Connection-Oriented Vs. Connectionless services (Pros & Cons) & (Design Issue)

Connection-Oriented Services

  In short connection-oriented service is one that sets a connection between communication entities before any data communication is commenced.  A connection-oriented service is a technique used to transport data at the session layers, connection-oriented service requires a connection to be established between the sender and the receiver before any real data is transferred.  This handles real-time traffic efficiently than connectionless protocols because data is received by the receiver in the same order it was sent. Asynchronous Transfer Mode (ATM) is a connection-oriented service.

Connectionless Services

As the name suggests, a connectionless service is a type of service that does not require the connection to be established between the sender and the receiver.  We can think of connectionless service as a postal service because we do not require any connection to established before we mail anything.  Technically, a connectionless service is data communication between two nodes where the sender sends data without making sure whether the receiver is ready to receive data or not. The data sent over connectionless service may travel through different routes to reach the final destination.  Each data packet has the destination address and the data packet is routed independently irrespective of the other packets. The data packet in connectionless service is usually called datagrams.

Comparison of advantages and disadvantages.

Advantages of Connection-Oriented Service

  • Connection-Oriented is reliable service:

A good example of a connection-oriented service is a telephone system. Connection-Oriented Service is reliable because there is no or very little chance of data loss. Connection-Oriented service can be used for long and steady communication.

  • The sequencing of data packets is guaranteed.

In connection-Oriented Service, Packets follows the same route, so there is a guarantee of data packets sequencing.  The receiver is guaranteed to receive the data in perfect condition. Since the data sent via connection-oriented service is reliable and the sequencing of data packets is guaranteed, this service is preferred for long and steady communication. 

  • Problems of duplicate data packets are alleviated.

Since the connection-oriented service follows one route to transfer data for the entire period of connection there is very less, or no chance of data packets being duplicated. On the other hand, data congestions are less frequent.

Advantages of Connectionless Services

  • It is useful for broadcast and multicast.

When I mean multicast, I meant the capability to send data to multiuser at a given time. Since the connectionless service does not require the end to end connection to be established it enables the power to send messages to multiple recipients.

  • Communication is not disrupted

If the router fails due to unforeseen circumstances or congestion occurs the data packets are routed through the alternative route, which helps to protect the sent data packets and it makes sure that the data is delivered. 

  • Quick Connection

As we know that the connection-oriented services require the connection to be established before any data can be sent. It takes time to establish a connection, but in the case of connectionless service, it does not require any time for circuit setup.  It doesn’t matter if the connection is made or not, we can send data at any given time. So, it is quick.

Disadvantages of Connection-Oriented Service

  • Low Bandwidth.

Since it takes time to establish the connection and relinquish the connection the data transfer speed is less. 

  • No alternative ways to continue communication.

If the network congestions occur or router fails due to some issue there are no alternative ways to continue communication because connection-oriented service only follows one route for data transfer. 

  • Resource allocation is needed before communication. This often leads to under-utilized network resources

Disadvantages of Connectionless Service

  • It is not a reliable connection

Take a postal system as an example of a connectionless service. We are never sure if the information we sent will reach the right recipient. In connectionless service, there is a high chance of data being lost, wrong delivery or out-of-sequence delivery, which makes the connectionless service non-reliable.

  • The sequencing of data is not guaranteed.

Connectionless service uses multiple routes to transfer a single data so we cannot be sure if the data received by the receiver is properly sequenced. Sometimes it results in the duplication of the data packets.

  • Each data packet requires longer data fields since it should hold all the destination address and the routing information.  Connectionless service is a port to network congestion.

Comparison of the design issues

  • Reliability: From our above observation we can say that the Connection-oriented service is reliable in terms of data transfer and security. Connectionless service is not reliable because there might be a loss of data packets. Although the connection-oriented service looks reliable in many aspects, in my personal opinion connectionless is more reliable than connection-oriented.  If we look into the setup of connection-oriented service, the cost of the connection is way more expensive than the connectionless, it is time-consuming.  The connectionless service is cheap and is less time-consuming.
  • Error Control: Many errors might occur in the design of the service. The service should be designed in such a way that it’s capable of handling most of the errors by itself. Connectionless service has error control technology available in comparison to connection-oriented service.  For example, take the data routing technology in connectionless service, this technology makes sure that the sent data is delivered to the recipient even in case of failure of routers. Connection-oriented service does not offer this technology.  Many error detecting and error-correcting codes can be found for connectionless service.
  • Flow Control: The connection should be developed in such a way that each user can receive data no matter at what rate the data is transferred.  If a sender sends data at high speed and the receiver has lower speed, there must be a mechanism to control the speed at which data is received at the receiver ends and that mechanism should be capable of protecting the loss of data.

Other issues to consider are

  1. Routing / Addressing
  2. Scalability
  3. Security

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