This International Standard specifies multilink procedures where a multiplicity of parallel data links at the data link layer are used to provide a variable bandwidth data link between network layer entities. The multilink procedures (MLP) exist as a new upper sublayer of the data link layer, operating between the network layer and a multiplicity of single data link protocol functions (SLPs) in the data link layer (see figure 1).
This International Standard does not specify the way in which the SLPs indicate to the MLP that the transmission of a multilink frame has successfully been completed.
These multilink procedures do not preclude the use of different single link procedures, each with differing delay characteristics and/or line speeds to form one multilink group.
When the procedures defined by this International Standard are to be used on one or more parallel data links, both ends of the data link must know that these procedures are to be used before the first multilink frame is sent. This could be achieved by a prior agreement that all communications on this data link will use these procedures, or by one of the SLPs negotiating the use of these procedures, or by some other means. The method by which both ends achieve a common understanding as to the use or non-use of these multilink procedures is not defined in this International Standard.