Network Working Group B. Aboba
Request for Comments: 2194 Microsoft
Category: Informational J. Lu
AimQuest Corp.
J. Alsop
i-Pass Alliance
J. Ding
Asiainfo
W. Wang
Merit Network, Inc.
September 1997

Review of Roaming Implementations

1. Status of this Memo

This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.

2. Abstract

This document reviews the design and functionality of existing
roaming implementations. "Roaming capability" may be loosely defined
as the ability to use any one of multiple Internet service providers
(ISPs), while maintaining a formal, customer-vendor relationship with
only one. Examples of cases where roaming capability might be
required include ISP "confederations" and ISP-provided corporate
network Access support.

3. IntrodUCtion

Considerable interest has arisen recently in a set of features that
fit within the general category of "roaming capability" for Internet
users. Interested parties have included:

Regional Internet Service Providers (ISPs) operating within a
particular state or province, looking to combine their efforts
with those of other regional providers to offer service over a
wider area.

National ISPs wishing to combine their operations with those of
one or more ISPs in another nation to offer more comprehensive
service in a group of countries or on a continent.

Businesses desiring to offer their employees a comprehensive
package of access services on a global basis. Those services may

include Internet access as well as secure access to corporate
intranets via a Virtual Private Network (VPN), enabled by
tunneling protocols such as PPTP, L2F, or L2TP.

What is required to provide roaming capability? The following list
is a first cut at defining the requirements for successful roaming
among an arbitrary set of ISPs:

Phone number presentation
Phone number exchange
Phone book compilation
Phone book update
Connection management
Authentication
NAS Configuration/Authorization
Address assignment and routing
Security
Accounting

In this document we review existing roaming implementations,
describing their functionality within this framework. In addition to
full fledged roaming implementations, we will also review
implementations that, while not meeting the strict definition of
roaming, address several of these problem elements. These
implementations typically fall into the category of shared use
networks or non-IP dialup networks.

3.1. Terminology

This document frequently uses the following terms:

home ISP This is the Internet service provider with whom the user
maintains an account relationship.

local ISP This is the Internet service provider whom the user calls
in order to get access. Where roaming is implemented the local
ISP may be different from the home ISP.

phone book
This is a database or document containing data pertaining to
dialup access, including phone numbers and any associated
attributes.

shared use network
This is an IP dialup network whose use is shared by two or
more organizations. Shared use networks typically implement
distributed authentication and accounting in order to
facilitate the relationship among the sharing parties. Since
these facilities are also required for implementation of
roaming, implementation of shared use is frequently a first
step toward development of roaming capabilities. In fact, one
of the ways by which a provider may offer roaming service is
to conclude shared use agreements with multiple networks.
However, to date the ability to accomplish this has been
hampered by lack of interoperability among shared use
implementations.

non-IP dialup network
This is a dialup network providing user access to the member
systems via protocols other than IP. These networks may
implement phone book synchronization facilities, in order to
provide systems, administrators and users with a current list
of participating systems. Examples of non-IP dialup networks
supporting phone book synchronization include FidoNet and
WWIVnet.

4. Global Reach Internet Consortium (GRIC)

Led by a US-based Internet technology developer, AimQuest
Corporation, ten Internet Service Providers (ISPs) from the USA,
Australia, China, Japan, Hong Kong, Malaysia, Singapore, Taiwan, and
Thailand formed the Global Reach Internet Connection (GRIC) in May,
1996. The goals of GRIC were to facilitate the implementation of a
global roaming service and to coordinate billing and settlement among
the membership. Commercial operation began in December of 1996, and
GRIC has grown to over 100 major ISPs and Telcos from all over the
world, including NETCOM, USA; KDD and Mitsubishi, Japan; iStar,
Canada; Easynet, UK; Connect.com, Australia; Iprolink, Switzerland;
Singapore Telecom; Chunghwa Telecom, Taiwan; and Telekom Malaysia.
Information on GRIC is available from http://www.gric.net/.

In implementing their roaming service, GRIC members have chosen
software developed by AimQuest. AimQuest Corporation's roaming
implementation comprises the following major components: the
AimTraveler Authentication Server (AAS), the AimTraveler Routing
Server (ARS), and the AimQuest Internet Management System (AIMS),
software designed to facilitate the billing process. Information on
the AimQuest roaming implementation is available from
http://www.aimquest.com/.

The AimTraveler Authentication Server (AAS) runs at each member ISP
location, and handles incoming authentication requests from NAS
devices and other AASes. The AimTraveler Routing Server (ARS) can run
anywhere. A single routing server can be used where centralized
routing is desired, or multiple routing servers can be run in order
to increase speed and reliability or to gateway to networks of
particularly large partners.

The first version of the AimTraveler software, deployed by AimQuest
in May, 1996, supported direct authentication between members of the
roaming consortium, but as GRIC grew, management of the relationships
between the authentication servers became a problem. In August. 1996,
AimQuest began development of the AimTraveler Routing Server (ARS) in
order to improve scalability.

The routing server is comprised of two elements: The Central
Accounting Server and the Central Routing Server. The Central
Accounting Server collects all the roaming accounting data for
settlement. The Central Routing Server manages and maintains
information on the authentication servers in the roaming consortium.
Adding, deleting, or updating ISP authentication server information
(e.g. adding a new member ISP) may be accomplished by editing of a
configuration file on the Central Routing Server. The configuration
files of the AimTraveler Authentication Servers do not need to be
modified.

The AimTraveler Authentication and Routing Servers are available for
various UNIX platforms. Versions for Windows NT are under
development. The AimTraveler Authentication Server supports both the
UNIX passWord file and Kerberos.

The AimQuest Internet Management System (AIMS) is designed for large
ISPs who need a centralized management system for all ISP operations,
including sales, trouble-ticketing, service, and billing. AIMS
produces usage and transaction statement reports, and includes a
settlement module to produce settlement/billing reports for the
roaming consortium members. Based on these reports, the providers
charge their ISP/roaming customers, and pay/settle the roaming
balance among the providers. AIMS currently runs on
Sun/Solaris/Oracle. A version for Windows NT and SQL Server is
eXPected to become available in Q4 1996.

4.1. Phone number presentation

Currently there are two principal methods by which GRIC users can
discover available phone numbers: a Web-based Directory provided by
the GRIC secretariat, and a GRIC phone book client on the user PC
with dialing capability.

4.1.1. Web based directory

A directory of GRIC phone numbers is available on the GRIC home page,
http://www.gric.com/. The list of numbers is arranged by country and
provider. For each provider within a country, this directory,
provided in the form of a table, offers the following information:

Provider address, voice phone and fax
Customer support phone number
Provider domain name
Primary Domain Name Server
Secondary Domain Name Server
Dial-up IP Address
News server
Web page
POP phone numbers (i.e. 1-408-366-9000)
POP locations (i.e. Berkeley)
Proxy addresses
Dialer configuration

In order to discover phone numbers using the Web-based directory, it
is expected that users will be online, and will navigate to the
appropriate country and provider. They then look up the number and
insert it into the AimQuest Ranger dialer.

4.1.2. GRIC phone book client

The GRIC phone book client software provides for phone book
presentation as well as automated updating of phone numbers. The
GRIC phone book includes a list of countries, states, cities and
area/city codes, as well as detailed provider information, including
the cutomer support phone number, and Internet server configuration
info. The Phone book, developed with Java, is available for download
from the AimQuest Web site:

http://www.aimquest.com/dialer.Html

4.2. Phone number exchange

GRIC members submit information both about themselves and their POPs
to the GRIC secretariat, which is run by AimQuest. The GRIC
secretariat then compiles a new phone book and provides updates on
the GRIC FTP and Web servers.

GRIC users then download the phone numbers either in Windows .ini
file format or in HTML.

4.3. Phone book compilation

GRIC phone books are compiled manually, and represent a concatenation
of available numbers from all the members of the roaming consortium,
with no policy application. As new POPs come online, the numbers are
forwarded to GRIC, which adds them to the phone book servers.

4.4. Phone book update

Phone numbers in the GRIC phone book client are updated automatically
upon connection. The AimTraveler server includes an address book
which contains the phone numbers of all the roaming consortium
members.

4.5. Connection management

The AimTraveler software supports SLIP and PPP, as well as PAP and
CHAP authentication.

4.6. Authentication

GRIC implements distributed authentication, utilizing the user's e-
mail address as the userID (i.e. "liu@Aimnet.com") presented to the
remote NAS device.

After the initial PPP authentication exchange, the userID, domain,
and pasword information (or in the case of CHAP, the challenge and
the response) are then passed by the NAS to the AimTraveler
Authentication Server which supports both TACACS+ and RADIUS.

If the authentication request comes from a regular customer login,
normal user id and password authentication is performed. If the user
requesting authentication is a "roamer," (has a userID with an @ and
domain name), the authentication server sends an query to the closest
routing server. When AimTraveler Routing Server receives the
authentication request, it first authenticates the AAS sending the
request, and if this is successful, it checks its authentication
server table. If it is able to match the domain of the user to that
of a "Home ISP", then the Home ISP authentication server's routing
information are sent back to the local ISP's authentication server.
Based on the information received from the routing server, the AAS
makes an authentication request to the user's Home ISP AAS for user
id and password verification.

If the user is a valid user, the Home ISP authentication server sends
a "permission granted" message back to the Local ISP authentication
server. The Local ISP authentication server then requests the NAS to
grant the user a dynamic IP address from its address pool. If the

username or password is incorrect, the Home ISP AAS will send a
rejection message to the Local ISP AAS, and the user will be dropped
by the NAS.

If multiple routing servers are installed, and the query to the first
routing server does not result in a match, the query is forwarded to
the next routing server. The server queries are cached on the routing
servers, improving speed for repeated queries. The cache is sustained
until a routing server table entry is updated or deleted. Updating
or deleting results in a message to all neighbor routing servers to
delete their caches.

The local authentication server also receives the accounting data
from the NAS. If the data is for a regular customer login, the data
is written to the Local ISP AAS log file. If the data is for a
"roamer," the data is written to three places: the Local ISP AAS log
file, the Home ISP AAS log file, and the ARS log file.

If the local ISP authentication server has caching turned on, then it
will cache information on Home ISP authentication server
configurations sent by the routing server. This means that if the
same domain is queried again, the local authentication server does
not need to query the routing server again. The local cache is
cleared when the local authentication server receives an update
message from the routing server or system manager.

4.7. NAS Configuration/Authorization

AimTraveler is comprised of two components, a Client(AAS) and a
Server(ARS).

The AimTraveler Client acts as the PPP dial-up authentication server.
When it detects an '@' sign in the userID field, it queries the
AimTraverler Server for routing information, then forwards the
authentication request to user's home authentication server. The
AimTraveler Server, a centralized routing server, contains the
authorized ISP's domain name, authentication servers and other
information.

The AimTraveler currently supports RADIUS and TACACS+, and could be
extended to support other authentication protocols. It also receives
all the accounting records, which are subsequently used as input data
for billing.

Since ISPs' NAS devices may be configured differently, the attributes
returned by the home ISP AAS are discarded.

4.8. Address assignment and routing

All addresses in GRIC are assigned dynamically from within the
address pool of the local ISP. Static addresses and routed LAN
connections will be considered in the future, when GRIC offers
corporate roaming service, with the implementation of tunneling
protocols

4.9. Security

The user's password is hashed with MD5 before being sent from the
Local ISP AAS to the Home ISP AAS. An encryption key is shared
between the AAS and ARS. The current version of AimTraveler AAS does
not support token cards or tunneling protocols.

4.10. Accounting

The AimTraveler Authentication Server (AAS) software can act as
either a RADIUS or TACACS+ accounting server. When accounting
information is received from the NAS, the local AimTraveler
Authentication Server (AAS) sends accounting data (user name, domain
name, login time) to both the Central Accounting Server (part of the
ARS) and the user's Home ISP AimTraveler authentication server. In
the case of GRIC, the Central Accounting Server is run by AimQuest.

The data sent to the central accounting server and home ISP are
identical except for the form of user id and time stamp. For a
traveler whose home ISP is in the US, but who is traveling in Japan,
the Local (Japanese) ISP AimTraveler authentication server will
receive an accounting record timestamped with Japan time while the
Home (US) ISP AimTraveler authentication server will receive an
accounting record timestamped with the appropriate US timezone.

The accounting data includes 2 new attributes for settlement
reporting:

Attribute Number Type
--------- ------ ----

Roaming-Server-ID 101 string
Isp-ID 102 string

The Roaming-Server-ID attribute identifies the AAS sending the
authentication request. The Isp-ID attribute identifies the local
ISP. Using this information the home ISP can track the roaming
activities of its users (where their users are logging in).

The AimTraveler Server running at AimQuest keeps a record of all
roaming transactions, which are used as input to the settlement and
billing process. At the end of each month, AimQuest provides a
roaming transaction summary to GRIC members using AIMS. The AIMS
software is configurable so that it takes into account the settlement
rules agreed to by GRIC members.

5. i-Pass implementation

5.1. Overview

i-Pass Alliance Inc., based in Mountain View, California, has
developed and operates a commercial authentication and settlement
clearinghouse service which provides global roaming between Internet
service providers. The service is fully operational.

i-Pass Alliance Inc. has additional Offices in Toronto, Singapore,
and London. More information on i-Pass can be oBTained from
http://www.ipass.com.

The i-Pass network consists of a number of servers that provide
real-time authentication services to partner ISPs. Authentication
requests and accounting records for roaming users are encrypted and
sent to an i-Pass serverwhere they are logged, and then forwarded to
a home ISP for authentication and/or logging.

Periodically, i-Pass reconciles all accounting records, generates
billing statements, and acts as a single point for collecting and
remitting payments.

i-Pass provides its service only to ISPs and channel partners. It
does not attempt to establish a business relationship with
individual-user customers of an ISP.

5.2. Access Point Database (APD)

i-Pass maintains a list of roaming access points in an Oracle
database. This list is searchable by geographical region using a Web
browser, and may be downloaded in its entirety using FTP. The
information stored for each access point includes:

Name of service provider
Country
State or Province
City or Region
Telephone number
Technical support phone number
Service types available

Technical information (help file)
Service pricing information

The Access Point Database is maintained by i-Pass staff, based on
input from i-Pass partners.

5.3. Phone number presentation

ni-Pass has developed a Windows application wth a simple point and
click interface called the "i-Pass Dial Wizard", which assists end-
users in selecting and connecting to a local Internet access point.

The Dial Wizard allows users to first select the country in which
they are roaming. A list of states, provinces, or other regions in
the selected country is then presented. Finally a list of access
points within the state or province is presented. The Dial Wizard
displays the city name, modem phone number, and price information for
each access point within the state or region.

When the user selects the desired access point, a Windows 95 "DialUp
Networking" icon is created for that access point. If there is a
login script associated with the access point, the DialUp Scripting
tool is automatically configured. This means that end-users never
have to configure any login scripting requirements.

The Dial Wizard has a built-in phonebook containing all the i-Pass
access points. The phonebook may be automatically refreshed from a
master copy located onISPs web site.

The Dial Wizard is provided free of charge to i-Pass partners. i-
Pass also provides the i-Pass Dial Wizard Customization Kit which
allows ISP partners to generate customized versions of the Dial
Wizard with their own logo, etc.

5.4. Authentication

There are three entities involved in servicing an authentication
request:

Local ISP At the local ISP, the authentication server is modified to
recognize user IDs of the form username@auth_domain as being
remote authentication requests. These requests are forwarded
to an i-Pass server.

i-Pass Server
The i-Pass server receives the authentication request, logs
it, and forwards it to the home ISP identified by the
auth_domain portion of the user ID.

Home ISP The home ISP receives the authentication request, performs
authentication using its normal authentication method, and
returns a YES/NO response to the i-Pass server, which in turn
forwards the reply to the originating ISP.

i-Pass provides software components which run on the authentication
servers of the local and home ISPs. Each member ISP must integrate
these components with the native authentication method being used by
the ISP. To simplify this task, i-Pass has developed "drop-in"
interfaces for the most commonly used authentication methods. At the
date of writing, the following interfaces are supported:

Livingston RADIUS
Ascend RADIUS
Merit RADIUS
TACACS+
Xylogics erpcd (Versions 10 and 11)

A generic interface is also provided which authenticates based on the
standard UNIX password file. This is intended as a starting point
for ISPs using authentication methods other than those listed above.

The software integration effort for a typical ISP is on the order of
2-5 man-days including testing. Platforms currently supported
include:

Solaris 2.5 (Sparc).LI
Solaris 2.5 (Intel)
BSDI
Digital Unix
Linux
FreeBSD
HP/UX

ISPs may chooe to provide authentication for their end-users roaming
elsewhere, but not to provide access points to the i-Pass network.
In this case the software integration effort is greatly reduced and
can be as little as 1/2 a man-day.

5.5. Accounting

Accounting transactions are handled in the same way as authentication
requests. In addition to being logged at the i-Pass servers,

accounting transactions are sent in real-time to the home ISP. This
is intended to allow ISPs to update users' credit limit information
on a real-time basis (to the extent that this capability is supported
by their billing and accounting systems).

Settlement is performed monthly. The settlement process involves
calculating the costs associated with each individual session, and
aggregating them for each ISP. A net amount is then calculated which
is either due from i-Pass to the ISP, or from the ISP to i-Pass,
depending on the actual usage pattern.

The following reports are supplied to member ISPs:

A Monthly Statement showing summaries of usage, service provided,
and any adjustments along with the net amount owing.

A Call Detail Report showing roaming usage by the ISP's customers.

A Service Provided report showing detailed usage of the ISP's
facilities by remote users.

The above reports are generated as ASCII documents and are
distributed to i-Pass partners electronically, either by e-mail or
from a secure area on the i-Pass web site. Hard-copy output is
available on request.

The Call Detail Report is also generated as a comma-delimited ASCII
file suitable for import into the ISP's billing database. The Call
Detail Report will normally be used by the ISP to generate end-user
billing for roaming usage.

5.6. Security

All transactions between ISPs and the i-Pass servers are
encrypted using the SSL protocol. Public key certificates are
verified at both the client and server. i-Pass issues these
certificates and acts as the Cetificate Authority.

Transactions are also verified based on a number of other criteria
such as source IP address.

5.7. Operations

i-Pass operates several authentication server sites. Each site
consists of two redundant server systems located in secure facilities
and "close" to the Internet backbone. The authentication server
sites are geographically distributed to minimize the possibility of
failure due to natural disasters etc.

i-Pass maintains a Network Operations Center in Mountain View which
is staffed on a 7x24 basis. Its functions include monitoring the i-
Pass authentication servers, monitoring authentication servers
located at partner facilities, and dealing with problem reports.

6. ChinaNet implementation

ChinaNet, owned by China Telecom, is China's largest Internet
backbone. Constructed by Asiainfo, a Dallas based system integration
company, it has 31 backbone nodes in 31 Chinese provincial capital
cities. Each province is building its own provincial network, has
its own dialup servers, and administers its own user base.

In order to allow hinaNet users to be able to access nodes outside
their province while traveling, a nationwide roaming system has been
implemented. The roaming system was developed by AsiaInfo, and is
based on the RADIUS protocol.

6.1. Phone number presentation

Since China Telecom uses one phone number (163) for nationwide
Internet access, most cities have the same Internet access number.
Therefore a phone book is not currently required for the ChinaNet
implementation. A web-based phone book will be added in a future
software release in order to support nationwide ISP/CSP telephone
numbers and HTTP server addresses.

6.2. Connection management

The current roaming client and server supports both PPP and SLIP.

6.3. Address assignment and routing

ChinaNet only supports dynamic IP address assignment for roaming
users. In addition, static addresses are supported for users
authenticating within their home province.

6.4. Authentication

When user accesses a local NAS, it provides its userID either as
"username" or "username@realm". The NAS will pass the userID and
password to the RADIUS proxy/server. If the "username" notation is
used, the Radius proxy/server will assume that the user is a local
user and will handle local authentication accordingly. If "user-
name@realm" is used, the RADIUS proxy/server will process it as a
roaming request.

When the RADIUS proxy/server handles a request from a roaming user,
it will first check the cache to see if the user information is
already stored there. If there is a cache hit, the RADIUS
proxy/server do the local authentication accordingly. If it does not
find user information in its cache, it will act as a proxy,
forwarding the authentication request to the home RADIUS server.
When the home RADIUS server responds, the local server will forward
the response to the NAS. If the user is authenticated by the home
server, the local RADIUS proxy will cache the user information for a
period of time (3 days by default).

Caching is used to avoid frequent proxying of requests and responses
between the local RADIUS proxy and the home RADIUS server. When the
home RADIUS server sends back a valid authentication response, the
local RADIUS proxy/server will cache the user information for a
period of time (3 days by default). When the user next authenticates
directly against the home RADIUS server, the home RADIUS server will
send a request to the local server or servers to clear the user's
information from the cache.

6.4.1. Extended hierarchy

In some provinces, the local telecommunications administration
Provincial ISP) further delegates control to county access nodes,
creating another level of hierarchy. This is done to improve
scalability and to avoid having the provincial ISP databases grow too
large. In the current implementation, each provincial ISP maintains
its own central RADIUS server, including information on all users in
the province, while county nodes maintain distributed RADIUS servers.
For intra-province roaming requests the local RADIUS proxy/server
will directly forward the request to the home RADIUS server.

However, for inter-province roaming requests, the local RADIUS server
does not forward the request directly to the home RADIUS server.
Instead, the request is forwarded to the central provincial RADIUS
server for the home province. This implementation is suitable only
when county level ISPs do not mind combining and sharing their user
information. In this instance, this is acceptable, since all county
level ISPs are part of China Telecom. In a future release, this
multi-layer hierarchy will be implemented using multi-layer proxy
RADIUS, in a manner more resembling DNS.

6.5. Security

Encryption is used between the local RADIUS proxy/server and the home
RADIUS server. Public/Private key encryption will be supported in the
next release. IP tunneling and token card support is under
consideration.

6.6. Accounting

Accounting information is transferred between the local RADIUS
accounting proxy/server and home RADIUS accounting server. Every day
each node sends a summary accounting information record to a central
server in order to support nationwide settlement. The central server
is run by the central Data Communication Bureau of China Telecom.
Every month the central server sends the settlement bill to the
provincial ISPs.

6.7. Inter-ISP/CSP roaming

ChinaNet supports both ISP and CSP (Content Service Provider) roaming
on its system. For example, Shanghai Online, a Web-based commercial
content service, uses RADIUS for authentication of ChinaNet users who
do not have a Shanghai Online account. In order to support this, the
Shanghai Online servers function as a RADIUS client authenticating
against the home RADIUS server. When users access a protected
document on the HTTP server, they are prompted to send a
username/password for authentication. The user then responds with
their userID in "user-name@realm" notation.

A CGI script on the HTTP server then acts as a RADIUS authentication
client, sending the request to the home RADIUS server. After the home
RADIUS server responds, the CGI script passes the information to the
local authentication agent. From this point forward, everything is
taken care of by the local Web authentication mechanism.

7. Microsoft implementation

Microsoft's roaming implementation was originally developed in order
to support the Microsoft Network (MSN), which now offers Internet
access in seven countries: US, Canada, France, Germany, UK, Japan,
and Australia. In each of these countries, service is offered in
cooperation with access partners. Since users are able to connect to
the access partner networks while maintaining a customer-vendor
relationship with MSN, this implementation fits within the definition
of roaming as used in this document.

7.1. Implementation overview

The first version of the Microsoft roaming software was deployed by
the MSN partners in April, 1996. This version included a Phone Book
manager tool running under Windows 95, as well as a RADIUS
server/proxy implementation running under Windows NT; TACACS+ is

currently not supported. Additional components now under development
include a Connection Manager client for Windows 95 as well as an
HTTP-based phone book server for Windows NT. The Phone Book manager
tool is also being upgraded to provide for more automated phone book
compilation.

7.2. Phone number presentation

The Connection Manager is responsible for the presentation and
updating of phone numbers, as well as for dialing and making
connections. In order to select phone numbers, users are asked to
select the desired country and region/state. Phone numbers are then
presented in the area selected. The primary numbers are those from
the users service provider which match the service type (Analog,
ISDN, Analog & IDN), country and region/state selected. The other
numbers (selected clicking on the More button) are those for other
service providers that have a roaming agreement with the users
service provider.

7.2.1. Cost data

Cost data is not presented to users along with the phone numbers.
However, such information may be made available by other means, such
as via a Web page.

7.2.2. Default phone book format

The Connection Manager supports the ability to customize the phone
book format, and it is expected that many ISPs will make use of this
capability. However, for those who wish to use it "off the shelf" a
default phone book format is provided. The default phone book is
comprised of several files, including:

Service profile
Phone Book
Region file

The service profile provides information on a given service, which
may be an isolated Internet Service Provider, or may represent a
roaming consortium. The service profile, which is in .ini file
format, is comprised of the following information:

The name of the service
The filename of the service's big icon
The filename of the service's little icon
A description of the service
The service phone book filename

The service phone book version number
The service regions file
The URL of the service phone book server
The prefix used by the service (i.e. "MSN/aboba")
The suffix or domain used by the service (i.e. "aboba@msn.com")
Whether the user name is optional for the service
Whether the password is optional for the service
Maximum length of the user name for the service
Maximum length of the password for the service
Information on service password handling (lowercase, mixed case, etc.)
Number of redials for this service
Delay between redials for this service
References to other service providers that have roaming agreements
The service profile filenames for each of the references
Mask and match phone book filters for each of the references
(these are 32 bit numbers that are applied against the capability
flags in the phone book)
The dial-up connection properties configuration
(this is the DUN connectoid name)

The phone book file is a comma delimited ASCII file containing the
following data:

Unique number identifying a particular record (Index)
Country ID
A zero-base index into the region file
City
Area code
Local phone number
Minimum Speed
Maximum speed
Capability Flags:
Bit 0: 0=Toll, 1=Toll free
Bit 1: 0=X25, 1=IP
Bit 2: 0=Analog, 1=No analog support
Bit 3: 0=no ISDN support, 1=ISDN
Bit 4: 0
Bit 5: 0
Bit 6: 0=No Internet access, 1=Internet access
Bit 7: 0=No signup access, 1=Signup access
Bit 8-31: reserved
The filename of the dialup network file
(typically refers to a script associated with the number)

A sample phone book file is shown below:

65031,1,1,Aniston,205,5551212,2400,2400,1,0,myfile
200255,1,1,Auburn/Opelika,334,5551212,9600,28800,0,10,
200133,1,1,Birmingham,205,5551212,9600,28800,0,10,
130,1,1,Birmingham,205,3275411,9600,14400,9,0,yourfile
65034,1,1,Birmingham,205,3285719,9600,14400,1,0,myfile

7.2.3. Additional attributes

As described previously, it is likely that some ISPs will require
additional phone number attributes or provider information beyond
that supported in the default phone book format. Attributes of
interest may vary between providers, or may arise as a result of the
introduction of new technologies. As a result, the set of phone
number attributes is likely to evolve over time, and extensibility in
the phone book format is highly desirable.

For example, in addition to the attributes provided in the default
phone book, the following additional attributes have been requested
by customers:

Multicast support flag
External/internal flag (to differentiate display between the
"internal" or "other" list box)
Priority (for control of presentation order)
Modem protocol capabilities (V.34, V.32bis, etc.)
ISDN protocol capabilities (V.110, V.120, etc.)
No password flag (for numbers using telephone-based billing)
Provider name

7.2.4. Addition of information on providers

The default phone book does not provide a mechanism for display of
information on the individual ISPs within the roaming consortium,
only for the consortium as a whole. For example, the provider icons
(big and little) are included in the service profile. The service
description information is expected to contain the customer support
number. However, this information cannot be provided on an
individual basis for each of the members of a roaming consortium.
Additional information useful on a per-provider basis would include:

Provider voice phone number
Provider icon
Provider fax phone number
Provider customer support phone number

7.3. Phone number exchange

Currently phone number exchange is not supported by the phone book
server. As a result, in the MSN implementation, phone number exchange
is handled manually. As new POPs come online, the numbers are
forwarded to MSN, which tests the numbers and approves them for
addition to the phone book server. Updated phone books are produced
and loaded on the phone book server on a weekly basis.

7.4. Phone book compilation

The Phone Book Manager tool was created in order to make it easier
for the access partners to create and update their phone books. It
supports addition, removal, and editing of phone numbers, generating
both a new phone book, as well as associated difference files.

With version 1 of the Phone Book Administration tool, phone books are
compiled manually, and represent a concatenation of available numbers
from all partners, with no policy application. With version 1, the
updates are prepared by the partners and forwarded to MSN, which
tests the numbers and approves them for addition to the phone book.
The updates are then concatenated together to form the global update
file.

The new version of the Phone Book Administration tool automates much
of the phone book compilation process, making it possible for phone
book compilation to be decentralized with each partner running their
own phone book server. Partners can then maintain and test their
individual phone books and post them on their own Phone Book Server.

7.5. Phone book update

There is a mechanism to download phone book deltas, as well as to
download arbitrary executables which can perform more complex update
processing. Digital signatures are only used on the downloading of
executables, since only these represent a security threat - the
Connection Manager client does not check for digital signatures on
deltas because bogus deltas can't really cause any harm.

The Connection Manager updates the phone book each time the user logs
on. This is accomplished via an HTTP GET request to the phone book
server. When the server is examining the request, it can take into
account things like the OS version on the client, the language on the
client, the version of Connection Manager on the client, and the
version of the phone book on the client, in order to determine what
it wants to send back.

In the GET response, the phone book server responds with the
difference files necessary to update the client's phone book to the
latest version. The client then builds the new phone book by
successively applying these difference files. This process results
in the update of the entire phone book, and is simple enough to allow
it to be easily implemented on a variety of HTTP servers, either as a
CGI script or (on NT) as an ISAPI DLL.

The difference files used in the default phone book consist of a
list of phone book entries, each uniquely identified by their index
number. Additions consist of phone book entries with all the
information filed in; deletions are signified by entries with all
entries zeroed out. A sample difference file is shown below:

65031,1,1,Aniston,205,5551212,2400,2400,1,0,myfile
200255,1,1,Auburn/Opelika,334,5551212,9600,28800,0,10,
200133,0,0,0,0,0,0,0,0,0
130,1,1,Birmingham,205,5551211,9600,14400,9,0,yourfile
65034,1,1,Birmingham,205,5551210,9600,14400,1,0,myfile

7.6. Connection management

The Connection Manager can support any protocol which can be
configured via use of Windows Dialup Networking, including PPP and
SLIP running over IP. The default setting is for the IP address as
well as the DNS server IP address to be assigned by the NAS. The DNS
server assignment capability is described in [1].

7.7. Authentication

The Connection Manager client and RADIUS proxy/server both support
suffix style notation (i.e. "aboba@msn.com"), as well as a prefix
notation ("MSN/aboba").

The prefix notation was developed for use with NAS devices with small
maximum userID lengths. For these devices the compactness of the
prefix notation significantly increases the number of characters
available for the userID field. However, as an increasing number of
NAS devices are now supporting 253 octet userIDs (the maximum
supported by RADIUS) the need for prefix notation is declining.

After receiving the userID from the Connection Manager client, the
NAS device passes the userID/domain and password information (or in
the case of CHAP, the challenge and the response) to the RADIUS

proxy. The RADIUS proxy then checks if the domain is authorized for
roaming by examining a static configuration file. If the domain is
authorized, the RADIUS proxy then forwards the request to the
appropriate RADIUS server. The domain to server mapping is also made
via a static configuration file.

While static configuration files work well for small roaming
consortia, for larger consortia static configuration will become
tedious. Potentially more scalable solutions include use of DNS SRV
records for the domain to RADIUS server mapping.

7.8. NAS configuration/authorization

Although the attributes returned by the home RADIUS server may make
sense to home NAS devices, the local NAS may be configured
differently, or may be from a different vendor. As a result, it may
be necessary for the RADIUS proxy to edit the attribute set returned
by the home RADIUS server, in order to provide the local NAS with the
appropriate configuration information. The editing occurs via
attribute discard and insertion of attributes by the proxy.

Alternatively, the home RADIUS server may be configured not to return
any network-specific attributes, and to allow these to be inserted by
the local RADIUS proxy.

Attributes most likely to cause conflicts include:

Framed-IP-Address Framed-IP-Netmask Framed-Routing Framed-Route
Filter-Id Vendor-Specific Session-Timeout Idle-Timeout
Termination-Action

Conflicts relating to IP address assignment and routing are very
common. Where dynamic address assignment is used, an IP address pool
appropriate for the local NAS can be substituted for the IP address
pool designated by the home RADIUS server.

However, not all address conflicts can be resolved by editing. In
some cases, (i.e., assignment of a static network address for a LAN)
it may not be possible for the local NAS to accept the home RADIUS
server's address assignment, yet the roaming hosts may not be able to
accept an alternative assignment.

Filter IDs also pose a problem. It is possible that the local NAS may
not implement a filter corresponding to that designated by the home
RADIUS server. Even if an equivalent filter is implemented, in order
to guarantee correct operation, the proxy's configuration must track
changes in the filter configurations of each of the members of the

roaming consortium. In practice this is likely to be unworkable.
Direct upload of filter configuration is not a solution either,
because of the wide variation in filter languages supported in
today's NAS devices.

Since by definition vendor specific attributes have meaning only to
devices created by that vendor, use of these attributes is
problematic within a heterogeneous roaming consortium. While it is
possible to edit these attributes, or even to discard them or allow
them to be ignored, this may not always be acceptable. In cases where
vendor specific attributes relate to security, it may not be
acceptable for the proxy to modify or discard these attributes; the
only acceptable action may be for the local NAS to drop the user.
Unfortunately, RADIUS does not distinguish between mandatory and
optional attributes, so that there is no way for the proxy to take
guidance from the server.

Conflicts over session or idle timeouts may result if since both the
local and home ISP feel the need to adjust these parameters. While
the home ISP may wish to adjust the parameter to match the user's
software, the local ISP may wish to adjust it to match its own
service policy. As long as the desired parameters do not differ too
greatly, a compromise is often possible.

7.9. Address assignment and routing

While the Connection Manager software supports both static and
dynamic address assignment, in the MSN implementation, all addresses
are dynamically assigned.

However, selected partners also offer LAN connectivity to their
customers, usually via static address assignment. However, these
accounts do not have roaming privileges since no mechanism has been
put in place for allowing these static routes to move between
providers.

Users looking to do LAN roaming between providers are encouraged to
select a router supporting Network Address Translation (NAT). NAT
versions implemented in several low-end routers are compatible with
the dynamic addressing used on MSN, as well as supporting DHCP on the
LAN side.

7.10. Security

The RADIUS proxy/server implementation does not support token cards
or tunneling protocols.

7.11. Accounting

In the MSN roaming implementation, the accounting data exchange
process is specified in terms of an accounting record format, and a
method by which the records are transferred from the partners to MSN,
which acts as the settlement agent. Defining the interaction in
terms of record formats and transfer protocols implies that the
partners do not communicate with the settlement agent using NAS
accounting protocols. As a result, accounting protocol
interoperability is not be required.

However, for this advantage to be fully realized, it is necessary for
the accounting record format to be extensible. This makes it more
likely that the format can be adapted for use with the wide variety
of accounting protocols in current use (such as SNMP, syslog, RADIUS,
and TACACS+), as well as future protocols. After all, if the record
format cannot express the metrics provided by a particular partner's
accounting protocol, then the record format will not be of much
usefor a heterogeneous roaming consortium.

7.11.1. Accounting record format

The Microsoft RADIUS proxy/server supports the ability to customize
the accounting record format, and it is expected that some ISPs will
make use of this capability. However for those who want to use it
"off the shelf" a default accounting record format is provided. The
accounting record includes information provided by RADIUS:

User Name (String; the user's ID, including prefix or suffix)
NAS IP address (Integer; the IP address of the user's NAS)
NAS Port (Integer; identifies the physical port on the NAS)
Service Type (Integer; identifies the service provided to the user)
NAS Identifier (Integer; unique identifier for the NAS)
Status Type (Integer; indicates session start and stop,
as well as accounting on and off)
Delay Time (Integer; time client has been trying to send)
Input Octets (Integer; in stop record, octets received from port)
Output Octets (Integer; in stop record, octets sent to port)
Session ID (Integer; unique ID linking start and stop records)
Authentication (Integer; indicates how user was authenticated)
Session Time (Integer; in stop record, seconds of received service)
Input Packets (Integer; in stop record, packets received from port)
Output Packets (Integer; in stop record, packets sent to port)
Termination Cause (Integer; in stop record, indicates termination cause)
Multi-Session ID (String; for linking of multiple related sessions)
Link Count (Integer; number of links up when record was generated)
NAS Port Type (Integer; indicates async vs. sync ISDN, V.120, etc.)

However, since this default format is not extensible, it cannot
easily be adapted to protocols other than RADIUS, services other than
dialup (i.e. dedicated connections) or rated events (i.e. file
downloads). This is a serious limitation, and as a result, customers
have requested a more general accounting record format.

7.11.2. Transfer mechanism

Prior to being transferred, the accounting records are compressed so
as to save bandwidth. The transfer of accounting records is handled
via FTP, with the transfer being initiated by the receiving party,
rather than by the sending party. A duplicate set of records is kept
by the local ISP for verification purposes.

8. Merit Network Implementation

8.1. Overview

MichNet is a regional IP backbone network operated within the state
of Michigan by Merit Network, Inc., a nonprofit corporation based in
Ann Arbor, Michigan. Started in 1966, MichNet currently provides
backbone level Internet connectivity and dial-in IP services to its
member and affiliate universities, colleges, K-12 schools, libraries,
government institutions, other nonprofit organizations, and
commercial business entities.

As of May 1, 1997, MichNet had 11 members and 405 affiliates. Its
shared dial-in service operated 133 sites in Michigan and one in
Washington, D.C, with 4774 dial-in lines. Additional dial-in lines
and sites are being installed daily.

MichNet also provides national and international dial-in services to
its members and affiliates through an 800 number and other external
services contracting with national and global service providers.

The phone numbers of all MichNet shared dial-in sites are published
both on the Merit web site and in the MichNet newsletters. Merit also
provides links to information about the national and international
service sites through their respective providers' web sites. Such
information can be found at http://www.merit.edu/mich-
net/shared.dialin/.

8.1.1. MichNet State-Wide Shared Dial-In Services

Each MichNet shared dial-in service site is owned and maintained by
either Merit or by a member or affiliate organization. All sites must
support PPP and Telnet connections.

Each organization participating in the shared dial-in service is
assigned a realm-name. Typically the realm-name resembles a fully
qualified domain name. Users accessing the shared dial-in service
identify themselves by using a MichNet AccessID which consists of
their local id concatenated with "@" followed by the realm-name -
e.g. user@realm

Merit operates a set of Authentication, Authorization and Accounting
(AAA) servers supporting the RADIUS protocol which are called core
servers. The core servers support all the dial-in service sites and
act as proxy servers to other AAA servers running at the
participating organizations. For security reasons, Merit staff run
all core servers; in particular, the user password is in the clear
when the proxy core server decodes an incoming request and then re-
encodes it and forwards it out again,

The core servers also enforce a common policy among all dial-in
servers. The most important policy is that each provider of access
must make dial-in ports available to others when the provider's own
users do not have a need for them. To implement this policy, the
proxy server distinguishes between realms that are owners and realms
that are guests.

One piece of the policy determining whether the provider's
organization has need of the port, is implemented by having the proxy
core server track the realms associated with each of the sessions
connected at a particular huntgroup. If there are few ports available
(where few is determined by a formula) then guests are denied access.
Guests are also assigned a time limit and their sessions are
terminated after some amount of time (currently one hour during prime
time, two hours during non-prime time).

The other part of the policy is to limit the number of guests that
are allowed to connect. This is done by limiting the number of
simultaneous guest sessions for realms. Each realm is allocated a
number of "simultaneous access tokens" - SATs. When a guest session
is authorized the end server for the realm decrements the count of
available SATs, and when the session is terminated the count of SATs
is incremented. A Merit specific attribute is added to the request
by the core if the session will be a "guest" and will require a SAT.
The end server must include a reply with an attribute containing the
name of the "token pool" from which the token for this session is
taken. The effect of this is to limit the number of guests connected
to the network to the total number of tokens allocated to all realms.

Each realm is authenticated and authorized by its own AAA server. The
proxy core servers forward requests to the appropriate server based
on a configuration file showing where each realm is to be
authenticated. Requests from realms not in the configuration are
dropped.

The Merit AAA server software supports this policy. Merit provides
this software to member and affiliate organizations. The software is
designed to work with many existing authentication servers, such as
Kerberos IV, UNIX password, TACACS, TACACS+, and RADIUS. This
enables most institutions to utilize the authentication mechanism
they have in place.

8.1.2. MichNet National and International Dial-In Services

In addition to the MichNet shared dial-in service, Merit also
provides access from locations outside of Michigan by interconnecting
with other dial-in services. These services are typically billed by
connect time. Merit acts as the accounting agent between its member
and affiliate organizations and the outside service provider.

The services currently supported are a national 800 number and
service via the ADP/Autonet dial-in network. Connection with
IBM/Advantis is being tested, and several other service interconnects
are being investigated.

Calls placed by a Merit member/affiliate user to these external
dial-in services are authenticated by having each of those services
forward RADIUS authentication requests and accounting messages to a
Merit proxy core server. The core forwards the requests to the
member/affiliate server for approval. Session records are logged at
the Merit core server and at the member/affiliate erver. Merit bills
members/affiliates monthly, based on processing of the accounting
logs. The members and affiliates are responsible for rebilling their
users.

The Merit AAA software supports the ability to request positive
confirmation of acceptance of charges, and provides tools for
accumulating and reporting on use by realm and by user.

8.2. Authentication and Authorization

Authentication of a Telnet session is supported using the traditional
id and password method, with the id being a MichNet AccessID of the
form user@realm, while a PPP session may be authenticated either
using an AccessID and password within a script, or using PAP.
Support for challenge/response authentication mechanisms using EAP is
under development.

When a user dials into a MichNet shared dial-in port, the NAS sends
an Access-Request to a core AAA server using the RADIUS protocol.
First the core server applies any appropriate huntgroup access
policies to the request. If the Request fails the policy check, an
Access-Reject is returned to the NAS. Otherwise, the core server
forwards it to the user's home authentication server according to the
user's realm. The home authentication server authenticates and
authorizes the access request. An Access-Accept or Access-Reject is
sent back to the core server. If an Access-Accept is sent, the home
server will create a dial-in session identifier which is unique to
this session and insert it in a Class attribute in the Access-Accept.
The core server looks at the request and the response from the home
server again and decides either to accept or reject the request.
Finally, the core server sends either an Access-Accept or Access-
Reject to the NAS.

When a user dials into a contracted ISP's huntgrup (MichNet National
and International Service), the ISP sends a RADIUS access request to
a Merit core server. The rest of the authentication and authorization
path is the same as in the shared dial-in service, except that no
huntgroup access policy is applied but a Huntgroup-Service attribute
is sent to the home authentication server with its value being the
name of the service, and a copy of the attribute must be returned by
the home server with a flag appended to the original value to
indicate a positive authorization of user access to the specified
service.

The MichNet shared dial-in service typically requires authorization
of some sort, for example, a user dialing into a huntgroup as a guest
must be authorized with a token from the user's realm. Participating
institutions have control in defining authorization rules. Currently
authorization may be done using any combination of the user's group
status and user's account status. A set of programming interfaces is
also provided for incorporating new authorization policies.

8.3. Accounting

In the Merit AAA server, a session is defined as starting from the
moment the user connects to the NAS, and ending at the point when the
user disconnects. During the course of a session, both the core
server and the home server maintain status information about the
session. This allows the AAA servers to apply policies based on the
current status, e.g. limit guest access by realm to number of

available tokens, or to limit number of simultaneous sessions for a
given AccessID. Information such as whether the session is for a
guest, whether it used a token, and other information is included
with the accounting stop information when it is logged. Merit has
made enhancements to the RADIUS protocol, that are local to the AAA
server, to support maintenance of session status information.

When a user session is successfully authenticated, the NAS sends out
a RADIUS accounting start request to the core server. The core server
forwards that request to the user's home server. The home server
updates the status of the session and then responds to the core. The
core server in turn responds to the NAS. In the accounting Start
request, a NAS conforming to the RADIUS specification must return the
Class attribute and value it received in the Access-Accept for the
session, thus sending back the dial-in session identifier created by
the session's home server.

When a user ends a session, an accounting stop request is sent
through the same path. the same path. The dial-in session
identifier is again returned by the NAS, providing a means of
uniquely identifying a session. By configuring the finite state
machine in each of the AAA servers, any accounting requests may be
logged by any of the servers where the accounting requests are
received.

Because the same session logs are available on every server in the
path of a session's authorization and accounting message, problems
with reconciliation of specific sessions may be resolved easily. For
the shared dial-in service, there are no usage charges. Merit has
tools to verify that organizations do not authorize more guest
sessions than the number of SATs allocated to the organization. For
surcharged sessions, Merit sends each organization a summary bill
each month. Files with detail session records are available for
problem resolution. Each organization is responsible for billing its
own users, and should have the same session records as are collected
by Merit.

Merit receives a monthly invoice from other dial-in service providers
and pays them directly, after first verifying that the charges
correspond to the session records logged by Merit.

8.4. Software and Development

Merit has developed the AAA server software which supports the above
capabilities initially by modifying the RADIUS server provided by
Livingston, and later by doing a nearly total rewrite of the software
to make enhancement and extension of capabilites easier. Merit makes
a basic version of its server freely available for noncommercial use.

Merit has started the Merit AAA Server Consortium which consists of
Merit and a number of NAS vedors, ISPs and server software vendors.
The consortium supports ongoing development of the Merit AAA server.
The goal is to build a server that supports proxy as well as end
server capabilities, that is feature rich, and that interoperates
with major vendors' NAS products.

The building block of the Merit AAA server, the
Authentication/Authorization Transfer Vector (AATV), is a very
powerful concept that enables the ultimate modularity and flexibility
of the AAA server. The structure and methods of the AATV model are
published with all versions of the AAA server.

Objects for extending the authorization server are also available in
the enhanced version of the AAA server. Merit is also looking at ways
to provide a method of extending the AAA server in its executable
form, to improve the server efficiency and scalability, and to
provide better monitoring, instrumentation and administration of the
server.

9. FidoNet implementation

Since its birth in 1984, FidoNet has supported phone book
synchronization among its member nodes, which now number
approximately 35,000. As a non-IP dialup network, FidoNet does not
provide IP services to members, and does not utilize IP-based
authentication technology. Instead member nodes offer bulletin-board
services, including access to mail and conferences known as echoes.

In order to be able to communicate with each other, FidoNet member
systems require a sychronized phone book, known as the Nodelist. The
purpose of the Nodelist is to enable resolution of FidoNet addresses
(expressed in the form zone:network/node, or 1:161/445) to phone
numbers. As a dialup network, FidoNet requires phone numbers in
order to be deliver mail and conference traffic.

In order to minimize the effort required in regularly synchronizing a
phone book of 35,000 entries, the weekly Nodelist updates are
transmitted as difference files. These difference files, known as
the Nodediff, produce the Nodelist for the current week when applied
to the previous week's Nodelist. In order to minimize transfer time,
Nodediffs are compressed prior to transfer.

Information on FidoNet, as well as FidoNet Technical Standards (FTS)
documents (including the Nodelist specification) and standards
proposals are available from the FidoNet archive at
http://www.fidonet.org/.

9.1. Scaling issues

With a Nodelist of 35,000 entries, the FidoNet Nodelist is now 3.1 MB
in size, and the weekly Nodediffs are 175 KB. In compressed form, the
Nodelist is approximately 1 MB, and the weekly Nodediff is 90 KB. As
a result, the transfer of the Nodediff takes approximately 45 seconds
using a 28,800 bps modem.

In order to improve scalability, the implementation of a domain name
service approach is examined in [8]. The proposal evisages use of a
capability analagous to the DNS ISDN record in order to map names to
phone numbers, coupled with an additional record to provide the
attributes associated with a given name.

9.2. Phone number presentation

While FidoNet member systems perform hone book synchronization, users
need only know the FidoNet address of the systems they wish to
contact. As a result users do not need to maintain copies of the
Nodelist on their own systems. This is similar to the Internet, where
the DNS takes care of the domain name to IP address mapping, so that
users do not have to remember IP addresses.

Nevertheless, FidoNet systems often find it useful to be able to
present lists of nodes, and as a result, FidoNet Nodelist compilers
typically produce a representation of the Nodelist that can be
searched or displayed online, as well as one that is used by the
system dialer.

9.2.1. FidoNet Nodelist format

The FidoNet Nodelist format is documented in detail in [3]. The
Nodelist file consists of lines of data as well as comment lines,
which begin with a semi-colon. The first line of the Nodelist is a
general interest comment line that includes the date and the day
number, as well as a 16-bit CRC. The CRC is included so as to allow
the system assembling the new Nodelist to verify its integrity.

Each Nodelist data line contains eight comma separated fields:

Keyword
Zone/Region/Net/Node number
Node name
Location
Sysop name
Phone number
Maximum Baud rate
Flags (optional)

FidoNet Nodelists are arranged geographically, with systems in the
same zone, region, and network being grouped together. As a result,
FidoNet Nodelists do not require a separate regions file. Among other
things, the keyword field can be used to indicate that a system is
temporarily out of service.

Reference [3] discusses Nodelist flags in considerable detail. Among
other things, the flags include information on supported modem
modulation and error correction protocols. Reference [4] also
proposes a series of ISDN capability flags, and [5] proposes flags to
indicate times of system availability.

9.3. Phone number exchange

FidoNet coordinators are responsible for maintaining up to date
information on their networks, regions, and zones. Every week network
coordinators submit to their regional coordinators updated versions
of their portions of the Nodelist. The regional coordinators then
compile the submissions from their network coordinators, and submit
them to the zone coordinator. The zone coordinators then exchange
their submissions to produce the new Nodelist. As a result, it is
possible that the view from different zones may differ at any given
time.

9.3.1. The Nodediff

The format of the Nodediff is discussed in detail in [3]. In
preparing the Nodediffs, network coordinators may transmit only their
difference updates, which can be collated to produce the Nodediff
directly.

One weakness in the current approach is that there is no security
applied to the coordinator submissions. This leaves oen the
possibility of propagation of fraudulent updates. In order to address
this, [6] proposes addition of a shared secret to the update files.

9.3.2. Addition of nodes

In order to apply for allocation of a FidoNet address and membership
in the Nodelist, systems must demonstrate that they are functioning
by sending mail to the local network coordinator. Once the local
network coordinator receives the application, they then allocate a
new FidoNet address, and add a Nodelist entry.

9.3.3. Deletion of nodes

Since FidoNet nodes are required to be functioning during the zone
mail hour in order to receive mail, and since nodes receive the
weekly Nodelist from their local network coordinators on a weekly
basis, there is a built-in mechanism for discovery of non-functional
nodes.

Nodes found to be down are reported to the local network coordinator
and subsequently marked as down within the Nodelist. Nodes remaining
down for more than two weeks may be removed from the Nodelist, at the
discretion of the network coordinator.

9.4. Phone book update

The Nodelist contains the phone numbers and associated attributes of
each participating system. New Nodelists become available on Fridays,
and are made available to participating systems by their local
network coordinators, who in turn receive them from the regional and
zone coordinators.

While it is standard practice for participating systems to get their
Nodelists from their local network coordinators, should the local
network coordinator not be available for some reason, either the
updates or the complete Nodelist may be picked up from other network,
or regional coordinators. Please note that since the view from
different zones may differ, nodes wishing to update their Nodelists
should not contact systems from outside their zone.

9.5. Phone book compilation

Once FidoNet systems have received the Nodediff, the apply it to the
previous week's Nodelist in order to prepare a new Nodelist. In
order to receive Nodediffs and compile the Nodelist, the following
software is required:

A FidoNet-compatible mailer implementation, used to transfer files
A Nodelist compiler

One of the purposes of the Nodelist compiler is to apply Nodediffs to
the previous Nodelist in order to produce an updated Nodelist. The
other purpose is to compile the updated Nodelist into the format
required by the particular mailer implementation used by the member
system. It is important to note that while the Nodelist and Nodediff
formats are standardized (FTS-0005), as is the file transfer protocol
(FTS-0001), the compiled format used by each mailer is implementation
dependent.

One reason that compiled formats to differ is the addition of out of
band information to the Nodelist during the compilation process.
Added information includes phone call costs as well as shared
secrets.

9.5.1. Cost data

Although cost information is not part of the Nodelist, in compiling
the Nodelist into the format used by the mailer, Nodelist compilers
support the addition of cost information. This information is then
subsequently used to guide mailer behavior.

Since phone call costs depend on the rates charged by the local phone
company, this information is local in nature and is typically entered
into the Nodelist compiler's configuration file by the system
administrator.

9.5.2. Shared secrets

In FidoNet, shared secrets are used for authenticated sessions
between systems. Such authenticated sessions are particularly
important between the local, regional and zone coordinators who
handle preparation and transmission of the Nodediffs. A single shared
secret is used per system.

9.6. Accounting

Within FidoNet, the need for accounting arises primarily from the
need of local, regional and zone coordinators to be reimbursed for
their expenses. In order to support this, utilities have been
developed to account for network usage at the system level according
to various metrics. However, the accounting techniques are not
applied at the user level. Distributed authentication and acounting
are not implemented and therefore users may not roam between systems.

10. Acknowledgements

Thanks to Glen Zorn of Microsoft and Lynn Liu and Tao Wang of
AimQuest for useful discussions of this problem space.

Security Considerations

Security issues are discussed in sections 5.6 and 6.5.

11. References

[1] Cobb, S., "PPP Internet Protocol Control Protocol Extensions for
Name Server Addresses", RFC1877, Microsoft, December 1995.

[2] Fielding, R., et al., "Hypertext Transfer Protocol - HTTP/1.1.",
RFC2068, UC Irvine, January, 1997.

[3] Baker, B., R. Moore, D. Nugent. "The Distribution
Nodelist." FTS-0005, February, 1996.

[4] Lentz, A. "ISDN Nodelist flags." FSC-0091, June, 1996.

[5] Thomas, D. J. "A Proposed Nodelist flag indicating Online Times
of a Node." FSC-0062, April, 1996.

[6] Kolin, L. "Security Passwords in Nodelist Update Files."
FSC-0055, March, 1991.

[7] Gwinn, R., D. Dodell. "Nodelist Flag Changes Draft Document."
FSC-0009, November, 1987.

[8] Heller, R. "A Proposal for A FidoNet Domain Name
Service." FSC-0069, December, 1992.

[9] Rigney, C., Rubens, A., Simpson, W., and S. Willens, "Remote
Authentication Dial In User Service (RADIUS)", RFC2058, Livingston,
Merit, Daydreamer, January 1997.

[10] Rigney, C., "RADIUS Accounting", RFC2059, Livingston, January
1997.

12. Authors' Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: 206-936-6605
EMail: bernarda@microsoft.com

Juan Lu
AimQuest Corporation
1381 McCarthy Blvd.
Milpitas, California 95035

Phone: 408-273-2730 ext. 2762
EMail: juanlu@aimnet.net

John Alsop
i-Pass Alliance Inc.
650 Castro St., Suite 280
Mountain View, CA 94041

Phone: 415-968-2200
Fax: 415-968-2266
EMail: jalsop@ipass.com

James Ding
Asiainfo
One Galleria Tower
13355 Noel Road, #1340
Dallas, TX 75240

Phone: 214-788-4141
Fax: 214-788-0729
EMail: ding@bjai.asiainfo.com

Wei Wang
Merit Network, Inc.
4251 Plymouth Rd., Suite C
Ann Arbor, MI 48105-2785

Phone: 313-764-2874
EMail: weiwang@merit.edu