TCP/IP Suite
Dr. Amer ElKhairy
Department of Computer Networking
Princess Noura University
Communications Software

Communications Software


Network Operating System (NOS)


Provides error checking, message formatting,
communications logs, data security and privacy, and
translation capabilities for networks.
Systems software that controls the computer systems and
devices on a network and allows them to communicate with
each other.
Network Management Software

Enables a manager on a networked desktop to monitor the
use of individual computers and shared hardware, scan for
viruses, and ensure compliance with software licenses.
33
Protocols


Rules that ensure communications among computers
of different types and from different manufacturers.
Rules that determine the form of signal being
transmitted, encoded, error detection and correction,
etc.
5-3
Protocols

TCP/IP


The protocol suite for the Internet
Transmission Control Protocol (TCP)


Internet Protocol (IP)



Provides a reliable byte-stream transfer service between two
endpoints on an internet
Defines a delivery mechanism for packets of data sent
between all systems on an Internet
Widely used by business, even for internal networks
Standard originally developed by the U.S.
government to link defense research agencies; it is
the primary communication protocol of the Internet.
5-4
Protocol (Idea)
Protocol (Idea)
Host
Host
Application
Channel
Host
Application
Host
Host
Protocol (Idea)
Application programs
Process-to-process channels
Host-to-host connectivity
Hardware
Protocol (Idea)
Application programs
Request/reply Message stream
channel
channel
Host-to-host connectivity
Hardware




When and how to start a channel?
When and how to close a channel?
How to protect the channel against invasion?
How to handle multiple applications?
Applications

Linking Personal Computers to Mainframe Computers


Voice Mail


Download and upload information.
Enables users to leave, receive, and store verbal
messages for and from other users.
Electronic Mail (e-mail)

Enables a sender to connect a computer to a network,
type messages, and send it to another person on the
network.
39
Applications

Electronic Software Distribution


Involves installing software on a file server for
users to share by signing onto the network and
requesting that the software be downloaded onto
their computers over a network.
Electronic Document Distribution

Transporting documents -- such as sales reports,
policy manuals, and advertising brochures -- over
communications lines and networks.
40
Telecommunications Applications
Videoconferencing
41
How the Internet Works

Protocol



Backbone


A protocol that operates at the transport layer and is used in
combination with IP by most Internet applications
It ensures that computers in Internet can understand the
message sending among each others.
One of the Internet’s high-speed, long distance
communications links.
IP Address/Port



IP address is the unique identification on a computer that is
connecting to the Internet.
Ports are the input/output locations of a computer where
messages should send in or out.
If an IP address is analogy to a country, then the Port
addresses will be analogy to the ports of that country.
TCP/IP PROTOCOL SUITE
The layers in the TCP/IP protocol suite do not exactly
match those in the OSI model. The original TCP/IP
protocol suite was defined as having four layers:
host-to-network, internet, transport, and application.
However, when TCP/IP is compared to OSI, we can
say that the TCP/IP protocol suite is made of five
layers: physical, data link, network, transport, and
application.
TCP/IP




Transmission control Protocol/Internet Protocol
Developed by DARPA
No official protocol standard
Can identify five layers





Application
Host-to-Host (transport)
Internet
Network Access
Physical
OSI & TCP/IP Models
TCP/IP Protocol Suite
Application
Presentation
Session
Transport
TELNET
FTP
SMTP
DNS
SNMP
DHCP
RIP
RTP
RTCP
Transmission
Control Protocol
User Datagram
Protocol
OSPF
ICMP
IGMP
Internet Protocol
Network
ARP / RARP
Data link
Physical
Ethernet
Token Bus
Token Ring
FDDI
The Upper Layers
OSI
TCP / IP
Application (Layer7)
Presentation (Layer6)
Session (Layer 5)
Session
Presentation
Application
Application
The Session Layer



The Session layer permits two parties to hold
ongoing communications called a session
across a network.
Not found in TCP/IP model
In TCP/IP its characteristics are provided by the
TCP protocol.
(Transport Layer)
The Presentation Layer


The Presentation Layer handles data format
information for networked communications. This
is done by converting data into a generic format
that could be understood by both sides.
Not found in TCP/IP model
In TCP/IP, this function is provided by the
Application Layer.
e.g. External Data Representation Standard (XDR)
Multipurpose Internet Mail Extensions (MIME)
The Application Layer
The Application Layer is the top layer of the reference
model. It provides a set of interfaces for applications to
obtain access to networked services as well as access
to the kinds of network services that support
applications directly.

OSI
TCP/IP
- FTAM,VT,MHS,DS,CMIP
- FTP,SMTP,TELNET,DNS,SNMP

Although the notion of an application process is
common to both, their approaches to constructing
application entities is different.
Approaches use in constructing
application entities

The diagram below provides an overall view on the
methods use by both the OSI and TCP/IP model.
ISO Approach



Sometime called Horizontal Approach
OSI asserts that distributed applications operate
over a strict hierarchy of layers and are
constructed from a common tool kit of
standardized application service elements.
In OSI, each distributed application service
selects functions from a large common “toolbox”
of application service element (ASEs) and
complements these with application service
elements that perform functions specific to given
end-user service .
TCP/IP Approach



Sometime called Vertical Approach
In TCP/IP, each application entity is composed
of whatever set of function it needs beyond end
to end transport to support a distributed
communications service.
Most of these application processes builds on
what it needs and assumes only that an
underlying transport mechanism (datagram or
connection) will be provided.
Transport Layer

OSI
TCP / IP
Transport (Layer 4)
Transport (TCP/UDP)
The functionality of the transport layer is to
provide “transparent transfer of data from a
source end open system to a destination end
open system” (ISO / IEC 7498: 1984).
Transport Layer

Transport is responsible for creating and
maintaining the basic end-to-end connection
between communicating open systems, ensuring
that the bits delivered to the receiver are the same
as the bits transmitted by the sender; in the same
order and without modification, loss or duplication
OSI Transport Layer



It takes the information to be sent and breaks it into
individual packets that are sent and reassembled into a
complete message by the Transport Layer at the
receiving node
Also provide a signaling service for the remote node so
that the sending node is notified when its data is
received successfully by the receiving node
Transport Layer protocols include the capability to
acknowledge the receipt of a packet; if no
acknowledgement is received, the Transport Layer
protocol can retransmit the packet or time-out the
connection and signal an error
OSI Transport Layer



Transport protocols can also mark packets with sequencing
information so that the destination system can properly
order the packets if they’re received out-of-sequence
In addition, Transport protocols provide facilities for
insuring the integrity of packets and requesting
retransmission should the packet become garbled when
routed.
Transport protocols provide the capability for multiple
application processes to access the network by using
individual local addresses to determine the destination
process for each data stream.
TCP/IP Transport Layer


Defines two standard transport protocols: TCP and
UDP
TCP implements a reliable data-stream protocol



UDP implements an unreliable data-stream
 connectionless
UDP is useful in many applications


connection oriented
e.g. Where data needs to be broadcasted or
multicasted
Primary difference is that UDP does not necessarily
provide reliable data transmission
TCP/IP Transport Layer

Many programs will use a separate TCP
connection as well as a UDP connection
TCP/IP Transport Layer: UDP



User Datagram Protocol. Its status is standard and
almost every TCP/IP implementation intended for small
data units transfer or those which can afford to lose a
little amount of data (such as multimedia streaming) will
include UDP.
UDP is basically an application interface to IP. It adds
no reliability, flow-control, or error recovery to IP.
It simply serves as a multiplexer/demultiplexer for
sending and receiving datagrams, using ports to direct
the datagrams.
TCP/IP Transport Layer: UDP
TCP/IP Transport Layer: UDP




UDP provides a mechanism for one application to send
a datagram to another.
The UDP layer can be regarded as being extremely thin
and consequently has low overheads, but it requires the
application to take responsibility for error recovery and
so on.
Applications sending datagrams to a host need to
identify a target that is more specific than the IP
address, since datagrams are normally directed to
certain processes and not to the system as a whole.
UDP provides this by using ports.
UDP datagram format





Each UDP datagram is sent within a single IP datagram.
Although, the IP datagram may be fragmented during
transmission, the receiving IP implementation will
reassemble it before presenting it to the UDP layer.
All IP implementations are required to accept datagrams
of 576 bytes, which means that, allowing for maximumsize IP header of 60 bytes, a UDP datagram of 516
bytes is acceptable to all implementations.
Many implementations will accept larger datagrams, but
this is not guaranteed.
The UDP datagram has a 8-byte.
UDP datagram format
UDP datagram format

Be aware that UDP and IP do not provide guaranteed
delivery, flow-control, or error recovery, so these must
be provided by the application.

Standard applications using UDP include:





Trivial File Transfer (TFTP)
Domain Name System name server (DNS)
Remote Procedure Call (RPC)
Network File System (NFS)
Simple Network Management Protocol (SNMP
TCP/IP Transport Layer: TCP




Transmission Control Protocol. Its status is standard,
and in practice every TCP/IP implementation that is not
used exclusively for routing will include TCP.
TCP provides considerably more facilities for
applications than UDP. Specifically, this includes error
recovery, flow control, and reliability.
TCP is a connection-oriented protocol, unlike UDP,
which is connectionless.
Most of the user application protocols, such as Telnet
and FTP, use TCP. The two processes
TCP/IP Transport Layer: TCP

The two processes communicate with each other over a
TCP connection (Inter-Process Communication - IPC).
TCP/IP Transport Layer: TCP



The primary purpose of TCP is to provide a reliable
logical circuit or connection service between pairs of
processes.
It does not assume reliability from the lower-level
protocols (such as IP), so TCP must guarantee this
itself.
TCP can be characterized by the following facilities it
provides for the applications using it:
TCP/IP Transport Layer: TCP

Stream Data Transfer:




From the application's viewpoint, TCP transfers a contiguous
stream of bytes through the network. The application does
not have to bother with chopping the data into basic blocks.
TCP does this by grouping the bytes into TCP segments,
which are passed to the IP layer for transmission to the
destination.
TCP itself decides how to segment the data, and it can
forward the data at its own convenience.
Sometimes, an application needs to be sure that all the data
passed to TCP has actually been transmitted to the
destination.
Byte Stream Service


To the lower layers, TCP handles data in blocks, the segments.
To the higher layers TCP handles data as a sequence of bytes
and does not identify boundaries between bytes.
40
TCP/IP Transport Layer: TCP

Reliability:



TCP assigns a sequence number to each byte
transmitted, and expects a positive acknowledgment
(ACK) from the receiving TCP layer. If the ACK is not
received within a timeout interval, the data is
retransmitted.
Since the data is transmitted in blocks (TCP segments),
only the sequence number of the first data byte in the
segment is sent to the destination host.
The receiving TCP uses the sequence numbers to
rearrange the segments when they arrive out of order, and
to eliminate duplicate segments.
TCP/IP Transport Layer: TCP

Flow Control:



The receiving TCP, when sending an ACK back to the
sender, also indicates to the sender the number of bytes it
can receive (beyond the last received TCP segment)
without causing overrun and overflow in its internal
buffers. This is sent in the ACK in the form of the highest
sequence number it can receive without problems.
This mechanism is also referred to as a windowmechanism.
Multiplexing:

Achieved through the use of ports, just as with UDP.
TCP/IP Transport Layer: TCP

Logical Connections:


The reliability and flow control mechanisms require that
TCP initializes and maintains certain status information for
each data stream. The combination of this status,
including sockets, sequence numbers and window sizes,
is called a logical connection. Each connection is uniquely
identified by the pair of sockets used by the sending and
receiving processes.
Full Duplex:

TCP provides for concurrent data streams in both
directions.
TCP: Three-Way Handshake

With reliable TCP sessions, before a host can send
information to another host, a handshake process
must take place to establish the connection.
TCP: The window principle

A simple transport protocol might use the following
principle: send a packet and then wait for an
acknowledgment from the receiver before sending the
next packet. If the ACK is not received within a certain
amount of time, retransmit the packet.
TCP: The window principle

Use of ACK
TCP: The window principle


TCP allows the regulation of the flow of segments,
ensuring that one host doesn’t flood another host with
too many segments, overflowing its receiving buffer.
TCP uses a sliding windowing mechanism to assist
with flow control. For example, if the window size is 1,
a host can send only one segment and must then wait
for a corresponding acknowledgment before sending
the next segment. If the window size is 20, a host can
send 20 segments and must wait for the single
acknowledgment of the sent 20 segments before
sending 20 additional segments.
TCP: The window principle
TCP: The window principle
TCP: The window principle



The window size is determined by the receiver when
the connection is established and is variable during the
data transfer.
Each ACK message will include the window size that
the receiver is ready to deal with at that particular time.
Remember that TCP will block bytes into segments,
and a TCP segment only carries the sequence number
of the first byte in the segment.
TCP: The window principle
A: Bytes that are transmitted and have been acknowledged.
B: Bytes that are sent but not yet acknowledged.
C: Bytes that can be sent without waiting for any acknowledgment.
D: Bytes that cannot be sent yet.
TCP Format
TCP segments have a 20 byte header with >= 0 bytes of data.
IP header TCP header
20 bytes
TCP data
20 bytes
0
15 16
Source Port Number
31
Destination Port Number
Sequence number (32 bits)
header
length
0
Flags
window size
TCP checksum
urgent pointer
Options (if any)
DATA
52
20 bytes
Acknowledgement number (32 bits)
TCP segment format





Source Port: The 16-bit source port number, used by the
receiver to reply.
Destination Port: The 16-bit destination port number.
Sequence Number: The sequence number of the first data
byte in this segment. If SYN bit is set, this is the initial
sequence number (ISN) and the first data byte is ISN+1.
Acknowledgment Number: If the ACK control bit is set,
this field contains the value of the next sequence number
that the receiver is expecting to receive.
Data Offset: The number of 32-bit words in the TCP
header. It indicates where the data begins.
TCP segment format







Reserved: Six bits reserved for future use; must be zero.
URG: Indicates that the urgent pointer field is significant in
this segment.
ACK: Indicates that the acknowledgment field is significant
in this segment.
PSH: tells the receiver to pass this data to the application
as soon as possible (Flush).
RST: Resets the connection.
SYN: synchronize sequence number to initiate a
connection .
FIN: No more data from sender (Final).
TCP segment format



Window: Used in ACK segments. It specifies the number of
data bytes, beginning with the one indicated in the
acknowledgment number field that the receiver is willing to
accept.
Checksum: The 16-bit one's complement of the one's
complement sum of all 16-bit words in a pseudo-header,
the TCP header, and the TCP data. While computing the
checksum, the checksum field itself is considered zero.
Urgent Pointer: Points to the first data octet following the
urgent data. Only significant when the URG control bit is
set.
TCP segment format



Options: Just as in the case of IP datagram options,
options can be either:
– A single byte containing the option number
– A variable length option in the following
TCP header fields

Options:
End of
Options
kind=0
1 byte
NOP
(no operation)
kind=1
1 byte
Maximum
Segment Size
Window Scale
Factor
Timestamp
kind=2
len=4
maximum
segment size
1 byte
1 byte
2 bytes
kind=3
len=3
shift count
1 byte
1 byte
1 byte
kind=8
len=10
timestamp value
timestamp echo reply
1 byte
1 byte
4 bytes
4 bytes
57
TCP header fields

Options:



NOP is used to pad TCP header to multiples of 4
bytes
Maximum Segment Size
Window Scale Options



Increases the TCP window from 16 to 32 bits, I.e.,
the window size is interpreted differently
This option can only be used in the SYN segment
(first segment) during connection establishment time
Timestamp Option

Can be used for roundtrip measurements
58
TCP/IP Transport Layer:
Ports & Sockets



TCP and UDP introduce the concepts of ports and
sockets.
The concepts of the port and socket are needed to
determine which local process at a given host actually
communicates with which process, at which remote
host, using which protocol.
Each process that wants to communicate with another
process identifies itself to the TCP/IP protocol suite by
one or more ports.
TCP/IP Transport Layer: Ports


A port is a 16-bit number, used by the host-to-host
protocol to identify to which higher level protocol or
application program (process) it must deliver incoming
messages.
Port numbers fall under three types:



Well-known
Registered
Dynamically assigned
TCP/IP Transport Layer: Ports



Well-known: These port numbers range from 0 to
1023 and are assigned by the Internet Assigned
Number Authority (IANA) to applications commonly
used on the Internet.
Registered: These port numbers range from 1024 to
49,151 and are assigned by IANA for proprietary
applications, such as Microsoft SQL Server, Oracle,
and many others.
Dynamically assigned: These port numbers range
from 49,152 to 65,535 and are dynamically assigned
by the operating system to use for a session.
TCP/IP Transport Layer: Ports

A few examples of applications (and their ports) that
use TCP:





HTTP (80),
FTP (21),
SMTP (25), and
telnet (23).
A few examples of UDP applications, along with their
assigned port numbers:



DNS queries (53),
SNMP (161), and
TFTP (69).
TCP/IP Transport Layer: Sockets





The socket interface is one of several application
programming (API) interfaces to the communication
protocols.
Designed to be a generic communication programming
interface, socket APIs were first introduced by 4.2 Berkeley
Software Distribution (BSD).
Although it has not been standardized, Berkeley socket
API has become a de facto industry standard abstraction
for network TCP/IP socket implementation.
Consider the following terminologies:
A socket address is the triple:
<protocol, local-address, local port>
TCP/IP Transport Layer: Sockets




For example, in the TCP/IP (version 4) suite:
<TCP, 192.168.14.234, 8080>
A conversation is the communication link between two
processes.
An association is the 5-tuple that completely specifies the
two processes that comprise a connection:
<protocol, local-address, local-port, foreign-address,
foreign-port>
In the TCP/IP (version 4) suite, the following could be a
valid association:
<TCP, 192.168.14.234, 1500, 192.168.44, 22>
TCP/IP Transport Layer: Sockets

A half-association is either:
<protocol, local-address, local-process>
or
<protocol, foreign-address, foreign-process>
which each specify half of a connection.

The half-association is also called a socket or a transport
address. That is, a socket is an endpoint for
communication that can be named and addressed in a
network.
Addresses, Ports and Sockets
• Like apartments and mailboxes
–
–
–
–
–
You are the application
Your apartment building address is the address
Your mailbox is the port
The post-office is the network
The socket is the key that gives you access to
the right mailbox
Types of Sockets
• Two different types of sockets :
 stream vs. datagram
• Stream socket :( a. k. a. connection- oriented socket)
 It provides reliable, connected networking service
 Error free; no out- of- order packets (uses TCP)
 applications: telnet, http, …
• Datagram socket :( a. k. a. connectionless socket)
 It provides unreliable, best- effort networking service
 Packets may be lost; may arrive out of order (uses UDP)
 applications: streaming audio/ video (Realplayer), …
Client – high level view
Create a socket
Setup the server address
Connect to the server
Read/write data
Shutdown connection
Server – high level view
Create a socket
Bind the socket
Listen for connections
Accept new client connections
Read/write to client connections
Shutdown connection
structurestructure
Ipv4Hostent
socket address
struct
hostent{ {
struct
socketaddr_in
char
/*official
name
of host*/
uint8_t * h_name
sin_len; /*length
of the
structure
(16)*/
char
**
h_aliases;
/*
pointer
ot
array
of\
int connect_ socket( char *hostname, int port) {
sa_falimily_t sin_family /* AF_INT*/
pointers
aliasport
name*/
in_port_t
sin_port /* 16 bit
TCP ortoUDP
number*/
int sock;
int
h_addrtype
/*
host
address
type*/
struct in_addr sin_addr /* 32 bit Ipv4 address */
struct sockaddr_in sin;
h_length
/* length of address */
charint
sin_zero(8)/* unused*/
char
**
h_addr_list
/*prt to array of ptrs with \
struct hostent *host;
}
IPv4 or IPv6 address*/
sock = socket( AF_ INET, SOCK_ STREAM, 0);
}
if (sock == -1)
return sock;
host = gethostbyname( hostname);
if (host == NULL) {
close( sock);
return -1;
}
Socket(int family , int type, in t protocol);
return nonnegative value for OK, -1 for error
Resolve the host
struct hostent *gethostbyname( const char *hostname);
/*Return nonnull pointer if OK, NULL on error */
connect(int socketfd, const struct sockaddr * servaddr,
memset (& sin, 0, sizeof( sin));
socket_t addrlen)
sin. sin_ family = AF_ INET;
/*Perform the TCP three way handshaking*/
sin. sin_ port = htons( port);
sin. sin_ addr. s_ addr = *( unsigned long *) host-> h_ addr_ list[ 0]; unit16_t htons(unit16_t host16bitvaule)
/*Change the port number from host byte
if (connect( sock, (struct sockaddr *) &sin, sizeof( sin)) != 0) {
network byte order */
close (sock);
return -1;
}
return sock;
}
Listening on a port (TCP)
int make_ listen_ socket (int port) {
struct sockaddr_ in sin;
int sock;
sock = socket( AF_ INET, SOCK_ STREAM, 0);
Make the socket
if (sock < 0)
return -1;
memset(& sin, 0, sizeof(sin));
sin. sin_family = AF_ INET;
Setup up the struct
sin. sin_addr. s_addr = htonl(INADDR_ANY);
sin. sin_port = htons( port);
if (bind( sock, (struct sockaddr *) &sin, sizeof(
sin)) < 0)
Bind
return -1;
return sock;
bind(int sockfd, const struct sockaddr * myaddr, socklen_t addrlen);
/* return 0 if OK, -1 on error
}
assigns a local protocol adress to a socket*/
Accepting a client connection (TCP)
int get_ client_ socket( int listen_socket) {
struct sockaddr_ in sin;
int sock;
int sin_ len;
memset(&sin, 0, sizeof(sin));
Setup up the struct
sin_ len = sizeof(sin);
sock = accept(listen_socket, (struct sockaddr *) &sin,
&sin_ len);
Accept the client connection
return sock;
}
accept(int sockefd, struct sockaddr * claddr, socklen_t * addrlen)
/* return nonnegative descriptor if OK, -1 on error
return the next completed connection from the front of the
completed connection queue.
if the queue is empty,
the process is put to sleep(assuming blocking socket)*/
Sending / Receiving Data

With a connection (SOCK_STREAM):

int count = send(sock, &buf, len, flags);





int count = recv(sock, &buf, len, flags);





count: # bytes transmitted (-1 if error)
buf: char[], buffer to be transmitted
len: integer, length of buffer (in bytes) to transmit
flags: integer, special options, usually just 0
count: # bytes received (-1 if error)
buf: void[], stores received bytes
len: # bytes received
flags: integer, special options, usually just 0
Calls are blocking [returns only after data is sent (to
socket buf) / received]
socket()
bind()
TCP Client
Socket()
connect() Connection establishment
write()
TCP Server
Well-known port
listen()
accept()
blocks until connection from client
read()
process request
read()
close()
write()
read()
close()
Comparing Transport for both Models

The features of UDP and TCP defined at TCP/IP
Transport Layer correspond to many of the
requirements of the OSI Transport Layer. There is a
bit of bleed over for requirements in the session
layer of OSI since sequence numbers, and port
values can help to allow the Operating System to
keep track of sessions, but most of the TCP and UDP
functions and specifications map to the OSI
Transport Layer.
Comparing Transport for both Models

The TCP/IP and OSI architecture models both employ
all connection and connectionless models at
transport layer. However, the internet architecture
refers to the two models in TCP/IP as simply
“connections” and “datagrams.” But the OSI
reference model, with its penchant for “precise”
terminology, uses the terms connection-mode and
connection-oriented for the connection model and
the term connectionless-mode for the connectionless
model.
Network vs. Internet
OSI
TCP / IP
Network (Layer 3)
Internet
TCP/IP Internet Layer




An Internet is an interconnection of two or more
networks
Internet layer handles tasks similar to network
access layer, but between networks rather than
between nodes on a network
Uses IP for addressing and routing across networks
Implemented in workstations and routers
Internet Layer


TCP/IP supports the Internetworking Protocol.
IP uses four supporting protocols : ARP, RARP,
ICMP, and IGMP.





IP (Internetworking Protocol)
ARP (Address Resolution Protocol)
RARP (Reverse Address Resolution Protocol)
ICMP (Internet Control Message Protocol)
IGMP (Internet Group Message Protocol)
Network vs. Internet

Internet (IP) Addresses
 The internet network address is more commonly called
the “IP address.” It consists of 32 bits, some of which
are allocated to a high-order network-number part and
the remainder of which are allocated to a low-order
host-number part. The distribution of bits - how many
form the network number, and how many are
therefore left for the host number - can be done in one
of three different ways, giving three different classes of
IP address
Internetworking



Interconnected networks, usually implies
TCP/IP
Can appear to users as a single large
network
The global Internet is the largest example,
but intranets and extranets are also examples
Internetworking
Addresses
Addresses
Figure 2.18 Relationship of layers and addresses in TCP/IP
Physical and Data Link Layers



At the physical and data link layers, TCP/IP does
not define any specific protocol.
It supports all the standard and proprietary
protocols.
A network in a TCP/IP internetwork can be a localarea network or a wide-area network.
De-jure vs. De-facto (OSI)

OSI





Standard legislated by official recognized body. (ISO)
The OSI reference model was devised before the protocols were
invented. This ordering means that the model was not biased
toward one particular set of protocols, which made it quite
general. The down side of this ordering is that the designers did
not have much experience with the subject and did not have a
good idea of which functionality to put in which layer.
Being general, the protocols in the OSI model are better hidden
than in the TCP/IP model and can be replaced relatively easily as
the technology changes.
Not so widespread as compared with TCP/IP. (complex , costly)
More commonly used as teaching aids.
De-jure vs. De-facto (TCP/IP)

TCP/IP




Standards adopted due to widespread use. (Internet)
The protocols came first, and the model was really just a
description of the existing protocols. There was no problem with
the protocols fitting the model, but it is hardly possible to be use
to describe other models.
“Get the job done" orientation.
Over the years it has handled most challenges by growing to
meet the needs.
More popular standard for internetworking for several reasons :



relatively simple and robust compared to alternatives such as OSI
available on virtually every hardware and operating system
platform (often free)
the protocol suite on which the Internet depends.
Getting the Data Through the Internet




Layer 3 protocols are primarily designed to move data from
one local network to another local network within an
internetwork.
Layer 3 addresses must include identifiers that enable
intermediary network devices to locate hosts on different
networks
At the boundary of each local network, an intermediary
network device, usually a router, decapsulates the frame to
read the destination host address contained in the header
of the packet, the Layer 3 PDU
Routers use the network identifier portion of this address to
determine which path to use to reach the destination host.
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Getting Data to the End Device





The host physical address, is contained in the header of the
Layer 2 PDU, called a frame.
Layer 2 is concerned with the delivery of messages on a
single local network.
The Layer 2 address is unique on the local network and
represents the address of the end device on the physical
media.
In a LAN using Ethernet, this address is called the Media
Access Control (MAC) address.
When two end devices communicate on the local Ethernet
network, the frames that are exchanged between them
contain the destination and source MAC addresses.
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Getting Data to the End Device

Once a frame is successfully received by the destination
host, the Layer 2 address information is removed as the
data is decapsulated and moved up the protocol stack to
Layer 3.
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