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Internet Protocol
The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packetswitched internetwork.
IP is a network layer protocol in the Internet protocol suite and is encapsulated in a data link layer protocol
(e.g., Ethernet). As a lower layer protocol, IP provides the service of communicable unique global
addressing amongst computers
Source: Wikipedia
W. Daca, Politechnika Szczecińska, Wydział Elektryczny, 2007/08
Internet Protocol / Packetization
Data from an upper layer protocol is encapsulated inside one or more packets/datagrams (the terms are
basically synonymous in IP). No circuit setup is needed before a host tries to send packets to a host it has
previously not communicated with (this is the point of a packet-switched network), thus IP (Internet
protocol) is a connectionless protocol.
This is quite unlike Public Switched Telephone Networks that require the setup of a circuit before a phone
call may go through (a connection-oriented protocol).
Source: Wikipedia
Internet Protocol / Services provided by IP
Because of the abstraction provided by encapsulation, IP can be used over a heterogeneous network
(i.e., a network connecting two computers can be any mix of Ethernet, ATM, FDDI, Wi-Fi, token ring, etc.)
and it makes no difference to the upper layer protocols. Each data link layer can (and does) have its own
method of addressing (or possibly the complete lack of it), with a corresponding need to resolve IP
addresses to data link addresses. This address resolution is handled by the Address Resolution Protocol
(ARP).
Source: Wikipedia
Internet Protocol / Reliability
IP provides an unreliable service (i.e., best effort delivery). This means that the network makes no
guarantees about the packet and none, some, or all of the following may apply:
•
•
•
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data corruption
out-of-order delivery (Given packet A is sent before packet B, packet B can arrive before
packet A.)
duplicate arrival
lost or dropped/discarded packages
To address any of these reliability issues, an upper layer protocol must handle it. For example, to
ensure in-order delivery the upper layer may have to cache data until it can be passed up in order.
The primary reason for the lack of reliability is to reduce the complexity of routers.
Source: Wikipedia
Internet Protocol / Version history
In May, 1974, the Institute of Electrical and Electronic Engineers (IEEE) published a paper titled "A
Protocol for Packet Network Interconnection." The paper's authors -- Vinton Cerf and Robert Kahn -described a protocol called "TCP" that incorporated both connection-oriented and datagram services.
IP is the common element found in today's public Internet. The current and most popular network layer
protocol in use today is IPv4. IPv4 is described in RFC-791 (1981).
IPv6 is the proposed successor to IPv4 whose most prominent change is the addressing. IPv4 uses 32-bit
addresses (~4 billion addresses) while IPv6 uses 128-bit addresses (~3.4×1038 addresses).
Source: Wikipedia
Internet Protocol / IP suite
The IP suite uses encapsulation to provide abstraction of protocols and services. Generally a protocol at a
higher level uses a protocol at a lower level to help accomplish its aims.
Source: Wikipedia
Internet Protocol / IP suite implementation
Today, most commercial operating systems include and install the TCP/IP stack by default. For most
users, there is no need to look for implementations. TCP/IP is included in all commercial Unix systems,
Mac OS X, and all free-software Unix-like systems such as Linux distributions and BSD systems, as well
as Microsoft Windows
Source: Wikipedia
DNS, TFTP, TLS/SSL, FTP, Gopher, HTTP, IMAP, IRC, NNTP, POP3, SIP, SMTP, SNMP, SSH,
TELNET, ECHO, RTP, PNRP, rlogin, ENRP
Application
Routing protocols like BGP, which for a variety of reasons run over TCP, may also be considered part of
the application or network layer.
Transport
TCP, UDP, DCCP, SCTP, IL, RUDP
Internet
Routing protocols like OSPF, which run over IP, are also to be considered part of the network layer, as
they provide path selection. ICMP and IGMP run over IP and are considered part of the network layer, as
they provide control information.
IP (IPv4, IPv6)
ARP and RARP operate underneath IP but above the link layer so they belong somewhere in between.
Network access (combines Data link
and Physical)
Ethernet, Wi-Fi, token ring, PPP, SLIP, FDDI, ATM, Frame Relay, SMDS

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