7705 SAR Interfaces
70
Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
3.2.1.2 Protocol Field (PID)
The protocol field is two octets. Its value identifies the datagram encapsulated in the
Information field of the packet. In the case of MP, the PID also identifies the presence
of a 4-octet MP header (or 2-octet, if negotiated).
A PID of 0x003d identifies the packet as MP data with an MP header.
The LCP packets and protocol states of the MLPPP session follow those defined by
PPP in RFC 1661. The options used during the LCP state for creating an MLPPP
NCP session are described in the sections that follow.
3.2.1.3 B&E Bits
The B&E bits are used to indicate the start and end of a packet. Ingress packets to
the MLPPP process will have an MTU, which may or may not be larger than the
maximum received reconstructed unit (MRRU) of the MLPPP network. The B&E bits
manage the fragmentation of ingress packets when the packet exceeds the MRRU.
The B-bit indicates the first (or beginning) packet of a given fragment. The E-bit
indicates the last (or ending) packet of a fragment. If there is no fragmentation of the
ingress packet, both B&E bits are set to true (=1).
3.2.1.4 Sequence Number
Sequence numbers can be either 12 or 24 bits long. The sequence number is 0 for
the first fragment on a newly constructed bundle and increments by one for each
fragment sent on that bundle. The receiver keeps track of the incoming sequence
numbers on each link in a bundle and reconstructs the desired unbundled flow
through processing of the received sequence numbers and B&E bits. For a detailed
description of the algorithm, refer to RFC 1990.
3.2.1.5 Information Field
The Information field is zero or more octets. The Information field contains the
datagram for the protocol specified in the protocol field.
The MRRU will have the same default value as the MTU for PPP. The MRRU is
always negotiated during LCP.
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