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

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

CLIENT/SERVER APPLICATION:
CONNECTIVITY
The 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.

CLIENT/SERVER APPLICATION:
CONNECTIVITY

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)

INTERFACE IN THREE LAYERS
• Graphical user interface.
• Process request interface.
• Transaction and query manager interface.

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.

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)

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.

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

ISSUES IN IPC
Synchronous vs. Asynchronous IPC
Buffered vs unbuffered IPC
Reliable vs unreliable (best effort)
Ordered vs unordered
Streams vs messages

SYNCHRONIZATION
Message passing may be either blocking or non-blocking.
Blocking is considered synchronous
Non-blocking is considered asynchronous send and receive primitives may
be either blocking or non-blocking.

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

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)

BUFFERING
Queue of messages attached to the link; implemented in one of three ways.
1. Zero capacity – 0 messages
Sender must wait for receiver (rendezvous).
2.Bounded capacity – finite length of n messages or N bytes. Sender must
wait if link full.

RELIABLE AND ORDERED COMMUNICATION
IPC within a computer is always reliable but messages sent across a network
can get “lost”
Reliable communication, e.g. TCP
Unreliable or best effort communication, e.g UDP
Ordered communication
TCP messages always delivered in order
UDP messages may not be delivered in same order as they were sent

STREAMS VS MESSAGES
Streams
A “stream” of data is exchanged between sender and receiver
No message boundaries
Examples: “pipes” in UNIX, TCP streams
Messages
Sender & receiver see the same set of distinct messages
Examples: “message queues” in UNIX, UDP messages/datagrams

WIDE AREA NETWORK
What Is a WAN?
Point-to-Point Links
Switching
WAN Devices

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.

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.

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.

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

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

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

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.

TOKEN RING
A 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

TOKEN RING(cont.)
Created about the Same Time as Ethernet.
Standardized as 802.5
16 Mbps maximum speed
Token Passing Media Access Control
Special token frame circulates around the ring when no station is
transmitting
When a station gets the token, it may transmit a frame
When a station finishes sending the frame, it releases the token
Token Passing is Complex and Expensive

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.

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 frame
Deal with active monitor going down.

ETHERNET
It 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 threeOriginal (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, calledIn 1985, the Computer Society of the IEEE started a project, called
Project 802, to set standards to enable intercommunication amongProject 802, to set standards to enable intercommunication among
equipment from a variety of manufacturers.equipment from a variety of manufacturers.
Current version is calledCurrent version is called IEEE Ethernet

ETHERNET(CONT.)
Ethernet evolution for four generations

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

ETHERNET(CONT.)
10BaseT
Uses twisted pair Cat3 cable
Star-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

ETHERNET(CONT.)
10Base-T implementation

ETHERNET(CONT.)
10Base-F implementation

ETHERNET(CONT.)
Fast Ethernet
100 Mbps transmission rate
same frame format, media access, and collision detection rules as 10 Mbps Ethernet
can combine 10 Mbps Ethernet and Fast Ethernet on same network using a switch
media: twisted pair (CAT 5) or fiber optic cable (no coax)
Star-wire topology
Similar to 10BASE-T
CAT 3
CAT 5

ETHERNET(CONT.)
Fast Ethernet implementations

FDDI
Fiber 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).

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

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.

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

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

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

FDDI(cont.)
Advantages
FDDI 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.
Disadvantages
There'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.

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).

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.

NETWORK MANAGEMENT
A 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

NETWORK MANAGEMENT(CONT.)
components assist
●
Network device discoveryNetwork 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.

NETWORK MANAGEMENT(CONT.)
Tasks
●
Fault management
●
Configuration management
●
Performance management
●
Security management
●
Inventory management
●
Accounting management

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

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?

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

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

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

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

NETWORK MANAGEMENT SOFTWARE
●
Commercially
●
many offerings, UNIX and PC based
– HP OpenView
– SunNet Manager
– Cabletron Spectrum

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

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

NETWORK ACQUISITION
Before 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.

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.

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.

PC-LEVEL PROCESSING UNITS
Client/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

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.

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.

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.

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

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.

PEN
Pen-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.

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.

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.

UNIX WORKSTATION
User 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 intensive
Applications requiring UNIX, X-terminals connected to a UNIX
presentation server
Have more processing power than a PC client

X-TERMINALS
Provide the capability to perform only presentation services at the
workstation
Processing services are provided by another UNIX, Windows 3.x, NT,
OS/2 2.x, or VMS server
Minimum memory configuration requirement is 4-8 Mbytes RAM

SERVER HARDWARE
Vary according to the complexity of the application and the distribution of
work
Servers are multiuser devices, the number of active users is also a major
sizing factor
32-bit preemptive multitasking operating systems with storage protection
are preferred in the multiuser environment

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