Networking CS509
01. Introduction
Data Communication
De nitions:
data: information presented in whatever form is agreed upon by
the parties creating and using the data.
Data communications: are the exchange of data between two
devices via some form of transmission medium such as a wire
cable.
Effectiveness of a data communications:
4 fundamental characteristics
TAJD: Timeliness, Accuracy, Jitter, Delivery
1. Timeliness. The system must deliver data in a timely manner.
delivering data as they are produced, in the same order, and
without signi cant delay. This kind of delivery is called real-
time transmission.
2. Accuracy. must deliver the data accurately. if the data have
been altered in transmission and left uncorrected are unusable.
3. Jitter. refers to the variation in the packet arrival time. It is the
uneven delay in the delivery of audio or video packets.
4. Delivery. must deliver data to the correct destination. Data
must be received by the intended device or user and only by that
device or user.
Components of data communication system
5 components
Sender sends a Message to Receiver through a Medium encoded in
Protocol
1. Message. The message is the information (data) to be
communicated. any form: text, numbers, pictures, audio, and
video.
2. Sender:
3. Receiver:
the device that sends or receives the data message. It can be
a computer, workstation, telephone handset, video camera, and
so on
4. Medium. The transmission medium is the physical path by
which a message travels from sender to receiver. Some
examples of transmission media include twisted-pair wire,
coaxial cable, ber-optic cable, and radio waves.
5. Protocol. is a set of rules that govern data communications. It
represents an agreement between the communicating devices.
Data Flow
Simplex, Half-Duplex, Full-duplex
1. Simplex: one direction, one-way street, Ex: Keyboards,
Monitors
2. Half-duplex: each can send and receive but not in the same
time
3. Full-duplex: both send and receive in the same time, either 2
separate transmission path (physical) or the capacity of channel
is divided
Networks
def. : network is the interconnection of a set of devices capable of
communication.
according to de nition we have Host/end system and Connecting devices
router, which connects the network to other networks
switch, which connects devices together
modem (modulator-demodulator), which changes the form of
data
Network Criteria
performance, reliability, and security.
1. Performance
measured
a. Transit time is the amount of time required for
a message to travel from one device to
another.
b. Response time is the elapsed time between an
inquiry and a response.
Depends on factors
a. number of users
b. type of medium
c. capabilities of the connected hardware
d. the ef ciency of the software.
evaluated by two metrics: throughput and delay. We often
need more throughput and less delay. contradiction
2. Reliability measured by the frequency of failure, the time it
takes a link to recover from a failure, and the network’s
robustness in
a catastrophe.
3. Security protecting data from unauthorized access, protecting
data from damage and development, and implementing policies
and procedures for recovery from breaches and data losses.
Physical Structure
link is a communications pathway that transfers data from one device to
another. For communication to occur, two devices must be connected in some way
to the same link at the same time.
Type of connection
Point-to-Point: dedicated link between two devices. Ex. remote
control infrared.
Multi-Point also called multidrop: more than 2 devices share
single link. the capacity is shared.
spatially shared: several devices can use the
link simultaneously
timeshared: If users must take turns
Physical Topology
refers to the way in which a network is laid out physically
The topology of a network is the geometric representation of the
relationship of all the links and linking devices (usually called nodes) to one
another.
1. Mesh
every device has a dedicated point-to-point link to every other
device
each host must have I/O ports = (n-1) to connect to (n-1) hosts
Advantages of Mesh:
a. each connection carries its own data load
b. no traf c problem
c. robust when one link becomes unusable
d. privacy and security for only intended recipient,
fault-isolation and fault-identi cation made easy
by redirecting traf c away from suspected host
disadvantages:
a. amount of cabling
b. number of I/O Ports
Example: backbone connecting the main computers of a hybrid
network that can include several other topologies. Ex. Local
telephones
2. Star
each device has a dedicated point-to-point link only to a central
controller, usually called a hub
Advantages:
a. each host needs one link and one I/O device to
connect to any n hosts, less cabling
b. easier to maintain, install and con gure, moving
or deletion only on affected links
c. robust: one link fails, other links remains active
d. fault identi cation & fault isolation. As long as
the hub is working,
Disadvantages:
a. dependency on one single point, the hub.
b. cabling: Mesh > star > Bus or Ring
commonly used in LAN (High-Speed LAN often uses star with
central hub)
3. Bus
is multipoint. One long cable acts as a backbone to link all the
devices in a network
Node -> Drop Line -> Tap (connector) -> Backbone (main cable)
signal becomes weaker as it travels farther. limit on the number
of taps a bus can support and on the distance between those
taps.
Advantages: ease of installation, less cabling,
Disadvantages:
dif cult reconnection and fault isolation
dif cult to add new devices. requires
modi cation of backbone
Signal re ection at the taps can cause
degradation in quality. This degradation can be
controlled by limiting the number and spacing of
devices connected to a given length of cable
fault or break in the bus cable stops all
transmission even between devices on the same
side, re ecting signals and creating noise on
both directions
was the rst topologies used in LANs
4. Ring
dedicated point-to-point connection with only the two devices
on either side of it
signal is passed along the ring in one direction, from device to
device, until it reaches its destination.
Each device in the ring incorporates a repeater. When a device
receives a signal intended for another device, its repeater
regenerates the bits and passes them along
a. easy to install and recon gure
b. Each device is linked to only its immediate
neighbors (either physically or logically)
c. To add or delete a device requires changing only
two connections.
d. in a ring a signal is circulating at all times
e. fault-isolation: If one device does not receive a
signal within a speci ed period, it can issue an
alarm. The alarm alerts the network operator to
the problem and its location
disadvantages:
a. unidirectional traf c
b. a break in the ring can disable the entire network
c. This weakness can be solved by using a dual ring
or a switch capable of closing off the break
IBM uses it in its LANs, Token Ring.
the need for higher-speed LANs has made this topology less popular.
Network Types
1. LAN (Local Area Network)
usually privately owned and connects some hosts in a single of ce,
building, or campus.
2 or more hosts
small home or business building
each host has an address (identi er)
each packet sent by host contains host & destination address
in the past, packet sent from one host was received by all other
hosts, the destination accept it and other hosts drop it.
today by using smart connecting switch it sends the packets to
destination
2. WAN (Wide Area Network)
same as LAN but differs in the following:
LAN interconnects hosts; a WAN interconnects connecting
devices such as switches, routers or modems.
LAN is normally limited in size, spanning an of ce, a building,
or a campus; a WAN has a wider geographical span, spanning a
town, a state, a country, or even the world.
LAN is normally privately owned by the organization that uses
it; a WAN is normally created and run by communication
companies and leased by an organization that uses it.
1. Point-to-Point WAN: network that connects two
communicating devices through a transmission media (cable or
air).
2. Switched WAN: a network with more than two ends, backbone
of global communication today, several point-to-point WANs
connected by switches.
3. Internetwork
LANs and WANs are not isolated in modern world. as they are connected
to one another. when 2 or more networks are connected they are internetwork.
router blocks the message if it's sent to the same of ce, and switches
direct it to its destination.
4. Switching
an internetwork is a switched network in which a switch connects at least
two links together. to forward data from a network to another
1. Circuit-Switched Network: dedicated connection, called a
circuit, is always available between the two end systems; the
switch can only make it active or inactive
2. Packet-Switched Network: the communication between the
two ends is done in blocks of data called packets.
5. the Internet
composed of thousands of interconnected networks
At the top level, the backbones are large networks owned by
some communication companies such as Sprint, Verizon
The backbone networks are connected through some complex
switching systems, called peering points.
At the second level, there are smaller networks, called provider
networks, that use the services of the backbones for a fee. The
provider networks are connected to backbones and sometimes
to other provider networks.
The customer networks are networks at the edge of the Internet
that actually use the services provided by the Internet. They pay
fees to provider networks for receiving services.
Backbones and provider networks are also called Internet
Service Providers (ISPs).
Accessing the Internet:
the user needs to be physically connected to an ISP. The
physical connection is normally done through a point-to-point
WAN
a. dial-up: modem converts data to voice, very
slow and when using the landline the connection
is lost
b. DSL: allows the line to be used simultaneously
for voice and data communication.
c. Cable Networks: using cable TV service, higher
speed connection, speed varies according to
number of users using the same cable.
d. Wireless Networks: can connect to wireless
WAN
e. Direct Connection: the organization leases a
high-speed WAN from a carrier provider and
connects itself to a regional ISP.
Standards and Administration
Internet Standards
An Internet draft is a working document (a work in progress) with no
of cial status and a six-month lifetime.
Upon recommendation from the Internet authorities, a draft may be
published as a Request for Comment (RFC)
Each RFC is edited, assigned a number, and made available to all
interested parties.
The Internet Engineering Task Force (IETF) is a forum of working
groups managed by the Internet Engineering Steering Group (IESG). IETF is
responsible for identifying operational problems and proposing solutions to
these problems. IETF also develops and reviews speci cations intended as
Internet standards.
