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?
A.
Mark VOIP traffic with IP precedence 6 and configure only fair-queue’ on the links
B.
Configure the scheduler allocate 3000 1000 command to allow the OoS code to have enough
CPU cycles
C.
Enable class-based traffic shaping on the VOIP traffic class
D.
Enable Layer 2 fragmentation and interleaving on the links
E.
Enable Frame Relay on the links and send voice and data on different Frame Relay PVCs
Explanation:
Link Fragmentation and Interleaving
Link fragmentation and interleaving (LFI) is a Layer 2 technique in which all Layer 2 frames are
broken into small, equal-size fragments, and transmitted over the link in an interleaved fashion.
When fragmentation and interleaving are in effect, the network device fragments all frames waiting
in the queuing system where it prioritizes smaller frames. Then, the network device sends the
fragments over the link. Small frames may be scheduled behind larger frames in the WFQ system.
LFI fragments all frames, which reduces the queuing delay of small frames because they are sent
almost immediately. Link fragmentation reduces delay and jitter by normalizing packet sizes of
larger packets in order to offer more regular transmission opportunities to the voice packets.
The following LFI mechanisms are implemented in Cisco IOS:
Multilink PPP with interleaving is by far the most common and widely used form of LFI.
FRF.11 Annex C LFI is used with Voice over Frame Relay (VoFR).
FRF.12 Frame Relay LFI is used with Frame Relay data connections.
Interleaving for Multilink PPP Configuration Task List
To configure MLP, perform the tasks described in the following sections. The task in the first
section is required; the task in the remaining section is optional.
• Configuring MLP Interleaving (Required)
• Displaying Interleaving Statistics (Optional)
• Monitoring PPP and MLP Interfaces (Optional)
Configuring MLP Interleaving
MLP support for interleaving can be configured on virtual templates, dialer interfaces, and ISDN
BRI or PRI interfaces. To configure interleaving, perform the following steps:
Step 1 Configure the dialer interface, BRI interface, PRI interface, or virtual interface template, as
defined in the relevant Cisco IOS documents, Step 2 Configure MLP and interleaving on the
interface or template.
Note Fair queueing, which is enabled by default, must remain enabled on the interface.
To configure MLP and interleaving on a configured and operational interface or virtual interface
template, use the following commands in interface configuration mode:
Monitoring PPP and MLP Interfaces To monitor virtual interfaces, use the following command in
EXEC mode:http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcflfi.html#wp1000892