173


A b%-b( 2s. fcs! and !%83


4ata5 data5 6 cstr 2s.ed3

4ata5 data5 6 cstr 2s.fsa3

4ata5 data5 6 cstr 2s.fsc3

4ata5 data5 6 cstr 2s.fse3

)scomm.output 4ATA5

4ATA58

nd sub

Algorithm-#: From-Ph!-"a!er.

This procedure fetches an arrived frame from the receiver buffer/

decode it 2i.e. each ( bit s0mbol is converted to its origin % bits replica3

using the (-% procedure/ and reassemble the frame.

+ub 9rom-ph0-la0er 23&1 mscomm.input ; enter a s0mbol of data.

arrivedframe.sd1 '1

&1 mscomm.input

arrivedframe.sd! '1

'1 b(-b% 2 mscomm.input3

'! b(-b% 2 mscomm.input3

arrivedframe.fc '1 6 '!


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'1 b(-b% 2 mscomm.input3

'! b(-b% 2 mscomm.input3

arrivedframe.da1 '1 6 '!


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=oto Loop1

Loop! r.ed mscomm.input

Loop# mscomm.inputlen 1 ; enter one s0mbol each time.

arrivedframe. fsa mscomm.input

arrivedframe. fsc mscomm.input

arrivedframe. fse mscomm.input

)scomm.inputlen ! ; enter to s0mbols each time.

nd sub

Algorithm-$: Prepare-MAC-Frame

This procedure assembles a )AC control frame of a t0pe specified b0

the t0pe variable as an argument.

*repare-)AC-frame 2t0pe as string3

s.sd1 sd1

s.sd!sd!+elect case t0pe

Case to'en

s.fc 1!>

Case claim

s.fc ?(

Case *"=s.fc ?>

Case +)*

s.fc ?,

Case A)*

s.fc ??

Case 4AT

s.fc ?7

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nd select

If t0pe claim then

s.da1 una1

s.da! una!

=oto Loop(

end if

s.da1 1

s.da! 1

Loop( s.sa1 sa1

s.sa! sa!

s.ed ed

s.fsa ,

s.fsc ,

s.fse ,

nd sub

Algorithm %&:CRC-'enerator.

This procedure calculates the value of the frame chec' sum of the

frame s and put this value in s.fsc1 and s.fsc! fields.

crc-gen 2 s23 as b0te/ length as integer 3

4im crcarr 2173 as integer

4im dat as integer4im C as b0te

4im Crc1 as b0te/ Crc! as b0te

9or I8 to 17

Crcarr 2I3 8

ext I

9or I8 to length

C s 2I3

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9or @8 to ,

If c and 2h13 1 then

4at 1

lse: dat 8

nd if

Call shift-right 2dat/ crcarr3

CC mode !

ext @

ext i

Crc1Crc!8

9or I8 to ,

Crc1Crc16 crcarr 2I3 < !B I

Crc!Crc!6 crcarr 2I6,3 < !B I

ext I

nd sub

Algorithm-(: )AT-Re*pon*e.

This procedure is called hen a 4AT )AC control frame is received.

It chec's eather this frame is sent b0 this station or b0 another one

through monitoring the value of frame-status. 4AT/ and ta'es the suitable

action.

+ub 4AT-response 2frame-sataus. 4AT as oolean/ arrivedframe as

dataframe3

+elect case frame-sataus. 4AT

Case true ;the station sent 4AT frame previosl0

Chec'-address-status 2arrivedframe3

If status true then

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*repare-)AC-frame 2+)*3 ;send a +)* )AC frame

To-ph0-la0er 2ss3

lse: print the source address is used b0 another stationD:

Call b0pass-satate

nd if

Case false ;the 4AT frame is sent b0 another station

If arrivedframe.sa sa then

+et-frame-address-status 2arrivedframe3

nd if

To-ph0-la0er 2arrivedframe3

nd select

Algorithm-+: ,MP-Re*pon*e

This procedure is activated in response to detection of arrival of an

+)* frame. It chec's eather this frame is sent b0 this station or b0

another one through monitoring the value of frame-status. +)*/ and ta'esthe suitable action.

+)*-response 2framestatus. +)* as oolean/ arrivedframe as dataframe3

+elect case framestatus. +)*

Case true

If arrivedframe.fsa , and arrivedframe.fsc , thenEpdate-EA 2arrivedframe3 ;update the upstream

neighbor address

lse:

nd if

Case false ;this frame is sent b0 another station

if arrivedframe.fsa , then

Epdate-EA 2arrivedframe3

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set-frame-status 2arrivedframe3

to-ph0-la0er 2arrivedframe3

prepare-)AC-frame 2+)*3

to-ph0-la0er 2s3

lse


nd if

nd select

nd sub

Algorithm-: AMP-Re*pon*e.

This procedure is called in response to arrival of an A)* frame. It

chec's eather this frame is sent b0 this station or b0 another one through

monitoring the value of frame-status. A)*/ and ta'es the suitable action.

A)*-response 2framestatus. A)* as oolean/ r as dataframe3

+elect case framestatus. A)*

Case true

If arrivedframe .sa sa then

If arrivedframe.fsa , and r.fsc , then

*repare-)AC-frame 2A)*3

To-ph0-la0er 2s3

lse:

*repare-)AC-frame 2to'en3

To-ph0-la0er2s3

nd if

nd if

Case false

If r.fsa , and r.fsc , then

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Epdate-EA 2arrivedframe3

*repare-)AC-frame 2+)*3

To-ph0-la0er2s3

lse:

"estart-timer 2A)*3


nd if

nd select

nd sub

Algorithm-: PR'-Re*pon*e.

This procedure is called in response to arrival of a *"= frame. It

chec's eather this frame is sent b0 this station or b0 another one through

monitoring the value of frame-status. *"=/ and ta'es the suitable action.

*"=-response 2framestatus. *"= as oolean/ arrivedframe as dataframe3+elect case framestatus. *"=

Case true

If r.sa sa then

*repare-)AC-frame 2A)*3

To-ph0-la0er 2s3

nd ifCase false


Call idle-state

nd select

Algorithm-1/: CT-Re*pon*e.

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This procedure is activated in response to arrival of a CT )AC frame.

It chec's the framestatus. CT to ma'e a correct response to this frame.

CT-response 2framestatus. CT as oolean/ arrivedframe as dataframe3

+elect case framestatus. CT

Case true

If arrivedframe.sa sa and arrivedframe.da EA then

e-active-monitor ;this station is being the active monitor

lse:

+tandb0-state ;there is some error and the station onl0

; monitor passing of periodic frame.

nd if

Case false

+elect case activemonitor ; the station chec's eather it is the

; present active monitor

Case true ;the station is the present active monitorarrivedframe.sa sa

arrivedframe.da EA


Case false ; the station is not an active monitor


nd selectnd select

nd sub

Algorithm-11: ,tart-Timer.

This procedure activated the timer hich is specified b0 the argument

name.

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+ub +tart-timer 2ame as string3

ame.enabled true

nd sub

Algorithm %1: ,top-Timer.

This procedure is called henever it is reFuired to turn a timer off. The

timer is specified b0 the argument name.

+top-timer 2name as string3

ame.enabled false

nd sub

Algorithm %1#: re*tart-timer

This procedure activated henever it is reFuired to restart the timer hich

is specified b0 the argument name.

+ub "estart-timer 2name as string3If ame.enabled false then

ame.enabled true

lse:

ame.enabled false

ame.enabled true

nd ifnd sub

Algorithm-1$: 0!pa**-,tate.

In this state the station or's onl0 as a repeater. It @ust retransmit the

incoming data ithout an0 proceesing.

+top-timer 2T"T3

+top-timer 2T$T3

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+top-timer 2A)*3

+top-timer 2AC&3

mscomm.inputLen 1

mscomm.inputThreshold 1

Loop aite-for-event 2nevent3

If nevent frame-arrival then

mscomm.output mscomm.input

=oto loop

nd sub

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algorithm for fddi system

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