NT1210 Introduction to Networking

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NT1210 Introduction to Networking

• Unit 7
• Chapter 7, Wide Area Networks

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Objectives

• Identify the major needs and stakeholders for
  computer networks and network applications.
• Identify the classifications of networks and how
  they are applied to various types of enterprises.
• Explain the functionality and use of typical
  network protocols.
• Analyze network components and their primary
  functions in a typical data network from both
  logical and physical perspectives.

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Objectives

• Differentiate among major types of LAN and WAN
  technologies and specifications and determine how
  each is used in a data network.
• Explain basic security requirements for networks.
• Use network tools to monitor protocols and
  traffic characteristics.
• Use preferred techniques and necessary tools to
  troubleshoot common network problems.
• Differentiate among WAN technologies available
  from service providers

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Objectives

• Evaluate how WAN devices function
• Define and describe WAN protocols
• Evaluate troubleshooting techniques for WAN
  connections

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Introducing Wide Area Networks Basic Telco
Services

• Telephone, Telcos, and companies that grew from
  original Bell System impact how todays WANs work
• Telcos built huge networks to support voice
  traffic, long before computers could create and
  send bits

Figure 7-1
Timeline Comparison of Inventions Compared to
Telephone
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Introducing Wide Area Networks Basic Telco
Services Circuit Switching
Figure 7-2
Early Voice Telco Creates One Analog Electrical
Circuit Between Phones
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Introducing Wide Area Networks Basic Telco
Services Circuit Switching

• Switched Analog Circuits for Data To create
  first WAN connections, early computing devices
  had to act like telephones
• One computer device would make phone call to
  other computer, encoding its bits using analog
  electrical signals

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Introducing Wide Area Networks Basic Telco
Services Circuit Switching
Figure 7-4
Connecting from a PC to an ISP, Using Modems and
an Analog Telco Circuit
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Introducing Wide Area Networks Basic Telco
Services Circuit Switching

• Beginning mid-20th century Telcos transformed
• Invention and commercialization of computers
  Started with few computers being rare and unusual
  to world where most companies owned computers
• Migration from Telcos as government monopolies to
  free-market competition Governments started
  removing monopoly status from different parts of
  Telcos business so allowed competition
• Computerization of Telcos own network
  Revolutionized how Telco built its internal
  network to create better services at lower cost

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Introducing Wide Area Networks Basic Telco
Services Circuit Switching

• Digital Circuits and Leased Lines Telcos
  started offering service that used digital
  circuit between customer devices
• Endpoints still had circuit between them but
  could encode signal as bits with different
  electrical signals that followed encoding rules

Figure 7-5
More Modern Routers Using a Digital Leased Line
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Introducing Wide Area Networks Basic Telco
Services Circuit Switching

• Switched Circuits and Circuit Switching When
  user calls phone number, various circuit
  switches connect circuit on both sides of
  switch (see arrowed lines)
• Circuit switches create effect of end-to-end
  circuit by switching/connecting circuits on
  various links

Figure 7-6
Circuit Switching
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Introducing Wide Area Networks Basic Telco
Services Circuit Switching

• Circuit Communication path between two endpoints
• Circuit Switching Logic used by Telco network
  and devices called circuit switches that allows
  them to switch circuits in and out of different
  physical trunks to create end-to-end circuit
  through network
• Switched Circuit End-to-end circuit through
  Telco that changes over time because user calls
  number, hangs up, calls another number, and so on
• Dedicated Circuit (leased line) Circuit between
  two specific devices Telco never takes down

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Introducing Wide Area Networks Basic Telco
Services Packet Switching

• Packet Switching Telcos next started offering
  WAN services using packet switching services

Figure 7-7
General Timeline Circuit Switching, Digital
Circuits, and Packet Switching
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Introducing Wide Area Networks Basic Telco
Services Packet Switching

• All customer devices need direct connection to
  WAN via circuit to packet switching service
• Customers All devices can send data to every
  other device connected to packet switched service
• Telco (service provider) Must look at meaning of
  bits in customers headers and make forwarding
  decision per packet

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Introducing Wide Area Networks Basic Telco
Services Packet Switching

• Packet Switching Example

Figure 7-8
Example of Packet Switching Service
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Introducing Wide Area Networks Routers

• Connect LANs to WANs

Figure 7-9
Layer 3 IP Forwarding Logic
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Introducing Wide Area Networks Routers

• LAN might be simple Ethernet-only LAN
• LAN might be simple 802.11 WLAN
• LAN might be more complex campus LAN with both
  wired and wireless LANs

Figure 7-10
Example Enterprise Network, With LAN and WAN
Details Revealed
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Introducing Wide Area Networks Routers

• Encapsulation and De-encapsulation

Figure 7-11
Encapsulation that Happens During the IP Packet
Forwarding Process
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Introducing Wide Area Networks Topologies

• Point-to-Point Topology Basic WAN service
• LAN with10BASE-T or 100BASE-T cable has 2-pair 1
  pair for sending data in each direction
• Both LAN and WAN topologies allow full duplex
  operation and can share 1 link

Figure 7-12
Point-to-Point Topologies in WAN and LAN
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Introducing Wide Area Networks Topologies

• Hub and Spoke Topologies
• Reduces number of leased lines
• Provides way for packets to reach all sites
• Connects one router (hub router) to all other
  routers using leased lines

Figure 7-13
WAN Hub and Spoke Topology Vs. LAN Star Topology
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Introducing Wide Area Networks Topologies

• Multipoint topologies Hub-and-spoke topology has
  some disadvantages
• Uses leased lines that might have to run hundreds
  or thousands of miles at large expense
• Packets that go from one spoke site to another
  spoke site have to cross multiple WAN links

Figure 7-14
WAN Multipoint Topology
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Understanding Leased Line WAN Links

• Distance limitations No single circuit extends
  entire distance between two routers
• Point to point circuits really series of
  circuits

Figure 7-16
Leased Line Shorter Electrical Circuits, Knitted
Together
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Understanding Leased Line WAN Links

• Telco installs physical cable between equipment
  in CO to customer site
• 2-pair cable typically runs underground into
  customer buildings terminating near customers
  router

Figure 7-18
Cables in a Relatively Short Leased Line
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Understanding Leased Line WAN Links

• Customer needs to plan for cabling at end of
  Telcos leased line cable
• Example Customers router connects to cable
  installed by Telco

Figure 7-19
Components and Responsibilities on One Side of a
Leased Line
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Understanding Leased Line WAN Links

• Leased line has Channel Services Unit/Data
  Services Unit (CSU/DSU) function on each side of
  line at customer site
• Each site uses either internal or external
  CSU/DSU
• Internal CSU/DSU sits inside router as part of
  serial interface card

Figure 7-20
Customer Equipment and Cabling with External
CSU/DSU
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Understanding Leased Line WAN Links

• Example Cisco router with two slots for
  removable router interface cards (WICs) where
  serial cards are install
• Serial card on left has built-in CSU/DSU and
  uses RJ-48 connector
• Serial card on right does not have CSU/DSU so
  relies on external CSU/DSU

1921 router http//www.cisco.com/en/US/prod/colla
teral/voicesw/ps6789/ps7290/ps10589/data_sheet_c78
-598389.html WIC-1CSU http//www.cisco.com/en/US/
prod/collateral/routers/ps221/product_data_sheet09
186a00801a9184.html http//www.cisco.com/en/US/pr
od/collateral/routers/ps5853/data_sheeet_serial_hi
gh_speed_waniInt_cards_for_1861.html
Figure 7-22
Photos of Router and Removable WAN Cards
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Understanding Leased Line WAN Links

• Key steps for installing leased lines
• Order leased line from Telco include specs on
  line speed, cable connectors required, and exact
  location where cable should be installed
  (address, floor, identifying information for
  exact room)
• Install router and serial interface cards in
  router as needed by leased line
• If interface card does not have internal CSU/DSU,
  choose CSU/DSU and matching cable
• Physically connect all cables
• Configure devices (beyond scope of this chapter)

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Break
Take 10
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Understanding Leased Line WAN Links Multiplexing

• Possible solution Telco could install three T1
  trunk lines between CO switches

Figure 7-24
Telco Switching Connecting Incoming Customer T1s
to T1 Trunks
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Understanding Leased Line WAN Links Multiplexing

• More efficient solution Time Division
  Multiplexing (TDM) uses TDM switches and one T3
  trunk
• Telco connects cable using T3 card in each TDM
  switch to use T3 link (43.736 Mbps28 times T1
  speed)

Figure 7-25
CO Switches Multiplexing T1 Bits onto Faster T3
Circuit
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Understanding Leased Line WAN Links

• Customer buys T1 line at each site with full T1
  speed (1.536 Mbps)
• What happens if customer router can only transmit
  at 768 Kbps?

Figure 7-29
Speed Differences on a 768-Kbps Leased Line WAN
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Understanding Leased Line WAN Links
Type of Line Geography Speed Number of Channels
DS0 USA 64 Kbps N/A
DS1 (T1) USA 1.544 Mbps 24 DS0
DS3 (T3) USA 43.736 Mbps 28 DS1
E0 Europe 64 Kbps N/A
E1 Europe 2.048 Mbps 32 E0
E3 Europe 34.368 Mbps 16 E1
J0 Japan 64 Kbps N/A
J1 Japan 1.544 Mbps 24 J0
J3 Japan 32.064 Mbps 20 J1
30 E0 channels are available for customer data
2 E0 channels are for other functions.
Table 7-3
Summary of Carrier TDM Line Standards
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Understanding Packet Switching and Multi-Access
WANs

• With packet switching, link capacity between
  switches used to forward packets as needed or
  available

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Understanding Packet Switching and Multi-Access
WANs Frame Relay

• Frame Relay Allows any device connected to
  network to communicate with any other network and
  details of Frame Relay design do not matter

Figure 7-44
Typical Drawing of a Frame Relay Design, One
Customer, Ignoring Details
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Understanding Packet Switching and Multi-Access
WANs Frame Relay

• Frame Relay physical links Edge between customer
  site and Frame Relay network
• Point of Presence (PoP) Where Telco
  devices/cables interface with customer premises
• DTE (Data Terminal Equipment) Customer device
  (e.g., router)
• Frame Relay switch Telco device that forwards
  customer frames (also called DCE Data
  Communications Equipment)
• Access link Physical link between DTE and DCE
• DLCI Data Link Control Identifier, used instead
  of IP address

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Understanding Packet Switching and Multi-Access
WANs Frame Relay

• Frame Relay terms

Figure 7-45
One Possible Telco Implementation of the Frame
Relay Network
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Understanding Packet Switching and Multi-Access
WANs

• Packet Switching Services SONET speeds

Name (Rounded) Line Speed (in Mbps)
OC-1 52
OC-3 155
OC-12 622
OC-24 1244
OC-48 2488
OC-96 4976
OC-192 9952
Table 7-5
SONET Optical Carrier (OC) Names and (Rounded)
Line Speeds
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Summary, This Chapter

• Compared switched circuits as used for a typical
  home telephone call with two computers sending
  data over a similar switched circuit using
  modems.
• Explained the basic differences between a circuit
  switching WAN service and a packet switching WAN
  service from the customers perspective.
• Illustrated the reasons why IP routers work well
  at forwarding data between different types of
  LANs and WANs.
• Drew common WAN topologies.

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Summary, This Chapter

• Drew and contrasted the different customer-site
  cabling for a leased line WAN installed between
  two routers.
• Listed the types of physical links in the US
  T-carrier hierarchy, their approximate speeds,
  and the specific number of slowed-speed channels
  that fit in the next higher-speed line.
• Explained how Telcos use CSU/DSUs to match a
  leased line speed to a physical DS1 line, using
  an example of a 768 Kbps fractional T1 leased
  line between two routers.
• Compared and contrast the HDLC and PPP standards.

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Summary, This Chapter

• Explained the differences between packet
  switching and circuit switching from the Telco
  perspective.
• Used an example network, explain how with Frame
  Relay, a router can have one physical link
  connected to the WAN, but send data to many other
  destination routers.
• Listed the other WAN packet switching services,
  and show whether they were introduced before or
  after Frame Relay.

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Questions? Comments?
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Unit 7 Assignment

• Unit 7 Assignment 1 Wide Area Networks Review
• Complete the multiple-choice questions
• Complete the Define Key Terms table and the List
  the Words Inside the Acronyms table.
• Reading Assignment. Read Chapter 8

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Unit 7 Lab

• Complete all Labs in Chapter 7 of the lab book.
• Lab should be completed in class.
• Uncompleted Lab must be submitted in the next
  class.

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Research Project

• Unit 7 Research Project 1 Chapter 8 Mind Maps
  (NT1210 Graded Assignments)