VoLTE Lawful Interception

VoLTE – Introduction

VoLTE Lawful Interception has been the main telecom service since the inception of mobile telephony. It is still relevant and is increasing as well in this day and age of mobile data and IP-based telecom technology. In Evolved Packet System (EPS), which is completely IP-based technology, delivering voice service can only be realized using either Circuit-Switched Fallback (CSFB) or Voice over LTE (VoLTE).
While CSFB offers voice services to LTE interception users without utilizing IMS by temporarily moving the user from the LTE network to a legacy network i.e. 2G/3G system which can then serve voice calls over a circuit-switched network. Whereas VoLTE is a digital packet voice service that is delivered over IP via an LTE access network utilizing IMS (IP Multimedia Subsystem) technology.

VoLTE: Lawful Interception

Lawful Interception of VoLTE is a complex process as a VoLTE call invokes two systems, i.e. EPC and IMS. Moreover, there are multiple network elements in these two systems that can provide IRI and CC of the target. PertSol offers two different approaches for the interception of VoLTE calls depending upon the MNO’s network and requirements:

i. By Interception of EPC nodes
ii. By Interception of both EPC and IMS nodes

Lawful Interception through EPC Nodes

MNO’s which already has an existing LI solution for its IMS system can use this approach. In this approach, PertSol will provide its LI solution (iNterceptor) which will intercept the EPC traffic (including VoLTE) by integrating with the EPC nodes (Intercept Access Points) like MME, SGW and PGW. It also facilitates the VoLTE interception for inbound roamers using S8HR interception as explained in below section. 

Lawful Interception through EPC & IMS Nodes

PertSol iNterceptor can also be implemented as a combined LI solution for both IMS and LTE network of an MNO. This approach will involve integration with IMS IAPs in addition with the EPC IAPs explained in the first approach.

The IMS access points that will be integrated for VoLTE interception are CSCF, BGF, TAS and MGW.

Lawful Interception: VoLTE Roaming Scenario

VoLTE roaming can be carried out using two ways, as defined in 3GPP specifications:

i. Local Breakout (LBO): Local Breakout mechanism requires the visited network to have an IMS system in its network. In LBO the roaming user is connected to the PDN-GW of the visited network and all the traffic is transported via visited network’s PDN-GW, without using the PDN-GW of home network.

ii. S8 Home Routing (S8HR): S8HR makes use of the home network PDN-GW and does not require the visited network to have an IMS system. The roaming user traffic is to the PDN-GW of home network, via S-GW of visited network, which then forwards it to the IMS network for completing the call.

S8 Home Routing (S8HR) is the preferred VoLTE roaming architecture of most of the mobile network operators as it does not dependent on the IMS system of the visited network. PertSol offers two ways of intercepting VoLTE calls for inbound roamer in S8HR roaming scenario:

i. Active Interception – By using BBIFF functionality of SGW

ii. Passive Interception – By intercepting S8 interface

S8HR Active Interception

PertSol iNterceptor is capable of intercepting the VoLTE calls of inbound roamer by providing LI Mirror IMS State Function (LMISF). For active interception of VoLTE calls, the SGW shall support BBIFF functionality (Bearer Binding Intercept and Forward Function). This approach is as per 3GPP TS 33.107 specifications and the recommendations of GSMA PRD IR.65. It requires implementation of proprietary interfaces Xia / Xib. Moreover this approach can also be extended to 5G with minor changes.

S8HR Active Interception
S8HR Passive Interception

In S8HR Passive Lawful Interception, PertSol uses its iNteliProbe which functions as an LI Access Point and investigates the traffic data tapped from the S8 interface between S-GW of the visited network and PDN-GW of the home network. It requires passive taps at the appropriate point in the VPLMN to duplicate the complete S8 traffic. This approach can also be used for 5G (N9 interface) or 5G Interception.

S8HR Passive Interaction
iNterceptor Benefits

Lawful Interception

Lawful Interception System

PertSol iNterceptor is a Lawful Interception system unified for network operators and telecom service providers which is fully compliant with international standards and has a proven track record. It is a complete solution that is capable of handling both circuit switch and packet switch traffic from both legacies as well as the latest telecom technologies including 2G,OTT Interception,3G, 4G, 5G, IMS,5G Interception, NGN, PSTN, IPLC, IFMS, PS Interception, DPI Interception etc.

The core purpose of iNterceptor is to intercept the traffic and convert intercepted traffic into a format suitable for delivery to National Authorities or Law Enforcement agencies, over a secure network. It can also retain the intercepted traffic for future use by the LEAs compliant with international standards and has a proven track record.

iNterceptor along with PertSol iNteliProbe forms one of the most comprehensive interception solutions available in the market. PertSol iNteliProbe supports capturing 100% of traffic, decoding the traffic from layer 2 to layer 7, and then either transmittal of interception of data and decoded data to the LEAs or its storage for future use. The probes actively support the capture and reconstruction of all non-encrypted IP, and voice traffic this includes reconstruction and capture of VoIP calls, TDM calls, and IP traffic reconstruction.

iNterceptor Lawful Interception is designed to change and adapts as per the latest network upgradation and technologies. It protects investments through its modular setup, accommodating network expansion as well as network changes. It can also integrate with existing Lawful Interception vendors incorporating it into a centrally managed unified solution.

5G Ready Solutions

PertSol works closely with the leading telecom company, MNOs, network equipment providers, and regulators to evolve its products as per the technology and market trends. In its bid to keep track of the market and latest technology, PertSol has upgraded its product as per the 5G standards released by 3GPP in its Release 15. PertSol iNterceptor has also been upgraded to fulfill lawful interception system requirements for both standalone and non-standalone 5G networks.

Technical Specification:

  • Supported Telecom Network & Services:
    • XDSL, Cable, IPLC
    • Email (POP3, SMTP, IMAP, Webmail)
    • IPv4 & IPv6
    • VoIP (SIP, RTP, H.323, SCCP)
    • PoC (Push-to-talk over Cellular)
    • SMS, MMS, Voicemail
    • WLAN
    • IoT, M2M

Services Data Voice Video Call
Messenger Chat SMS VoIP Email Social MediaNetworkPSTN4GIMSIMS2G/3G5GNGNBroadband

Multi-Vendor Support

iNterceptor has an extensive list of modules to support direct integration with major versions of network elements. These modules have proven their worth and stability in the field. PertSol maintains an active relationship with these vendors to keep up to date with new versions of the network equipment, verified with an IOT (Interoperability Test) in the vendor lab where possible. iNterceptor supports all the major NEPs of the world like Nokia, Ericsson, Cisco, Brocade, Alcatel Lucent, ZTE, Huawei, Samsung, Juniper, Genband, Comverse, Arris, Nortel, Open wave, Qualcomm, and many more.

Supported Network Interface

    • Ethernet (1GE, 10GE, 40GE)
    • SDH (STM-1)
    • TDM (E1/T1/J1)
    • ATM
    • ISDN
    • SS7 Interfaces

Output & Delivery Format

iNterceptor supports the following output and delivery formats.

Technical Standards
Some of the main LI standards that iNterceptor complies with are mentioned below:


    • TS 101 671 (Voice)
    • TS 101 331 (Generic)
    • TS 102 232-1, TS 102 232-2, TS 102 232-3, TS 102 232-4, TS 102 232-5, TS 102 232-6
    • TS 103 120
    • TR 103 690 (e-Warrant)


    • J-STD-025A & J-STD-025B
    • T1.724
    • T1.IAS
    • TIA-1066
    • ATIS-10021


    • TS 33.106
    • TS 33.107
    • TS 33.108
    • TS 33.126
    • TS 33.127
    • TS 33.128

Packet Cable 1.5 & 2.0

    • PKT-SP-EM-I08
    • TS 33.107
    • PKT-SP-ESP1.5
    • PKT-SP-ES-DCI-I01
    • PKT-SP-ES-INF-I02
    • CBIS

iNterceptor: Benefits

iNterceptor is capable of handling networks with very high throughput requirements. It can handle multiple 100 Gbps links and is capable of selecting required traffic from these links. PertSol iNteliProbe has been tested and implemented for traffic up to 40 Gbps per probe. The integrity check mechanism periodically checks the network elements and if required corrects the erroneous states. It will query the network element for the placed intercepts and add missing intercepts, remove invalid intercepts, etc. This mechanism is used to detect and correct both network flaws as well as tampering with the interception solution. In case of correction of an erroneous state, this will be notified to the operator.

iNterceptor has a vast range of Input/Output adapters which makes it compatible with all the available access technologies and network equipment of all the major equipment providers. If required, customer-specific Input or Output adapters can be developed.
iNterceptor allows configuration of multiple Input and Output Adapters to be combined in one system and support any situation like inter-working between different technologies or scaling up to include latest technology. Due to iNterceptor’s modularity, telecom operators can leverage their investment for a longer duration and scale up their network with more flexibility.

Due to its design philosophy, iNterceptor can support hybrid networks with equipment from different vendors on same server. When networks grow or change, iNterceptor can easily be extended to cater for the growth in traffic volumes or new types of network elements. Unified solution for all interception requirements of a service provider which is compliant to international standards like 3GPP, ETSI, ATSI, ANSI, CALEA and others. It also complies with local LI regulations of many countries across the world.

Lawful Interception vendors provide a proven and mature solution that continues to benefit from functional enhancement and feature evolution. It has been deployed in varied networks, enabling TSPs / Law Enforcement Agencies to benefit.