Zte ZXR10 ZSR V2 Series Product Description page 21

link creation/maintenance/removal, upper-layer protocol negotiation, authentication, and
other functions.
PPP consists of LCP and NCP. It supports the point-to-point interface (such as
E1/T1/POS) link creation by negotiation and link maintenance, and provides a upper-layer
protocol packet with a packet encapsulation format different from Ethernet protocol.
A upper-layer protocol packet (such as IP packets and MPLS packet) is only
encapsulated with two bytes of protocol fields in the front, and is added with a PPP header
with two fixed values, namely, 0xFF03. The header can be removed through negotiation.
The PPP negotiation has three stages: LCP, authentication (optional) and NCP:

The authentication is optional and it is generally used for an access router to
authenticate an access user.

NCP consists of IPCP, IPv6CP, MPLSCP, OSINLCP and BCP. IPCP (supporting
IPv4) must make link negotiation and the rest is selected as needed. After successful
negotiation with IPCP, PPP port is set to UP.
Compared with the Ethernet encapsulation:

PPP has a higher bandwidth utilization ratio, which has a better effect on short packet.
And its header encapsulation is simpler, and complex Ethernet MAC header
encapsulation and decapsulation are removed from packet transceiving mechanism.

But PPP state machine is more complex than Ethernet because PPP interface is set
to UP only after successful negotiation and then the packet is received at the upper
layer.
The default protocol state of a PPP interface is down after creation, and it is UP after
successful PPP link negotiation. Both sides periodically send LCP keep-alive packets to
each other. If there is no ECHO response to continuous N (N>=1) keep-alive request
packets, the link is set to down and the protocol state is set to down to trigger route
recalculation and route update.
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ZXR10 ZSR V2 Series Router Product Description
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