Transcript Network7

NT1210 Introduction to Networking
Unit 7:
Chapter 7, Wide Area Networks
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 today’s WANs work
 Telcos built huge networks to support voice traffic, long
before computers could create and send bits
Timeline Comparison of Inventions Compared to Telephone
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Figure 7-1
Introducing Wide Area Networks: Basic
Telco Services – Circuit Switching
Early Voice: Telco Creates One Analog Electrical Circuit Between Phones
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Figure 7-2
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
Connecting from a PC to an ISP, Using Modems and an Analog Telco Circuit
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Figure 7-4
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 freemarket competition: Governments started removing monopoly
status from different parts of Telcos’ business so allowed
competition
 Computerization of Telco’s 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
More Modern Routers Using a Digital Leased Line
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Figure 7-5
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
Circuit Switching
Figure 7-6
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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
General Timeline: Circuit Switching, Digital Circuits, and Packet Switching
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Figure 7-7
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
customer’s headers and make forwarding decision per
packet
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Introducing Wide Area Networks: Basic
Telco Services – Packet Switching
Packet Switching Example
Example of Packet Switching Service
Figure 7-8
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Introducing Wide Area Networks: Routers
 Connect LANs to WANs
Layer 3 IP Forwarding Logic
Figure 7-9
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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
Example Enterprise Network, With LAN and WAN Details Revealed
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Figure 7-10
Introducing Wide Area Networks: Routers
 Encapsulation and De-encapsulation
Encapsulation that Happens During the IP Packet Forwarding Process
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Figure 7-11
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
Point-to-Point Topologies in WAN and LAN
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Figure 7-12
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
WAN Hub and Spoke Topology Vs. LAN Star Topology
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Figure 7-13
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
WAN Multipoint Topology
Figure 7-14
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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
Leased Line: Shorter Electrical Circuits, Knitted Together
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Figure 7-16
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 customer’s router
Cables in a Relatively Short Leased Line
Figure 7-18
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Understanding Leased Line WAN Links
 Customer needs to plan for cabling at end of Telco’s
leased line cable
 Example: Customer’s router connects to cable installed
by Telco
Components and Responsibilities on One Side of a Leased Line
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Figure 7-19
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
Customer Equipment and Cabling with External CSU/DSU
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Figure 7-20
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/collateral/voicesw/ps6789/ps7290/ps10589/data_sheet_c78-598389.html
WIC-1CSU: http://www.cisco.com/en/US/prod/collateral/routers/ps221/product_data_sheet09186a00801a9184.html
http://www.cisco.com/en/US/prod/collateral/routers/ps5853/data_sheeet_serial_high_speed_waniInt_cards_for_1861.html
Photos of Router and Removable WAN Cards
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Figure 7-22
Understanding Leased Line WAN Links
 Key steps for installing leased lines
1. 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)
2. Install router and serial interface cards in router as needed by
leased line
3. If interface card does not have internal CSU/DSU, choose
CSU/DSU and matching cable
4. Physically connect all cables
5. 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
Telco Switching Connecting Incoming Customer T1s to T1 Trunks
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Figure 7-24
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 Mbps—28 times T1 speed)
CO Switches Multiplexing T1 Bits onto Faster T3 Circuit
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Figure 7-25
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?
Speed Differences on a 768-Kbps Leased Line WAN
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Figure 7-29
Understanding Leased Line WAN Links
Type of Line
Geography
DS0
USA
Speed
64 Kbps
Number of Channels
N/A
DS1 (T1)
USA
1.544 Mbps
24 DS0
DS3 (T3)
E0
USA
Europe
43.736 Mbps
64 Kbps
28 DS1
N/A
E1
Europe
2.048 Mbps
32* E0
E3
J0
Europe
Japan
34.368 Mbps
64 Kbps
16 E1
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.
Summary of Carrier TDM Line Standards
Table 7-3
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Understanding Packet Switching and MultiAccess WANs
 With packet switching, link capacity between switches
used to forward packets as needed or available
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Understanding Packet Switching and MultiAccess 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
Typical Drawing of a Frame Relay Design, One Customer, Ignoring Details
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Figure 7-44
Understanding Packet Switching and MultiAccess 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 MultiAccess WANs: Frame Relay
 Frame Relay terms
One Possible Telco Implementation of the Frame Relay Network
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Figure 7-45
Understanding Packet Switching and MultiAccess WANs
 Packet Switching Services: SONET speeds
Name
OC-1
OC-3
OC-12
OC-24
OC-48
OC-96
OC-192
(Rounded)
Line Speed (in
Mbps)
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155
622
1244
2488
4976
9952
SONET Optical Carrier (OC) Names and (Rounded) Line Speeds
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Table 7-5
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 customer’s 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
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.
Research Project
• Unit 7 Research Project 1: Chapter 8 Mind
Maps (NT1210 Graded Assignments)