Protocols
COM211 Communications and Networks
CDA College
Olga Pelekanou
Email: fe_olga@mail.ru
www.cdacollege.ac.cy/site/info-com-technology-ll/
Communication Protocols
A communications protocol is a system of
digital message formats and rules for
exchanging those messages in or between
computing systems and in telecommunications.
Protocols may include signaling, authentication
and error detection and correction capabilities.
A protocol defines the syntax, semantics, and
synchronization of communication. A protocol
can therefore be implemented as hardware or
software or both.
Layering
Layering :
 decomposes the problem of building a network into more
manageable components. Rather than implementing a
monolithic piece of software that does everything you will
ever want, you can implement several layers, each of
which solves one part of the problem.
 it provides a more modular design. If you decide that you
want to add some new service, you may only need to
modify the functionality at one layer, reusing the
functions provided at all the other layers.
Encapsulation
Wrapping data in a particular protocol
header.
OSI and TCP/IP
Client/Server Model
In the client/server model, the device requesting
the information is called a client and the device
responding to the request is called a server.
Client and server processes are considered to
be in the Application layer. The client begins the
exchange by requesting data from the server,
which responds by sending one or more streams
of data to the client. Application layer protocols
describe the format of the requests and
responses between clients and servers.
Peer to Peer
Application Layer Protocols
HTTP
 POP
 SMTP
 SSH
 DNS
 FTP

HTTP
HyperText Transport Protocol. An
application-level protocol based on a
request/reply paradigm and used in the
World Wide Web. HTTP uses TCP
connections to transfer data. Use TCP port
80.
POP
Post Office Protocol (POP) is an
application-layer Internet standard protocol
used by local e-mail clients to retrieve email from a remote server over a TCP/IP
connection and port 110.
SMTP
Simple Mail Transfer Protocol. The
electronic mail protocol of the Internet.
SMTP was first defined by RFC 821.
SMTP is specified for outgoing mail
transport and uses TCP port 25.
SSH
The Secure Shell (SSH) provides a
remote, encrypted login service and is
intended to replace the less secure Telnet
and rlogin programs used in the early days
of the Internet. Use TCP port 22.
DNS
Domain name system. The distributed
naming system of the Internet, used to
resolve host names (ex. cdacollage.ac.cy)
into IP addresses (ex. 67.15.203.26). DNS
is implemented by a hierarchy of name
servers. Use UDP port 53.
FTP
File Transfer Protocol. The standard
protocol of the Internet architecture for
transferring files between hosts. Built on
top of TCP. Use TCP port 21 for control
commands and TCP port 20 for data
transfer.
Share a Printer in Windows 7
Step 1

Go to Control Panel and click on “Choose
homegroup and sharing options” or just
type “homegroup” without quotes into the
start menu search bar.
Share a Printer in Windows 7
Step 2

Next click on the Create a homegroup
button.
Share a Printer in Windows 7
Step 3

In the Create a Home Group screen select
what you want to share with the other
machines.
Share a Printer in Windows 7
Step 4

After the group is created you will get a
password to access it from the other
computers.
Share a Printer in Windows 7
Step 5

After you get the Password you’re brought
back to the Home Group screen where
you can make additional changes if you
want.
Share a Printer in Windows 7
Step 6

On the other Windows 7 computer(s) go
into the HomeGroup feature and click to
join the group you just created.
Share a Printer in Windows 7
Step 7

Enter in the password that was created for
the HomeGroup.
Share a Printer in Windows 7
Step 8

When the password is accepted the
connection will take place and your
finished.
Share a Printer in Windows 7
Step 9

To share a printer make sure to select Printers
when creating the group and when you go into
Devices and Printers on the Start menu you
should see it and can set it as the default if you
wish.
Share a Printer in Windows 7


If you don’t want to use a password at all go into the Network and Sharing
Center under advanced options and turn off password protected sharing.
Another thing you might want to do is create a shortcut to the
HomeGroup. I just go into Network and copy the icon to my desktop by
Right-Clicking and dragging it. A more direct approach is to create
shortcuts directly to the shared public folders but of course it’s completely
up to you.