Network Fundamentals

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Chapter 11

• Network Fundamentals

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Network Classifications

• Topology
• Star, hierarchical, mesh, bus, ring, hybrid
• Ownership
• Private, public
• Purpose or transmission type
• E-mail, value-added networks, packed data
  networks
• Geography
• WAN, MAN, LAN

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Topology - Star

• Circuits radiate from central node
• Advantages
• Easy to control and expand network
• Disadvantages
• Central node is single point of failure
• Central node can get overloaded
• Examples
• PBX, Computer cluster, some Ethernets
• Question to consider
• How do you control/manage the network?

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Star Network
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Topology - Hierarchical (Tree)

• Top node is root, or head-end
• Advantage
• No single point of failure
• Lower levels can communicate even if host is lost
• Example
• Cable TV network

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Hierarchical Network
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Topology - Mesh

• Nodes highly interconnected
• Fully-connected mesh - each node connects to all
  others
• Advantage
• Redundant connections
• Disadvantage
• Lots of interconnects
• Example
• Public telephone network

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Mesh Network
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Topology - Bus

• Nodes tap into a bus cable
• All stations independent
• Advantage
• No single point of failure
• Typically run at high speed
• Disadvantage
• Limited distance and number of attached devices
• Faults hard to find
• Example
• Old Ethernet was logical and physical bus
• New Ethernet is logical bus, physical star

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Bus Network
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Topology - Ring

• Devices tap into closed ring
• Signals move around ring from source to
  destination
• Each node reads message address and either copies
  message or passes it on
• Advantage
• Each node checks for errors
• Disadvantage
• Single point of failure in unidirectional ring
• Bi-directional ring more robust

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Unidirectional Ring Network
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Bi-directional Ring
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Topology - Hybrid Networks

• Larger networks tend to be hybrids, or
  combinations of topologies

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Hybrid Network
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Classification by Geography

• WAN - wide area network
• Large geographical area
• Typically star topology, but also mesh or tree
• MAN - metropolitan area network
• City-wide network
• Standardized by 802.6
• High bandwidth
• LAN - local area network
• Most common type
• Small area

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Classification by Transmission Technology -
Circuit Switched

• When two sites are connected, a dedicated line
  exists between them
• Line may be temporary
• Developed for public telephone network
• Can handle data
• Not efficient - Why?

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Circuit-Switched Network
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Classification by Transmission Technology -
Packet Switched

• Also called packet data network (PDN)
• Example ARPANET, Internet
• Messages in digital form, broken up into
  fixed-length pieces (packets)
• Packets contain (among other things)
• Source and destination address
• Location code to tell where it is in message
• Packets can travel different routes
• Reassembled at destination

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Classification by Transmission Technology -
Packet Switched

• PDN connection types
• Switched virtual circuit
• Source and destination establish fixed route that
  exists for the duration of session
• Permanent virtual circuit
• Virtual circuit is long-term
• Example leased circuit
• Datagram
• Message packets are sent along most efficient
  routes at that time
• Packets can arrive out of order
• Example X.25 is a ITU-T standard for PDN

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Packet-Switched Network
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Classification by Transmission Technology - Frame
Relay

• Designed to reduce overhead in X.25 networks
• Also, PDNs use ACK after each packet before
  sending next
• Message divided into variable-length frames
  (layer 2)
• Reassembled at destination
• Circuit congestion drops throughput considerably
• Customer guaranteed a CIR (Committed Information
  Rate)
• Speed may be greater than CIR (port speed)
• Compare to EIR (Excess Information Rate)
• Network discards frames during congestion
• Reduces throughput until CIR reached

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Asynchronous Transfer Mode

• Evolution of frame relay
• Reverts back to using packets called cells
• 53 octets long, fixed length
• More efficient to assemble and disassemble
• WANs use it in T-3 (44.7 Mbps) or higher speed
  circuits
• LANs use ATM in fiber-optic backbones
• LAN Emulation (LANE)
• OC-1 (51.84 Mbps) is minimum speed
• Most services minimize delays in transmission
• Good for synchronized audio and video
• Realtime Services
• Constant Bit Rate (CBR)
• Realtime Variable Bit Rate (rt-VBR)
• Non-Realtime Services
• Non-Realtime Variable Bit Rate (nrt-VBR)
• Available Bit Rate (ABR)
• Unspecified Bit Rate (UBR) (delays and cell loss
  possible)

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Interconnecting Networks

• Networks have different characteristics
• Users want transparency
• Do not want to worry about how messages are
  transmitted
• LANs, MANs, WANs connected with an internet
• Terminology
• End system - computer or other device
• Subnetwork - networks of end systems, part of an
  internet
• Intermediate system - interface subnets to main
  communication links
• Example bridges and routers

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TCP/IP

• Transmission Control Protocol / Internet Protocol
• Developed as part of ARPANET
• Now it is the protocol used for Internet traffic
• Provides packet data transfer between
  incompatible computer operating systems

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Comparing OSI Model and TCP/IP
OSI
TCP/IP
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Some TCP/IP Protocols

• W. Stallings, Data and Computer Communications, 6
  ed., Upper Saddle River, NJ, Prentice Hall, 2000

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Some TCP/IP Process Layer Protocols

• Telnet
• Virtual terminal utility enabling access to
  remote hosts
• FTP - File Transfer Protocol
• File transfer utility
• SMTP - Simple Mail Transfer Protocol
• Main protocol responsible for transmission and
  distribution of e-mail
• SNMP - Simple Network Management Protocol
• Main protocol responsible for transmission of
  vital network and system statistics and commands
• HTTP - Hypertext Transfer Protocol
• Main protocol responsible for transmission of
  information throughout the World Wide Web
• TFTP Trivial File Transfer Protocol
• Uses UDP
• Inherently unsecure

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Some TCP/IP Host-to-Host Layer Protocols

• TCP
• Connection oriented
• Reliable
• Connection established between both ends before
  data transfer begins
• Creates a virtual circuit between end-user
  applications
• Responsible for
• Breaking messages into segments (segmentation)
• Reassembling messages at destination (reassembly)
• Handles retransmitting dropped packets

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Some TCP/IP Host-to-Host Layer Protocols

• UDP - User Datagram Protocol
• Connectionless protocol
• No acknowledgements
• Unreliable
• No checking for segment delivery and sequencing
• Depends on higher layers for reliability

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Some TCP/IP Internet Layer Protocols

• IP - Internet Protocol
• Main protocol of the entire TCP/IP protocol suite
  responsible primarily for addressing and routing
  of packets
• Connectionless, best-effort delivery

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Some TCP/IP Internet Layer Protocols

• RIP - Routing Information Protocol
• Interior routing protocol used to disseminate
  routing information within an autonomous system
• Autonomous system
• Group of routers exchanging information via a
  common routing protocol
• Group of routers and networks managed by a single
  organization
• Always a connection between any two nodes (except
  during failure)
• Distance-vector protocol
• Hop count determines shortest path
• Often used in LANs

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IP Header
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Some IP Header Fields

• Minimum IP header size is 20 octets
• More if options are used
• Version
• Presently Version 6 (replaced Version 4)
• TTL (Time To Live)
• Time in seconds that a packet can remain valid
• Internet nodes must decrease by 1 second
• When TTL reaches zero, packet is discarded
• Device discarding sends packet back ICMP message
  saying packet was dropped
• Since internet nodes process packets in less than
  1 second, TTL is essentially the maximum hop
  count
• Used by TRACEROUTE utility

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Some IP Header Fields

• Transport protocol
• Number identifying the TCP protocol in the
  payload
• Source IP address
• 32-bit source IP address
• Destination IP address
• 32-bit destination address
• Data
• Host-to-Host (TCP) layer protocol data follows IP
  header

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TCP Header
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TCP Header Fields

• Minimum TCP header size is 20 bytes
• More if options are used
• Source port
• Number of calling port
• Initiator of request is client process
• Generally not significant
• Destination port
• Number of called port
• Grantor of request is the server process
• Identifies one of the destination processes such
  as HTTP
• Data
• Process (Application) layer protocol data follows
  TCP header

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Popular Port Numbers
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TCP/IP Transmit Receiver Process

• Transmission process
• Host-to-Host (TCP) layer receives data from
  Process (Application) layer and adds TCP header
• Sends this segment to Internet (IP) layer
• Internet layer receives segment from TCP layer
  and adds IP header
• Sends this packet to Network Access (Data Link
  Physical) layer
• Network Access layer receives packet from
  Internet layer and adds its own header and
  trailer
• Sends this frame out over network
• Receive process
• Process reverses
• Each layer strips off its header and / or trailer
  as information moves up the protocol stack

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End-to-End Delivery
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Message Routing

• Connection-oriented
• Network switches or routers set up data path
  before transmission
• Virtual circuit
• Packets arrive in order
• Connectionless
• Datagram
• Packets can take different paths to destination
• Destination host must put packets in order
• Intermediate routers decide on paths
• Routers communicate with each other to determine
  best path for packet to travel

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Intranets

• Intranet - internal company network
• Used for sharing information
• Usually access the Internet through firewalls
• Restricts access of company network from Internet
  side

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Internet
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Software for Network Management

• Functions
• Monitor network status and display status
  conditions
• Log pertinent network operational data for
  storage
• Example statistics, errors, and alarms
• Provide operator with control functions to
  optimize network performance

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Protocol Analyzers

• Protocol analyzers are used to analyze traffic on
  networks (WAN and LAN)
• Interpret the protocol fields
• Workstation-based analyzers are software packages
  that use the workstations NIC to capture frames
  on the network
• Ethernet card programmed to respond to all MAC
  addresses, not just its own (and broadcasts)
• Strips off MAC framing and passes IP information
  up to Internet (Network) layer
• Called promiscuous mode