352-011 · Question #66
The enterprise customer ABC Corp will deploy a centralized unified communications application to provide voice, and instant messaging to their branch offices. Some of the branch offices are located…
B (VAD) and F (G.729) are the correct answers. Both are zero-cost configuration changes that directly address bandwidth constraints on the 1.5 Mb/s WAN link. G.729 uses only 8 kbps per call versus G.711's 64 kbps - an 8x reduction - making it ideal for bandwidth-limited remote…
Question
The enterprise customer ABC Corp will deploy a centralized unified communications application to provide voice, and instant messaging to their branch offices. Some of the branch offices are located in remote locations and are connected via a 1.5 Mb/s Layer 3 VPN connection. Which two ways are the most cost-effective to ensure that this new application is implemented properly? (Choose two)
Options
- AUse a low bitrate codec such as G 711
- BSet voice activity detection to avoid sending packets when the conversations is silent
- CEnable VRF-Lite on the CE router to create a separate voice VRF
- DSet LFI on the WAN connections to interleave the small voice packets with the large data packets
- ESet WAN optimization on the CE router to compress the voice packets for improved bandwidth
- FUse a low bitrate codec such as G 729
Explanation
B (VAD) and F (G.729) are the correct answers.
Both are zero-cost configuration changes that directly address bandwidth constraints on the 1.5 Mb/s WAN link. G.729 uses only 8 kbps per call versus G.711's 64 kbps - an 8x reduction - making it ideal for bandwidth-limited remote sites. Voice Activity Detection (VAD) compounds those savings by suppressing packet transmission during silence, which accounts for roughly 50–60% of a typical conversation.
Why the distractors are wrong:
- A (G.711) - G.711 is a high-bitrate codec at 64 kbps; the question stem even labels it "low bitrate," which is incorrect and a trap.
- C (VRF-Lite) - Creates routing isolation between VPNs but does nothing to reduce bandwidth consumption; it's a Layer 3 segmentation tool, not a QoS or bandwidth solution.
- D (LFI) - Link Fragmentation and Interleaving reduces serialization delay on slow links by interleaving small voice packets between fragmented data packets, but it doesn't save bandwidth and is not the most cost-effective fit when the core problem is capacity.
- E (WAN optimization/compression) - Voice codecs like G.729 produce compressed, low-entropy payloads that yield negligible gains from further compression; WAN optimization appliances also add hardware/license cost.
Memory tip: Think "Squeeze and Silence" - G.729 squeezes the bitrate (8 kbps), and VAD handles the silence. Together they're the cheapest, purest software fixes for a constrained WAN link.
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