nt1210 introduction to networking unit 7: chapter 7, wide area networks
TRANSCRIPT
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
Figure 7-1Timeline Comparison of Inventions Compared to Telephone5
Introducing Wide Area Networks: Basic Telco Services – Circuit Switching
Figure 7-2Early Voice: Telco Creates One Analog Electrical Circuit Between Phones6
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 7-4Connecting from a PC to an ISP, Using Modems and an Analog Telco Circuit8
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 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
Figure 7-5More Modern Routers Using a Digital Leased Line10
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 7-6Circuit Switching11
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 7-7General Timeline: Circuit Switching, Digital Circuits, and Packet Switching13
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 SwitchingPacket Switching Example
Figure 7-8Example of Packet Switching Service15
Introducing Wide Area Networks: Routers
Connect LANs to WANs
Figure 7-9Layer 3 IP Forwarding Logic16
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 7-10Example Enterprise Network, With LAN and WAN Details Revealed17
Introducing Wide Area Networks: Routers
Encapsulation and De-encapsulation
Figure 7-11Encapsulation that Happens During the IP Packet Forwarding Process18
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 7-12Point-to-Point Topologies in WAN and LAN19
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 7-13WAN Hub and Spoke Topology Vs. LAN Star Topology20
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 7-14WAN Multipoint Topology21
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 7-16Leased Line: Shorter Electrical Circuits, Knitted Together22
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
Figure 7-18Cables in a Relatively Short Leased Line23
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
Figure 7-19Components and Responsibilities on One Side of a Leased Line24
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 7-20Customer Equipment and Cabling with External CSU/DSU25
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
Figure 7-22Photos of Router and Removable WAN Cards
1921 router… http://www.cisco.com/en/US/prod/collateral/voicesw/ps6789/ps7290/ps10589/data_sheet_c78-598389.htmlWIC-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 26
Understanding Leased Line WAN Links
Key steps for installing leased lines1. 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
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Take 10
Understanding Leased Line WAN Links: Multiplexing
Possible solution: Telco could install three T1 trunk lines between CO switches
Figure 7-24Telco Switching Connecting Incoming Customer T1s to T1 Trunks29
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)
Figure 7-25CO Switches Multiplexing T1 Bits onto Faster T3 Circuit30
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 7-29Speed Differences on a 768-Kbps Leased Line WAN31
Understanding Leased Line WAN Links
Table 7-3Summary of Carrier TDM Line Standards
* 30 E0 channels are available for customer data; 2 E0 channels are for other functions.
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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
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 7-44Typical Drawing of a Frame Relay Design, One Customer, Ignoring Details34
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 7-45One Possible Telco Implementation of the Frame Relay Network36
Understanding Packet Switching and Multi-Access WANs
Packet Switching Services: SONET speeds
Table 7-5SONET Optical Carrier (OC) Names and (Rounded) Line Speeds
Name
(Rounded) Line Speed (in
Mbps)OC-1 52OC-3 155
OC-12 622OC-24 1244OC-48 2488OC-96 4976OC-192 9952
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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 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)