Enterprise and Wide Area Networks

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Enterprise and Wide Area Networks

• ITEC 370
• George Vaughan
• Franklin University

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Sources for Slides

• Material in these slides comes primarily from
  course text, Guide to Networking
  Essentials,Tomsho, Tittel, Johnson (2007).
• Other sources are cited in line and listed in
  reference section.

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TCP/IP and OSI Models
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Creating Larger Networks Tomsho, Tittel, Johnson
(2007)

• Ways to stretch or expand network capabilities
• Physically expanding to support additional
  computers
• Segmenting the network into smaller pieces to
  filter and manage network traffic
• Collision Domains
• Broadcast Domains
• Extending the network to connect separate LANs
• Connecting two or more disjointed networking
  environments
• Many devices can accomplish these tasks
• Repeaters, bridges, switches, routers, and
  gateways

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Repeaters and Hubs

• Accepts a signal, and regenerates it.
• Common Collision Domain
• Common Broadcast Domain
• Operates at OSI layer 1.
• Operates at bit level
• no frame knowledge.
• Does not use Protocol Data Units (PDU).
• Half-Duplex communication.
• Can connect different media (i.e. Fiber to TP).
• A Hub is a multi-port Repeater.
• Only one device can transmit at a time
• Collisions can occur between any connected device.

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Repeaters Tomsho, Tittel, Johnson (2007)
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Bridges

• Segments (divides) a network in two.
• 2 separate Collision Domains
• Common Broadcast Domain
• Can filter frames
• Operates at Layer 2 (PDU Frame).
• Full-Duplex communication.
• Operates in software
• If destination is in same segment as sender,
  bridge drops frame.
• Transparent (learning) bridges
• Knows nothing upon boot.
• Builds bridging table based on port, source MAC
  and destination MAC.
• Learns which MACs (based on ports) are on which
  segment.
• Slower than repeaters, hubs.
• Broadcast frames sent to all other ports.
• Can connect different types of networks (ring,
  Ethernet).

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Switches

• Switch high-speed, multi-port bridge.
• A switch with n ports has
• n separate Collision Domains
• Common Broadcast Domain
• Can filter frames.
• Operates at Layer 2 (PDU Frame).
• Full-Duplex communication.
• Operates in hardware (faster than bridges).
• Each port provides a separate collision domain.
• Full bandwidth available to communicating ports.
• Broadcast frames are forwarded.

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Switching Methods

• Cut-Through
• Fastest transmission
• All errors forwarded
• Reads just enough of frame to determine source
  and destination.
• Fragment Free
• Medium transmission
• All errors, except frame fragments, are
  forwarded.
• Read just enough of frame to guarantee frame is
  at least minimum size.
• Store-and-Forward
• Slowest transmission
• No error frames forwarded
• Entire frame is read and Frame Check Sequence
  (FSC) is checked.

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VLANs

• Switches can support Virtual LANs (VLANs)
• Multiple logical LANs on one switch
• n separate Collision Domains
• n Broadcast Domains
• However, devices in one segment cannot talk to
  devices in another segment without adding a
  router.
• Allows administrator to group logically devices
  instead of just by physical location.
• Each VLAN is assigned a unique network number.
• Router needed for VLANs to inter-communicate.

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Switches Tomsho, Tittel, Johnson (2007)
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Routers

• Operates at Layer 3 (PDU Packets).
• n separate Collision Domains
• n Broadcast Domains
• Used to create inter-network from different
  networks.
• Broadcast frames are NOT forwarded.
• Can be used to form multi-path networks (i.e.
  more than one path between source and
  destination).
• Each network segment is assigned a network
  address.

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Collision and Broadcast DomainsTomsho, Tittel,
Johnson (2007)
Broadcast Domain
Broadcast Domain
Collision Domains
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Routers and Multi-path Networks

• Routers determine path for each packet based on
• Network address of destination
• Routing tables
• Routers can send information from one network
  type to another.
• Discards any broadcast packet or packet not
  understood.

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Routers Tomsho, Tittel, Johnson (2007)
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Routing Tables

• Routing tables keep track of network addresses
  (IP Addresses)
• Not hardware addresses (MAC addresses).
• Distance to destination network (measured in
  Hops).
• A hop indicates a router.
• Example If hops 2, then packet must go through
  2 more routers before reaching destination
  network.
• Router may choose different paths to same
  destination for load balancing.

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Populating Routing Tables

• Static Routing
• Routing tables manually populated.
• Router always uses same path to destination.
• Dynamic Routing
• Uses discovery process to populate table.
• Shares routing table with other routers.

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Router Best Path Algorithms

• Distance-Vector Algorithm (DVA)
• Calculates a route metric based on hops and
  bandwidth, network delays, etc.
• DVAs share routing tables
• Routing Information Protocol (RIP) is a DVA
• Link-State Algorithm (LSA)
• Metric is speed of link
• A router sends status of its interfaces to other
  routers.
• Requires more CPU, but is more efficient than DVA
• Open Shortest Path First (OSPF) is a LSA.

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Gateways

• Translates information between 2 different
  protocols or data formats (example TCP/IP).
• Used to connect LANs to WANs
• Gateways strip off all network information from
  the packet down to the raw data.
• Raw data is repackaged in new protocol or format.

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Digital Connectivity Tomsho, Tittel, Johnson
(2007)

• Because computers and LANs transmit data
  digitally, using digital techniques to connect
  LANs over long distances to form a WAN makes more
  sense than using digital-to-analog conversion
• Digital Data Service (DDS) lines are direct or
  point-to-point synchronous communication links
  with 2.4, 4.8, 9.6, or 56 Kbps transmission rates
• E.g., ISDN, T1, T3, and switched 56K
• DDS uses a communication device called Channel
  Service Unit/Data Service Unit (CSU/DSU)

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Digital Connectivity (continued) Tomsho, Tittel,
Johnson (2007)
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Digital Modems Tomsho, Tittel, Johnson (2007)

• The interface for ISDN is sometimes called a
  digital modem
• Consists of network termination (NT) device and
  terminal adapter (TA) equipment
• Cable TV operators and telcos that offer digital
  connections for Small Office/Home Office also use
  the term modem
• Technically, both uses of term modem are
  incorrect
• Some CATV systems do indeed use analog signaling,
  so the term cable modem is correct in these
  cases

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Digital Modems (continued) Tomsho, Tittel,
Johnson (2007)

• Cable modems transmit signals to/from Internet
  points of presence using broadband CATV network
• Provide shared media access bandwidth
• Security was a concern in early networks (users
  could eavesdrop other communication sessions)
• DSL uses the same twisted-pair phone lines that
  deliver voice services
• Connections are not shared (guaranteed bandwidth)
• Disadvantage distance limitation between the
  users location and the nearest central office
• Most common types ADSL (asynchronous digital
  subscriber line) and SDSL

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T1 Tomsho, Tittel, Johnson (2007)

• T1 is a DDS technology that uses two two-wire
  pairs to transmit full-duplex data signals at a
  maximum rate of 1.544 Mbps
• Digital link that organizations purchase or lease
• Subscribing to one or more channels instead of an
  entire T1 is possible with fractional T1
• In some countries, the E1 technology is used
• Multiplexing enables several communication
  streams to travel simultaneously over the same
  cable segment
• Can increase DS-1 rates up to DS-4 speeds

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T1 (continued) Tomsho, Tittel, Johnson (2007)
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T3 Tomsho, Tittel, Johnson (2007)

• A T3 line has 28 T1s or 672 channels and supports
  a data rate of 44.736 Mbps
• Many large service providers offer both T3 and
  fractional T3 leased lines with transmission
  rates of 6 Mbps and up
• A single T3 commonly replaces several T1 lines

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References

• Tomsho, Tittel, Johnson (2007). Guide to
  Networking Essentials. Boston Thompson Course
  Technology.
• Odom, Knott (2006). Networking Basics CCNA 1
  Companion Guide. Indianapolis Cisco Press
• Wikipedia (n.d.). OSI Model. Retrieved 09/12/2006
  from http//en.wikipedia.org/wiki/OSI_Model