わくわくIT資格勉強記

Which of the following is not a data link layer (OSI Layer 2) protocol?
　A. Ethernet
　B. ATM
　C. Cell-Relay
　D. PPP

There is no protocol called Cell-Reay; the other answers are all Data Link protocols.

Which of the following is not a function of PPP?
　A. Provide support for multiple upper-layer protocols.
　B. Support the connection of multiple devices on a single link.
　C. Support authentication.
　D. Support data integrity via a CRC on frame contens.

There is an address field, but is not used as there is no need for addressing on a point-to-point link.

Which of the following ATM AAL types is associated with an incorrect description?
　A. AAL3/4 -- Connection-oriented service
　B. AAL5 -- Connectionless service
　C. AAL2 -- Variable bit rate traffic
　D. AAL1 -- High bit rate traffic

AAL1 is constant bit rate traffic.

Which of the following technologies ensure that a unicast packet is visible only to the device with the specific destination address?
　A. Ethernet
　B. Switched Ethernet
　C. Satellite
　D. Wireless LAN

An Ethernet switch will forward the frame to the corect port based on a destination address in its FDB; all the other technologies broadcast all frames to all devices.

The advantage of using multicast packets instead of broadcast packet is .
　A. Broadcast are received by every host.
　B. Multicast is newer technology.
　C. Broadcast are processed by every host.
　D. Multicast provides multiple address for flexibility.

Depending on the switch technology in use, multicast packets might also be received by every host, but every host would not process the multicast packets if they are not in the multicast group. Every device must strip the Ethernet header and examine the contents of the upper layers of a broadcast to determine if the packet is intended for it or not. This is a major disadvantage for broadcast traffic.

A PPP frame has several field that are not used, like addressing.
Why do these fields exist in the frame?
　A. They are reserved for future use.
　B. They are legacy fields from older versions of PPP headers.
　C. PPP is based on the HDLC frame format.
　D. PPP can be adapted for use on multi-point networks and might need the fields.

The HDLC protocol used the fields that PPP does not, and the fields are a legacy of this.

ATM uses 53-byte cells, which is quite a bit smaller than the maximum Ethernet frame.
What is the purpose of having such a small cell size?
　A. To support latency-sensitive applications like voice traffic
　B. To provide less overhead on ATM switches
　C. To support the use of multiple classes of service
　D. To provide the ability to do switching in hardware

This is the primary factor behind the small size of the cells. The other answers don't address the core reason for the size of the cells.

What is the purpose of the ATM Adaptation Layer?
　A. It determines the amount of data in the cell.
　B. It maps data from upper-layer service classes to ATM cells.
　C. It adaptes Ethernet frames to ATM cells.
　D. It wraps a header around the ATM cell.

ATM supports many classes of service, but data from upper-layer protocols must be mapped to the 53-byte ATM cells For example, IP datagrams are encapsulated in an AAL5 frame, which is then encapsulated in individual ATM cells.

What are two main types of Ethernet frames?
　A. Thinnet and Thicknet
　B. 10baseT and 100baseT
　C. DIX Ethernet and Ethernet II
　D. 802.3 and Ethernet II

These are the two main types of Ethernet frames. The other answere are incorrect.

Which of the following values for the Ethertype/length fields indicates an 802.3 frame (numbers are in decimal)?
　A. 64
　B. 1540
　C. 2048
　D. 9000

A value less then 1536 indicates an 802.3 frame.

The original Thicknet standard had maximum cable length as well as a minimum distance for stations to tap into the cable.
Based on the description of CSMA/CD, what is the most likely reason for these distance requirements?
　A. A signal might be too weak to travel farther than the maximum distance.
　B. Every station on the wire had to be able to "detect" a collision in order to function properly.
　C. Too many taps in the cable would weaken the wire.
　D. Thicknet cable came in fixed lengths.

Based on our description of CSMA/CD, it is implied that each station needs to be able to determine when other stations are transmitting, which means that each station needs to be within a certain distance of other stations so that the electrical signals can reach it in no more than a fixed amount of time.

An Ethernet MAC address consists of .
　A. A 4-byte number in four parts
　B. A 4-byte number in two parts
　C. A 6-byte number in two parts
　D. A 6-byte number int four parts

The two parts are the vendor OUI and the vendor-chosen hardware address.

When an Ethernet station wants to transmit information, the process it follows is .
　A. Just start transmitting.
　B. Listen for other stations transmitting; if none, then begin transmitting.
　C. Transmit whenever it receives the token.
　D. Issue a transmit request, an transmit when given authorization to do so.

This is a brief description of the "carrier sence multiple access" part of the CSMA/CD protocol.

What happens when two or more Ethernet stations attempt to transmit at the same time?
　A. This is impossible on half-duplex.
　B. The signal results in a collision, the stations stop, and the stations all wait the same amount of time to retransmit.
　C. The signal results in a collision, and the stations retransmit based on a configured priority.
　D. The signal results in a collision, and the stations stop and retransmit after waiting a random amount of time.

This is a bief description of how Ethernet stations retransmit after collision. They wait a random amount of time to try to ensure that the same stations don't transmit at the same time again.

Which of the following Ethernet standards is not matched correctly?
　A. 10 Mb Ethernet -- Fiber or copper cable
　B. 100 Mb Ethernet -- Fiber or copper cable
　C. 1 Gig Ethernet -- Fiber cable only
　D. All of the above are correct.

Gigabit Ethernet can run over copper cabling as well.