CLCOR Protocols And Endpoints — 15 Questions

Question 1

You are configuring a G.729 codec for a WAN link. To ensure that the voice quality remains acceptable while minimizing bandwidth, which feature must be enabled to prevent excessive packet overhead?

Accepted Answer

Payload size adjustment. VAD (Voice Activity Detection) suppresses silence, saving bandwidth, but is often recommended to be disabled if voice quality is the primary concern, or enabled to conserve bandwidth.

Answer

DSCP marking

Answer

Jitter buffer sizing

Answer

RTCP feedback

Question 2

A SIP endpoint is behind a NAT device. The endpoint registers successfully, but audio is one-way. What feature should be enabled on the SIP Profile to handle this issue?

Accepted Answer

Media Termination Point (MTP) Required. The 'SIP Rel1XX' or 'SIP OPTIONS Ping' are common, but 'NAT Support' or 'SIP Privacy' settings are often required. Specifically, 'SIP Profile' configuration to support NAT traversal (media termination point usage) is key.

Answer

SIP OPTIONS Ping

Answer

Disable DTMF Relay

Answer

Enable Early Media

Question 3

Which TWO parameters are defined within a SIP Profile in CUCM?

Accepted Answer

MTP required flag. SIP timers and feature flags (like MTP requirements) are defined here.

Answer

Device Pool

Answer

Location bandwidth

Answer

Codec Preference

Question 4

A Webex Desk Pro is failing to provision via the Cisco Webex Control Hub. The device displays 'Provisioning Error'. Which configuration component is primarily responsible for holding the authentication credentials required for the device to pull its configuration?

Accepted Answer

Activation Code. The Activation Code or the specific Device Configuration profile in Control Hub provides the credentials needed for the device to authenticate against the cloud service.

Answer

TFTP Address

Answer

SIP Digest User

Answer

VLAN ID

Question 5

An endpoint sends a SIP REGISTER request. CUCM returns a 401 Unauthorized response. What is the next logical step in the SIP signaling flow for the endpoint?

Accepted Answer

Resend REGISTER with Authorization header. The 401 response challenges the endpoint to provide credentials (Digest authentication). The endpoint must resend the REGISTER request with the Authorization header.

Answer

Switch to SCCP

Answer

Terminate the TCP connection

Answer

Send a SIP INVITE

Question 6

When configuring an IP phone for automatic provisioning, which DHCP option is most commonly used to provide the TFTP server address to the phone?

Accepted Answer

Option 150. DHCP Option 150 is the standard method for Cisco IP Phones to discover the TFTP server address.

Answer

Option 43

Answer

Option 66

Answer

Option 12

Question 7

An endpoint using the Opus codec is experiencing one-way audio. The SDP exchange indicates that the endpoint is offering a wideband range. Where in CUCM would you modify the Region settings to force the use of a specific codec for this endpoint?

Accepted Answer

Region Settings. The Region settings in CUCM define the maximum audio bit rate between regions; the codec is chosen based on these region constraints.

Answer

Service Parameters

Answer

Device Pool

Answer

SIP Profile

Question 8

A Cisco IP Phone 8841 is failing to register to Cisco Unified Communications Manager. You check the phone settings and see the TFTP server address is correct. Which protocol and port should you monitor on the gateway or firewall to verify the initial registration attempt?

Accepted Answer

SIP UDP 5060. SIP registration uses UDP or TCP port 5060 for non-secure, or TLS port 5061 for secure registration.

Answer

SCCP 2000

Answer

TFTP 69

Answer

HTTP 8080

Question 9

You are troubleshooting a scenario where G.711 is being used instead of the expected Opus codec between two endpoints in the same region. What is the most likely cause in the CUCM configuration?

Accepted Answer

Audio Codec Preference List. If the 'Audio Codec Preference List' or the 'Region' setting does not include Opus as a supported codec, CUCM will fall back to G.711.

Answer

Phone NTP settings

Answer

SIP Trunk Security Profile mismatch

Answer

Location-based bandwidth limit

Question 10

You need to verify that an endpoint is correctly sending RTCP reports to Cisco Unified Communications Manager. Which field in the RTCP packet header would you examine to track the jitter statistics?

Accepted Answer

Interarrival Jitter. RTCP SR (Sender Report) and RR (Receiver Report) packets contain interarrival jitter fields to help calculate network quality.

Answer

Sequence Number

Answer

SSRC

Answer

Timestamp

Question 11

Which protocol is primarily used for the transmission of real-time voice and video data between two endpoints?

Accepted Answer

RTP. RTP (Real-time Transport Protocol) is the standard for media transport.

Answer

SCCP

Answer

TFTP

Answer

SIP

Question 12

You are monitoring RTP traffic using a protocol analyzer. You observe that the Payload Type field in the RTP header is set to 0. Which codec is currently in use?

Accepted Answer

G.711 PCMU. In G.711 PCMU (u-law), the assigned payload type is 0 according to RFC 3551.

Answer

G.729

Answer

Opus

Answer

G.711 PCMA

Question 13

You are troubleshooting intermittent audio quality. You notice that RTCP packets are arriving with high variance. What does this indicate?

Accepted Answer

Jitter. Intermittent audio quality and high variance in RTCP reports point directly to network jitter.

Answer

Latency

Answer

Codec Mismatch

Answer

Packet Loss

Question 14

Which component in the Cisco Collaboration architecture provides the initial configuration files (XML) to an IP phone upon registration?

Accepted Answer

TFTP Service. The TFTP service in CUCM acts as the repository for device configuration files.

Answer

CallManager Service

Answer

CTI Manager

Answer

Webex Control Hub

Question 15

You need to support Opus codec on a Cisco IP Phone 8865. Which configuration object must be updated to allow this codec?

Accepted Answer

Audio Codec Preference List. The 'Common Phone Profile' or 'SIP Profile' doesn't contain codec lists; the 'Audio Codec Preference List' must be modified and applied to the device or the region/location configuration.

Answer

SIP Profile

Answer

Common Phone Profile

Answer

Device Defaults