Technical data

Conﬁguring Serial Lines

A serial connection is made between two systems using modems and telephone

lines or other serial lines. TCP/IP Services supports serial connections using the

PPP (Point-to-Point Protocol) and SLIP (Serial Line IP) protocols. SLIP includes

CSLIP (compressed SLIP). You can use any standard OpenVMS terminal device

as a PPP or SLIP line. (PPP is available for OpenVMS Alpha systems only.)

This chapter reviews key concepts and describes:

• How to set up a PPP interface (Section 3.2)

• How to set up a SLIP interface (Section 3.3)

• How to solve serial line problems (Section 3.4)

3.1 Key Concepts

If your OpenVMS system is part of a large network, you will probably use both

PPP and SLIP for your serial connections. As an Internet standard, PPP is often

preferred because it ensures interoperability between systems from a wide variety

of vendors. PPP provides a way for your OpenVMS Alpha system to establish a

dynamic IP network connection over a serial line without an additional router or

additional server hardware.

SLIP has been in use for a longer period of time and is available for most

terminal servers and in most PC implementations of TCP/IP. Because SLIP and

PPP do not communicate with each other, hosts wanting to communicate must

use the same protocol. For example, if your terminal server supports only SLIP,

remote hosts that connect through this server must also use SLIP.

3.1.1 PPP and SLIP

One of the largest applications for IP over serial lines is dialup access. With

this type of conﬁguration, the OpenVMS host answers calls and establishes a

connection initiated by a user on a client host. The client host can be another

OpenVMS system, a UNIX system, or a PC. Or users on the host can originate

the dialup connection to a remote host or terminal server running the same

protocol.

Dedicated serial lines running PPP or SLIP can also be used to connect separate

LANs into a single WAN. In such a conﬁguration, the host at each end of the

serial connection is always the same; no other hosts are allowed to connect to

either serial device.

Conﬁguring Serial Lines 3–1