Chapter 3 Flashcards
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.
Leased line
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).
Wide area network (WAN)
A common abbreviation for telephone company
Telco
A type of interface on a router, used to connect to some types of WAN links, particularly leased lines and Frame Relay access links.
Serial interface
A bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). Abbreviation is HDLC
High-Level Data Link Control
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.
Digital subscriber line (DSL)
An Internet access technology that uses a cable TV (CATV) cable, normally used for video, to send and recieve data.
Cable internet
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.
Ethernet over MPLS (Multi-protocol label switching)
Most Layer 1 and 2 networking technology falls into what two primary categories?
Wide Area Networks (WAN)
Local Area Networks (LAN)
You pay for and own _____, but you lease _____.
LANs;
WANs
In the cabling for a leased line, what typically connects four-wire line provided by a Telco?
CSU/DSU
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
c. 256 Kbps
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
b. Type
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.
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.
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
b. DSL
c. Cable Internet
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.
c. He uses the old phone, cabled to an existing telephone port and not to any new device.
Generic term referring to a company that a company that provides any form of WAN connectivity, including Internet services.
Service Provider
What term refers to the fact that the topology stretches between two points, and two points only?
Point to point
A specific type of leased line that transmits data at 1.544 megabits per second.
T1
A type of line that refers to the fact that the data sent over the line cannot be copied by other telco customers.
Private line
Each Telco company has Customer Premises Equipment (CPE), which includes what three main devices?
router, serial interface card, CSU/DSU
Each router used in a Telco company uses a serial interface card, which acts somewhat like what?
Ethernet NIC
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.
Channel Service Unit / data service unit (CSU/DSU)
At a Telco, a router is connected to the CSU/DSU using a short _____ cable only if an external CSU/DSU is used.
serial
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.
48
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).
64;
1.5
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.
Data Terminal Cables (DTE)
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.
Data Communications Cable (DCE)
The DCE cable has a _____ connector, while the DTE cable has a _____ connector
female;
male
The _____ cable also does the equivalent task of an Ethernet crossover cable by swapping the transmit and receive wire pairs.
DCE
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.
clocking
What command is used to configure serial clocking?
clock rate
A leased-line provides a layer _____ service.
1
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?
High-Level Data Link Control (HDLC)
Point-to-Point Protocol (PPP)
HDLC uses a point-to-point topology. When information is sent using this protocol, where does the data go?
The other end of the link
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.
implied
What is the Ethernet equivalent to the HDLC “flag” field in an HDLC header?
Preamble, SFD
What Cisco proprietary HDLC header field identifies the type of Layer 3 packet encapsulated inside the frame?
Type
What HDLC header field lists a recognizable bit pattern so that the receiving nodes realize that a new frame is arriving?
Flag
What HDLC header field is mostly used for purposes no longer in use today for links between routers?
Control
What HDLC header field is used by the error detection process?
FCS
What HDLC header field identifies the destination device?
Address
What organization standardized HDLC?
ISO
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.
Type
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?
Higher cost;
Longer lead times
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.
router
The (fiber) Ethernet link leaves the customer building and connects to some nearby SP location called a _____.
Point of Presence (PoP)
The one Ethernet WAN service goes by two names: Ethernet ______ and Ethernet ______.
emulation;
Ethernet over Multiprotocol Label Switching (EoMPLS)
EoMPLS provides a ____________ connection between two customer devices.
Point to Point
The middle of the internet, called the Internet _____, exists as WANs and LANs owned and operated by Internet Service Providers (ISP).
core
All WAN links including the lines connecting a home or office to an ISP usually go by what name?
Internet Access Link
Digital Subscriber Line (DSL) uses what kind of cabling that is already installed in the home?
Phone line
Cable Internet uses what kind of cabling that is already installed in the home?
Cable TV (CATV)
______ creates a relatively short (miles long, not tens of miles) high-speed link WAN between a telco customer and an ISP.
DSL
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.
short
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 _____.
PSTN (Public Switched Telephone Network)
To add DSL service in a home, what two things need to be added at the customer site and CO?
DSL capable devices at home;
DSL equipment at CO
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?
higher electrical frequencies used for DSL
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.
DSLAM (DSL Access Multiplexer)
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).
asymmetric
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.
coaxial
Both DSL and Cable Internet offer fast speeds, but which one generally runs faster?
Cable
