1993.10.22 SUBJECT: SNA FUNCTIONAL LAYERS °³¿ä: ¸ðµç communication network architectures ÀÇ ³»ÀçµÈ ±âº» °³³ä Àº ÀßÁ¤ÀÇµÈ functional layers ·Î network function À» ³ª´«´Ù. *** »ðÀÔÀÚ·á *** 1. Data link control -°¡Àå ÇÏÀ§(SNA define) ÀÇ layer. -This layer is responsible for the transmission of data between two nodes over a particular physical link -°¡ÀåÁß¿äÇÑ ±â´ÉÁßÀÇ Çϳª´Â to detect and recover from the transmission errors that inevitaly occur.. cf) physical control layer addresses the transmission of bit streams over a physical circuit. It is important to point out that the SNA architecture itself does not define the functions that are performed in the phyical control layer, and specific method of transmitting bits are not defined by SNA. Various methods of physical transmission can be employed in an SNA network, including computer channels, telephone lines, satellite links, and microwave transmission. The techniques used for phisical transmission are defined outside the SNA architecture. 2.Path control -ÀÌ ..path control layer ´Â network À» ÅëÇÏ¿© message °¡ Åë°úµÇ´Â path »ó ¿¡¼ÀÇ Routing ¿¡ °ü°èµÈ´Ù. -º¹ÀâÇÑ network ¿¡¼´Â ¿©·¯°³ÀÇ Node ¸¦ ÅëÇÏ¿© ºÐ¸®µÈ ¼ö°³ÀÇ data link ¸¦ °æÀ¯ÇÑ´Ù. .¶ÇÇÑ, ¿©·¯°³ÀÇ Domain À» °æÀ¯ÇÒ¼öµµ ÀÖ´Ù. 3.Transmission control -The third functional layer, it keeps track of the status of sessions that are in progress, controls the pacing of data flow within a session, and sees that the units of data that make up a message are sent and received in the proper sequence. -This layer also provides an optional data encryption/decryption facility. 4.Data Flow control -it is concerned with the overall intefrity of the flow of data during a session between two network addressable units. -this can involve determinig the mode of sending and receving, managing groups of related messages, and determing what type of response mode to use. 5.Function Management -The uppermost SNA functional layer is highly complex and can be thought of as being divided into sublayers:a functional management data services sublayers and a NAU services manager sublayer. fig 3.1 5-1.Function management Data Services -ÀÌ sub-area ´Â high-level SNA service ¿Í ´ÙÀ½ÀÇ 2 °¡Áö ÁÖ¿äÇÑ ±â´ÉÀ» Á¦°ø °¡)Coordinating the interface between the network user and the network and the presentation of information to the user ³ª)Controlling and coordinating the activities of the network as a whole and of all the sessions that are active. 5-2.NAU Services manager -ÀÌ layer ´Â service ¸¦ function management data services ¿Í data flow control °ú trasmission control layer ¿¡ service ¸¦ Á¦°øÇÑ´Ù. 6.Application Layer -ÀÌ application layer ´Â user ¸¦ ³ªÅ¸³½´Ù. user ´Â SNA network ¿Í interface ÇÏ´Â application °ú people ÀÌ´Ù. physical coltrol layer ¿Í ¸¶Âù°¡Áö·Î ÀÌ application layer µµ SNA architec- ture ¿¡ Á¤ÀǵǾî ÀÖÁö ¾Ê´Ù. ºñ·Ï ÀÌ layer °¡ Áß¿äÇÏÁö¸¸ SNA architectuer ÀÇ ¹Û¿¡ Á¤ÀǵǾîÀÖ´Ù. ÀÌ layered structure °¡ SNA architecture ¸¦ ´õ ¹ßÀü ½ÃÅ°°Ô µÈ´Ù. Áï, ÇϳªÀÇ »õ·Î¿î ±â¼úÀÌ °³¹ßµÇ¾úÀ»¶§ ÀÎÁ¢ÇÑ ´Ù¸¥ layer ÀÇ ¼ö Á¤À̳ª ¿µÇâÀ» ÁÖÁö¾Ê°í¼ efficiency ³ª module ´ÜÀ§ÀÇ º¯È¸¦ °¡´ÉÇÏ°Ô ÇÑ´Ù.-SNA ¸¦ ±¸¼ºÇÏ´Â µÎ°¡ÁöÀÇ Áß¿äÇÑ ¿ä¼Ò´Â NAUs(network addressable units) ¿Í path control network ÀÌ´Ù. NAUs ´Â Top three layer ·Î ±¸ÇöµÈ´Ù. function management, data flow control, transmission control ÀÌ´Ù.ÀÌ layer ÀÇ °¡ÀåÁß¿äÇÑ ±â´ÉÀº ù°, network user °¡ network À» ÅëÇÏ¿© data ¸¦ ÁÖ°í ¹Þ °ÔÇϴ°ÍÀÌ°í µÑ°´Â,network operator ¸¦ µ½°í network À» control, managing ÇÑ´Ù. Path control network component ´Â path control layer , data link control layer ¸¦ Æ÷ÇÔÇÏ°í ÀÖ´Ù. ÀÌ layer µéÀº network À» ÅëÇÑ data routing,flowing ±×¸®°í ´ÙÀ½³ëµå±îÁöÀÇ data transmission À» Ã¥ÀÓÁø´Ù. *** »ðÀÔÀÚ·á *** -The layered approach to network architectures makes it necessary to discuss two different types of communication . Áï, physical communication °ú logical communicationÀÌ´Ù. ¿©±â¼ physical communication layer ´Â µ¿ÀÏÇÑ node »ó¿¡¼ ÀÎÁ¢ÇÑ node µé°£ ¿¡ ÀϾ´Â communication À» ¸»Çϸç logical communication Àº two communi- cating node °£ÀÇ functionally paired layer ¿¡ ÀϾ´Â°ÍÀ» ¸»ÇÑ´Ù. -SNA ´Â single node ¿¡¼ ÀÎÁ¢ÇÑ layer °£¿¡ ÀϾ´Â communication À» Á¤ÀÇ Çϴµ¥ ÀÌ°ÍÀº ÀÎÁ¢ÇÑ layer °£¿¡ ±³È¯µÇ¾î¾ßÇÒ Á¤º¸¿Í °¢ layer ¿¡ ¼ÓÇÏ´Â ±â ´ÉµéÀ» ³ªÅ¸³¿.À¸·Î½á ÀÌ·ç¾î Áø´Ù. ¶ÇÇÑ, message °¡ ¼ö°³ÀÇ data link ¸¦ °Å Ãļ ¿øÇÏ´Â ¸ñÀûÁö ±îÁö µµ´ÞÇÏ´Â Multiple node µµ ÀÖ´Ù. (Fig 3-7) -À§¿¡¼ ¼³¸íÇÑ ¹Ù·Î¼, data ´Â ´Ù¾çÇÑ SNA function layer ¸¦ ÅëÇÏ¿© pass up-down µÈ´Ù. physical communication ÀÌ ÀϾ´Â µ¿¾È , ´Ù¸¥Á¾·ùÀÇ communication ÀÌ logical ÇÏ°Ô ÀϾÙ. Áï, ¸¶Ä¡ user °¡ º¸±â¿¡´Â °¢ layer °£ÀÇ logical ÇÏ°Ô ÀϾ´Â°ÍÀ¸·Î ³ªÅ¸³ª¸ç À̸¦ peer-to-peer communication À̶ó°í ÇÑ´Ù. -SNA ´Â peer-to-peer communication À» ¸Å¿ì Á¤È®ÇÏ°Ô Á¤ÀÇÇÏ¸ç °¢ layer ¿¡¼ ºÙ°ÔµÇ´Â message header ÀÇ format ÀÌ SNA architecture ÀÇ ºÎºÐÀ¸·Î½á ³ªÅ¸³ ´Ù.¶ÇÇÑ SNA protocol Àº ¶³¾îÁø Node »ó¿¡¼ °¢°¢ ´ëÀÀÇÏ´Â layer °¡ interac- tionÇϴ°¡¸¦ Á¤ÀÇÇÑ´Ù.Peer protocol Àº header ¿¡ Æ÷ÇÔµÈ parameter µéÀÇ ÀÇ ¹Ì¿Í ÀÌ parameter µé¿¡ ÀÇÇؼ ÀϾ´Â action ¿¡ ´ëÇؼµµ Á¤ÀÇÇÑ´Ù.À̸®ÇÏ ¿© ÇϳªÀÇ H/W ¿Í S/W product À» »ç¿ëÇÏ¿© ±¸ÇöµÈ SNA node ´Â ´Ù¸¥ product set À» »ç¿ëÇÏ´Â Node ¿Í communicate ÇÒ¼ö°¡ Àִµ¥ µÎ Node ¸ðµÎ SNA format °ú Protocol À» µû¸¦¶§ °¡´ÉÇÑ°ÍÀÌ´Ù. -SNA functions are assigned to well-defined functional layers. The data link control layer is responsiblefor the transmission of data between two nodes over a particular physical link. The data link control layer uses the services of a physical control layer that is defined outside the SNA architecture. The path control layer routes data from one node to the next. The transmission control layer tracks session status, controls the pacing of data flow, and sees that data units are properly sequenced, The data flow control layer manages the overall integrity of data flow during asession. The function managenent layer is divided into two sublayers--- function management data services and NAU services manager. The function management data services sublayer controls the interface with network user and manages the activitices of the network as a whole. The NAU services manager sublayer provides services to lower-level layers.Two types of communication occur as data are transmitted through an SNA network. Communication between adjacent layers takes place as data pass from one layer to the next.Data are physically passes down through the various functioal layers in the sending node, across over physicall circuits, and back up through the functional layers in the receiving node. Control information is added and then stripped off by the various functional layers.Peer-to-Peer communication is communication that logically taked place between the complementary layers in the sending and receiving nodes. The SNA architecture defines protocols that specify how equivalent layers in different nodes are to interact and defines the formats for headers that are added to messages by the various functional layers. Revision History Created on Oct 22 ,1993