NT1210 Introduction to Networking Unit 7: Chapter 7, Wide Area Networks

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.

2

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

3

Objectives

Evaluate how WAN devices function

Define and describe WAN protocols

Evaluate troubleshooting techniques for WAN connections

4

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


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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Figure 7-4Connecting from a PC to an ISP, Using Modems and an Analog Telco Circuit8


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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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


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


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


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


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


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


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


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


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


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


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

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6789/ps7290/ps10589/data_sheet_c78-598389.html

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6789/ps7290/ps10589/data_sheet_c78-598389.html

http://www.cisco.com/en/US/prod/collateral/routers/ps221/product_data_sheet09186a00801a9184.html

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


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


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


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


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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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)

Documents

NT1210 Introduction to Networking Unit 7: Chapter 7, Wide Area Networks