Multi-Link Point-to-Point Protocol

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The Multi-Link Point-to-Point Protocol (MLPPP) is a variation on the Point-to-Point Protocol (PPP) that makes it possible to deploy multiple Physical Layer connections and have them perceived as a single Data Link Layer connection by the upper layer protocols. Also known as PPP Multilink, MLPPP is typically used as a bandwidth-on-demand technique.

MLPPP implements a form of inverse multiplexing, also known as link aggregation. It is most commonly found with dial-up connections. For example, a user could dial up two POTS or ISDN connections and then use MLPPP to inverse multiplex them into a single, higher-speed connection. This requires that both devices be capable of engaging the multilink version of PPP. Although it was originally intended to be used over dial-up connections (specifically ISDN), it can now be implemented using any underlying network fabric that supports a PPP connection (e.g., PPPoE, PPPoA, leased lines with PPP, etc.).

MLPPP is defined in | RFC 1990, which updates and obsoletes | RFC 1717. (PPP Multilink Protocol, August 1996). It is supported by MS Windows, Linux, and most Unix systems, as well as most routers on the market.

The multilink capability is based on the negotiation of a Link Control Protocol (LCP) option that makes it possible for one device to signal to a second device, with which it is attempting to establish a PPP connection, that it is capable of combining multiple individual links into an inverse multiplexed "bundle". The negotiation occurs at the start of the LCP exchange, and the transmission of the multilink option implies three things about the transmitter:

  • It is capable of supporting a multilink, also known as a bundle;
  • It is capable of receiving upper layer protocol data units (PDU) that have been fragmented using the multilink header and of reassembling the fragmented protocols into the original PDU;
  • It is capable of receiving PDUs up to a specified size, even if that size is larger than the maximum receive unit (MRU) for any of the individual links.

PodSnacks

<mp3>http://podcast.hill-vt.com/podsnacks/2007q3/mlppp-bonding.mp3%7Cdownload</mp3> | Multilink PPP