This section introduces PPP configurations and terms that are used in this guide.
Solaris PPP 4.0 supports a number of configurations.
Switched access, or dial-up, configurations
Hardwired, or leased-line configurations
The previous figure shows a basic PPP link. The link has the following parts:
Two machines, usually in separate physical locations, called peers. A peer could be a personal computer, engineering workstation, large server, or even a commercial router, depending on a site's requirements.
Serial interface on each peer. On Solaris machines, this interface could be cua, hih, or other interface, depending on whether you configure asynchronous or synchronous PPP.
Physical link, such as a serial cable, a modem connection, or a leased line from a network provider, such as a T1 or T3 line.
The most commonly used PPP configuration is the dial-up link. In a dial-up link, the local peer dials up the remote peer to establish the connection and run PPP. In the dial-up process, the local peer calls the remote peer's telephone number to initiate the link.
A common dial-up scenario includes a computer in a user's home that calls a peer at an ISP, configured to receive incoming calls. Another dial-up scenario is a corporate site where a local machine in one building uses a PPP link to transmit data to a peer in another building.
In this guide, the local peer that initiates the dial-up connection is referred to as the dial-out machine. The peer that receives the incoming call is referred to as the dial-in server, although this machine is simply the target peer of the dial-out machine.
PPP is not a client-server protocol. Some PPP documents use the terms “client” and “server” to refer to telephone call establishment. A dial-in server is not a true server like a file server or name server. Dial-in server is a widely used PPP term because dial-in machines often “serve” network accessibility to more than one dial-out machine. Nevertheless, the dial-in server is simply the target peer of the dial-out machine.
The configuration for the dial-out (Location 1) side of the link is composed of the following elements:
Dial-out machine, typically a personal computer or workstation in an individual's home.
Serial interface on the dial-out machine. /dev/cua/a or /dev/cua/b is the standard serial interface for outgoing calls on machines that run Solaris software.
Asynchronous modem or ISDN terminal adapter (TA) connected to a telephone jack.
Telephone lines and services of a telephone company.
Telephone jack or similar connector, connected to the telephone network
Asynchronous modem or ISDN TA
Serial interface on the dial-in server, either ttya or ttyb for incoming calls
Dial-in server, which is connected to a network, such as a corporate intranet, or, in the instance of an ISP, the global Internet
External ISDN TAs have faster speeds than modems, but you configure them in basically the same way. The major difference in configuring an ISDN TA is in the chat script, which requires commands specific to the TA's manufacturer. Refer to Chat Script for External ISDN TA for information on chat scripts for ISDN TAs.
PPP configuration files on both the dial-out and dial-in peers contain instructions for setting up the link. The following process occurs as the dial-up link is initiated:
User or process on the dial-out machine runs the pppd command to start the link.
Dial-out machine reads its PPP configuration files and sends instructions over the serial line to its modem, including the phone number of the dial-in server.
Modem dials the phone number and establishes a telephone connection with the modem on the dial-in server.
If necessary, the dial-out machine sends commands to the dial-in server to invoke PPP on the server.
Modem attached to the dial-in server begins link negotiation with the modem on the dial-out machine.
The series of text strings that the dial-out machine sends to the modem and dial-in server are contained in a file called a chat script.
When modem-to-modem negotiation completes, the modem on the dial-out machine reports “CONNECT.”
PPP on both peers enters Establish phase, where Link Control Protocol (LCP) negotiates basic link parameters and the use of authentication.
If necessary, the peers authenticate each other.
PPP's Network Control Protocols (NCPs) negotiate the use of network protocols, such as IPv4 or IPv6.
A hardwired, leased-line PPP configuration involves two peers that are connected by a link that consists of a switched or unswitched digital service leased from a provider. Solaris PPP 4.0 works over any full-duplex, point-to-point leased-line medium. Typically, a company rents a hardwired link from a network provider to connect to an ISP or other remote site.
Both dial-up and leased-line links involve two peers that are connected by a communications medium. The next table summarizes the differences between the link types.
Leased Line |
Dial-up Line |
---|---|
Always connected unless a system administrator or power failure takes it down |
Initiated on demand, when a user tries to call a remote peer |
Uses synchronous communications |
Uses asynchronous communications |
Rented from a provider |
Uses existing telephone lines |
Requires synchronous units |
Uses less costly modems |
Requires specialized interfaces |
Uses standard serial interfaces that are included on most computers |
The parts of the leased-line link include:
Two peers, one at each end of the link. Each peer might be a workstation or server. Often the peer functions as a router between its network or the Internet, and the opposite peer.
Synchronous interface on each peer. Some machines that run Solaris software require you to purchase a synchronous interface card, such as HSI/S, to connect to a leased line. Other machines, such as UltraSPARCTM workstations, have built-in synchronous interfaces.
CSU/DSU synchronous digital unit on each peer, which connects the synchronous port to the leased line.
A CSU might be built-in to the DSU, or owned by you, or leased from a provider, depending on your locale. The DSU gives the Solaris machine a standard synchronous serial interface. With Frame Relay, the Frame Relay Access Device (FRAD) performs the serial interface adaptation.
Leased line, providing switched or unswitched digital services. Some examples are SONET/SDH, Frame Relay PVC, and T1.
SONET is called an octet synchronous link. PPP uses a framing mechanism similar to asynchronous framing over a SONET line. PPP does not use the expected bit-synchronous protocol.
On most types of leased lines, peers do not actually dial each other. Rather, a company purchases a leased-line service to explicitly connect between two fixed locations. Sometimes the two peers at either end of the leased line are at different physical locations of the same company. Another scenario is a company that sets up a router on a leased line that is connected to an ISP.
Leased lines are less commonly used than dial-up links, though the hardwired links are easier to set up. Hardwired links do not require chat scripts. Authentication is often not used because both peers are known to each other when a line is leased. After the two peers initiate PPP over the link, it stays active unless the leased line fails or either peer explicitly terminates the link.
A peer on a leased line that runs Solaris PPP 4.0 uses most of the same configuration files that define a dial-up link.
The following process occurs to initiate communication over the leased line: