Tài liệu học CCNA kỳ 1 mod11 tranport and application layer

NIIT-ICT Hanoi info@niithanoi.vnOverview • The TCP/IP transport layer does the work of transporting data between applications on source and destination devices.. Transport services inclu

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Module 11 Transport and Application Layer

NIIT-ICT Hanoi info@niithanoi.vn

Contents

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Overview

• The TCP/IP transport layer does the work of transporting data between

applications on source and destination devices

• This module will describe the functions and services of this critical layer

of the TCP/IP network model

• Many of the network applicationsthat are found at the TCP/IP

application layer are familiar to even casual network users For

example: HTTP, FTP and SMTP v.v

Introduction

• Transport layer used to transport and regulate the flow of information

from the source to the destination, reliably and accurately End-to-end

control and reliability are provided by sliding windows, sequencing

numbers, and acknowledgments

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Introduction to transport layer

• The transport layer establishes a logical connectionbetween the

endpoints of the network Transport services segment and reassemble

several upper-layer applicationsonto the same transport layer data

stream

• The transport layer defines end-to-end connectivitybetween host

applications Transport services include the following basic services:

-Segmentation of upper-layerapplication data

- Establishment of end-to-endoperations

-Transport of segmentsfrom one end host to another end host

-Flow controlprovided by sliding windows

-Reliabilityprovided by sequence numbers and acknowledgments

Flow control

• Flow control avoids the problem of a transmitting host overflowing the

buffers in the receiving host TCP provides the mechanism for flow

control by allowing the sending and receiving host to communicate

The two hosts then establish a data-transfer rate that is agreeable to

both

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Multiplexing

• Multiple applicationscan share the same transport connectionin the

OSI reference model

• Different applications can send data segments on a come,

first-servedbasis The segments that arrive first will be taken care of first

This is referred to as the multiplexing of upper-layer conversations

Establishing a Connection

• One function of the

transport layer is to

establish a

connection-oriented sessionbetween

similar devices at the

application layer For data

transfer to begin, boththe

sending and receiving

applications inform the

respective operating

systems that a connection

will be initiated and the

first handshake requests

synchronization

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Flow Control

When datagrams arrive too

quickly for a host or gateway

to process and the transport

function can issue a “not

ready”indicator to the

sender to stop sending data

When the receiver can

handle additional data, the

receiver sends a “ready”

transport indicator When

this indicator is received, the

sender can resume the

segment transmission

Three-way handshake

• A three-way handshake is the synchronization process is required for

the connection establish Synchronization is done through an

exchange of connection establishing segments that carry a control bit

called SYN as in the figure

• The three-way handshake is necessary and is required in the

connection-oriented connection

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Windowing and Acknowledgment

Transmission Control

Protocol (TCP)

• Transmission Control Protocol provides reliable full-duplex data

transmission

• TCP is responsible for breaking messages into segments,

reassembling them at the destination station, resending anything that is

not received, and reassembling messages from the segments, uses a

virtual circuit between end-user applications

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TCP Header format:

• Source Port 16 bits.

• Destination Port 16 bits.

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• Sequence Number: 32 bits

– The sequence number of the

first data octet in this segment (except when SYN is present).

– The sequence number of the

first data octet in this segment (except when SYN is present).

• Acknowledgment Number: 32 bits

– This field contains the value of the

next sequence number the sender of

the segment is expecting to receive.

– This field contains the value of the

next sequence number the sender of

the segment is expecting to receive.

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• Control Bits: 8 bits

– ACK: Acknowledgment field significant

– RST: Reset the connection

– SYN: Synchronize sequence numbers

– FIN: No more data from sender

• Control Bits: 8 bits

– ACK : Acknowledgment field significant

– RST : Reset the connection

– SYN : Synchronize sequence numbers

– FIN : No more data from sender

• Window: 16 bits

– The number of data octets beginning

with the one indicated in the

acknowledgment field which the sender

of this segment is willing to accept.

– The number of data octets beginning

with the one indicated in the

acknowledgment field which the sender

of this segment is willing to accept.

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TCP header fields

• Source & Destination port – Number of the calling, called port

• Sequence number – Number used to ensure correct sequencing of

the arriving data

• Acknowledgment number – Next expected TCP octet

• HLEN – Number of 32-bit words in the header

• Reserved – Set to zero

• Code bits – Control functions, such as setup and termination of a

session

• Window – Number of octets that the sender is willing to accept

• Checksum – Calculated checksum of the header and data fields

• Urgent pointer – Indicates the end of the urgent data

• Option – One option currently defined, maximum TCP segment size

• Data – Upper-layer protocol data

User Datagram Protocol (UDP)

• UDP is a simpleprotocol that exchanges datagrams, without

acknowledgments or guaranteed delivery Error processing and

retransmission must be handled by higher layer protocols

• UDP is designed for applications that do not need to put

sequencesof segments together

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UDP header fields

• Source port – Number of the calling port

• Destination port – Number of the called port

• Length – Number of bytes including header and data

• Checksum – Calculated checksum of the header and data fields

• Data – Upper-layer protocol data

• The protocols that use UDP include:

- TFTP (Trivial File Transfer Protocol)

- SNMP (Simple Network Management Protocol)

- DHCP (Dynamic Host Control Protocol)

- DNS (Domain Name System)

TCP and UDP port numbers

• Both TCP and UDP use port (socket) numbers to pass information

to the upper layers.Port numbers are used to keep track of

different conversationscrossing the network at the same time

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• Application software developers agree to use well-known port numbers

that are issued by the Internet Assigned Numbers Authority (IANA)

• Numbers < 1024are considered well-known ports numbers

• Numbers > 1024are dynamically assignedports numbers

• Registered port numbersare those registered for vendor-specific

applications.Most of these are above 1024

• End systems use port numbers to select the proper application The

source host dynamically assigns originating source port numbers

These numbers are always greater than 1024

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Introduction to the TCP/IP application layer

When the TCP/IP model was designed, the session and presentation layers from the OSI model were bundled into the

application layer of the TCP model This means that issues of

representation, encoding, and dialog control are handled in the application layer rather than in separate lower layers as

in the OSI model

Domain Name System(DNS)

• A domain naming system was developed in order to associate the

contents of the site with the address of that site The Domain Name

System (DNS) is a system used on the Internet for translating names

of domains and their publicly advertised network nodes into IP

addresses

.

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Domain Name System(DNS)

com vn

.

Address

of com server

Address

of com

server Address of

yahoo.com server

Address of

yahoo.com

server

Address of www.yahoo.com

Address of

www.yahoo.com

Address of

www.yahoo.com

Address of

www.yahoo.com

Request

Reply

File Transfer Protocol (FTP)

FTP is a reliable,

connection-oriented servicethat uses TCP

to transfer files between

systems that support FTP The

main purpose of FTP is to

transfer files from one computer

to another by copying and

moving files from servers to

clients, and from clients to

servers

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Trivial File Transfer Protocol (TFTP)

• TFTP is a connectionless service that uses User Datagram Protocol

(UDP).TFTP is used on the router to transfer configuration filesand

Cisco IOS imagesand to transfer files between systems that support

TFTP TFTP has no provisions for user authentication It operates

faster than FTP and in a stable environmentit works reliably

Hypertext Transfer Protocol (HTTP)

• Hypertext Transfer Protocol (HTTP) works with the World Wide Web,

which is the fastest growing and most used part of the Internet A Web

browser is a client-server application

• The Web pages are created with a format language called Hypertext

Markup Language (HTML)

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Simple Mail Transfer Protocol (SMTP)

• When a mail server receives a message destined for a local client, it stores that

message and waits for the client to collect the mail

• The most popular mail client protocols are POP3 and IMAP4, which both use

TCP to transport data Even though mail clients use these special protocols to

collect mail, they almost always use SMTP to send mail

• When checking the configuration of a mail client, verify that the SMTP and POP

or IMAP settings are correctly configured A good way to test if a mail server is

reachable is to Telnet to the SMTP port (25) or to the POP3 port (110).

Simple Network Management Protocol (SNMP)

The Simple Network

Management Protocol

(SNMP) is an application

layer protocol that

facilitates the exchange of

management information

between network devices

SNMP enables network

administrators to manage

network performance, find

and solve network

problems, and plan for

network growth.SNMP

uses UDP as its transport

layer protocol

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Key Component of SNMP

• Network management system (NMS) – NMS executes applications

that monitor and control managed devices The bulk of the processing

and memory resourcesrequired for network management are provided

by NMS One or more NMSsmust exist on any managed network

• Managed devices – Managed devices are network nodes that contain

an SNMP agentand that reside on a managed network Managed

devices collect and store management information and make this

information available to NMSs using SNMP Managed devices,

sometimes called network elements, can be routers, access servers,

switches, and bridges, hubs, computer hosts, or printers

• Agents – Agents are network-management software modulesthat

reside in managed devices An agent has local knowledge of

management information and translates that information into a form

compatible with SNMP

Telnet

Telnet client software provides the ability to login to a remote Internet host

that is running a Telnet server application and then to execute

commands from the command line

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Summary

• The functions of the TCP/IP transport layer

• Flow control

• The processes of establishing a connection between peer systems

• Windowing

• Acknowledgment

• Transport layer protocols

• TCP and UDP header formats

• TCP and UDP port numbers

• The processes and protocols at the TCP/IP application layer

• Domain Name Services, File Transfer Protocols, Simple Mail Transfer

Protocol

• Simple Network Management Protocol, Telnet

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