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*Keypoints:Know the above OSI model definitions backward and forward.Know that the OSI model was originally developed so different vendor networks could workwith each other.Know the 2 sublayers of the Data Link Layer and the function of each.Know that the Network Layer devices have 4 characteristics: 1) Two-part addresses, 2) Userouting tables, 3) Use broadcast addresses, and 4) provide path selection.Connection-oriented vs. Connectionless CommunicationConnection-orientated
Connection oriented communication is supported by TCP on port 6. It is reliable because a session is
guaranteed, and acknowledgements are issued and received at the transport layer. This is accomplished
via a process known as Positive Acknowledgement. When the sender transmits a packet a timer is set.
If the sender does not receive an acknowledgement before the timer expires, the packet is retransmitted.
Connection-oriented service involves three phases:
Call Setup
During the connection establishment phase, a single path between the source and destination systems is
determined. Network resources are typically reserved at this time to ensure a consistent grade of service
(such as a guaranteed throughput rate).
Data transfer
During the data transfer phase, data is transmitted sequentially over the path that has been established.
Data always arrives at the destination system in the order it was sent.
Call termination
During the connection termination phase, an established connection that is no longer needed is termi-
nated. Further communication between the source and destination systems requires a new connection to
be established.
Connection-oriented service has two significant disadvantages as compared to a connectionless net-
work service:
Static path selection
Because all traffic must travel along the same static path, a failure anywhere along the path causes the
connection to fail.