Configuring Quality of Service Parameters
pvc 0/33
vbr-rt 320 320 30
tx-ring-limit 3
protocol ppp Virtual-Template1
!
interface Virtual-Template1
bandwidth 320
ip unnumbered Loopback1
ip mroute-cache
service-policy output 1751_ADSL
ppp multilink
ppp multilink fragment-delay 4
ppp multilink interleave
!
access-list 100 permit udp any any precedence critical
!
dial-peer voice 201 voip
destination-pattern 3640200
session target ipv4:10.0.0.11
ip qos dscp cs4 media
ip qos dscp cs4 signalling
MLP Bundling
Multilink PPP (MLP), standardized in RFC 1990, is similar to load balancing techniques in that it sends
packets across the individual links in a round-robin fashion. However, MLP adds three significant
capabilities:
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Additionally, when more bandwidth is needed, additional links can be added to the bundle by simply
configuring them as members of the bundle. No reconfiguration at the network layer, such as new
addressing, is needed. This is also a significant factor when considering the use of advanced router
services. For example, a specific QoS can be configured once for the bundle as a whole rather than on
each link in the bundle. The trade-off for the increased functionality is that MLP requires greater CPU
processing than load-balancing solutions. Packet reordering, fragment reassembly, and the MLP
protocol itself increase the CPU load.
Note
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•
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Configuring an ADSL WAN Interface Card on Cisco 1700 Series Routers
26
Because MLP works at the link layer, it makes an MLP bundle appear as one logical link to the upper
layer protocols in the router. Thus, only one network address needs to be configured for the entire
MLP bundle.
MLP keeps track of packet sequencing and buffers packets that arrive early. With this ability, MLP
preserves packet order across the entire MLP bundle.
Packet fragmentation can be enabled to split large data packets into smaller packet fragments that
are individually transmitted across the links. In many circumstances, fragmentation can increase the
efficiency of the MLP link.
The fragment delay on the multilink interface should be configured on the basis of the desired
maximum delay for interleaved packets. Interleaving is useful only at low bandwidths, usually
below 1 Mbps, and it is dependent on the link bandwidths, not the bundle bandwidth.
It is recommended that IP CEF be turned on. IP CEF will result in better performance and ease of
configuration.
Virtual template (VT) should be used (instead of dialer interface) when configuring either
authentication or dynamic address assignment for MLP with LFI.
OL-3317-03
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