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 UWA week 13 (1st semester, week 5) ↓
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1:21pm Tue 26th Mar, ANONYMOUS

In the slotted aloha, if a node is looking to retransmit message, does it not consider any new messages it may have to send while trying to retransmit? More specifically, each node has chance to transmit a new message, if a node is trying to retransmit will its chance to transmit new message be 0% as its focusing on retransmitting, or do we have to develop a queue of pending messages for each node?


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2:43pm Tue 26th Mar, Christopher M.

ANONYMOUS wrote:
> In the slotted aloha, if a node is looking to retransmit message, does it not consider any new messages it may have to send while trying to retransmit? > > More specifically, each node has chance to transmit a new message, if a node is trying to retransmit will its chance to transmit new message be 0% as its focusing on retransmitting, or do we have to develop a queue of pending messages for each node?
We've been discussing Aloha in the context of the data-link layer, with the DLL needing to successfully transmit one frame before beginning the process for the *next* one. We should complete the re-transmission, before starting a new transmission (else the carried messages would arrive out-of-order).


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2:57pm Tue 26th Mar, ANONYMOUS

What I meant is that the parameter is [the probability that a node has a new frame for transmission], if a specific node is already trying to retransmit, do we ignore any new frames for that node. As in context, I believe a node may be able to get a new frame it needs to transmit while it is still attempting to retransmit an older frame that has collided. Or am i missing something?


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3:09pm Wed 27th Mar, Christopher M.

ANONYMOUS wrote:
> What I meant is that the parameter is [the probability that a node has a new frame for transmission], if a specific node is already trying to retransmit, do we ignore any new frames for that node.
You don't *ignore* the new frames from that node, your DLL simply des not accept them from the layer above until the older frame has been successfully transmitted.
> As in context, I believe a node may be able to get a new frame it needs to transmit while it is still attempting to retransmit an older frame that has collided.
(although we're not coding this question in any language), but in cnet if the DLL implements a stop-and-wait protocol, we temporarily disable the AL so that it won't inform us of any new frames for delivery. Then re-enable it when the older frame has gone and been acknowledged.

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