S  2  `^BLTT TTT *This section covers the following topics:*6 "a)Application service elements". b)Application contexts6 "26.Application Service Elements"_ KThis clause identifies the application service elements (.I.ab:ASEs;) that K>e various Message Handling services are provided areP_ Kspecified in Recommendation X.419. These protocols are known as .I.ab:P1;, K. .I.ab:P3;, and .I.ab:P7;.c ONote The nature of a message's content does not enter into the definition of OdPMessage Handling ACs because the content is encapsulated (as an Octet String) inPDJ 0the protocols by means of which it is conveyed.0 ect (e.g., P^ Jan ASN.1 Set comprising an Integer command code and an IA5 String command JdDJPargument). It is distinguished from the APDU's transfer syntax which is how the P`JMLinformation object is represented for transmission between two open systems Ld P(e.g., one octet denoting an ASN.1 Set, followed by one octet giving the length P' of the Set, etc.).d PThe ACs by means of which tha result of its use by the AC's Nb NASEs. Conventionally one assigns a name to the set of APDUs associated either N\ Hwith each individual ASE or with the AC as a whole. The initiator of an H] Iassociation indicates to the responder the one or more abstract syntaxes IX Dassociated with the AC by conveying their names to it via the ACSE.Dd PThe abstract syntax of an APDU is its structure as an information objarameters are to be L  exchanged). [ GEvery AC is named (by an ASN.1 Object Identifier). The initiator of an Gd Passociation indicates to the responder the AC that will govern the association'sPO ;use by conveying the AC's name to it by means of the ACSE.;d PAn AC also identifies by name (an ASN.1 Object Identifier) the abstract syntaxesPb Nof the APDUs that an association may carry as n is to be established (e.g., what E_J Kinitialization parameters are to be exchanged), what ASEs are to engage in KcOpeer-to-peer communication over the association, what constraints (if any) are O\ Hto be imposed upon their individual use of the association, whether the H_ Kinitiator or responder is the consumer of each asymmetric ASE, and how the K` Lassociation is to be released (e.g., what finalization pe ACSE is defined in Recommendation X.217.-. 27.Application Contexts_ KIn OSI the communication capabilities (i.e., ASEs) of two open systems are KY Emarshalled for a particular purpose by means of application contexts Ea M(.I.ab:ACs;). An AC is a detailed specification of the use of an association M@ ,between two open systems, i.e., a protocol.,Y EAn AC specifies how the associatios)--between open systems PN :so as to ensure their safe-storage at their destinations.:A -The RTSE is defined in Recommendation X.218.-2 26.4.3Association Controld PThe Association Control Service Element (.I.ab:ACSE;) is the means by which all Pd Papplication associations between open systems are established, released, and in P,JMother respects managed.ADJ-Thstructure their request-response interactions OB .between consuming and supplying open systems..A -The ROSE is defined in Recommendation X.219.-0 26.4.2Reliable Transfer^ JThe Reliable Transfer Service Element (.I.ab:RTSE;) is the means by which J^ Jvarious symmetric and asymmetric Message Handling ASEs convey information Jd Pobjects--especially large ones (e.g., facsimile message PaJ M| ACSE | SY | +------+------+ +- Legend -------+ | SY symmetric | | ASY M4  asymmetric | +----------------+ d PThe supporting ASEs, summarized in the table, are individually introduced in theP#clauses below.0 26.4.1Remote Operationsb NThe Remote Operations Service Element (.I.ab:ROSE;) is the means by which the Nc Oasymmetric Message Handling ASEs L MASE.) 26.4Supporting ASEscDJOThe general-purpose ASEs upon which Message Handling ASEs depend are listed in O_ Kthe first column of Table 12/X.402. For each listed ASE, the second column KE 1indicates whether it is symmetric or asymmetric.17 #Table .T.:12/X.402 Supporting ASEs#d P+------+------+ | ASE | Form | +------+------+ | ROSE | SY | | RTSE | SY | NThe Message Retrieval Service Element (.I.ab:MRSE;) is the means by which the N< (retrieval transmittal step is effected.(5 !26.3.5Message Administration!d PThe Message Administration Service Element (.I.ab:MASE;) is the means by which aP` LUA, MS, or MTA places on file with one another information that enables and L`JMLcontrols their subsequent interaction by means of the MSSE, MDSE, MRSE, and ffected.'1 26.3.2Message Submissionc OThe Message Submission Service Element (.I.ab:MSSE;) is the means by which the O= )submission transmittal step is effected.)/ 26.3.3Message Deliverya MThe Message Delivery Service Element (.I.ab:MDSE;) is the means by which the M; 'delivery transmittal step is effected.'0 26.3.4Message Retrievalb SY symmetric C consumer | | ASY asymmetric S supplierP5J !| +----------------------------+!d PThe Message Handling ASEs, summarized in the table, are individually introduced PS ?in the clauses below. Each is defined in Recommendation X.419.?/ 26.3.1Message Transfera MThe Message Transfer Service Element (.I.ab:MTSE;) is the means by which the M;'transfer transmittal step is e +--------------------+ | ASE | Form | UA MS MTA AU | D^ J+------+------+--------------------+ | MTSE | SY | - - CS - | Jd P+------+------+--------------------+ | MSSE | ASY | C CS S - | | MDSEPdDJP| ASY | C C S - | | MRSE | ASY | C S - - | | MASE | ASY P\ H | C CS S - | +------+------+--------------------+ +- Legend Hd P-------------------+ |11/X.402. For each ASE listed, the second column indicatesP[ Gwhether it is symmetric or asymmetric. The third column identifies the Gc Ofunctional objects--UAs, MSs, MTAs, and AUs--that are associated with the ASE, O7 #either as consumer or as supplier.#=JM)Table .T.:11/X.402 Message Handling ASEs)d P+------+------+--------------------+ | | | Functional Objects | | PX D | | 03 | | 04 | | 05 | | 06 | | 07 | | 08 | | 09 | | 10 | | Od P11 | | 12 | | 13 | | 14 | | 15 | | 16 | | 17 | | 18 | | 19 | | 20 | | 21 | | 22 PN :| | 23 | | 24 | | 25 | | 26 | | 27 | | 28 | | 29 | +----+:A -Figure .F.:15/X.402 Multiple Asymmetric ASEs-/ 26.3Message Handling ASEsb NThe ASEs that provide the various Message Handling services are listed in the Nd Pfirst column of Table r Asymmetric ASEs4[ GAs indicated, the four roles described above are defined relative to a Gb Nparticular ASE. When an AE comprises several asymmetric ASEs, these roles are Nd Passigned independently for each ASE. Thus, as shown in Figure 15/X.402, a singlePd PUE might serve as the consumer with respect to one ASE and as the supplier with P(respect to another.c O+----+ | 01 | | 02 | asymmetric ASE x.!d Pd)x-.I.gl:consuming ASE;: An asymmetric ASE x configured for co-location withP' an x-consuming-UE.cDJO+----+ | 01 | | 02 | | 03 | | 04 | | 05 | | 06 | | 07 | | 08 | | 09 | | 10 | | OdJ P11 | | 12 | | 13 | | 14 | | 15 | | 16 | | 17 | | 18 | | 19 | | 20 | | 21 | | 22 PN :| | 23 | | 24 | | 25 | | 26 | | 27 | | 28 | | 29 | +----+:H 4Figure .F.:14/X.402 Terminology fo 14/X.402 and inP/ the following terminology:a Ma)x-.I.gl:supplying UE;: An application process that supplies the service M5JM!represented by asymmetric ASE x.!d Pb)x-.I.gl:supplying ASE;: An asymmetric ASE x configured for co-location withP' an x-supplying-UE.a Mc)x-.I.gl:consuming UE;: An application process that consumes the service M5 !represented by 14 | | 15 | | 16 | | 17 | | 18 | | 19 | | 20 | | 21 | | 22 PN :| | 23 | | 24 | | 25 | | 26 | | 27 | | 28 | | 29 | +----+:F 2Figure .F.:13/X.402 Symmetric and Asymmetric ASEs2d PWith respect to a particular asymmetric ASE, one UE supplies a service which thePd Pother consumes. The ASEs co-located with the UEs assist in the service's supply Pd Pand consumption. The resulting four roles are captured in Figured Pconsumes a service, but not both, depending upon how the ASE is configured. The P_ KASE for message delivery, e.g., is asymmetric because only the open system Kc Oembodying an MTA offers the associated service and only the other open system, O< (which embodies a UA or MS, consumes it.(cO+----+ | 01 | | 02 | | 03 | | 04 | | 05 | | 06 | | 07 | | 08 | | 09 | | 10 | | Od P11 | | 12 | | 13 | |# distinguished:cJ Oa).I.gl:symmetric;: Said of an ASE by means of which a UE both supplies and OaDJMconsumes a service. The ASE for message transfer, e.g., is symmetric because M` Lboth open systems, each of which embodies an MTA, offer and may consume the L@ ,service of message transfer by means of it.,^ Jb).I.gl:asymmetric;: Said of an ASE by means of which a UE supplies or JNote Strictly speaking, an open system's role is determined by the behavior ofP^ Jits application processes. In the Message Handling context an application Jd Pprocess realizes a functional object of one of the types defined in clause 7. A PF 2UE in turn is one part of an application process.27 #26.2Symmetric and Asymmetric ASEs#[ GThe following two kinds of ASE, illustrated in Figure 13/X.402, can be G OAn ASE plays the largely mechanical role of translating requests and responses Ob Nmade by its UE to and from the form dictated by the application protocol that Nd Pgoverns the ASE's interaction with its peer ASE in the open system to which the P] Iassociation connects it. The ASE realizes an abstract service, or a part I[JMGthereof, for purposes of OSI communication (see Recommendation X.407).Gd Pombined in a K` Lsingle AE, they must be designed to coordinate their use of the application L!  association. c O+----+ | 01 | | 02 | | 03 | | 04 | | 05 | | 06 | | 07 | | 08 | | 09 | | 10 | | OdP11 | | 12 | | 13 | | 14 | | 15 | | 16 | | 17 | | 18 | | 19 | | 20 | | 21 | | 22 PN :| | 23 | | 24 | | 25 | | 26 | | 27 | | 28 | | 29 | +----+:8 $Figure .F.:12/X.402 The ASE Concept$cres to play its role."\DJHThe relationship between two AEs in different open systems is called an Ha Mapplication association. The ASEs in each open system communicate with their Mc Opeer ASEs in the other open system via a presentation connection between them. Od PThat communication is what creates and sustains the relationship embodied in theP_ Kapplication association. For several ASEs to be successfully cing open systems. Only the OSI-related portions of the open systems, O] Icalled AEs, are shown. Each AE comprises a UE and one or more ASEs. A UE Id Prepresents the controlling or organizing portion of an AE which defines the openPdJ Psystem's role (e.g., that of an MTA). An ASE represents one of the communicationPb Ncapability sets, or services (e.g., for message submission or transfer), that N6 "the UE requi` LNote Besides the ASEs discussed, the MHS relies upon the Directory Access LbJMNService Element defined in Recommendation X.519. However, since that ASE does Nd Pnot figure in the ACs for Message Handling (see Recommendation X.419), it is notP$ discussed here.) 26.1The ASE ConceptY EThe ASE concept is illustrated in Figure 12/X.402, which depicts two Ec OcommunicatG 3figure in the OSI realization of Message Handling.3d PIn OSI the communication capabilities of open systems are organized into groups PaMof related capabilities called ASEs. The present clause reviews this concept M\ Hfrom the OSI Reference Model, draws a distinction between symmetric and Hb Nasymmetric ASEs, and introduces the ASEs defined for or supportive of Message N  Handling. 1mance=] I " 25.OverviewTDJ@This section describes how the MHS is realized by means of OSI.@> *This section covers the following topics:*6 "a)Application service elements". b)Application contexts6 "26.Application Service Elements"_ KThis clause identifies the application service elements (.I.ab:ASEs;) that K