Acronyms Cellular

GPRS - (General Packet Radio Service)
GPRS is used in more that 200 countries and is used in 2G and 3 G cellular networks. Packet orientated mobile data service that offers best effort service. GPRS extends the GSM packet circuit switched data capabilities and offers the following services

• Internet Access (Always on)
• MMS (Multimedia Messaging Service)
• PoC/PTT (Push to talk over cellular)
• Instant Messaging and Presence
• Internet Applications using WAP (Wireless Application Protocol)
• P2P (Point to Point service inter-networking with IP

GPRS connection is established by leveraging its APN (Access Point Name). APN is used to define services such as SMS, MMS, WAP, and internet communication to services such as WWW and email.

VLR - (Visitor Location Register)
A database of the subscribers who have roamed into the domain of another MNO (Mobile Network Operator/MSC (Mobile Switching Center).

Data stored in the VLR Database include:

• IMSI (the subscriber's identity number)
• Authentication data
• MSISDN (Mobile Subscriber's phone number)
• GSM services that the subscriber is allowed to access
• Access point (GPRS) subscribed
• The HLR address of the subscriber

Responsibilities of the VLR are:

• Inform the HLR that a subscriber has arrived in the particular area covered by the VLR
• Track where the subscriber is within the VLR area (location area) when no call is ongoing
• Authorize which services the subscriber is eligible
• Allocate roaming numbers during the processing of incoming calls
• Purge the subscriber record if a subscriber becomes inactive while in the area of a VLR. The VLR deletes the subscriber's data after a fixed time period of inactivity and informs the HLR
• Delete the subscriber record when a subscriber explicitly moves to another, as instructed by the HLR.

HLR - (Home Location Register)
Central database that contains details of each Mobile Subscriber that is authorized to use the GSM core network. HLRs stores the information of every SIM card issued by the mobile network operator. SIM cards have a unique identifier called an IMSI which is the primary key to each HLR record. MSISDN (Telephone Number) information is also kept within the SIM and is also primary key in the HLR database.

Data stored in the HLR using the IMSI record

• GSM services that the subscriber has requested
• GPRS settings authorizing the subscriber to the access packet services
• Current location of subscriber (VLR and serving GPRS support node/SGSN).
• Call divert settings applicable for each associated MSISDN.

The main responsibility of the HLR is to manage the movement of SIMs and MS.

Process used by the HLR to manage the movement of MS and SIMs

• Manage the mobility of subscribers by means of updating their position in administrative areas called location areas.
• Send the subscriber data to a VLR or SGSN when a subscriber first roams onto another MNO's network
• Broker between the G-MSC or SMSC and the subscriber's current VLR in order to allow incoming calls or text messages to be delivered
• Remove subscriber data from the previous VLR when a subscriber has roamed away from the visiting MNO's network

GGSN - (Gateway GPRS Supporting Node)

GGSN is a core component in a GPRS network. GGSN provides the gateway between a GPRS network and an external packet switched network such as the Internet or X.25. The external network does not have any visibility into the GPRS infrastructure and appears as a router to the packet switched network. If a user is inactive then the data is discarded but on the other hand if the user is active the GGSN forwards the data to the SGSN that is servicing the mobile user. Mobile originated packets are sent to the right network by the GGSN. GGSN converts GPRS packets that come form the SGSN into a PDP (Packet Data Units) format and then sent out to the packet switched network, in the opposite direction PDP's are converted to the GSM address of the destination mobile subscriber.

GGSN functions include:

• IP address assignment
• Default router for mobile subscribers 
• IP pool management and address mapping
• QoS
• PDP context enforcement
• Subscriber screening

SGSN - (Servicing GPRS Supporting Node)

SGSN is responsible for the delivery of data packets from the mobile devices with its respective geographical service area.

SGSN performs the following:

• Mobility Management which includes attach/detach and location management
• Packet Routing and Transfer
• Logical Link Management 
• Authentication and Charging Functions

Location register of a SGSN stores the following information:
Location Information

• Current Cell
• Current VLR

User Profiles

• IMSI
• Addresses

Other SGSN Functions Include:

• Detunnel GTP packets from the GGSN (downlink)
• Tunnel IP packets toward the GGSN (uplink)
• Carry out mobility management as Standby mode mobile moves from one Routing Area to another Routing Area
• Billing user data

APN - (Access Point Name)
APN is a protocol that allows a smartphone or computer access to the internet leveraging a mobile phone network and is used in 3GPP networks like GPRS and EPC. The GSM carrier will determine what connection should be created and configure the network identifier (APN) accordingly this can include:

• Security Methods used
• Whether a private connection is used
• IP addresses

The APN identifies the IP Packet Data Network (PDN) that the mobile subscriber communicates with this includes the type of service used such as:

• MMS
• WAP

The APN is made up by two parts which include the Network Identifier and Operator Identifier.

Network Identifier - Defines the external network to which the GGSN is located. It may include the service requested by the mobile subscriber. This is mandatory
Operator Identifier - Defines the mobile operators packet domain network in which the GGSN is located. Optional. MCC/MNC uniquely identifies the mobile operator.

The APN is used in a DNS query to a private DNS network. This process (called APN resolution) finally gives the IP address of the GGSN which should serve the access point. At this point a PDP context can be activated.

SIM - (Subscriber Identity Module)
SIM is used in mobile phones and computers and is an integrated circuit which securely stores the IMSI. The IMSI is used to identify a subscriber on a mobile device. SIMs can be transfered between mobile devices. SIM cards contain the following:

• ICCID (unique serial number of the SIM)
• IMSI (Identify the subscriber)
• Secruity authentication and ciphering information
• Information about the local network (this is temporary)
• List of services the user is authorized to use and 2 passwords PIN and PUK

MSISDN (Mobile Station International Subscriber Directory Number)
MSISDN is the phone number of the SIM card in a mobile phone. MSISN and the IMSI are used to identify the mobile subscriber.

IMSI - (International Mobile Subscriber Identity)
SIM cards are identified on the mobile network operator networks by a unique IMSI.
The format is:

• The first 3 digits represent the Mobile Country Code (MCC).
• The next 2 or 3 digits represent the Mobile Network Code (MNC). 3 digit MNC codes are allowed by E.212 but are not widely implemented.
• The next digits represent the mobile station identification number. Normally there will be 10 digits but would be fewer in the case of a 3 digit MNC or if national regulations indicate that the total length of the IMSI should be less than 15 digits.

IMEI - (International Mobile Equipment Identity)
IMEI is a used to uniquely identify mobile phones.This does not uniquely identify the subscriber as the identity of the subscriber comes from the IMSI. Most phones allow you to view the IMEI from inside the battery compartment or by entering *#06# on the keypad of the mobile phone. When a phone is stolen the owner of the mobile device can call the network operator and have their phone "blacklisted", this ensures that nobody can use the phone even if the SIM card has been changed.

MVNO - (Mobile Virtual Network Operator)
MVNO is a mobile network operator that does not have its own mobile network infrastrucutre orlicensed frequency allocation of radio spectrum. MVNO are similiar as resellers of traditional phone and internet services.

MNC - (Mobile Network Code)
MNC is used with the Mobile Country Code (MCC)to uniquely identify an MNO using the iDEN, TETRA, GSM/LTE, CDMA, and UMTS public land mobile networks and some satellite mobile networks. Usually stored on the SIM card and is part of the IMSI.

MCC - (Mobile Country Code)
MCC is used to identifying MS in cellular networks. MCC is often used in combination with a Mobile Network Code in order to uniquely identify a MNO. Usually stored on the SIM card and is part of the IMSI.

PDP - (Packet Data Protocol)
A Mobile Subscriber creates an active session a Packet Data Protocol context is created. The PDP context is a data structure present on both the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN) which contains the subscriber's session information. Mobile Subscribers that want to GPRS must attach and then activate a PDP context. This allocates a PDP context data structure in the SGSN that the subscriber is currently visiting and the GGSN serving the subscriber's access point.
The data recorded includes:

• Subscriber's IP address
• Subscriber's IMSI
• Subscriber's

Tunnel Endpoint ID (TEID) at the GGSN
Tunnel Endpoint ID (TEID) at the SGSN
The Tunnel Endpoint ID (TEID) is a number allocated by the GSN which identifies the tunneled data related to a particular PDP context. Several PDP contexts may use the same IP address.

ICCID - (Integrated Circuit Card Identifier)
Integrated circuit card identifier (ICCID) number is used to uniquely identify each SIM card. ICCIDs printed on the SIM card and also stored in the SIM card itself.
ICCID is composed of the following:
Issuer identification number (IIN) - Maximum of seven digits:

• Major industry identifier (MII), 2 fixed digits, 89 for telecommunication purposes.
• Country code, 1-3 digits, as defined by ITU-T recommendation E.164.
• Issuer identifier, 1-4 digits.

Individual account identification

• Individual account identification number. Its length is variable but every number under one IIN will have the same length.