{HEAD ~ A method} of implementing a storage function in a passive optical network system 1, further including a groupcast LINK ID allocation step; in said optical line terminal, allocating a groupcast LINK ID to data requiring storage; and sending said data requiring storage with {TAIL ~ a broadcast method} to all the optical network units 
{ HEAD ~ A method } of implementing a storage function in a passive optical network system 1 , further including a groupcast LINK ID allocation step ; in said optical line terminal , allocating a groupcast LINK ID to data requiring storage ; and sending said data requiring storage with { TAIL ~ a broadcast method } to all the optical network units
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