CCENT Concepts Pt. 3

Question 1

Bit Rate of DS0

Answer 1

64 kps

Question 2

Bit Rate of DS1 (T1)

Answer 2

1.544 Mbps (24 DS0s, plus 8 kpbs

overhead)

Question 3

Bit Rate of DS3 (T3)

Answer 3

44.736 Mbps (28 DS1s, plus

management overhead)

Question 4

Bit Rate of E1

Answer 4

2.048 Mbps (32 DS0s)

Question 5

Bit Rate of E3

Answer 5

34.368 Mbps (16 E1s, plus

management overhead)

Question 6

Bit Rate of J1 (Y1)

Answer 6

2.048 Mbps (32 DS0s; Japanese

standard)

Question 7

HDLC Framing

Answer 7

Standard HDLC (No Type Field)
Flag - 1 Byte
Address - 1 Byte
Control - 1 Byte
Data - Variable
FCS - 4 Bytes
Proprietary Cisco HDLC (Adds Type Field)

Question 8

Synchronous

Answer 8

The imposition of time ordering on a bit stream. Practically, a device tries to
use the same speed as another device on the other end of a serial link.
However, by examining transitions between voltage states on the link, the
device can notice slight variation in the speed on each end and can adjust its
speed accordingly.

Question 9

Clock source

Answer 9

The device to which the other devices
on the link adjust their speed when
using synchronous links.

Question 10

CSU/DSU

Answer 10

Channel service unit/data service unit. Used on digital links as an interface to
the telephone company in the United States. Routers typically use a short
cable from a serial interface to a CSU/DSU, which is attached to the line from
the telco with a similar configuration at the other router on the other end of the
link.

Question 11

Telco

Answer 11

Telephone Company.

Question 12

Four-wire circuit

Answer 12

A line from the telco with four wires, composed of
two twisted-pair wires. Each pair is used to send in
one direction, so a four-wire ciruit allows full-duplex
communications.

Question 13

T1

Answer 13

A line from the telco that allows
transmission of data at 1.544
Mbps.

Question 14

E1

Answer 14

Similar to a T1, but used in Europe. It
uses a rate of 2.048 Mbps and 32
64-kbps channels.

Question 15

Access Link

Answer 15

In Frame Relay, the physical serial link that connects a Frame Relay DTE
device, usually a router, to a Frame Relay switch. This access link uses the
same physical layer standards as do point-to-point leased lines.

Question 16

back-to-back link

Answer 16

A serial link between two routers, created without CSU/DSUs, by connecting a
DTE cable to one router and a DCE cable to the other. Typically used in labs
to build serial links without the expense of a actual leased line from the telco.

Question 17

DTE (Layer 1)

Answer 17

Data Terminal Equipment. From a Layer 1 perspective, the DTE synchronizes
its clock based on the clock sent by the DCE. From a packet-switching
perspective, the DTE is the device outside the service provider’s network,
typically a router.

Question 18

DCE (Layer 1)

Answer 18

Data communication equipment. From a physical layer perspective, the device
providing the clocking on a WAN link, typically a CSU/DSU, is the DCE. From
a packet-switching perspective, the service provider’s switch, to which a router
might connect, is considered the DCE.

Question 19

Frame Relay

Answer 19

An International standard data-link protocol that defines the capabilities to
create a frame-switched (packet-switched) service, allowing DTE devices
(typically routers) to send data to many other devices using a single physical
connection to the Frame Relay service.

Question 20

HDLC

Answer 20

High-Level Data Link Control. A bitoriented
synchronous data link layer
protocol developed by the International
Organization Standardization (ISO).

Question 21

Leased Line

Answer 21

A serial communication 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 bit between the two sites, the service is considered
to be a leased service.

Question 22

Packet Switching

Answer 22

A generic reference to network services, typically WAN services, in which the
service examines the contents of the transmitted data to make some type of
forwarding decision. This term is mainly used to contrast with the WAN term
circuit switching, in which the provider sets up a (Layer 1) circuit between two
devices, and the provider makes no attempt to interpret the meaning of the
bits.

Question 23

PPP

Answer 23

Point-to-Point Protocol. A protocol that provides
router-to-router and host-to-network connections
over synchronous point-to-point and asynchronous
point-to-point circuits.