4.1 PPP
4.1.3 PPP layer functions
PPP uses a layered architecture, as shown in the Figure. With its lower-level functions, PPP can use:
  • Synchronous physical media, such as those that connect Integrated Services Digital Network (ISDN) networks.
  • Asynchronous physical media, such as those that use basic telephone service for modem dialup connections.

With its higher-level functions, PPP supports or encapsulates several network-layer protocols with NCPs. These higher-layer protocols include the following:

  • BCP -- Bridge Control Protocol 
  • IPCP -- Internet Protocol Control Protocol 
  • IPXCP -- Internetwork Packet Exchange Control Protocol

These are functional fields containing standardized codes to indicate the network-layer protocol type that PPP encapsulates. 

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