Transcript ccna1_mod11_gw

Module 11
TCP Application and
Transport
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Transport Layer
• The primary duties of the transport layer, Layer 4 of the OSI
model, are 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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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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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. The synchronization requires each side to
send its own initial sequence number and to receive a
confirmation of exchange in an acknowledgment (ACK) from
the other side.
This exchange is called the
three-way handshake.
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Windowing
• Windowing is a flow-control mechanism.
• Windowing requires that the source device receive an
acknowledgment from the destination after transmitting a
certain amount of data.
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Acknowledgement
• Positive acknowledgment
with retransmission is one
technique that guarantees
reliable delivery of data.
• Positive acknowledgment
requires a recipient to
communicate with the
source and send back an
acknowledgment message
when the data is received.
• Segments that are not
acknowledged within a given
time period will result in a
retransmission.
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TCP/IP
• Transmission Control Protocol (TCP) is a connection-oriented
Layer 4 protocol
• 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.
• The protocols that use TCP include:
– FTP (File Transfer Protocol)
– HTTP (Hypertext Transfer Protocol)
– SMTP (Simple Mail Transfer Protocol)
– Telnet
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UDP
• User Datagram Protocol (UDP) is the connectionless transport
protocol
• UDP is a simple protocol that exchanges datagrams, without
acknowledgments or guaranteed delivery
• UDP uses no windowing or acknowledgments so reliability, if
needed, is provided by application layer protocols
• 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)
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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 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 vendorspecific applications. Most of these are above 1024.
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Port Numbers
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TCP/IP Model
Application Layer
• TCP/IP application layer
includes the session and
presentation layers from the
OSI 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
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TCP/IP Protocols
• The TCP/IP protocols that support file transfer, e-mail, and
remote login are probably the most familiar to users of the
Internet.
• These protocols include the following applications:
– Domain Name System (DNS)
– File Transfer Protocol (FTP)
– Hypertext Transfer Protocol (HTTP)
– Simple Mail Transfer Protocol (SMTP)
– Simple Network Management Protocol (SNMP)
– Telnet
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DNS
• 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.
• A domain is a group of computers that are associated by their
geographical location or their business type.
• There are more than 200 top-level domains on the Internet,
examples include the following:
.us – United States
.uk – United Kingdom
• There are also generic names, examples include the following:
.edu – educational sites
.com – commercial sites
.gov – government sites
.org – non-profit sites
.net – network service
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FTP and TFTP
• FTP is a reliable, connection-oriented service that uses TCP to
transfer files between systems that support FTP
• When files are copied from a server, FTP first establishes a
control connection between the client and the server.
• Data transfer can occur in
ASCII mode or in binary
mode.
• After the file transfer has
ended, the data connection
terminates automatically.
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TFTP
• TFTP is a connectionless service that uses User Datagram
Protocol (UDP).
• TFTP is used on the router to transfer configuration files and
Cisco IOS images
• TFTP is designed to be small and easy to implement.
• TFTP can read, write, or mail files to or from a remote server
but it cannot list directories and currently has no provisions for
user authentication
• It is useful in some LANs because it operates faster than FTP
and in a stable environment it works reliably.
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HTTP
• Hypertext Transfer Protocol (HTTP) works with the World Wide
Web
• An address location is known as an Uniform Resource Locator
(URL)
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SMTP
• Email servers communicate with each other using the Simple
Mail Transfer Protocol (SMTP) to send and receive mail.
• 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.
• The SMTP protocol does not offer much in the way of security
and does not require any authentication.
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SMTP
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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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SNMP
• An SNMP managed network consists of the following three key
components:
– Network management system (NMS) – NMS executes
applications that monitor and control managed devices. The
bulk of the processing and memory resources required for
network management are provided by NMS.
– Managed devices –Managed devices, sometimes called
network elements, can be routers, access servers, switches,
and bridges, hubs, computer hosts, or printers.
– Agents –An agent has local knowledge of management
information and translates that information into a form
compatible with SNMP.
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SNMP
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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.
• Telnet works at the application layer of the TCP/IP model.
Therefore, Telnet works at the top three layers of the OSI
model.
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