642-813 Q&A – Prepare infrastructure to support advanced services (31-35)

Section4 – Prepare infrastructure to support advanced services

QUESTION NO: 31
What are three functions of the Cisco wireless LAN controller, which is being used in the Centralized WLAN solution network? (Select three)
A. Authentication
B. Mobility
C. Security management
D. Transmission of beacon frames
E. Real-time portions of MAC management
F. Real-time aspects of the 802.11 prtocol management
G. SNMP collection
Answer: ABC

Explanation:
In the Cisco Centralized Wireless LAN Architecture, access points operate in lightweight mode.
The access points associate to a Cisco wireless LAN controller. The controller manages the configuration, firmware, and control transactions such as 802.1x authentications. In addition, all wireless data traffic is tunneled through the controller.
The Lightweight Access Point Protocol (LWAPP) is an IETF draft protocol that defines the control messaging for setup and path authentication and run-time operations. LWAPP also defines the tunneling mechanism for data traffic.
A lightweight access point discovers a controller using LWAPP discovery mechanisms and then sends it an LWAPP join request. The controller sends the access point an LWAPP join response allowing the access point to join the controller. When the access point is joined to the controller, it downloads its software if the revisions on the access point and controller do not match.
Subsequently, the access point is completely under the control of the controller.
No lightweight access point can operate independently from a WLC, including those upgraded from an autonomous AP. Each lightweight access point must discover a WLC, issue an LWAPP join request, and if successful, receive a join response to become joined to a controller.

QUESTION NO: 32
Which two statements about voice traffic are true? (Choose two.)
A.Voice packets are typically around 60 to 120 bytes.
B.Voice packets are typically around 600 to 1200 bytes.
C.Voice packets are typically around 60 to 120 KB.
D.For voice quality, packet loss should be less than 1 percent and delay should be no more than 150 ms.
E.For voice quality, packet loss should be less than 2 percent and delay should be no more than 250 ms.
F.A typical voice call requires 17 kbps to 106 kbps of guaranteed priority bandwidth plus an additional 15 kbps per call for voice-control traffic.
Answer: A D
Explanation:
QoS Requirements for Voice:
Voice calls, either one-to-one or on a conference connection capability, require the following:
* <=150 ms of one-way latency from mouth to ear (per the ITU G.114 standard)
* <= 30 ms jitter
* <= 1 percent packet loss
* Voice packets are typically small (60 to 120 bytes)
* 17 to 106 kbps of guaranteed priority bandwidth per call (depending on the sampling rate, codec, and Layer 2 overhead)
* 150 bps (plus Layer 2 overhead) (not 15 kbps) per phone of guaranteed bandwidth for voice control traffic
The choice of codec has impacts in many areas. The most important is the capacity planning on the network, because the bandwidth consumed in different codecs varies.

QUESTION NO: 33
Network topology exhibit:

What are three requirements for configuring Cisco Aironet access points (APs) in a WLAN network which will allow for all wireless clients to work without service interruption while roaming from access point to access point? (Choose three.)
A. All access points should be configured with a unique IP subnet range.
B. All access points should be configured with the same guest mode SSID.
C. All access points should be configured with identical VLANs.
D. All access points should be configured within the same IP subnet.
E. All access points should be configured with identical SSIDs.
F. All access points should be configured only with the native VLAN.
Answer: C,D,E

QUESTION NO: 34
You work as a network technician at Company.com. Please study the exhibit carefully. In this Company wireless network, the LAP (lightweight access point) attempts to register to a WLC (Wireless LAN Controller). What kind of message is transmitted?

A. The lightweight access point will send Layer 2 and Layer 3 Lightweight Access Point (LWAPP) mode discovery request messages at the same time.
B. The lightweight access point will send Layer 3 Lightweight Access Point (LWAPP) mode discovery request messages only.
C. The lightweight access point will send Layer 2 Lightweight Access Point (LWAPP) mode discovery request messages. If the attempt fails, the LAP will try Layer 3 LWAPP WLC discovery.
D. The lightweight access point will send Layer 2 Lightweight Access Point (LWAPP) mode discovery request messages only.
Answer: C
Explanation:
This procedure for a LAP to register with a WLC is: The LAP issues a DHCP request to a DHCP server in order to get an IP address, unless an assignment was made previously with a static IP address. If Layer 2 LWAPP mode is supported on the LAP, the LAP broadcasts an LWAPP discovery message in a Layer 2 LWAPP frame. Any WLC that is connected to the network and that is configured for Layer 2 LWAPP mode responds with a Layer 2 discovery response. If the LAP does not support Layer 2 mode, or if the WLC or the LAP fails to receive an LWAPP discovery response to the Layer 2 LWAPP discovery message broadcast, the LAP proceeds to step 3. If step 1 fails, or if the LAP or the WLC does not support Layer 2 LWAPP mode, the LAP attempts a Layer 3 LWAPP WLC discovery. If step 3 fails, the LAP resets and returns to step 1.

QUESTION NO: 35
Which issue or set of issues does the Lightweight Access Point Protocol (LWAPP) address?
A. Reduction of processing in wireless controllers
B. Distributed approach to authentication, encryption, and policy enforcement
C. Access point discovery, information exchange, and configuration
D. Provides security by blocking communication between access points and wireless clients
Answer: C