Anna University Coimbatore 2009 B.E Electronics

needed? How many ports are needed for every device?
Number of cables=n (n-1)/2=6(6-1)/2=15
Number of ports per device=n-1=6-1=5
11. Group the OSI layers by function.
The 7 layers of the OSI model belonging to 3 subgroups. Physical, data
link and network layers are the network support layers; they deal with the physical
aspects of moving data from 1 device to a different. Session, presentation and
application layers are the user support layers; they allow interoperability among
unrelated software systems. The transport layer ensures end-to-end reliable data
transmission.
12. elaborate header and trailers and how do they get added and removed?
every layer in the sending machine adds its own info to the message it
receives from the layer just above it and passes the whole package to the layer just
beneath it. This info is added in the form of headers or trailers. Headers are
added to the message at the layers 6,5,4,3, and 2. A trailer is added at layer2. At the
receiving machine, the headers or trailers attached to the data unit at the
corresponding sending layers are removed, and actions improper to that layer are
taken.
13. The transport layer creates a communication ranging from the source and
destination. elaborate the 3 events involved in a connection?
Creating a connection involves 3 steps: connection establishment, data
transfer and connection release.
14. What is the DC component?
Direct current is a zero-frequency signal with constant amplitude.
15. How does NRZ-L differ from NRZ-I?
In the NRZ-L sequence, positive and negative voltages have specific meanings:
positive for 0 and negative for 1. in the NRZ-I sequence, the voltages are
meaningless. Instead, the receiver looks for modifications from 1 level to a different as its
basis for recognition of 1s.
16. Using HDB3, encode the bit stream 10000000000100. presume the number of
1s so far is odd and the 1st one is positive.
17. elaborate the functions of a DTE? elaborate the functions of a DCE?
Amplitude
Time
1 0 0 0 0 0 0 0 0 0 0 one 0 0
Data terminal equipment is a device that is an info source or an
info sink. It is connected to a network through a DCE.
Data circuit-terminating equipment is a device used as an interface ranging from a DTE
and a network.
18. What does the electrical specification of EIA-232 describe?
The electrical specification of EIA-232 describes that signals other than data must

Earning:   Approval pending.