Method and apparatus of multiplexing digital signal

A packet signal transmission system for transmitting a plurality of packets, comprising:

• at least M first transmission lines having a first transmission rate (A), wherein M is an integer;
• at least N first intermediate lines, each of said first intermediate lines having a transmission rate which is less than said first transmission rate (A), wherein N>M;
• first means connected to said first transmission lines for distributing input packets successively received from each of said first transmission lines to said first intermediate lines in accordance with an order of arrival of said input packets so that each of said first intermediate lines carries a packet stream which includes input packets received from said first transmission lines;
• and
• second means for multiplexing a plurality of packet streams received from said first intermediate lines to one of a plurality of second transmission lines so that each of said packet streams received from said intermediate lines is carried through time slots periodically defined on the one of said second transmission lines;
• said first and second means being constructed such that a transmission capacity (MXA) of said first transmission lines is equal to or smaller than a sum of transmission capacities of said second transmission lines.