‫‪Chapter 1‬‬
‫‪Introduction‬‬
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Uses of Computer Networks
•Business Applications
•Home Applications
•Mobile Users
•Social Issues
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Business Applications of Networks
• A network with two clients and one server.
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Business Applications of Networks (2)
• The client-server model involves requests and replies.
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Home Network Applications
•Access to remote information
•Person-to-person communication such
BitTorrent
•Interactive entertainment
•Electronic commerce
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Home Network Applications (2)
• In peer-to-peer system there are no fixed clients and servers.
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Home Network Applications (3)
• Some forms of e-commerce.
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Mobile Network Users
• Combinations of wireless networks and mobile computing.
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Network Hardware
•Local Area Networks
•Metropolitan Area Networks
•Wide Area Networks
•Wireless Networks
•Home Networks
•Internetworks
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Broadcast Networks (2)
• Classification of interconnected processors by scale.
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PANs (Personal Area Networks
•PANs (Personal Area Networks) let devices
communicate over the range of a person. A
common example is a wireless network that
connects a computer with its peripherals
such as short-range wireless network called
Bluetooth
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Local Area Networks
A LAN is a privately owned network that operates
within and nearby a single building like a home,
office or factory.
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• Two broadcast networks
• (a) Bus
• (b) Ring
‫‪Examples of LAN Devices‬‬
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Metropolitan Area Networks
• A metropolitan area network based on cable TV.
A MAN (Metropolitan Area Network) covers a city
Examples:
 cable television networks
 IEEE 802.16 and is popularly known as WiMAX.
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Wide Area Networks
• Relation between hosts on LANs and the subnet.
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Wide Area Networks (2)
• A stream of packets from sender to receiver.
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Wireless Networks
•Categories of wireless networks:
•System interconnection
•Wireless LANs
•Wireless WANs
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Wireless Networks (2)
• (a) Bluetooth configuration
• (b) Wireless LAN
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Wireless Networks (3)
• (a) Individual mobile computers
• (b) A flying LAN
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Home Network Categories
•Computers (desktop PC, PDA, shared peripherals
•Entertainment (TV, DVD, VCR, camera, stereo, MP3)
•Telecomm (telephone, cell phone, intercom, fax)
•Appliances (microwave, fridge, clock, furnace, airco)
•Telemetry (utility meter, burglar alarm, babycam).
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Network Software
•Protocol Hierarchies
•Design Issues for the Layers
•Connection-Oriented and Connectionless Services
•Service Primitives
•The Relationship of Services to Protocols
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Network Software
Protocol Hierarchies
• Layers, protocols, and interfaces.
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‫)‪Protocol Hierarchies (2‬‬
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Protocol Hierarchies (3)
• Example information flow supporting virtual communication in layer
5.
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Design Issues for the Layers
•
•
•
•
•
•
•
•
Addressing
Error Control
Flow Control
Multiplexing
Routing
Resource Allocation
Confidentiality
Authentication
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Connection-Oriented and Connectionless
Services
• Six different types of service.
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Service Primitives
• Five service primitives for implementing a simple connection-oriented
service.
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Service Primitives (2)
• Packets sent in a simple client-server interaction on a connectionoriented network.
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Services to Protocols Relationship
• The relationship between a service and a protocol.
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Reference Models
•The OSI Reference Model
•The TCP/IP Reference Model
•A Comparison of OSI and TCP/IP
•A Critique of the OSI Model and Protocols
•A Critique of the TCP/IP Reference Model
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 Reference Models
The OSI
reference
model.
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 The Physical Layer
• The physical layer is concerned with transmitting
raw bits over a communication channel.
• making sure that when one side sends a 1 bit it is
received by the other side as a 1 bit, not as a 0 bit.
• what electrical signals should be used to represent
a 1 and a 0,
• how many nanoseconds a bit lasts,
• how many pins the network connector has, and
what each pin is used for.
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 The Data Link Layer
• The main task of the data link layer having the sender break
up the input data into data frames (typically a few hundred
or a few thousand bytes) and transmit the frames
sequentially.
• If the service is reliable, the receiver confirms correct receipt
of each frame by sending back an acknowledgement frame.
• let the transmitter know when the receiver can accept more
data.
• Broadcast networks have an additional issue in the data link
layer: how to control access to the shared channel. A special
sublayer of the data link layer, the medium access control
sublayer, deals with this problem.
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 The Network Layer
• The network layer controls the operation of the subnet.
• determining how packets are routed from source to destination.
• They can also be determined at the start of each conversation,
for example, a terminal session, such as a login to a remote
machine,
• determined anew for each packet to reflect the current network
load.
• If too many packets are present in the subnet at the same time,
they will get in one another’s way, forming bottlenecks. Handling
congestion is also a responsibility of the network layer,
• quality of service provided (delay, transit time, jitter, etc.) is also a
network layer issue.
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 The Transport Layer
• The basic function of the transport layer is to accept data from
above it,
• split it up into smaller units if need be, pass these to the network
layer,
• ensure that the pieces all arrive correctly at the other end.
• The transport layer also determines what type of service to
provide to the session layer,
• The most popular type of transport connection is an error-free
point-to-point channel that delivers messages or bytes in the
order in which they were sent.
• The type of service is determined when the connection is
established.
• The transport layer is a true end-to-end layer; it carries data all
the way from the source to the destination.
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 The Session Layer
• The session layer allows users on different machines to
establish sessions between them.
• Sessions offer various services, including dialog control
(keeping track of whose turn it is to transmit),
synchronization (checkpointing long transmissions to allow
them to pick up from where they left off in the event of a
crash and subsequent recovery).
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 The Presentation Layer
• Unlike the lower layers, which are mostly concerned with
moving bits around, the presentation layer is concerned
with the syntax and semantics of the information
transmitted.
• In order to make it possible for computers with different
internal data representations to communicate, the data
structures to be exchanged can be defined in an abstract
way, along with a standard encoding to be used ‘‘on the
wire.’’ The presentation layer manages these abstract data
structures and allows higher-level data structures (e.g.,
banking records) to be defined and exchanged.
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 The Application Layer
• The application layer contains a variety of protocols that are
commonly needed by users. One widely used application
protocol is HTTP (HyperText Transfer Protocol), which is
the basis for the World Wide Web. When a browser wants a
Web page, it sends the name of the page it wants to the server
hosting the page using HTTP. The server then sends the page
back. Other application protocols are used for file transfer,
electronic mail, and network news.
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Reference Models (2)
• The TCP/IP reference model.
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 The Link Layer
• The lowest layer in the model, the link layer describes what links
such as serial lines and classic Ethernet must do to meet the needs of
this connectionless internet layer.
• It is not really a layer at all, in the normal sense of the term, but
rather an interface between hosts and transmission links.
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 The internet layer
• The internet layer is corresponding roughly to the OSI network layer.
• Its job is to permit hosts to inject packets into any network and have them
travel independently to the destination (potentially on a different
network).
• The internet layer defines an official packet format and protocol called
IP (Internet Protocol), plus a companion protocol called ICMP (Internet
Control Message Protocol) that helps it function. The job of the
internet layer is to deliver IP packets where they are supposed to go.
Packet routing is clearly a major issue here, as is congestion (though IP
has not proven effective at avoiding congestion).
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 The Transport Layer
• the transport layer. It is designed to allow peer entities on the source
and destination hosts to carry on a conversation, just as in the OSI
transport layer. Two end-to-end transport protocols have been
defined here. The first one,
1. TCP(Transmission Control Protocol), is a reliable connectionoriented protocol that allows a byte stream originating on one
machine to be delivered without error on any other machine in
the internet.
 It segments the incoming byte stream into discrete
messages and passes each one on to the internet layer.
 At the destination, the receiving TCP process
reassembles the received messages into the output
stream.
 TCP also handles flow control to make sure a fast sender
cannot swamp a slow receiver with more messages than
it can handle.
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2.
UDP (User Datagram Protocol), is an unreliable, connectionless protocol for
applications that do not use sequencing or flow control.
It is also widely used for one-shot, client-server-type request-reply queries
and applications in which prompt delivery is more important than accurate
delivery, such as transmitting speech or video.
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 The Application Layer
• Applications simply include any session and presentation functions that
they require.
• It contains all the higher-level protocols. The early ones included
 virtual terminal (TELNET),
 file transfer (FTP),
 electronic mail (SMTP).
 Domain Name System (DNS), for mapping host names onto their
network addresses,
 HTTP, the protocol for fetching pages on the World Wide Web,
 RTP, the protocol for delivering real-time media such as voice or
movies
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Reference Models (3)
• Protocols and networks in the TCP/IP model initially.
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 Asynchronous transfer mode (ATM)
• Asynchronous transfer mode (ATM) is a switching technique used by
telecommunication networks that
• uses asynchronous time-division multiplexing to encode data into
small, fixed-sized cells. This is different from Ethernet or Internet,
which use variable packet sizes for data or frames.
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A cell is defined as a small,
fixed-size block of
information.
 Why using ATM cells?
• Asynchronous transfer mode was designed with cells in mind. This is
because voice data is converted to packets and is forced to share a
network with burst data (large packet data) passing through the
same medium. So, no matter how small the voice packets are, they
always encounter full-sized data packets, and could experience
maximum queuing delays. This is why all data packets should be of
the same size.
• ATM creates fixed routes between two points before data transfer
begins, which differs from TCP/IP, where data is divided into packets,
each of which takes a different route to get to its destination.
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ATM Virtual Circuits
• A virtual circuit.
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 ATM Architecture
ATM is a cell-switched network consists of the following components:
1. The user access devices, called the endpoints, are
2. connected through a user-to-network interface (UNI) to the
switches inside the network.
3. The switches are connected through network-to-network
interfaces (NNIs).
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‫‪ ATM Architecture‬‬
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 Virtual Connections
Connection between two endpoints is accomplished through
transmission paths, virtual paths, and virtual circuits.
1. A transmission path (TP) is the physical connection (wire, cable,
satellite, and so on) between an endpoint and a switch or between
two switches. A transmission path is divided into several virtual
paths.
2. A virtual path (VP) provides a connection or a set of connections
between two switches. Cell networks are based on virtual circuits
(VCs).
3. All cells belonging to a single message follow the same virtual
circuit and remain in their original order until they reach their
destination.
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ATM Virtual Circuits (2)
• An ATM cell.
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The ATM Reference Model
• The ATM reference model.
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The ATM Reference Model (2)
• The ATM layers and sublayers and their functions.
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