Name: ALIS

Text: LAWFUL INTERCEPTION FOR
3G AND 4G NETWORKS
WHITE PAPER
............................................................................................................................................
January, 2012
Aqsacom Document No. 100458 (v2.0)

Copyright 2003-2012 Aqsacom Inc. and Aqsacom SA. No portion of this document may be reproduced without the
expressed permission of Aqsacom. The data and figures of this document have been presented for illustrative
purposes only. Aqsacom assumes no liability for errors or omissions.

Table of Contents

1

Introduction .................................................................................................................. 3

2

Mobile Network Types .................................................................................................. 3
2.1

2.1.1

Earlier Generations (Pre-3G) ........................................................................... 4

2.1.2

3G and Later .................................................................................................... 5

2.2
3

3G Technology and Deployments .......................................................................... 3

4G Evolutionary Paths ............................................................................................ 7

Wireless Network Architecture Overview .................................................................. 11
3.1

3.XG Networks ...................................................................................................... 11

3.2

4G Type Networks ................................................................................................ 15

3.2.1

LTE Networks ................................................................................................ 15

3.2.2

WiMAX .......................................................................................................... 17

4

The Architecture of Lawful Interception..................................................................... 19

5

Lawful Interception Configurations for 3G and 4G Networks .................................... 21
5.1

3G Network Interception ..................................................................................... 21

5.2

LTE Network Interception .................................................................................... 23

5.3

WiMAX Network Interception.............................................................................. 25

5.4

Location-Dependent Interception Issues ............................................................. 27

6

Aqsacom’s ALIS Mediation Platform........................................................................... 28

7

ALIS Implementation in 3G / 4G Networks ................................................................. 30

8

Summary ..................................................................................................................... 35

9

References .................................................................................................................. 37

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LAWFUL INTERCEPTION FOR 3G AND 4G NETWORKS
Aqsacom SA and Aqsacom Inc.

1 Introduction
Since the original 2004 publication of our earlier White Paper Lawful Interception for 3G
Networks, considerable progress in the evolution of mobile networks has taken place.
Original 3G specification drafts and deployments were oriented towards a migration
from legacy GSM / GPRS architectures. More recently, 3G networks have taken on
newer architectures for higher data throughputs with enhanced subscriber capacity,
giving way to the deployment of so called “4G” networks.
Given that commercial wireless networks are at various stages of deployment, a common
and systematic methodology for the implementation of lawful interception systems is
evermore critical. Aqsacom has therefore prepared this White Paper with the goal of
addressing a systematic approach to lawful interception, as applied to 3G networks and
evolutionary paths to the 4G realm.
This document will first provide a brief description of the various mobile network
technologies now deployed in commercial wireless networks, followed by a discussion on
the transistion toward the newer “long term evolution” technologies. We then discuss
possible configurations for lawful interception of the evolving mobile networks, followed
by descriptions of approaches to 3G / 4G interception solutions now available from
Aqsacom.

2 Mobile Network Types
In this section we cover the various types of networks currently in use by commercial
mobile network operators, starting with 3G networks as a baseline of comparison for
past and future types of services. We conclude this section with a description of current
and evolving “4G Networks.”
2.1

3G Technology and Deployments

Despite the publicity and earlier hype of carriers promoting their 3G wireless services,
the term “3G” remains rather loosely used. 3G mobile’s broad definition calls for the
support of enhanced multimedia services (voice, data, video) and applications (E-mail,
cell phone, paging, Web browsing), all at data rates higher than those of the earlier

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generations of wireless services. Strictly speaking, the “official” definition of 3G is a
series of performance specifications and reference architectures set forth by the
International Telecommunications Union (ITU) International Mobile Telecommunications
IMT-2000 group. These requirements call for a network to conform to the Universal
Mobile Telephone System (UMTS) and possess uplink/downlink data transmission speeds
at 2 Mbs, 384 kbs, and 144 kbs for indoor pico cell, outdoor micro cell, and outdoor
macro cell settings, respectively (see Table 2-1).
Table 2-1: Summary of IMT 2000 Requirements for “3G”
Coverage

Min. up/down data rate

Indoor (Pico Cell)

2 Mbps

Local Pedestrian (Micro Cell)

384 kbs

Regional or Vehicular Traffic (Macro Cell)

144 kbs

True UMTS, otherwise informally known as WCDMA because of the UMTS’ use of
Wideband CDMA (Code Division Multiple Access) modulation in the air space, conforms
to the IMT-2000 “3G” requirements. Nevertheless, many transmission standards do not
fit the speed requirements even though their proponents continue to classify such
standards as 3G. Some networks use technologies that allow for data rates that
substantially exceed the IMT-2000 standards. These networks can be considered 3.XG or
even 4G (discussed later in this document).
2.1.1 Earlier Generations (Pre-3G)
For background purposes, we begin discussing pre-3G wireless network architectures and
implementations. Such networks remain important in the context of lawful interception
because they continue to be widely used given the backward compatibility of the newer
wireless technologies to the earlier ones; i.e., most so-called 3G handsets and devices will
operate on the earlier 2G networks. Furthermore, 2G networks remain the norm in
many parts of the developed and developing worlds where 3G networking technology
has not yet been deployed, or has been delayed in anticipation of 4G deployments.
The following summarize the capabilities of the transmission standards, some of which
may be better described as “2.5G” (e.g., EDGE or CDMA2000 1X).
GPRS (General Packet Radio Service):
This service complements GSM voice and rides within the 200 kHz band reserved
for GSM channelization. It is a packet-based service with a theoretical
transmission speed of up to 172 kbs, although current operator implementations
and handsets typically operate at much slower speeds. The packet mode enables
the service to be “always connected.” GPRS remains a commonplace wireless

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networking technology wherever GSM is deployed, mainly for support of the
large base of legacy GPRS handsets and modems still in use as well as fall-back
radio infrastructure from more advanced networking.
EDGE (Enhanced Data Rates for GSM and TDMA Evolution):
EDGE updates GPRS technology by using higher-order data coding schemes for
the radio links; however, EDGE’s radio modulation maintains the time slot TDM
methods of GSM. This backward compatibility to GSM makes network upgrades
to EDGE manageable, although not necessarily trivial to perform on a large scale.
Because it maintains GSM legacy, it is referred to as a “2.5G” network evolution.
Despite its theoretical transmission speed of over 300 kbs, users will be more
likely to find rates of from about 20 to 100 kbs. EDGE continues to be a heavily
used data service worldwide given the ubiquity of legacy GSM network
infrastructure and the simple fact that many users still do not possess 3G
handsets and other devices.
CDMA2000 1X RTT:
This standard follows from the CDMAOne (CDMA IS95) group in that it applies the
same 1.25 MHz channel bandwidths as its earlier generation system (hence the
term 1X). RTT stands for Radio Transmission Technology. This standard supports
theoretical data transmission rates of 307 kbs. CDMAOne and CDMA2000 are
widely deployed in the US, Canada, China, the Asia/Pacific region, as well as in
Africa [1], but market pressures are now encouraging CDMA network operators to
migrate towards 4G technologies.
2.1.2 3G and Later
So-called 3G services presently dominate the operations and services of wireless network
operators throughout the developed world. Wireless network operators have embraced
3G technologies, especially at the radio level, because of WCDMA’s more efficient use of
radio spectrum, thereby enabling the support of more voice customers for a given
amount of bandwidth resources. Of course, 3G networks support ubiquitous data
services as well, which are taking on exponential customer growth thanks to the
disruptive nature of newer generations of smart phones (e.g., the Apple iPhone and
iPhone-like devices), smart phone applications (“apps”), and tablets and other devices
that will be linked to wireless networks and rely on wireless data services.
UMTS (WCDMA):
UMTS (Universal Mobile Telephone System) has been developed under the 3GPP
(3rd Generation Partnership Project) Working Group and proposed as the
underlying architecture supporting the “true” 3G standard It is commonly called
“WCDMA” (Wideband CDMA) because of its use of CDMA in the air space

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modulation. The standard makes use of 5 MHz for transmission and 5 MHz for
reception, thereby consuming relatively more bandwidth than its distant cousin
GSM (200 kHz). WCDMA has been widely rolled out throughout Europe, Asia, and
the US by the legacy GSM carriers and constitutes the predominant latergeneration network architecture presently in place worldwide [2].
CDMA2000 1X EV-DO and later revisions:

data

voice

This represents the next evolutionary step up from networking based on the
CDMAone standard (hence the term “EV”). The standard makes use of
Qualcomm’s High Data Rate (HDR) system, which supports packet data rates of up
to 2.4 Mbs. Qualcomm holds core patents to this technology, as it does in the
other technologies behind the CDMA and WCDMA standards. CDMA2000 1X EVDO (DO = Data Optimized) has supplanted 1x RTT in most markets served by
CDMA, and can support true mobile 3G services according to the IMT-2000 3G
definition [1]. Nevertheless, 1x RTT is still used as a “fall back” by handsets when
EV-DO is not available. The 1xEV-DO specification has undergone revisions, from
the original CDMA2000 1X release, through rel. 0, then onto revs. A and B, and
most recently DO Advanced (see Figure 2-1). Each revision aims to achieve higher
service performance, such as faster call set-up times, lower latency, and higher
uplink and downlink data rates – the latter through higher order modulation
schemes and more efficient use of radio spectrum.
CDMA2000 1x

1X Enhancements

DL: 153 kbps
UL: 153 kbps

1x Advanced

DL: 153 kbps
UL: 153 kbps

1xEV-DO Rel. 0

1XEV-DO Rev. A

DL: 2.4 Mbps
UL: 153 kbps

DL: 3.1 Mbps
UL: 1.8 Mbps

2007

2008

2009

DL: 153 kbps
UL: 153 kbps
Multi-Carrier
EV-DO

HW upgrade
Rev. B

DL: 9.3 Mbps DL: 14.7 Mbps
UL: 5.4 Mbps UL: 5.4 Mbps

2010

2011

DO Advanced
DL: 32 Mbps
UL: 12.4 Mbps

2012

2013

Figure 2-1. Migration of CDMA networking towards higher data speeds (based on [1]).

HSPA (High Speed Packet Access) and HSPA+
This technology mainly constitutes an upgrade to the radio interface of 3G UMTS
networks, thanks to more advanced data coding schemes. In effect, it is a 3.XG
type networking technology, and has enabled carriers to facilitate their race
towards 4G-type services. Deployments are divided into High Speed Downlink
Packet Access (HSDPA), which can offer up to 14.4 Mbs, and High Speed Uplink
Packet Access (HSUPA) which can allow for up to 5. 8 Mbs. HSPA+, otherwise
known as HSPA Evolution, attains higher data rates (42 Mbs downlink, 11 Mbs
uplink) through the use of MIMO antenna technologies and advanced data coding
and radio channel combining methods (see Figure 2-2). In analogy to EDGE’s
upgrade path from GPRS, HSPA can be built over existing UMTS networking

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infrastructure; however, increased user bandwidths with reduced latency can be
achieved by migrating the underlying network core infrastructure to an all-IP
network. Such migrations, in effect, prepare operators for Long Term Evolution
deployments, which are currently just beginning (discussed further below). HSPA
and HSPA+ networks are now becoming prevalent in developed markets where
existing 3G infrastructure is already deployed, especially in the US, Europe, and
parts of the Asia / Pacific, and sometimes are marketed as a “4G” service.
Rel-99

Rel-5

Rel-6

Rel-7

Rel-8

WCDMA HSDPA

HSUPA

HSPA+

HSPA+

DL: 1.8 – 14.4 Mbps
UL: 384 kbps

DL: 1.8 – 14.4 Mbps
UL: 5.7 Mbps

DL: 28 Mbps
UL: 11 Mbps

DL: 42 Mbps
UL: 11 Mbps

2009

2010

Rel-9
and beyond

HSPA+
DL: 84 Mbps and higher
UL: 23 Mbps and higher

2011

2012

Figure 2-2. Migration of 3G networking towards higher speeds, thanks to HSPA and HSPA+ advancements
in the radio layer (based on [3]).

TD-SCDMA (Time Domain Synchronous Code Division Multiple Access)
This standard was developed by the Chinese Academy of Telecommunications
Technology, Datong, and Siemens [4]. The standard addresses the Chinese
government’s concern that China was too dependent on 3G mobile technology
from Western companies. TD-SCDMA has an alternative air interface to WCDMA
in UMTS networks, and proponents of the standard claim that it can achieve 3G
functionality at a substantially lower cost than WCDMA / UMTS. The standard is
covered in 3GPP Release 4 and its commercial deployment was timed with the
2008 Summer Olympics in Beijing. TD-SCDMA was intended not only to serve as
a platform for 3G data services for mobile subscribers, but also to facilitate the
deployment of conventional voice services that competes against wireline voice
or where wireline is not available. TD-SCDMA supports data links of up to 2 Mbs,
thereby qualifying it (in theory) as a true 3G standard. Its deployment began in
earnest during 2009 (after years of delay) by China Mobile, China’s largest
wireless operator. Given the similarity of TD-SCDMA’s and Western UMTS’ core
network elements beyond the radio level, lawful interception network
implementations for TD-SCDMA are similar to those for UMTS.
2.2

4G Evolutionary Paths

As was the case with 3G terminology, the use of “4G” to describe later evolutions in
commercial wireless technology, architecture, and performance remains rather loose. In
marketing by carriers and equipment suppliers, 4G often encompasses networks based
on HSPA+, various forms of Long Term Evolution (LTE) networking, and WiMAX.

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However, the strict definition of “4G” is defined by the International Telecommunications
Union (ITU)’s IMTS-Advanced (IMT-A) systems specifications (much as IMT-2000 paved
the way towards defining true 3G network services)1. It should not be forgotten that
important aims of 4G services (and its close precursors) are not only to provide high
bandwidth data services to end users, but also to make more efficient use of spectrum to
accommodate more users of traditional voice and text messaging in a given service area.
The two dominant networking paths that are typically considered as “4G,” whether
strictly complying to the above definition or not, are Long Term Evolution (LTE) and
WiMAX.
Long Term Evolution (LTE)
LTE represents a series of evolutions proposed by the 3GPP that build from the 3GPP’s
recommendations on 3G networks. The incumbent operators of wireless networks are
advocating LTE for future 4G services. These operators include those who have pursued
legacy WCDMA/HSPA/EDGE as well as CDMA2000 paths. This industry constitutes a
formidable base with which to produce economies of scale in 4G networking
infrastructure and user equipment.
LTE draws from earlier 3GPP technical specification releases, culminating in Release 8,
which covers the first formal LTE specification. LTE Release 8 features include:
High spectral efficiency through the use of an OFDM downlink and DFTS-OFDM
uplink between the base stations and user equipment, utilizing bandwidths of 1.4,
3, 5, 10, 15 and 20 MHz. This will support peak data rates of up to 300 Mbs on
the downlink and 75 Mbs on the uplink.
Very low latency.
Support of variable bandwidths.
Simplified networking and protocol architecture, where many of the user
equipment control functions are moved to the radio base station (now called
“eNodeB” in LTE parlance).
Compatibility with legacy networks, including CDMA2000.
Efficient multicast and broadcast.
Support of self organizing network operation.
Despite the advances advocated by LTE Release 8, many of which are now included in
early LTE deployments, only those LTE networks conforming to the 3GPP’s LTE-Advanced

1

On 21 October 2010, the ITU's Radiocommunication Sector (ITU-R) announced their completion of their
assessment of six candidate submissions for the global 4G mobile wireless broadband technology, otherwise
known as IMT-Advanced. Harmonization among these proposals resulted in two technologies, "LTEAdvanced" and "WirelessMAN-Advanced" being accorded the official designation of IMT-Advanced,
qualifying them as true 4G technologies. The latter technology is a form of WiMAX.
See
http://www.itu.int/net/ pressoffice/press_releases/2010/40.aspx

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(LTE-A) specifications truly conform to the ITU International Mobile Telecommunications
Advanced (IMT-A) 4G network definition. IMT-A overall’s aim is to provide much higher
data rates (100 Mbps and 1 Gbps data rates for high and low mobility, respectively, and
in the uplinks and downlinks), backward compatibility with networks based on earlier
IMT-compliant networking technologies, support of multiple radio access systems,
ubiquitous availability of user equipment, high quality mobile services, and worldwide
roaming [5]. LTE-A will also impact both the radio layers as well as the core of the
wireless network, and therefore require substantial investment by the carriers, albeit
such investments can be incremental over time through incremental network
development steps. Section 3 of this White Paper will go into specific details of the
network developments.
LTE-Advanced specifications and recommended technical approaches are currently workin-progress and to be reflected in 3GPP Release 10 and beyond. The overall aim is to
provide much higher data rates (100 Mbps and 1 Gbps data rates for high and low
mobility, respectively, and in the uplinks and downlinks), backward compatibility with
networks based on earlier IMT-compliant networking technologies, support of multiple
radio access systems, ubiquitous availability of user equipment, high quality mobile
services, and worldwide roaming [5]. LTE-A will also impact both the radio layers as well
as the core of the wireless network, and therefore require substantial investment by the
carriers, albeit such investments can be incremental over time through incremental
network development steps. Section 3 of this White Paper will go into specific details of
the network developments.
WiMAX (Worldwide Interoperability for Microwave Access):
WiMAX2 as a marketing and implementation effort was born from the success of WiFi,3
the latter of which has spread the use of low cost IEEE 802.11 wireless local area
networking and cross-vendor interoperation. The philosophy has been re-applied by the
WiMAX Forum, an industry group formed by companies to promote the WiMAX
standards and ensure equipment interoperability. One important aim of WiMAX is to
provide ubiquitous broadband access over metropolitan area scale. The technology is
based on a series of upgrades to the IEEE 802.16 wireless standard. Originally intended
for fixed-position broadband point-to-point network backhaul and point-to-multipoint
metropolitan area networking, this standard has been extended to support ubiquitous
fixed access (802.16-2004) and mobility (IEEE 802.16e-2005). To achieve transmission

2

WiMAX® stands for “Worldwide Interoperability for Microwave Access.” The term was created and
trademarked by the WiMAX Forum. The WiMAX Forum® is an industry-led, not-for-profit organization
formed to certify and promote the compatibility and interoperability of broadband wireless products based
upon the harmonized IEEE 802.16m standard.
3

The term Wi-Fi is a trademark of the Wi-Fi Alliance, a group of industry players advancing the
deployment of 802.11 systems and their compatibility.

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efficiency, WiMAX calls for the use of scalable OFDMA operating within Time Domain
Division (TDD) or Frequency Domain Division (FDD) profiles, with channel sizes ranging in
size from 3.5 to 10 MHz. Data rates of dozens of Mbps are theoretically possible up 50
km and less for mobile; however, these rates will be subject to environmental, line-ofsite, and distance factors. WiMAX data rates up to 1 Gbs are envisioned through the use
of MIMO antennas and other enhancements, as covered in the IEEE 802.16m standard.
This standard has been proposed for Mobile WiMAX Release 2 and is now recognized by
the ITU as an IMT-A 4G technology.
WiMAX compliant network services are now being deployed in the US under the Clear
brand, which is offered by Clearwire (a venture of Sprint, Intel, Google, and the cable TV
companies Comcast, Time Warner, and Bright House). The service operates over a
licensed 2.5 GHz band that had been held by Sprint.
To achieve a competitive jump in capturing the nascent 4G market space while the
incumbent wireless operators await their LTE deployments, Clearwire is presently
positioning their service as an alternative to wireline and 3G wireless broadband services
for mobile as well as home users. The company offers WiMAX-compliant modems and
smart phones as part of the service. For mobile users, these modems fall back to Sprint’s
3G broadband data service where WiMAX coverage is not present. WiMAX speeds are
advertised to be in the range of 3 to 6 Mbs for downlinks and up to 1 Mbs for the uplink.
Although impressive compared to the effective speeds of today’s common 3G offers,
these rates are far from the true 4G specifications.
South Korea also constitutes an early driver of WiMAX, thanks in part to the heavy
investment in this technology by Korean telecoms equipment manufactures. Major
carriers such as KT and SK Telecom offer WiMAX 802.16e services there. Numerous
WiMAX services are found worldwide, often offered by smaller entrepreneurial firms
competing against incumbent fixed and wireless carriers.
Considerable controversy in the communications industry persists on the merits of
WiMAX vs. LTE. Generally, WiMAX deployments are being driven by entrepreneurial
organizations desiring to capture early access to the broadband wireless market. By
contrast, LTE deployments are driven by established wireless network operators and the
equipment suppliers who have traditionally served them. From the point of view of
performance and cost of operation, no definitive preference towards WiMAX or LTE can
be reached given the current status of deployments of both services. Both use similar
radio technologies and spectrum, which essentially levels the playing field on the air side
of the networks. Issues of interaction or migration from one network type to the other,
as driven by market demand, remain to be explored.

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3 Wireless Network Architecture Overview
Before discussing the specifics of how lawful interception is applied to 3G and later
networks, it is instructive to review the overall network topologies of 3G UMTS,
CDMA2000, WiMAX, and LTE. These technologies have either been deployed by most of
the wireless network operators throughout the world, undergoing deployments, or will
be deployed in the immediate years to come.
3.1

3.XG Networks

Networks based on UMTS and CDMA are quite similar, particularly within the core
networking functions. Figures 3-1 and 3-2 provide generalized descriptions of UMTS and
CDMA2000 networks. Both interconnect a group of Base Transceiver Stations (BTS)
through a common Base Station Controller (BSC – see terminology definitions following
each figure). From the BSC, circuit switched and packet data are sent, respectively, to
some form of a Mobile Switching Center and packet manipulation system (Packet Data
Serving Node or PSDN for CDMA2000, and Serving GPRS Support Node or SGSN for
UMTS). There is also some level of commonality in the signaling and database functions
within the two networking technologies. Note each network device shown does not
have to represent a separate physical device, and many of the network elements can be
combined into a single network device. Slight variations in the network architecture can
occur depending on the choice of vendors and desired features.
Upgrades of UMTS networks to accommodate HSDPA and HSDPA+ are performed mainly
at the level of the BTS, where earlier generation WCDMA transmitter / receiver
subsystems are augmented for HSDPA / HSDPA capabilities. Other than impacting the
overall data rates and volumes within the underlying core networking, there is no
significant change in the lawful interception architecture or mechanism (discussed in
Section 5).

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to IPv6 Networks

to PSTN,
other networks

MRF

MGCF
BTS

HSS
VLR

IMS-MGW

BSC /
RNC

BTS

EIR
CSCF
AS

SGSN
BTS

AUC
Switched Voice / Data

SMSC

Packet Data

G-GSN

Signaling and Control

TSGW

to Internet

Figure 3-1. Generalized view of a mobile 3G network based on UMTS. This diagram corresponds to
Release 5 and later of the UMTS specification. Configuration is nominal and varies by equipment vendors.
Some functions may be combined into a single network entity.
UMTS Network Terms [6,7]
BSC (Base Station Controller). Controls and coordinates the function and data flow to/from a group of BTSs
that are connected to it.
BTS (Base Transceiver Station). Contains RF and other network elements serving as the air interface
between the network and mobile handsets.
GGSN (Gateway GPRS Support Node). Enables packet flow between the SGSN and the outside world, the
latter typically the public Internet. This is a relic of GPRS that is also implemented in UMTS.
IMS-MGW (IP Multimedia Subsystem - Media Gateway). Routes switched data from the BSC/RCN, via IP,
ATM, or other NGN type networks, to the PSTN and other public or private networks. Used in later
revisions to UMTS (e.g., Releases 5 and later).

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MGCF (Media Gateway Control Function). Controls the Media Gateway, in part, by interacting with
network signaling (e.g., SS7). Used in later revisions to UMTS (e.g., Release 5).
MRF (Media Resource Function). Manages enhanced services and other applications over 3G networks,
including voice mail, conferencing, pre-paid calling, messaging, etc.
RNC (Radio Network Controller). Same as BSC. Controls a group of base stations covering a given territory.
SGSN (Serving GPRS Support Node). Core element of GPRS networks and also used in UMTS. Responsible
for routing of packets between the BSC/RNC and the GGSN. More specifically, the SGSN handles: a)
encryption, decryption, and authentication of packets; b) session management and communication set-up
with the mobile subscriber; c) logical link management to the mobile subscriber, d) packet flow and
signaling to/from other nodes (HLR, BSC/RCN, GGSN, etc.); and e) tracks charges to subscriber based on
services consumed. In some vendor implementations, the SGSN and GGSN can reside on the same
equipment chassis.
TGSW (Transport Signaling Gateway). Serves as signaling interface (e.g., SSL) between MGW and PSTN.
Registers, Controllers, Signaling Devices
AS (Application Server). Operates in conjunction with the MRF for executing enhanced calling and
data services.
AUC (Authentication Center). Stores user information for authentication purposes to prevent
unauthorized use of a subscriber’s account.
HSS (Home Subscriber Server). Includes the functions of the Home Location Register (HLR) as well
as other functions for managing user mobility and multimedia applications over IP networks.
VLR (Visitor Location Register). When the user moves outside of the home territory of the HLR,
the VLR records the presence of the user in a new territory and relays this information back to the
user’s home HLR. If the user roams into the network of a different carrier, the new network’s VLR
will record this action.
EIR (Equipment Identity Register). Lists all devices that the network considers valid. If a mobile
device is stolen, the EIR would prevent access of this device to the network.
CSCF (Call Session Control Function). Handles call set up and termination, state and event
management, billing information, location-based services and other functions according to vendor
implementation.
SMSC (SMS Center). System for managing Short Message Service through network signaling.

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to PSTN,
other networks

MSC
IWF
BTS
HLR
VLR

MRF
BSC

BTS

EIR
AS

PDSN
BTS

AUC

FA

SMSC

switched voice / data
packet data

AAA

signaling and control

HA

to Internet

Figure 3-2. General overview of a typical 3G mobile network based on CDMA2000 technology. For the
sake of generality, the Foreign Agent function is included in the PDSN although it can likewise
accommodate the Home Agent as well.
CDMA2000 Network Terms
AAA (Authentication, Authorization, and Accounting server). Handles user access to the Internet in typical
3G configurations.
BSC (Base Station Controller). Controls and coordinates the function and data flow to/from a group of BTSs
that are connected to it.
BTS (Base Transceiver Station). Contains RF and other network elements serving as the air interface
between the network and mobile handsets.
IWF (Inter-working Function). Generally serves as a gateway between circuit-switched CDMA networking
and outside public switched networks. Different manufacturers provide different levels of functionality in
their IWF systems (e.g., remote access, interface to Internet effectively making the IWF operate as a PDSN).
MRF (Media Resource Function). Manages enhanced services and other applications over 3G networks,
including voice mail, conferencing, pre-paid calling, messaging, etc.
MSC (Mobile Switching Center). A switch that provides a connection between the local BSC and the MSC of
a remote network. The MSC establishes circuit-switched call between two networks, while accounting for
signaling (e.g., from SS7 networks).

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PDSN (Packet Data Serving Node). Extracts packets from BSC that are destined for transmission over the
Internet, and likewise routes packets from the Internet to the BSC.
Registers, Controllers, Signaling Devices
AS (Application Server). Operates in conjunction with the MRF for executing enhanced calling and
data services.
AUC (Authentication Center). Stores user information for authentication purposes to prevent
unauthorized use of a subscriber’s account.
HLR (Home Location Register). Contains user profile and handles updates to billing based on
usage of the subscribed to services.
HA (Home Agent). Records location and assigned IP address of a handset not connected to its
home network.
FA (Foreign Agent). Records location, assigned IP address, and other information about a handset
visiting a network.
VLR (Visiting Location Register). When the user moves outside of the home territory of the HLR,
the VLR records the presence of the user in a new territory and relays this information back to the
user’s home HLR. If the user roams into the network of a different carrier, the new network’s VLR
will record this action.
EIR (Equipment Identity Register). Lists all devices that the network considers valid. If a mobile
device is stolen, the EIR would prevent access of this device to the network.
SMSC (SMS Center). System for managing Short Message Service through network signaling.

3.2

4G Type Networks

We now briefly describe the architecture of 4G networks. Note we use the term “4G”
rather loosely here to refer to the newer generations of wireless network services based
on WiMAX and LTE.
3.2.1 LTE Networks
Long Term Evolution networking attempts to provide a transition path from 3G type
networking towards a true LTE-A network with a fully IP (Internet Protocol) core known
as the Evolved Packet Core (EPC – earlier known as the System Architecture Evolution or
SAE). Figure 3-3 describes the LTE architecture, whose aim is to “flatten” the overall
topology to allow for more efficient packet transfer between the User Equipment (UE)
and Packet Data Network (PDN – typically the public Internet), while also allowing for the
service of legacy wireless networks. In reality, different network operators will be at
different states of LTE implementation; therefore, only parts of the network architecture
shown in Figure 3-3 may be present in the networks of carriers claiming to run “LTE
services.”

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To media gateway f or
circuit-switched voice

(optional)

GERAN

SGSN

UTRAN

HSS
IMS

PCRF
Operator IP Services

MME

UE

Serving
GW

eNB

Trusted non-3GPP
IP Access

PDN
GW

Trusted / Untrusted non3GPP / 3GPP IP Access

Internet

ePDG

UE
UE

UE
Untrusted non-3GPP
IP Access

switched voice / data
packet data

signaling and control

Figure 3-3. General overview of an LTE network (the Serving GPRS Support Node, or SGSN, is optional and
mainly pertains to evolutions of UMTS networks).

The Network Elements of Figure 3-3 will now be briefly described:
eNB. This represents the Evolved Radio Access Network, otherwise known as eNodeB. This network
element operates the radio interfaces to the User Equipment (UE) through Radio Link Control, Medium
Access Control (MAC), data compression, Radio Resource Control, and other functions to access the radio
portion of the network. In contrast to 3G, eNodeB is aimed to reflect a simpler aspect of 4G architecture by
condensing the BTS and Base Station Controllers of the earlier technology into one network element. In
effect, this enables a closer tie-in of the radio side of the network to the underlying packet network.
Serving GW (Serving Gateway). This element routes and forwards user data packets from the eNodeB, as
well as from the SGSN of earlier generation parts of the network (namely the GPRS / EDGE Radio Access
Network and UMTS Terrestrial Access Network, or GERAN and UTRAN, respectively). The Serving Gateway
also supports handovers between multiple eNBs and storage of UE “contexts,” which are parameters
associated with the user’s IP data stream and corresponding User Equipment. More importantly, the
Serving Gateway is an important collection point for lawful interception purposes, as will be discussed in
Sections 5 and 7.
MME (Mobility Management Entity). This network element tracks when UE attempts to access the
network, while maintaining the connectivity of UE devices already within range. Among its many functions,
it assigns the Serving Gateway upon network re-attachment of a UE to another eNB within the same LTE

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network, interacts with the Home Subscriber System (HSS) for user authentication, enforces roaming
restrictions, manages ciphering of signaling, etc. The MME also handles signaling with earlier generation
networks (through its interface to the SGSN of such networks), while also providing support for lawful
interception signaling capture.
PDN GW (Packet Data Network Gateway). This serves as the interface between the UE and one or more
packet data networks. The PDN GW performs numerous functions, including packet filtering on a user-byuser basis, policy enforcement, and collection of the Content of Communication for lawful interception.
ePDG (Evolved Packet Data Gateway). The ePDG provides an interface that enables the connectivity of
untrusted UE (such as that connected to a WiFi network) between the Evolved Packet Core and non-3GPP
network.
IMS (IP Multimedia Subsystem) is a standards-driven architecture for providing Voice over IP and other
media-intensive services to end users and between end users.

Also shown in Figure 3-3 is the SGSN (Serving GPRS Support Node), which as described in
Section 3.1 handles user connectivity and control for earlier 3GPP networks. In the
context of the LTE, updated versions of the SGSN are equipped with an interface to the
Evolved Packet Core (through the MME). The PCRF (Policy and Changing Rules Function)
is a 3GPP-defined network entity that controls network resources (e.g., allocation of
subscriber bandwidth, quota management, service tiers), applications, and subscriber
interaction in real time. IP Multimedia Subsystem (IMS) extensions are typically covered
under the Operator IP Services.
3.2.2 WiMAX
The overall architecture of WiMAX networks is depicted in Figure 3-4 [8]. This figure
conforms to the Network Reference Model established by the WiMAX Forum. The
network elements are defined as follows, bearing in mind that some of these functions
can be combined into a single piece of equipment:
ASN (Access Service Network). The ASN encompasses network functions required to support radio access
to the Mobile Station (MS – which is the User Equipment in the parlance of the 3GPP LTE description in the
previous section). These functions include:
Radio Resource Management.
WiMAX Layer 2 connectivity with the MS.
Transfer of Authentication, Authorization, and Accounting (AAA) messages to the subscriber’s
WiMAX subscriber Home Network Service Provider (SNP).
Network discovery and selection of the WiMAX subscriber’s preferred NSP.
Relay functionality for establishing Layer 3 connectivity (e.g., IP) between the MS and the network.
The ASN also supports how the communications from the MS to the terrestrial network is tunneled.
The network functions of the ASN are embedded within one or more Base Stations (BS) and the ASN
Gateway (ASN GW). The Base Stations are the network elements responsible for the radio access(through
the MAC and PHY layers of the IEEE 802.16 standards suite. Connectivity to the underlying IP networks and
subscriber services management are handled via the ASN Gateway (ASN GW), as indicated in Figure 3-4.

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CSN (Connectivity Service Network). This represents a set of network functions that provide IP network
connectivity to the subscribers using the WiMAX services. It contains routers, AAA proxy servers,
subscriber databases, and interconnections to other WiMAX service networks. Specific functions within
this block include:
MS IP address endpoint allocation.
Internet access.
AAA proxy or server.
Policy and Admission Control according to user profiles.
ASN-CSN tunneling support.
WiMAX subscriber billing and inter-operator settlement.
Inter-CSN tunneling for subscriber roaming.
Inter-ASN mobility.
WiMAX services for location based services, peer-to-peer services, authorization and / or
connectivity to IP multimedia services.

It is at the CSN that lawful interception collection takes places, as will be discussed in
detail in Sections 5 and 7. As indicated in Figure 3-4, multiple CSNs may interconnect to
the ASN Gateway of a common radio infrastructure. Likewise, multiple ASNs can serve a
given MS. While these features of WiMAX allow for flexibility in the services offered to
the subscriber, they can also make lawful interception more challenging.

ASN

BS

MS

ASN
GW

CSN
CSN

BS

Packet Data
Signaling and Control

ASP Network
or Internet

Another
ASN

ASP Network
or Internet

Figure 3-4. General architecture of a WiMAX network (from [8]).

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4 The Architecture of Lawful Interception
Figure 4-1 depicts a generalized view of the lawful interception process, which typically
calls for the use of a mediation platform to handle the provisioning of the interceptions
as well as the collection and delivery of intercepted traffic from various forms of
communications services provided by a wireless carrier. Here the use of mediation is
critical for assuring legally and standards-compliant interception capabilities as wireless
carriers add capacity, add features, and transition their networks through the numerous
evolutions described in Sections 2 and 3. Of note is the separation of Law Enforcement
Agency (LEA) functions from the interception functions performed by the network
operator. This is indicated in Figure 4-1 by the demarcation line between the Network
and Services Operator Domain and the Law Enforcement Domain. The cloud to the left
of Figure 4-1 represents a conceptual network that contains one or more Network
Elements (NE) that perform a function in the lawful interception processes, such as in the
collection of intercepted traffic from switches, routers, or network probes (explained
further below).
Network and Services Operator Domain

Law Enforcement Domain

Communications Network

NE
LI Request

NE

MEDIATION
Delivery of
intercepted traffic

NE

Law
Enforcement
Agency

NE

Figure 4-1. Simplified view of lawful interception architecture. Of primary interest is the use of a
Mediation Platform to convey intercepted data from the network to the LEA in a standards-compliant
manner.

The Reference Architecture for lawful interception, as proposed by European
Telecommunications Standards Institute (ETSI), is shown in Figure 4-2 [9]. This
architecture attempts to define a systematic and extensible means by which network
operators and LEAs interact, especially as networks grow in sophistication and scope of
services. The architecture is widely applied worldwide, albeit with slight variations in
terminology for different parts of the world. The architecture is also general in that it
applies to both legacy voice services (wireless or wireline) as well as interception of
packet data networks. Of particular note is the separation of lawful interception
management functions (mainly interception order set-up and tear down, as demanded

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from the LEA), delivery of intercepted call data from the network operator to the LEA,
and conveyance of call content, also from the network operator to the LEA.
Communications between the network operator and LEA are via the Handover Interfaces
(designated HI). Handover Interface 1 (HI1) supports the provisioning of the interception
order via the Administration Function. Handover Interface 2 (HI2) supports the delivery
of Intercept Related Information (IRI; e.g., destination of call, source of a call, time of the
call, duration, etc.) from the network to the LEA. Handover Interface 3 (HI3) supports the
delivery of the Content of Communications (CC) from the network to the LEA. Also of
importance are the “Collection Functions,” which gather the intercepted data from
various switches and probes in the network, and the “Mediation Functions,” which
format the collected IRI and CC data into standardized data representations. The
mediation functions for IRI and CC are also responsible for delivering their products to
one or more LEAs.
The Collection Functions operate in two manners: as an External Interception Function
(EIF) and as an Internal Interception Function (IIF). The Internal Interception Function
collects intercepted traffic from within network elements that have such capabilities. For
example, voice switches, gateways, and routers are often supplied with built-in lawful
interception capabilities that collect and replicate targeted subscriber traffic. These
capabilities may or may not be useful, depending on the implementation of such
equipment in the service provider’s network. The External Interception Function makes
use of probes that are attached to points in the network that provide the requisite
visibility to the types of traffic being collected for interception purposes. These collection
points will be discussed in Section 5. EIFs are used when the network elements do not
support IIFs or the network entity IIFs are inadequate.
Also indicated in Figure 4-2 is the Handover Interface HI-a, which is not a formal part of
the ETSI architecture but included here to represent the feedback of an Operations and
Maintenance function to the LEA. This interface supports, for example, the conveyance
of alarms indicating failure of an interception process.
In the context of Figure 4-2, Aqsacom addresses the function of Collection by providing
probes for EIF or support for the IIF capabilities of networking equipment from major
vendors. Likewise, Aqsacom plays a major role in providing Mediation capabilities to the
network operators, as will be described in Section 6.

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Network Operator / Service Provider Domain

LEA Domain

Interception
Management
System
Administration
Function

Network
External
Interception
Functions
(EIF)

HI1
(Provisioning/
Reporting)

IRI Mediation
Function

HI2
(IRI)

CC Mediation
Function

Network
Internal
Interception
Functions
(IIF)

HI3
(CC)

Operations &
Maintenance
Function

HI-a

(Alarms)

Law Enforcement
Monitoring Facility
(LEMF)

Collection
Function

Figure 4-2. ETSI-defined Reference Architecture for lawful interception. Note the separation of lawful
interception management functions (HI1), call-related data (HI2), and call content (HI3) in the interaction
between the LEA and communication service provider (based on [9]). This diagram is mainly logical;
Aqsacom supports IRI, CC, and Alarms transmission over a common TCP connection.

5 Lawful Interception Configurations for 3G and 4G Networks
5.1

3G Network Interception

Given the general background discussion that has been provided thus far on the wireless
network and lawful interception (LI) technologies, we describe the reference
architectures for LI as these architectures relate to the specific types of wireless
networking.
3G CDMA and UMTS are generally very similar in their lawful interception
implementations, albeit slight differences do occur. For example, UMTS target identifiers
apply the Subscriber Identify Module (or SIM card) ID of the target’s mobile device. In
contrast, CDMA phones do not use removable subscriber cards, thus require the
interception process to be tied to the subject’s handset identifier (Mobile Equipment

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Identifier). Figure 5-1 depicts the Reference Model for the interception of 3G networks;
in this case the model pertains to the interception of circuit-switched networks. This
depiction (based on that published by 3GPP) is sufficiently general to include both UMTS
and CDMA2000. In summary, it shows that:
LI management commands are conveyed between the Administrative Function
(ADMF) and other network elements via the X1 interface,
Intercepted Intercept Related Information (IRI) is conveyed via the X2 interface,
and
Intercepted Content of Communications (CC) is gathered via the X3 interface.
The MSC Server, GMSC Server, MGW, and IWF functions shown in Figure 5-1 were
described in Section 3; in the context of the interception model their corresponding
boxes represent interception processes which can rely on Internal Interception Functions
or External Interception Functions (probes), as described in Section 4. The diagram also
mentions the Gateway Mobile Switching Center Server (GMSC Server), which
interconnects the MSC to the networking of other wireless operators.
Note X3 can convey both bulk content (bearer) and signaling information, which are
ultimately conveyed to the LEA via Handover HI3. The shaded boxes represent functions
performed by Aqsacom’s core product, the ALIS Mediation Platform (discussed further in
Sections 6 and 7).
A similar diagram pertaining to packet data services is provided in Figure 5-2. The
models of Figures 5-1 and 5-2 apply a Mediation Function to separate the LEA from the
data gathering functions within the network. This separation is the core contribution of
the ETSI Reference Architecture and the LI standards based on it (Figure 4-2). It is this
separation that enables LEAs and network operators to configure interception systems in
a generalized manner, covering a wide range of services and technologies, including
wireline voice, wireless voice, wired and wireless data, and emerging services such as
VOIP.

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HI1
X1_1

X1_2

X1_3

X2

MSC Server,
GMSC Server

Mediation
Function

ADMF

HI2
Delivery
Function 2

Mediation
Function

Monitoring
Center

HI3

X3

MGW,
IWF

LEA

X3

Delivery
Function 3

Mediation
Function

Figure 5-1. Interception model for circuit-switched services within a 3G mobile network (generalized for
CDMA2000 and UMTS) (based on [10]). Functions in shaded boxes are implemented in the Aqsacom ALIS
mediation platform (described in Sections 6 and 7).

HI1
X1_1

ADMF

Mediation
Function
X1_2

X1_3

GSN
PDSN

X2

HI2
Delivery
Function 2

Mediation
Function

LEA
Monitoring
Center

HI3
X3

Delivery
Function 3

Mediation
Function

Figure 5-2. Interception model for packet data services (including IP) within a 3G mobile network
(generalized for CDMA2000 and UMTS) (based on [10]). Functions in the shaded boxes are implemented in
the Aqsacom mediation platform (described in Sections 6 and 7).

5.2

LTE Network Interception

As mentioned in Section 3, “LTE” networks are more typically 3G UMTS or even
CDMA2000 networks with added elements to increase radio transmission bandwidth and

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/ or to support evolution towards the Evolved Packet Core (EPC). Therefore, the
interception of typical LTE networks nowadays follows that described for 3G networks
above. For LTE networks that support EPC elements, Figures 5-3a and 5-3b describe the
interception model. Noteworthy in this model is the central role of the Mobility
Management Entity (MME) in collecting IRI from the data streams to and from the eNode
of home and visiting subscribers. Likewise, the Home Subscriber Server (HSS) provides
mapping information between subscriber-related network events (e.g., logging in / out
from the network), subscriber identity, and subscriber mobility for IRI.
CC is obtained through the Serving Gateway (S-GW) and / or PDN Gateway (PDN-GW)
elements. When these elements apply an Internal Interception Function, they duplicate
the targeted packets and route them to the Mediation Function. Alternatively, an
External Interception Function through a probing system can be deployed for the CC
collection. In this case the probe must monitor the packets to and from the S-GW or
PDN-GW, then duplicate the targeted packets and deliver the copies to the Mediation
Function.
Also shown are the interfaces to the Evolved Packet Data Gateway (ePDG) and AAA
services, which would be applied for the interception of traffic from non-3GPP sources
(e.g., WiFi). AAA information is typically needed to obtain the mapping between a
subscriber’s identity and the allocated IP address of their packets. Traffic can be
collected from AAA and ePDG devices via Internal Interception Functions (when available)
or probes – the latter likely to become more common practice.

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HI1
X1_1

ADMF

Mediation
Function

X1_2

X1_3

HI2
Delivery
Function 2

X2

MME or
HSS

X3

Monitoring
Center

Mediation
Function

HI3

X2
S-GW,
PDN-GW

LEA

Delivery
Function 2

Mediation
Function

HI1
X1_1

ADMF

Mediation
Function
X1_2

X1_3

HI2
AAA

X2

Delivery
Function 2

Mediation
Function

LEA
Monitoring
Center

HI3
ePDG

X3

Delivery
Function 3

Mediation
Function

Figures 5-3. (5-3a – top): Interception model for LTE networks. (5-3b- bottom): Interception model for the
support of non-3GPP subscribers (both figures based on [11]). Functions in the shaded boxes are
implemented in the Aqsacom ALIS mediation platform (see Sections 6 and 7).

5.3

WiMAX Network Interception

Figure 5-4 provides the lawful interception Reference Model for WiMAX. Overall, it
resembles the models for the other wireless network interception models discussed

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above, except that the WiMAX Forum introduced the notion of “Internet Access Points
(IAPs)” to serve as the interface between the network elements and the interception
functions. The IAPs may take the form of Internal Interception Functions, such as those
built into the ASN-GW and routers within the network, or External Interception Functions,
which are implemented using probes. Of importance are the roles of Authentication,
Authorization, and Accounting (AAA) and Home Agent (HA) elements in the interception
processes. AAA information from the CSN, usually extracted by a probe (supplied by
Aqsacom), contains essential IP-to-subscriber mapping information. The Home Agent,
which is contained within the CSN (see Figure 5-4), is used to establish a “home base” for
the subscriber such that when the subscriber roams, packet flow that otherwise would
connect to the subscriber’s home ASN is tunneled by the HA to the ASN in which the
subscriber is visiting. Thus, the HA provides important roaming information about the
subscriber as well as capture of packets that are routed to / from a foreign ASN that the
subscriber is visiting.
WiMAX interception calls for the use of a Charging User Identifier (CUI), which serves as
an alias of the target. The CUI prevents disclosure of the target’s identification as
network elements within the home or visiting network are instructed, by way of the CUI,
to carry out interceptions of the target’s traffic. The mapping of the CUI and target
identity is performed by the AAA entity, and disclosed to the LEA who subsequently uses
the CUI in the LI requests. When intercepting a roaming subscriber, interception takes
place in the visited network in a manner similar to interception in the subscriber’s home
network.

HI1
ASN-GW / ASN

IAP

Mediation
Function

ADMF

HI2
AAA

IAP

IRI

Delivery
Function 2

Mediation
Function

LEA
Monitoring
Center

HI3
HA

IAP

CC

Mediation
Function

Delivery
Function
3

IRI / CC
Administrative

Figure 5-4. Network Reference Model for the interception of WiMAX networks (adapted from [12]).

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5.4

Location-Dependent Interception Issues

The issue of location of the interception target may come into play for two reasons:
1) To track the location of the target in real time as he / she moves about.
Here the use of location information for LI remains rather vague in that no formal
standards have been introduced to formally track the movement of a target for
lawful interception purposes, despite how useful as this information may appear.
This situation has arisen, in part, because of the vagueness of laws in many
jurisdictions concerning the application of mobile phone data for surveillance.
Location-dependent interception can also be hampered because the required
accuracy, typically to within the range of the nearest base station, may not be
adequate to pinpoint the location of the target. Technical means are generally
available to enhance the accuracy of position determination to 50 m or so;
systems that perform such positioning rely on Global Positioning Satellite (GPS),
triangulation methods that apply multiple towers, statistical methods that track
the motion of the target, or any combination of these. Nevertheless, formal LI
procedures incorporating these positioning technologies have yet to be ratified by
standards bodies.
2) To restrict lawful interception only to geographical territories that authorize or
allow it.
Legal complications can arise when the target crosses boundaries controlled by
different LEAs, not all of which have authorized the interception or have the same
interception policies. Consider the case where a given Base Station Controller,
eNode, or equivalent wireless network entity may cover many different
Interception Areas (IAs). When a moving target’s communications must be
intercepted, a check must therefore be made to ensure that the corresponding
LEA initiating the interception can in fact receive intercepted information from
the IA where the target is located at a given point in time. Checks for valid IAs,
when such checks are called for, need to be performed by the LI delivery
functions and other network elements such as the MSC, GMSC, CSCF, and IWF.
There is also the notion of geographic vs. identity-driven interception. The first is when
all subjects at a given location become targets of an LI procedure. This can be useful
when tracking the presence of targets in sparsely populated zones. Identity-driven LI is
the more common form of LI where targets are identified by specific identity information
(e.g., the SIM card’s International Mobile Subscriber Identity or IMSI; the handset’s
International Mobile Equipment Identity or IMEI). In both cases, novel target detection
methods must be employed to include the notion of location in the surveillance.

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6 Aqsacom’s ALIS Mediation Platform
The Aqsacom real time Lawful Interception System, known as ALIS, reflects Aqsacom’s
ongoing philosophy of meeting the challenges of lawful interception in a highly
systematic, low cost manner over networks supporting a diversity of services. The
platform makes the deployment of lawful interception systems easier for the
communications operator, while simplifying the processes of data collection and analysis
for the law enforcement agency (LEA). It also addresses the growing lawful interception
needs and requirements of newly emerging services, including those based on wireless
3G, 4G, broadband IP, satellite, voice-over-IP, and other technologies.
The system’s client/server “multilayered” architecture comprises two functional
elements: ALIS-M for target interception provisioning, and ALIS-D for the mediation and
delivery of interception content (see Figure 6-1). The processes of Mediation, Delivery,
and Provisioning are represented by each layer of the architecture. The vertical
bidirectional arrows represent “technology connectors” that provide the interfaces to
network elements and probes for the interception provisioning and traffic collection.
ALIS-D carries out delivery of the intercepted traffic to the LEA, after national-compliant
interception data formatting. Provisioning of the interceptions is by the LEA or via a
court-mandated procedure. Both ALIS-M and ALIS-D may reside on the same computing
and data collection platform, or they may reside on separate platforms. If necessary,
ALIS-D platforms may be distributed throughout networks depending on the services,
geography, and anticipated surveillance load to be supported.
GSM

UMTS

CDMA

PSTN

WiMAX

VoIP

LTE

Mediation

ALIS-D
LEA

Delivery

ALIS-M

Provisioning

LEA
Figure 6-1. Architecture of the Aqsacom ALIS platform.

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Features and functions of ALIS include:
Provisioning
ALIS-M is responsible for provisioning a lawful interception session. Provisioning falls
under the ADMF (Administrative Management Function), discussed in Figures 5-1
through 5-4 above. Specific tasks of provisioning include start, stop, query and
modification of lawful interception operations, audit, consistency checking, etc. These
tasks are generally invoked by the courts or, in some case, the LEA, and securely
communicated to ALIS, which typically resides within the network operator’s premises.
ALIS’ user-friendly graphical interface allows for the easy automation of many
operational interception tasks, such as the automatic triggering or stopping of an
interception operation at predefined dates and times.
Multi-administration
More than one LEA can independently manage surveillance sessions over one ALIS
platform, even when tracking the same target. All data flows are secure to ensure that
no interception data are leaked between LEAs.
Mediation and Delivery Management
Mediation is carried out by the ALIS-D platform, which gathers data from diverse
intercept points within the network, formats the data, and delivers the information to
the LEA over a secure network (typically a VPN, secure FTP, and ISDN). As discussed in
Section 4, intercept data takes the form of Call Data (otherwise known as Intercept
Related Information) and Content of Communication (Call Content). Both types of data
are delivered via separate channels. The data are also formatted by ALIS-D to conform to
national standards such as CALEA. To ensure reliable real time delivery of interception
information to the LEA, ALIS implements adequate buffering to account for nominal
transmission outages or other unforeseen interruptions between the network operator
and LEA.
Secure Access
Clearly ALIS, as any lawful interception system, must have highly controlled and secure
access allowing for operation only by cleared personnel. Aqsacom takes this point very
seriously, and has incorporated a number of safeguard technologies to assure secure
access. These technologies include smart tokens and biometrics.

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Reliable Operation
ALIS systems can be configured with hot-swappable component parts (e.g., disk drives,
power supplies, CPU cards, network cards, etc.) to assure uninterrupted operation in the
event of component failure. Likewise, multiple ALIS platforms can be configured for
application-level redundancy to enable the switch-over of one ALIS system to another in
the rare event that an ALIS platform fails.
Distributed Operation
One ALIS-M management system can control multiple ALIS-D mediation systems. This
enables the balancing of interception traffic load processing among multiple ALIS-D
systems. One ALIS-M can also control multiple ALIS-D systems that are placed throughout
geographically diverse network points in the CSP’s network
Billing
ALIS can be adapted to provide a variety of billing plans where the network operator
invoices the LEA. These plans include billing on a per-LI session basis, per LI change basis,
flat rate, per special service, and other plans. Likewise, billing can be configured to
facilitate the operation of a LI service bureau, where several network operators share a
common LI infrastructure. This configuration is attractive to those operators that are too
small to invest in LI equipment and who claim that the frequency of LI requests from
LEAs is not sufficient to justify the investment. In this case, billing can be addressed to
the subscribing network operator, or one of many LEAs ordering the interception request.
Alarms, Statistics, Logging
ALIS provides a wide array of alarms (e.g., notification when a session is interrupted),
statistics (number of active interceptions in a given interval in time, utilization of LI
system resources), and logs for tracking of past LI events.
Hardware / Operating System
ALIS makes use of off-the-shelf industrial strength PC hardware. This allows for easy
parts replacement and reduced cost. All software runs under the Windows, Solaris, and
Linux operating systems.

7 ALIS Implementation in 3G / 4G Networks
Figure 7-1 depicts the implementation of ALIS as a mediation platform in a UMTS
network. The network’s interception configuration follows the Interception Reference
Models described in Section 5. Of note are the call data (IRI), call content (CC), and LI
management paths leading between ALIS-D and ALIS-M and the appropriate network
elements and functions. For simplicity, the diagram does not distinguish between the

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use of probes and Internal Interception Functions of the network elements, the
availability of the latter depending on equipment vendor and implementation.
Furthermore, not all of the connections between the ALIS platforms and the network
elements need to occur – this diagram is mainly intended to illustrate the possible
connections. Note that the Law Enforcement Agency (LEA) receives the formatted IRI
and CC interception products from ALIS-D via a VPN, ISDN link, or dedicated line (none of
which are shown). The LEA’s Law Enforcement Monitoring Facility (LEMF) should follow
LI standards to allow acceptance of the CC and IRI data through FTP, ROSE, or TCP/IPbased protocols.
Provisioning of the interceptions typically start as a court order that presents the
interception order to the Network Operator, who then manually enters the interception
parameters into the ALIS-M Graphical User Interface (GUI). In some countries, the LEA is
permitted to remotely enter the interception order directly into ALIS-M, although this is
not standard practice for lawful interception.
Figure 7-2 provides a similar diagram for CDMA2000, where the LI network configuration
is quite similar. As in Figure 7-1, we depict a number of different possibilities for
collecting the intercepted traffic and sending this traffic to ALIS-D.
Figure 7-3 illustrates the use of ALIS in the interception of LTE “4G” networks. Given that
LTE networks can constitute a mix of legacy 2G, 3G, and 4G network architectures and
technologies, it is somewhat difficult to pinpoint a single, representative interception
scheme for LTE networks. Nevertheless, the diagram of Figure 7-3 makes such an
attempt. Following the Interception Reference Architectures of Section 5, the Serving
GW and / or PDN-GW operate as interception traffic collection points for IRI and CC
collection (assuming the use of their Internal Interception Functions, when available). IRI
and CC from legacy subscriber services can be collected from the Evolved Packet Data
Gateway (ePDG). Also indicated is the collection of IRI data, or data that can support the
assembly of IRI data, from the Home Subscriber Server (HSS). Interceptions can also be
conducted at the level of the SGSN when a 2G / 3G network is supported. This would
follow the schema described for 3G UMTS or CDMA networks described in Figures 7-1
and 7-2. Alternatively, interception for these legacy networks could be conducted via the
Serving GW. The operations with the LEA are as described for Figure 7-1.
Figure 7-4 describes how the ALIS platforms can support the interception of WiMAX
networks. CC is typically collected from the Access Service Network Gateway (ASN-GW)
via a probe or from an Internal Interception Function if supported by these gateways.
Interception data may also be collected by the Home Agent, or by probes connected to
the networking supporting the HA. The AAA resources within the CSNs also provide
important information in the assembly of the IRI (e.g., subscriber log-in / log-out and IP
address mappings to the subscriber). The interception of AAA packets is typically
performed with a probe, such as that supplied by Aqsacom. The operations with the LEA
are as described in Figure 7-1.

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Interception products must be delivered from ALIS to the LEA in a highly secure manner.
In the 3G and 4G configuration described above, this delivery is typically over TCP or UDP
sockets connecting ALIS to the LEA’s monitoring facility. In this context, AQSACOM
supports IPSEC IKEv1 or IKEv2 to assure secure delivery of the products. In addition, a
single TCP or multiple TCP links can be applied in the delivery of interception products to
a given LEA. Of course, multiple TCP links would be established when interception
products need to be delivered to more than one LEA. Support of more than one LEA
reflects ALIS’ multi-administration capabilities.
Note implementations of UMTS, CDMA, LTE, and WiMAX networks will vary according to
the CSP’s choice of equipment vendors and the state of the CSP’s network as it evolves
towards more advanced implementations. It is for this reason that all of the network
diagram figures in this White Paper should not be considered as Aqsacom’s advocating
any recommended or fixed LI configuration presented herein.
to IPv6 Networks

to PSTN,
other networks

MRF

MGCF
BTS

HSS
VLR

IMS-MGW

BSC /
RNC

BTS

EIR
CSCF
AS

SGSN
BTS

AUC
SMSC

G-GSN

Switched Voice / Data

TSGW

Packet Data

ALIS-D

Signaling and Control
Content of Communication
Intercept Related Inf ormation
Interception Administration

LEA
to Internet

ALIS-M

Figure 7-1. Role of the Aqsacom ALIS mediation system in the interception of UMTS 3G mobile networks
(Release 5 and later).

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to PSTN,
other networks

MSC
IWF
BTS
HLR
VLR

MRF
BSC

BTS

EIR
AS

PDSN

AUC

BTS

SMSC

FA

AAA
Switched Voice / Data
Packet Data

Signaling and Control
Content of Communication
Intercept Related Inf ormation
Interception Administration

ALIS-D

HA

to Internet

LEA

ALIS-M

Figure 7-2. Role of the Aqsacom ALIS mediation system in the interception of CDMA 3G mobile networks.

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Aqsacom Document No. 100458

To media gateway f or
circuit-switched voice

(optional)
GERAN

SGSN

UTRAN

HSS
IMS

PCRF
Operator IP Services

MME

UE

Serving
GW

eNB

Trusted non-3GPP
IP Access

UE

Trusted / Untrusted non3GPP / 3GPP IP Access

PDN
GW

Internet

ePDG

UE
Switched Voice / Data
Packet Data
Signaling and Control
Content of Communication
Intercept Related Inf ormation

Interception Administration

ALIS-D

Untrusted non-3GPP
IP Access

ALIS-M

UE

LEA

Figure 7-3. Role of Aqsacom ALIS mediation system in the interception of mobile networks based on LTE
architectures containing the Evolved Packet Core (EPC) and legacy wireless networks.

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MS

ASN

BS

ASN
GW

CSN
CSN
HA

BS

HA

ASP Network
or Internet

Another
ASN

AAA

AAA

ASP Network
or Internet

Packet Data
Signaling and Control
Content of Communication
Intercept Related Inf ormation
Interception Administration

ALIS-D
LEA

ALIS-M
Figure 7-4. Role of Aqsacom ALIS mediation system in the interception of WiMAX mobile networks.

8 Summary
This White Paper has presented an overview of 3G and 4G mobile services and methods
supporting the lawful interception of targets subscribing to these services. The LI
processes are delineated by architectures, such as those specified by ETSI, 3GPP, the
WiMAX Forum, and other standards bodies, that facilitate systematic implementations
and provisioning of lawful interception systems. However, challenges to lawful
interception remain, including the need to support a diversity of services, vendor
technologies, wireless networking technologies, voice, and a multiplicty of high speed
speed data services.
Aqsacom’s ALIS mediation platform offers a comprehensive solution to the above
challenges, while conforming to emerging mainstream networking architectures and
lawful interception regulations worldwide:

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No Network Modifications
Designed for seamless integration and interoperation with existing mobile networks, ALIS
interoperates with switching and networking equipment from most major vendors. This
equipment vendor independence ensures that no network modifications are needed to
support cumbersome vendor-dependent lawful interception configurations, and that
networks comprising a mix of vendors can be equally well supported. The result is rapid
lawful interception installation, at reduced costs, while supporting future network
evolutions.
Most Technologies and Services Supported
ALIS operates over UMTS, CDMA2000, LTE and WiMAX networks, as well as IP, wireline,
and legacy 2G (e.g., GSM) networks. Thus, subsribers to a network operator’s mixed
service offer of wireline and mobile 3G / 4G services can be targeted, regardless of what
services they are using. Perhaps more important, operation of the ALIS platform is
essentially identical over the types of services implemented. For example, a common
platform and operator interface can handle the interception of subscribers who make
use of a Network Operator’s wireline, Internet access, GSM, 3G or 4G services. This alows
the operators of the interception system to quickly adapt to new services. As a result,
operator training costs diminish.
No Detection by the Mobile Subscriber
Subscribers are completely unaware of whether or not they are being intercepted,
thanks to Aqsacom’s use of signalling information that is inherently processed within
mobile networks.
Intact LEA Investment
Standards-compliance also means interoperability of the network with the LEA. Thus a
LEA’s investment in analysis tools remains intact as new networks and services come on
line.
ALIS’ complete set of funcitonalities
The comprehensive set of features and capabilities of the ALIS platform ensures easy,
reliable, and secure operation of the system from both the network operator’s and LEA’s
point of view.

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9 References
[1]

CDMA Development Group worldwide statistics (see www.cdg.org)

[2]

UMTS Forum. See http://www.umts-forum.org

[3]

HSPA+ for Enhanced Mobile Broadband, White Paper, Qualcomm Inc., February
2009.

[4]

TD-SCDMA Forum. See http://www.tdscdma-forum.org

[5]

Recommendations from the ITU-R M.1645

[6]

3rd Generation Partnership Project TR 21.905 V6.6.0 (2004-03), “Technical
Specification Group Services and System Aspects; Vocabulary for 3GPP
Specifications (Release 6),” March 2004.

[7]

3rd Generation Partnership Project TS 23.002 V6.4.0, “Technical Specification
Group Services and Systems Aspects; Network architecture (Release 6),” March
2004.

[8]

WiMAX Forum Network Architecture: Architecture Tenets, Reference Model and
Reference Points Base Specification, WiMAX Forum, WMF-T32-001-R015v01, 21
November 2009.

[9]

ETSI Standard ETSI ES 201 671 V2.1.1 (2001-09), “Handover interface for the
lawful interception of telecommunications traffic,” September 2001.

[10]

3rd Generation Partnership Project, Technical Specification 3GPP TS 33.107 V6.0.0
(2003-09), “Lawful interception architecture and functions (Release 6),”
September 2003.

[11]

3rd Generation Partnership Project; Technical Specification Group Services and
System Aspects; 3G Security; Lawful interception architecture and functions, 3GPP
TS 33.107 V8.8.0 (2009-06), June 2009.

[12]

WiMAX Forum Network Architecture: Architecture Tenets, Reference Model and
Reference Points, WiMAX Broadband Access Lawful Intercept: Overview, WiMAX
Forum, WMF-T32-106-R015v01, 21 November 2009.

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