Editing IP Multimedia Subsystem (section)

{{Short description|Architectural framework of telecommunications}}
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{{Technical|date=December 2010}}
{{Abbreviations|article|date=May 2011}}
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The '''IP Multimedia Subsystem''' or '''IP Multimedia Core Network Subsystem''' ('''IMS''') is a standardised [[Architectural Framework|architectural framework]] for delivering IP [[multimedia]] services. Historically, mobile phones have provided voice call services over a [[circuit switching|circuit-switched]]-style network, rather than strictly over an IP [[packet switching|packet-switched]] network.  Various [[voice over IP]] technologies are available on smartphones; IMS provides a standard protocol across vendors.

IMS was originally designed by the wireless [[Standardization|standards]] body [[3rd Generation Partnership Project]] (3GPP), as a part of the vision for evolving mobile networks beyond [[GSM]]. Its original formulation (3GPP Rel-5) represented an approach for delivering Internet services over [[GPRS]].  This vision was later updated by 3GPP, [[3GPP2]] and [[European Telecommunications Standards Institute|ETSI]] [[TISPAN]] by requiring support of networks other than [[GPRS]], such as [[Wireless LAN]], [[CDMA2000]] and fixed lines.

IMS uses [[IETF]] protocols wherever possible, e.g., the [[Session Initiation Protocol]] (SIP). According to the 3GPP, IMS is not intended to standardize applications, but rather to aid the access of multimedia and voice applications from wireless and wireline terminals, i.e., to create a form of [[Fixed–mobile convergence|fixed-mobile convergence]] (FMC).<ref name="23.228">{{citation
  | author = Technical Specification Group Services and System Aspects
  | title = IP Multimedia Subsystem (IMS), Stage 2, TS 23.228
  | publisher = 3rd Generation Partnership Project 
  | year = 2006
}}</ref> This is done by having a horizontal control layer that isolates the access network from the [[service layer]]. From a logical architecture perspective, services need not have their own control functions, as the control layer is a common horizontal layer. However, in implementation this does not necessarily map into greater reduced cost and complexity.

Alternative and overlapping technologies for access and provisioning of services across wired and wireless networks include combinations of [[Generic Access Network]], [[softswitch]]es and "naked" SIP.

Since it is becoming increasingly easier to access content and contacts using mechanisms outside the control of traditional wireless/fixed operators, the interest of IMS is being challenged.<ref>{{citation| author = Alexander Harrowell, Staff Writer| title = A Pointless Multimedia Subsystem?| url = http://www.allbusiness.com/primary-metal-manufacturing/foundries-nonferrous/4104136-1.html| publisher = Mobile Communications International|date=October 2006|archive-url=https://web.archive.org/web/20100918042052/http://www.allbusiness.com/primary-metal-manufacturing/foundries-nonferrous/4104136-1.html|archive-date=2010-09-18}}</ref>

Examples of global standards based on IMS are [[Multimedia telephony|MMTel]] which is the basis for Voice over LTE ([[VoLTE]]), [[Generic Access Network|Wi-Fi Calling]] (VoWIFI), [[Video over LTE]] (ViLTE), SMS/MMS over WiFi and LTE, [[USSD|Unstructured Supplementary Service Data]] (USSD) over LTE, and [[Rich Communication Services]] (RCS), which is also known as joyn or Advanced Messaging, and now RCS is operator's implementation. RCS also further added Presence/EAB (enhanced address book) functionality.<ref>{{Citation|last1=Zhao|first1=Peng|title=A New Mechanism of EAB in RCS|date=2012|url=https://doi.org/10.1007/978-3-642-27708-5_33|work=Knowledge Discovery and Data Mining|pages=247–254|editor-last=Tan|editor-first=Honghua|series=Advances in Intelligent and Soft Computing|place=Berlin, Heidelberg|publisher=Springer|language=en|doi=10.1007/978-3-642-27708-5_33|isbn=978-3-642-27708-5|access-date=2021-04-08|last2=Wei|first2=Qun|last3=Xia|first3=Hailun|last4=Zeng|first4=Zhimin|url-access=subscription}}</ref>