350-001 · Question #120
An expanding company is deploying leased lines between its main site and two remote sites. The bandwidth of the leased lines is 128kb/s each, terminated on different serial interfaces on the main…
The correct answer is D. enable Layer 2 fragmentation and interleaving on the links. On low-speed serial links (128 kbps), the root cause of this problem is serialization delay - the time required to place an entire packet onto the wire. A large data packet (e.g., 1500-byte MTU) takes approximately 94 ms to serialize at 128 kbps, which far exceeds the 150 ms…
Question
An expanding company is deploying leased lines between its main site and two remote sites. The bandwidth of the leased lines is 128kb/s each, terminated on different serial interfaces on the main router. These links are used for combined VOIP and data traffic. The network administrator has implemented a VOIP solution to reduce costs, and has therefore reserved sufficient bandwidth in a low latency queue on each interface for the VOIP traffic. Users now complain about bad voice quality although no drops are observed in the low latency queue. What action will likely fix this problem?
Options
- Amark VOIP traffic with IP precedence 6 and configure only 'fair-queue' on the links
- Bconfigure the scheduler allocate 3000 1000 command to allow the QoS code to have enough CPU
- Cenable class-based traffic shaping on the VoIP traffic class
- Denable Layer 2 fragmentation and interleaving on the links
- Eenable Frame Relay on the links and send voice and data on different Frame Relay PVCs
How the community answered
(52 responses)- A4% (2)
- B2% (1)
- C8% (4)
- D67% (35)
- E19% (10)
Explanation
On low-speed serial links (128 kbps), the root cause of this problem is serialization delay - the time required to place an entire packet onto the wire. A large data packet (e.g., 1500-byte MTU) takes approximately 94 ms to serialize at 128 kbps, which far exceeds the 150 ms one-way delay budget for VoIP. Even though the LLQ (Low Latency Queue) has reserved bandwidth, a VoIP packet arriving while a large data packet is already being serialized must wait for that transmission to finish. Link Fragmentation and Interleaving (LFI) solves this by breaking large data packets into smaller fragments and interleaving VoIP packets between those fragments, dramatically reducing the maximum serialization delay experienced by voice traffic.
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