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Multiplexing
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ÿÿÿÿÿÿÿÿÿÿ ÇÔ¸Õ¡Ò÷Óÿÿÿ Multiplexingÿÿÿ ¶Ù¡¹ÓÁÒãªé§Ò¹ÊÓËÃѺ¡ÒõԴµèÍÊ×èÍÊÒ÷Õèà»ç¹ÃÐÂзҧä¡Å (long-haul communication) ªØ´¢Í§ÊÒÂÊÑÒ³ (Trunk) ·Õè¹ÓÁÒãªé㹡ÒõԴµèÍÃÐÂзҧä¡Å ( long-haul network) à»ç¹àÊé¹ã¹Óáʧ·ÕèÁÕ»ÃÐÊÔ·¸ÔÀÒ¾ÊÙ§ ËÃ×ÍÊÒÂâ¤áÍ¡àªÕÂÅ ËÃ×ͼèÒ¹äÁâ¤ÃàÇ¿ ¡ÒÃàª×èÍÁµè͹ÕéÊÒÁÒö¹ÓàÊÕ§¼èÒ¹ä»ä´éã¹ÍѵÃÒÊ٧㹻ÃÔÁÒ³ÁÒ¡ áÅÐÊÒÁÒöÊ觼èÒ¹ÊÑÒ³àÊÕ§ä»ä´é·Ñ¹·Õâ´ÂãªéÇÔ¸Õ¡Òà multiplexing
ÿÿÿÿÿÿÿÿÿÿÿÿ ¨Ò¡ÃÙ» áÊ´§ãËéàËç¹Ë¹éÒ·Õè¢Í§¡ÒÃ·Ó multiplexing ã¹ÃٻẺ·Õè§èÒÂÁըӹǹÍÔ¹¾Ø· ¨Ó¹Ç¹ n ÍÔ¹¾Ø·à¢éÒä»·ÕèÁÑŵÔà¾Å¡à«ÍÃì ( multiplexer) µÑÇÁÑŵÔà¾Å¡à«ÍÃìµèÍàª×èÍÁà¢éҡѺÊÒÂàª×èÍÁµèÍ ( link) àÊé¹à´ÕÂÇà¢éҡѺ demultiplexer ´éÇ link ÁÕ¤ÇÒÁÊÒÁÒö 㹡ÒÃÊ觼èÒ¹ÊÑÒ³ä´é¨Ó¹Ç¹ n ªèͧÊÑÒ³ (channel) µÑÇ multiplexer ¨ÐÃÇÁàÍÒ¢éÍÁÙÅ ( multiplex) ¨Ò¡ input line ¨Ó¹Ç¹ n line áÅÐÊ觼èÒ¹ÊÒÂÊÑÒ³àª×èÍÁµèÍ ( data link) ·ÕèÁÕ¤ÇÒÁÊÒÁÒöÊÙ§ àÁ×èÍ demultiplexer ÃѺ stream ¢éÍÁÙÅ·Õèà»ç¹ multiplexed ÁÒá¡ ( demultiplexers) Í͡仵ÒÁªèͧÊÑÒ³áÅéǹÓÊè§ä»Âѧ output line ·Õèµéͧ¡ÒÃ
¡ÒùÓàÍÒÇÔ¸Õ¡Òà multiplexing ÁÒãªé§Ò¹ÍÂèÒ§á¾ÃèËÅÒÂÁÒ¡¢Öé¹ à»ç¹à¾ÃÒÐà˵ؼŴѧ¹Õé
ÿÿÿÿÿÿÿÿÿÿÿ ÍѵÃÒ¡ÒÃÊ觢éÍÁÙÅÂÔè§ÊÙ§ÁÒ¡¢Öé¹à·èÒäà cost - effective ¡ÒÃŧ·Ø¹ÊÓËÃѺ transmission facility ¹Ñ蹤×ÍÊÓËÃѺ application ·Õè¡Ó˹´ãËéáÅÐÀÒÂãµéÃÐÂзҧ·Õè¡Ó˹´ãËé¤èÒãªé¨èÒµèÍ Kbps Ŵŧ àÁ×èÍà¾ÔèÁÍѵÃÒ¡ÒÃÊ觢éÍÁÙŢͧ transmission facility 㹷ӹͧà´ÕÂǡѹ¤èÒãªé¨èÒ¢ͧÍØ»¡Ã³ìÊÓËÃѺÊ觡ÃШÒ¢éÍÁÙÅ ( transmission) áÅСÒÃÃѺµèÍ Kbps ÁÕ¤èÒÅ´Å´àÁ×èÍà¾ÔèÁ data rate
ÍØ»¡Ã³ìÊ×èÍÊÒâéÍÁÙÅáµèÅÐÍÂèÒ§µéͧ¡ÒÃÍѵÃÒ¡ÒÃÃѺÊ觢éÍÁÙÅ ã¹ÍѵÃÒ·Õè¾ÍàËÁÒÐàªè¹ ÊÓËÃѺ terminal áÅÐ personal computer application ÍѵÃÒ¡ÒÃÃѺÊ觢éÍÁÙÅ¢¹Ò´ 9600 bps áÅÐ 64 kbps ¡ç¶×ÍÇèÒà¾Õ§¾Í
Multiplexing à»ç¹à·¤¹Ô¤ÇÔ¸Õ¡ÒÃÊ觢éÍÁÙÅ仾ÃéÍÁ¡Ñ¹ã¹àÊé¹·Ò§à´ÕÂǡѹ Ãкº Multiplexing ÁÕÍÂÙè 2 Ãкº ¤×Í
- MUX à¢éÒÃËÑÊ
- DEMUX ¶Í´ÃËÑÊ
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»ÃÐàÀ·¢Í§ Multiplexing
Frequency - Division Multiplexing (FDM)
Wave - Division Multiplexing (WDM)
Time - Division Multiplexing (TDM)
- Synchronous TDM
- Asynchronous TDM
1. Frequency - Division Multiplexing (FDM)
Frequency - division Multiplexing ( FDM ) FDM Ê觢éÍÁÙÅẺ Analog ¨Ðʹã¨àÃ×èͧ¤ÇÒÁ¶Õè ·Ó˹éÒ·Õèà»ç¹·Ñé§ Input áÅÐ Output ¨ÐÁÕ ¤ÇÒÁ¡ÇéÒ§¢Í§ÊÑÒ³ÁÒ¡ ã¹áµèÅÐÊÑÒ³¶Ù¡à»ÅÕè¹â´Âãªé carrier frequency ËÅѧ¨Ò¡Êè§áµèÅÐÊÑÒ³¨ÐäÁè¡Ç¹¡Ñ¹ àªè¹ broadcast radio
¡ÒûÃÐÁÇżŠFDM (FDM Process)
- â·ÃÈѾ·ìáµèÅеÑǨÐãªé¤Å×蹤ÇÒÁ¶Õè¤ÅéÒ¡ѹ
- áÅШж١¹ÓÁÒÃÇÁÊÑÒ³ ( Multiplexing) ´éÇ carrier ·ÓãËéµèÒ§¡Ñ¹ áÅéǨ֧Êè§ÊÑÒ³ÍÍ¡ä»áÅÐ link µéͧÁÕà¾Õ§¾Í·Õè¨ÐÊè§
- ¡è͹¨ÐÊè§ä»ã¹ÊÒÂáÅÐá¡ÊÑÒ³·Õè¼ÙéÃѺ
- DeMultiplexing ¨ÐÁÕ filter ¤Í·Ó˹éÒ·Õèá¡ÊÑҳ仵ÒÁÍØ»¡Ã³ìáµèÅеÑÇÇèÒ¤Å×蹢ͧ¼ÙéÃѺµÑÇä˹
- áÅзÓ˹éÒ·Õèá¡ carrier ÍÍ¡¨Ò¡ÊÑÒ³áÅÐá¡ data ãËéÍØ»¡Ã³ì¼ÙéÃѺáµèÅеÑÇ
2. Wave - Division Multiplexing (WDM)
ÁÕ concept ãËé FDM ¡àÇé¹ DeMultiplexing ·ÕèÃÇÁáÅÐÊè§ã¹ÊÒ fiber optic ÃÇÁàÍÒ¤Å×è¹·ÕèÁÕ¤ÇÒÁ¶ÕèᵡµèÒ§¡Ñ¹·ÕèÁÕ¤ÇÒÁ¶ÕèÊÙ§Í͡仾ÃéÍÁ æ ¡Ñ¹ ËÅÑ¡¡ÒçèÒ æ áµèà·¤â¹âÅÂիѺ«é͹ ᡤÅ×è¹áʧä»à»ç¹ÊÑҳ俿éÒ ËÅÑ¡¡ÒÃàËÁ×͹ FDM à¾ÃÒÐãªé¤ÇÒÁ¶Õè㹡Ò÷Óáµèà·¤â¹âÅÂիѺ«é͹à¾ÃÒÐÁÕ¡ÒÃËÑ¡àˢͧáʧ
3. Time - division Multiplexing ( TDM )
TDM ¨Ðʹã¨àÃ×èͧ¢Í§àÇÅÒ àËÁÒСѺ§Ò¹´éÒ¹ Digital áÅÐÁդسÊÁºÑµÔ 㹡ÒÃãªé link à´ÕÂǡѹä´é áµè¨ÐàÃÕ§仵ÒÁàÊé¹·Ò§ TDM ¨ÐÁÕÍÂÙèÊͧÅѡɳР¤×Í
1. Character Interleaving µéͧÁÕ¡ÒÃÊ觢éÍÁÙÅÍÂèÒ§¹éÍ 8 bit
2. Bit Interleaving ¾Ô¨ÒóҢéÍÁÙÅà»ç¹ bit àÃÕ§¡Ñ¹à¢éÒÁÒ
Interleaving
Synchronous TDM ÊÒÁÒöà»ÃÕºàËÁ×͹¡Ñº Switch ·ÕèËÁعàÁ×èÍ Switch ËÁع¶Ö§¼ÙéÊè§ ¡ç¨Ð´Ö§¢éÍÁÙÅ·ÕÅÐ 1 µÑÇáÅÐËÁع´éǤÇÒÁàÃçÇ·Õ褧·Õè áµè¶éÒäÁèÁÕ¢éÍÁÙŨÐà»ç¹ slot ÇèÒ§ Swithch ¨ÐËÁع´éÇÂÍØ»¡Ã³ì¶Ö§ÍØ»¡Ã³ì ·ÕèÍѵÃÒ¤§·ÕèáÅÐÁÕ¤èҺ͡ÊÔ觷Õè¡Ó˹´ ¡Ãкǹ¡ÒùÕéàÃÕ¡ÇèÒ Interleaved
TDM áºè§ä´é 2 ·Ò§ ¤×Í
- Synchronous
- Asynchronous
Synchronous TDM
µÑÇ Multiplexer ¨Ðà»ç¹µÑǤé¹ËÒÇèÒ Device ä˹µéͧ¡ÒÃÊè§â´ÂäÁèʹã¨ÇèÒ Device ¹Õé¨ÐÊè§ËÃ×ÍäÁè ËÃ×Í Device ¹ÕéàÊÕÂËÃ×ÍäÁè «Ö觨ش¹Õé·ÓãËéàÊÕÂàÇÅÒ à¡Ô´¡Òà ÊÔé¹à»Å×ͧ·ÃѾÂÒ¡Ã áÅШÐáºè§àÇÅÒä»ãËéà¤Ã×èͧÍ×è¹äÁèä´é¨Ð¶Ù¡¨Í§äÇé੾ÒÐà¤Ã×èͧ
Asynchronous TDM
Asynchronous TDM ËÃ×Í STDM (Statistical Time Division Multiplexing) Ẻáºè§µÒÁàÇÅÒ´éÇÂÊ¶ÔµÔ à»ç¹à·¤¹Ô¤¡ÒûԴÃÙÃÑèǢͧ Synchronous ËÅÕ¡àÅÕ觢ÂСÒÃàÊÕÂà»ÅèҢͧ ·ÃѾÂÒ¡Ã ·ÓãËéÃкºâ´ÂÃÇÁ´Õ¢Öé¹
STDM (Statistical Time Division Multiplexing)
ã¹ synchronous ¨ÐÁÕ slot à·èҡѹ·Ø¡µÑÇ ¨ÐÊÃéÒ§ slot µÒÁ¤ÇÒÁµéͧ¡ÒÃ㹡ÒÃÊ觢éÍÁÙÅ Multiplexing ¨ÐµÃǨÊͺ¢éÍÁÙÅã¹ line áÅÐÊ觢éÍÁÙŨ¹¡ÃзÑè§ frame àµçÁÍѵÃÒ¢éÍÁÙÅ·ÕèÊ觵èÓ¡ÇèÒÍØ»¡Ã³ì·Õè¨ÐÊè§
Framing
No flag ËÃ×Í SYNC ÁÕ˹éÒ·Õè¤Íº͡ address µéͧÁÕ¡ÅäÅ㹡Òú͡áµèÅÐ frame â´ÂãªéËÅÑ¡¡Òôѧ¹Õé
- ¨ÐÁÕ 1 ºÔµã¹¡ÒäǺ¤ØÁáµèÅÐ TDM frame
- Identifible à»ç¹µÑǤǺ¤ØÁã¹áµèÅÐ frame
- 01010101 äÁè¹èÒ¨ÐÍÂÙ躹ªèͧ¢éÍÁÙÅ
- ÊÒÁÒöà»ÃÕºà·Õº¡ÒÃà¢éÒÁÒáµèÅЪèͧÊÑÒ³´éÇÂÃٻẺ Sync
multiplexing ÊÒÁÒöᡤÇÒÁᵡµèÒ§¢Í§ÊÑÒ³µèÒ§æ àªè¹ á¡àÇÅÒ á¡¾×é¹·Õè áÅÐᡤÇÒÁ¶Õè¢Í§ÊÑÒ³áµèÅЪ¹Ô´ÍÍ¡¨Ò¡¡Ñ¹ 
ÁÑŵÔà¾Åç¡à«ÍÃì (Multiplexer)
¡Ò÷ӧҹ¢Í§ÁÑŵÔà¾Åç¡à«ÍÃìÿÿ ÁÑŵÔà¾Åç¡à«ÍÃì¨ÐÃѺÊÑÒ³¢éÍÁÙŨҡ¼ÙéÊ觢éÍÁÙŨҡáËÅ觵鹷ҧµèÒ§æÿÿ «Ö觵éͧ¡ÒèÐÊ觢éÍÁÙÅä»Âѧ»ÅÒ·ҧ㹷ÕèµèÒ§æ¡Ñ¹ÿÿ ´Ñ§¹Ñé¹ÊÑÒ³¢éÍÁÙŵèÒ§æàÁ×èͼèÒ¹ÁÑŵÔà¾Åç¡«ìà«ÍÃì ÁÑŵÔà¾Åç¡«ìà«ÍÃì¡ç¨ÐàÃÕ§ÃÇÁ(ÁÑŵÔà¾Åç¡«ì)¡Ñ¹ÍÂÙèã¹ÊÒÂÊ觢éÍÁÙÅà¾Õ§ÊÒÂà´ÕÂÇÿÿ áÅÐàÁ×èÍÊÑÒ³¢éÍÁÙÅ·Ñé§ËÁ´ÁÒ ¶Ö§à¤Ã×èͧÁÑŵÔà¾Åç¡«ìà«ÍÃìªÖè§àÃÕ¡ÇèÒ ÍØ»¡Ã³ì´ÕÁÑŵÔà¾Åç¡«ìà«ÍÃìÍÕ¡à¤Ã×èͧ˹Ö觷ҧ»ÅÒ·ҧ ÊÑÒ³·Ñé§ËÁ´¡ç¨Ð¶Ù¡á¡ ( ´ÕÁÑŵÔà¾Åç¡«ì) ÍÍ¡¨Ò¡¡Ñ¹ä»µÒÁà¤Ã×èͧÃѺ»ÅÒ·ҧ¢Í§áµèÅЪèͧ·Ò§ÊÒÂÊ觢éÍÁÙÅ·Õèãªé㹡ÒÃÊ觢éÍÁÙŨеéͧÁÕ¤ÇÒÁ¨ØÊÙ§ ¨Ö§¨ÐÊÒÁÒöÃͧÃѺ»ÃÔÁÒ³¢éÍÁÙŨӹǹÁÒ¡·Õè¶Ù¡Ê觼èÒ¹ÁÒ¾ÃéÍÁæ¡Ñ¹ä´éÿÿ ÊÒÂÊ觢éÍÁÙŴѧ¡ÅèÒÇÿÿ ä´éá¡èÿÿ ÊÒÂâ¤àÍ¡ÿÿ ÊÒÂä¿àºÍÃìÍÍ»
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•ÿ ¡ÒÃÁÑŵÔà¾Åç¡«ìẺáºè§µÒÁ¤ÇÒÁ¶Õèÿÿ (Frequency Division Multiplexing)ÿ ËÃ×Í FDM «Öè§à»ç¹áºº·Õè¹ÔÂÁãªé¡Ñ¹ÁÒ¡·ÕèÊØ´â´Â੾ÒдéÒ¹ÇÔ·ÂØáÅÐâ·Ã·Ñȹì
•ÿ ¡ÒÃÁÑŵÔà¾Åç¡«ìẺáºè§µÒÁàÇÅÒÿÿ (Time Division Multiplexing)ÿ ËÃ×Í TDMÿ «Öè§ÃÙé¨Ñ¡¡Ñ¹´Õ㹪×èͧ͢«Ô§â¤Ã¹ÑÊ TDM (Synchronous TDM) ÊèǹãËè¨Ðãªé㹡ÒÃÁÑŵÔà¾Åç¡«ìÊÑÒ³àÊÕ§´Ô¨ÔµÍÅÿÿ àªè¹ á¼è¹à¾Å§ CD
•ÿ ¡ÒÃÁÑŵÔà¾Åç¡«ìẺáºè§µÒÁàÇÅÒ´éÇÂÊ¶ÔµÔ ( Statistical Time Division Multiplexing) ËÃ×Í STDM «Öè§ÁÕèª×èÍàÃÕ¡ÍÕ¡ÍÂèҧ˹Öè§ÇèÒ ÍЫԧâ¤Ã¹ÑÊ TDM (Asynchronous TDM) ËÃ×ÍÍÔ¹à·ÅÅÔਹ·ì TDM(Intelligent TDM) ã¹·Õè¹ÕéàÃÒ¨Ðãªéª×èÍàÃÕ¡ÊÑé¹æÇèÒ STDM ÊÓËÃѺ STDM à»ç¹ÇÔ¸Õ¡ÒÃÁÑŵÔà¾Åç¡«ì·Õè»ÃѺ»Ãا¡Ò÷ӧҹÁÒ¨Ò¡ÇÔ¸Õ«Ô§â¤Ã¹ÑÊ TDM ãËéÁÕ»ÃÐÊÔ·¸ÔÀÒ¾ÊÙ§ÂÔ觢Öé¹à¾×èÍÃͧÃѺ¨Ó¹Ç¹ªèͧ·Ò§ãËéä´éÁÒ¡¢Öé¹
˹èǤǺ¤ØÁ¡ÒÃá¡ÊÑÒ³ ( Cluster Control Unit)
