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Networking Basics CCNA 1 Chapter 11

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Networking Basics CCNA 1 Chapter 11 The TCP/IP Transport Layer TCP/IP transport layer includes several protocols Transmission Control Protocol (TCP) User Datagram ... – PowerPoint PPT presentation

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Title: Networking Basics CCNA 1 Chapter 11


1
Networking Basics CCNA 1Chapter 11
2
The TCP/IP Transport Layer
  • TCP/IP transport layer includes several protocols
  • Transmission Control Protocol (TCP)
  • User Datagram Protocol (UDP)
  • TCP has more functions
  • UDP has less overhead
  • Main goal of the transport layer
  • Provide the service of taking data from one
    application process on one computer and
    delivering that data to the correct application
    process on another computer

3
The TCP/IP Transport Layer
  • Comparing transport and internet layers
  • Internet layer delivers packets from one computer
    to another, but is not concerned with which
    application sent the data or which application on
    the receiving computer needs the data
  • If multiple instances of an application are
    running on the destination computer, the
    transport layer works to ensure the proper
    instance gets the data and not the others

4
The TCP/IP Transport Layer
  • Comparing TCP and UDP

5
The TCP/IP Transport Layer
  • Flow Control and Windowing
  • When a host sends data using TCP, the receiving
    host can control how fast each TCP sender sends
    the data over time this is called flow control
  • Flow control is used for many reasons
  • Receiver needs time to process the data
  • Receiver has finite amount of memory, so if data
    keeps arriving, it could run out of memory

6
The TCP/IP Transport Layer
  • Flow Control Through Dynamic Sliding Windows
  • Receiver tells sender how many bytes the sending
    host can send before it receives an
    acknowledgement a value called a window
  • When the sending host has sent an entire windows
    worth of data, it must wait for an
    acknowledgement, slowing its rate of sending data
  • The window size can be increased to allow a
    faster transfer rate

7
The TCP/IP Transport Layer
  • Dynamic Windowing

8
The TCP/IP Transport Layer
  • Flow Control Through Withholding Acknowledgements
  • After a sending host has sent one window worth of
    bytes, it must wait to send more
  • The receiver can wait to send acknowledgements,
    which prevents the sender from sending more data
  • This process of withholding acknowledgements is
    sometimes known as start/stop flow control

9
The TCP/IP Transport Layer
  • Withholding Acknowledgements

10
The TCP/IP Transport Layer
  • Establishing and Terminating TCP Connections
  • TCP is a connection-oriented protocol
  • Allows it to set initial values to the window and
    to initialize sequence number values
  • TCP uses a process called a three-way handshake
    to create a new TCP connection
  • Uses three TCP segments that use two of the TCP
    flags in the TCP header
  • The synchronize (SYN) flag
  • The acknowledge (ACK) flag

11
The TCP/IP Transport Layer
  • Three-Way TCP Connection Establishment

12
The TCP/IP Transport Layer
  • TCP Error Recovery (Reliability)
  • TCP is a reliable protocol (at least in a
    networking perspective)
  • Performs error recovery
  • All data eventually gets to the destination, even
    if some is initially lost in transport

13
The TCP/IP Transport Layer
  • TCP Acknowledgements with no Error Recovery Needed

14
The TCP/IP Transport Layer
  • TCP Error Recovery (Reliability)
  • TCP uses two header fields to signal to other
    computer as to whether a segment was received
  • Sequence number
  • Keeps track of all the bytes sent over a TCP
    connection
  • Acknowledgement number
  • Lets the sending device know the number of the
    segment the receiving device expects next
  • Practice of stating the next byte expected to be
    received is called a forward acknowledgement or
    expectational acknowledgement

15
The TCP/IP Transport Layer
  • TCP Error Recovery

16
The TCP/IP Transport Layer
  • TCP Error Recovery (Reliability)
  • If a segment is lost or destroyed during
    transmission, the receiving PC requests that it
    be retransmitted
  • If an acknowledgement is not received by the
    sending PC within a certain time (a timer has
    been set), the sending PC resends the segment

17
The TCP/IP Transport Layer
  • Segmentation, Reassembly, and In-Order Delivery
  • TCP segmentation refers to the process of
    accepting a large chunk of data from the
    application protocol and breaking it into pieces
    that are small enough for transmission
  • The size of the segment is limited
  • Ethernet limits frames to 1500 data bytes in the
    data field of a frame
  • IP and TCP headers are each 20 bytes long
  • Maximum data portion is therefore 1460 bytes

18
The TCP/IP Transport Layer
  • Segmentation, Reassembly, and In-Order Delivery
  • TCP on the receiving computer reassembles data
    into its original form
  • The data is put in the correct order
  • If segments of a file are assembled out-of-order,
    the file is useless
  • TCP provides a guarantee of in-order delivery

19
The TCP/IP Transport Layer
  • Segmentation, Reassembly, and In-Order Delivery
  • Due to IP routing, a TCP receiver can receive
    data out of order
  • If multiple routes exist between a source and a
    destination, routers can load-balance over
    several routes
  • Packets can arrive out of order

20
The TCP/IP Transport Layer
  • TCP Providing In-Order Delivery

21
The TCP/IP Transport Layer
  • TCP and UDP Header Reference
  • TCP and UDP use a header to hold information for
    performing tasks
  • TCP needs ACK and SYN flags
  • First two fields in TCP and UDP are identical
  • Both use port numbers to identify application
    processes
  • TCP has a longer header (20 bytes vs. 8 bytes)

22
The TCP/IP Transport Layer
  • TCP and UDP Headers

23
The TCP/IP Transport Layer
  • TCP Header Fields

24
The TCP/IP Transport Layer
  • TCP Header Fields

25
The TCP/IP Transport Layer
  • UDP Header Fields

26
The TCP/IP Transport Layer
  • Identifying Application Processes Using Port
    Numbers
  • Both TCP and UDP identify the specific
    application process that sends the data and the
    application process that needs to receive the
    data
  • To make this determination, TCP and UDP use port
    numbers
  • Each application uses a different local port
    number

27
The TCP/IP Transport Layer
  • Using Port Numbers to Identify the Correct
    Application Process

28
The TCP/IP Transport Layer
  • Identifying Application Processes Using Port
    Numbers
  • In previous slide, the application was assigned a
    dynamic port number by the host computer
  • A host typically dynamically allocates port
    numbers of value 1024 (210) through 65,535 (216 -
    1)
  • When a host starts a new application process, it
    allocates a dynamic port number that is not
    already in use by another process
  • By each process having its own port number, a PC
    can have multiple conversations with other PCs
    (sometimes called multiplexing)

29
The TCP/IP Transport Layer
  • Identifying Application Processes Using Port
    Numbers
  • Connection to Servers Well-Known Ports
  • Most TCP/IP applications use a client/server
    model for communications
  • Servers cannot use dynamic port numbers because
    clients must know ahead of time what port numbers
    servers use
  • Servers must wait and listen on certain port
    numbers for client requests

30
The TCP/IP Transport Layer
  • Identifying Application Processes Using Port
    Numbers
  • Connection to Servers Well-Known Ports
    (continued)
  • For servers to work well, TCP/IP defines one or
    more well-known ports, each reserved for use by a
    specific application protocol
  • For example, HTTP connects to a server listening
    on port 80
  • A server might be a single, high-powered
    computer in this chapter it means TCP/IP
    software application, one that uses port numbers
  • Multiple software server applications could be
    running on one physical server

31
The TCP/IP Transport Layer
  • Client Connecting to Well-Known Port of a Web
    Server (80)

32
The TCP/IP Transport Layer
  • Popular Applications and Their Well-Known Port
    Numbers

33
The TCP/IP Transport Layer
  • Identifying Application Processes Using Port
    Numbers
  • Comparing Well-Known, Dynamic, and Registered
    Ports
  • IANA assigns the values for well-known ports and
    for registered port numbers
  • Registered ports are assigned to servers that the
    average end-user can start, such as
    instant-messaging applications
  • Well-known ports are started by IT staff for
    applications such as web servers, email, FTP
    servers

34
The TCP/IP Transport Layer
  • Uses of Port Numbers

35
The TCP/IP Transport Layer
  • Identifying Application Processes Using Port
    Numbers
  • Comparing Well-Known, Dynamic, and Registered
    Ports (continued)
  • Both TCP and UDP use port numbers
  • To see the port numbers used on a computers
    running a Microsoft OS, use the netstat an
    command

36
The TCP/IP Application Layer
  • The TCP/IP application layer performs the same
    functions as the top three layers of the OSI
    model
  • Defines format of data being transferred
  • Performs encryption
  • Sets protocol rules for transferring data
  • Sets up combinations of messages, called dialogs
    or sessions, that must be sent before a
    transaction can be considered complete
  • Do not confuse the application layer with the
    applications themselves!

37
The TCP/IP Application Layer
  • Distinction Between an E-Mail Application and
    E-Mail Application Layer Protocols

38
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • Domain Name System (DNS) resolves names into IP
    addresses
  • Hypertext Transfer Protocol (HTTP) transfers
    files from web servers to web browsers
  • Simple Mail Transfer Protocol (SMTP) and Post
    Office Protocol version 3 (POP3) send and
    receive e-mail, respectively
  • File Transfer Protocol (FTP) stores and
    retrieves files

39
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • Name Resolution Using DNS
  • Easier to remember names than IP addresses
  • A name like www.cisco.com is generically called a
    hostname
  • The cisco.com part is the domain name
  • The last part (.com) is a top-level domain

40
The TCP/IP Application Layer
  • DNS Resolution After Inserting a URL into a Web
    Browser

41
The TCP/IP Application Layer
  • Common High-Level DNS Domains

42
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • World Wide Web and HTTP
  • Web server software stores information that the
    web server wants to make available to web
    browsers such as Internet Explorer and Firefox
  • Web servers use HTTP to transfer the files that
    make up a web page

43
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • World Wide Web and HTTP (continued)
  • HTTP transfer process
  • The browser asks the web server to send one file
    that contains instructions and displayable
    content
  • The browser displays the files contents
  • The browser looks for instructions inside the
    first file, which might tell it to get more files
  • The browser asks the web server for additional
    files
  • The browser displays the additional content,
    which might include instructions to download
    additional files
  • The process continues until all files are
    downloaded and displayed
  • HTTP uses a GET request to ask for a file

44
The TCP/IP Application Layer
  • HTTP Transfers Three Files

45
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • World Wide Web and HTTP (continued)
  • The term HTTP is from the first type of file
    supported by a web browser
  • Hyper Text Markup Language (HTML)
  • Web browsers needed to download files of this
    type, so HTTP was created as a protocol to handle
    HTML files
  • Universal Resource Locators (URLs), commonly
    referred to as web addresses, identify web pages
    that need to be displayed, or a hyperlink can be
    clicked on

46
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • E-Mail Protocols SMTP and POP3
  • A PC sends mail to its SMTP server using its
    e-mail client software
  • The SMTP server forwards the e-mail to the
    destination SMTP server
  • The destination PC retrieves the e-mail with the
    POP3 protocol used by its e-mail client

47
The TCP/IP Application Layer
  • Process of Sending an E-Mail

48
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • E-Mail Protocols SMTP and POP3 (continued)
  • In some cases, the physical server sending the
    e-mail is a different server than the one used
    for checking e-mail
  • POP3 is the most common protocol for an incoming
    e-mail server, but IMAP4 is sometimes used
  • Most SMTP servers are configured to only accept
    e-mail from inside the same internetwork, due to
    security reasons

49
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • E-Mail Protocols File Transfer Protocol
  • File Transfer Protocol (FTP) supports file
    transfers
  • FTP clients store files on FTP servers and can
    retrieve files from them

50
The TCP/IP Application Layer
  • Application Protocols Used by End Users
  • E-Mail Protocols File Transfer Protocol
    (continued)
  • FTP uses two separate TCP connections
  • Control connection uses well-known port 21 on the
    FTP server and sends control information such as
    data transfer mode
  • Connection on well-known port 20 is used for
    actual data transfer

51
The TCP/IP Application Layer
  • Application Protocols Often Used for Network
    Management
  • Three primary network management protocols
  • Trivial File Transfer Protocol (TFTP) works
    similar to FTP, but with some benefits when used
    on networking devices
  • Simple Network Management Protocol (SNMP) Allows
    management software (the client) to query
    networking devices (the server) to manage and
    control the networking devices
  • Telnet allows a client to emulate a terminal
    allows a user to sit at one computer (the Telnet
    client) and to use a remote computer (the Telnet
    server) through a text-based interface

52
The TCP/IP Application Layer
  • Three primary network management protocols
    (continued)
  • TFTP
  • Performs some of the same functions as FTP
  • TFTP has some advantages server software is
    small, allows routers and switches to transfer
    files without consuming too much permanent
    storage space
  • Most network engineers use a TFTP client package
    and a TFTP server package on their PCs

53
The TCP/IP Application Layer
  • Three primary network management protocols
    (continued)
  • SNMP
  • Allows a network engineer to monitor an
    internetworks status
  • The Network Management System (NMS) software can
    perform this function
  • Uses SNMP GET requests
  • The managed device (router, switch) must run an
    SNMP agent to be able to reply to the GET requests

54
The TCP/IP Application Layer
  • NMS Using SNMP GETs to Retrieve Information from
    SNMP Agents

55
The TCP/IP Application Layer
  • Three primary network management protocols
    (continued)
  • Telnet
  • Allows a user to sit at one computer and access
    another IP host by using Telnet client software
    (the other host must run Telnet server software)
  • After connecting, the user at the Telnet client
    (called the local host) can issue commands that
    are executed on the other IP host (called the
    remote host)
  • Telnet is the primary tool for remotely accessing
    routers and switches
  • Cisco routers and switches come with built-in
    Telnet servers

56
The TCP/IP Application Layer
  • Telnet Client Accessing a Router

57
The TCP/IP Application Layer
  • Application Protocol Summary
  • Many other application protocols exist, but the
    ones mentioned in this chapter are the mainstream
  • The protocols all share a common feature
  • They use a TCP transport layer protocol (either
    TCP or UDP
  • TCP HTTP, SMTP, POP3, FTP, and Telnet
  • UDP DNS, TFTP, SNMP
  • UDP does not do error recovery implements error
    recovery at the application layer
  • DNS and SNMP use a timeout mechanism that allows
    them to resend a request or allows the user to
    repeat the action

58
Summary
  • Primary duty of the transport layer (OSI Layer
    4), is to take data from the application process
    on one computer and deliver the data to the
    correct application process on another computer
  • Both TCP and UDP identify data from upper-layer
    applications based on port number
  • UDP provides only basic delivery of data and
    identification of applications by port number
  • TCP provides additional functions, including
    error recovery (reliability), flow control,
    segmentation and re-assembly, and in-order data
    delivery
  • TCP uses connection-oriented logic, connecting
    dynamically with a three-way handshake

59
Summary
  • TCP numbers the first byte of each segment with a
    sequence number
  • TCP acknowledges the receipt of data by using an
    acknowledgement number
  • This process allows a receiving host to tell the
    sender to resend data
  • The sequence numbers allow the receiving host to
    put data in the correct order before giving it to
    the application

60
Summary
  • Flow control ensures a transmitting node does not
    overwhelm a receiving node
  • The simplest method of flow control is when a
    receiving host sends a not ready signal by
    withholding acknowledgements
  • TCP also uses dynamic windowing, which is a more
    efficient process
  • Dynamic windowing allows the receiving host to
    vary the amount of data a sender can send before
    it has to receive an acknowledgement

61
Summary
  • Positive acknowledgement with retransmission
    refers to the process of explicitly acknowledging
    received data, with the sender resending any
    unacknowledged segments
  • Connection-oriented TCP provides a wide range of
    functions, but UDP has some advantages
  • UDP has less overhead (an 8-byte header versus a
    20-byte header for TCP)
  • UDP does not slow down because of flow control

62
Summary
  • Popular application layer protocols
  • DNS Used in IP networks to translate names of
    network nodes into IP addresses
  • FTP Transfers files between networks
  • HTTP Delivers HTML documents to a client
    application, such as a web browser
  • SMTP Provides e-mail services
  • SNMP Monitors and controls network devices and
    manages configurations, statistics collection,
    performance and security
  • Telnet Used to log in to a remote host that runs
    a Telnet server application and then to execute
    commands from the command line
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