Virtual Private Networks

It combines public and private network.
It is limited to single organization but they use public connection for connectivity.
These connections are sometimes called tunnels or connect sites.
Each site sees tunnel as point-to-point link.

Guaranteeing Absolute Privacy

VPNs packets are encrypted so if an outsider does gets the packets, they will not be able to interpret information inside it.

Service Paradigm

Each packet in a network needs to follow a format dictated by the hardware which is called interface paradigms or service paradigms
There are 2 types of it:

Connection Oriented Service

Similar to the telephone systems.
End points maintain the connection as long as they are communicating.

One end point requests to communicate and the other one grants the access.

Continuous and Burst Traffic

The connection does not disappear when data is not sent.
The connection for audio and video is designed continuous meanwhile other networks might use burst traffic

Simplex and Full Duplex Connection

Some connections are full duplex.
To establish a simplex connection between 2 computers, there needs to be 2 connections established.
one from computer A to B and other one from B to A.

Connection Duration and Persistence

There are 2 types:

Switched Virtual Circuit

Computer maintains permanent connection to the network and network makes connections on demand.

Permanent Switched Circuit

These are originally hard wired and now configured at system unit time.

Service Guarantees

Some connection-oriented networks might provide guarantees about the service that computer will receive.
These can be in form of: - Throughput rate - Maximum packet loss rate - ATM provides statistical guarantee about performance.

Stream of Message Interface

Some provides streams where there is no boundary over data chunk size such as 60 characters.
Others deliver message interface with same sized chunks.

Connectionless Service

Similar to postal system.
End points put data into packets which are sent to network for delivery.

Interior and Exterior Service Paradigm

Sometimes, the network can use entirely different paradigm externally and internally.
For example: ARPANET uses connection-oriented internally and connection-less externally