IMS VoLTE and 3GPP Nodes

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Next generation networks utilize an exhaustive list of architectural components that need to work seamlessly to enable end-to-end services for customers that demand connectivity and content at any-time, any-place and on any device.

Industry organizations such as the 3GPP, ETSI, IETF, ITU, GSMA, WBA and several others have gone to great length in specifying architectural reference models, naming conventions and interface functionality. The following is a list of select interfaces, network nodes and acronyms to better navigate the technical aspects of modern service delivery networks.

Nodes | Acronyms


Node AbbreviationFull NameApplicable NetworkNode FunctionsReferences
AAA Server Authentication, Authorization and Accounting ServerWLANProvides AAA (Authentication, Authorization and Accounting) and location management. Can interact with operator’s HSS or HLR in some applications to enable device connectivity to services via the mobile core or EPC.TS 23.002
AF Application FunctionIMS/VoLTEThe AF platform (for example, P-CSCF) supports control of bearer resources and flow based bearer charging. It communicates with the PCRF to transfer QoS related service information. TS 23.002
ANDSF Access Network Discovery and Selection FunctionWLANProvides network discovery and selection assistance along with policy information to the UE.TS 23.002 TS 23.402
AS Application ServerIMS/VoLTESIP Application servers (AS) host and execute subscriber services, and interface with the S-CSCF using SIP. Also referred to as SIP Application Server, OSA Application Server, or CAMEL IM-SSF.TS 29.364 TS 23.218 IETF RFC 3261
AuC Authentication CenterUMTSAssociated with the HLR, the AuC holds the identity key information for an operator’s mobile subscribers.TS 23.002
BBERF Bearer Binding and Event Reporting FunctionEPCBearer policy enforcement point for application of QoS policy.TS 23.002
BG Border GatewayGPRS,UMTS,EPCAn inter-operator gateway between PLMNs that provides security and interoperability.TS 23.002
BGCF Related Product
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Highly reliable, scalable IMS-ready combined MGCF/BGCF class 4 softswitch.

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Breakout Gateway Control FunctionIMS/VoLTESelects the network in which PSTN breakout is to occur and, within the network which MGCF where the breakout is to occur.TS 23.002 TS 23.228 
BM-SC Broadcast-Multicast Service CenterUMTS,EPCProvides services and a content entry point for Multimedia Broadcast Multicast Services.TS 23.002 TS 23.246
BSC Base Station ControllerGERANThe BSC provides control for one or more BTSs. The BSC monitors signaling power, initiates handovers of UEs between BTS and provides connectivity to MSCs and packet data core network elements.TS23.002
BSF Bootstrapping Server FunctionUMTS,EPCBootstrapping Server Function is element in mobile networks that is part of a generic authentication architecture to support authentication and authorization of various network application functions.TS 33.220
BTS Base Transceiver StationGERANThe BTS provides communications between a subscriber’s UE and the mobile network. One or more BTS nodes are connected to a BSC.TS23.002
CCF Charging Collection FunctionIMS/VoLTEThe CCF, similar to the Charging Gateway Function in UMTS mobile core and EPC, provide the means to collect session and event based charging information from the network elements.TS 32.200
CSCF Call Session Control FunctionIMS/VoLTEThe CSCF processes SIP signaling in the IMS network. Its roles include SIP proxy, interrogating function, SIP registration, and other SIP service functions. CSCF entities include the Proxy CSCF (P-CSCF), Serving CSCF (S-CSCF) and Interrogating CSCF (I-CSCF).TS 23.228
DEA Diameter Edge AgentEPCThe Diameter Edge Agent provides security, Diameter mediation, routing, and Diameter translation (IWF) capabilities for signaling inter-operator signaling messages used to support 4G-to-4G and 3G-to-4G roaming scenarios.
DRA Diameter Routing AgentEPCA Diameter Routing Agent provides centralized Diameter signaling and routing management in and between EPC networks. The DRA supports proxy features like protocol mediation along with message relay capabilities. Other features include PCRF binding and SLF lookup capabilities in networks that contain more than one PCRF and HSS respectively.TS 29.213 TS 29.228 IETF RFC 6733
DSC Diameter Signaling ControllerEPCA Diameter Signaling Controller provides Diameter interworking (IWF), routing (DRA), and security (DEA) features to manage signaling messages for EPC networks. It also provides support for enabling 4G-to-4G and 3G-to-4G roaming. Some more advanced platforms support interworking of RADIUS for Wi-Fi offload applications along with EAP-SIM authentication capabilities.
EIR Equipment Identity RegisterGPRS,UMTSThe EIR stores user device related information such as white, grey or black listed IMEIs and compares that to UEs wanting access to the network.TS23.002
eNode B Evolved Node BLTEThe eNode B is the element in an LTE networks that provides the connection between the UE and mobile core network.TS23.002 TS 36.300
ePDG Evolved Packet Data GatewayWLANThe ePDG provides functionality similar to the PDG for EPC deployments.TS 23.402 TS 23.002
GGSN Gateway GPRS Support NodeGPRS,UMTSThe GGSN provides gateway functionality between the packet data mobile core network and both public and private IP networks. It provides policy enforcement of user plane services and control plane tunnel management for the PLMN. TS 23.008 TS 23.060 TS 23.008
HLR Home Location RegisterGSM,GPRS,UMTSThe HLR is the primary subscriber database for mobile networks. It stores user account information, location and allowed services and is used to authenticate and authorize subscriber connectivity to services on the mobile network.TS 11.31 TS 23.002
HSS Home Subscriber ServerEPC,IMS/VoLTEThe HSS is the next generation subscriber data management platform. Like the HLR, it is the primary subscriber database that contains user-related and subscription-related information. Its functions include HLR and AuC functionality as well as mobility management, user security information and key generation, service authorization support, access support and authorization and call session establishment support.TS 29.336 TS 23.002
IBCF Interconnection Border Control FunctionIMS/VoLTEAn IBCF provides application specific functions at the SIP/SDP protocol layer in order to perform interconnection between two operator domains. It enables communication between IPv6 and IPv4 SIP applications. network topology hiding, controlling transport plane functions, screening of SIP signalling information, selecting the appropriate signalling interconnect and generation of charging data records.TS 23.228
I-CSCF Interrogating CSCFIMS/VoLTEThe contact point within an operator's network for all IMS connections destined to a subscriber of that operator or a roaming subscriber currently located within that network operator's service area.TS 23.228
IMS AGW IP Multimedia Subsystem Access GatewayIMS/VoLTEThe IMS Access Gateway provides handling, forwarding and remote NAT traversal of media packets between the IP-CAN and IMS core.
IMS ALG IMS Application Level GatewayIMS/VoLTEThe IMS ALG is part of the P-CSCF and provides control of the IMS Access Gateway for media plane handling, monitoring and management of media flows, IP address translation for devices behind a NAT, SIP header manipulation and modification, sharing of policy with IMS AG for bandwidth policing and DSCP packet marking.
IMS IWF IP Multimedia Subsystem Interworking FunctionIMS/VoLTEProvides the functionality necessary to allow signaling interworking between a PLMN and other fixed networks (ISDN, PSTN and PDNs).TS 29.007
IMS MGW IP Multimedia Subsystem Media GatewayIMS/VoLTEInteracts with MGCF and terminates bearer channels from a switched circuit network and media streams from a packet network (e.g., RTP streams in an IP network). It can support media conversion, bearer control and payload processing using codecs, echo cancellers and other on-board resources.TS 29.232 TS 29.332
IWF Interworking FunctionEPCProvides MAP/SS7 to Diameter translation between Visited MME and Home HLR. Also provides Diameter to MAP conversion between MME and Equipment Identity Register.TS 29.305 RFC 6733
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Media Gateway Control FunctionIMS/VoLTEThe MGCF controls the parts of the call state that pertain to connection control for media channels in an IMS-MGW. It communicates with the CSCF complex and selects the appropriate node depending on the routing number for incoming calls from legacy networks. It also performs protocol conversion between ISUP and the IM subsystem call control protocols.TS 29.332 TS 23.002
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Media GatewayGPRS,UMTSInteracts with MGCF and terminates bearer channels from a switched circuit network and media streams from a packet network (e.g., RTP streams in an IP network). It can support media conversion, bearer control and payload processing using codecs, echo cancellers and other on-board resources.TS 29.232 TS 29.332 TS 23.002
MME Mobility Management EntityEPCResponsible for the control plane signaling exchanges between eNode B nodes, SGSNs in 3G networks and EPC network elements. It provides management of UE context creation, mobility control and bearer control.TS 29.118 TS 29.272 TS 29.171 TS 29.172
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Media Resource BrokerIMS/VoLTEThe MRB supports the sharing of a pool of different MRF resources and assigns them accordingly as required by the sessions or applications.TS 23.218 TS 23.002
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Multimedia Resource FunctionIMS/VoLTEThe MRF is composed of two components: the Multimedia Resource Function Controller (MRFC) and the Multimedia Resource Function Processor (MRFP). Together they provide control of media stream resources, generate CDRs, bearer control, media mixing, announcements, transcoding, conferencing and analysis.
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Multimedia Resource Function ControllerIMS/VoLTEThe MRFC controls the media stream resources in the MRFP, interprets information coming from an AS and S-CSCF, controls the MRFP, and also generates CDRs.
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Multimedia Resource Function ProcessorIMS/VoLTEMRFP resources are controlled by the MRFC. The MRFP performs functions such as mixing incoming media streams, sources media streams for multimedia announcements, and provides other services including audio transcoding and media analysis.TS 29.333 TS 23.002 TS 23.228
MSC Mobile-services Switching CenterGPRS,UMTSThe Mobile-services Switching Center provides circuit switched services to and from mobile subscribers. It connects to the RAN and performs the signaling and switching to connect intra-PLMN subscribers as well as inter-PLMN end points. The MSC is comprised of two entities: the MSC server which provides the signaling and supports capabilities like location registration and handover management; and the Circuit Switched MGW that handles the subscriber bearer channels.TS 23.002
Node B Node BUTRANSimilar to the BTS, the Node B provides communications between a subscriber’s UE over the air interface and the mobile network. One or more Node Bs can connect to a RNC.TS 23.002
OCS Online Charging SystemEPCThe OCS supports real-time usage based charging of event and session based bearer services. It also provides account balance management in conjunction with other platforms such as recharge servers. It supports monitoring of spending and usage limits and enables enforcement through the PCRF and PCEF functions.TS 32.296 TS 23.203 TS 32.240
OFCS Offline Charging SystemEPCThe OFCS performs various charging functions used for offline charging. It collects and processes charging events and it generates CDRs for subsequent offline downstream billing processes.TS 32.240 TS 23.203 TS 32.999 
PCEF Policy and Charging Enforcement FunctionEPCThe PCEF provides the enforcement point for policy and charging control of IP bearer resources.
PCRF Policy and Charging Rules FunctionEPCThe Policy and Charging Rules Function (PCRF) acts as a policy decision point for policy and charging control of service data flows and applications that is sends to the PCEF for enforcement.TS 23.203
P-CSCF Proxy CSCFIMS/VoLTEThe Proxy CSCF provides session control and security between the IMS core and IP-CAN. It’s the first contact point for the UE within IMS network. The P-CSCF locates an Interrogating CSCF for the UE which in turn identifies the appropriate Serving CSCF to use.TS 23.228
PDF Policy Decision FunctionUMTSThe PDF acts as a Policy Decision Point in Release 6 networks to provide service based local policy control via the GGSN.TS 29.209
PDG Packet Data GatewayWLANThe PDG provides access, routing and other functionality for packet services to a WLAN connected user.TS 23.234
PGW PDN (Packet Data Network) GatewayEPCThe PGW provides gateway functionality between the EPC and both private and public IP networks (for example, the Internet). It provides policy enforcement of user plane services and control plane tunnel management for the PLMN. TS 23.002 TS 23.401 TS 23.402 TS 36.300
PNA Presence Network AgentIMS/VoLTEThe PNA receives and converts presence information from various IMS, 2G, 3G and WLAN elements.TS 23.141
RNC Radio Network ControllerUTRANProvides control of node B resources and access to both circuit switched and packet switched core networks. The RNC provides functions like radio resource management, handover management, and cyphering.
S-CSCF Serving CSCFIMS/VoLTEThe S-CSCF handles the core session control in IMS/VoLTE networks. It communicates with the HSS for subscriber profile information, handles registrations and routes sessions the appropriate application server or media resource.TS 23.228
SGSN Serving GPRS Support NodeGPRS,UMTSResponsible for the delivery of data packets between the RAN and the mobile core. It stores subscriber data and enables context creation through authentication of user credentials. Other tasks include routing, location information storage, mobility management and charging. TS 44.065 TS 23.002
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Signaling GatewayIMS/VoLTEA Signaling Gateway (SGW) interfaces with the signaling plane of the CS (Circuit Switched domain). It transforms lower layer protocols as Stream Control Transmission Protocol (SCTP, an Internet Protocol (IP) protocol) into Message Transfer Part (MTP, an Signaling System 7 (SS7) protocol), to pass ISDN User Part (ISUP) from the MGCF to the CS network.TS 29.163 TS 23.002
S-GW Serving GatewayEPCThe S-GW provides tunnel creation and management of the EPS bearers. It also acts as the anchor for user plane connections during handover events between eNode Bs within the same LTE network or with other Radio Access Technologies.
SLF Subscriber Location FunctionIMS/VoLTE,EPCThe SLF helps resolve the appropriate HSS subscriber data repository to use when multiple HSSs are present in the network.TS 23.228 TS 23.002
SPR Subscription Profile RepositoryEPC,UMTSThe SPR contains subscriber related information on subscriptions for use by PCRF for policy enforcement on bearer services. The SPR can contain information on a subscriber’s allowed services, QoS, IMS capabilities, special policies, quota/spending limits and other subscriber related data and subscriptions.TS 29.214 TS 23.002 TS 23.203
TDF Traffic Detection FunctionEPCWorking with the PCRF the TDF is used to detect, monitor and report on applications to help enforce policy.TS 23.203
THIG Topology Hiding Inter-network GatewayIMS/VoLTE,EPCBorder element used to hide internal network addresses from external entities. THIG functionality is present in nodes like the IBCF for IMS/VoLTE networks and a DEA for EPC.
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Transition GatewayIMS/VoLTEProvides network address/port translation and IPv4/IPv6 protocol translation between operator networks.TS 23.228
WAG WLAN Access GatewayWLANThe WLAN access gateway provides filtering, policy enforcement and charging functionality on traffic for a subscriber using wireless LAN access wanting services from a 3GPP network.TS 23.002