Transcript presentation9

COMP3122
Network Management
Richard Henson
Worcester Business School
March 2011
Week 9 – Thin Clients,
Connectivity, Mixed Networks,
and Virtualisation
• Objectives
– explain the reasoning behind using different levels for clientbased processing
– explain the similarities and differences in practical
implementations that deliver client-server functionality to the
desktop
– identify the software and hardware requirements for data one
one type of network to be forwarded onto another
– explain the process of terminal emulation and how terminal
services and other software can deliver this to the desktop
– Relate issues of bandwidth to the use of thin clients and
terminal services
A matter of Fashion or
Functionality?
• In the very early days of networking, there
were no clients… (or even users!)
– all computer input via cards and tape
– output only to printers
• When clients (or VDUS) were introduced,
early 1970s, they really were “dumb”!
– microprocessor only just been invented!
– interrupt driven processing hadn’t been implemented
The dawn of the
“intelligent client”
• First “8 bit” processor (Intel 8008)
available in 1973…
– took two years to develop a motherboard &
operating system
• expected that “users” would write their own apps
– 1975, the first microcomputer: The Altair
• scope for “intelligence on the desktop”
• By 1981, microcomputers popular in the
home…
– IBM PC was introduced to see whether business
would make use of desktop computing…
Success of the Business Micro
• Businesses used the IBM micro
– applications became commercially available
– large organisations wanted to exchange data…
• between desktops
• between desktop and server
• Through OSI & IEEE802 standards, the
networked PC & LANs became possible:
– centralised computers could interface with
microcomputers
– popular early implementations:
– Novell Netware
– DEC PCSA
Servers provide Services
• In the early days, the server (host) was king
– user device VDU (Visual Display Unit) or Terminal
had no processing ability
– everything controlled from the centre
• Once microcomputers could connect to
servers
– host-VDU/terminal -> server-client
– clients provided richer user experience
• But, servers retained control
– provided client access to resources via services
Clients make services
accessible to users…
• Servers hold secure data…
– should be kept well away from users!
• Users can only access data/resources on a
client-server network via a request to a server
• Depending on the server architecture:
– make requests directly via commands inputted
from a dumb terminal
– make requests from an intelligent client through
interprocess communication
Dumb Terminals
• Strictly speaking, not network devices at all!
– no local processing capability
• Still useful for allowing remote input and output
to a computer in a different location
– e.g. Bank ATM machines
– e.g. Travel Agent on-line booking facilities
• Advantages:
–
–
–
–
provide secure authentication to secure systems
work with low bandwidth
fairly robust
no local software, little to go wrong
Limitations of
Dumb Terminals
• Only offer a limited functionality to the
desktop user
– low resolution screen display
– fairly basic user interface
• Not really clients at all:
– can’t be used for client-server applications
– can’t support peripheral devices
Levels of Distribution in ClientServer computing
Client end
Server end
• Between them, client
and server need to
handle:
– processing
– storage
– resources
– applications
– security
The Basic Client
• Needs software to enable and manage
communication with the server
– MUST have some processing capability
– interprocess communication needs a common clientserver communication protocol e.g. TCP/IP
• First client service request in a user session is
likely to be domain logon…
– handled by redirector process:
• client-end requests services
• server-end either either accepts or rejects service requests
Installation of Domain Clients
• Much more complex than dumb terminals
– (just needed to be plugged in and switched
on!)
• Need to install an operating system and
networking software:
– EITHER manually using appropriate media
containing the necessary software
– OR by one of the previously discussed remote
methods from a shared distribution folder on a
server
• Final part:
– installed client needs to become part of the
domain so users can use it to log on
– Involves registering with active directory
Where to put Applications?
• Could be installed on the Server
– run remotely like web-based “SaaS” (software-as-aService) systems
– use local CPU power to run applications
• Problems:
– bandwidth (high – very high if application
downloaded)
– lot of CPU cycles on the server if many users on
SaaS
– local availability of dlls, drivers etc. to run the
required applications
End-User Computing & FAT Clients
• Users wanted to do it all from their own desktop
• Networks often slow…
– became standard practice to take distribution even further:
• install, access, run applications on clients
• Client machines running applications using their own
CPU cycles…
– took processing away from the centre: welcome
– allowed users to do their own thing: unwelcome!
– saved money on expensive, centralised computing:
management buy-in
• Result…
– most organisations rapidly put end-ser computing (and FAT
clients) into practice
Terminal Emulation
• All about making a PC or other device
behave as if it was a dumb terminal (!)
(thin client becomes 2D?)
– achieved through software running on client that
effectively bypasses the CPU for many processes
and sends them to the server
• Historically, terminal emulation has produced
a text-based screen display
– low usage of bandwidth
• Windows-based terminal emulation products
available for some time
– but.. higher usage of bandwidth to support GUI
Why Use Terminal
Emulation?
• Advantages:
– lower TCO
• makes use of old PCs (even old Pentium I, II)
• saves money having to upgrade existing machines
–
–
–
–
screen response very fast
enhanced security (no use of local memory or h/d)
remote server access for administrators
remote client support
• Disadvantages
– extra CPU and memory demands on the server
– still use some bandwidth
• clients running applications locally would use zero bandwidth
Terminal Emulation Options
• Citrix Metaframe
– very popular before Windows released
Terminal Server
– still an important player…
• Windows Terminal Server
– why bother with something else if the
product is already supplied… and
works?
Windows Servers &
Terminal Server (1)
• Like Citrix, allows multiuser access to a
Server at low bandwidth (e.g. using a
standard telephone link)
• Windows-based applications can run on the
server and utilise just a user interface at the
client end
– low bandwidth because just keystrokes, mouse
clicks and mouse movements are communicated
• Standard interface: users may have different
hardware, but the screen display will be the
same, no matter what the platform
Windows Servers &
Terminal Server (2)
• Terminal Server
–
–
–
–
Manages resources at the server end for each client session
Gives each user their unique desktop
Receives and processes all keystrokes and mouse actions
Directs all display output to the appropriate client
• Terminal Client:
– Just displays the desktop and GUI
Windows Servers &
Terminal Server (3)
• A Terminal Services client “session”
– opens on the client as a window within the existing
local desktop
– remote desktop runs within that window
– only uses CPU power to connect with the server
and display the user interface
– strictly speaking a “thin” client, but uses very few
local CPU cycles beyond those needed to run the
operating system
Windows Servers &
Terminal Server (4)
• Communications Protocol
– RDP (Remote Desktop Protocol)
– optimised to display graphical elements to
the clients
– application layer
– runs on top of TCP/IP
– like Microsoft NetMeeting, based on ITU
T120 standard
• http://www.imtc.org
Low Hardware & OS Requirements
of Terminal Services…
• Windows 2000/XP:
– 32Mb RAM, Pentium processor
• Windows 98:
– 16Mb RAM, 486
• Windows 95 (or even 3.1!!)
– 16Mb RAM, 386
• Windows CE
– depends on the vendor
• If non-windows platform
– use Citrix metaframe
Client-end Terminal
Services Software
• Versions:
– 16-bit for Windows-based computers running very
old Windows for Workgroups with the 32-bit
TCP/IP stack
– 32-bit Windows-based computers
– 64-bit with recent Windows (e.g. w2k3 r2)…
• Client support for:
– Windows CE Handheld PC
– Windows-based terminals
Applications and
Terminal Services
• 32-bit applications run more
efficiently
– using legacy 16-bit apps:
• reduced number of users can be
connected
• increased memory overhead
• 64-bit systems even more efficient..
Terminal Services
(Windows 2003 Enhancements)
• More users supported per high-end server
• Windows Management Instrumentation (WMI)
provider enhances remote management capabilities
• "Terminal Services Client“ -> Remote Desktop
Connection
– RDP 5.1 client features a much improved user interface
• Remote desktop users can:
– save connection settings
– easily switch between windowed and full screen mode
– dynamically alter their remote experience to match the
available bandwidth
Terminal Services & Windows 2003 -
continued
• Many local resources now available within the remote
session, including:
– client file system, smart cards, audio (output), serial ports,
printers (including network), and the clipboard
• Allows users to easily take advantage of the
capabilities of their client device from within the
remote session
– e.g. files can be opened, saved and printed to the users local
PC, regardless of whether the application is running locally
or remotely
– improved software restriction policies, roaming profile
enhancements, and new application compatibility modes.
– colour depth can be selected from 256 colors (8-bit) to True
Color (24-bit), and resolution can be set from 640 x 480 up
to 1600 x 120
Terminal Servers
• Preferably member servers, not domain
controllers
– need plenty of RAM (4-10 Mb required for
each user)
– recommended installed on an NTFS
partition (multisession security for each
users “live” data) & use fast, reliable hard
disks (pref SCSI, SCSI-2 and RAID)
– need a high performance network adapter
card
Unix
Terminal Emulation
• Microsoft favours FAT client
• Unix favours Thin client or terminal
emulation
– Packages like UWIN:
• runs via a PC
• emulates terminal services
• give features of a traditional Unix operating
system on a Windows platform desktop
Virtualisation (Windows 2008
Server, Citrix, VMware, etc.)
•
The use of software to allow a
piece of hardware to run multiple
operating system images at the
same time
– Possible to run Windows OS
under Mac OS
– run multiple versions of Windows
OS on the same PC
•
•
Slightly different from terminal
services but getting popular…
Enables the creation of a “virtual”
(rather than actual) version of any
software environment on the
desktop, e.g. Operating Systems,
a server, a storage device or
networks, an application
“The Cloud”
• Outsourcing on a grand scale…
– With connectivity via world wide web
• “Back to the Future”
– Quote from IBM in 1950s:
• “I think there is a world market for about five computers.”
attributed to J. Watson
– “The cloud” will behave like just one massive
mainframe computer providing all user services
– no FAT clients needed… just enough processing at
the client end to run a browser
• could be a very small device
• could use wireless protocols to connect…
What (physically) is The Cloud
• Lots of servers connected together in clusters to
provided different services
• Attractive but…
– has disadvantages of outsourcing in terms of control
– With extra challenge that the user doesn’t know
where there data physically is at a particular time…
SCARY?
• Server location also a matter of some concern
for legal reasons…
Thanks for listening
