Mobile computing is mostly associated with laptops, PDAs, and cellular phones and the data exchange between them. Mobile hardware components, such as external hard disks, flash drives, or digital cameras, can be connected to laptops or desktop systems. A number of software components are involved in mobile computing scenarios and some applications are tailor-made for mobile use.
The hardware of laptops differs from that of a normal desktop system. This is because criteria like exchangeability, occupied space, and power consumption are relevant properties. The manufacturers of mobile hardware have developed the PCMCIA (Personal Computer Memory Card International Association) standard. This standard covers memory cards, network interface cards, ISDN and modem cards, and external hard disks. How the support for such hardware is implemented in Linux, what needs to be taken into account during configuration, what software is available for the control of PCMCIA, and how to troubleshoot any possible problems is described in Chapter 31, PCMCIA.
The inclusion of energy-optimized system components when manufacturing laptops contributes to their suitability for use without access to the electrical power grid. Their contribution towards conservation of power is at least as important as that of the operating system. SUSE Linux supports various methods that influence the power consumption of a laptop and have varying effects on the operating time under battery power. The following list is in descending order of contribution towards power conservation:
Throttling the CPU speed
Switching off the display illumination during pauses
Manually adjusting the display illumination
Disconnecting unused, hotplug-enabled accessories (USB CD-ROM, external mouse, unused PCMCIA cards, etc.)
Spinning down the hard disk when idling
Detailed background information about power management in SUSE Linux and about operating the YaST power management module is provided in Chapter 33, Power Management.
Your system needs to adapt to changing operating environments when used for mobile computing. A lot of services depend on the environment and the underlying clients must be reconfigured. SUSE Linux handles this task for you.
The services affected in the case of a laptop commuting back and forth between a small home network and an office network are:
This includes IP address assignment, name resolution, Internet connectivity, and connectivity to other networks.
A current database of available printers and an available print server must be present, depending on the network.
As with printing, the list of the corresponding servers must be current.
If your laptop is temporarily connected to a beamer or an external monitor, the different display configurations must be available.
SUSE Linux offers several ways of integrating a laptop into existing operating environments:
SCPM (system configuration profile management) allows storage of arbitrary configuration states of a system into a kind of “snapshot” called a profile. Profiles can be created for different situations. They are useful when a system is operated in changing environments (home network, office network). It is always possible to switch between profiles. Find information about SCPM in Chapter 32, System Configuration Profile Management. You can use the kicker applet Profile Chooser in KDE to switch between profiles. The application requires the root password before switching.
NetworkManager is especially tailored for mobile networking on laptops. It provides a means to easily and automatically switch between network environments or different types of networks, such as wireless LAN and ethernet. NetworkManager supports WEP and WPA-PSK encryption in wireless LANs, dial-up connections (with smpppd). Both desktop environments (GNOME and KDE) include a front-end to NetworkManager.
Table 30.1. Use Cases for NetworkManager
is a laptop
is sometimes attached to different networks
provides network services (such as DNS or DHCP)
only uses a static IP address
Use the YaST tools to configure networking whenever NetworkManager should not handle network configuration.
For more information about NetworkManager and its applets refer to Section 18.5, “Managing Network Connections with NetworkManager”.
The service location protocol (SLP) simplifies the connection of a laptop to an existing network. Without SLP, the administrator of a laptop usually requires detailed knowledge of the services available in a network. SLP broadcasts the availability of a certain type of service to all clients in a local network. Applications that support SLP can process the information dispatched by SLP and be configured automatically. SLP can even be used for the installation of a system, sparing the effort of searching for a suitable installation source. Find detailed information about SLP in Chapter 19, SLP Services in the Network.
The emphasis of SCPM lies on enabling and maintaining reproducible system conditions. SLP makes configuration of a networked computer a lot easier by automating much of it.
There are various special task areas in mobile use that are covered by dedicated software: system monitoring (especially the battery charge), data synchronization, and wireless communication with peripherals and the Internet. The following sections cover the most important applications that SUSE Linux provides for each task.
Two KDE system monitoring tools are provided by SUSE Linux:
KPowersave is an applet that displays the state of the rechargeable battery in the control panel. The icon adjusts to represent the type of power supply. When working on AC power, a small plug icon is displayed. When working on batteries, the icon changes to a battery. The corresponding menu opens the YaST module for power management after requesting the root password. This allows setting the behavior of the system under different types of power supply. Find information about power management and about the corresponding YaST module in Chapter 33, Power Management.
KSysguard is an independent application that gathers all measurable parameters of the system into one monitoring environment. KSysguard has monitors for ACPI (battery status), CPU load, network, partitioning, and memory usage. It can also watch and display all system processes. The presentation and filtering of the collected data can be customized. It is possible to monitor different system parameters in various data pages or collect the data of various machines in parallel over the network. KSysguard can also run as a daemon on machines without a KDE environment. Find more information about this program in its integrated help function or in the SUSE help pages.
In the GNOME desktop, use the panel applet GNOME ACPI and the application System Monitor.
When switching between working on a mobile machine disconnected from the network and working at a networked workstation in an office, it is necessary to keep processed data synchronized across all instances. This could include e-mail folders, directories, and individual files that need to be present for work on the road as well as at the office. The solution in both cases is as follows:
Use an IMAP account for storing your e-mails in the office
network. Then access the e-mails from the workstation using any
disconnected IMAP–enabled e-mail client, like Mozilla Thunderbird
Mail, Evolution, or KMail as described in Applications.
client must be configured so that the same folder is always accessed
Sent messages. This ensures that all messages
are available along with their status information after the
synchronization process has completed. Use an SMTP server implemented
in the mail client for sending messages instead of the systemwide MTA
postfix or sendmail to receive reliable feedback about unsent mail.
There are several utilities suitable for synchronizing data between a laptop and a workstation. For detailed information, refer to Chapter 27, File Synchronization.
As well as connecting to a home or office network with a cable, a laptop can also wirelessly connect to other computers, peripherals, cellular phones, or PDAs. Linux supports three types of wireless communication:
With the largest range of these wireless technologies, WLAN is the only one suitable for the operation of large and sometimes even spatially disjointed networks. Single machines can connect with each other to form an independent wireless network or access the Internet. Devices called access points act as base stations for WLAN-enabled devices and act as intermediaries for access to the Internet. A mobile user can switch among access points depending on location and which access point is offering the best connection. Like in cellular telephony, a large network is available to WLAN users without binding them to a specific location for accessing it. Find details about WLAN in Section 34.1, “Wireless LAN”.
Bluetooth has the broadest application spectrum of all wireless technologies. It can be used for communication between computers (laptops) and PDAs or cellular phones, as can IrDA. It can also be used to connect various computers within visible range. Bluetooth is also used to connect wireless system components, like a keyboard or mouse. The range of this technology is, however, not sufficient to connect remote systems to a network. WLAN is the technology of choice for communicating through physical obstacles like walls. Find more information about Bluetooth, its applications, and configuration in Section 34.2, “Bluetooth”.
IrDA is the wireless technology with the shortest range. Both communication parties must be within viewing distance of each other. Obstacles like walls cannot be overcome. One possible application of IrDA is the transmission of a file from a laptop to a cellular phone. The short path from the laptop to the cellular phone is then covered using IrDA. The long range transport of the file to the recipient of the file is handled by the mobile network. Another application of IrDA is the wireless transmission of printing jobs in the office. Find more information about IrDA in Section 34.3, “Infrared Data Transmission”.
Ideally, you protect data on your laptop against unauthorized access in multiple ways. Possible security measures can be taken in the following areas:
Always physically secure your system against theft whenever possible. Various securing tools, like chains, are available in retail stores.
Important data should not only be encrypted during transmission, but also on the hard disk. This ensures its safety in case of theft. The creation of an encrypted partition with SUSE Linux is described in Section 4.3, “Encrypting Partitions and Files”.
|Data Security and Suspend to Disk|
Encrypted partitions are not unmounted during a suspend to disk event. Thus, all data on these partitions is available to any party who manages to steal the hardware and issue a resume of the hard disk.
Any transfer of data should be secured, no matter how it takes place. Find general security issues regarding Linux and networks in Section 4.5, “Security and Confidentiality”. Security measures related to wireless networking are provided in Chapter 34, Wireless Communication.