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2013 Latest Cisco 350-001 Exam Section 3: Leased Line Protocols (4 Questions)

QUESTION NO: 1
With regard to PPPoA, which of the following statements are true? (Choose all that apply.)
A. PPPoA contains information about NCP LCP and supports all AAL.
B. PPPoA uses adaptation layer 5 (AAL5) as the framed protocol and is used primarily in xDSL.
C. PPPoA is not a standard based protocol.
D. In PPPoA architecture, IP address allocation for the subscriber CPE uses IPCP negotiation.
E. PPPoA supports all ppp features except password PAP CHAP.
Answer: B, D
Explanation:
Point-to-Point Protocol (PPP) (RFC 1331) provides a standard method of encapsulating higher layer protocols across point-to-point connections. It extends the High-Level Data Link Control (HDLC) packet structure with a 16-bit protocol identifier that contains information about the content of the packet. The packet contains three types of information:
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Link Control Protocol (LCP) negotiates link parameters, packet size, or type of authentication
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Network Control Protocol (NCP) contains information about higher layer protocols including IP and IPX, and their control protocols (IPCP for IP)
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Data frames containing data PPP over ATM adaptation layer 5 (AAL5) (RFC 2364) uses AAL5 as the framed protocol, which supports both PVC and SVC. PPPoA was primarily implemented as part of ADSL. It relies on RFC1483, operating in either Logical Link Control-Subnetwork Access Protocol (LLC-SNAP) or VC-Mux mode. A customer premise equipment (CPE) device encapsulates the PPP session based on this RFC for transport across the ADSL loop and the digital subscriber line access multiplexer (DSLAM). Incorrect Answers:
A.
PPPoA does not support every AAL and uses only AAL5.
C.
PPPoA is standards based.
E.
CHAP (Challenge authentication protocol) is supported in PPPoA.
Reference:
http://www.cisco.com/warp/public/794/pppoa_arch.html

QUESTION NO: 2
Under one of the serial interfaces of your router you see the following configured:
Interface serial 0/0 Encapsulation PPP IP address 10.1.1.1 255.255.255.252 Invert txclock
What is a reason for the “invert txclock” command being configured?
A. It synchronizes TXD and RXD clocks.
B. It corrects systems that use long cables that experience high error rates when operating at the higher transmission speeds.
C. It is used for adjusting the transmit clock properties of the PPP negotiation process.
D. It inverts the phase of the local clock used for timing incoming data the serial line.
E. It is used to allow the interface to provide clocking, rather than receiving clocking from the line.
Answer: B
Explanation:
Systems that use long cables or cables that are not transmitting the TxC signal (transmit echoed clock line, also known as TXCE or SCTE clock) can experience high error rates when operating at the higher transmission speeds. For example, if a PA-8T synchronous serial port adapter is reporting a high number of error packets, a phase shift might be the problem. Inverting the clock might correct this shift.
Incorrect Answers:
B. The invert txclock command is not related to PPP.
E. This describes the purpose of the clocking source configuration for a serial line. The correct configuration command for determining the clocking source is “clock source”.

QUESTION NO: 3 A router has a T1 private line connection, with the encapsulation type set to HDLC. Which of the following are transfer modes that could be supported over this HDLC circuit? (Choose all that apply)
A. LAPB
B. ARB
C. ABM
D. ARM
E. NRM
F. LAPD
Answer: A, C, D, and E
Explanation:
The following are all transfer types supported by HDLC: ARM – Asynchronous Response Mode. It is an HDLC communication mode involving one primary and at least one secondary, where either the primary or one of the secondaries can initiate transmissions. ABM – Asynchronous Balanced Mode. It is an HDLC and derivative protocol, communication mode supporting peer-oriented point-to-point communications between two stations, where either station can initiate transmission. NRM – Normal Response Mode LAPB – Link Access Procedure Balanced
Incorrect Answers:
B, F. ARB and LAPD are not acronyms that apply to HDLC.

QUESTION NO: 4 A Testking branch office uses Telnet and FTP to access an application at the main office over a point to point T1 HDLC link. You wish to increase the performance over this link through the use of a compression algorithm. What compression type will provide the best performance improvement?
A. Compressed Real-time Transport Protocol
B. TCP header compression
C. Stacker compression
D. Predictor compression
Answer: C
Explanation:
You can configure point-to-point software compression for all LAPB, PPP, and HDLC encapsulations using either the predictor or stacker compression methods. Compression reduces the size of frames via lossless data compression. HDLC encapsulations support the Stacker compression algorithm. PPP and LAPB encapsulations support both predictor and Stacker compression algorithms. When compression is performed in software installed in the router’s main processor, it might significantly affect system performance. Compression requires that both ends of the serial link be configured to use compression.
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