3. Contents
• What is the internet?
• The internet edge
• The internet core
• Delay, loss and throughput in packet switched
networks
• Reference models
• Example networks
• Guided transmission media
• Wireless transmission
4. What is the internet?
• A Nuts-and-Bolts Description
• Services
Connection oriented and connection less services
• Protocol
A protocol defines the format and the order of messages exchanged
between two or more communicating entities, as well as the actions
taken on the transmission and/or receipt of a message or other event.
The Transmission Control Protocol (TCP) and the Internet Protocol (IP)
are two of the most important protocols in the Internet. The IP
protocol specifies the format of the packets that are sent and received
among routers and end systems.
7. The network edge
The Internet’s end
systems include
desktop, servers, and
mobile devices.
End systems are also
referred to as hosts
because they host
application programs
such as a Web browser
program, a Web server
program.
9. Access networks
• The network that physically connects an end system to the
first router (also known as the “edge router”) on a path from
the end system to any other distant end system.
• The two most prevalent types of broadband residential
access are digital subscriber line (DSL) and cable.
12. Physical media
• Physical media fall into two categories:
Guided media
Unguided media.
• With guided media, the waves are guided along a solid
medium, such as a fiber-optic cable, a twisted-pair copper
wire, or a coaxial cable.
• With unguided media, the waves propagate in the
atmosphere and in outer space, such as in a wireless LAN or
a digital satellite channel
13. Network core
Packet switching
In a network application, end systems exchange messages with
each other. To send a message from a source end system to a
destination end system, the source breaks long messages into
smaller chunks of data known as packets. Between source and
destination, each packet travels through communication links and
packet switches
• Store and forward transmission
Most packet switches use store-and-forward transmission at
the inputs to the links. Store-and-forward transmission means that
the packet switch must receive the entire packet before it can
begin to transmit the first bit of the packet onto the outbound link.
14. The source has transmitted some of packet 1, and the front of packet 1 has
already arrived at the router. Because the router employs store-and-forwarding,
at this instant of time, the router cannot transmit the bits it has received; instead
it must first buffer the packet’s bits. Only after the router has received all of the
packet’s bits can it begin to transmit the packet onto the outbound link.
17. Types of delay
• Nodal processing delay
• Queuing delay
• Transmission delay
• Propagation delay
These delays accumulate to
give total nodal delay.
18. Processing delay
• The processing delay is, the time needed to check for bit-
level errors in the packet that occurred in transmitting the
packet’s bits from the upstream node to router A.
• The time required to examine the packet’s header and
determine where to direct the packet is part of the
processing delay.
Queueing delay
• If the traffic is heavy and many other packets are also
waiting to be transmitted, the queuing delay will be long.
• If the queue is empty and no other packet is currently being
transmitted, then packet’s queuing delay will be zero.
19. Transmission Delay
This is the amount of time required to transmit all of the
packet’s bits into the link. Transmission delays are typically on
the order of microseconds to milliseconds in practice.
Propagation Delay
Once a bit is pushed into the link, it needs to propagate to
router B. The time required to propagate from the beginning
of the link to router B is the propagation delay. The bit
propagates at the propagation speed of the link. The
propagation speed depends on the physical medium of the
link.
20. Packet Loss
With no place to store a packet, a router will drop that
packet; that is, the packet will be lost.
Throughput
In computer networks, throughput refers to the rate at which
data is successfully transmitted over a communication
channel during a specific period, often measured in bits per
second (bps).
