H.1.6 Implementation Considerations (Informative)

The LDAP database can be used as a documentation tool. Documenting the configuration for both managed and legacy machines makes upgrading easier and reduces the error rate for manually configured legacy equipment.

There are various possible implementation strategies for clients performing lookups within the LDAP database. For example, before initiating a DICOM association to a specific AE, a client implementation could either:

  1. Query the LDAP database to obtain hostname and port for the specific AE Title immediately prior to initiating a DICOM association.

  2. Maintain a local cache of AE Title, hostname and port information and only query the LDAP database if the specific AE Title is not found in the local cache.

The advantages of maintaining a local cache include performance (by avoiding frequent lookups) and reliability (should the LDAP server be temporarily unavailable). The disadvantage of a cache is that it can become outdated over time. Client implementations should provide appropriate mechanisms to purge locally cached information.

Client caches may cause confusion during updates. Manual steps may be needed to trigger immediate updates. LDAP database replication also may introduce delays and inconsistencies. Database replication may also require manual intervention to force updates to occur immediately.

One strategy to reduce client cache problems is to re-acquire new DNS and LDAP information after any network association information. Often the first symptom of stale cache information is association failures due to the use of obsolete configuration information.

Some LDAP servers do not support a “modify DN” operation. For example, in the case of renaming a device on such a server, a tree copy operation may be needed to create a new object tree using the new name, followed by removal of the old object tree. After such a rename the device may need to search using other attributes when finding its own configuration information, e.g. the device serial number.