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CLIENT SERVER COMPUTING – UNIT III II ME CSE 2015-16 ODD SEMESTER (III SEMESTER)

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CLIENT SERVER COMPUTING – UNIT III II ME CSE

2015-16 ODD SEMESTER (III SEMESTER)

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TOPICS Connectivity Communication interface technology Interposes communication Wide area network technologies Network topologies Network management Client-server system development Client-server system hardware PC-level preprocessing unit Macintosh Notebooks Pen UNIX workstation X-terminals Server hardware

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CLIENT/SERVER APPLICATION: CONNECTIVITYThe communication middleware software provides the

means through which clients and servers communicate to perform specific actions.

Middleware provides basis for logical view of Client/Server architecture.

Moreover, middleware enables the realization of the promises of distributed Client/Server computing concepts.

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CLIENT/SERVER APPLICATION: CONNECTIVITY

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CLIENT/SERVER APPLICATION: LAYERED ARCHITECTURE

• In client/server architecture as a design approach, the functional components of an application are partitioned in a manner that allows them to be spread and executed across different computing platforms, and share access to one or more common repositories.

• Client/ server architecture is therefore a design approach that distributes the functional processing of an application across two or more different processing platforms. The phrase ‘client/server’ reflects the role played by an application’s functions as they interact with one another.

• One or more of these functions is to provide a service, typically in the form of a database server that is commonly used by other functions across the application(s)

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INTERFACE IN THREE LAYERS

• Graphical user interface.• Process request interface.• Transaction and query manager interface.

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INTERFACE

• An interface enables a component in one layer to communicate with a component in another layer; it also enables a component to interact with another component in the same layer.

• Communication between components in the same layer is indicated by a semi-circular arrow. Moreover, we can say that this describes a collection of mutually cooperating components that make request to each other, both within and across layers, with its components working together thus, and processing various requests

• Wherever they comes from; a business application comes to life.

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INTERFACE

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INTERPOSES COMMUNICATION (IPC)• Mechanism for processes to communicate and to synchronize

their actions. • Message system – processes communicate with each other

without resorting to shared variables. • IPC facility provides two operations:❍ send(message) – message size fixed or variable❍ receive(message) ❒ If P and Q wish to communicate, they need

to: ❍ establish a communication link between them ❍exchange messages via send/receive ❒ Implementation of

communication link ❍ physical (e.g., shared memory, hardware bus) ❍ logical (e.g., logical properties)

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DIRECT COMMUNICATION

• Processes must name each other explicitly:❍ send (P, message) – send a message to process P❍ receive(Q, message) – receive a message from process Q• Only makes sense on a single computer unless distributed operating

system that implements a global process name space is being used• Properties of communication link❍ Links are established automatically.❍ A link is associated with exactly one pair of communicating

processes.❍ The link may be unidirectional, but is usually bidirectional.

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INDIRECT COMMUNICATION• Messages are directed and received from mailboxes (also

referred to as ports). ❍ Each mailbox has a unique id/address ❒ Primitives are

defined as: • send(A, message) – send a message to mailbox A receive(A,

message) – receive a message from mailbox A ❍ The mailbox address A can be local or remote ❒ Operations ❍ create a new mailbox ❍ send and receive messages through mailbox ❍ destroy a mailbox

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ISSUES IN IPC

Synchronous vs. Asynchronous IPCBuffered vs unbuffered IPCReliable vs unreliable (best effort)Ordered vs unorderedStreams vs messages

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SYNCHRONIZATION

Message passing may be either blocking or non-blocking.

Blocking is considered synchronousNon-blocking is considered asynchronous send and

receive primitives may be either blocking or non-blocking.

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SYNCHRONIZATION

• Synchronization• Synchronous receive❍ Receiving process blocks until message is copied into• user-level buffer• Asynchronous receive❍ Receiving process issues a receive operation (specifying a

buffer) and then carries on with other tasks❍ It either polls the OS to find out if the receive has completed or

gets an interrupt when the receive has completed❍ Threads allow you to program an asynchronous receive in a

synchronous way• Issue a synchronous receive with one thread while carrying out

other tasks with other threads

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SYNCHRONIZATION

• OS view vs Programming Languages view of• synchronous communication• OS view❍ synchronous send ⇒ sender blocks until message has been copied from

application buffers to kernel buffer❍ Asynchronous send ⇒ sender continues processing after notifying OS of the buffer

in which the message is stored; have to be careful to not overwrite buffer until it is safe to do so

PL view:❍ synchronous send ⇒ sender blocks until message has been received by the

receiver❍ asynchronous send ⇒ sender carries on with other tasks after sending message

(OS view of synchronous communication is asynchronous from the PL viewpoint)

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BUFFERING

Queue of messages attached to the link; implemented in one of three ways.

1. Zero capacity – 0 messagesSender must wait for receiver (rendezvous).2.Bounded capacity – finite length of n messages or N

bytes. Sender must wait if link full.

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RELIABLE AND ORDERED COMMUNICATION

IPC within a computer is always reliable but messages sent across a network can get “lost”

Reliable communication, e.g. TCPUnreliable or best effort communication, e.g UDPOrdered communicationTCP messages always delivered in orderUDP messages may not be delivered in same order as

they were sent

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STREAMS VS MESSAGES

StreamsA “stream” of data is exchanged between sender and receiverNo message boundariesExamples: “pipes” in UNIX, TCP streamsMessagesSender & receiver see the same set of distinct messagesExamples: “message queues” in UNIX, UDP messages/datagrams

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WIDE AREA NETWORKWhat Is a WAN? Point-to-Point Links Switching WAN Devices

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WHAT IS A WAN?

• A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

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POINT-TO-POINT LINKS

• A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network.

• Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only.

• These circuits are generally priced based on bandwidth required and distance between the two connected points.

• Point-to-point links are generally more expensive than shared services such as Frame Relay.

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CIRCUIT SWITCHING

• Switched circuits allow data connections that can be initiated when needed and terminated when communication is complete.

• This works much like a normal telephone line works for voice communication.

• Integrated Services Digital Network (ISDN) is a good example of circuit switching.

• When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network.

• In the case of ISDN circuits, the device actually places a call to the telephone number of the remote ISDN circuit.

• When the two networks are connected and authenticated, they can transfer data.

• When the data transmission is complete, the call can be terminated.

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WAN DEVICES A WAN switch is a

multiport internetworking device used in carrier networks. These devices typically switch such traffic as Frame Relay, X.25, and SMDS, and operate at the data link layer of the OSI reference mode

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ACCESS SERVER

An access server acts as a concentration point for dial-in and dial-out connections.

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MODEM

• A modem is a device that interprets digital and analog signals, enabling data to be transmitted over voice-grade telephone lines.

• At the source, digital signals are converted to a form suitable for transmission over analog communication facilities.

• At the destination, these analog signals are returned to their digital form

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ISDN TERMINAL ADAPTER

• An ISDN terminal adapter is a device used to connect ISDN Basic Rate Interface (BRI) connections to other interfaces, such as EIA/TIA-232 on a router.

• A terminal adapter is essentially an ISDN modem, although it is called a terminal adapter because it does not actually convert analog to digital signals.

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TOKEN RINGA Token Ring network is a local area network (LAN) in

which all computers are connected in a ring or star topology and a bit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time.

The Token Ring protocol is the second most widely-used protocol on local area networks after Ethernet.

The IBM Token Ring protocol led to a standard version, specified as IEEE 802.5

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TOKEN RING(cont.)Created about the Same Time as Ethernet.Standardized as 802.516 Mbps maximum speedToken Passing Media Access ControlSpecial token frame circulates around the ring when no station is transmittingWhen a station gets the token, it may transmit a frameWhen a station finishes sending the frame, it releases the tokenToken Passing is Complex and Expensive

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TOKEN RING(CONT.)

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TOKEN RING(cont.)Cable Types•Type 1–A shielded data grade cable with two solid wire twisted pairs.–Available in indoor and outdoor versions.

•Type 2–A Type 1 indoor cable with four solid twisted pairs of 24 AWG wire. –Contains four voice grade wires along with four data grade wires.

•Type 3–Unused existing telephone wire or EIA category 3 wire (4 Mbps operation).–Category 4 is needed for 16 Mbps (speed of the Token Ring) operation. –Must use a special media filter.

•Type 5–100/140 micron fiber cable used for fiber optic repeater links.

•Type 6– Often used for patch cables.•Patch cables can be used for MAU-to-MAU connection or from a wall outlet to a network attachment.

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TOKEN RING(cont.)Token Maintenance Issues

Loss of token (no token circulating)Duplication of token (forgeries or mistakes)The need to designate one station as the active ring monitor.Persistently circulating frameDeal with active monitor going down.

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ETHERNETIt is a LAN protocol that is used in Bus and Star topologies and implements CSMA/CD as the medium access method.Original (traditional) Ethernet developed in 1980 by three Original (traditional) Ethernet developed in 1980 by three companies: Digital, Intel, Xerox (DIX).companies: Digital, Intel, Xerox (DIX).In 1985, the Computer Society of the IEEE started a project, called In 1985, the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication among Project 802, to set standards to enable intercommunication among equipment from a variety of manufacturers.equipment from a variety of manufacturers.Current version is called Current version is called IEEE Ethernet

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ETHERNET(CONT.)Ethernet evolution for four generations

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ETHERNET(CONT.)Connection of stations to the medium using 10Base2

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ETHERNET(CONT.)10BaseTUses twisted pair Cat3 cableStar-wire topology

• A hub functions as a repeater with additional functions

• Fewer cable problems, easier to troubleshoot than coax

• Cable length at most 100 meters

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ETHERNET(CONT.)10Base-T implementation

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ETHERNET(CONT.)10Base-F implementation

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ETHERNET(CONT.)Fast Ethernet100 Mbps transmission ratesame frame format, media access, and collision detection rules as 10 Mbps Ethernetcan combine 10 Mbps Ethernet and Fast Ethernet on same network using a switchmedia: twisted pair (CAT 5) or fiber optic cable (no coax)Star-wire topologySimilar to 10BASE-T

CAT 3

CAT 5

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ETHERNET(CONT.)Fast Ethernet implementations

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FDDIFiber Distributed Data Interface (FDDI)FDDI is a set of ANSI and ISO standards for data

transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles).

The FDDI protocol is based on the token ring protocol.In addition to being large geographically, an FDDI local

area network can support thousands of users.FDDI is frequently used on the backbone for a wide area

network (WAN).

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FDDI(cont.)An FDDI network contains two token rings, one for possible

backup in case the primary ring fails.The primary ring offers up to 100 Mbps capacity. If the

secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps.

The single ring can extend the maximum distance; a dual ring can extend 100 km (62 miles).

FDDI is a product of American National Standards Committee X3-T9 and conforms to the Open Systems Interconnection (OSI) model

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FDDI(cont.) FDDI token passing allows multiple frames to circulate around the ring at the same time. Priority levels of a data frame and token can be set to allow servers to send more data

frames. Time sensitive data may also be given higher priority. The second ring in a FDDI network is a method of adjusting when there are breaks in the

cable. The primary ring is normally used, but if the nearest downstream neighbor stops

responding the data is sent on the secondary ring in attempt to reach the computer. Therefore a break in the cable will result in the secondary ring being used. There are two network cards which are:

Dual attachment stations (DAS) used for servers and concentrators are attached to both rings.

Single Attachment stations (SAS) attached to one ring and used to attach workstations to concentrators.

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FDDI(cont.)FDDI Uses Counter-Rotating Primary and Secondary

Rings

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FDDI(cont.)FDDI Specifications Map to the OSI Hierarchical Model

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FDDI(cont.)CharacteristicsTopology - Double ring.Cable - Fiber.Speed - 100Mbps.Maximum segment length - 2000 meters.Media access - Token passing.Maximum nodes on the network - 500.

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FDDI(cont.)AdvantagesFDDI supports real-time allocation of network bandwidth.This allows you to use a wide array of different types of traffic.FDDI has a dual ring that is fault-tolerant. The benefit here is that if a station on the ring fails or if the cable becomes damaged, the dual ring is automaticaly doubled back onto itself into a single ring.The FDDI compensates for wiring failures. The stations wrap within themselves when the wiring fails.Optical bypass switches are used that can help prevent ring segmentation. The faild stations are eliminated from the ring.

DisadvantagesThere's a potential for multiple ring failures.As the network grows, this possibility grows larger and larger.The use of fiber optic cables are expensive.This has kept many companies from deploying FDDI in a widespread manner. Instead, they have been using copper wire and the similar method of CDDI.

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CDDI(cont.)Copper Data Distribution Interface (CDDI)CDDI is the copper version of FDDI.Copper data distribution interface (CDDI) is an implementation of fiber distributed

data interface (FDDI) networking.CDDI uses cabling, which is unshielded twisted pair cables (UTP) made of copper.CDDI also uses the same protocols and constructs as FDDI, but uses copper wire

as the medium.CDDI/FDDI was considered a good system for implementing a campus network

backbone in the early to mid 1990s.However, it has since been rendered obsolete by Ethernet and then Gigabit

Ethernet and is no longer used.This term is also known as twisted-pair distributed data interface (TP-DDI).

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CDDI(cont.) This network can support thousands of users or terminals as well as cover a wide

geographical area. CDDI is not widely applied due to the decrease in the price of fiber optic installation, which

has greater efficiency, a much higher bandwidth and an immunity to interference. Data transfer in CDDI has a throughput of 100 Mbps when using a redundancy architecture. CDDI is the same networking system as FDDI, although the medium for the transmission is

copper twisted-pair wire instead of fiber optic cables. Copper cables are no longer widely used because they can only stretch as far as 100 meters,

compared to 1,000 meters for fiber optic cables. CDDI is commonly implemented in a wide geographical area For a local area network (LAN), CDDI (Copper Distributed Data Interface) is a standard for

data transmission based on FDDI (Fiber Distributed Data Interface) that uses shielded twisted-pair (STP) or unshielded twisted pair (UTP) copper wire instead of fiber optic lines.

CDDI supports a dual-ring capacity of 200 Mbps.

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NETWORK MANAGEMENTA network management system (NMS) is a set of hardware and/or software tools that allow an IT professional to supervise the individual components of a network within a larger network management framework

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NETWORK MANAGEMENT(CONT.)components assist●Network device discovery Network device discovery - identifying what devices are present on a network.●Network device monitoring - monitoring at the device level to determine the health of network components and the extent to which their performance matches capacity plans and intra-enterprise service-level agreements (SLAs).●Network performance analysis - tracking performance indicators such as bandwidth utilization, packet loss, latency, availability and uptime of routers, switches and other Simple Network Management Protocol (SNMP) -enabled devices.●Intelligent notifications - configurable alerts that will respond to specific network scenarios by paging, emailing, calling or texting a network administrator.

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NETWORK MANAGEMENT(CONT.)Tasks

● Fault management● Configuration management● Performance management● Security management● Inventory management● Accounting management

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FAULT MANAGEMENT

● Detection● Exception alarm generation● Investigation and analysis● Statistics for steady state behaviour characterisation

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CONFIGURATION MANAGEMENT

● Installation of new hardware/software● Tracking changes in control configuration

● who, what and why!● Revert/undo changes● Change management● Configuration audit

● does it do what was intended?

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IP Route Management

● Routing integrity● Consistency with customer requirements● Consistency with external peers● Conformance with imposed policy constraints

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SECURITY MANAGEMENT● Exception alarm generation● Detection● Uniform access controls to resources● Backup

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PERFORMANCE MANAGEMENT● Availability and Reliability metrics● Quality metrics● Real-time measurement● Historical analysis

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ACCOUNTING MANAGEMENT● Identifying consumers and suppliers of network

resources● Mapping network resources to customer identity● Charge back

● volumetric data● time data● date time of day

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NETWORK MANAGEMENT SOFTWARE● Commercially

● many offerings, UNIX and PC based– HP OpenView– SunNet Manager– Cabletron Spectrum

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SIMPLE NETWORK MANAGEMENT PROTOCOL(SNMP)SNMP is a tool (protocol) that allows for remote and local management of items on the network including servers, workstations, routers, switches and other managed devices.➢Comprised of agents and SNMP is a tool (protocol) that allows for remote and local management of items on the network including servers, workstations, routers, switches and other managed devices. Comprised of agents and managers ManagerManager - process running on a management workstation that requests information about devices on the network Agent - process running on each managed node collecting information about the device it is running on

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SNMP(cont.) Advantages Standardized Universally supported Extendible Portable Allows distributed management access Lightweight protocol

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NETWORK ACQUISITIONBefore selecting client hardware for end users, most

organizations should define standards for classes of users. This set of standards simplifies the selection of the

appropriate client hardware for a user and allows buyers to arrange purchasing agreements to gain volume pricing discounts.

There are a number of issues to consider when selecting the client workstation, including processor type, coprocessor capability, internal bus structure, size of the base unit, and so on.

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NETWORK ACQUISITION(cont.)However, of these issues, one of the most overlooked regarding

client/server applications is the use of a GUI. GUI applications require VGA or better screen drivers.Screens, larger than the 15-inch PC standard, are required for users

who normally display several active windows at one time the more windows active on-screen, the larger the monitor viewing area requirements.

The use of image, graphics, or full-motion video requires a large screen with very high resolution for regular usage.

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NETWORK ACQUISITION(cont.)It is important to remember that productivity is dramatically

affected by inability to easily read the screen all day. Inappropriate resolution will lead to fatigue and inefficiency.

The enterprise on the desk requires that adequate bandwidth be available to provide responsiveness to the desktop user.

If regular access to off LAN data is required, a router based internetworking implementation will be required.

If only occasional off LAN access is required, bridges can be used.

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A CLIENT-SERVER NETWORK

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PC-LEVEL PROCESSING UNITSClient/server applications vary considerably in their client processing

requirements and their I/O demands on the client processor and server. In general, clients that support protected-mode addressing should be

purchased. This implies the use of 32-bit processors—perhaps with a 16-bit I/O

bus if the I/O requirement is low. Low means the client isn't required to send and receive large amounts

of data, such as images, which could be 100K bytes or larger, on a constant basis

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PC-LEVEL PROCESSING UNITS(cont.)As multiwindowed and multimedia applications become prevalent

during 1994, many applications will require the bandwidth only provided by a 32-bit I/O bus using VESA VL-bus or Intel PCI technology.

Windowed applications require considerable processing power to provide adequate response levels.

The introduction of application integration via DCE, OLE, and DOE significantly increases the process ing requirements at the desktop.

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PC-LEVEL PROCESSING UNITS(cont.)The recommended minimum configuration for desktop processors has the

processing capacity of a 33Mhz Intel 486SX. By early 1995, the minimum requirement will be the processing capacity of a

50Mhz Intel 486DX or a 33Mhz Intel Pentium.

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PC-LEVEL PROCESSING UNITS(cont.)

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NOTEBOOKS

Users working remotely on a regular basis may find that a notebook computer best satisfies their requirements.

The notebook computer is the fastest growing market today. The current technology in this area is available for Intel PC, Apple

Macintosh, and SPARC UNIX processors. Because notebooks are "miniaturized," their disk drives are often not

comparable to full-size desktop units. Thus, the relatively slower speed of disk I/O on notebooks makes it

preferable to install extra RAM, creating "virtual" disk drives.

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NOTEBOOKS(cont.)

A minimal configuration is a processor with the equivalent processing power of a 33Mhz Intel 486SX, 8mbytes of RAM and 140Mbytes of disk.

In addition, the notebook with battery should weigh less than seven pounds and have a battery life of three hours.

Color support is an option during 1994 but will be mandatory for all by 1995.

In addition, if the application will run a remote GUI, it is desirable to install software to compress the GUI and V.32 modem communications at 9600 bps or V.32bis at 14400 bps, employing V.42 and V.42bis compression

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NOTEBOOKS(cont.)

The effective throughput is two to three times the baud rate because of compression.

The use of MNP4 and V.42 or MNP5 and V.42bis error correction enables these speeds to work effectively even during noisy line conditions.

The introduction of PCMCIA technology, credit card size modems, and flash memory are available to upgrade the notebook.

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NOTEBOOKS(cont.)

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PENPen-based clients provide the capability to operate applications

using a pen to point and select or write without the need for a mouse or keyboard.

Frequently, they are used for verification, selection, and inquiry applications where selection lists are available.

Developers using this technology use object-oriented software techniques that are RAM-intensive.

The introduction of personal digital assistant (PDA) technology in 1993 has opened the market to pocket size computing.

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PEN(cont.)During 1994, this technology will mature with increased storage

capacity through cheaper, denser RAM and flash memory technology.

The screen resolution will improve, and applications will be developed that are not dependent upon cursive writing recognition.

The PDA market is price-sensitive to a $500-$1000 device with the capability to run a Windows-like operating environment in 4MB of RAM, a 20Mhz Intel 486SX processor, and 8MB of flash memory.

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PEN(cont.)Devices with this capability will appear in 1994, and significant

applications beyond personal diaries will be in use.During 1995, 16MB of RAM and 32MB of flash memory will begin

to appear, enabling these devices to reach a mass market beyond 1996.

In combination with wireless technology advances, this will become the personal information source for electronic news, magazines, books, and so on.

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UNIX WORKSTATIONUser running Client/Server applications form DOS or

Windows typically run only a single business process at a time

Used when the client processing needs are intensiveApplications requiring UNIX, X-terminals connected to

a UNIX presentation serverHave more processing power than a PC client

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X-TERMINALSProvide the capability to perform only presentation

services at the workstationProcessing services are provided by another UNIX,

Windows 3.x, NT, OS/2 2.x, or VMS serverMinimum memory configuration requirement is 4-8

Mbytes RAM

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SERVER HARDWAREVary according to the complexity of the application

and the distribution of workServers are multiuser devices, the number of active

users is also a major sizing factor32-bit preemptive multitasking operating systems

with storage protection are preferred in the multiuser environment