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Any Questions?. Chapter 4-Fundamentals of WANS. OSI Layer 1 for Point-to-Point WANs OSI Layer 2 for Point-to-Point WANs Frame Relay and Packet-Switching Services. Do I know this?. Go through the Quiz- 5 minutes.

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Chapter 4 fundamentals of wans l.jpg
Chapter 4-Fundamentals of WANS

  • OSI Layer 1 for Point-to-Point WANs

  • OSI Layer 2 for Point-to-Point WANs

  • Frame Relay and Packet-Switching

  • Services


Do i know this l.jpg
Do I know this?

Go through the Quiz-

5 minutes


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1. Which of the following best describes the main function of OSI Layer 1 protocols?

a. Framing

b. Delivery of bits from one device to another

c. Addressing

d. Local Management Interface (LMI)

e. DLCI


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1. Which of the following best describes the main function of OSI Layer 1 protocols?

a. Framing

b. Delivery of bits from one device to another

c. Addressing

d. Local Management Interface (LMI)

e. DLCI

Answer: B


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2. Which of the following typically connects to a four-wire line provided by a telco?

a. Router serial interface

b. CSU/DSU

c. Transceiver

d. Switch serial interface


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2. Which of the following typically connects to a four-wire line provided by a telco?

a. Router serial interface

b. CSU/DSU

c. Transceiver

d. Switch serial interface

Answer: B


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3. Which of the following typically connects to a V.35 or RS-232 end of a cable when

cabling a leased line?

a. Router serial interface

b. CSU/DSU

c. Transceiver

d. Switch serial interface


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3. Which of the following typically connects to a V.35 or RS-232 end of a cable when

cabling a leased line?

a. Router serial interface

b. CSU/DSU

c. Transceiver

d. Switch serial interface

Answer: B


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4. On a point-to-point WAN link using a leased line between two routers located

hundreds of miles apart, what devices are considered to be the DTE devices?

a. Routers

b. CSU/DSU

c. The central office equipment

d. A chip on the processor of each router

e. None of these answers are correct.


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4. On a point-to-point WAN link using a leased line between two routers located

hundreds of miles apart, what devices are considered to be the DTE devices?

a. Routers

b. CSU/DSU

c. The central office equipment

d. A chip on the processor of each router

e. None of these answers are correct.

Answer: A


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5. Which of the following functions of OSI Layer 2 is specified by the protocol standard

for PPP, but is implemented with a Cisco proprietary header field for HDLC?

a. Framing

b. Arbitration

c. Addressing

d. Error detection

e. Identifying the type of protocol that is inside the frame


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5. Which of the following functions of OSI Layer 2 is specified by the protocol standard

for PPP, but is implemented with a Cisco proprietary header field for HDLC?

a. Framing

b. Arbitration

c. Addressing

d. Error detection

e. Identifying the type of protocol that is inside the frame

Answer: E


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6. Imagine that Router1 has three point-to-point serial links, one link each to three remote routers. Which of the following is true about the required HDLC addressing at Router1?

a. Router1 must use HDLC addresses 1, 2, and 3.

b. Router1 must use any three unique addresses between 1 and 1023.

c. Router1 must use any three unique addresses between 16 and 1000.

d. Router1 must use three sequential unique addresses between 1 and 1023.

e. None of these answers are correct.


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6. Imagine that Router1 has three point-to-point serial links, one link each to three remote routers. Which of the following is true about the required HDLC addressing at Router1?

a. Router1 must use HDLC addresses 1, 2, and 3.

b. Router1 must use any three unique addresses between 1 and 1023.

c. Router1 must use any three unique addresses between 16 and 1000.

d. Router1 must use three sequential unique addresses between 1 and 1023.

e. None of these answers are correct.

Answer: E


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7. What is the name of the Frame Relay field used to identify Frame Relay virtual circuits?

a. Data-link connection identifier

b. Data-link circuit identifier

c. Data-link connection indicator

d. Data-link circuit indicator

e. None of these answers are correct.


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7. What is the name of the Frame Relay field used to identify Frame Relay virtual circuits?

a. Data-link connection identifier

b. Data-link circuit identifier

c. Data-link connection indicator

d. Data-link circuit indicator

e. None of these answers are correct.

Answer: A


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8. Which of the following is true about Frame Relay virtual circuits (VCs)?

a. Each VC requires a separate access link.

b. Multiple VCs can share the same access link.

c. All VCs sharing the same access link must connect to the same router on the

other side of the VC.

d. All VCs on the same access link must use the same DLCI.


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8. Which of the following is true about Frame Relay virtual circuits (VCs)?

a. Each VC requires a separate access link.

b. Multiple VCs can share the same access link.

c. All VCs sharing the same access link must connect to the same router on the

other side of the VC.

d. All VCs on the same access link must use the same DLCI.

Answer: B



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OSI Layer 1 for Point to Point WANs

  • What is a WAN

  • What is a point to point WAN?

  • If layer 1 is sending bits, how are buts sent point to point

    • Leased Line??

  • Point to Point WAN acts like Ethernet

    • Ethernet can’t go so lon


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WANs

  • A WAN is usually a link over a distance that is longer than LAN technologies support

    • Or

  • Over a distance where you do not have right of way and a telco/Service Provider already has links


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Getting Point to Point Service

  • Leased Lines

    • Have you worked with them for Voice or Data?


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WAN from the Customer Viewpoint

  • Know the terminology

    • I think you already do!

  • CO, CSU/DSU


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Who owns What

  • Customer Premise Equipment and the demarc

    • Sometimes the provider owns the CSU/DSU and even the router

  • Telco usually provides a 4 wire connection

    • RJ-48


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WAN Cabling Standards

  • Lots of different interfaces for routers

    • Synchronous and Asynchronous

  • Connector chosen base on the router and CSU/DSU capability


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Clock Rates, Sync and DCE/DTE

  • Synchronous networks use a clock signal

  • Has to be shared by all devices

    • Clock Rate, Bandwidth, link speed

  • Usually the CSU/DSU is set to get clocking from Telco/Provider

    • Router is set to get clock from CSU/DSU (default)

  • CSU/DSU is DCE

  • Router is DTE


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LAB Links

  • No CSU/DSU

  • DTE to DCE cable

  • Have to see which is connected

    • Show controllers commands

  • DCE needs to set clock rate

    • Configure terminal

    • Interface serial0

    • Clock rate 64000


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Link Speeds

  • Digital Voice circuits designed around PCM

    • 64000 bits per second

    • 64 Kilobits per second

    • DS0

  • T1-DS1

    • 24 DS0 + 8 kbps overhead

    • 1.544 Mbps

  • T3-DS3

    • 28 T1

    • 44.736 Mbps


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OSI Layer 2 Point to Point

  • Can’t use Ethernet

    • HDLC and PPP

  • HDLC-was standards based Framing

  • Needed Type field to tell what layer 3 protocol is being used

    • Cisco Proprietary HDLC


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HDLC

  • Address really isn’t used

  • Error Detection with FCS on trailer

  • Cisco adds the protocol Type field


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Point to Point Protocol (PPP)

  • PPP very similar to HDLC

  • Identical framing to Cisco’s HDLC

  • Discard frames with FCS errors

  • PPP is more common than HDLC

    • More feature rich

    • Includes authentication




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Frame Relay and Packet Switching

  • Packet Switching

    • Similar Physical connectivity

    • Different Logical Set-up

  • Frame-Relay and ATM are common

  • Packet Switching scales to multiple locations better


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Frame Relay

  • Allows a single physical link to support multiple logical connections

    • Point to Multi-point

  • With PPP you need a different physical connection for each location


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Frame Relay Basics

  • More Detailed Protocol

    • Addressing is more important

  • Physical line between router and Frame-Relay Switch

    • Access Link

  • Frame Relay switch looks at addressing infromation to decide where to send Frame


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Frame Relay

  • Provider creates Virtual Circuits (VC)

    • Define path from one router to another router

    • VCs are associated with a Data Link Connection Identifier (DLCI)

  • Frame/Packet Switching Service

  • VC is a logical path-can go through many Frame Switches


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Frame Relay benefits

  • R1 will have 2 DLCI’s programmed in

  • Committed Information Rate (CIR) defines minimum speed for each link

  • Lower cost than leased lines



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