olution services to one of the largest archival collections in the United States. There are also approaches such as Electronic Numbering (ENUM) [24], which use a translation between SIP URIs and .164 numbers into IP addresses. Unfortunately, the IP information is stored within the DNS and is therefore restricted to the centralized administration, similar to dynamic DNS. These approaches require a third-party update and modification of the DNS entry in order to update this information. This operation is generally performed by © 2009 by Taylor & Francis Group, LLC SIP Mobility Technologies and the Use of Persistent Identifiers a user with administrative rights over the DNS domain. Due to the low level of security implemented in the DNS protocol per se, attacks on ENUM and DNS are very easy to implement with approaches such as the corruption of DNS caches. The handle system has an encrypted storage and query mech- anism that allows every connection to be encrypted and every response to be challenged. Furthermore, handle administration is completely distributed, allowing for a very secure infrastructure. In the next sections we will explore the concepts associated with SIP mobility while contrasting the current practices with the use of persistent identifiers. 10.3.1 H-SIP: Abstraction Layer As mentioned before, our proposed approach uses handles as globally unique identifiers to locate and identify SIP architectural elements. This abstraction allows the system to route calls independent of user location and domain association. We refer to the modified SIP framework as the Handle-SIP or H-SIP. Note that we have also exploited this abstraction approach at the level of network devices and services in [30,32]. Briefly, the Handle System [10-13] is intended to be a means of universal basic access to registered digital objects [33]. It provides a distributed, secure, and global name service for administration and resolution of handles over the Internet. A handle is a persistent name that can be associated with a set of at