TCP
Transmission Control Protocol (TCP) is
a connection-oriented protocol, which operates on the Transport Layer
of the TCP/IP and OSI Models. TCP is the de facto standard of the
Internet and provides full-duplex data transmission. When TCP receives
data from the upper layers of the OSI Model, it guarantees reliable
delivery to remote networks. TCP is useful for transmitting large
amounts of data reliably, but with the penalty of large ACK overhead
consuming bandwidth. 
UDP
User Datagram Protocol (UDP) is a
connectionless protocol, which operates on the Transport Layer of the
TCP/IP and OSI Models. Because UDP is an unreliable delivery service,
it does not require receiving protocols to acknowledge the receipt of
a packet. An advantage UDP has over TCP is because it does not
concentrate on establishing a connection, it can transmit more
information in a less amount of time than TCP. Useful for transmitting
small amounts of data where reliability is less crucial, UDP lacks the
overhead caused by ACKs. 
POP3
Post Office Protocol Version 3 (POP3),
which uses TCP port 110, is a mail protocol that is responsible for
holding email until delivery. When an SMTP server sends an email
message to a POP3 server, POP3 holds onto to the message until a
request is made by the user to have the data delivered. Thus POP3
transfers mail files from a mail server to a mail client. 
SMTP
The Simple Mail Transfer Protocol (SMTP),
which uses TCP port 25, allows users to be able to send and receive
email over the Internet. It is the SMTP's responsibility to
make sure that the email is sent to the POP3 server. 
SNMP
Simple Network Management Protocol (SNMP),
which uses TCP port 161, allows simple maintenance and remote
monitoring of any device on a network. Administrators are able address
issues, such as problems with a network card in a server, a program or
service on the server, or a device such as a hub or a router by using
SNMP.
Two approaches an administrator can
take when managing a network device using SNMP are a central
management system and the management information base (MIB). The
management system allows the administrator to view performance and
operation statistics of the network devices, enabling him or her to
diagnose a network remotely. 
FTP
File Transfer Protocol (FTP) is a fast,
connection-oriented, error-free protocol and uses TCP ports 20 and 21.
FTP allows data to be transferred between servers and clients. In
order for FTP to connect to a remote server, the IP address or host
name must be provided. FTP must be able to resolve IP addresses to host
names in order to establish a connection. 
HTTP
Hypertext Transfer Protocol (HTTP), which
uses TCP port 80, allows clients to transfer documents written in Hypertext Markup
Language (HTML) over the World Wide Web for display by a browser. It is the
universal display language of the Internet. 
IP
Internet Protocol (IP) is a routable
(routed) connectionless protocol, which operates on the Network Layer
of the OSI and TCP/IP Models. IP is the de facto standard for the
Internet and provides packet delivery and addressing for source and
destination.
Because IP is a connectionless delivery
service, it is unreliable and does not guarantee that the packets
received will be in the order sent, if received at all. 
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