Q1- List 5 end devices, 6 intermediate devices, and 3 forms
of networking media.
A1-
- End devices: desktop computer, laptop computer,
server, PDA, cellular mobile phone, printer, security camera, IP phone,
electronic point of sale device, automatic teller machine
- Intermediate device: repeater, hub, wireless
access point, switch, router, modem, and firewall
- Networking media: copper cable, fiber cable,
radio (wireless)
Q2- Compare and contrast the following terms: Network, LAN,
WAN, internetwork, and the Internet.
A2-
- Network – a group of interconnected
devices capable of carrying many different types of communications, including
traditional computer data, interactive voice, video, and entertainment
products.
- LAN – a local network, or group of
interconnected local networks that are under the same administrative
control. In the past, LANs were thought
of only as small networks that existed in a single physical location. While LANs can be as small as a single local
network installed in a home or small office, LANs now include interconnected
local networks consisting of many hundreds of hosts, installed in multiple
buildings and locations. All of the
local networks within a LAN are under one administrative control group that
governs the security and access control policies that are in force on the
network
-
WAN – Telecommunications service
providers (TSP) operate large regional networks spanning long distances.
Individual organizations usually lease connections through a telecommunications
service provider network. These networks
that connect LANs in geographically separated locations are Wide Area Networks
(WANs). Although the organization
maintains all of the policies and administration of the LANs at both ends of
the connection, the policies within the communications service provider network
are controlled by the TSP. WANs use specifically designed network devices to
make the interconnections between LANs.
- Internetwork - Al mesh of interconnected
networks is used. Some of these interconnected networks are owned by large
public and private organizations, such as government agencies or industrial
enterprises, and are reserved for their exclusive use. The most well-known and
widely used publicly accessible internetwork is the Internet.
- Internet - The most well-known and widely
used publicly accessible internetwork. The Internet is created by the
interconnection of networks belonging to Internet Service Providers
(ISPs). These ISP networks connect to
each other to provide access for users all over the world. Ensuring effective communication across this
diverse infrastructure requires the application of consistent and commonly
recognized technologies and protocols as well as the cooperation of many
network administration agencies.
Q3- Compare and contrast the layers of the OSI model with the
TCP/IP protocol stack.
A3- There
are two basic types of networking models: protocol models and reference models.
- A protocol model closely matches the structure
of a particular protocol suite. The hierarchical set of related protocols in a
suite t represents all the functionality required to interface the human
network with the data network. The 4-layer TCP/IP model is a protocol model
because it describes the functions that occur at each layer of protocols within
the TCP/IP suite.
- A reference model provides a common reference
for maintaining consistency within all types of network protocols and services.
A reference model is not intended to be an implementation specification or to
provide a sufficient level of detail to define precisely the services of the
network architecture. The primary purpose of a reference model is to aid in
clearer understanding of the functions and process involved. The 7-layer Open
Systems Interconnection (OSI) model is the most widely known internetwork
reference model. It is used for data
network design, operation specifications, and troubleshooting.
- The protocols that make up the TCP/IP protocol
suite can be described in terms of the OSI reference model. In the OSI model, the Network Access layer
and the Application layer of the TCP/IP model are further divided to describe
discreet functions that need to occur at these layers.
- At the Network Access Layer, the TCP/IP protocol
suite does not specify which protocols to use when transmitting over a physical
medium; it only describes the handoff from the Internet Layer to the physical
network protocols. The OSI Layers 1 and 2 discuss the necessary procedures to
access the media and the physical means to send data over a network.
- The key parallels between the two network models
occur at the OSI model Layers 3 and 4.
OSI Model Layer 3, the Network layer, almost universally is used to
discuss and document the range of processes that occur in all data networks to
address and route messages through an internetwork. The Internet Protocol (IP)
is the TCP/IP suite protocol that includes the functionality described at Layer
3.
- Layer 4, the Transport layer of the OSI model,
is often used to describe general services or functions that manage individual
conversations between source and destination hosts. These functions include
acknowledgement, error recovery, and sequencing. At this layer, the TCP/IP
protocols Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)
provide the necessary functionality.
- The TCP/IP Application layer includes a number
of protocols that provide specific functionality to a variety of end user
applications. The OSI model Layers 5, 6
and 7 are used as references for application software developers and vendors to
produce products that need to access networks for communications.
Q4: Explain why networking models are used
A4: Although
the TCP/IP and OSI models are the primary models used when discussing network
functionality, designers of network protocols, services, or devices can create
their own models to represent their products. Ultimately, designers are
required to communicate to the industry by relating their product or service to
either the OSI model or the TCP/IP model, or to both.
As a
reference model, the OSI model provides an extensive list of functions and
services that can occur at each layer.
It also describes the interaction of each layer with the layers directly
above and below it. Whereas TCP/IP model
layers are referred to by name, the seven OSI model layers are usually referred
to by number.
There are
benefits to using a layered model to describe network protocols and operations:
- Assists in protocol design, because protocols
that operate at a specific layer have defined information that they act upon
and a defined interface to the layers above and below
- Fosters competition because products from
different vendors can work together
- Prevents technology or capability changes in one
layer from affecting other layers above and below
- Provides a common language to describe
networking functions and capabilities
Q5: Elaborate on the following terms: protocol, PDUs, and
encapsulation.
A5:
Protocol:
All
communication, whether face-to-face or over a network, is governed by
predetermined rules called protocols.
These protocols are specific to the characteristics of the
conversation. In our day-to-day personal
communication, the rules we use to communicate over one medium, like a
telephone call, are not necessarily the same as the protocols for using another
medium, such as a sending a letter.
Successful
communication between hosts on a network requires the interaction of many
different protocols. A group of
interrelated protocols that are necessary to perform a communication function
is called a protocol suite. These
protocols are implemented in software and hardware that is on each host and
network device.
PDU &
Encapsulation:
As
application data is passed down the protocol stack on its way to be transmitted
across the network media, various protocols add information to it at each
level. This is commonly known as the
encapsulation process.
The form
that a piece of data takes at any layer is called a Protocol Data Unit (PDU).
During encapsulation, each succeeding layer encapsulates the PDU that it
receives from the layer above in accordance with the protocol being used. At
each stage of the process, a PDU has a different name to reflect its new
appearance. PDUs within the protocols of
the TCP/IP suite are:
-
Data – The general term for the PDU used at the
Application layer
-
Segment – Transport Layer PDU
-
Packet – Internetwork Layer PDU
-
Frame – Network Access Layer PDU
Q6: Explain the postal metaphor or encapsulation.
A6:
Individual pages of a letter are written and numbered sequentially. Each page
is sealed in a separate envelope that is then addressed to the recipient. The
letters are posted and put in a mailbag (labelled with the destination) with
many other envelops each containing a page of different letters and addressed
to recipients. Many mailbags are loaded into a van and transported towards the
destination. Along the way the mailbags may be transferred to other vans or
different modes of transport – trucks, trains, aircraft, ships. At the
destination the mailbags are unloaded and emptied. The envelopes are delivered
to the destination addresses. At one address all the envelopes received are
opened, the page removed from each one, and the pages re-assembled into the
letter.
The envelope,
and then the mailbag and the vans/trucks/aircraft, each do not care what is in
the "container" that they carry. The letter itself is not used to
provide information to assist in its delivery. The address on the envelope, the
label on the mailbag or the delivery instructions to the van driver are what
direct the letter towards its destination.
Data
encapsulation follows the same principle – it is the addresses used in each
layer of encapsulation that direct the data towards its destination not the
data itself.
Q7: what are the unique roles of Layer 2, Layer 3, and Layer
4 addresses?
A7:
- Layer 4 addresses (ports) identify the
individual applications sending or receiving data.
- Layer 3 (logical) addresses identify devices and
their networks.
Layer 2 (physical) addresses identify devices on
a local network
