3.4 PPP Compression
3.4.3 PPP multilink
Multilink PPP provides load balancing over dialer interfaces-including ISDN, synchronous, and asynchronous interfaces. MLP can improve throughput and reduce latency between systems by splitting packets and sending the fragments over parallel circuits, as shown in the Figure. Prior to MLP, two or more ISDN B channels could not be used in a standardized way while ensuring sequencing. MLP is most effective when used with ISDN.

MLP solves several problems related to load balancing across multiple WAN links, including the following:

  • Multivendor interoperability (as specified by RFC 1990, which replaces RFC 1717)
  • Packet fragmentation, improving latency of each packet (supports RFC 1990 fragmentation and packet-sequencing specifications)
  • Packet sequence and load calculation

Multilink PPP Fragments

Multilink fragments are called packets (per RFC 1990, section 3, page 7, which states “individual fragments, which are the 'packets' in the Multilink Protocol.”).

This feature negotiates the Maximum Received Reconstructed Unit (MRRU) option during the PPP LCP negotiation to indicate to its peer that it can combine multiple physical links into a bundle.

Prior to the adoption of RFC 1990, there was no standardized way to use both of the B channels and ensure proper sequencing.

MLP is interoperable between Cisco routers running Cisco IOS software and Cisco 700 series routers, and with most routers that conform to RFC 1990.

Use MLP with applications in which bandwidth requirements are dynamic, such as remote LAN access applications for telecommuters or small office, home office (SOHO) environments.