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CCNA Semester1
Module 11
TCP/IP Appl ic at ion and Tr ansport
Objectives
Functions of the TCP/IP transport layer
TCP concepts and processes
TCP/IP application layer
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TCP/IP Transport Layer
Why we need a transport layer?
Layer 1 allows bit streams to be createdand to travel.
Layer 2 packages those data packets into
frames to be converted to bit streams andmakes data-link delivery possible.
Layer 3 packages data from upper layers inpackets and makes routing and networkdelivery possible.
But they made no provision for assuringour data reliably travels end-to-end acrossthe vast network path.
But they made no provision for assuringour data reliably travels end-to-end across
the vast network path.
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Introduction to transport layer
The transport layer data stream is a logicalconnection between the endpoints of a network.
Its primary duties are to transport and regulate theflow of information from source to destination
reliably and accurately. Transport services include the following basic
services: Segmentation of upper-layer application data
Establishment of end-to-end operations
Transport of segments from one end host to another end host
Flow control provided by sliding windows
Reliability provided by sequence numbers and
acknowledgments
Flow Control
Avoids the problem of a host at one side ofthe connection overflowing the buffers in thehost at the other side.
The two hosts then establish a data-transferrate that is agreeable to both.
Ensures the integrity of the data
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Session Establishment
Multiple applications can share the same transportconnection in the OSI reference model.
Different applications can send data segments on a first-come, first-served basis. This is referred to as the
multiplexing of upper-layer conversations.
TCP and UDP
The emphasis of this curriculum is onTCP/IP Ethernet networks.
The TCP/IP protocol of the OSI model Layer
4 (transport layer) has two protocols - TCPand UDP.
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TCP/IP Protocol Stack
Port
Both TCP and UDP use port (or socket)numbers to pass information to the upperlayers.
RFCRFC--17
0017
00
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Range of ports
2 bytes: 0 65535. Numbers below 255 : for public applications.
Numbers from 255 - 1023 : assigned to companiesfor marketable applications.
Numbers above 1023 : are unregulated.
End systems use port numbers to selectproper applications.
Originating source port numbers aredynamically assigned by the source host;usually, it is a number larger than 1023.
TCP
TCP supplies a virtual circuit between end-userapplications. These are its characteristics:
connection-oriented.
reliable.
divides outgoing messages into segments.
reassembles messages at the destination station.
re-sends anything not received.
Protocols that use TCP include FTP, SMTP, HTTP,Telnet
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TCP Header format
Protocol that provides reliable full-duplexdata transmission.
RFCRFC--7
61
761
TCP Header format: Port number
Source Port 16 bits.
Destination Port 16 bits.
Source Port 16 bits.
Destination Port 16 bits.
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TCP Header format: Sequence
Sequence Number: 32 bits
The sequence number of thefirst data octet in this segment
(except when SYN is present).
Sequence Number: 32 bits
The sequence number of thefirst data octet in this segment
(except when SYN is present).
TCP Header format: Acknowledgment
Acknowledgment Number: 32 bits
This field contains the value of thenext sequence number the sender ofthe segment is expecting to receive.
Acknowledgment Number: 32 bits
This field contains the value of thenext sequence number the sender ofthe segment is expecting to receive.
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TCP Header format: Code bits
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
TCP Header format: Window
Window: 16 bits
The number of data octets beginning
with the one indicated in theacknowledgment field which the senderof this segment is willing to accept.
Window: 16 bits
The number of data octets beginningwith the one indicated in theacknowledgment field which the senderof this segment is willing to accept.
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Three-way handshake
TCP: Simple acknowledgment
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TCP: Sliding window acknowledgment
TCP: Sequence and acknowledgment
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UDP
UDP transports data unreliably between hosts.Following are the characteristics:
Connectionless.
Unreliable. Transmit messages (called user datagrams).
Provides no software checking for message delivery(unreliable).
Does not reassemble incoming messages.
Uses no acknowledgements.
Protocols that use include TFTP, SNMP, DHCP, DNS
UDP Header format
UDP is a simple protocol that exchangesdatagrams, without acknowledgments or
guaranteed delivery.
RFCRFC--76
876
8
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TCP/IP Application Layer
Application Layer: TCP/IP vs. OSI
The session and presentation layers from theOSI model were bundled into the applicationlayer of the TCP model.
This means that issues of representation,encoding, and dialog control are handled in theapplication layer rather than in separate lowerlayers as in the OSI model.
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Session: Functions
Presentation: Functions
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TCP/IP Application Layer
Handles high-levelprotocols, issues ofrepresentation, encoding,and dialog control.
The TCP/IP combines allapplication-related issuesinto one layer, and assuresthis data is properlypackaged for the next layer.
FTP, HTTP, SMTP, DNS,SNMP ...
Format of data, datastructure, encode
Dialog control, sessionmanagement
Interfaces
Direct network application:
The application layer provides a direct interface for the rest ofthe OSI model by using network applications.
Client server: WEB, FTP, Mail
Indirect network application: The application layer provides an indirect interface for the restof the OSI model by using standalone applications.
The redirector directs requests from local computer to theproper network resources. Applications on client never have torecognize the network.
Redirector: network driver, network printer
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Client-Server application
The client side is located on the localcomputer and is the requestor of theservices.
The server side is located on a remotecomputer and provides services inresponse to the clients requests.
The client side is located on the localcomputer and is the requestor of theservices.
The server side is located on a remotecomputer and provides services inresponse to the clients requests.
Network driver
The applications on the client never haveto recognize the network.
Redirectors expand the capabilities ofnon-network software.
The applications on the client never haveto recognize the network.
Redirectors expand the capabilities ofnon-network software.
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Make and Break a connection
The connection to the server wasmaintained only long enough to processthe transaction.
Example : WWW, E-mail
The connection to the server wasmaintained until the user determines thathe/she has finished.
Example : FTP, Telnet
DNS
The Domain Name System (DNS) is a systemused on the Internet for translating names ofdomains and their publicly advertised network
nodes into IP addresses. A domain is a group of computers that are
associated by their geographical location ortheir business type.
The DNS system is set up in a hierarchy thatcreates different levels of DNS servers.
Eg: http://www.cdit.com.vn/itc/
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DNS: System
vnnvnn comcom eduedu govgov
comcom eduedu govgov ukukfrfrvnvn
.
DNS: Resolve www.yahoo.com
vnnvnn yahooyahoo
comcomvnvn
.
Address
of com
server
Address
ofcom
serverAddress of
yahoo.com
server
Address of
yahoo.com
server
Address of
www.yahoo.com
Address of
www.yahoo.com
Address ofwww.yahoo.com
Address ofwww.yahoo.com
RequestRequestRequest
ReplyReplyReply
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FTP
File Transfer Protocol (FTP) is a reliable,connection-oriented service that uses TCP totransfer files between systems that support FTP.
When files are copied from a server, FTP firstestablishes a control connection between theclient and the server. Then a second connectionis established, which is a link between thecomputers through which the data istransferred.
TFTP
Trivial File Transfer Protocol (TFTP) is aconnectionless service that uses UDP.
TFTP is designed to be small and easy toimplement.
TFTP is used on the router to transferconfiguration files and Cisco IOS imagesand to transfer files between systems thatsupport TFTP.
TFTP can read, write, or mail files to or froma remote server but it cannot list directories
and currently has no provisions for userauthentication.
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HTTP
Hypertext Transfer Protocol (HTTP) works with theWorld Wide Web, which is the fastest growing and mostused part of the Internet.
A Web browser is a client-server application, which
means that it requires both a client and a servercomponent in order to function.
A Web browser presents data in multimedia formats. Ahyperlink is an object, word, phrase, or picture, on aWeb page. When that hyperlink is clicked, it directs thebrowser to a new Web page.
The Web page contains, often hidden within its HTMLdescription, an address location known as a Uniform
Resource Locator (URL).
Telnet
Telnet client software provides the ability tologin to a remote Internet host that is running aTelnet server application and then to executecommands from the command line.
Telnet works at the application layer of theTCP/IP model. Therefore, Telnet works at the topthree layers of the OSI model. The applicationlayer deals with commands. The presentationlayer handles formatting, usually ASCII. Thesession layer transmits.
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SMTP
Email servers communicatewith each other using theSimple Mail TransferProtocol (SMTP) to sendand receive mail. The SMTPprotocol transports emailmessages in ASCII formatusing TCP.
The most popular mailclient protocols are POP3and IMAP4, which both useTCP to transport data.
A good way to test if a mail
server is reachable is toTelnet to the SMTP port (25)or to the POP3 port (110).
SNMP
The Simple NetworkManagement Protocol (SNMP)is an application layer protocolthat facilitates the exchange ofmanagement information
between network devices.
An SNMP managed networkconsists of the following:
Network managementsystem (NMS)
Managed device
Agents
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Lab Companion
11.2.4 Protocol Inspector, TCP and HTTP
Summary
TCP/IP transport layer functions
TCP concepts and processes
TCP and UDP header format
TCP and UDP port TCP/IP application layer functions
TCP/IP application layer protocols
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