Chapter 7
1.
Define
the following parameters for a switching network:
· N: number of hops between two given stations
·L: message
length, in bits
·B: data
rate, in bps, on all links
·P: packet
size, in bits
·H: overhead
(header), in bits per packet
·S: call
setup time (circuit-switched or virtual circuit), in seconds
·D:
propagation delay per hop, in seconds
Compute the end-to-end delay for circuit switching,
virtual circuit packet switching, and datagram packet switching. Assume that
there is no node delay.
2.
Consider
a packet-switched network of N nodes,
connected by the following topologies:
a. Star:
one central node with no attached station; all other nodes attach to the
central
node.
For each case, give the average number of hops
between stations.
Answer:
c. One hop
3.
Flow
control mechanisms are used at both levels 2 and 3 of X.25. Are both necessary,
Or is this redundant? Explain.
Layer 2 flow
control regulates total flow of data between DTE and DCE.
Layer 3 flow
control regulates flow over a single virtual circuit.
4.
In
X.25, the virtual-circuit number used by one station of two communicating
stations
Is different from the virtual-circuit number used by
the other station. Why would this
Be so? After all, it is the same full-duplex virtual
circuit.
The
virtual circuit number only had local significance (no global management of
Numbers).