Answers to the Chapter 8 Q&A Section 773
34
Define the terms TE1, TE2, and TA. Which term(s) imply that one of the other two must be
in use?
Terminal Equipment 1, Terminal Equipment 2, and terminal adapter. A TE2 device
requires a TA. A TE2 uses the R reference point. An S reference point is needed to perform
ISDN signaling; it is provided in that case by the TA.
35
What reference point is used between the customer premise and the phone company in
North America? What about in Europe?
The U interface is used in North America. Elsewhere, the T interface is used. The NT1
function, the dividing point between the T and U reference points, is implemented in telco
equipment outside North America.
36
Define the term SBus, and give one example of when it would be useful.
SBus is a bus with many devices sharing the S reference point. ISDN-capable phones,
faxes, and computers that wish to share the same BRI connect to the same NT1 using an
SBus. The SPIDs include subaddresses to distinguish among the multiple devices when
using an SBus.
37
What data link (OSI Layer 2) protocols are valid on an ISDN B channel?
HDLC, PPP, and LAPB are all valid options. PPP is the preferred choice, however. If
using DDR to more than one site, PAP or CHAP authentication is required. If used, PPP
must be used. PPP also provides automatic IP address assignment, which is convenient for
PC dial-in.
38
Define the terms PAP and CHAP. Which one(s) send the passwords in clear text format?
Password Authentication Protocol, Challenge Handshake Authentication Protocol. PAP
sends the passwords as simple text, whereas CHAP uses MD5 hashing to protect the
password contents.
39
Define MLPPP. Describe the typical home or small office use of MLPPP.
Multilink Point-to-Point Protocol. MLPPP is used to treat multiple B channels as a single
link because MLPPP fragments packets and sends different fragments across the multiple
links to balance the traffic. MLPPP is very useful for sharing two B channels in home or
small office use. It is not restricted to home use.
40
CHAP configuration uses names and passwords. Given Routers A and B, describe what
names and passwords must match in the respective CHAP configurations.
Router A has name B and a corresponding password configured. Router B has name A and
the same password configured. The names used are the host names of the routers unless
the CHAP name is configured.
apA.fm Page 773 Monday, March 20, 2000 5:24 PM