Chapter 3

Question 1

A serial communications circuit between two points, provided by some service provider, typically a telephone company (telco). Because the telco does not sell a physical cable between the two endpoints, instead charging a monthly fee for the ability to send bits between the two sites.

Answer 1

Leased line

Question 2

A part of a larger network that implements mostly OSI Layer 1 and 2 technology, connects sites that typically sit far apart, and uses a business model in which a consumer (individual or business) must lease the service from a service provider (often a telco).

Answer 2

Wide area network (WAN)

Question 3

A common abbreviation for telephone company

Answer 3

Telco

Question 4

A type of interface on a router, used to connect to some types of WAN links, particularly leased lines and Frame Relay access links.

Answer 4

Serial interface

Question 5

A bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). Abbreviation is HDLC

Answer 5

High-Level Data Link Control

Question 6

Public network technology that delivers high bandwidth over conventional telco local-loop copper wiring at limited distances. Typically used as an Internet access technology, connecting a user to an ISP.

Answer 6

Digital subscriber line (DSL)

Question 7

An Internet access technology that uses a cable TV (CATV) cable, normally used for video, to send and recieve data.

Answer 7

Cable internet

Question 8

A term referring specifically to how a service provider can create an Ethernet WAN service using an MPLS network. More generally, a term referring to Ethernet WAN services.

Answer 8

Ethernet over MPLS (Multi-protocol label switching)

Question 9

Most Layer 1 and 2 networking technology falls into what two primary categories?

Answer 9

Wide Area Networks (WAN)

Local Area Networks (LAN)

Question 10

You pay for and own _____, but you lease _____.

Answer 10

LANs;

WANs

Question 11

In the cabling for a leased line, what typically connects four-wire line provided by a Telco?

Answer 11

CSU/DSU

Question 12

Which of the following is an accurate speed at which a leased line can operate in the United States?

a. 100 Mbps
b. 100 Kbps
c. 256 Kbps
d. 6.4 Mbps

Answer 12

c. 256 Kbps

Question 13

Which of the following fields in the HDLC header used by Cisco routers does Cisco add, beyond the ISO standard HDLC?

a. Flag
b. Type
c. Address
d. FCS

Answer 13

b. Type

Question 14

Two routers, R1 and R2, connect using an Ethernet over MPLS service. The service provides point-to-point service between these two routers only, as a Layer 2 Ethernet service. Which of the following are the most likely to be true about this WAN? (Choose two answers.)

a. R1 will connect to a physical Ethernet link, with the other end of the cable connected to R2.
b. R1 will connect to a physical Ethernet link, with the other end of the cable connected to a device at the WAN service provider point of presence.
c. R1 will forward data-link frames to R2 using an HDLC header/trailer.
d. R1 will forward data-link frames to R2 using an Ethernet header/trailer.

Answer 14

b. R1 will connect to a physical Ethernet link, with the other end of the cable connected to a device at the WAN service provider point of presence.
d. R1 will forward data-link frames to R2 using an Ethernet header/trailer.

Question 15

Which of the following Internet access technologies, used to connect a site to an ISP, offers asymmetric speeds? (Choose two answers.)

a. Leased lines
b. DSL
c. Cable Internet
d. BGP

Answer 15

b. DSL

c. Cable Internet

Question 16

Fred has just added DSL service at his home, with a separate DSL modem and consumer-grade router with four Ethernet ports. Fred wants to use the same old phone he was using before the installation of DSL. Which is most likely true about the phone cabling and phone used with his new DSL installation?

a. He uses the old phone, cabled to one of the router/switch device’s Ethernet ports.
b. He uses the old phone, cabled to the DSL modem’s ports.
c. He uses the old phone, cabled to an existing telephone port and not to any new device.
d. The old phone must be replaced with a digital phone.

Answer 16

c. He uses the old phone, cabled to an existing telephone port and not to any new device.

Question 17

Generic term referring to a company that a company that provides any form of WAN connectivity, including Internet services.

Answer 17

Service Provider

Question 18

What term refers to the fact that the topology stretches between two points, and two points only?

Answer 18

Point to point

Question 19

A specific type of leased line that transmits data at 1.544 megabits per second.

Answer 19

T1

Question 20

A type of line that refers to the fact that the data sent over the line cannot be copied by other telco customers.

Answer 20

Private line

Question 21

Each Telco company has Customer Premises Equipment (CPE), which includes what three main devices?

Answer 21

router, serial interface card, CSU/DSU

Question 22

Each router used in a Telco company uses a serial interface card, which acts somewhat like what?

Answer 22

Ethernet NIC

Question 23

The physical link in a Telco company requires a function called _____, which can be integrated into the serial interface card in the router or sit outside the router as an external device.

Answer 23

Channel Service Unit / data service unit (CSU/DSU)

Question 24

At a Telco, a router is connected to the CSU/DSU using a short _____ cable only if an external CSU/DSU is used.

Answer 24

serial

Question 25

The four-wire cable from the telco plugs in to the CSU/DSU, typically using an RJ-__ connector that has the same size and shape as an RJ-45 connector.

Answer 25

48

Question 26

Slower-speed leased-line links run at multiples of _____ kbps (kilobits per second), while faster links run at multiples of about _____ Mbps (megabits per second).

Answer 26

64; | 1.5

Question 27

To create a WAN link in a home lab, the serial cables normally used between a router and an external CSU/DSU are called _____ cables.

Answer 27

Data Terminal Cables (DTE)

Question 28

To create a physical WAN link in a lab, you need two serial cables: one serial DTE cable, plus a similar but slightly different matching _____ cable.

Answer 28

Data Communications Cable (DCE)

Question 29

The DCE cable has a _____ connector, while the DTE cable has a _____ connector

Answer 29

female; | male

Question 30

The _____ cable also does the equivalent task of an Ethernet crossover cable by swapping the transmit and receive wire pairs.

Answer 30

DCE

Question 31

The CSU/DSU normally provides a function called _____, in which it tells the router exactly when to send each bit through signaling over the serial cable.

Answer 31

clocking

Question 32

What command is used to configure serial clocking?

Answer 32

clock rate

Question 33

A leased-line provides a layer _____ service.

Answer 33

1

Question 34

Because leased lines define only the Layer 1 transmission service, many companies and standards organizations have created data-link protocols to control and use leased lines. What are the two most popular data link layer protocols used today for leased lines between two routers?

Answer 34

High-Level Data Link Control (HDLC) | Point-to-Point Protocol (PPP)

Question 35

HDLC uses a point-to-point topology. When information is sent using this protocol, where does the data go?

Answer 35

The other end of the link

Question 36

Even though HDLC has a destination field, the destination is _____. In years past these circuits included more than two devices, which is why the destination field is still included.

Answer 36

implied

Question 37

What is the Ethernet equivalent to the HDLC "flag" field in an HDLC header?

Answer 37

Preamble, SFD

Question 38

What Cisco proprietary HDLC header field identifies the type of Layer 3 packet encapsulated inside the frame?

Answer 38

Type

Question 39

What HDLC header field lists a recognizable bit pattern so that the receiving nodes realize that a new frame is arriving?

Answer 39

Flag

Question 40

What HDLC header field is mostly used for purposes no longer in use today for links between routers?

Answer 40

Control

Question 41

What HDLC header field is used by the error detection process?

Answer 41

FCS

Question 42

What HDLC header field identifies the destination device?

Answer 42

Address

Question 43

What organization standardized HDLC?

Answer 43

ISO

Question 44

ISO standard HDLC does not have a _____ field, and routers need to know the type of packet inside the frame. Cisco developed a propriety variation of HDLC adding this field.

Answer 44

Type

Question 45

Leased lines are simple for the customer, are widely available, are of high quality, and are private. What are the negatives compared to newer WAN technologies?

Answer 45

Higher cost; | Longer lead times

Question 46

Ethernet WANs have become a popular alternative to a leased-line WANs due to increasing the cabling distance that can now be used. WAN SP's using Ethernet, the customer would connect to an Ethernet link using a _____ interface.

Answer 46

router

Question 47

The (fiber) Ethernet link leaves the customer building and connects to some nearby SP location called a _____.

Answer 47

Point of Presence (PoP)

Question 48

The one Ethernet WAN service goes by two names: Ethernet ______ and Ethernet ______.

Answer 48

emulation; | Ethernet over Multiprotocol Label Switching (EoMPLS)

Question 49

EoMPLS provides a ____________ connection between two customer devices.

Answer 49

Point to Point

Question 50

The middle of the internet, called the Internet _____, exists as WANs and LANs owned and operated by Internet Service Providers (ISP).

Answer 50

core

Question 51

All WAN links including the lines connecting a home or office to an ISP usually go by what name?

Answer 51

Internet Access Link

Question 52

Digital Subscriber Line (DSL) uses what kind of cabling that is already installed in the home?

Answer 52

Phone line

Question 53

Cable Internet uses what kind of cabling that is already installed in the home?

Answer 53

Cable TV (CATV)

Question 54

______ creates a relatively short (miles long, not tens of miles) high-speed link WAN between a telco customer and an ISP.

Answer 54

DSL

Question 55

DSL, as a technology, does not try to replace leased lines, which run between any two sites, for potentially very long distances. DSL instead just provides a _____ physical link from a home to the telco’s network, allowing access to the Internet.

Answer 55

short

Question 56

The Telco switch installed at the CO supports the ability to set up voice calls, take them down, and forward the voice through the worldwide voice network, called the _____.

Answer 56

PSTN (Public Switched Telephone Network)

Question 57

To add DSL service in a home, what two things need to be added at the customer site and CO?

Answer 57

DSL capable devices at home; | DSL equipment at CO

Question 58

Once DSL is integrated into a home office, telephones may now also need a short extra cable with a filter in it, installed at the wall jack, to filter out the sounds of what?

Answer 58

higher electrical frequencies used for DSL

Question 59

The _____ installed in the CO of the Telco splits out data over to a router then to the Internet. It also splits out voice signals over to the voice switch.

Answer 59

DSLAM (DSL Access Multiplexer)

Question 60

DSL supports _____ speeds, meaning that the transmission speed from the ISP toward the home (downstream) is much faster than the transmissions toward the ISP (upstream).

Answer 60

asymmetric

Question 61

Cable Internet also uses the same basic in-home cabling concepts as does DSL, however a _____ cable is used instead of a telephone line and a cable modem is used instead of a DSL modem.

Answer 61

coaxial

Question 62

Both DSL and Cable Internet offer fast speeds, but which one generally runs faster?

Answer 62

Cable