Pertemuan 23 Layer Transport

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Pertemuan 23Layer Transport
Matakuliah H0174/Jaringan Komputer Tahun
2006 Versi 1/0
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Learning Outcomes

• Pada akhir pertemuan ini, diharapkan mahasiswa
• akan mampu
• Menjelaskan fungsi Transport Layer

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Outline Materi

• TCP
• UDP

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Transport layer duties
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Addressing

• TCP uses the concept of source and destination
  port numbers which uniquely identify a particular
  communicating process on a host.
• Port numbers
• Well known port numbers (defined by IANA)
• Server applications run by privileged users to
  communicate on these ports (0 1023)
• Registered ports (1024 - 49151)
• Administratively assigned to some specific
  applications.
• Private ports/Ephemereal (49152 - 65535)
• application associated with them. Used by
  applications that are ephemeral in nature

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Well-Known Port Addresses

• Port 80 HTTP (web server)
• Port 25 SMTP (mail server)
• Port 23 Telnet
• Port 22 SSH
• Port 110 POP3

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IP Addresses vs Port Numbers
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Application Addressing

• Target user specified by User identification
  called socket in TCP/IP
• Consist of usually IP address (host), port
• Port represents a particular transport service
  (TS) user
• Transport entity identification
• Generally only one per host
• If more than one, then usually one of each type
• Specify transport protocol (TCP, UDP)
• Host address
• An attached network device
• In an internet, a global internet address

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Socket address
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Multiplexing

• Multiple users employ same transport protocol
• User identified by port number or service access
  point (SAP)
• May also multiplex with respect to network
  services used

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Transport Layer Protocol

• Transmission Control Protocol
• Connection oriented
• RFC 793
• User Datagram Protocol (UDP)
• Connectionless
• RFC 768

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Types of data deliveries
The transport layer is responsible for
process-to-process delivery
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TCP segment format
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TCP Services

• Reliable communication between pairs of processes
• Across variety of reliable and unreliable
  networks and internets
• Two labeling facilities
• Data stream push
• TCP user can require transmission of all data up
  to push flag
• Receiver will deliver in same manner
• Avoids waiting for full buffers
• Urgent data signal
• Indicates urgent data is upcoming in stream
• User decides how to handle it

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TCP Mechanisms

• Connection establishment
• Three way handshake
• Between pairs of ports
• One port can connect to multiple destinations

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Connection Establishment
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TCP Mechanisms

• The bytes of data being transferred in each
  connection are numbered by TCP. The numbering
  starts with a randomly generated number
• The value of the sequence number field in a
  segment defines the number of the first data byte
  contained in that segment
• The value of the acknowledgment field in a
  segment defines the number of the next byte a
  party expects to receive
• The acknowledgment number is cumulative.
• Data transfer
• Logical stream of octets, Octets numbered modulo
  223
• Flow control by credit allocation of number of
  octets
• Data buffered at transmitter and receiver

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UDP

• UDP is a connectionless, unreliable protocol that
  has no flow and error control
• It uses port numbers to multiplex data from the
  application layer (e.g. network management)
• Delivery and duplication control not guaranteed
• Reduced overhead
• UDP is a convenient transport-layer protocol for
  applications that provide flow and error control.
  It is also used by multimedia applications

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User datagram format
The calculation of checksum and its inclusion in
the user datagram are optional
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Pertemuan 24Layer Application
Matakuliah H0174/Jaringan Komputer Tahun
2006 Versi 1/0
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Learning Outcomes

• Pada akhir pertemuan ini, diharapkan mahasiswa
• akan mampu
• Menjelaskan peran Application Layer

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Outline Materi

• SMTP
• HTTP

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Electronic Mail

• Most heavily used application on any network
• Simple Mail Transfer Protocol (SMTP)
• TCP/IP
• Delivery of simple text messages
• Multi-purpose Internet Mail Extension (MIME)
• Delivery of other types of data
• Voice, images, video clips

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SMTP

• RFC 821
• Not concerned with format of messages or data
• Covered in RFC 822 (see later)
• SMTP uses info written on envelope of mail
• Message header
• Does not look at contents
• Message body
• Except
• Standardize message character set to 7 bit ASCII
• Add log info to start of message
• Shows path taken

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Basic Operation

• Mail created by user agent program (mail client)
• Message consists of
• Header containing recipients address and other
  info
• Body containing user data
• Messages queued and sent as input to SMTP sender
  program
• Typically a server process (daemon on UNIX)

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SMTP Sender

• Takes message from queue
• Transmits to proper destination host
• Via SMTP transaction
• Over one or more TCP connections to port 25
• Host may have multiple senders active
• Host should be able to create receivers on demand
• When delivery complete, sender deletes
  destination from list for that message
• When all destinations processed, message is
  deleted

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SMTP Receiver

• Accepts arriving message
• Places in user mailbox or copies to outgoing
  queue for forwarding
• Receiver must
• Verify local mail destinations
• Deal with errors
• Transmission
• Lack of disk space
• Sender responsible for message until receiver
  confirm complete transfer
• Indicates mail has arrived at host, not user

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SMTP Mail Flow
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Text Messages RFC 882

• Message viewed as having envelope and contents
• Envelope contains information required to
  transmit and deliver message
• Message is sequence of lines of text
• Uses general memo framework
• Header usually keyword followed by colon followed
  by arguments

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MIME

• Multipurpose Internet Mail Extension (MIME)
  Extension to RFC822
• SMTP can not transmit executables
• Can not transmit text including international
  characters (e.g. â, å, ä, è, é, ê, ë)
• Need 8 bit ASCII
• Servers may reject mail over certain size
• Translation between ASCII and EBCDIC not standard
• SMTP gateways to X.400 can not handle none text
  data in X.400 messages
• Some SMTP implementations do not adhere to
  standard
• CRLF, truncate or wrap long lines, removal of
  white space, etc.

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Overview of MIME

• Five new message header fields
• MIME version
• Content type
• Content transfer encoding
• Content Id
• Content Description
• Number of content formats defines
• Transfer encoding defined

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HTTP

• Hypertext Transfer Protocol
• Underlying protocol of the World Wide Web
• Not a protocol for transferring hypertext
• For transmitting information with efficiency
  necessary for hypertext jumps
• Can transfer plain text, hypertext, audio,
  images, and Internet accessible information

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HTTP Overview

• Transaction oriented client/server protocol
• Usually between Web browser (clinet) and Web
  server
• Uses TCP connections
• Stateless
• Each transaction treated independently
• Each new TCP connection for each transaction
• Terminate connection when transaction complete

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Headers
HTTP uses the services of TCP on well-known port
80
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Retrieve Image
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Distributed services
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Browser architecture
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Categories of Web documents
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Static document
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Dynamic document
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Active document