a e St Token Bus

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??a???? µe S??t??? (Token Bus)
Ge????, ??a? d?a???? µe s??t??? ?s?d??aµe? µe ??a
da?t???? µe s??t??? (token ring) ?ta? ??a? ??µß??
staµat?se? t?? e?p?µp?, st???e? µ?a ad?a??
s??t??? (idle token) st?? ep?µe?? ??µß? Se ??a
d?a??? µe s??t???, ? ep?µe??? ??µß?? ????eta?
a??a??eta, ep?µ???? p??pe? ? s??t??? ?a pe????e?
µ?a d?e????s?. ?ts?, ?e?d????µe se
p??sa?µ?st???t?ta e?? ß???? t?? ap?d?s??.
??a s?st?µa e??tapa?t?se??(polling) e??a?
pa??µ??? µe ??a d?a??? µe s??t???. ??t? ? ???e
??µß?? ?a st???e? t? s??t??? st?? ep?µe?? ??µß?,
e?d?p??e? t?? ??µß?-a????? (master node) ?t? ??e?
te?e??se? t? µet?d?s? ?a? t?te ? ??µß??-a??????
e??µe???e? t?? ep?µe?? ??µß?. CSMA/CA (Carrier
Sense Multiple Access with Collision Avoidance)
?? ad?a?e?? s??t??e? se ??a d?a??? µp????? ?
a?t??atasta???? ap? ?s???a. ? ep?µe??? ??µß??
?e???? t? µet?d?s? af?? a???se? ?t? ? d?a????
e??a? se ?at?stas? ?s???a? (silent). ?? ?
ep?µe??? ??µß?? de? ??e? pa??ta, d?ad??????
??µß?? ?e?????? se d?ad????? d?ast?µata ?s???a?
(?µµes? s??t???)
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pa??de??µa ?? d?a???? µ???? ?ate????s?? st?
Expressnet (s?????? ?pt???? ??e?) (Expressnet
Unidirectional Buses)
???d?s? t?? t????? t?? pa??t?? ap? t?? ??µß? 1
?a? p??? ta ??t? st? d?a???
Se d?a????? µ???? ?ate????s??, ? s??d?asµ??
?µµes?? s??ta???, a????e?s?? f????t?? ?a?
d??ta??? t?? ??µß?? (??a t?? ep???s? ??p????
s???????) d??e? ??a p??? e?d?af???? s?st?µa. ??
ep?µe??? p??? ta ??t? ??µß?? a????e t?
s??????s? ?a? staµat??e t? µet?d?s?. ???e ??µß??
µe ded?µ??a µetad?de? ?ta? a????e?e? ?s???a st?
d?a???. ????????? ?p????e? p?? t?? ep?µ???? p???
ta p??? ??µß?? ??a t?? a????e?s? t??
f????t??. ??t? e??a? ?d??? ??a t?? ep?µe?? p???
ta ??t? ??µß?.
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???a???µ??? ??a??t?s?
Se s?????e? µ????? f??t??, e??a? ?????ß??? t?
s?st?µa e??tapa?t?se?? (polling) (? t? ?a
d?ad?de?? s??t??e? ? ?a ???s?µ?p??e?? TDM ??a ?a
???e?? µ?a ???t?s?). ???a? p??t?µ?te?? ?a
p?a?µat?p??e?? µ?a ???a???µ??? a?a??t?s?.
?? ??µß?? e??a? a???µ?µ???? d?ad??? St?? p??t?
s??sµ?, ???? ?? ??µß?? µe pa??t? st?????? 1. ?? ?
???d?? e??a? 1, t?te ???? ?? ??µß?? t?? ?p???? t?
p?? s?µa?t??? ??f?? e??a? 0 ?a? ?? ?p???? ?????
??a pa??t? st?????? 1 ??p ? st?at?????
???a???µ???? a?a??t?s?? ß??s?e? t? µ????te?a
a???µ?µ??? ??µß? µe pa??t? se t? p???-
ß?µata. ??t? e??a? p??t?µ?te?? ap?
??a s?????sµ??? s?st?µa e??tapa?t?se?? ??a µ????
f??t?, a??? ?e???te?? ??a µe???? f??t?. ?p???e?
?a? p??ß??µa d??a??s???? (??s? ???a?e t??
d?ad???? ta?t?t?te? t?? ??µß?? st? t???? ???e
??????)
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???t?a µet?d?s?? ?ad??-pa??t??
S????? e?e??e?? ap? s??????se?? (Collision free
set) S????? s??d?sµ?? p?? µp????? ?a
µetaf????? pa??ta ta?t?????a, ????? s??????se??
st??? d??te? st?? ???e? t?? s??d?sµ??.
?????sµa e?e??e?? ap? s??????se?? (Collision free
vector)
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????p?e??a µe d?a??es? ?????? (TDM) ??a d??t?a
µet?d?s?? ?ad??-pa??t??
d?a??sµata e?e??e?a ap? s??????se??

• L ? a???µ?? t?? s??d?sµ??
• ??se µ?a s??sµ? se ???e s????? e?e??e?? ap?
  s??????se??

d????sµa p?? d??e? ??a p??? µ???? µ????(???sµa)
t?? ?????? ???s?? ???e s??d?sµ??
pa?????ta? ???s?µ?t?ta? (utilization vector)
Ge????te?a ?st? aj ??a p??? µ???? µ???? t??
?????? p?? t? j-st? s????? e?e??e?? ap?
s??????se?? ???s?µ?p??e?ta? ?a? ?p??
d????sµa p?? d??e? ??a p??? µ???? µ????(???sµa)
t?? ?????? ???s?? ???e s??d?sµ??

• ?ed?µ???? ß?e? aj t?t??a ?ste

• ??af??et??? ?s?????, ?ta? ta e?e??e?a ap?
  s??????se?? s????a a??????? (st?? p?a?µat???t?ta
  a??µa ?a? ??a ??a stat??? d??t??, e??a?
  NP-complete)

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S??µata ??e???t?s?? S??????se?? ??a ?ad??-pa??ta
?a??de??µa Aloha µe s??sµ?? ?? p??ß??µa e??a? ?
a?a???p?st?a st?? a?at??f?d?t?s? pa?.1
s??????s? st?? 2 (a??? ? 1 de? t? ???e?)
pa?.2
?a? ?? 2 µetad?se?? e??a? ep?t??e?? a??? ?p???e?
µ?a s??????s? st?? 2 ? ?p???? de? ???e? a? ?
µet?d?s? p???????ta? ?? a?t??
??s? ??t?? a?af???? pa??d?s?? (ACKs) p??pe? ?a
ap?st?????ta?
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?????e?s? F????t?? ?a? ???? ?ate???µµ???? G?aµµ??
??a ???t?a µet?d?s?? ?ad??-pa??t??
? a????e?s? f????t?? de ?e?t????e? p??ta ?
??µß?? i µetad?de? st?? j. ? k a????e?e? t?
?a???? ad?a??? ?a? µetad?de?. ?p?t??esµa
s??????s?
?? p??ß??µa t?? ???µµ???? te?µat????
???? ?ate???µµ???? ??aµµ?? (busy tone) ? ??µß??
p?? ?aµß??e? ded?µ??a, µetad?de? se µ?a ????
s????t?ta ??a? ??? ?at??e?µ???? ??aµµ??. ?? ?????
??µß?? a???? a?t?? t?? ??? ?a? de µetad?d???.
???? ?ate???µµ???? ??aµµ??
???? ??t?µa ep????? t?? a?t??a? µet?d?s??
p?????sµ??
????
?? ???s?µ?p??e?ta? µ?a µe???? a?t??a µet?d?s??,
apa?t???ta? ????te??? e?d??µes?? sta?µ?? ??a ?a
ft?se? t? pa??t? st?? p?????sµ?, a??? ?ts?
p???a????ta? pa?eµß???? se ??????
???ste?.
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???e???? ???ef???a
sta?µ?? ß?s?? (base station) ????t?? sta?µ??
(mobile station)
MSC ???t?? ????t?? µeta?????(mobile switching
center)
??a ?e???af??? pe????? ?????eta? se e?a???????
?????e?, p?? ? ???e µ?a ??e? ??a sta?µ? ß?s??
???t?? ??µ?s?a? ???ef???a?
F???t??e? ??a t? d??µ?????s? t?? e??µ???s?
p????f????? pe??????, asf??e?a, ????s? ??p
?? ?????e? p?? e??a? ???t? ? µ?a st?? ???? de
µp????? ?a ???s?µ?p???s??? t?? ?d?e? s????t?te?
???? p??a???
pa?eµß???? ? µ?a st?? ????.
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Se ???e ?????? a?t?st???e? µ?a µp??ta s????t?t??
(???e µp??ta µp??e? ?a e??p??et?se? ??a? a???µ?
????t??). ???? ?????e? p?? e??a? ap? 3 ?a? p???
µp????? ?a ????? t?? ?d?a µp??ta.
??e????t?µa ??a s????t?ta µp??e? ?a
?a?a???s?µ?p????e? (????? µe???e? pa?eµß???? ap?
???e? ?????e?)
?e???e?t?µata a) ?ta? ta ????t? d?as?????? ta
s????a µeta?? ???e???, ?a p??pe? ?a t??? d??e?
??a s????t?ta (hand over)
ß) ?? ? ?ata??µ? t?? ????t?? µ?sa st?? ?????e?
de? e??a? ?s????p?µ??? t?te ????µe µ? ap?d?t???
???s? t?? s????t?t?? (ep?µ???? µp????µe ?a ????µe
?a??te?a ap?te??sµata µe d??aµ??? a???es?
s????t?t?? st?? ?????e?, ap ?,t? µe stat???
a???es?)
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???µe??se?? ??p??es?a? ???µ?????s? ???se??
(Location Updates Call
Routing)
?? ????t? ?ata???e?ta? se ??a s???e???µ???
MSC(?d?a) ?ta? ta ????t? µeta??????ta? se ???e?
pe??????, e??µe???eta? ? ?ata????t?? st? MSC
?d?a? p?? t??e? t?? pa???sa t?p??es?a t??
????t?? St?? pe??pt?s? ???s??, ?a?e?ta? t?
MSC-?d?a, d?aß??eta? ? ?ata????t?? t?p??es?a? ?a?
a???????? ? ???s? p????e?ta? st? ?at?????? MSC
?a? ap? e?e? st?? ep?s?ept?µe?e? BS (visiting
base stations).