tcp/ip training basic concepts

TCP/IP Protocol Suite 1

TCP/IP Protocol Suite

معرفي پروتكلهاي TCP/IP

ارائه دهندهاميرحسين پناهي

1391خرداد

بنام خدا


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 LayerNetwork LayerTransport LayerSession Layer

Presentation LayerApplication LayerSummary 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 theprotocol 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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