Overview of LFI in MLPPP
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Alcatel-Lucent
Beta Beta
OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
OVERVIEW OF LFI IN MLPPP
Multilink is negotiated during the initial LCP option negotiation. It permits a system
to indicate to its peer that it is capable of combining multiple physical links into a
"bundle". A system indicates to its peer that it is willing to do multilink by sending
the multilink option as part of the initial LCP option negotiation. Refer to RFC 1990
for further details.
Fragments are created on the MLPPP link based on the ‘fragment delay’
configured on the MLPPP bundle interface. The fragment size is calculated based
on the fragment delay value and the link speed. Hence, fragment size could be
different for different links on the same MLPPP bundle based on different link
speeds.
To interleave the voice packets and data fragments, QoS policy must be
configured on the MLPPP bundle. This will make sure that the same QoS policy is
applied to all the link interfaces in the MLPPP bundle and hence similar treatment
is done to packets irrespective of which link eventually it passes through.
Slippage on multilink interface allows configuration of buffer in terms of MRU,
which represent number of fragments to be stored without getting reassembled.
The default value will be 32 MRU size packets to be stored. The range will be 16-
256 MRU worth of data.
PACKET FORMATS
Network Protocol packets are first encapsulated according to the normal PPP
procedures (2 bytes of Protocol ID of the Network Protocol being carried through
PPP), and large packets are broken up into multiple segments sized appropriately
(based on serialization delay configured). Sender must not include the Address
and Control Field (2 bytes) in the logical entity to be fragmented. A new PPP
header consisting of the Multilink Protocol Identifier, and the Multilink header is
inserted before each section. (Thus the first fragment of a multilink packet in PPP
will have two headers, one for the fragment, followed by the header for the packet
itself containing the Network Protocol ID).
PPP multilink fragments are encapsulated using the protocol identifier 0x00-0x3d.
Following the protocol identifier is a four byte header containing a sequence
number, and two one bit fields indicating that the fragment begins a packet or
terminates a packet.
Individual fragments by default will have long sequence number, therefore, have
the following format:
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