- Connection-oriented protocols also known as session-based protocols, virtual circuits or sequenced packet exchanges – provide a reliable two-way connection service over a session.
- Each packet of information gets exchanged over a session.
- Duplicate packets are detected and discarded by the session services.
- Overhead associated with creating and managing the session. If a session is lost, one of the parties must reestablish it.
- This can be a problem for fault-tolerant servers that require automatic switch overs to a backup server if the primary server fails.
- The backup server needs to reestablish all the outstanding sessions with clients.
- Datagrams also known as connectionless protocols or transmits and pray protocols provide a simple but unreliable form of exchange.
- The more powerful datagram protocols such as NetBIOS provide broadcast capabilities.
- NetBIOS allows you to send datagrams to a named entity, to a select group of entities (multicast), or to all entities on a network (broadcast).
- Datagrams are unreliable in the sense that they are not acknowledged or tracked through a sequence number.
- Some stacks (ex: LAN Server’s MailSlots) provide an acknowledged datagram service.
- Datagrams are very useful to have in “discovery” types of situations. These are situations where you discover things about your network environment by broadcasting queries and learning who is out there from the response.
- Broadcast can be used to obtain bids for services or to advertise the avilability of new services.
- Broadcast datagrams provide the capability of creating electronic “bazaars”
- The alternative to broadcast is to use a network directory service.
- Datagrams are also very useful in situations where there is a need to send a quick message (or) important message.
- Ex: All the systems have to send the “I am alive” message periodically to the network manager.
- The ordinary method may need 500 sessions for each computer in the network and not possible.
- Instead the system can broadcast the datagram to the manager.
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