Masahiro Goshima (Goshima.Masahiro@lab.ntt.co.jp)
NTT Network Service Systems Laboratories
Tohru Kidera (Kidera.Tohru@lab.ntt.co.jp)
NTT Network Service Systems Laboratories
Satoshi Takamatsu (firstname.lastname@example.org)
Kazumichi Takazawa (email@example.com)
An increase in the Internet use has caused the number of Internet dial-up users using NTT PSTN to grow. Most users dial up through the PSTN to access the Internet. NTT primarily has a usage-based tariff system for the Internet dial-up traffic. The holding time of dial-up connections is estimated to be more than five times as long as that of normal telephone calls. The corresponding investment required to accommodate the increasing number of users is putting a heavy burden on ISPs. Figure 1.1 illustrates how the current network architecture is facing a number of problems as Internet usage continues to grow.
To resolve these problems, we clearly need new network architecture. One such solution is shown in Figure 1.2. The idea behind this architecture is to detect and then separate the Internet dial-up calls from voice traffic at the Ingress Switch. The calls are then transported over an IP transport network to an ISP. How users dial up to access the Internet remains the same. In this network architecture, instead of going through the Ingress Switch, the transit network and the Egress Switch, the Internet dial-up calls only go through the Ingress Switch in the PSTN. Instead of sharing the common resources in the PSTN with the other users, end users of this service are exclusively assigned the internal switch resource in the Ingress Switch. Therefore, flat-rate services can be offered even in a usage based tariff system. The statistical multiplexing capabilities in IP transport network enable the Internet dial-up calls to be effectively transported over IP transport network, thus greatly reducing the additional investment in PSTN required to accommodate the increasing Internet dial-up traffic. In this new architecture, the Remote Access Server (RAS) which is connected to an Ingress Switch off-loads the dial-up Internet traffic from the existing PSTN, passes it through the high- speed IP transport network, and then transports it to the targeted Internet Service Provider (ISP). The ISP can avoid the increased investment in RASs needed to accommodate more users and can focus on its core competencies.
To examine the feasibility of this network architecture, NTT East and NTT West started a trial service named gIP Connectivity Serviceh in some areas of Tokyo and Osaka last November. In addition to assessing the feasibility of the network architecture, the trial service will look at user demands requirements, the possible impact of the Internet dial-up traffic on ordinary telephone calls and user traffic characteristics.
If the results of the feasibility
study are positive, NTT East and NTT West will launch a commercial IP Connectivity
Service. This paper details the trial service, including the network configuration,
the services offered to end users, and the interface between ISPs and NTT.
2. Overview of the trial service
2.1 Network configuration
In the IP Connectivity Service, Internet traffic from end users is transported through a Regional IP Network provided by NTT East and West to the ISPs end users have signed up with. The network configuration of the IP Connectivity Service is illustrated in Fig. 2.1.
Each ISP is connected to the Network
Terminator in the Regional IP Network of NTT East and West using a leased
line. And they allow the end users of the IP Connectivity Service to connect
through the Regional IP Network. End user dials a specified telephone number
using the normal dial-up protocol through an ISDN line and connects to
the RASs. Then, the end user can access the
Internet through the Regional IP Network. The end user simply selects the
ISP she/he has signed up with when she/he dials.
2.2 Service conditions for end users
The IP Connectivity Service is overviewed below.
The IP Connectivity Service is being provided as a trial service in the limited areas of Tokyo and Osaka for a one year period starting from last November. The target users of this service are end users who are connected via ISDN switch in the service area. They can access the Internet via the ISDN 1-B channel at a flat rate. The ISPs end users have signed up with must be connected to the Regional IP Network.
2.3 Service conditions for ISPs
The conditions for ISPs connected to this IP Connectivity Service are given below.
3.Technical Overview of IP Connectivity Service
3.1 End user authentication
An end user of the IP Connectivity Service can connect to her/his ISP using the normal dial-up connection protocol. This being so, to levy charges accurately and prevent illegal access, we have to identify end users at NTT and at the ISP. Two end user authentication functions are therefore needed. One verifies that the calling end user belongs to the IP Connectivity Service at the NTT network. The other verifies that the end user belongs to the ISP at the ISP network.
The first end user authentication procedure is processed at the ISDN switch in the NTT network. If a calling user identified by her/his caller-ID belongs to the IP Connectivity Service, she/he is allowed to connect to the RAS. This is called screening. In doing the processing, the ISDN switch does not charge according to the amount of time used; the IP Connectivity Service has a flat rate charge.
The second end user authentication
procedure is based on user information managed at authentication servers
at each ISP. When a call from a user is being connected, the end user sends
a username and password according to the PPP dial-up protocol. The Network
Terminator in the Regional IP Network will receive this username and password
from the end user and sends them to the authentication server in the ISP
network. This server authenticates the end user and the information to
accept or reject this user is sent to the Network Terminator. The end user
receives this information from the Network Terminator, and, if accepted,
she/he can connect to the Internet through the ISP. The RADIUS protocol
is used between the Network Terminator and the ISP authentication server.
The RADIUS protocol is an authentication protocol used by many ISPs.
3.2 IP addresses
The end user can connect to the Internet through the ISP she/he has signed up with. The IP addresses of the ISP therefore need to be set at the interfaces described below.
The end user needs an IP address of the ISP in the same way as that done using the dial-up connection. This IP address must be a global one that can be used to communicate with servers on the Internet.
The IP Connectivity Service allows the end user to connect at any time, so the ISP will have to prepare IP addresses for all end users and assign them to the end users.
3.3 Assigning an IP address to end-user
The IP addresses for end users described in 3.1 are assigned to end user terminals by PPP negotiation.
There are two ways of assigning these IP addresses.
Here, the IP addresses pooled at the authentication server at the ISP are assigned to the end user when the end user is dialing up.
3.4 Selection of ISP by end user
The IP Connectivity Service allows an end user to select the ISP she/he wants to connect to when she/he is dialing up. To enable this, the destination ISP must be specified from the key information sent by the end user to the RAS. The IP Connectivity Service uses the username of the PPP as the key information. The format of the username is the user-id for user authentication at the ISP, and g@h is used as a delimiter and identifier to specify the ISP. For example, in case of the end user whose user-id is guser1h and signed up with ISP A whose ISP identifier is gisp-a.ne.jph, she/he sets her/his username firstname.lastname@example.org on her/his terminal and dials up to the ISP A using this username.
After the call is connected at the
RAS, the end user is authenticated and the end user terminal sends a username
to the RAS. At this point, the RAS queries the ISP connection control server.
The ISP connection control server specifies the Network Terminator of the
destination ISP by the ISP identifier gisp-a.ne.jph. After the Network
Terminator is specified, the userfs call will be transferred to the Network
Terminator assigned for each ISP.
4. Current trial status and future plans
As to the current trial service status, the number of total end-users in NTT East and NTT West has already increased well over the initial projected number. The number of total ISPs in NTT East and NTT West has already exceeded the initial projected number. If the results of the feasibility study are positive, NTT East and NTT West will launch a commercial IP Connectivity Service.