Anna University Coimbatore 2009 B.E Electronics

UNIT III
NETWORK LAYER
1. elaborate the network support layers and the user support layers?
Network support layers:
The network support layers are Physical layer, Data link layer and Network layer. These
deals with electrical specifications, physical connection, transport timing and reliability.
User support layers:
The user support layers are: Session layer, Presentation layer, Application layer. These
allow interoperability among unrelated software system.
2. With a neat diagram discuss the relationship of IEEE Project to the OSI model?
Other layers
Network
Data link
Physical
Other layers
Network
Logical Link Control
Media Access Control
Physical
The IEEE has subdivided the data link layer into 2 sub layers:
* Logical link control (LLC)
* Medium access control (MAC)
LLC is non-architecture specific. The MAC sub layer contains a number of
distinct modules, every carries proprietary info specific to the LAN product being
used.
3. elaborate the functions of LLC?
The IEEE project 802 models takes the structure of an HDLC frame and divides it
into two sets of functions. 1 set contains the end user portion of the HDLC frame - the
logical address, control information, and data. These functions are handled by the IEEE
802.2 logical link control (LLC) protocol.
4. elaborate the functions of MAC?
MAC sub layer resolves the contention for the shared media. It contains
synchronization, flag, flow and fault control specifications necessary to move
info from 1 place to another, as well as the physical address of the next station
to receive and route a packet.
5. What is protocol data unit?
The data unit in the LLC level is called Protocol Data Unit (PDU). It contains four
fields.
· Destination Service Point Address (DSAP)
· Source Service Access Point
· Control field
· info field
6. elaborate headers and trailers and how do they get added and removed?
The control data added to the beginning of a data is called headers. The control
data added to the end of a data is called trailers. At the sending machine, when the
message passes through the layers every layer adds the headers or trailers. At the receiving
machine, every layer removes the data meant for it and passes the rest to the next layer.
7. elaborate the responsibilities of network layer?
The network layer is responsible for the source-to-destination delivery of packet across
multiple network links. The specific responsibilities of network layer include the

Earning:   Approval pending.