Chapter 3 - Fundamentals of WANs Flashcards
In the cabling for a leased line, which of the following typically connects to a four wire line provided by a telco?
a. Router serial interface without internal CSU/DSU
b. CSU/DSU
c. Router serial interface with internal transceiver
d. Switch serial interface
B.
The four-wire circuit cable supplied by the telco connects to the device acting as the CSU/DSU. That can be an external CSU/DSU or a CSU/DSU integrated into a router serial interface card. LAN switches do not have serial interfaces, and router serial interfaces do not have transceivers.
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.
Leased lines can run at various preset speeds. These include multiples of 64 kbps, up through 24 times 64 kbps. The speeds can also be multiples of T1 speed (1.544 Mbps), up to 28 times that speed.
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.
The standard HDLC header does not include a Type field, which identifies the type of packet encapsulated inside the HDLC frame.
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 and D.
The physical installation uses a model in which each router uses a physical Ethernet link to connect to some SP device in an SP facility called a point of presence
(PoP). The Ethernet link does not span from each customer device to the other. From a data-link perspective, both routers use the same Ethernet standard header and trailer used on LANs; HDLC does not matter on these Ethernet WAN links.
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 and C.
Leased lines transmit data at the same speed in both directions, making them a symmetric service. DSL and cable Internet offer asymmetric speeds, with a faster downstream speed. BGP is a routing protocol and not an Internet access technology.
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.
With DSL, the requirements on the phone’s wiring are unchanged. The phone can connect to any working telephone jack, as if the DSL modem and router did not exist.
