ETSI TS 102 232-3 V3.7.1 (2017-11)

TECHNICAL SPECIFICATION
Lawful Interception (LI);
Handover Interface and
Service-Specific Details (SSD) for IP delivery;
Part 3: Service-specific details for internet access services

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2 ETSI TS 102 232-3 V3.7.1 (2017-11)

Reference
RTS/LI-00150-3
Keywords
access, internet, IP, lawful interception, security,
service
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3 ETSI TS 102 232-3 V3.7.1 (2017-11)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definitions and abbreviations . 8
3.1 Definitions . 8
3.2 Abbreviations . 9
4 General . 10
4.1 Internet Access Service (IAS) . 10
4.2 Target identity and IP address . 10
4.3 Lawful Interception requirements . 11
4.3.0 Introduction. 11
4.3.1 Target identity . 11
4.3.2 Result of interception . 11
4.3.3 Intercept related information messages. 12
4.3.4 Time constraints . 13
4.3.5 Preventing over and under collection of intercept data . 13
5 System model . 13
5.1 Reference network topologies . 13
5.1.0 Introduction. 13
5.1.1 Dial-up access . 14
5.1.2 xDSL access. 15
5.1.3 Cable modem access . 16
5.1.4 IEEE 802.11 Access (with Wireless LAN profile) . 16
5.2 Reference scenarios . 17
5.2.1 Logon . 17
5.2.2 Multi logon . 17
5.2.3 Multilink logon . 17
5.2.4 IP transport. 17
5.2.5 Logoff . 18
5.2.6 Connection loss . 18
6 Intercept Related Information (IRI) . 19
6.1 IRI events . 19
6.2 HI2 attributes . 20
6.2.0 List of HI2 attributes . 20
6.2.1 Use of targetIPAddress, additionalIPAddress and otherTargetIdentifiers fields . 21
6.2.2 Use of location field . 22
7 Content of Communication (CC) . 22
7.1 CC events . 22
7.2 HI3 attributes . 22
8 ASN.1 for IRI and CC . 22
Annex A (informative): Stage 1 - RADIUS characteristics . 28
A.1 Network topology . 28
A.1.0 RADIUS deployment options. 28
A.1.1 RADIUS server . 28
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4 ETSI TS 102 232-3 V3.7.1 (2017-11)
A.1.2 RADIUS proxy . 29
A.2 RADIUS service . 30
A.2.1 Authentication service . 30
A.2.2 Accounting service . 30
A.2.3 IPv6 . 31
A.3 RADIUS protocol . 31
A.3.1 Authentication protocol . 31
A.3.2 Accounting protocol . 32
A.4 RADIUS main attributes . 32
A.5 RADIUS interception . 33
A.5.0 Introduction . 33
A.5.1 Collecting RADIUS packets. 33
A.5.2 Processing RADIUS packets . 33
A.5.2.1 Mapping events to RADIUS packets . 33
A.5.2.2 Functional model . 34
A.5.2.3 RADIUS spoofing . 38
A.5.2.4 Mapping of Acct-Terminate-Cause to endReason . 38
A.5.2.5 Use of Event-Time . 39
A.5.2.6 Use of targetIPAddress, additionalIPAddress and otherTargetIdentifiers fields . 39
A.5.3 Mapping RADIUS on the IRI structure . 39
Annex B (informative): Stage 1 - DHCP characteristics . 43
B.1 Network topology . 43
B.2 DHCP service . 43
B.3 BOOTP protocol . 44
B.4 DHCP protocol . 44
B.4.0 Overview . 44
B.4.1 Address assignment . 46
B.4.2 Message transmission and relay agents . 46
B.4.3 Security and authentication . 46
B.5 DHCP main attributes . 46
B.6 DHCP interception . 47
B.6.1 Introduction . 47
B.6.2 DHCP packets . 48
B.6.3 State machine . 48
B.6.3.0 Overview . 48
B.6.3.1 Mapping DHCP packets to events . 49
B.6.3.2 Timers and administrative events . 49
B.6.3.3 State information . 49
B.6.3.4 State machine diagram . 50
B.6.4 Mapping DHCP on the IRI structure . 50
Annex C (informative): IP IRI interception . 52
C.1 Introduction . 52
C.2 Requirements . 52
C.3 Proposed implementation . 52
Annex D (informative): TCP and UDP IRI interception . 53
D.1 Introduction . 53
D.2 Requirements . 53
D.3 HI2 requirements . 53
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5 ETSI TS 102 232-3 V3.7.1 (2017-11)
D.4 HI3 requirements . 54
D.5 General requirements . 54
Annex E (informative): Bibliography . 55
Annex F (informative): Change Request history . 56
History . 59

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6 ETSI TS 102 232-3 V3.7.1 (2017-11)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
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ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Lawful Interception (LI).
The present document is part 3 of a multi-part deliverable. Full details of the entire series can be found in part 1 [2].
The ASN.1 module is also available as an electronic attachment to the original document from the ETSI site (see
clause 8 for more details).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
The intention of the present document has been to follow the advice given at ETSI meetings in all cases.
The present document focuses on intercepting IP data in relation to the use of Internet Access Services (IAS) and is to
be used in conjunction with ETSI TS 102 232-1 [2]. In the latter document the handing over of the intercepted data is
described.
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7 ETSI TS 102 232-3 V3.7.1 (2017-11)
1 Scope
The present document contains a stage 1 description of the interception information in relation to the process of binding
a "target identity" to an IP address when providing Internet access and a stage 2 description of when Intercept Related
Information (IRI) and Content of Communication (CC) need to be sent, and what information it needs to contain.
The study includes but is not restricted to IRI based on application of Dynamic Host Configuration Protocol (DHCP)
and Remote Authentication Dial-in User Service (RADIUS) technology for binding a "target identity" to an IP address
and CC for the intercepted IP packets.
The definition of the Handover Interface 2 (HI2) and Handover Interface 3 (HI3) is outside the scope of the present
document. For the handover interface is referred to ETSI TS 102 232-1 [2].
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI TS 101 671: "Lawful Interception (LI); Handover interface for the lawful interception of
telecommunications traffic".
NOTE: Periodically ETSI TS 101 671 is published as ETSI ES 201 671. A reference to the latest version of the
TS as above reflects the latest stable content from ETSI/TC LI.
[2] ETSI TS 102 232-1: "Lawful Interception (LI); Handover Interface and Service-Specific Details
(SSD) for IP delivery; Part 1: Handover specification for IP delivery".
[3] IETF RFC 1122: "Requirements for Internet Hosts - Communication Layers".
[4] IETF RFC 1570: "PPP LCP Extensions".
[5] IETF RFC 1990: "The PPP Multilink Protocol (MP)".
[6] IETF RFC 2131: "Dynamic Host Configuration Protocol".
[7] IETF RFC 7542: "The Network Access Identifier".
[8] IETF RFC 2865: "Remote Authentication Dial In User Service (RADIUS)".
[9] IETF RFC 2866: "RADIUS Accounting".
[10] IETF RFC 3046: "DHCP Relay Agent Information Option".
[11] IETF RFC 3118: "Authentication for DHCP Messages".
[12] IETF RFC 3396: "Encoding Long Options in the Dynamic Host Configuration Protocol
(DHCPv4)".
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8 ETSI TS 102 232-3 V3.7.1 (2017-11)
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[13] IEEE 802.11 (ISO/IEC 8802-11): "IEEE Standard for Information technology -
Telecommunications and information exchange between systems - Local and metropolitan area
networks - Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications".
[14] Recommendation ITU-T X.680: "Information technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation".
[15] IETF RFC 2132: "DHCP Options and BOOTP Vendor Extensions".
[16] ISO 3166-1: "Codes for the representation of names of countries and their subdivisions --
Part 1: Country codes".
[17] IETF RFC 2869: "RADIUS Extensions".
[18] IETF RFC 3162: "RADIUS and IPv6".
[19] IETF RFC 4818: "RADIUS Delegated-IPv6-Prefix Attribute".
[20] IETF RFC 6911: "RADIUS Attributes for IPv6 Access Networks".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TR 102 205: "Methods for Testing and Specification (MTS); UML 2.0 action syntax
feasibility study".
[i.2] IEEE 802.1X-2001TM: "IEEE Standards for Local and Metropolitan Area Networks: Port-Based
Network Access Control".
[i.3] draft-ietf-dhc-agentopt-radius-04.txt: "RADIUS Attributes Sub-option for the DHCP Relay Agent
Information Option".
[i.4] IANA bootp parameters.
NOTE: Available at http://www.iana.org/assignments/bootp-dhcp-parameters.
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in ETSI TS 102 232-1 [2] and the following
apply:
access provider: Communications Service Provider (CSP), providing access to a network
NOTE: In the context of the present document, the network access is defined as IP based network access to the
Internet.
access service: set of access methods provided to a user to access a service and/or a supplementary service
NOTE: In the context of the present document, the service to be accessed is defined as the Internet.
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9 ETSI TS 102 232-3 V3.7.1 (2017-11)
accounting: act of collecting information on resource usage for the purpose of trend analysis, auditing, billing, or cost
allocation
authentication: property by which the correct identity of an entity or party is established with a required assurance
authorization: property by which the access rights to resources are established and enforced
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AAA Authentication, Authorization and Accounting
ACK Acknowledge
ADSL Asymmetric Digital Subscriber Line
ANP Access Network Provider
AP Access Provider
ARP Address Resolution Protocol
ASN.1 Abstract Syntax Notation One
ATM Asynchronous Transfer Mode
BOOTP BOOTstrap Protocol
CC Content of Communication
CHAP Challenge Handshake Authentication Protocol
CIN Communication Identity Number
CMTS Cable Modem Termination System
CPE Customer Premises Equipment
CSP Communications Service Provider (covers all AP/NWO/SvP)
DHCP Dynamic Host Configuration Protocol
DNS Domain Name System
DoS Denial of Service
DSL Digital Subscriber Line
DSLAM Digital Subscriber Line Access Multiplexer
FQDN Fully Qualified Domain Name
GWR GateWay Router
HI1 Handover Interface 1 (for Administrative Information)
HI2 Handover Interface 2 (for Intercept Related Information)
HI3 Handover Interface 3 (for Content of Communication)
IANA Internet Assigned Numbers Authority
IAP Internet Access Provider
IAS Internet Access Service
IETF International Engineering Task Force
IF Interception Function
IIF Internal Interception Function
IP Internet Protocol
IPCC Internet Protocol Call Content
IPFIX Internet Protocol Flow Information eXport
IPSEC Internet Protocol Security
IRI Intercept Related Information
ISDN Integrated Services Digital Network
ISP Internet Service Provider
LAN Local Area Network
LCP Link Control Protocol
LEA Law Enforcement Agency
LEMF Law Enforcement Monitoring Facility
LI Lawful Interception
MAC Media Access Control
MF Mediation Function
NA Not Applicable
NAS Network Access Server
NIC Network Interface Controller
NWO NetWork Operator
OID Object IDentifier
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OSI Open Systems Interconnection
PAP Password Authentication Protocol
PC Personal Computer
PDA Personal Digital Assistant
PDU Packet Data Unit
POP Point of Presence
PPP Point-to-Point Protocol
PPPoA Point-to-Point Protocol over ATM
PPPoE Point-to-Point Protocol over Ethernet
PSTN Public Switched Telephone Network
QoS Quality of Service
RADIUS Remote Authentication Dial-In User Service
SLIP Serial Line Interface Protocol
SvP Service Provider
TCP Transmission Control Protocol
TCP/IP Transmission Control Protocol/Internet Protocol
TLV Type-Length Value
UDP User Datagram Protocol
WAN Wide Area Network
WINS Windows Internet Name Service
4 General
4.1 Internet Access Service (IAS)
An Internet Access Service (IAS) provides access to the Internet to end users via a modem connected to a telephone,
cable or wireless access network owned by a NetWork Operator (NWO). The IAS is typically provided by an Internet
Access Provider (IAP) or Internet Service Providers (ISP), where an ISP also provides supplementary services such as
E-Mail, Chat, News, etc. For the remainder of the present document, the provider of the Internet Access Service (IAS)
will be referred to as IAP and although NWO and IAP may be the same party, in all figures in the present document,
they are depicted as separate entities.

Customer
Access
IAP
Premises
Internet
Network Network
Equipment
(CPE)
Customer NWO IAP/ISP
Figure 1: Internet access
The customer typically connects to the IAP via a Telco or cable company owned access network, such as the
PSTN/ISDN telephony network for dial-up and xDSL access, the cable-TV network for cable modem access or
alternatively a IEEE 802.11 [13] Wireless LAN.
The service provided by the IAP is no more and no less than to provide a user with a valid IP address for transporting
and receiving data over an IP based network and to provide transit access to the Internet for this data.
4.2 Target identity and IP address
Before the IAP can provide a user with a valid IP address, there is a need for Authentication, Authorization and during
or at the end of the communication session there is a need for Accounting.
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11 ETSI TS 102 232-3 V3.7.1 (2017-11)
In order to perform these functions, the IAP may deploy equipment in its network that implements an Authentication,
Authorization and Accounting (AAA) protocol such as RADIUS. The other protocol mentioned in the scope
declaration, DHCP, is not really an AAA protocol, since it does very limited authentication and no authorization or
accounting. DHCP can assign IP addresses and provide network configuration information to the user and is therefore
often used in combination with RADIUS or other (proprietary) equipment.
When a user is authenticated and authorized, the IAP will assign an IP address to the user. The assignment of the IP
address can be performed by using RADIUS, DHCP or a combination of the two. In the latter case, often the RADIUS
server will act as a client to the DHCP server, where the DHCP server assigns the IP address and the RADIUS server
forwards the information towards the user. The user will use the assigned IP address to communicate over the Internet
and therefore, for the duration of the session, traffic from and to this user can be identified by means of this IP address.
In some cases (e.g. dial-up access), the Network Access Server (NAS) may assign the IP address to the user; either from
a local IP address pool or by using DHCP and does not use RADIUS authentication for IP address assignment.
From an LI perspective, the moments of assignment and deassignment of the IP address and the protocol used for it are
of interest. It is at the moment of assignment, and only at that particular moment, that the target identity can be tied to a
dynamically assigned IP address, which can then further be used to intercept IP traffic from the particular user. At the
moment of deassignment, interception of IP data based on that particular IP address shall stop immediately, since the IP
address may be handed out to another user shortly after.
4.3 Lawful Interception requirements
4.3.0 Introduction
This clause lists the requirements for Lawful Interception. These requirements are derived from higher-level
requirements listed in ETSI TS 101 671 [1] and ETSI TS 102 232-1 [2] and are specific to Internet Access Services
(IAS). These requirements focus on both the administrative part of Internet access for delivery over HI2 as well as
capturing traffic for delivery over HI3.
4.3.1 Target identity
Where the special properties of a given service, and the justified requirements of the LEAs, necessitate the use of
various identifying characteristics for determination of the traffic to be intercepted, the provider (CSP) shall ensure that
the traffic can be intercepted on the basis of these characteristics.
In each case the characteristics shall be identifiable without unreasonable effort and shall be such that they allow clear
determination of the traffic to be intercepted.
The target identity will be dependent on the access mechanism used and the parameters available with the AP. The
target identity could be based on:
a) Username or Network Access Identifier (as defined in IETF RFC 7542 [7]).
b) IP address (IPv4 or IPv6).
c) Ethernet address.
d) Dial-in number calling line identity.
e) Cable modem identifier.
f) Other unique identifier agreed between AP and LEA.
The target identity shall uniquely identify the target in the provider's network. Investigations prior to the interception
might involve other identifiers such as a DNS name (Fully Qualified Domain Name (FQDN)). Further study may yield
more types of target identity.
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4.3.2 Result of interception
The network operator, access provider or service provider shall provide Intercept Related Information (IRI), in relation
to each target service:
a) When an attempt is made to access the access network.
b) When an access to the access network is permitted.
c) When an access to the access network is not permitted.
d) On change of status (e.g. in the access network).
e) On change of location (this can be related or unrelated to the communication or at all times when the apparatus
is switched on).
The IRI shall contain:
a) Identities used by or associated with the target identity (e.g. dial-in calling line number and called line number,
access server identity, Ethernet addresses, access device identifier).
b) Details of services used and their associated parameters.
c) Information relating to status.
d) Timestamps.
Content of Communication (CC) shall be provided for every IP datagram sent through the IAP's network that:
a) Has the target's IP address as the IP source address.
b) Has the target's IP address as the IP destination address.
The CC Content of communication shall contain:
a) A stream of octets for every captured datagram, containing a copy of the datagram from layer 3 upwards.
NOTE: Due to the possibility of IP source address spoofing, the fact that an intercepted packet has the target's IP
address as the IP source address does not guarantee that the packet was transmitted by the target;
i.e. an intercept in place at the interface connected to the target may not include packets originating from
other users spoofing the target's IP address and will not include packets from the actual target that contain
a spoofed IP address.
4.3.3 Intercept related information messages
Intercept Related Information (IRI) shall be conveyed to the LEMF in messages, or IRI data records, respectively. Four
types of IRI records are defined:
1) IRI-BEGIN record at the first event of a communication attempt, opening the IRI transaction.
2) IRI-END record at the end of a communication attempt, closing the IRI transaction.
3) IRI-CONTINUE record at any time during a communication attempt within the IRI transaction.
4) IRI-REPORT record used in general for non-communication related events.
For a description of the use and purpose of the various IRI records refer to ETSI TS 102 232-1 [2].
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13 ETSI TS 102 232-3 V3.7.1 (2017-11)
4.3.4 Time constraints
The delays for generating the Intercept Related Information (IRI) will only be caused by the access protocol handling
and the automated forwarding of this information to the delivery function.
The interception that takes places as a result of the identification of the target in the access service will experience no
unnecessary delay. The delay will only be caused by the access protocol handling and the automated forwarding of this
information to the interception function(s).
4.3.5 Preventing over and under collection of intercept data
Measures shall be taken to:
1) enable timely detection of system, network or software failures that may cause the interception system to over
or under collect data;
2) take appropriate action to prevent further over or under collection; and
3) report on the anomaly to allow for corrective action by the LEA.
NOTE 1: The terms over and under collection refer to either wrongfully including data that is not part of the
intercept or not capturing data that should have been part of the intercept.
If an interception is started based on an IP-address binding event that contains session-timeout information and at the
time of the expected session-timeout no explicit session-termination event has been captured, the interception shall be
stopped and the situation shall be reported upon.
If an IP-address binding event is captured that contains an IP address already in use in an active intercept, but for a
different user, the intercept shall be stopped and the situation shall be reported upon.
NOTE 2: Due to various kinds of failures or delays in the LI infrastructure, the event indicating the logoff of a
target could be missed by the Interception function. The actual logoff would release the IP address for
reassignment to another user, which would lead to a serious kind of over collection.
5 System model
5.1 Reference network topologies
5.1.0 Introduction
This clause describes a number of reference network topologies, typically used for Internet access over various types of
access networks.
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5.1.1 Dial-up access
Internet access over a switched telephony network is typically referred to as dial-up access. Figure 2 shows the principal
equipment involved in this kind of Internet access.
IAP
PSTN
IP-enabled ("V.90")
Internet
NAS
network
ISDN
device modem
AAA
IAP/ISP
Customer NWO
Figure 2: Dial-up access
The CPE for dial-up access typically consists of a computer, laptop or PDA that is equipped with a modem connected to
the regular telephone network. Via this modem, the telephone number of the Network Access Server (NAS) of the IAP
is dialled. The NAS answers the call and the NAS and the end-user typically establish a Point-to-Point Protocol (PPP)
connection. Due to the distributed nature of dial-up access, a user may dial into any NAS in the network.
Once the PPP connection is established, the NAS will request the user to identify himself and to provide a password.
The NAS will then request the AAA server in the IAP infrastructure (for dial-up access typically a RADIUS server) to
perform the authentication based on the provided username and password. Additionally, the AAA server will check
whether the user is authorized to use the Internet Access Service (IAS). If so, the AAA server may provide the NAS
with an IP address that is to be used by the user. In other cases, the NAS allocates the IP address from a locally
configured pool of addresses and the AAA server does not know the IP address at the time of authentication.
Next, the NAS informs the user about the assigned IP addresses and other network configuration information, such as
the address of the DNS server and/or the address of the gateway to the Internet. The CPE can now set-up its IP protocol
stack and establish IP based communication with the Internet.
After the NAS has established a PPP session with the CPE, the NAS may provide the Accounting server with
information indicating the start of the session and the parameters in use for the session (e.g. IP addresses, NAS address).
The Accounting server may be a physically separate server from the Authentication/Authorization server. In the case in
which the NAS assigns IP addresses from a local pool, this is the first time the IP addresses assigned to the target is
known externally to the NAS.
At the end of the session, either when the user logs off or when the connection to the NAS is lost, the NAS will provide
the Accounting server with details regarding usage of the Internet connection, e.g. duration, bytes sent and received, etc.
This information can be used for accounting purposes.
From an LI perspective, the assignment of IP addresses, in relation to the usernames they are assigned to, as well as the
moment of deassignment, i.e. the exchange of accounting information, are of interest.
NOTE: Many IAPs also support tunnelling the PPP session from the NAS to a home gateway either at another
location within the IAP or residing on another network (e.g. another IAP or an enterprise). The standard
protocol used to support this is Layer 2 Tunnelling Protocol which tunnels the PPP frames from the NAS
to the home gateway. Proprietary tunnelling techniques might also be used based on the service provider.
Many of the technologies described in the present document may be used to support the tunnelling service
(e.g. RADIUS); however, since this service is not an Internet Access Service (IAS) as defined in the
present document, it is outside the scope of the present document.
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15 ETSI TS 102 232-3 V3.7.1 (2017-11)
5.1.2 xDSL access
Internet access over the local loop by means of using specialized equipment for achieving a high bandwidth over copper
wire is commonly referred to as xDSL Access. There is great variety of possible architectures and technologies that can
be applied for realizing an xDSL network. Therefore, figure 3 only shows the principal equipment involved in this kind
of Internet access.
PSTN
IAP
Router / xDSL
IP-enabled Edge
GWR
Internet
DSLAM
local
network
Bridge modem router
device
loop
AAA
Customer IAP/ISP
NWO
Figure 3: xDSL access
The CPE can consist of a single IP enabled device which is connected to an xDSL modem or, in order to support
multiple IP enabled devices to share the xDSL connection, to a router or bridge that is connected to an xDSL modem.
The modem is connected to the copper wire of the telephone network, the local loop. In the telephone switch, this wire,
and wires from other xDSL lines, are connected to the DSL Access Multiplexer (DSLAM). By utilizing frequencies
above the telephone bandwidth, the xDSL modem and the DSLAM can encode more data to achieve a higher
bandwidth than would otherwise be possible in the restricted frequency range of a PSTN network.
For large scale xDSL infrastructures, two main approaches are used for protocol layering; PPP over ATM (PPPoA) and
PPP ov
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