The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is a standardised
architectural framework
An enterprise architecture framework (EA framework) defines how to create and use an enterprise architecture. An architecture framework provides principles and practices for creating and using the architecture description of a system. It struct ...
for delivering IP
multimedia
Multimedia is a form of communication that uses a combination of different content forms such as text, audio, images, animations, or video into a single interactive presentation, in contrast to tradition ...
services. Historically, mobile phones have provided voice call services over a
circuit-switched
Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full b ...
-style network, rather than strictly over an IP
packet-switched
In telecommunications, packet switching is a method of grouping data into '' packets'' that are transmitted over a digital network. Packets are made of a header and a payload. Data in the header is used by networking hardware to direct the pac ...
network. Alternative methods of delivering voice (
VoIP
Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
) or other multimedia services have become available on smartphones, but they have not become standardized across the industry. IMS is an architectural framework that provides such standardization.
IMS was originally designed by the wireless
standards Standard may refer to:
Symbols
* Colours, standards and guidons, kinds of military signs
* Standard (emblem), a type of a large symbol or emblem used for identification
Norms, conventions or requirements
* Standard (metrology), an object th ...
body
3rd Generation Partnership Project (3GPP), as a part of the vision for evolving mobile networks beyond
GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
. Its original formulation (3GPP Rel-5) represented an approach for delivering Internet services over
GPRS
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
. This vision was later updated by 3GPP,
3GPP2
The 3rd Generation Partnership Project 2 (3GPP2) is a collaboration between telecommunications associations to make a globally applicable third generation ( 3G) mobile phone system specification within the scope of the ITU's IMT-2000 project. In ...
and
ETSI
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...
TISPAN
The Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN) is a standardization body of ETSI, specializing in fixed networks and Internet convergence. It was formed in 2003 from the amalgamation of the ETSI bodies Tel ...
by requiring support of networks other than
GPRS
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
, such as
Wireless LAN
A wireless LAN (WLAN) is a wireless computer network
A wireless network is a computer network that uses wireless data connections between network nodes.
Wireless networking is a method by which homes, telecommunications networks and bus ...
,
CDMA2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible ...
and fixed lines.
IMS uses
IETF
The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and a ...
protocols wherever possible, e.g., the
Session Initiation Protocol
The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telepho ...
(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 (FMC).
This is done by having a horizontal control layer that isolates the access network from the
service layer
In intelligent networks (IN) and cellular networks, service layer is a conceptual layer within a network service provider architecture. It aims at providing middleware that serves third-party value-added services and applications at a higher a ...
. 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
Generic Access Network (GAN) is a protocol that extends mobile voice, data and multimedia ( IP Multimedia Subsystem/ Session Initiation Protocol (IMS/SIP)) applications over IP networks. Unlicensed Mobile Access (UMA) is the commercial name used by ...
,
softswitch
A softswitch (''software switch'') is a call-switching node in a telecommunications network, based not on the specialized switching hardware of the traditional telephone exchange, but implemented in software running on a general-purpose computing ...
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.
Examples of global standards based on IMS are
MMTel which is the basis for Voice over LTE (
VoLTE
Voice over LTE (VoLTE) is an LTE high-speed wireless communication standard for mobile phones and data terminals, including Internet of things (IoT) devices and wearables. VoLTE has up to three times more voice and data capacity than older 3G U ...
),
Wi-Fi Calling
Voice over Wireless LAN (VoWLAN), also Voice over WiFi (VoWiFi), is the use of a wireless broadband network according to the IEEE 802.11 standards for the purpose of vocal conversation. In essence, it is Voice over IP (VoIP) over a Wi-Fi networ ...
(VoWIFI),
Video over LTE ViLTE, an acronym for "Video over LTE", is a conversational (i.e. person to person) video service based on the IP Multimedia Subsystem (IMS) core network like VoLTE. It has specific profiles for the control and VoLTE of the video service and uses ...
(ViLTE), SMS/MMS over WiFi and LTE, USSD over LTE, and
Rich Communication Services
Rich Communication Services (RCS) is a communication protocol between mobile telephone carriers and between phone and carrier, aiming at replacing SMS messages with a text-message system that is richer, provides phonebook polling (for service dis ...
(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.
History
*IMS was defined by an industry forum called 3G.IP, formed in 1999. 3G.IP developed the initial IMS architecture, which was brought to the 3rd Generation Partnership Project (
3GPP), as part of their standardization work for
3G mobile phone systems in
UMTS
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Inte ...
networks. It first appeared in Release 5 (
evolution from 2G to 3G networks), when SIP-based multimedia was added. Support for the older
GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
and
GPRS
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
networks was also provided.
*
3GPP2
The 3rd Generation Partnership Project 2 (3GPP2) is a collaboration between telecommunications associations to make a globally applicable third generation ( 3G) mobile phone system specification within the scope of the ITU's IMT-2000 project. In ...
(a different organization from 3GPP) based their CDMA2000 Multimedia Domain (MMD) on 3GPP IMS, adding support for
CDMA2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible ...
.
* 3GPP release 6 added interworking with
WLAN
A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building ...
, inter-operability between IMS using different IP-connectivity networks, routing group identities, multiple registration and forking, presence, speech recognition and speech-enabled services (
Push to talk
Push-to-talk (PTT), also known as press-to-transmit, is a method of having conversations or talking on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode.
H ...
).
* 3GPP release 7 added support for
fixed
Fixed may refer to:
* ''Fixed'' (EP), EP by Nine Inch Nails
* ''Fixed'', an upcoming 2D adult animated film directed by Genndy Tartakovsky
* Fixed (typeface), a collection of monospace bitmap fonts that is distributed with the X Window System
* ...
networks by working together with
TISPAN
The Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN) is a standardization body of ETSI, specializing in fixed networks and Internet convergence. It was formed in 2003 from the amalgamation of the ETSI bodies Tel ...
release R1.1, the function of AGCF (access gateway control function) and PES (
PSTN
The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...
emulation service) are introduced to the wire-line network for the sake of inheritance of services which can be provided in PSTN network. AGCF works as a bridge interconnecting the IMS networks and the Megaco/H.248 networks. Megaco/H.248 networks offers the possibility to connect terminals of the old legacy networks to the new generation of networks based on IP networks. AGCF acts a SIP User agent towards the IMS and performs the role of P-CSCF. SIP User Agent functionality is included in the AGCF, and not on the customer device but in the network itself. Also added voice call continuity between circuit switching and packet switching domain (
VCC), fixed broadband connection to the IMS, interworking with non-IMS networks, policy and charging control (
PCC
PCC may refer to:
Science and technology
* Pearson correlation coefficient (''r''), in statistics
* Periodic counter-current chromatography, a type of affinity chromatography
* Portable C Compiler, an early compiler for the C programming language
...
), emergency sessions. It also added SMS over IP.
* 3GPP release 8 added support for
LTE /
SAE
SAE or Sae may refer to:
Science and technology
:
* Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate
* Serious adverse event, in a clinical trial
* Simultaneous Auth ...
, multimedia session continuity, enhanced emergency sessions, SMS over SGs
and IMS centralized services.
* 3GPP release 9 added support for IMS emergency calls over
GPRS
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
and
EPS, enhancements to
multimedia telephony, IMS
media plane security, enhancements to services centralization and continuity.
* 3GPP release 10 added support for inter device transfer, enhancements to the single radio voice call continuity (SRVCC), enhancements to IMS emergency sessions.
* 3GPP release 11 added
USSD
Unstructured Supplementary Service Data (USSD), sometimes referred to as "quick codes" or "feature codes", is a communications protocol used by GSM cellular telephones to communicate with the mobile network operator's computers. USSD can be used ...
simulation service, network-provided location information for IMS,
SMS
Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
submit and delivery without MSISDN in IMS, and overload control.
Some operators opposed IMS because it was seen as complex and expensive.
In response, a cut-down version of IMS -- enough of IMS to support voice and SMS over the LTE network -- was defined and standardized in 2010 as
Voice over LTE
Voice over LTE (VoLTE) is an LTE high-speed wireless communication standard for mobile phones and data terminals, including Internet of things (IoT) devices and wearables. VoLTE has up to three times more voice and data capacity than older 3G U ...
(VoLTE).
[
Ian Poole, editor]
"What is Voice over LTE, VoLTE"
Architecture
Each of the functions in the diagram is explained below.
The IP multimedia core network subsystem is a collection of different functions, linked by standardized interfaces, which grouped form one IMS administrative network.
[{{{cite web, title=3GPP Stage 2 Specifications, url= http://www.3gpp.org/ftp/Specs/html-info/23228.htm] A function is not a node (hardware box): An implementer is free to combine two functions in one node, or to split a single function into two or more nodes. Each node can also be present multiple times in a single network, for dimensioning, load balancing or organizational issues.
Access network
The user can connect to IMS in various ways, most of which use the standard IP. IMS terminals (such as
mobile phone
A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...
s,
personal digital assistant
A personal digital assistant (PDA), also known as a handheld PC, is a variety mobile device which functions as a personal information manager. PDAs have been mostly displaced by the widespread adoption of highly capable smartphones, in partic ...
s (PDAs) and computers) can register directly on IMS, even when they are
roaming
Roaming is a wireless telecommunication term typically used with mobile devices, such as mobile phones. It refers to a mobile phone being used outside the range of its native network and connecting to another available cell network.
Technical ...
in another network or country (the visited network). The only requirement is that they can use IP and run SIP user agents.
Fixed access
Fixed access: In personal communications service (PCS), terminal access to a network in which there is a set relationship between a terminal and the access interface
Interface or interfacing may refer to:
Academic journals
* ''Interface'' ...
(e.g.,
digital subscriber line
Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric di ...
(DSL),
cable modem
A cable modem is a type of network bridge that provides bi-directional data communication via radio frequency channels on a hybrid fibre-coaxial (HFC), radio frequency over glass (RFoG) and coaxial cable infrastructure. Cable modems are primaril ...
s,
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
,
FTTx
Fiber to the ''x'' (FTTX; also spelled "fibre") or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber op ...
), mobile access (e.g.
5G NR
5G NR (New Radio) is a new radio access technology (RAT) developed by 3GPP for the 5G (fifth generation) mobile network. It was designed to be the global standard for the air interface of 5G networks. As with 4G (LTE), it is based on OFDM.
The ...
,
LTE,
W-CDMA
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Inte ...
,
CDMA2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible ...
,
GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
,
GPRS
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
) and wireless access (e.g.,
WLAN
A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building ...
,
WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide physical layer (PHY) and media access control (MAC) options.
The WiMAX ...
) are all supported. Other phone systems like
plain old telephone service
Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1 ...
(POTS—the old analogue telephones),
H.323
H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, m ...
and non IMS-compatible systems, are supported through
gateways.
Core network
HSS – Home subscriber server:
The ''home subscriber server'' (HSS), or ''user profile server function'' (UPSF), is a master user database that supports the IMS network entities that actually handle
calls
Call or Calls may refer to:
Arts, entertainment, and media Games
* Call, a type of betting in poker
* Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage
Music and dance
* Call (band), from Lahore, Paki ...
. It contains the subscription-related information (subscriber
profiles), performs
authentication
Authentication (from ''authentikos'', "real, genuine", from αὐθέντης ''authentes'', "author") is the act of proving an assertion, such as the identity of a computer system user. In contrast with identification, the act of indicati ...
and
authorization
Authorization or authorisation (see spelling differences) is the function of specifying access rights/privileges to resources, which is related to general information security and computer security, and to access control in particular. More for ...
of the user, and can provide information about the subscriber's location and IP information. It is similar to the GSM
home location register
Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobile ...
(HLR) and
Authentication centre (AuC).
A ''
subscriber location function'' (SLF) is needed to map user addresses when multiple HSSs are used.
User identities:
Various identities may be associated with IMS: IP multimedia private identity (IMPI), IP multimedia public identity (IMPU), globally routable user agent URI (GRUU), wildcarded public user identity. Both IMPI and IMPU are not phone numbers or other series of digits, but
uniform resource identifier
A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, conc ...
(URIs), that can be digits (a Tel URI, such as ''tel:+1-555-123-4567'') or alphanumeric identifiers (a SIP URI, such as ''sip:john.doe@example.com" ).
IP Multimedia Private Identity:
The ''IP Multimedia Private Identity'' (IMPI) is a unique permanently allocated global identity assigned by the home network operator, it has the form of an Network Access Identifier(NAI) i.e. user.name@domain, and is used, for example, for Registration, Authorization, Administration, and Accounting purposes. Every IMS user shall have one IMPI.
IP Multimedia Public Identity:
The ''IP Multimedia Public Identity'' (IMPU) is used by any user for requesting communications to other users (e.g. this might be included on a
business card
Business cards are cards bearing business information about a company or individual. They are shared during formal introductions as a convenience and a memory aid. A business card typically includes the giver's name, company or business aff ...
). Also known as Address of Record (AOR). There can be multiple IMPU per IMPI. The IMPU can also be shared with another phone, so that both can be reached with the same identity (for example, a single phone-number for an entire family).
Globally Routable User Agent URI:
''Globally Routable User Agent URI'' (GRUU) is an identity that identifies a unique combination of IMPU and
UE instance.
There are two types of GRUU: Public-GRUU (P-GRUU) and Temporary GRUU (T-GRUU).
*P-GRUU reveal the IMPU and are very long lived.
*T-GRUU do not reveal the IMPU and are valid until the contact is explicitly de-registered or the current registration expires
Wildcarded Public User Identity:
A ''wildcarded Public User Identity'' expresses a set of IMPU grouped together.
The HSS subscriber database contains the IMPU, IMPI,
IMSI,
MSISDN, subscriber service profiles, service triggers, and other information.
Call Session Control Function (CSCF)
Several roles of SIP servers or proxies, collectively called Call Session Control Function (CSCF), are used to process SIP signaling packets in the IMS.
* A ''Proxy-CSCF'' (P-CSCF) is a
SIP proxy
The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telephon ...
that is the first point of contact for the IMS terminal. It can be located either in the visited network (in full IMS networks) or in the home network (when the visited network is not IMS compliant yet). Some networks may use a
Session Border Controller
A session border controller (SBC) is a network element deployed to protect SIP based voice over Internet Protocol (VoIP) networks.
Early deployments of SBCs were focused on the borders between two service provider networks in a peering environme ...
(SBC) for this function. The P-CSCF is at its core a specialized SBC for the
User–network interface In telecommunications, a user–network interface (UNI) is a demarcation point between the responsibility of the service provider and the responsibility of the subscriber. This is distinct from a network-to-network interface (NNI) that defines a si ...
which not only protects the network, but also the IMS terminal. The use of an additional SBC between the IMS terminal and the P-CSCF is unnecessary and infeasible due to the signaling being encrypted on this leg. The terminal discovers its P-CSCF with either
DHCP
The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...
, or it may be configured (e.g. during initial provisioning or via a 3GPP IMS Management Object (MO)) or in the
ISIM or assigned in the
PDP Context
The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile telephony, mobile networks to transmit Internet Protocol, IP packets to external networks such as the Internet. The GPRS syst ...
(in
General Packet Radio Service
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Inst ...
(GPRS)).
** It is assigned to an IMS terminal before registration, and does not change for the duration of the registration.
** It sits on the path of all signaling, and can inspect every signal; the IMS terminal must ignore any other unencrypted signaling.
** It provides subscriber authentication and may establish an
IPsec
In computing, Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in ...
or
TLS security association with the IMS terminal. This prevents
spoofing attack
In the context of information security, and especially network security, a spoofing attack is a situation in which a person or program successfully identifies as another by falsifying data, to gain an illegitimate advantage.
Internet Spoofing and ...
s and
replay attack
A replay attack (also known as a repeat attack or playback attack) is a form of network attack in which valid data transmission is maliciously or fraudulently repeated or delayed. This is carried out either by the originator or by an adversary wh ...
s and protects the privacy of the subscriber.
** It inspects the signaling and ensures that the IMS terminals do not misbehave (e.g. change normal signaling routes, disobey home network's routing policy).
** It can compress and decompress SIP messages using
SigComp, which reduces the round-trip over slow radio links.
** It may include a Policy Decision Function (PDF), which authorizes media plane resources e.g.,
quality of service
Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...
(QoS) over the media plane. It is used for policy control, bandwidth management, etc. The PDF can also be a separate function.
** It also generates charging records.
* An ''Interrogating-CSCF'' (I-CSCF) is another SIP function located at the edge of an administrative domain. Its IP address is published in the
Domain Name System
The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...
(DNS) of the domain (using
NAPTR A Name Authority Pointer (NAPTR) is a type of resource record in the Domain Name System of the Internet.
NAPTR records are most commonly used for applications in Internet telephony, for example, in the mapping of servers and user addresses in the ...
and
SRV SRV may refer to:
Computing
*SRV record as used in the Domain Name System
* /srv, a directory on Unix-like computer systems
Music
*Stevie Ray Vaughan, American blues and blues-rock guitarist (1954–1990)
*"S.R.V.", an instrumental track from gui ...
type of DNS records), so that remote servers can find it, and use it as a forwarding point (e.g., registering) for SIP packets to this domain.
** it queries the HSS to retrieve the address of the S-CSCF and assign it to a user performing SIP registration
** it also forwards SIP request or response to the S-CSCF
** Up to Release 6 it can also be used to hide the internal network from the outside world (encrypting parts of the SIP message), in which case it's called a ''Topology Hiding Inter-network Gateway'' (THIG). From Release 7 onwards this "entry point" function is removed from the I-CSCF and is now part of the ''Interconnection Border Control Function'' (IBCF). The IBCF is used as gateway to external networks, and provides
NAT
Nat or NAT may refer to:
Computing
* Network address translation (NAT), in computer networking
Organizations
* National Actors Theatre, New York City, U.S.
* National AIDS trust, a British charity
* National Archives of Thailand
* National As ...
and
firewall
Firewall may refer to:
* Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts
* Firewall (construction), a barrier inside a building, designed to limit the spre ...
functions (
pinholing). The IBCF is a
session border controller
A session border controller (SBC) is a network element deployed to protect SIP based voice over Internet Protocol (VoIP) networks.
Early deployments of SBCs were focused on the borders between two service provider networks in a peering environme ...
specialized for the
network-to-network interface
In telecommunications, a network-to-network interface (NNI) is an interface that specifies signaling and management functions between two networks. An NNI circuit can be used for interconnection of signalling (e.g., Signalling System No. 7, SS7), ...
(NNI).
* A ''Serving-CSCF'' (S-CSCF) is the central node of the signaling plane. It is a SIP server, but performs session control too. It is always located in the home network. It uses Diameter Cx and Dx interfaces to the HSS to download user profiles and upload user-to-S-CSCF associations (the user profile is only cached locally for processing reasons and is not changed). All necessary subscriber profile information is loaded from the HSS.
** it handles SIP registrations, which allows it to bind the user location (e.g., the
IP address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
of the terminal) and the SIP address
** it sits on the path of all signaling messages of the locally registered users, and can inspect every message
** it decides to which application server(s) the SIP message will be forwarded, in order to provide their services
** it provides routing services, typically using
Electronic Numbering (ENUM) lookups
** it enforces the policy of the network operator
** there can be multiple S-CSCFs in the network for
load distribution
In computing, load balancing is the process of distributing a set of tasks over a set of resources (computing units), with the aim of making their overall processing more efficient. Load balancing can optimize the response time and avoid unevenl ...
and
high availability
High availability (HA) is a characteristic of a system which aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period.
Modernization has resulted in an increased reliance on these systems. Fo ...
reasons. It's the HSS that assigns the S-CSCF to a user, when it's queried by the I-CSCF. There are multiple options for this purpose, including a mandatory/optional capabilities to be matched between subscribers and S-CSCFs.
Application servers
{{see also, Next generation network services
SIP
Application server
An application server is a server that hosts applications or software that delivers a business application through a communication protocol.
An application server framework is a service layer model. It includes software components available to a ...
s (AS) host and execute
services
Service may refer to:
Activities
* Administrative service, a required part of the workload of university faculty
* Civil service, the body of employees of a government
* Community service, volunteer service for the benefit of a community or a pu ...
, and interface with the S-CSCF using SIP. An example of an application server that is being developed in 3GPP is the
Voice call continuity The 3GPP has defined the Voice Call Continuity (VCC) specifications in order to describe how a voice call can be persisted, as a mobile phone moves between circuit switched and packet switched radio domains (3GPP TS 23.206).
Many mobile phones are ...
Function (VCC Server). Depending on the actual service, the AS can operate in SIP proxy mode, SIP UA (
user agent
In computing, a user agent is any software, acting on behalf of a user, which "retrieves, renders and facilitates end-user interaction with Web content". A user agent is therefore a special kind of software agent.
Some prominent examples of us ...
) mode or SIP
B2BUA A back-to-back user agent (B2BUA) is a logical network element in Session Initiation Protocol (SIP) applications., ''SIP: Session Initiation Protocol'', IETF, The Internet Society (2002) SIP is a signaling protocol for managing multimedia Voice ove ...
mode. An AS can be located in the home network or in an external third-party network. If located in the home network, it can query the HSS with the Diameter Sh or Si interfaces (for a SIP-AS).
* SIP AS: Host and execute IMS specific services
* ''IP Multimedia Service Switching Function'' (IM-SSF): Interfaces SIP to
CAP
A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 3200 BC. Caps typically have a visor, or no brim at all. They are popular in casual and informal se ...
to communicate with
CAMEL
A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. C ...
Application Servers
*
OSA service capability server (OSA SCS): Interfaces SIP to the OSA framework;
= Functional model
=
The AS-ILCM (Application Server - Incoming Leg Control Model) and AS-OLCM (Application Server - Outgoing Leg Control Model) store transaction state, and may optionally store session state depending on the specific service being executed.
The AS-ILCM interfaces to the S-CSCF (ILCM) for an incoming leg and the AS-OLCM interfaces to the S-CSCF (OLCM) for an outgoing leg.
Application Logic provides the service(s) and interacts between the AS-ILCM and AS-OLCM.
= Public Service Identity
=
Public Service Identities (PSI) are identities that identify services, which are hosted by application servers. As user identities, PSI takes the form of either a SIP or Tel URI. PSIs are stored in the HSS either as a distinct PSI or as a wildcarded PSI:
* a distinct PSI contains the PSI that is used in routing
* a wildcarded PSI represents a collection of PSIs.
Media servers
The ''Media Resource Function'' (MRF) provides media related functions such as
media manipulation
Media manipulation is a series of related techniques in which partisans create an image or argument that favors their particular interests. Such tactics may include the use of logical fallacies, manipulation, outright deception (disinformation) ...
(e.g. voice stream mixing) and playing of tones and announcements.
Each MRF is further divided into a ''media resource function controller'' (MRFC) and a ''media resource function processor'' (MRFP).
* The MRFC is a signalling plane node that interprets information coming from an AS and S-CSCF to control the MRFP
* The MRFP is a media plane node used to mix, source or process media streams. It can also manage access right to shared resources.
The ''Media Resource Broker'' (MRB) is a functional entity that is responsible for both collection of appropriate published MRF information and supplying of appropriate MRF information to consuming entities such as the AS. MRB can be used in two modes:
* Query mode: AS queries the MRB for media and sets up the call using the response of MRB
* In-Line Mode: AS sends a SIP INVITE to the MRB. The MRB sets up the call
Breakout gateway
A ''Breakout Gateway Control Function'' (BGCF) is a SIP proxy which processes requests for routing from an S-CSCF when the S-CSCF has determined that the session cannot be routed using DNS or ENUM/DNS. It includes routing functionality based on telephone numbers.
PSTN gateways
A PSTN/CS gateway interfaces with
PSTN
The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...
circuit switched
Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full b ...
(CS) networks. For signalling, CS networks use
ISDN User Part
The ISDN (Integrated Services Digital Network) User Part or ISUP is part of Signaling System No. 7 (SS7), which is used to set up telephone calls in the public switched telephone network (PSTN). It is specified by the ITU-T as part of the Q.76x ser ...
(ISUP) (or
BICC) over
Message Transfer Part
The Message Transfer Part (MTP) is part of the Signaling System 7 (SS7) used for communication in Public Switched Telephone Networks. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication ...
(MTP), while IMS uses SIP over IP. For media, CS networks use
Pulse-code modulation
Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the ...
(PCM), while IMS uses
Real-time Transport Protocol
The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP networks. RTP is used in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applicatio ...
(RTP).
* A signalling gateway (SGW) interfaces with the signalling plane of the CS. It transforms lower layer protocols as
Stream Control Transmission Protocol
The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the p ...
(SCTP, an IP protocol) into
Message Transfer Part
The Message Transfer Part (MTP) is part of the Signaling System 7 (SS7) used for communication in Public Switched Telephone Networks. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication ...
(MTP, a
Signalling System 7
Signalling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down telephone calls in most parts of the world-wide public switched telephone network (PSTN). The protocol also perform ...
(SS7) protocol), to pass
ISDN User Part
The ISDN (Integrated Services Digital Network) User Part or ISUP is part of Signaling System No. 7 (SS7), which is used to set up telephone calls in the public switched telephone network (PSTN). It is specified by the ITU-T as part of the Q.76x ser ...
(ISUP) from the MGCF to the CS network. The SGW does call control protocol conversion between SIP and ISUP/BICC under the control of the MGCF.
* A ''media gateway controller function'' (MGCF) is a SIP endpoint that interfaces with the SGW over SCTP. It also controls the resources in a ''
Media Gateway'' (MGW) across an
H.248
The Gateway Control Protocol (Megaco, H.248) is an implementation of the media gateway control protocol architecture for providing telecommunication services across a converged internetwork consisting of the traditional public switched telephone ...
interface.
* A ''
media gateway'' (MGW) interfaces with the media plane of the CS network, by converting between
RTP and
PCM. It can also transcode when the
codec
A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder.
In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or da ...
s don't match (e.g., IMS might use
AMR, PSTN might use
G.711
G.711 is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at 64 kbit/s. G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second ...
).
Media resources
Media Resources are those components that operate on the media plane and are under the control of IMS core functions. Specifically, ''
Media Server
A media server is a computer appliance or an application software that stores digital media (video, audio or images) and makes it available over a network.
Media servers range from servers that provide video on demand to smaller personal comput ...
'' (MS) and ''
Media gateway'' (MGW)
NGN interconnection
There are two types of
next-generation networking interconnection:
* ''
Service-oriented interconnection Service-oriented may refer to:
* Service-orientation, in business computing
* Service-oriented architecture (SOA), related to the above meaning
* Service-oriented development of applications (SODA), a way of producing service-oriented architecture ...
'' (
SoIx): The physical and logical linking of NGN domains that allows carriers and service providers to offer services over NGN (i.e., IMS and PES) platforms with control, signalling (i.e., session based), which provides defined levels of interoperability. For instance, this is the case of "carrier grade" voice and/or multimedia services over IP interconnection. "Defined levels of interoperability" are dependent upon the service or the QoS or the Security, etc.
* ''
Connectivity-oriented interconnection'' (
CoIx
''Coix'' is a genus of Asian and Australian plants in the grass family.
The best-known species is '' Coix lacryma-jobi,'' widely called Job's tears. Its variety ''Coix lacryma-jobi'' var. ''ma-yuen'' is cultivated in many warm regions as a s ...
): The physical and logical linking of carriers and service providers based on simple IP connectivity irrespective of the levels of interoperability. For example, an IP interconnection of this type is not aware of the specific end to end service and, as a consequence, service specific network performance, QoS and security requirements are not necessarily assured. This definition does not exclude that some services may provide a defined level of interoperability. However, only SoIx fully satisfies NGN interoperability requirements.
An NGN interconnection mode can be direct or indirect. Direct interconnection refers to the interconnection between two network domains without any intermediate network domain. Indirect interconnection at one layer refers to the interconnection between two network domains with one or more intermediate network domain(s) acting as
transit networks. The intermediate network domain(s) provide(s) transit functionality to the two other network domains. Different interconnection modes may be used for carrying
service layer
In intelligent networks (IN) and cellular networks, service layer is a conceptual layer within a network service provider architecture. It aims at providing middleware that serves third-party value-added services and applications at a higher a ...
signalling and media traffic.
Charging
Offline charging is applied to users who pay for their services periodically (e.g., at the end of the month).
Online charging, also known as credit-based charging, is used for
prepaid services, or real-time credit control of postpaid services. Both may be applied to the same session.
''Charging function addresses'' are addresses distributed to each IMS entities and provide a common location for each entity to send charging information. ''charging data function'' (CDF) addresses are used for offline billing and ''Online Charging Function'' (OCF) for online billing.
* Offline Charging : All the SIP network entities (P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS) involved in the session use the
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
Rf interface to send accounting information to a CDF located in the same domain. The CDF will collect all this information, and build a ''call detail record'' (CDR), which is sent to the billing system (BS) of the domain.
Each session carries an ''IMS Charging Identifier'' (ICID) as a unique identifier generated by the first IMS entity involved in a SIP transaction and used for the correlation with CDRs. ''Inter Operator Identifier'' (IOI) is a globally unique identifier shared between sending and receiving networks. Each domain has its own charging network. Billing systems in different domains will also exchange information, so that
roaming
Roaming is a wireless telecommunication term typically used with mobile devices, such as mobile phones. It refers to a mobile phone being used outside the range of its native network and connecting to another available cell network.
Technical ...
charges can be applied.
* Online charging : The S-CSCF talks to a ''IMS gateway function'' (IMS-GWF) which looks like a regular SIP application server. The IMS-GWF can signal the S-CSCF to terminate the session when the user runs out of credits during a session. The AS and MRFC use the
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
Ro interface towards an OCF.
** When ''immediate event charging'' (IEC) is used, a number of credit units is immediately deducted from the user's account by the ECF and the MRFC or AS is then authorized to provide the service. The service is not authorized when not enough credit units are available.
** When ''event charging with unit reservation'' (ECUR) is used, the ECF (event charging function) first reserves a number of credit units in the user's account and then authorizes the MRFC or the AS. After the service is over, the number of spent credit units is reported and deducted from the account; the reserved credit units are then cleared.
IMS-based PES architecture
IMS-based PES (PSTN Emulation System) provides IP networks services to analog devices. IMS-based PES allows non-IMS devices to appear to IMS as normal SIP users. Analog terminal using standard analog interfaces can connect to IMS-based PES in two ways:
* Via A-MGW (Access Media Gateway) that is linked and controlled by AGCF. AGCF is placed within the Operators network and controls multiple A-MGW. A-MGW and AGCF communicate using
H.248
The Gateway Control Protocol (Megaco, H.248) is an implementation of the media gateway control protocol architecture for providing telecommunication services across a converged internetwork consisting of the traditional public switched telephone ...
.1 (
Megaco
The Gateway Control Protocol (Megaco, H.248) is an implementation of the media gateway control protocol architecture for providing telecommunication services across a converged internetwork consisting of the traditional public switched telephone n ...
) over the P1 reference point. POTS phone connect to A-MGW over the z interface. The signalling is converted to H.248 in the A-MGW and passed to AGCF. AGCF interprets the H.248 signal and other inputs from the A-MGW to format H.248 messages into appropriate SIP messages. AGCF presents itself as P-CSCF to the S-CSCF and passes generated SIP messages to S-CSCF or to IP border via IBCF (Interconnection Border Control Function). Service presented to S-CSCF in SIP messages trigger PES AS. AGCF has also certain service independent logic, for example on receipt of off-hook event from A-MGW, the AGCF requests the A-MGW to play dial tone.
* Via VGW (VoIP-Gateway) or SIP Gateway/Adapter on customer premises. POTS phones via VOIP Gateway connect to P-CSCF directly. Operators mostly use
session border controller
A session border controller (SBC) is a network element deployed to protect SIP based voice over Internet Protocol (VoIP) networks.
Early deployments of SBCs were focused on the borders between two service provider networks in a peering environme ...
s between VoIP gateways and P-CSCFs for security and to hide network topology. VoIP gateway link to IMS using
SIP over Gm reference point. The conversion from POTS service over the z interface to SIP occurs in the customer premises VoIP gateway. POTS signaling is converted to SIP and passed on to P-CSCF. VGW acts as SIP user agent and appears to P-CSCF as SIP terminal.
Both A-MGW and VGW are unaware of the services. They only relay call control signalling to and from the PSTN terminal. Session control and handling is done by IMS components.
Interfaces description
{, class="wikitable"
, -
!Interface name
!IMS entities
!Description
!Protocol
!Technical specification
, -
, Cr
, MRFC, AS
, Used by MRFC to fetch documents (e.g. scripts, announcement files, and other resources) from an AS. Also used for media control related commands.
, HTTP over dedicated Transmission Control Protocol, TCP/SCTP channels
, -
, Cx
, (I-CSCF, S-CSCF), HSS
, Used to send subscriber data to the S-CSCF; including filter criteria and their priority. Also used to furnish CDF and/or OCF addresses.
, Diameter
, TS29.229, TS29.212
, -
, Dh
, AS (SIP AS, OSA, IM-SSF) <-> SLF
, Used by AS to find the HSS holding the user profile information in a multi-HSS environment. DH_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name.
, Diameter
, -
, Dx
, (I-CSCF or S-CSCF) <-> SLF
, Used by I-CSCF or S-CSCF to find a correct HSS in a multi-HSS environment. DX_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name.
, Diameter
, TS29.229, TS29.212
, -
, Gm
, UE, P-CSCF
, Used to exchange messages between SIP user equipment (UE) or Voip gateway and P-CSCF
, SIP
, -
, Go
, PDF, GGSN
, Allows operators to control QoS in a user plane and exchange charging correlation information between IMS and GPRS network
, Common Open Policy Service, COPS (Rel5), diameter (Rel6+)
, -
, Gq
, P-CSCF, PDF
, Used to exchange policy decisions-related information between P-CSCF and PDF
, Diameter
, -
, Gx
, PCEF, PCRF
, Used to exchange policy decisions-related information between PCEF and PCRF
, Diameter
, TS29.211, TS29.212
, -
, Gy
, PCEF, OCS
, Used for online flow-based bearer charging. Functionally equivalent to Ro interface
, Diameter
, TS23.203, TS32.299
, -
, ISC
, S-CSCF <-> AS
, Reference point between S-CSCF and AS. Main functions are to :
*Notify the AS of the registered IMPU, registration state and UE capabilities
*Supply the AS with information to allow it to execute multiple services
*Convey charging function addresses
, SIP
, -
, Ici
, IBCFs
, Used to exchange messages between an IBCF and another IBCF belonging to a different IMS network.
, SIP
, -
, Izi
, TrGWs
, Used to forward media streams from a TrGW to another TrGW belonging to a different IMS network.
, RTP
, -
, Ma
, I-CSCF <-> AS
, Main functions are to:
*Forward SIP requests which are destined to a public service identity hosted by the AS
*Originate a session on behalf of a user or public service identity, if the AS has no knowledge of a S-CSCF assigned to that user or public service identity
*Convey charging function addresses
, SIP
, -
, Mg
, MGCF -> I,S-CSCF
, MGCF converts ISDN User Part, ISUP signalling to SIP signalling and forwards SIP signalling to I-CSCF
, SIP
, -
, Mi
, S-CSCF -> BGCF
, Used to exchange messages between S-CSCF and BGCF
, SIP
, -
, Mj
, BGCF -> MGCF
, Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in the same IMS network to send SIP message from BGCF to MGCF
, SIP
, -
, Mk
, BGCF -> BGCF
, Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in another IMS network to send SIP message from BGCF to the BGCF in the other network
, SIP
, -
, Mm
, I-CSCF, S-CSCF, external IP network
, Used for exchanging messages between IMS and external IP networks
, SIP
, -
, Mn
, MGCF, IM-MGW
, Allows control of user-plane resources
, Megaco, H.248
, -
, Mp
, MRFC, MRFP
, Allows an MRFC to control media stream resources provided by an MRFP.
, Megaco, H.248
, -
, Mr
Mr'
, S-CSCF, MRFC
AS, MRFC
, Used to exchange information between S-CSCF and MRFC
Used to exchange session controls between AS and MRFC
, Application server sends SIP message to MRFC to play tone and announcement. This SIP message contains sufficient information to play tone and announcement or provide information to MRFC, so that it can ask more information from application server through Cr Interface.
, SIP
, -
, Mw
, P-CSCF, I-CSCF, S-CSCF, AGCF
, Used to exchange messages between CSCFs. AGCF appears as a P-CSCF to the other CSCFs
, SIP
, -
, Mx
, BGCF/CSCF, IBCF
, Used for the interworking with another IMS network, when the BGCF has determined that a breakout should occur in the other IMS network to send SIP message from BGCF to the IBCF in the other network
, SIP
, -
, P1
, AGCF, A-MGW
, Used for call control services by AGCF to control H.248 A-MGW and residential gateways
, H.248
, -
, P2
, AGCF, CSCF
, Reference point between AGCF and CSCF.
, SIP
, -
, Rc
, MRB, AS
, Used by the AS to request that media resources be assigned to a call when using MRB in-line mode or in query mode
, SIP, in query mode (not specified)
, -
, Rf
, P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS
, Used to exchange offline charging information with CDF
, Diameter
, TS32.299
, -
, Ro
, AS, MRFC, S-CSCF
, Used to exchange online charging information with OCF
, Diameter
, TS32.299
, -
, Rx
, P-CSCF, PCRF
, Used to exchange policy and charging related information between P-CSCF and PCRF
Replacement for the Gq reference point.
, Diameter
, TS29.214
, -
, Sh
, AS (SIP AS, OSA SCS), HSS
, Used to exchange User Profile information (e.g., user-related data, group lists, user-service-related information or user location information or charging function addresses (used when the AS has not received the third-party REGISTER for a user)) between an AS (SIP AS or OSA SCS) and HSS. Also allow AS to activate/deactivate filter criteria stored in the HSS on a per-subscriber basis
, Diameter
, -
, Si
, IM-SSF, HSS
, Transports CAMEL subscription information, including triggers for use by CAMEL-based application services information.
, Mobile Application Part, MAP
, -
, Sr
, MRFC, AS
, Used by MRFC to fetch documents (scripts and other resources) from an AS
, HTTP
, -
, Ut
, UE and SIP AS (SIP AS, OSA SCS, IM-SSF) PES AS and AGCF
, Facilitates the management of subscriber information related to services and settings
, HTTP(s), XCAP
, -
, z
, POTS, Analog phones and VoIP gateways
, Conversion of POTS services to SIP messages
,
Session handling
One of the most important features of IMS, that of allowing for a SIP application to be dynamically and differentially (based on the user's profile) triggered, is implemented as a filter-and-redirect signalling mechanism in the S-CSCF.
The S-CSCF might apply filter criteria to determine the need to forward SIP requests to AS. It is important to note that services for the originating party will be applied in the originating network, while the services for the terminating party will be applied in the terminating network, all in the respective S-CSCFs.
Initial filter criteria
An initial filter criteria (iFC) is an
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...
-based format used for describing control logic. iFCs represent a provisioned subscription of a user to an application. They are stored in the HSS as part of the IMS Subscription Profile and are downloaded to the S-CSCF upon user registration (for registered users) or on processing demand (for services, acting as unregistered users). iFCs are valid throughout the registration lifetime or until the User Profile is changed.
The iFC is composed of:
* Priority - determines the order of checking the trigger.
* Trigger point - logical condition(s) which is verified against initial dialog creating SIP requests or stand-alone SIP requests.
* Application server URI - specifies the application server to be forwarded to when the trigger point matches.
There are two types of iFCs:
* Shared - When provisioning, only a reference number (the shared iFC number) is assigned to the subscriber. During registration, only the number is sent to the CSCF, not the entire XML description. The complete XML will have previously been stored on the CSCF.
* Non-shared - when provisioning, the entire XML description of the iFC is assigned to the subscriber. During registration, the entire XML description is sent to the CSCF.
Security aspects of early IMS and non-3GPP systems
It is envisaged that security defined in TS 33.203 may not be available for a while especially because of the lack of
USIM/
ISIM interfaces and prevalence of devices that support
IPv4
Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...
. For this situation, to provide some protection against the most significant threats, 3GPP defines some security mechanisms, which are informally known as "early IMS security," in TR33.978. This mechanism relies on the authentication performed during the network attachment procedures, which binds between the user's profile and its IP address. This mechanism is also weak because the signaling is not protected on the
user–network interface In telecommunications, a user–network interface (UNI) is a demarcation point between the responsibility of the service provider and the responsibility of the subscriber. This is distinct from a network-to-network interface (NNI) that defines a si ...
.
CableLabs
Cable Television Laboratories, Inc. (CableLabs) is a nonprofit corporation promoting innovation as a research and development lab founded in 1988 by American cable operators. System operators from around the world are eligible to be members.
Th ...
in
PacketCable 2.0, which adopted also the IMS architecture but has no USIM/ISIM capabilities in their terminals, published deltas to the 3GPP specifications where the Digest-MD5 is a valid authentication option. Later on,
TISPAN
The Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN) is a standardization body of ETSI, specializing in fixed networks and Internet convergence. It was formed in 2003 from the amalgamation of the ETSI bodies Tel ...
also did a similar effort given their fixed networks scopes, although the procedures are different. To compensate for the lack of IPsec capabilities, TLS has been added as an option for securing the Gm interface. Later 3GPP Releases have included the Digest-MD5 method, towards a Common-IMS platform, yet in its own and again different approach. Although all 3 variants of Digest-MD5 authentication have the same functionality and are the same from the IMS terminal's perspective, the implementations on the Cx interface between the S-CSCF and the HSS are different.
See also
*
4G
*
Generic Access Network
Generic Access Network (GAN) is a protocol that extends mobile voice, data and multimedia ( IP Multimedia Subsystem/ Session Initiation Protocol (IMS/SIP)) applications over IP networks. Unlicensed Mobile Access (UMA) is the commercial name used by ...
*
Image share
Image Share is a service for sharing images between users during a mobile phone call. It has been specified for use in a 3GPP-compliant cellular network by the GSM Association in the PRD IR.79 Image Share Interoperability Specificatio
According t ...
*
OMA Instant Messaging and Presence Service
The OMA Instant Messaging and Presence Service (IMPS) is an Open Mobile Alliance enabler for Instant Messaging and Presence. The Wireless Village consortium developed the first cut of the specifications. After Wireless Village was merged with OM ...
*
IP connectivity access network IP-CAN (or IP connectivity access network) is an access network that provides Internet Protocol (IP) connectivity. The term is usually used in cellular context and usually refers to 3GPP access networks such as GPRS or EDGE, but can be also used t ...
*
Mobile broadband
Mobile broadband is the marketing term for Wireless broadband, wireless Internet access via mobile networks. Access to the network can be made through a portable modem, wireless modem, or a Tablet computer, tablet/smartphone (possibly Tetherin ...
*
Mobile VoIP
Mobile VoIP or simply mVoIP is an extension of mobility to a voice over IP network. Two types of communication are generally supported: cordless telephones using DECT or PCS protocols for short range or campus communications where all base stati ...
*
Peer-to-peer video sharing
*
Service capability interaction manager
*
System Architecture Evolution
System Architecture Evolution (SAE) is the core network architecture of mobile communications protocol group 3GPP's LTE wireless communication standard.
SAE is the evolution of the GPRS Core Network, but with a simplified architecture; an all-IP ...
*
SIMPLE
Simple or SIMPLE may refer to:
*Simplicity, the state or quality of being simple
Arts and entertainment
* ''Simple'' (album), by Andy Yorke, 2008, and its title track
* "Simple" (Florida Georgia Line song), 2018
* "Simple", a song by Johnn ...
*
SIP extensions for the IP multimedia subsystem
*
Text over IP
Text over IP (or ToIP) is a means of providing a real-time text (RTT) service that operates over IP-based networks. It complements Voice over IP (VoIP) and Video over IP.
Real-time text is streaming text that is transmitted as it is produced, allo ...
*
Ultra Mobile Broadband
Evolution-Data Optimized (EV-DO, EVDO, etc.) is a telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. EV-DO is an evolution of the CDMA2000 (IS-2000) standard which su ...
*
Video share
*
Voice call continuity The 3GPP has defined the Voice Call Continuity (VCC) specifications in order to describe how a voice call can be persisted, as a mobile phone moves between circuit switched and packet switched radio domains (3GPP TS 23.206).
Many mobile phones are ...
References
{{reflist
Further reading
* {{cite book, last2=García-Martín, first1=Gonzalo, last1=Camarillo, first2=Miguel A., title=The 3G IP multimedia subsystem (IMS) : Merging the Internet and the Cellular Worlds, date=2007, publisher=Wiley, location=Chichester
.a.isbn=978-0-470-01818-7, edition=2, url-access=registration, url=https://archive.org/details/3gipmultimediasu0000cama
* {{cite book, last=Poikselkä, first=Miikka, title=The IMS : IP multimedia concepts and services, date=2007, publisher=Wiley, location=Chichester
.a.isbn=978-0-470-01906-1, edition=2
* {{cite book, title=IP multimedia subsystem (IMS) handbook, date=2009, publisher=CRC Press, location=Boca Raton, isbn=978-1-4200-6459-9, editor=Syed A. Ahson, Mohammed Ilyas
* {{cite book, first1=Mark, last1=Wuthnow, first2=Matthew, last2=Stafford, first3=Jerry, last3=Shih, title=IMS : A New Model for Blending Applications, date=2010, publisher=CRC Press, location=Boca Raton, isbn=978-1-4200-9285-1
External links
A decent IMS tutorialIMS multi-page tutorialIMS Call Flows{{Authority control
Audio network protocols
3GPP_standards
LTE (telecommunication)
Multimedia
Network architecture
Telecommunications
Telecommunications infrastructure
Videotelephony
Voice over IP