Thin Client Server and Operating System

Frequently Asked Questions

kfetro@gmail.com — Mon, 25 Jan 2010 10:00:00 +0100

What is Lan Core?
Lan Core is a compendium of tools (software applications) used to assemble a network based on thin client technology, i.e. using thin client hardware, terminals or equivalent in the client side.
What is a thin client?
Referring to a hardware device, a thin client is basically a computer in which has been removed every component that meets any (almost one) of the following criteria: 1) the component is not strictly necessary, or 2) the functionality performed by the component can be provided by an external computer (a server or workstation).
Due to its minimum hardware requirements a thin client computer is usually small and lightweight (it can even be portable). Although can be find other kinds of computers working as thin clients, e.g. common personal computers (PC), obsolote or out-of-date computers, low-performance devices, etc.
What is a terminal?
Terminal should be understood as a synonym of thin client. This term is probably older than the term thin client, since it was used to refer to the consoles that were connected to mainframe computers in the 70s.
What is a workstation?
A workstation is a computer commonly connected to a local area network (LAN) and includes a multi-user operating system. This is basically the definition of any current personal computer (PC), and therefore a simple PC can be used as a workstation.
A workstation can also be known as a server in a thin client network.

The previous image shows a network scenario (based on a LAN), with two ways: i) PCs connected to a server, and ii) thin clients (terminals) to a workstation.

Pre-boot Execution Environment (PXE) protocol

kfetro@gmail.com — Mon, 18 Jan 2010 10:00:00 +0100

The Pre-boot Execution Environment (PXE) protocol (see PXE Internet Draft) is a combination of two protocols: the Dynamic Host Configuration Protocol (DHCP) and the Trivial File Transfer Protocol (TFTP). However, both protocols, DHCP and TFTP, require some modifications of their original specification to be compliant with the PXE specification (version 2.1). The first protocol, DHCP, is the most currently used protocol for the dynamic IP address allocation in a local area network (LAN). It is used by PXE to assign an IP address to a thin client during the boot, and locate the appropriate boot server (or servers) to continue booting over the network. After obtaining an IP address, the thin client downloads those packages needed to work: boot loader, operating system (kernel), file system, etc. And this is done using a file transfer protocol, the Trivial FTP or TFTP.

In the document DHCP Options and BOOTP Vendor Extensions (RFC 2132) are specified those options that should be added in the configuration of the DHCP service in order to make it compliant with PXE. The options to be added are:

Boot file name. The name of the bootable kernel image to be downloaded by the thin client.
Root path (optional).
Next server IP address (optional). DHCP and TFTP servers can be installed on different computers, in this case the DHCP service must provide the IP address of the computer where the TFTP server is located.

Optionally (we do not know the level of importance of it) must be taken into consideration the following proposed extension of the DHCP specification: Dynamic Host Configuration Protocol (DHCP) Options for the Intel Preboot eXecution Environment (PXE) (RFC 4578).

The basic TFTP protocol is defined in RFC 1350. However, the PXE protocol requires some modifications on the original specification of the TFTP protocol. RFC 2348 defines an extension of the basic TFTP protocol for larger block sizes required by PXE.

Multiple Remote Desktop Sessions in Windows

kfetro@gmail.com — Mon, 11 Jan 2010 10:00:00 +0100

Currently there exist some solutions that allow the connection of several remote sessions simultaneously on a Windows XP by using the native and proprietary Microsoft Remote Desktop Protocol (RDP). However, there are no free solutions, and these are essential in the Windows XP operating system because it does not provide (by default) terminal services for multiple users. Main of these applications are:

WinConnect by ThinSoft (Holdings) Inc.
XP Unlimited by IPConsult B.V.

On the other hand, there is a patch that allows to increase the number of clients that can stay simultaneously connected to a Windows XP Professional through terminal services, i.e. using the native RDP provided by Microsoft in (some of) their Windows systems.

Terminal Server Patch for Windows XP Professional with Service Pack 2. Self installation. Limited to three simultaneous sessions. Provided by sala source.
Terminal Server Patch for Windows XP Professional with Service Pack 2 or Service Pack 3. Non-tested!
Improved Terminal Server Patch for Windows XP Professional with Service Pack 2 without (known) limits on the number of simultaneous desktops (sessions). It includes a file with installation instructions.
Improved Terminal Server Patch for Windows XP Professional with Service Pack 3.

Installation requirements:

The only version of Windows XP that allows remote desktop access (by using the native RDP protocol) is the professional one. The home version of Windows XP does not support remote desktop access, and therefore it can not be patched.
The system must be updated with the Windows XP Service Pack 2 (SP2) or Service Pack 3 (SP3).

Configuration requirements:

Fast User Switching must be turned on. To check this feature you can follow the Microsoft instructions: Start, Control Panel, User Accounts, Change the way users log on or off, and verify that the check box Use Fast User Switching is turned on.
The Windows system cannot be configured within a domain, therefore the system must be only configured as a member of a workgroup. To check it go to: Start, Control Panel, System, select the Computer Name tabulation and click in Change. Then make sure that your computer is configured as a member of a workgroup.

Remote Desktop Protocols and Network Computing

kfetro@gmail.com — Mon, 04 Jan 2010 10:00:00 +0100

Remote desktop (initially known as virtual network computing) is a technique originally designed to control (or manage) a computer remotely through the desktop, and currently is the basis of thin client technology. Nowadays almost every operating system includes a native remote desktop protocol. Windows, Linux or Mac operating systems are not exceptions. Some of these protocols are:

Virtual Network Computing (VNC) is probably the first technique commonly used to manage remote desktops. It is based on a protocol called Remote FrameBuffer (RFB).
Remote Desktop Protocol (RDP). A proprietary protocol developed by Microsoft and included natively in most Windows operating systems as terminal services.
Independent Computing Architecture (ICA) designed by Citrix Systems. Another proprietary protocol initially designed to improve the poor remote desktop services provided by Windows in the beginning.
X Display Manager Control Protocol (XDMCP) is the remote desktop protocol provided by an X Window System (commonly called as X or X11). X is the desktop environment used in Unix-like operating systems. Note that X is primarily a protocol and it does not contain any specification for application user interface design. Instead, an X Window Manager is used.

Including other strategies such as the provided by NX technolgy.

NX is not really a protocol but an adaptation of the X Windows System with two new features: 1) compression of the communication to minimize the amount of information transmitted by the remote desktop, and 2) routing of information through a secure communication channel (e.g. by using a secure shell protocol, SSH).