CISCO NETWORKING ACADEMY PROGRAM (CNAP) SEMESTER 1/ MODULE 11 TCP/IP Application and Transport.

CISCO NETWORKING ACADEMY PROGRAM (CNAP)SEMESTER 1/ MODULE 11

TCP/IP Application and Transport

CISCO NETWORKING ACADEMY PROGRAMSEMESTER 1/ MODULE 11

Introduction to Transport Layer

• The TCP/IP transport layer does the work of transporting data between applications on source and destination devices.

• Ensure that segments delivered will be acknowledged to the sender

• Provide for retransmission of any segments that are acknowledged

• Put segments back into their correct sequence at the destination

• Provide congestion avoidance and control



TCP/IP Transport Layer


The primary functions that occur • To transport and regulate the flow of information from source to

destination, reliably and accurately. • To provide end-to-end control, provided by sliding windows and • To ensure a reliability in sequencing numbers and

acknowledgments

There are two protocols in TCP/IP transport layer:• User Datagram Protocol (UDP)• Transmission Control Protocol (TCP)

Flow Control Analogy


Flow Control


• To regulate the flow of information from source to destination, reliably and accurately, host tries to ensure that data is not lost

• The two hosts then establish a data-transfer rate that is agreeable to both• End-to-end control, provided by sliding windows, and reliability in

sequencing numbers and acknowledgments


Session Establishment, Maintenance and Termination

• Multiple applications can share the same transport connection in the OSI reference model.

• Transport functionality is accomplished on a segment-by-segment basis

• Transport layer can multiplex upper-layer conversations based on a segment-by-segment basis.





• One function of the transport layer is to establish a connection-oriented session between similar devices at the application layer.

• The connection is established and the transfer of data begins after all synchronization has occurred.

• During transfer, the two machines continue to communicate with their protocol software to verify that data is received correctly.

• Congestion can occur during data transfer for two reasons.

• high-speed computer might be capable of generating traffic faster than a network can transfer it.

• many computers simultaneously need to send datagrams to a single destination

Three-Way Handshake




Flow Control

• When datagrams arrive too quickly for a host or gateway to process, the host or gateway eventually exhausts its memory and must discard additional datagrams that arrive (Congestion).

• the transport function can issue a “not ready” indicator to the sender. 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

• TCP is a connection-oriented protocol.

• TCP requires connection establishment before data transfer begins.

• For a connection to be established or initialized, the two hosts must synchronize their Initial Sequence Numbers (ISNs).

• Each side must also receive the INS from the other side and send a confirming ACK.



Windowing and Acknowledgement


• Windowing is a flow control mechanism requiring that the source device receive an acknowledgment from the destination after transmitting a certain amount of data.

Low throughput


• The number of data packets the sender is allowed to have outstanding without having received an acknowledgment is known as the window size, or window.

• Windowing requires that the source device receive an acknowledgment from the destination after transmittinga certain amount of data.

• The receiving TCP process reports a “window” to the sending TCP.

• TCP window sizes are variable during the lifetime of a connection.

• Each acknowledgement contains a window advertisement that indicates the number of bytes the receiver can accept.




• Reliable delivery guarantees that a stream of data sent from one device is delivered through a data link to another device without duplication or data loss.

• Positive acknowledgment with retransmission is one technique that guarantees reliable delivery of data.

• TCP uses expectational acknowledgments.

• Expectational acknowledgements mean that the acknowledgment number refers to the packet that is next expected.




Acknowledgement


• If a sequence number is missing in the series, that segment is retransmitted.

• Segments that are not acknowledged within a given time period will result in a retransmission.

• Each segment is numbered before transmission

• At the receiving station, TCP reassembles the segments into a complete message.


Positive Acknowledgement and Retransmission


• It is used to provide reliability.• Positive acknowledgment requires a recipient to communicate with the

source and send back an acknowledgment message when the data is received.

• The sender keeps a record of each data packet (TCP segment), that it sends and expects an acknowledgment.

• Once the source sends a packet, it starts a timer and waits for an acknowledgment before sending the next packet.

• If the timer expires before the source receives an acknowledgment, the source retransmits the packet and starts the timer over again.


• TCP also maintains a congestion-control window.

• This window is normally the same size as the window of the receiver.

• However, this window is cut in half when a packet is lost, perhaps as a result of network congestion.

• This approach permits the window to be expanded or contracted as necessary to manage buffer space and processing.


TCP Congestion Control


Transmission Control Protocol (TCP)


• connection-oriented • reliable • divides outgoing messages into segments • reassembles messages at the destination station • re-sends anything not received • reassembles messages from incoming segments• The protocols that use TCP include:

• FTP (File Transfer Protocol)

• HTTP (Hypertext Transfer Protocol)

• SMTP (Simple Mail Transfer Protocol)

• Telnet


Transmission Control Protocol


• Source port – Number of the calling port

• Destination port – Number of the 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


Transmission Control Protocol


• 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


• connectionless • unreliable • transmit messages (called user datagrams) • provides no software checking for message delivery (unreliable) • does not reassemble incoming messages • uses no acknowledgments • provides no flow control

No sequence or acknowledgement fields

UDP Segment Format


User Datagram Protocol


The protocols that use TCP include: • TFTP (Trivial File Transfer Protocol) • SNMP (Simple Network Management Protocol) • DHCP (Dynamic Host Control Protocol) • DNS (Domain Name System)


Port Number


• Both TCP and UDP use port (socket) numbers to pass information to the upper layers.

• Port numbers are used to keep track of different conversations crossing the network at the

same time. • Port numbers have the following assigned ranges:

– Numbers below 1024 are considered well-known ports numbers.

– Numbers above 1024 are dynamically assigned ports numbers.

– Registered port numbers are those registered for vendor-specific applications. Most of these are above 1024.

• The source host dynamically assigns originating source port numbers. These numbers are always greater than 1023.



Port Numbers


Introduction to Application Layer

• TCP/IP application layer combine the functions of three upper layers together.

• This design assures that the TCP/IP model provides maximum flexibility at the application layer for developers of software.

Application Layer is responsible for:

• Identifying and establishing the availability of intended communication partner

• Synchronizing cooperating applications

• Establishing agreement on procedures for error recovery

• Controlling data integrity



Introduction to Application Layer


TCP/IP application Examples:• Domain Name System (DNS) • File Transfer Protocol (FTP) • Hypertext Transfer Protocol (HTTP) • Simple Mail Transfer Protocol (SMTP) • Simple Network Management Protocol (SNMP) • Telnet


Domain Name System


• 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.

• Examples: .th – Thailand, .us – United States , .uk – United Kingdom

• Domain name server is a device on a network• It responds to requests from clients to translate a domain name into the associated IP

address.• The DNS system is set up in a hierarchy that creates different levels of DNS servers.• If a local DNS server is able to translate a domain name into its associated IP

address, it does so, and returns the result to the client. • If it cannot translate the address, it passes the request up to the next higher-level DNS

server on the system


Domain Name System


• There are also generic names, which examples include the following:– .edu – educational sites

– .com – commercial sites

– .gov – government sites

– .org – non-profit sites

– .net – network service


File Transfer Protocol and Trivial File Transfer Protocol


• TFTP– is a connectionless service that uses UDP.– TFTP is used on the routers and switches to transfer files between systems that support TFTP– TFTP operates faster than FTP– TFTP has no provisions for user authentication.

• FTP– FTP is a reliable, connection-or

iented service that uses TCP to transfer files between systems that support FTP

– FTP is designed to download files or upload files.


Hypertext Transfer Protocol


• HTTP works with the World Wide Web, which is the fastest growing and most used part of the Internet.

• One of the main reasons for the extraordinary growth of the Web is the ease with which it allows access to information.

• A Web browser (along with all the other network applications covered in this chapter) is a client-server application, which means that it requires both a client and a server component in order to function.

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

Markup Language (HTML). • The Web page contains, often hidden within its HTML description, a

n address location known as a Uniform Resource Locator (URL).


Simple Mail Transfer Protocol


• Email servers communicate with each other using the Simple Mail Transfer Protocol (SMTP) to send and receive mail.

• The SMTP protocol transports email messages in ASCII format using TCP.

• Mail can be collected by using program that access the mail server files directly or collect their mail using one of many network protocols:

– POP3 and IMAP4, which both use TCP to transport data.


Simple Network Management

• 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 transportlayer protocol.


SNMP three components:

• Network management system (NMS)

• Managed devices

• Agents


Telnet


• Terminal emulation (Telnet) software provides the ability to remotely access another computer.

• It allows you to log in to an Internet host and execute commands. • A Telnet client is referred to as a local host, and a Telnet server, which

uses special software called a daemon, is referred to as a remote host.

Date post:	11-Jan-2016
Category:	Documents
Upload:	randell-french
View:	222 times
Download:	0 times

CISCO NETWORKING ACADEMY PROGRAM (CNAP) SEMESTER 1/ MODULE 11 TCP/IP Application and Transport.

Documents