Internet DRAFT - draft-maglione-pana-acct-time
draft-maglione-pana-acct-time
PANA Working Group
Internet Draft R. Maglione
Expires: December, 2006 M. Ullio
V. Vercellone
Telecom Italia
June 2006
Problem Statement for a time-basis accounting in an "always-on"
Broadband Network access scenario
draft-maglione-pana-acct-time-00.txt
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Copyright (C) The Internet Society (2006).
Abstract
Two main models for providing DSL Internet Access are currently
available: one is based on PPP protocol and provides flexible AAA
(Authentication, Authorization and Accounting) mechanism, dynamic IP
address assignment and is generally used by Internet Service
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Problem Statement for a time-basis accounting June 2006
Providers (ISPs) for temporary or semi-permanent Broadband
connections which may be billed on a time-basis. The other is based
on DHCP or static IP addressing, generally lacks flexible AAA
mechanism and is most of the time associated to flat-rate broadband
connections. The evolution of services and access techniques may
quickly lead to a wide deployment of non-PPP based access model
associated with flat rates charge, providing "always-on" Internet
connections. However, even in this scenario, ISPs may still require
that some services are billed on a time basis. This Internet Draft
describes the problem typically faced by ISPs when a time-basis
billing model is required for non-PPP Broadband Connections. It also
introduces requirements that a possible solution should satisfy in
order to address the problem. Moreover the document covers a brief
analysis of the Status of Art.
Table of Contents
1. Specification of Requirements..................................2
2. Introduction...................................................2
3. Terminology....................................................3
4. Problem Statement..............................................4
5. Requirements of the Solution...................................5
6. Brief analysis of current possible approaches..................6
6.1 Web Portal based approach..................................6
6.2 DHCP based approach........................................7
6.3 PANA based approach........................................7
7. Conclusions....................................................8
8. Security Considerations........................................8
9. IANA Considerations............................................8
10. References....................................................8
Acknowledgments...................................................9
Author's Addresses................................................9
Intellectual Property Statement...................................9
Disclaimer of Validity...........................................10
Copyright Statement..............................................10
1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
2. Introduction
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Traditionally access to data networks typically involves the
establishment of logical connections realized through PPP [1] (Point-
to-Point Protocol) protocol sessions. This applies in particular for
clients connected on copper lines that use xDSL-type (Digital
Subscriber Line) transmission techniques, called Broadband Access
techniques, to connect to the Internet.
In such scenario, access functionalities are provided by edge
routers, called BRAS (Broadband Remote Access Servers), that
terminate the access connections and perform the routing functions
for the client traffic. The user terminal connects via DSLAM (Digital
Subscriber Line Access Multiplexer) to a broadband access network in
order to reach dedicated BRAS edge routers that provide Internet
connection.
------------- ------- ------
| User Terminal | ---- | DSLAM | --- | BRAS | --- | Internet |
------------- ------- ------
An increasing interest is being currently witnessed for the adoption
of "always-on" type access models; in that case, the terminal has a
"steady" connectivity to the network. The evolution towards an
increasing use of the "always-on" models is also motivated by the
need of an integrated offer, on xDSL broadband access lines, of VoIP
(Voice over IP) and video communication services; in fact, for this
type of applications, the terminal must always be on-line and
reachable from the network.
In this scenario Internet Service Providers are focused on providing
Triple-Play services (a bundle of voice, data and video services)
built on top of a convergent network infrastructure based on the IP
protocol.
The idea to build a single convergent network infrastructure to offer
heterogeneous services is mainly driven by a cost reduction objective
that an integrated and flexible network could achieve.
However the evolution toward a multi-service network will require new
mechanism to support different charging and accounting policies
according to different service requirements and access methodologies.
3. Terminology
Session:
a generic context that is created for every user who
interacts with the edge router device. Various types of
sessions may be defined, depending on the packet types that
are being handled by the session. In this problem statement
the term session refers namely to an IP session. This is a
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Layer 3 session because it includes all IP packets exchanged
with a subscriber device at a single IP address.
Broadband Remote Access Server (BRAS):
the edge router device that provides Internet connection.
ISP: Internet Service Provider (ISP):
a company that supplies Internet connectivity to home and business
customers.
Public Switched Telephone Network (PSTN):
the established international telephone system carrying voice data
over circuit switched connections.
Digital Subscriber Line (DSL):
a technology for bringing high-bandwidth information to homes and
small businesses over ordinary copper PSTN lines. The widely used
term xDSL refers to different variations of DSL, such as ADSL,
HDSL, VDSL and SDSL.
Network Access Provider (NAP):
a service provider that provides physical and link-layer
connectivity to an access network it manages.
Walled Garden:
in this context, the term is used to designate an environment
allowing to control the access from the users to a restricted set
of network resources, e.g. Web content and services.
4. Problem Statement
DSL access to the Service Provider network is currently based on
logical links built using PPP protocol.
This model is usually called "virtual dial-up" because it simulates
the traditional narrowband connection originally built by using modem
devices connected to PSTN lines.
The transition to the "virtual dial-up" technique happened smoothly
for two main reasons: it was based on standard and widely deployed
protocols like PPP and RADIUS [2] (and therefore could easily be
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Problem Statement for a time-basis accounting June 2006
integrated by ISP's in their network infrastructure) and it provided
the same user experience as the traditional dial-up service to end
users.
The evolution of xDSL technology will rapidly increase available
bandwidth for final users, driving the demand for value-added
services, such as VoIP, Video and Online Gaming (also known as
"triple" and "quadruple" play services) requiring "always on"
broadband connections. In such scenarios, the classical virtual dial
up approach is affected by scalability issues, and therefore it will
be gradually replaced by an "always-on" model based on IP sessions.
Evolving towards purely IP based access models also implies the
absence of Authorization and Accounting records which are normally
available when using virtual dial up approach: in this case,
deploying service charged on a time basis would be extremely
difficult. It could be argued that an always-on connection is
normally associated to a flat-rate charge; however the evolution of
ISP's service portfolio may still require a time base charging method
for value added services going beyond standard offers.
In other words, even with an "always-on" paradigm, it may still be
required to identify "sessions" associated with special services in
order to measure the exact duration of such services and charge them
on a time basis.
5. Requirements of the Solution
This section describes the requirements for a solution that provides
a non-PPP based access method to an IP network:
1)it MUST be able to authenticate the users before allowing them the
network access; this is required to guarantee an appropriate security
level and for associating to each user his profile typically
specifying also the accounting policies to be applied to the user;
2)it SHOULD support different authentication methods, in order to be
able to select the proper/adapted security level for different
scenarios;
3)it MUST support different accounting policies like time-basis
charging, volume-basis charging, flat and prepaid charging in order
to be applied to most common Service Provider commercial offers;
4)it MUST be able to dynamically modify the session attributes when a
particular event happens. Typical situation that may require ISPs to
modify user capabilities is when prepaid credit expires: in this case
ISP may want to provide to the user limited or no access to the
network;
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5)it MUST be able to modify the accounting policy related to a
specific session, without terminating the established session; this
allows ISPs to offer dynamic activation of new services that may
require different charging policy.
Moreover, in a particular scenario where the ISP and the NAP are not
the same entity, the ability to dynamically select the Internet
Service Provider MAY translate into an additional requirement for a
suitable solution.
6. Brief analysis of current possible approaches
There are currently different approaches that try to address the
time-basis billing problem in non-PPP based network scenario; they
can all be classified in three main categories:
a)a Service Selection architecture, based on the interaction with a
dedicated service access Web portal;
b)an architecture based on dynamic address assignment functionality
through DHCP (Dynamic Host Configuration Protocol) servers [4];
c)a solution based on PANA protocol [5] [6].
As the next sections will show, none of these approaches completely
satisfies all the requirements listed above, thus either a new
solution or an extension of an existing one, is required to solve the
problem.
6.1 Web Portal based approach
In the case of a Service Selection architecture, a Web portal could
typically be used to manage with the login for those users wishing to
access services with a time-based accounting. The Web portal allows
the selection of the desired service among those offered from the
network. This occurs by using the HTTP (HyperText Transfer Protocol)
[3] protocol, through an edge element of the IP network. As the user
opens the HTTP browser, his traffic is re-directed by the edge
network element towards the Web server, hosting the services access
portal, located on a specific IP subnet. The Web server asks the user
for its authentication credentials and, if that step is successful,
the Web server presents to the user a menu of the available services
out of which the desired service may be selected. Upon a service
request, an appropriate session is created and the associated RADIUS
accounting function started.
This approach has two main limitations:
it relies on redirection of http traffic thus it requires pre-
establishing an http session even if the end-user does not need to
send http traffic; it is not based on a standard solution but it
relies on proprietary methodologies.
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6.2 DHCP based approach
DHCP protocol is built on a client-server model, where designated
DHCP servers allocate network addresses and deliver configuration
parameters to dynamically configured hosts. DHCP supports three
mechanisms for IP address allocation: "automatic allocation",
"dynamic allocation" and "manual allocation". In "dynamic
allocation", DHCP assigns an IP address to a client for a limited
period of time (or until the client explicitly relinquishes the
address). Dynamic allocation is particularly useful for assigning an
address to a client that will only need temporary connection to the
network or for sharing a limited pool of IP addresses among a group
of clients that do not need permanent IP addresses.
The session duration can be identified by the interval between the
time the IP address request is received and the time the IP address
is released.
Time-basis accounting based on this approach may be inaccurate in
case the customer disconnects from the network without releasing the
address. In that case the DHCP server removes the related association
only when the configured lease time expires. While the initial
address request to the DHCP server can in fact be used to start a
time-based accounting procedure, the accounting stop can be adversely
affected in terms of accuracy if the client disconnects without
sending an explicit disconnection message, thus making it necessary
to wait for the lease time expiry. On the other hand a reduction in
the value of the lease time entails a more frequent interaction in
terms of messages with the DHCP server, thus finally limiting
scalability.
6.3 PANA based approach
PANA protocol has been designed to provide users authentication and
authorization in an IP-Based access network; it is able to transport
EAP protocol, thus it can work with EAP authentication methods. As
PANA is based on the IP protocol, it is independent from the link
layer technologies used. Therefore it can be adopted in an
heterogeneous access technology environment.
PANA is a very flexible protocol, it provides the capability to
dynamically modify different parameters of an established session,
but it is not currently able to change the accounting policy
associated to a specific session. This is a limitation for an ISP
that would like to offer a service that requires modifying the
charging policy according to the user behavior. For example, in the
broadband scenario, a user could subscribe to a service that allows
access to a controlled network portion, called Walled Garden, for a
flat rate charge. When the user tries to access to a destination
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outside the Walled Garden the ISP may want to adopt a time-basis
charging model for that specific traffic. This should be accomplished
without interrupting the user established session.
7. Conclusions
From the preliminary analysis described above, it appears that PANA
protocol is flexible and extensible enough to potentially address the
problem presented. We think that PANA framework could be leveraged,
with minimal impact, to satisfy the aforementioned requirements, that
will be further discussed in a next version of the contribution.
Therefore we ask the PANA Working Group to consider the time-basis
accounting problem as a discussion item within the PANA framework.
8. Security Considerations
This document raises no security issue.
9. IANA Considerations
This document has no actions for IANA.
10. References
[1] Simpson, W., "The Point-to-Point Protocol (PPP)", RFC1661, July
1994
[2] C. Rigney, S. Willens, Livingston, A. Rubens, Merit, W. Simpson,
Daydreamer "Remote Authentication Dial In User Service (RADIUS)",
RFC2865, June 2000
[3] Droms, R., "Dynamic Host Configuration Protocol", RFC2131, March
1997
[4] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999
[5] Jayaraman, P., "PANA Framework", draft-ietf-pana-framework-06
(work in progress), March 2006
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[6] Forsberg, D., "Protocol for Carrying Authentication for Network
Access (PANA)", draft-ietf-pana-pana-11 (work in progress), March
2006
Acknowledgments
We would like to thank Gerardo Giaretta for his valuable comments to
this document.
Author's Addresses
Roberta Maglione
Telecom Italia
Via G. Reiss Romoli 274
10148 Torino
Italy
Email: roberta.maglione@telecomitalia.it
Mario Ullio
Telecom Italia
Via G. Reiss Romoli 274
10148 Torino
Italy
Email: mario.ullio@telecomitalia.it
Vinicio Vercellone
Telecom Italia
Via G. Reiss Romoli 274
10148 Torino
Italy
Email: vinicio.vercellone@telecomitalia.it
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