Материал: part08

Note​

Inadditiontothesereasons,alocallydefinedlistofreasonsmaybeusedtoreflecterrorsthatcausedtheabortandoriginated​ in the Session, Transport, Network, Data Link, and Physical layers. The generation and handling of such errors is internal​ to an implementation and, therefore, is outside the scope of this communications Standard.​

7.4.2 A-P-ABORT Service Procedure​

When the UL service-provider detects an internal error, A-P-ABORT indication primitives shall be issued to acceptors in both AEs.​ The association shall be abnormally released. Requestors in both AEs shall not issue any further primitives for the association.​

7.5 Sequencing Information​

Interactions among the specific service procedures, discussed in Section 7.1, Section 7.2, Section 7.3 and Section 7.4 for the ACSE​ subset of the Upper Layer Service, are defined in clause 10 of ISO 8649 - The ACSE Service Definition.​

7.6 P-DATA Service​

ThisPresentationP-DATAServiceshallbeusedbyeitherAEtocausetheexchangeofapplicationinformation(i.e.,DICOMMessages).​ DICOM Messages shall be exchanged as defined in PS3.7. An association provides a simultaneous bi-directional exchange of P-​ DATA request/indication primitives.​

Figure 7-5 illustrates the transfer of data on an established association between two AEs.​

Figure 7-5. Data Transfer​

7.6.1 P-DATA Parameters​

Table 7-7 lists the parameter that shall be required for the P-DATA service.​

Table 7-7. P-DATA Service Parameter​

The Presentation Data Value List parameter shall contain one or more Presentation Data Values (PDV). Each PDV shall consist of​ twoparameters:aPresentationContextIDandUserDatavalues.TheUserDatavaluesaretakenfromtheAbstractSyntaxandencoded​ in the Transfer Syntax identified by the Presentation Context ID. This referenced Presentation Context ID identifies one of the​ presentationcontextsagreedtoatassociationtime.TheUserDatavaluesformatusedineachPDVbytheDICOMApplicationEntities​ is specified in Annex E.​

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8 DICOM OSI Upper Layer Profile​

Retired. See PS 3.8 2001.​

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9 DICOM Upper Layer Protocol for TCP/IP​

The DICOM Upper Layer Protocol specified in this section shall be used in conjunction with the TCP/IP transport layers..​

9.1 Use of the Transport Service Provided By TCP​

9.1.1 General​

There is a one-to-one relationship between a TCP Transport Connection and an Upper Layer Association. Therefore, the following​ rules apply:​

a.​Each Upper Layer Association shall be supported by one and only one TCP Transport Connection.​

b.​Each TCP Transport Connection shall support one and only one Upper Layer Association.​

TheServicesprovidedbytheTCPTransportServicesarenotformallydocumented.Thissection,therefore,makesuseof"commonly"​ usedtermsinanumberofTCPProgrammingInterfaceImplementations(e.g.,Sockets).However,thefollowingRFCsshallberequired​ for TCP/IP support. They specify the support needed for IPv4.​

a.​RFC793, Transmission Control Program - DARPA Internet Protocol Specification​

b.​RFC791, Internet Protocol - DARPA Internet Protocol Specification​

c.​RFC792, Internet Control Message Protocol - DARPA Internet Program Protocol Specification​

d.​RFC950, Internet Subnetting​

In addition, devices that support IPv6 shall comply with:​

a.​RFC1881, IPv6 Address Allocation Management​

b.​RFC2460, Internet Protocol, Version 6 (IPv6) Specification​

Note​

There are many other RFC's that may also apply to a particular implementation depending upon specific selections of​ hardware and software features.​

FortheestablishmentofaTCPconnection,aTCPportshallbeusedtoserveasthetransportselector.ADICOMULentityisidentified​ onagivensystemonthenetworkbyaportnumberuniquewithinthescopeofthissystem.PortnumbersofremoteDICOMULentities​ (well known port number or other numbers) shall be configurable on DICOM UL entities.​

Note​

ItisstronglyrecommendedthatsystemssupportingasingleDICOMULentityuseastheirportthe"wellknownport"registered​ for the DICOM Upper Layer Protocol: port number 104 (decimal), if the operating system permits access to privileged ports​ (in the range 0 to 1023), otherwise it is recommended that they use the "registered" port number 11112 (decimal). See "ht-​ tp://www.iana.org/assignments/port-numbers".​

Application Entities may also choose to access the TCP Transport Services via a Secure Transport Connection. The nature of this​ Secure Transport Connection is specified through Security Profiles (see PS3.15). Security Profiles select minimum mechanisms​ needed to support that profile. Other mechanisms may also be used if agreed to during establishment of the Secure Transport Con-​ nection.​

Note​

1.​DICOMdoesnotspecifyhowasecuretransportconnectionisestablished,orthesignificanceofanycertificatesexchanged​ during peer entity authentication. These issues are left up to the application, which is assumed to be following some​ security policy. Once the application has established a secure Transport Connection, then an Upper Layer Association​ can use that secure channel.​

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2.​TheremaybeaninteractionbetweenPDUsizeandrecordsizeofthesecureTransportConnectionthatimpactsefficiency​ of transport.​

3.​Registered ports for Secure Transport Connections are defined in PS3.15.​

9.1.2 Opening a TCP Transport Connection​

WhenanAssociationistobeestablishedbyaDICOMUpperLayerEntity,aTRANSPORTCONNECTrequestprimitiveshallbeissued​ to the TCP Transport Service (Active Open). Once the TCP Transport Connection Confirmation is received (Open Completed), an​ A-ASSOCIATE-RQ PDU shall be sent/written on the now established transport connection.​

When a DICOM Upper Layer Entity becomes activated (Association Idle State), it shall wait for TCP Transport Connections in a​ passive mode by initiating a "listen." When an incoming TCP Transport Connection Indication is received from the network, it is ac-​ cepted and a timer ARTIM (Association Request/Reject/Release Timer) shall be set. Any further exchange of PDUs (read/write) shall​ be performed as specified by the Upper Layer State Machine (including ARTIM Timer expiration before an A-ASSOCIATE-RQ PDU​ is received, see Section 9.2).​

9.1.3 Transferring Data On a TCP Connection​

Data exchange of PDUs (read/write) on an established TCP Connection shall follow the specifications of the DICOM Upper Layer​ Protocol State Machine (see Section 9.2) and the DICOM Upper Layer PDU structure (see Section 9.3).​

9.1.4 Closing a TCP Transport Connection​

TCP Transport Connections shall be closed using the "don't linger" option.​

A TCP Transport Connection is closed under a number of situations. These are described in the DICOM Upper Layer Protocol State​ Machine. Some typical cases are discussed below:​

a.​After an A-RELEASE-RQ has been sent and the A-RELEASE-RP PDU is received​

b.​WhenaTransportConnectionhasbeenestablishedbytheDICOMremoteULEntityandnoA-ASSOCIATE-RQisreceivedbefore​ the ARTIM Timer expires​

c.​When an A-ABORT PDU has been received​

d.​When an A-ABORT PDU has been sent and the ARTIM Timer expires before the Transport Connection is closed​

e.​When a TCP connection is being disconnected by the Transport Service Provider (e.g., network failure)​

f.​ When a TCP connection is being disconnected by the remote DICOM UL Entity​

Note​

1.​Except following the normal completion of an association reject, release or abort and in specific situations such as​ temporary lack of resources, an Upper Layer State Machine should not disconnect a TCP connection or reject its estab-​ lishment. The appropriate behavior is to use the Association Reject or Abort services.​

2.​The ARTIM Timer should not be used to oversee the Association Establishment or Release. Such a mechanism falls​ under the protocol definition of the layer above the DICOM Upper Layer (i.e., DICOM Application Entity, see PS3.7).​

9.1.5 ARTIM Timer​

The value of the ARTIM Timer used to manage the Request, Reject, and Release of associations on a DICOM UL entity shall be​ configurable to address a wide range of network configurations.​

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