1993.10.22

SUBJECT: SNA FUNCTIONAL LAYERS

°³¿ä: ¸ðµç communication network architectures ÀÇ ³»ÀçµÈ ±âº» °³³ä Àº ÀßÁ¤ÀǵÈ

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