• A n/w is a set of devices (often referred to as
node) connected by communication links.
• A node can be a computer, printer, or any
other devices capable of sending or receiving
data generated by other node s on the n/w.
• Most n/w’s are distributed processing , in
which the task is divided among multiple
• Instead of one large single machine being
responsible for all aspects of a process,
separate computers ( usually a pc, or a
workstation) handle a subnet.
• A n/w must be able to meet a certain number
• The most important of these are
It can be measured in many ways, including
transit time and response time.
Transit time is the amount of time required
for a message to travel from one device to
• Response time - it is the elapsed time
between an enquiry and a response.
• The performance of a n/w depends on the
number of factors including no. of users , the
type of transmission medium, the capabilities
of the connected hardware and the efficiency
of the software.
• Performance is evaluated by two networking
metrics : throughput and delay.
• We often need more throughput and less
• These two criteria are contradictory .
• If we try to send more data , it may increase
the throughput , but increases the delay.
• In addition to accuracy of delivery, n/w
reliability is measured in frequency of failure.
• The time it take to recover from a failure.
• N/w security issues include protecting data
from unauthorized access , protecting data
from damage and development , and
implementing policies and procedures for
recovery from losses .
Type of connections
• A network is two or more devices connected
• A link is a communications pathway that
transfers data from one device to another.
• There are two possible types of connections:
• Point-to- point , Multipoint
• A point-to-point connections provides a
dedicated link between the two devices .
• The entire capacity of the link is reserved for
transmission between the two devices.
• A multipoint connections is one in which more
than two specific devices share a single link .