How to Be an ISP
Revision 2.3 Mar/1999 - Marcio Saito

About this document
This document explains the basic hardware and software pieces necessary to provide dialup and dedicated Internet access services. Our focus in on small Internet Service Providers (ISPs) and our objective is to put the Cyclades products in the context of an ISP network and provide pointers to other basic hardware and software information.

The Basic ISP Network

ISP Network

The Internet and the WAN Up-link
    Of course, to provide Internet access services, an ISP network needs to be connected to the Internet. The connection is through one or more WAN up-links to Internet backbone providers or a higher-level ISP.
   Small ISPs usually start with a single Backbone provider and WAN up-link. As the number of users grows, there is the need for communication line and provider backups.
   The WAN up-link should be a permanent connection (typically a leased line with PPP or Frame Relay) and be dimensioned to support the external traffic generated by the local users.
   Dimensioning the bandwidth of the up-link is more an art than a science.
   The only way to absolutely guarantee that there will be no bandwidth bottleneck for Internet access would be simply to multiply the maximum throughput a user can generate by the number of access lines.
   But that is not practical because Internet traffic is of burst nature and not all the users generate continuous traffic all the time. For example, a Net surfer generates traffic only while a new WEB page is being downloaded. While the user is actually reading the information (which is usually most of the time) the line is idle.
   You have also to consider the outbound traffic (external users accessing internal WEB server, for example).
   So, dimensioning the up-link connection requires analysis of the user profile in your case and the number of people accessing your servers from the Internet. Here are some basic references for you to start with.
   Very small ISPs serving remote areas with only a small number of dialup users (let's say, 16 access lines) and without high-traffic local WEB servers can live with a switched 56kbps line.
   Most small-to-medium ISPs will need one or more fractional T1 or T1 lines to provide the bandwidth and redundancy necessary to support professional Internet services.
   Medium-to-large ISPs might need higher-speeds up-link connections, from multiple T1 lines and multiple higher-level providers to T3 and faster lines.

The Uplink Router
    The Up-link router needs to support the physical interface (typically serial for connection to an external DSU/CSU or direct T1/FT1 interface) and the data-link protocol (typically PPP or Frame Relay). It also has to be fast enough to support the throughput generated by the users without imposing a performance bottleneck.
   The Cyclades-PR3000 is a mid-range router that can provide a very attractive solution. Because of its flexibility and modularity, it can support any physical interface ranging from dialup connections to serial with external DSU/CSU to direct connection to the T1 line. Because it has 3 WAN slots, it can grow with your needs, support backup and alternative connections and also consolidate up-link access Router and Remote Access Server functions all in one box.
   The Cyclades-Pathrouter is a good option for small ISPs who are looking for a cost-effective solution for single T1, Fractional T1 or 56kbps up-links. It has 2 serial ports that can be connected to external DSU/CSUs and/or support backup links.

The PSTN and the dialup access lines
    The primary service provided by most ISPs is dialup access to the Internet. Home or business users dial in and get access to mail, WEB browsing and other Internet applications.
   A typical home user will be using a PC with Windows Operating System and will be connected through an analog modem (V.34 or V.90) and analog phone line. Power users might use terminal adapters and ISDN lines.
   The type and number of access lines is a function of the number of users and their profile. When dimensioning the number of lines, the objective is to have the minimum number that can still provide adequate access to all your customers.
   A factor to consider is the pattern of use during the day. Home users tend to connect in the evening through the night and perform more file transfers. Business users tend to generate traffic spread during the day. You need to consider worst case scenarios in order to prevent users from getting busy signals.
   As a basic reference, ISPs usually reserve 1 access line for each 10 customers. For a small number of access lines (the practical maximum number of analog phone lines you can get coming to the building), an ISP can use regular analog phone lines connected to analog modems and then to the Remote Access Server. Notice that ISPs using analog phone lines in the server side cannot support the new V.90/56kbps modem standard. When the number of lines grows, the Phone Company will install ISDN PRI or channelized T1 lines to bring the dialup calls directly to your building in digital form. Each ISDN PRI line is equivalent to 23 phone lines (23 data channels plus one control channel).

The Remote Access Server
    The Remote Access Server is the equipment that answers to the calls and provides PPP connectivity to the remote dialup clients.
   If you are using regular analog phone lines in the ISP side, those lines will be connected to a modem bank. Rack-mountable or professional modem banks are recommended for reliability. You would use V.34 modems to provide the fastest possible service (V.90 modems will work in V.34 mode if installed with analog phone lines in the ISP side).
   In this case, the modems are typically connected via RS-232 serial interfaces to the Terminal Server.
   The terminal server can be a stand-alone box with dedicated hardware and software. The Cyclades-PR3000/TS is a good example of product that can perform this function. The PR3000 has also the advantage of being modular and supporting both remote access server and routing functionality in one box.
   Some people prefer to build their own server-based terminal server. In this case, a PC server running Linux/Unix or NT acts as a terminal server. To connect the modem bank to the server, you need multiple RS-232 serial ports in the PC. Cyclades offers a complete range of multi-port serial cards, including the Cyclom-Y family of RISC based serial cards (cost-effective, for small-to-medium installations up to 32 ports) and the Cyclades-Z family of high-end solutions (high-performance, for medium to large or high-throughput installations up to 64 ports per PCI slot).
   If the dialup calls are coming through an ISDN PRI line, the Remote Access Server has to connect directly to it and usually it includes the digital modems (which can support V.90/56kbps) and the PPP terminal server in one box. Those remote access servers integrate a lot of functionality (they replace the terminal server, cabling and modems in a traditional configuration) and, because of that, are usually the most expensive piece of equipment in a small ISP network.
   The Cyclades-PR4000 is a Remote Access Server that supports connection to Ethernet (10 and 10/100BT), 2 T1/E1 PRI lines and up to 64 internal digital modems and is one of the most cost-effective and powerful solutions in its category. It also has a WAN slot and built-in router functionality that allows it to be a POP-in-a-box (see POPs later in this document).

The ISP Local Area Network
    The ISP backbone will typically be an Ethernet LAN that connects all the major components in the network. To implement that, the ISP will need an Ethernet 10BT hub (for small networks) or switch (for better performance in larger networks).
   10BT interfaces are good enough for the WAN equipment, but you may want to use 100BT for the server connections, specially if you have a lot of traffic.
The routers, remote access servers and other servers need to support Ethernet connectivity.

Point-of-Presence (POP)
    As an ISP grows, it needs to be present in other geographical areas to be able to provide dialup access using local phone numbers. They need to establish Points-of-Presence (POP) at the locations the customers are.
   A POP is basically the same network as the one described here for the central ISP site, with the exception that some of the servers (authentication, WEB, mail) don't need necessarily to be present (a POP can use the services from the central site). So, you can see a POP as a small ISP network that has the central ISP site as a "up-link provider".
   As previously said, the Cyclades-PR4000 and Cyclades-PR3000/TS can perform remote access server and router functions (POP-in-a-box).

Dedicated Access Services
    Besides providing dialup access to home and business users, the ISP can also provide dedicated connectivity to small and medium business.
   Those customers will typically be connected to the ISP site through a dedicated 56kbps or fractional T1 link using PPP or Frame Relay and an access router at their location.

The Routers for POP and Dedicated Service Access
    To connect POPs and corporate customers with dedicated service, the ISP needs routers at the central site. Ideally, they can support multiple remote sites simultaneously with different types of connection.
   The Cyclades-PR3000, with its ability to support a variety of physical interfaces and several simultaneous WAN links (up to 8, with the SSE-8) is the best fit for a central site router.
   In the POP or corporate customer site, there is a need of an access router that connects the LAN to the router in the central site through the WAN access line.
   The Cyclades-Pathrouter is usually the solution that provides the most cost-effective solution for access routing at the remote site.

The Authentication Server
   Dialup service requires a user database to control user access and a way to do accounting and billing.
   The Remote Access Server can support a small local database, but we strongly recommended a centralized authentication server in the network.
   A centralized server, besides allowing for growth by supporting multiple Remote Access Servers, can provide accounting and billing functions as well as allowing better control over the access lines (preventing a given user to use several dialup lines simultaneously, for example).
   The authentication server is usually a Linux/Unix or NT PC system (dedicated to authentication or shared with some other server function) and authentication server software. There are commercial products as well as good servers that can be downloaded from the Internet.
   Two of the most popular free authentication server software packages are:

    The remote access server must support the authentication protocol used by the authentication server. The Cyclades-PR3000/TS and Cyclades-PR4000 are compatible with any authentication server that supports RADIUS (which is the most common and recommended) or TACACS authentication protocols.

The WEB Server
   The ISP needs WEB Servers to host its own WEB site as well as to be able to provide WEB hosting services to the corporate users.
   A WEB Server will typically be a Linux/Unix or NT PC system (dedicated or shared with other server functions) with WEB server software. The most popular WEB servers are:

    Another option is WEB server appliances, equipment with dedicated hardware and software to support WEB hosting (so that you don't need to install software). Several companies also sell PCs pre-configured as WEB servers.

The Mail Server
    Mail Servers are another basic service provided by almost all ISPs.
   Mail server software runs in a Linux/Unix or NT PC server (dedicated or shared with other servers) and is responsible for routing/storing e-mail traffic. To allow users to read e-mail from outside the ISP network, you would need also a POP server.
   Examples of mail servers:

Other software modules and equipment to consider
    Besides the basic equipment and software, there are several other pieces of technology to consider when setting an ISP to provide more than just dialup access.

"No break" power systems to avoid service interruption and data corruption.