IS 3413

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IS 3413

• Chapter 8
• The Internet and TCP/IP
• Dr. Jan Clark
• SPRING, 2003

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Internet Society
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Basic Assumptions of ARPANET

• Physical network NOT completely reliable
• Network protocols could not be dependent on any
  proprietary hardware or software

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OSI vs. TCP/IP
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NOTE!

• TCP/IP was NOT designed specifically with the
  layers in mind and DOES NOT fit neatly with the
  OSI model.
• For EXAMPLE, TCP is considered to lap over both
  transport and network layers

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TCP/IP Transport Layer

• Responsible for assuring end-to-end delivery of
  data
• Primary Protocols
• TCP - Transmission Control Protocol
• UDP - User Datagram Protocol

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Internet Addressing Requirements

• MAC sublayer address (hardware address)
• Network address (IP address)
• Port address (identifies specific application or
  process - telnet 23, SMTP 25, HTTP 80, etc)

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Assigning Addresses

• Data link layer (MAC sublayer) address -
  uniquely, permanently encoded on the NIC
• Network layer (IP) addresses and application
  layer addresses go hand in hand. (www.uga.edu
  -application means 192.128.98.53 at the network
  layer)
• Network layer software translates the application
  layer address into an address better understood
  by the network layer (IP address)
• Computers must agree on port numbers before they
  can interoperate

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Port Numbers

• Many are pre-assigned - (Table 8.1)
• If not pre-assigned, sender must know port number
  of destination host for the required application
  (e.g. email, FTP, etc.)
• Both source and destination port numbers must be
  defined
• The Protocol (TCP vs. UDP) used for transmission
  is dependent upon the application.

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Network Layer Address

• Internet Protocol (IP) Address
• 4 bytes long (if IPv4), separated by .
• Example 128.192.78.4

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Data Encapsualtion/Decapsulation
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• Complex data communication systems do not use a
  single protocol to handle all transmission tasks.
  Instead, they rely upon a protocol suite, such
  as TCP/IP

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Internet Protocol (IP) Functions (network layer)

• Performs routing and addressing
• Connectionless datagram service
• Unreliable datagram service (packets may not be
  delivered)
• may arrive out of sequence
• Responsible for routing packets between nodes
• Active at all nodes
• Considered the "glue" that links heterogeneous
  networks, giving the illusion of a homogeneous
  one
• May fragment packet if too large for next network

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Internet Control Message Protocol (ICMP)

• Network layer protocol allows routers to send
  error and control messages about packet
  processing on IP networks
• Reports errors when a packet cannot reach its
  destination (I.e. network or destination
  unreachable
• Reports congestion I.e. buffer full
• Relays troubleshooting information I.e. ping to
  check to see if alive
• Reports time-outs I.e. when packets
  time-to-live counter reaches zero

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UDP - User Datagram Protocol Functions (transport
layer)

• Connectionless datagram service
• Unreliable datagram service
• All data reliability and integrity issues
  responsibility of application programs using UDP
• Application programs -TFTP, SNMP, DNS

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What is the Difference Between UDP and IP?

• Both are unreliable (packets may not arrive) and
  connectionless
• Both originally designed for smaller messages
• UDP relies upon IP to transport messages between
  networks - UPD header encapsulated in IP datagram
  as it travels across an internetwork

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TCP Functions

• Connection-oriented (virtual circuit) Designed
  for large applications (e.g. FTP)
• Reliable service for end-to-end connection
• Active ONLY at sending and receiving nodes
• Requests for retransmission at destination node
• Assures against duplication
• Stream-oriented flow control, based on virtual
  circuit connection
• Relies upon IP for packet delivery (same as UDP)
• Sliding window ACK
• Full duplex - concurrent transfers can take place
  in both directions

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TCP Packet
1
2
3
4
5
6
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User Data
1 Source ID 16 bits 2 Destination ID 16
bits 3 Sequence number 32 bits 4 ACK number 32
bits 5 Header length 4 bits 6 Unused 6
bits 7 Flags 6 bits 8 Flow control 16
bits 9 CRC 16 16 bits 10 Urgent pointer 16
bits 11 Options 16 bits
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TCP Three-Way Handshake

• Method of establishing a TCP connection
• A initiates TCP connection to B by sending sync
  bit and initial sequence number
• B sends back syn and ACK
• A sends ACK
• Example Netscape

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TCP Three-Way HandshakeEstablish Connection
Node A
Node B
Send SYN (SeqNumX)
Receive SYN X Send SYN (SeqNumY) ACK
(NumX1)
Receive SYN, ACK Send ACK (NumY1)
Receive ACK
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TCP Close Connection
Node A
Node B
Send FIN (SeqNumX)
Receive FIN X Send ACK (SeqNumX1) Inform
Node B application Application responds

Receive ACK
Receive Fin Send ACK (NumY1)
Receive ACK
Send FIN (SeqNumY)
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IPv4 VS IPv6

• IPv4 also has a 192-bit header
• Control information including source and
  destination address, packet sequence number,
  packet length, error checking information, etc.
• IPv6 has a 320-bit header
• Primary difference is increase in address from 32
  bits to 128 bits why is this good?

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Internet Address Problems

• Internet is quickly running out of addresses
• Although there are more than 1 billion possible
  addresses, they are assigned in groups,
  restricting the number of organizations
• One of the reasons behind the IPv6, providing 3.2
  x 1038 possible addresses

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ICANN

• Internet Corporation for assigning names and
  numbers
• Assigns network layer (IP addresses) and
  application layer addresses or domain names
  (www.utsa.edu).
• Classes A-C are assigned to organizations
• Sets rules by which new domain names are created
  and IP addresses are assigned to users
• Authorizes private companies to become domain
  name registrars (www.register.com)

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Domain Names
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Domain Name Servers
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Internet Address Classes

• Number of Addresses
• Class Available to User Address
  Structure Example
• Class A 16 million First byte fixed
  50.x.x.x
• Organization assigns last three bytes
• Class B 16,000 First two bytes fixed
  128.192.x.x
• Organization assigns last two bytes
• Class C 250 First three bytes fixed
  192.1.56.x
• Organization assigns last byte

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Subnets

• IP addresses are usually assigned so that all
  computers on the same local area network have a
  similar address
• Each LAN that is logically grouped together by IP
  number is called a TCP/IP subnet
• Customary to use the last byte of the IP address
  to indicate different subnets

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