- Recall that:
- In message/packet switching,
different message/packet
may traverse
a different path (route)
through the network...
Undesirable consequence:
- Because the nodes traversed
by the packets are not
determined a-priori:
- We cannot
make
resourse reservations
at the nodes along the path
(because the set of nodes can change)
(Resource reservations can provide guarantees on performance !!!)
- We cannot
make
resourse reservations
at the nodes along the path
- In message/packet switching,
different message/packet
may traverse
a different path (route)
through the network...
- Analogy:
- If I let my
GPS guide me
to my destination,
then:
- The GPS will be
able to re-route me
to the
fastest route to
get to my
destination
- However:
- I cannot make
any hotel reservation
beforehand !!!
(Because I may not pass by the hotel where I made the reservation !!!)
- I cannot make
any hotel reservation
beforehand !!!
- The GPS will be
able to re-route me
to the
fastest route to
get to my
destination
- If I let my
GPS guide me
to my destination,
then:
-
Queueing delay:
- A packet must
wait for its turn
to be transmitted:
- Queueing delay:
- Queueing delay of a packet =
the waiting time from:
- The time that
the packet arrives
at a switch,
until
- The time that the switch starts transmitting the packet
- The time that
the packet arrives
at a switch,
until
- Queueing delay of a packet =
the waiting time from:
- Important fact:
-
The queueing delay
can be several order of
magnitude (100x !!!) larger
that the
time needed
to transmit one packet:
-
The queueing delay
can be several order of
magnitude (100x !!!) larger
that the
time needed
to transmit one packet:
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