CCNA 1 Module 11

1
CCNA 1 Module 11

• TCP/IP Transport and Application Layers

2
Overview Objectives

• By the end of this chapter you should be able to
  
• - Describe how positive acknowledgement and
  retransmission (PAR) relates to TCP
• - Describe how TCP relates to multiple host
  conversations

3
TCP/IP Transport Layer

• The Transport Layer reliably and accurately
  transports and regulates the flow of information
  between source and destination.
• sliding windows
• sequencing numbers
• acknowledgments

4
TCP/IP Transport Layer

• Two primary duties of the transport layer are to
  provide flow control reliability. Services
  include
• Segmentation of upper-layer application data
• Establishment of end-to-end operations
• Transportation of segments from one end host to
  another
• Flow control provided by sliding windows
• Reliability provided by sequence numbers and
  acknowledgments
• Segments reassembled at destination

5
Transport Layer Flow Control

• Flow control ensures a source host does not
  overflow the buffers in a destination host.
• Too much data means lost data
• With flow control, the two hosts establish a data
  transfer rate

6
Session Establishment, Maintenance, Termination

• Layer 4 allows different conversations to occur
  simultaneously over one connection.
• Known as multiplexing
• different types of conversations are labelled
  with application specific port numbers
• Before data is transferred
• Synchronization occurs
• Connection is established
• Data is transferred

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A typical connection

• First handshake requests synchronization
• Second handshake acknowledges initial request,
  then requests synchronization in the opposite
  direction
• Third handshake is an acknowledgment informing
  destination a connection is established
• After connection is established, data transfer
  begins

8
Flow Control

• Congestion occurs for one of two reasons
• PC transmits data faster than the network can
  transmit
• Many devices transmitting data to the same
  destination
• If data arrives too quickly it is stored in
  memory (buffered)
• If data continues to arrive too quickly, data
  will be discarded (overflow)

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Flow Control

• Instead of allowing data to be lost, the
  destination sends a not ready indicator to the
  sender
• When destination can handle more data, it sends a
  ready indicator to the sender
• At the end of data transfer, the source host
  sends a signal indicating the end of the
  transmission (aka a flag or a semaphore)
• Destination acknowledges this and the connection
  is terminated

10
Three-way Handshake

• TCP is connection-oriented
• The connection is established before data
  transfer begins
• 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

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Three-way Handshake

• Sending host (A) initiates connection by sending
  a SYN packet to the receiving host (B) indicating
  its INS X
• A - gt B SYN, seq of A X
• B receives packet, records the seq of A X,
  replies with an ACK of X 1, and indicates its
  INS Y. The ACK of X 1 means host B has
  received all octets up to and including X and is
  expecting X1
• B - gt A ACK, seq of A X, SYN seq of B Y, ACK
  X 1
• A receives packet from B, it knows the seq of B
  Y, responds with ACK of Y 1, finalizing the
  connection process
• A - gt B ACK, seq of B Y, ACK Y 1

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Windowing

• Reliable data transfer is achieved by
  acknowledgments (ACK)
• ACKs sent after every packetlow throughput, so
  multiple packets are sent
• Number of packets a sender can transmit before it
  receives an ACK is known as the window size, or
  window

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Windowing Flow Control

• Expectational ACKs ACK number refers to the next
  packet that is expected
• Window size is dynamically negotiated

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Windowing Flow Control
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Windowing Flow Control
The ACK sent by the destination determines
whether the sender retransmits, or continues to
send as before.
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Acknowledgments
17
TCP Segment Format
Number of the called port
set to zero
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TCP/UDP Protocols

• TCP
• FTP
• HTTP
• SMTP
• Telnet

• UDP
• TFTP
• SNMP
• DHCP
• DNS

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UDP

• Connectionless
• No guaranteed delivery
• Reliability is provided by application layer
  protocols
• Applications do not need sequencing
• UDP Fields
• Source port Number of the port that sends data
• Destination port Port number that receives data
  
• Length Number of bytes in header and data
• Checksum Calculated checksum of the header and
  data fields
• Data Upper-layer protocol data

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TCP and UDP Port Numbers

• Port numbers are used to keep track of different
  conversations
• Numbers below 1024 are well-known ports numbers
• Numbers above 1024 are dynamically-assigned ports
  numbers
• Registered port numbers for vendor-specific
  applications are gt 1024

Memorise these port numbers! (Journal)
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TCP/IP Application Layer

• Session, Presentation, Application layers of
  the OSI model make up the TCP/IP Application
  layer
• Therefore, representation, encoding, and dialog
  control are all dealt with by this layer

22
TCP/IP Application Layer

• Applications
• DNS
• FTP
• HTTP
• SMTP
• SNMP
• Telnet

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Domain Name System - DNS

• Its difficult to associate an IP address with a
  particular site, especially lots of them
• DNS is used for translating domain names and
  their network nodes into IP addresses
• A domain is a group of computers associated by
  geographical location or their business type

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Domain Name System - DNS

• .edu educational sites
• .com commercial sites
• .gov government sites
• .org non-profit sites
• .net network service
• .au Australia
• .nz New Zealand
• .biz business sites

25
FTP and TFTP

• FTP
• Connection-oriented
• Reliable
• FTP protocol
• Data transfer can occur in ASCII mode or in
  binary mode
• After the file transfer, the data connection
  terminates automatically.

• TFTP
• Connectionless
• Unreliable
• UDP protocol
• No authentication
• Faster than TCP

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HTTP

• HyperText Transfer Protocol
• Requires a web browser
• a client server application
• Multimedia format
• HTML (HyperText Markup Language)
• Determines the content and layout of web pages
• URL Uniform Resource Locator
• http//www.cisco.com/edu/

protocol
Folder location on the server
Hostname and IP address
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HTTP
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Simple Mail Transfer Protocol - SMTP

• Transports email messages in ASCII format using
  TCP
• Mail servers store mail until the client request
  it
• SMTP usually used to send mail
• POP3 and IMAP4 are mail client protocols used to
  receive mail
• SMTP has little security no authentication

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Simple Network Management Protocol (SNMP)

• Application Layer protocol used to remotely learn
  about other devices
• Uses UDP
• Allows administrators to
• Manage network performance
• Find and plan network problems
• Plan for network growth

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E-Mail Message Going From an E-Mail Server to an
E-Mail Client
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SNMP Three Main Components

• Network management system (NMS) NMS executes
  applications to monitor and control managed
  devices. One or more NMSs must exist on any
  managed network
• Managed devices Managed devices are nodes
  containing an SNMP agent. They collect and store
  management information and make it available to
  NMSs using SNMP. (routers, access servers,
  switches, bridges, hubs, computer hosts, or
  printers)
• Agents Agents are network-management software
  modules in managed devices. Agents translate
  management information into a form compatible
  with SNMP

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Telnet

• Telnet is a TCP/IP Application protocol
• OSI Application layer commands
• OSI Presentation layer formatting (ASCII)
• OSI Session layer transmission
• A telnet client can log into a remote host
  (telnet server) and execute commands
• A telnet client is called a local host
• A telnet is a remote host
• Runs software called a daemon

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Summary

• By now you should be able to
• - Describe how TCP relates to multiple host
  conversations
• - Describe how positive acknowledgement and
  retransmission (PAR) relates to TCP