MIS 430

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MIS 430

• Chapter 5 Network and Transport Layers

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I. Overview

• Layers are very close move messages from end to
  end in a network
• Transport Layer accepts outgoing messages from
  the application layer
• Packetizes them
• Addresses them
• Network layer takes messages from the transport
  layer and routes them through the network
• Data Link Layer produces error-free delivery

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Introduction

• See fig 5-1 p. 145 for 5 OSI layers
• Note path of packets
• Note additional headers added at each layer
  encapsulation
• Remember that each layer talks to its
  counterpart layer at the other end

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II. Transport and Network Protocols

• Many similar protocols here can do the same
  thing TCP/IP, IPX/SPX, X.25, etc.
• Multiprotocol stacks (software) will process each
  protocols packets
• must analyze the packet to determine the protocol

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TCP/IP Internet Standard

• TCP/IP originally developed for ARPANET DoD
  network
• Produce error-free transmissions
• Compatible with variety of data link protocols
• TCP/IP is worlds most popular
• TCPtransmission control protocol (TL)
• IPInternet protocol (NL)

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TCP Transport Control Protocol

• Performs packetizing
• Breaks message into packets
• Numbers them (for reassembly later)
• Assures packets are delivered reliably
• Puts packets in order at destination
• See figure 5-2 p. 147 for TCP packet 192-bit
  header

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IP Internet Protocol

• Network layer protocol
• Performs addressing and routing
• IP SW must be at every node
• IP packet in figure 5-3 p. 147 192-bit header
• IPv4 32 bits4.3B IP addresses
• IPv6 128 bits3.4x1038 addresses! Simpler header
  structure but requires ALL computers be revised
  (Microsoft has upgrade)

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IPX/SPX Novell

• ISU still uses IPX/SPX but newer Novell Netware
  now uses TCP/IP
• SPX TL protocol and like TCP
• IPX NL protocol and like IP

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X.25 Packet Switching

• WAN global ITU standard for packet switched
  networks of common carriers
• Seldom used in North America
• Maps to lowest 3 levels of OSI model
• DTE (data terminal equipment or end devices) vs.
  DCE (data communications equipment or
  communications devices)
• PAD packet assembler/disassembler
• X. means digital data carried on digital network
  in ITU-T notation

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System network architecture-SNA

• IBM standard intended for end to end IBM network
• Used only on IBM compatible mainframes
• Uses proprietary protocols important concept in
  open standards environment
• Experts predict SNA will be replaced by TCP/IP
  and this will decline

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III. Transport Layer Functions

• Each application layer program has a unique
  TCP/IP port number
• 16-bit (2 byte) number up to 65536
• FTP21, Telnet23, HTTP80, SMTP25
• Can choose non standard port numbers and give
  application program that port
• http//someplace.com4567/index.htm

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Packetizing

• Given maximum packet size, most messages are
  split into gt1 packet
• Web browsers build page a packet at a time,
  especially streaming and graphics
• Email clients wait until all packets have arrived
  and are reassembled

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Connection oriented routing

• Sets up TCP connection as a virtual circuit
  between sender and receiver
• Once established, packets flow in same order
  until connection is closed
• Reassembling message is simple here

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Connectionless routing

• Each packet is treated separately and could take
  different paths
• May arrive out of sequence
• TCP packet replaced by UDP packet
• User Datagram Protocol packet is much smaller
  that TCP packet
• Often used when entire message fits one packet
  (control messages)

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Quality of service (QoS) routing

• Special type of connection oriented routing
• Different connections are assigned different
  priorities
• Email is low priority, videoconferencing high
  priority to assure smooth images

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IV. Network Addresses

• Application Layer URL misnt.indstate.edu
• at Cgttype Ping misnt.indstate.edu to see if
  active
• Network Layer IP 139.102.31.12
• Data Link Layer MAC SMC network card
  00-E0-29-92-24-54 (12 hex digits)
• at Cgt type winipcfg (Windows 95, 98, ME)
• at Cgt type ipconfig (Windows NT, 2000, XP)
• Must have an approved address to attach a
  computer to the Internet
• Servers have fixed (static) addresses, clients
  usually not

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Internet Addresses

• Network Solutions is the agent that provides
  domain names (called domain registrar)
• http//www.networksolutions.com
• .com, .org, .net, .mil, .gov plus several new
  extensions (.biz, .info, .bz, and .tv) latter two
  were originally country codes
• Country extensions .us, .ca, .il, .jp, .de, .iq
  http//www.isi.edu/in-notes/iana/assignments/count
  ry-codes

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Subnets

• Subnet refers to logical group of computers,
  often same physical network
• ISU uses 139.102.x.y Class B addresses
• X is the subnet and y is the computer
• SB 403 and servers 139.102.31.y
• SB faculty and staff 139.102.67.y and
  139.102.69.y
• Subnet mask 255.255.255.0 vs 255.255.0.0 parts
  refer to clients on the same subnet
• Partial-byte subnets 255.255.255.240 allows for
  16 computers per subnet 11111111 11111111
  11111111 11110000

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Static vs. Dynamic Addresses

• Static IP address always same, coded into the
  Network TCP/IP properties
• DHCP and bootp give out dynamic addresses at
  client boot up time
• Can reuse dynamic IP addresses
• In TCP/IP Properties, Obtain an IP address
  automatically
• Cannot assign a dynamic address to a server!
• At ISU, even though we use bootp you always get
  the same IP address (ISU is replacing bootp with
  DHCP for roaming)
• Register http//ithelp.indstate.edu/forms/bootp.h
  tml

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IP Address Lease

• Client is given an IP address for a certain
  length of time
• After that time expires, the IP address lease
  expires and someone else can use that IP address
• At Cgt prompt, type ipconfig /all to see IP
  address lease information. (In Windows 9x, type
  winipcfg)

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Address Resolution

• Server name resolution DNS stands for Domain
  Name Service
• Any time your computer does not know the IP
  address of a server, it calls the DNS to get it
• DNS may have to go to root DNS to get IP
• 139.102.48.35, 139.102.7.102, 139.102.1.10 are
  ISU DNS
• Once learned, this address is stored inside your
  computer until you shut down. Hint you may need
  to do a DNS Flush if your computer is acting up.
  Ask about this in class!
• DNS name is associated with domain name
  www.indstate.edu139.102.15.15
• DNS servers replicate automatically

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V. Routing

• Process of determining path through network of a
  message
• Implement via a Routing Table (for computer B)
• How many paths from A to G? ABCG, ADEFCG, ADEBCG,
  ABEFCG,

C
B
A
G
D
F
E
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Routing - 2

• Router points in the general direction of
  destination
• Ex for all IP 126.x.x.x addresses, go here
• Ex for all Texas destinations go here, otherwise
  go there
• Router contains software and builds routing
  tables dynamically to accommodate congestion,
  cuts, etc.
• Cisco has best dynamic routing software

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Tracing Your Route(rs)
C\WINDOWS\Desktopgttracert www.kelley.indiana.edu
Tracing route to kelley.iu.edu
129.79.121.231 over a maximum of 30 hops 1
27 ms 26 ms 38 ms 139.102.180.1 (this
was from my home!) 2 26 ms 33 ms 28 ms
139.102.7.3 3 30 ms 2981 ms 29 ms
139.102.1.254 4 45 ms 2971 ms 54 ms
ind-ag-2-atm6-0-1-12m.ind.net
157.91.9.174 5 1982 ms 2965 ms 69 ms
ihets-gw-1-atm-ind-ag-2.ind.net
199.8.76.250 6 1970 ms 59 ms
iupui-atm6-0-100.ind.net 157.91.6.34 7 1818
ms 2976 ms 56 ms 156.56.249.13 8 156 ms
2952 ms 148 ms wcc6-gw.ucs.indiana.edu
129.79.8.6 9 1969 ms 182 ms 140 ms
kelley.iu.edu 129.79.121.231 Trace complete.
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Types of Routing

• Centralized routing all decisions made by
  central computer
• Static routing all decisions made are fixed. If
  break in network, messages are held until routes
  refigured. Good for small networks with few
  alternative paths.
• Dynamic adapts to network conditions in
  decentralized fashion. Default mode with many
  paths, but requires lots of calculations by
  routers including network coordination traffic
  between routers.

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Routing Protocols

• How routers exchange information to build,
  maintain routing tables
• Autonomous system network operated by one
  organization
• Routing protocols inside such systems are
  interior routing protocols
• Routing protocols between autonomous systems are
  exterior routing protocols

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Internet Routing Protocols

• ICMP-Internet Control Message Protocol
• RIP-Routing Information Protocol
• BGP-Border Gateway Protocol
• OSPF-Open Shortest Path First
• EIGRP-Enhanced Interior Gateway Routing Protocol
• For the test know ICMP and RIP ?

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Multicasting

• Unicast message sent from one client to another
  client
• Multicast message sent from one node to a group
  of computers at same time
• Ex Ghost for imaging hard drives rebuild all
  computers with same packets
• Ex hearing a broadcast on the Internet like a
  seminar or workshop

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VI. TCP/IP Example

• A computer needs four TCP/IP settings
• Its IP address
• Subnet mask
• IP address of DNS server
• IP address of gateway leading outside subnet
• Can get these values
• automatically or
• they can be static values typed into TCP/IP
  Properties in Network control panel

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Example Network fig 5-14

• Four subnets 98, 95, 50, 75
• DNS server 128.192.254.4
• 4 Gateways, each with at least two IP addresses
  (internal/external)
• Bldg A 128.192.98.1 129.192.254.3 (error)
• Router 128.192.254.7 next to Internet cloud

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Resolving Addresses

• Known Address, Same Subnet
• Search IP address table, find
• Hand to Data Link layer, send packet
• Known Address, Different Subnet
• Search IP address table, find
• Go through gateway to other subnet
• Unknown Addresses
• Search IP address table, not found
• Perform DNS request, return address to table
• May go through gateway or out via router

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Bruces Router

• My home network has a Belkin wireless router
  http//139.102.180.53 with a special TCP port
  number
• It has the following ports
• WAN (connects to DSL modem)
• 4 wired LAN ports inside firewall
• Wireless LAN ports inside firewall
• More in chapters 6-7 with LANs