RFC 1717 (rfc1717) - Page 2 of 21

The PPP Multilink Protocol (MP)

RFC 1717                     PPP Multilink                 November 1994


   4. Trading Buffer Space Against Fragment Loss ..................    9
   4.1. Detecting Fragment Loss ...................................   10
   4.2. Buffer Space Requirements .................................   11
   5. PPP Link Control Protocol Extensions ........................   12
   5.1. Configuration Option Types ................................   12
   5.1.1. Multilink MRRU LCP option ...............................   13
   5.1.2. Short Sequence Number Header Format Option ..............   13
   5.1.3. Endpoint Discriminator Option ...........................   14
   6. Closing Member links ........................................   18
   7. Interaction with Other Protocols ............................   19
   8. Security Considerations .....................................   19
   9. References ..................................................   20
   10. Authors' Addresses .........................................   21

1.  Introduction

1.1.  Motivation

   Basic Rate and Primary Rate ISDN both offer the possibility of
   opening multiple simultaneous channels between systems, giving users
   additional bandwidth on demand (for additional cost).  Previous
   proposals for the transmission of internet protocols over ISDN have
   stated as a goal the ability to make use of this capability, (e.g.,
   Leifer et al., [1]).

   There are proposals being advanced for providing synchronization
   between multiple streams at the bit level (the BONDING proposals);
   such features are not as yet widely deployed, and may require
   additional hardware for end system.  Thus, it may be useful to have a
   purely software solution, or at least an interim measure.

   There are other instances where bandwidth on demand can be exploited,
   such as using a dialup async line at 28,800 baud to back up a leased
   synchronous line, or opening additional X.25 SVCs where the window
   size is limited to two by international agreement.

   The simplest possible algorithms of alternating packets between
   channels on a space available basis (which might be called the Bank
   Teller's algorithm) may have undesirable side effects due to
   reordering of packets.

   By means of a four-byte sequencing header, and simple synchronization
   rules, one can split packets among parallel virtual circuits between
   systems in such a way that packets do not become reordered, or at
   least the likelihood of this is greatly reduced.






Sklower, Lloyd, McGregor & Carr