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 {HEAD ~ a broadcast method} to {TAIL ~ all the optical network units} 
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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 { HEAD ~ a broadcast method } to { TAIL ~ all the optical network units }
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