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Network Glossary

AS - Application Servers

BGW - Border Gateway

IMS - IP Multimedia Subsystem; an architectural framework to deliver IP multimedia services to end users.

IP - Internet Protocol

SIP - Session Initiation Protocol; an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences.

DSL - Digital Subscriber Line

W-CDMA - Wideband Code Division Multiple Access

GSM - Global Service Mobile

GPRS - General Packet Radio Service

WLAN - Wireless Local Area Network

WiMAX - Broadband Wireless

IMSI - International Mobile Subscriber Identity

IMPI - IP Multimedia Private Identity

HSS - Home Subscriber Server

UPSF - User Profile Server Function

SLF = Subscriber Location Function

TMSI - Temporary Mobile Subscriber Identity

IMEI - International Mobile Equipment Identity. A unique, phone specific, device identity stored inthe phone.

MSISDN - Mobile Subscriber ISDN Number. The telephone number of a user.

IMPI - IP Multimedia Private Identity. Unique to the phone

IMPU - IP Multimedia Public Identity

URI - Unique Resource Identifiers

P-CSCF - Proxy-CSCF, first point of contact for the IMS terminal.

S-CSCF - Serving-CSCF, located in the home network, that acts as both the central node of the signalling plane and also performs session control.

I-CSCF - Interrogating-CSCF located at the edge of an administrative domain. Its IP address is published in the DNS of the domain, remote servers find it, and use it as a forwarding point for SIP packets to this domain.

SIP US - SIP user agent mode

SIP B2BUA - SIP back-to-back user agent mode.

DIAMETER

IM-SSF - IP Multimedia Service Switching Function

CAMEL Application Servers

CAP -

TTS - Text-to-speech conversion

MRFC - Media Resource Function Controller. A signalling plane node that acts as a SIP User Agent to the S-CSCF, and which controls the MRFP with a H.248 interface

MRFP - Media Resource Function Processor. A media plane node that implements all media-related functions.

BGCF - Breakout Gateway Control Function. A SIP server that includes routing functionality based on telephone numbers. It is only used when calling from the IMS to a phone in a circuit switched network, such as the PSTN or the PLMN.

CS - circuit switched networks.

SGW - Signalling Gateway. Interfaces with the signalling plane of the CS.

MGCF - Media Gateway Controller Function. Does call control protocol conversion between SIP and ISUP and interfaces with the SGW over SCTP.

It also controls the resources in an MGW with an H.248 interface.
An MGW [Media Gateway] interfaces with the media plane of the CS network, by converting between RTP and PCM. It can also transcode when the codecs don't match [e.g. IMS might use AMR, PSTN might use G.711].

Media Resources

Media Resources are those components that operate on the media plane and are under the control of IMS Core functions. Specifically:

Border GateWay [BGW]

A BGW [Border GateWay] operates under the control of the IBCF and interfaces with the media plane of another NGN - eg another SP [Service Provider] who has similarly migrated to IMS - and provides a media proxy of the RTP packets.

It can also transcode when the codecs and/or packetisation period don't match [e.g. SPa uses G.729 30ms and SPb uses G.711 20ms].

Charging

Charging is either done offline or online:

Offline charging - applied to users who pay for their services periodically [e.g., at the end of the month].
Online charging - credit-based chargingused for prepaid services, or real-time credit control of postpaid services.

Both may be applied to the same session.

Offline Charging

All the SIP network entities [P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS] involved in the session use the DIAMETER Rf interface to send accounting information to a CCF [Charging Collector Function] located in the same domain.

The CCF will collect all this information, build a CDR [Call Detail Record], and send this to the billing system [BS] of the domain.

Each session carries an ICID [IMS Charging Identifier] as a unique identifier. IOI [Inter Operator Identifier] parameters define the originating and terminating networks.

Each domain has its own charging network. Billing systems in different domains will also exchange information, so that roaming charges can be applied.

Online charging

The S-CSCF talks to an SCF [Session Charging Function].

The SCF 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 Ro interface towards an ECF [Event Charging Function].

When IEC [Immediate Event Charging] is used, a number of credit units is immediately deducted from the user's account by the ECF. The MRFC or AS is then authorized to provide the service. The service is not authorized when not enough credit units are available.

When ECUR [Event Charging with Unit Reservation] is used, the ECF 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.

Reference:Wikipedia