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Glossary

Telecoms terms and abbreviations can be a little confusing, even for the most experienced engineers. Here’s a short glossary of some of the terms we use.

A

ACK
Acknowledgement
ACM
Address Complete Message
AIN
Advanced Intelligent Network “The Advanced Intelligent Network (AIN) is a telephone network architecture that separates service logic from switching equipment, allowing new services to be added without having to redesign switches to support new services. Developed by Bell Communications Research, AIN is recognized as an industry standard in North America.”
AIOD
Automatic Identified Outward Calling
ANI
Automatic Number Identification
ANM
Answer Message
ANSI
American National Standards Institute ANSI facilitates the development of US domestic standards through consensus processes and communicates US standards to the international standards arena.
ANSI-41
Is the standard for transaction based functionality on non-GSM cellular networks. Provides provision of SMS / HLR Update type services.
API
Application Programming Interface “Access to the functionality of a software package is provided to a programmer/user through an API. The API could be a library that presents a set of function calls that a programmer can access at compile or run time or a GUI based API , message based API etc..”
ASCII
American Standard Code for Information Interchange (ANSI) “The ANSI 7-bit character code with, with an 8th bit for parity checking.”
ASN.1
Abstract Syntax Notation 1
“ASN.1 is an internationally standardised, vendor independent, platform independent, and language independent notation for specifying data structures at a high level of abstraction. Used extensively to encode data structures in SS7 for transaction based signalling - i.e. TCAP, MAP, INAP”
AUC
Authentication Centre
The AUC stores confidential data and keys in a GSM network that are used to provide security.

B

BCD
Binary Coded Decimal
BCD uses four bits to represent digits
BCI
Backward Call Indicators
BCLID
Bulk Calling Line Identification
BER
Basic Encoding Rules
BRA
Basic Rate Access ISDN
The provision of an ISDN service through 1.44kbits/s access
BSN
Backward Sequence Number

C

CAS
Channel Associated Signalling
Term given to protocols where dedicated channels are assigned to each traffic channel.
CCITT
Consultative Committee on International Telephone & Telegraph
This was the previous (before June 1994) for ITU-T
CCS
Common Channel Signalling
A mode of operation whereby the the signalling channel is used as a datalink to carry call control and management signals and is not dedicated to particular bearer channels in a fixed pattern.
CDMA
Code Division Multiple Access
“Under CDMA, communications channels are created by assigning a special coding scheme to information flows. CDMA-based second generation cellular radio systems are in use in parts of Asia and North and South America.”
CDSL
Customer Digital Subscriber Line
CGB
Circuit Group Blocking Message
CGU
Circuit Group Unblocking Message
CIC
Carrier Identification Code
The CIC is a number used by switches at each end of a point-to-point telephony circuit (controlled by ISUP or TUP) to identify a specific bearer channel. The bearer channel is typically a single time slot on a T-1/E-1 interface
CIDS
Calling Identity Delivery & Suppression
CLID
Calling Line ID
CLLI
Common Language Location Identification
CNAM
Calling NAMe - CNAM is an Intelligent Network service which allows delivery to the subscriber of the calling party number and a readable calling name in digital readout, identifying the caller to the called party.
COT
Continuity Test Message
CPG
Call Progress Message
CRA
Circuit Reservation Acknowledgement Message
CRC-4
Cyclic Redundancy Check
A method of checking for transmission errors in E1 trunk lines.
CRM
Circuit Reservation Message
CS-1
Capability Set 1
Refers to the SS7 Intelligent Network (IN) Standard ITU-T Intelligent Network CS-1 Standard
CSC
Circuit Supervision Control
CVR
Circuit Validation Response Message
CVT
Circuit Validation Test Message

D

DPC
Destination Point Code
The DPC is the Point Code Number for the piece of SS7 network equipment receiving SS7 Signalling
DPNSS
Digital Private Network Signalling System
A common channel signalling protocol for linking private digital exchanges (enabling PBX facilities such as call forwarding to work over the entire network)
DSL
Digital Subscriber Line
There are many forms of DSL - this is the transmission technology carrying signalling over the local loop
DSS1
Digital Subscriber Signalling System no 1
This is an ISDN user network interface. It is a common channel digital access signalling system. ITU-T recommendation is Q.931 and ETSI EN 300 403-1
DTMF
Dial Tone Multifrequency
A tone signalling system available to POTS users with a multi-frequency key pad

E

E1
“The European standard (see North American T1). E1 carries information at the rate of 2.048 millions bits per second. E1 30 channels, 2.048 Mbps.”
EIR
Equipment Identification Register The EIR in a GSM Network stores the serial numbers (supplied by manufacturers) of the mobile terminals IMEI.
ETSI
European Telecommunications Standards Institute ETSI produce regional telecom signalling protocol standards that are subsequently used in Europe and elsewhere.

F

FISU
Fill-in Signal Unit
FSK
Frequency Key Shifting
FSN
Forward Sequence Number
FSS
Facility Selective Service
FTP
Fast Transfer Protocol (IETF)

G

GPRS
General Packet Radio Services
Packet switched data radio technology for GSM Networks. GPRS connections are always open giving mobile terminal users the same kind of network availability they may be used to from corporate networks. There are no set up and clear down times associated with data calls made via GPRS. Terminals can therefore effectively become a part of the Internet.
GRS
Group Reset Message
GSC
Gateway Switching Center
GSM
Global System for Mobile communication
TDMA based second generation mobile Cellular Radio technology, originated in Europe but now used in over 100 countries around the world. GSM supports voice, data and text messaging and allows roaming between different networks, which means that GSM users can take their phones with them to many parts of the world.
GTT
Global Title Translations
GTV
Global Title Value

H

H.323
An ITU-T suite of protocols designed for controlling multimedia communications over IP
HDLC
High Level Data Link Control
HLR
Home Location Register
An HLR is a central database in a GSM network that stores all permanent subscriber data and the relevant temporary data of all subscribers.

I

IAM
Initial Address Message
ICP
Intelligent Call Processing
ICR
Intelligent Call Router
IDLC
Integrated Digital Loop Carrier
IDT
Integrated Digital Terminal
IEEE
Institute of Electrical and Electronics Engineers
IETF
Internet Engineering Task Force
IMEI
International Mobile Station Equipment Identity
The IMEI uniquely identifies GSM mobile terminals internationally - it's a serial number. Allocated by the manufacturer and registered in the network by operators in the EIR.
IMSI
International Mobile Subscriber Identity
When registering for a service on a GSM network a subscriber is assigned an IMSI number. Calls and services can only be used by a subscriber with a SIM card with a valid IMSI and IMEI number
INAP
Intelligent Network Application Part
SS7 Protocol enabling Intelligent Network services. Networks using INAP deliver easily programmable services on a per customer basis, such as follow-me, televoting, pre-paid, and credit card calls.
INR
Information Request Message
IP
Intelligent Peripheral or Internet Protocol (IETF)
IPC
Interprocess Communication
IPI
Intelligent Peripheral Interface
ISDN
Integrated Services Digital Network
ISDN - Integrated Services Digital Network (ISDN) is a CCITT standard, covering a range of voice, data, and image services. It provides end to end, simultaneous handling of digitised voice and data traffic on the same links, via the same exchanges.
ISDNUP
ISDN User Part
ISO
International Standards Organization
ISPC
International Signalling Point Code
ISUP
ISDN User Part (circuit related)
The functional part of the Signalling System No. 7 (SS7) protocol, (i.e., the part that specifies the interexchange signalling procedures for the setup and tear down of trunk calls between networks).
ITU
International Telecommunication Union
ITU-T
Telecommunication Standardization Sector (of ITU)
Before June 1994 the ITU-T was known as CCITT
ITU-TS
Telecommunication Standardization Sector (of ITU)
IVR
Interactive Voice Response
Interactive Voice Response refers to those systems that provide information in the form of recorded messages over telephone lines in response to user input

L

LAN
Local Area Network
A communication system that provides reliable high-speed, point to point, connections for routing data packets between devices in a single building or complex.
LCN
Logical Channel Number (x.25)
LI
Length Indicator
LINK SETS
Link Sets
Signalling data links are grouped into link sets. All links in a link set must connect to a single point code. Up to 16 links can be assigned to a single link set.
LNP
Local Number portability
LOCREQ
Location Request
LSSU
Link Status Signalling Unit

M

MAP
Mobility Application Part
The SS7 Protocol layer MAP provides a GSM Network with a mechanism to communicate between its component parts and other networks. It allows MSCs to communicate with VLR,HLR's and BSC's.It provides the underlying signalling for SMS and Location Based services.
MIN
Mobile Identification Number
MSC
Mobile Switching Center
The switching node of a GSM network is the Mobile Switching Centre. The MSC performs all the switching functions of a fixed-network switching node, e.g. routing path search,signal routing and service feature processing. In addition it has to control allocation of radio resources and subscriber mobility.
MSISDN
Mobile Station ISDN Number
The real telephone number of a GSM subscriber. A mobile subscriber can have many MSISDN numbers - for different services - voice,fax,data
MSRN
Mobile Station Roaming Number
A temporary location-dependent ISDN number on GSM Networks. It is assigned to the locally responsible VLR to each mobile station in its area.
MSU
Message Signalling Unit
MTP
Message Transfer Part
Provides physical, data link, and network layer functions. MTP transports information from the upper layers (including the user parts and SS7 applications) across the SS7 network and includes the network management procedures to reconfigure message routing in response to network failures. Refers to level 1 through 3 in the SS7 protocol stack (MTP1-MTP3).
MUX
Multiplexer
A device used to allow a single communication circuit to take the place of several parallel ones. At the other end of the link a demultiplexer separates the channels.

N

NCP
Network Control Point
NIC
Network Interface Card
An interface card allowing a node to be connected to a LAN.

O

OPC
Origination Point Code
The OPC is the Point Code of the SS7 equipment that is transmitting the SS7 signalling.

P

PBX
Private Branch Exchange
A switching system owned by a client that acts as an in-house telephone exchange with advanced features and capabilities.
PCM
Pulse Code Modulation
A method of digitally encoding speech
Point Code
A number that uniquely identifies a node in an SS7 network. Used to direct messages to the appropriate destination. Each switch, Service Control Point (SCP), Signal Transfer Point (STP), and IP (Intelligent Peripheral) has a unique point code in the SS7 network.
POTS
Plain Old Telephony System
PPP
Point-to-Point Protocol
PRI
Primary Rate Interface
PSTN
Public Switched Telephone Network

Q

Q.931
A well know ITU-T standard for access signalling between an ISDN terminal and narrow band ISDN network.

R

R2
Region or Register Signalling
R2 or CAS signalling is still in common use today (most widely MFC R2), but has been superseded by other forms of signalling such as ISDN and SS7.
RTP
Real-time Transport Protocol
Proxy server for RTP streams, that is supported on SS7 Media Gateway and Class 4 Softswitch

S

SCCP
Signalling Connection Control Part
This allows non-circuit related signalling (such as TCAP) to be carried over SS7 routes.
SCE
Service Creation Environment
This allows the creation of services in an SS7 Intelligent Network environment.
SCP
Service Control Point (SS7)
Service Control Points contain centralized network databases for providing enhanced services. The SCP accepts queries from the Service Switching Point (SSP) and returns the requested information to the requester.
SDLC
Synchronous Data Link Control
SDSL
Symmetric Digital Subscriber Line
SEP
Signalling Endpoint
SF
Status Field
SI
Service Indicator
SIB
Service Independent Building Blocks
In the area of SS7 based Intelligent Networks this refers to the abstract representation of IN capabilities that allow IN services to be built.
SIF
Signalling Information Field
SIM
Subscriber Identity Module
In GSM networks a subscriber is associated with a mobile station via the means of a personal chip card.
SIO
Signalling Information Octet
SIO contains information on the identity of the user of an SS7 MTP message - eg. ISUP, TCAP
SIP
Session Initiation Protocol
SIP is an IETF initiative that provides an alternative to the H.323 standard for VoIP signalling.
SLC
Signalling Link Code
SMPP
Short Message Peer to Peer
This protocol allows communication into and between SMSC's. Often this protocol is provided as a means of providing third party SMS applications with single or bulk SMS delivery.
SMS
Short Message Service
A text message service that enables short messages of generally no more than 140-160 characters in length to be sent and transmitted from a cell phone. In a GSM network this service is enabled by the SS7 MAP Protocol.
SMSC
Short Message Service Centre
A node in the network that receives all mobile originated text messages, determines the current status of the recipient, forwards the message to the appropriate destination subscriber, or stores them for later transmission.
SMTP
Simple Mail Transfer Protocol
SNMP
Simple Network Management Protocol (IETF)
SS7
Signalling System #7
SS7 is a global standard for telecommunications defined by the International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T). It provides protocol signalling standards for both fixed and cellular networks allowing for circuit based telephony calls and transaction based services - i.e. delivery of SMS, Intelligent Network Services.
SSP
Service Switching Point
Service Switching Points are telephone switches interconnected by SS7 links. SSPs perform call processing on calls that originate, tandem, or terminate at that site. SSPs generate SS7 messages to transfer call-related information to other SSPs or to query an SCP for routing instructions.
STP
Signalling Transfer Point
Signal Transfer Points are switches that relay messages between network switches and databases. Their main function is to route SS7 messages to the correct outgoing signalling link, based on SS7 message address fields.

T

T1
A North American standard - 1.544 Mbps point-to-point dedicated, digital circuit provided by the telephone companies. T1 (DS1): 24 channels, 1.544 Mbps.See E1 for European standard.
TCAP
Transaction Capabilities Application Part
Used for transporting non-circuit, transaction-oriented data across an SS7 network. Initially used for 800 number translation now used to implements services for applications such as GSM-MAP and IS-41. These applications provide IN services such as Home Location Register (HLR) or Short Message Service (SMS).
TCP
Transmission Control Protocol
TCP/IP
Transmission Control Protocol/Internet Protocol
TDMA
Time Division Multiple Access
A method of allowing lower-speed channels to share a high-speed communication circuit, by allocating separate time slots to each channel. Each channel has access to the entire bandwidth of the link for a restricted time.
TMSI
Temporary Mobile Subscriber Identity
In a GSM network the VLR can assign a TMSI in place of an IMSI for definite identification purposes in the area handled by the VLR.
TUP
Telephone Users Part

U

UDP
User Datagram Protocol
UMTS
Universal Mobile Telecommunications Service
UMTS provides the European standard for 3G specified by ETSI. Whereas GSM uses TDMA , where each device has a fixed time slot allocation for the duration of a call, UMTS uses W-CDMA.
USSD
Unstructured Supplementary Services Data
USSD is a means of transmitting data or instructions over GSM Networks. It operates by providing a connection across the GSM network over which data is sent. Text messages can be up to 182 characters in length.

V

VLR
Visitor Location Register
In a GSM network the VLR stores the data for all mobile stations that are currently staying in the administrative area of the associated MSC - typically there is a VLR per MSC.
VOIP
Voice Over Internet Protocol
Describes the provision of voice services over the packet based Internet Protocol - IP.
VPN
Virtual Private Network

W

WAN
Wide Area Network
WATS
Wide Area Telephone Service