R82 Carrier Security Administration Guide

GSM Overview

This section gives a quick overview of GPRS, UMTS, and LTE.

A Global System for Mobile Communications

The most widely deployed wireless networks worldwide are those based on Global System for Mobile Communications, or GSM. Formerly known as "Groupe Special Mobile," GSM is a world-wide standard for digital wireless mobile phones. The standard was originated by the European Conference of Postal and Telecommunications Administrations (CEPT) and further developed by the European Telecommunications Standards Institute (ETSI). It has been remarkably successful, with more than one billion people using GSM phones as of early 2004.

The ubiquity of the GSM standard makes intra-nation roaming very common, with international roaming frequently enabled by "roaming agreements" between operators. GSM differs from its predecessors most significantly in that both signaling and speech channels are digital. It has also been designed for a moderate level of security. GSM employs time division multiple access between stations on a frequency duplex pair of radio channels, with slow frequency hopping between channels.

General Packet Radio Services

General Packet Radio Services, or GPRS, is a GSM extension which allows packet switched data transmission. GPRS has been called 2.5G, as it is viewed as a stepping stone toward pure 3G systems like UMTS/W-CDMA or similar. GPRS is backward compatible with GSM, easing the migration path for GSM operators.

From the user's point of view, GPRS is a wireless extension of data networks. It can access multiple types of data networks, such as IP based networks like the public Internet, private intranet, both IPv4 and IPv6 protocols, and X.25 based networks. GPRS upgrades GSM data services providing:

• Point-to-point ( PTP) service: internetworking with the Internet (IP protocols) and X.25 networks.

• Point-to-multipoint ( PTM) service: point-to-multipoint multicast and point-to-multipoint group calls.

• Short Message Service ( SMS): bearer for SMS.

Thus mobile subscribers can receive an array of services, including web browsing, e-mail communications, intranet access and location-based services.

GPRS is an addition to GSM that enables packet based communications. Data transmitted by packet switching is faster and more efficient than circuit switching, the method used in 2G networks.

Universal Mobile Telecommunications System

Universal Mobile Telecommunications System, or UMTS, is one of the third generation (3G) mobile phone communication technologies. UMTS further extends the capabilities of GPRS networks, offering much higher air interface bandwidth. UMTS networks provide an average bandwidth of up to 384Kbit/sec, which is suitable for multimedia services such as video streaming and video conferencing.

IP Multimedia Subsystem

The IP Multimedia Subsystem (IMS) is a common architecture that allows cellular operators to provide multimedia services. Promoted by 3GPP, IMS uses SIP as its basic signaling protocol.

IMS uses SIP to register and authenticate the mobile user when joining a multimedia session, as well as to initiate the session by locating the destination of the session.

Long Term Evolution (LTE)

LTE, also known as 4G, is a cellular internet protocol designed to increase the speed and download capacity of mobile networks.

Basic Components of GPRS/UMTS Networks

On the Network

• PLMN (Public Land Mobile Network) - a mobile wireless network that uses land‑based radio transmitters or base stations.

• PDN (Packet Data Network) - a network that provides packetized data services, such as the Internet.

• GSN (GPRS Support Node) - refers to both SGSNs and GGSNs.

• SGSN (Serving GPRS Support Node) - sends and receives data from mobile stations.

• GGSN (Gateway GPRS Support Node) - acts as mediator between GPRS traffic on the PLMN and IP traffic.

• MS (Mobile Station) - a wireless device accessing network services.

Basic Components of LTE Networks

• SGW (Serving Gateway) - handles routes and forwards data packets.

• PGW (Packet Data Network Gateway) - the entry and exit point for traffic to user equipment.

• MME (Mobility Management Entity) - responsible for user equipment tracking.

Signaling Protocols

• GTP (GPRS Tunneling Protocol) - used to transport user data between GSNs.

• GTP-C (GPRS Tunneling Protocol - Control) - control messages to create, update and delete GTP tunnels.

• GTP-U (GPRS Tunneling Protocol - User) - user messages to carry user data packets.

Comparing GTP Versions

The most important differences between GTP version 0 and version 1 arise from the fact that GTP version 1 supports several different services simultaneously.

Port Changes

• The Control plane now uses UDP port 2123.
• The User plane now uses UDP port 2152.

Multiple PDP Contexts for the Same PDP Address

In GTP versions 1 and 2, multiple PDP contexts/sessions are allowed per PDP address and APN.

For an extensive list of industry-specific terms, see the Glossary.