TCP/IP Training Basic Concepts.

TCP/IP Protocol Suite 1
TCP/IP Protocol Suite
‫پروتكلهاي‬ ‫معرفي‬
TCP/IP
‫دهنده‬ ‫ارائه‬
‫پناهي‬ ‫اميرحسين‬
‫خرداد‬1391
‫خدا‬ ‫بنام‬

The OSI Model
Established in 1947, the International Standards Organization (ISO) is
a multinational body dedicated to worldwide agreement on
international standards. An ISO standard that covers all aspects of
network communications is the Open Systems Interconnection (OSI)
model. It was first introduced in the late 1970s.
The topics discussed in this section include:
Layered Architecture
Peer-to-Peer Processes
Encapsulation

ISO is the organization.
OSI is the model
Note:

The OSI model

OSI layers

An exchange using the OSI model

Layers in the OSI Model
The functions of each layer in the OSI model is briefly described.
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
Summary of Layers

The physical layer is responsible for Movement of individual bits from
one hop (node) to the next.
•Includes electrical and mechanical connection features
•Determines bit rates
•Should be synchronized in transmission clock
•Transmission modes: Simplex, Half and Full duplex
Note:
Physical layer

TCP/IP Protocol Suite 9TCP/IP Protocol Suite 9
The data link layer is responsible for moving frames from one hop
(node) to the next
•Framing
•Physical addressing
•Flow control
•Bit error control
•Access control in shared link(CSMA/CD/CA)
Note:
Data link layer

CSMA/CA

Hop-to-hop delivery

The network layer is responsible for the delivery of individual
packets from the source host to the destination host.
•Physical addressing
•Routing
Network layer
Note:

Source-to-destination delivery

The transport layer is responsible for the delivery of a message from one process to
another.
•Port addressing (Process Addressing)
•Segmentation and Reassembly by sequencing
•Connection control (connection-less/connection-oriented)
• flow control (window size)
•Error control (Acknowledgement)
Note:
Transport layer

The Session layer is responsible for synchronization of a message
•Synchronization point insertion and deletion for integrity
validation of message
•Dialog control by changing mode of transmission (half/full duplex)
Note:
Session layer

The presentation layer is responsible for:
•Translation (coding/decoding)
•Encryption/Decryption
•Compression/Decompression
Note:
Presentation layer

Application layer

Summary of layers

TCP/IP Protocol Suite
The TCP/IP protocol suite is made of five layers: physical, data link,
network, transport, and application. The first four layers provide
physical standards, network interface, internetworking, and transport
functions that correspond to the first four layers of the OSI model. The
three topmost layers in the OSI model, however, are represented in
TCP/IP by a single layer called the application layer.
Physical and Data Link Layers
Network Layer
Transport Layer
Application Layer

TCP/IP and OSI model

Addressing
Three different levels of addresses are used in an internet using the
TCP/IP protocols: physical (link) address, logical (IP) address, and
port address.
Physical Address
Logical Address
Port Address

Relationship of layers and addresses in TCP/IP

Physical addresses
In Figure a node with physical address 10 sends a frame to a node with physical
address 87. The two nodes are connected by a link. At the data link level this
frame contains physical (link) addresses in the header. These are the only
addresses needed. The rest of the header contains other information needed at
this level. The trailer usually contains extra bits needed for error detection.
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.

IP addresses
•In Figure we want to send data from a node
with network address A and physical
address 10, located on one LAN, to a node
with a network address P and physical
address 95, located on another LAN.
Because the two devices are located on
different networks, we cannot use link
addresses only; the link addresses have only
local jurisdiction. What we need here are
universal addresses that can pass through
the LAN boundaries. The network (logical)
addresses have this characteristic.
•The packet at the network layer contains
the logical addresses, which remain the
same from the original source to the final
destination (A and P, respectively, in the
figure). They will not change when we go
from network to network. However, the
physical addresses will change as the packet
moves from one network to another. The
boxes labeled routers are internetworking
devices.
132.24.75.9
An internet address in IPv4 in decimal
numbers

Figure 2.20 Port addresses
753
A 16-bit port address represented
as one single number.

•Figure shows an example of transport layer communication. Data
coming from the upper layers have port addresses j and k ( j is the
address of the sending process, and k is the address of the receiving
process). Since the data size is larger than the network layer can handle,
the data are split into two packets, each packet retaining the service-point
addresses ( j and k). Then in the network layer, network addresses (A and
P) are added to each packet.
•The packets can travel on different paths and arrive at the destination
either in order or out of order. The two packets are delivered to the
destination transport layer, which is responsible for removing the
network layer headers and combining the two pieces of data for delivery
to the upper layers
Port addresses

IP Versions
IP became the official protocol for the Internet in 1983. As the Internet
has evolved, so has IP. There have been six versions since its inception.
We look at the latter three versions here.
Version 4
Version 5
Version 6

Connecting Devices
LANs or WANs do not normally operate in isolation. They are
connected to one another or to the Internet. To connect LANs or
WANs, we use connecting devices. Connecting devices can operate in
different layers of the Internet model. We discuss three kinds of
connecting devices: repeaters (or hubs), bridges (or two-layer
switches), and routers (or three-layer switches). Repeaters and hubs
operate in the first layer of the Internet model. Bridges and two-layer
switches operate in the first two layers. Routers and three-layer
switches operate in the first three layers
Repeaters
Hubs
Bridges
Router

Figure 3.28 Connecting devices

Figure 3.29 Repeater

A repeater connects segments of a LAN.
Notes:
A repeater forwards every bit;
it has no filtering capability.
A repeater is a regenerator, not an amplifier.

Figure 3.30 Function of a repeater

A bridge has a table used in filtering
decisions.
Note:

Figure 3.31 Bridge

A bridge does not change the physical
(MAC) addresses in a frame.
Note:

Figure 3.32 Learning bridge

A router is a three-layer
(physical, data link, and network)
device.
Note:

A repeater or a bridge connects segments
of a LAN.
A router connects independent LANs or
WANs to create an internetwork
(internet).
Note:

Figure 3.33 Routing example

A router changes the physical addresses
in a packet.
Note:

CLASSFUL ADDRESSING
IP addresses, when started a few decades ago, used the concept of
classes. This architecture is called classful addressing. In the mid-
1990s, a new architecture, called classless addressing, was introduced
and will eventually supersede the original architecture. However, part
of the Internet is still using classful addressing, but the migration is
very fast.

Finding the class in binary notation

Finding the class in decimal notation

Netid and hostid

Masking concept
Default masks

The network address is the beginning
address of each block. It can be found
by applying the default mask to any
of the addresses in the block
(including itself). It retains the netid
of the block and sets the hostid to
zero.
Note:

Upon completion you will be able to:
ARP and RARP
• Understand the need for ARP
• Understand the cases in which ARP is used
• Understand the components and interactions in an ARP
package
• Understand the need for RARP
Objectives

ARP and RARP - Position in TCP/IP protocol suite

ARP
ARP associates an IP address with its physical address. On a typical physical network,
such as a LAN, each device on a link is identified by a physical or station address that is
usually imprinted on the NIC.

ARP packet / Encapsulation of ARP

Four cases using ARP

An ARP request is broadcast;
an ARP reply is unicast.
Note:

ARP Request/Reply packet Example

Proxy ARP

RARP
RARP finds the logical address for a machine that only knows its
physical address.

The RARP request packets are
broadcast;
the RARP reply packets are unicast.
Note:

RARP packet / Encapsulation of RARP packet

Internet Protocol
• Understand the format and fields of a datagram
• Understand the need for fragmentation and the fields involved
• Understand the options available in an IP datagram
• Be able to perform a checksum calculation
• Understand the components and interactions of an IP package
Objectives

Position of IP in TCP/IP protocol suite

DATAGRAM
A packet in the IP layer is called a datagram, a variable-length packet consisting of
two parts: header and data. The header is 20 to 60 bytes in length and contains
information essential to routing and delivery.

Service type or differentiated services
The precedence subfield was designed, but
never used in version 4.
Types of service

Default types of service

The total length field defines the total
length of the datagram including the
header.
Note:

Figure 8.4 Encapsulation of a small datagram in an Ethernet frame

Protocols field

TTL field
•This filed is used to make limitation of movement of a packet in the
internet
•After any hop in a router this filed is decremented one.
•If TTL equals zero, the packet will be discarded.

FRAGMENTATION
The format and size of a frame depend on the protocol used by the
physical network. A datagram may have to be fragmented to fit the
protocol regulations.

Flags field

Detailed fragmentation example

CHECKSUM
The error detection method used by most TCP/IP protocols is called
the checksum. The checksum protects against the corruption that may
occur during the transmission of a packet. It is redundant information
added to the packet.
Checksum Calculation at the Sender
Checksum Calculation at the Receiver
Checksum in the IP Packet

To create the checksum the sender does the following:
❏ The packet is divided into k sections, each of n bits.
❏ All sections are added together using 1’s complement
arithmetic.
❏ The final result is complemented to make the
checksum.
Note:

Figure 8.22 Checksum concept

Figure 8.23 Checksum in one’s complement arithmetic

User Datagram
Protocol
• Be able to explain process-to-process communication
• Know the format of a UDP user datagram
• Be able to calculate a UDP checksum
• Understand the operation of UDP
• Know when it is appropriate to use UDP
• Understand the modules in a UDP package
Objectives

Figure 11.1 Position of UDP in the TCP/IP protocol suite

11.1 PROCESS-TO-PROCESS
COMMUNICATION
Before we examine UDP, we must first understand host-to-host
communication and process-to-process communication and the
difference between them.
Port Numbers
Socket Addresses

Figure 11.2 UDP versus IP

Figure 11.3 Port numbers

Figure 11.4 IP addresses versus port numbers

Figure 11.5 ICANN ranges

The well-known port numbers are
less than 1024.
Note:

Table 11.1 Well-known ports used with UDP

Socket address

USER DATAGRAM
UDP packets are called user datagrams and have a fixed-size header of
8 bytes.

UDP length =
IP length − IP header’s length
Note:

11.3 CHECKSUM
UDP checksum calculation is different from the one for IP and ICMP.
Here the checksum includes three sections: a pseudoheader, the UDP
header, and the data coming from the application layer.
Checksum Calculation at Sender
Checksum Calculation at Receiver
Optional Use of the Checksum

Figure 11.8 Pseudoheader for checksum calculation

Figure 11.9 Checksum calculation of a simple UDP user datagram

UDP OPERATION
UDP uses concepts common to the transport layer. These concepts will
be discussed here briefly, and then expanded in the next chapter on the
TCP protocol.
Connectionless Services
Flow and Error Control
Encapsulation and Decapsulation
Queuing
Multiplexing and Demultiplexing

Figure 11.10 Encapsulation and decapsulation

Figure 11.11 Queues in UDP

Figure 11.12 Multiplexing and demultiplexing

Transmission
Control Protocol
• Be able to name and understand the services offered by TCP
• Understand TCP’s flow and error control and congestion control
• Be familiar with the fields in a TCP segment
• Understand the phases in a connection-oriented connection
• Understand the TCP transition state diagram
• Be able to name and understand the timers used in TCP
• Be familiar with the TCP options
Objectives

TCP/IP protocol suite

12.1 TCP SERVICES
We explain the services offered by TCP to the processes at the
application layer.
Process-to-Process Communication
Stream Delivery Service
Full-Duplex Communication
Connection-Oriented Service
Reliable Service

well-known ports used by TCP

Stream delivery

Sending and receiving buffers

TCP segments

TCP FEATURES
To provide the services mentioned in the previous section, TCP has
several features that are briefly summarized in this section.
Numbering System
Flow Control
Error Control
Congestion Control

The bytes of data being transferred in
each connection are numbered by TCP.
The numbering starts with a randomly
generated number.
Note:

The value in the sequence number
field of a segment defines the number
of the first data byte contained
in that segment.
Note:

The value of the acknowledgment
field in a segment defines the number
of the next byte a party expects to
receive.
The acknowledgment number is
cumulative.
Note:

SEGMENT
A packet in TCP is called a segment
Format
Encapsulation

TCP segment format

Control field

Figure 12.7 Pseudoheader added to the TCP datagram

The inclusion of the checksum in
TCP is mandatory.
Note:

Encapsulation and decapsulation

A TCP CONNECTION
TCP is connection-oriented. A connection-oriented transport protocol
establishes a virtual path between the source and destination. All of the
segments belonging to a message are then sent over this virtual path. A
connection-oriented transmission requires three phases: connection
establishment, data transfer, and connection termination.
Connection Establishment
Data Transfer
Connection Termination
Connection Reset

Connection establishment using three-way handshaking

A SYN segment cannot carry data,
but it consumes one sequence
number.
Note:

A SYN + ACK segment cannot carry
data, but does consume one
sequence number.
Note:

An ACK segment, if carrying no
data, consumes no sequence number.
Note:

Data transfer

The FIN segment consumes one
sequence number if it does not carry
data.
Note:

Connection termination using three-way handshaking

The FIN + ACK segment consumes
one sequence number if it does not
carry data.
Note:

Half-close

STATE TRANSITION DIAGRAM
To keep track of all the different events happening during connection
establishment, connection termination, and data transfer, the TCP
software is implemented as a finite state machine. .
Scenarios

Table 12.3 States for TCP

State transition diagram

Common scenario

Three-way handshake

Simultaneous open

Simultaneous close

Denying a connection

Aborting a connection

FLOW CONTROL
Flow control regulates the amount of data a source can send before
receiving an acknowledgment from the destination. TCP defines a
window that is imposed on the buffer of data delivered from the
application program.
Sliding Window Protocol
Silly Window Syndrome

Sliding window

A sliding window is used to make
transmission more efficient as well as
to control the flow of data so that the
destination does not become
overwhelmed with data.
TCP’s sliding windows are byte
oriented.
Note:

Example 5

Example 7

ERROR CONTROL
TCP provides reliability using error control, which detects corrupted,
lost, out-of-order, and duplicated segments. Error control in TCP is
achieved through the use of the checksum, acknowledgment, and time-
out.
Checksum
Acknowledgment
Acknowledgment Type
Retransmission
Out-of-Order Segments
Some Scenarios

ACK segments do not consume
sequence numbers and are not
acknowledged.
Note:

In modern implementations, a
retransmission occurs if the
retransmission timer expires or three
duplicate ACK segments have arrived.
Note:

No retransmission timer is set for an
ACK segment.
Note:

Data may arrive out of order and be
temporarily stored by the receiving TCP,
but TCP guarantees that no out-of-order
segment is delivered to the process.
Note:

Normal operation

Lost segment

The receiver TCP delivers only
ordered data to the process.
Note:

Fast retransmission

Lost acknowledgment

Lost acknowledgment corrected by resending a segment

Lost acknowledgments may create
deadlock if they are not properly
handled.
Note:

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TCP/IP Training Basic Concepts.

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