Transcript Module 1.7 comparison and critiquex

NETWORKING CONCEPTS
COMPARISON OF OSI AND TCP/IP
 Common features
 Both are based on the concept of stack of
independent protocols
 Functionality of layers is roughly similar
 In both models the layers up through and
including the transport layer are there to provide
an end-to-end, network- independent transport
service to processes wishing to communicate
 in both models, the layers above transport
are application-oriented users of the transport
service
COMPARISON OF OSI AND TCP/IP
 Differences
 1. Three concepts are central to the OSI model:
 1. Services.
 2. Interfaces.
 3. Protocols.
 Services.
 The service definition tells what the layer does, not
how entities above it access it or how the layer
works
 Interface
 tells the processes above it how to access it
COMPARISON OF OSI AND TCP/IP
 The TCP/IP model did not originally clearly
distinguish between services, interfaces, and
protocols
 protocols in the OSI model are better hidden
than in the TCP/IP model and can be replaced
relatively easily as the technology changes
 2. The OSI reference model was devised before the
corresponding protocols were invented
 With TCP/IP the reverse was true: the protocols
came first, and the model was really just a
description of the existing protocols
COMPARISON OF OSI AND TCP/IP
 3. Difference between the two models is the
number of layers: the OSI model has seven layers
and the TCP/IP model has four.
 4. The OSI model supports both connectionless
and connection oriented communication in the
network layer, but only connection-oriented
communication in the transport layer
 The TCP/IP model supports only one mode in the
network layer (connectionless) but both in the
transport layer
A CRITIQUE OF OSI
 OSI model never became a popular one
 Reasons are
 1. Bad timing.
 2. Bad technology.
 3. Bad implementations.
 Bad timing.
 The time at which a standard is established is
absolutely critical to its success.
A CRITIQUE OF OSI
•This figure shows the amount of activity
surrounding a new subject.
A CRITIQUE OF OSI
 When the subject is first discovered, there is a burst of
research activity in the form of discussions, papers,
and meetings.
 After a while this activity subsides(less intense),
corporations discover the subject, and the billiondollar wave of investment hits.
 standards be written in the trough in between these
two
 If they are written too early (before the research results
are well established), the subject may still be poorly
understood; the result is a bad standard.
A CRITIQUE OF OSI
 If they are written too late, so many companies may
have already made major investments in different ways
of doing things that the standards are effectively
ignored.
 If the interval between the two is very short (because
everyone is in a hurry to get started), the people
developing the standards may get crushed(deform).
 It now appears that the standard OSI protocols got
crushed
 The competing TCP/IP protocols were already in
widespread use by research universities by the time
the OSI protocols appeared.
A
CRITIQUE
OF
OSI
 Bad Technology
 The OSI model, along with its associated service
definitions and protocols, is extraordinarily complex.
 They are difficult to implement and ineffient in
operation.
 Problem with OSI is that some functions, such as
addressing, flow control, and error control, reappear
again and again in each layer.
 Bad implementation
 Because of complexity of models and protocols initial
implementations were huge , unwidely and slow.
 In contrast , one of the implementation of TCP/IP was
good and people began using it quickly which led to a
large user community
A CRITIQUE OF TCP/IP
 First, the model does not clearly distinguish the
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concepts of services, interfaces, and protocols.
Second, the TCP/IP model is not at all general and is
poorly suited to describing any protocol stack other
than TCP/IP.
Trying to use the TCP/IP model to describe Bluetooth,
for example, is completely impossible.
Third ,the host-to-network layer is not really a layer in
the normal sense of the term used in the context of
layered protocols.
Fourth, TCP/IP model does not distinguish between
the physical and data link layers.
A proper model should include both as separate layers.
The TCP/IP model does not do this.
NOVEL NETWARE
 Novell NetWare is the most popular network system in the
PC world.
 It provides transparent remote file access and numerous
other distributed network services, including printer
sharing and support for various applications such as
electronic mail transfer.
 NetWare was developed by Novell, Inc., and introduced in
the early 1980s.
 Novell Networks are based on the client/server model in
which at least one computer functions as a network file
server, which runs all of the NetWare protocols and
maintains the networks shared data on one or more disk
drives
 NOVEL NETWARE PROTOCOL SUITE
 Novell provides a suite of protocols developed
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specifically for NetWare.
The five main protocols used by NetWare are
Media Access Protocol.
Internetwork Packet Exchange/Sequenced Packet
Exchange (IPX/SPX).
Routing Information Protocol (RIP).
Service Advertising Protocol (SAP).
NetWare Core Protocol (NCP).
 Media Access Protocols:
 The NetWare suite of protocols supports several
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media-access protocols, including
Ethernet/IEEE 802.3,
Token Ring/IEEE 802.5,
Fiber Distributed Data Interface (FDDI), and
Point-to-Point Protocol (PPP)
 IPX(Internetwork Packet Exchange protocol):
 Routing and networking protocol at Network layer.
When a device to be communicated whith is located
on a different network, IPX routes the information to
the destination through any intermediate networks.
 It datagram-based, connectionless, unreliable protocol
that is equivalent to the IP
 SPX(Sequenced Packet Exchange protocol):
 Control protocol at the transport layer (layer 3) for
reliable, connection-oriented datagram transmission.
 SPX is similar to TCP in the TCP/IP suite
 Routing Information Protocol (RIP):
 Facilitate the exchange of routing information on a
NetWare network.
 In RIP, an extra field of data was added to the packet to
improve the decision criteria for selecting the fastest
route to a destination
 Service Advertisement Protocol (SAP):
 It is an IPX protocol through which network resources,
such as file servers and print servers, advertise their
addresses and the services they provide.
 Advertisements are sent via SAP every 60 seconds.
 This SAP packet contains information regarding the
servers which provide services.
 Using these SAP packets, clients on the network are
able to obtain the internetwork address of any servers
they can access
 NetWare Core Protocol (NCP):
 It defines the connection control and service request
encoding that make it possible for clients and servers
to interact.
 This is the protocol that provides transport and session
services.
 NetWare security is also provided within this protocol.