Similarities between Computer Networks and Postal Networks

While computer networks and postal networks have some differences, they have a lot of things in common, especially the basic principles of operation.

As we already know, computer networks use the principles of packet switching and next hop routing to achieve communication between remote computers.

Before comparing and contrasting computer and postal networks, a brief overview of the theory of operation of a postal network is given below. In postal networks,

• Communication happens in the form of short letters
• Letter is put inside an envelope
• Recipient and Sender address are written on envelope
• Envelope is then handed over to the postal department by posting it inside a post box
• Postal Department takes responsibility of letter delivery from sender to recipient
• Each letter is independently handled by postal department based on its address information
• Each post office has a routing table
• Routing table is consulted for routing an envelope to its destination
• Each post office passes on an envelope to one of its directly connected neighbors which it thinks is closer to the destination than itself
• Envelope is thus taken hop by hop by different post offices, closer and closer to the destination till it reaches destination
• Each hop is usually connected to its neighboring hop through either road, railway track, sea or air transport modes
• An envelope is carried between hops through one of these modes through appropriate vehicles and the mode may vary from hop to hop

Assume an envelope has to be taken from chennai (India) to Connecticut (USA)

A person writes a letter, seals it inside an envelope and posts it in the nearest post office, as illustrated in the diagram below:

A Letter creation process

The complete path typically taken by the envelope is illustrated in the diagram below:

Typical operation of a postal network

• Envelope is first taken from post box to head post office in chennai by road (van)
• It is then passed on to Mumbai by railway track (train) as Mumbai is India’s International gateway
• From Mumbai it is passed on to NewYork (USA) by air(plane)/sea(ship), as NewYork is a peer International gateway 
• It is then passed on from NewYork to Connecticut by road (van)
• From Connecticut head post office it is then delivered to the recipient by road (cycle/car)
• Envelope is thus delivered to recipient after being passed on between multiple hops through different transport modes
• No post office knows complete route taken by envelope !!
• Letters between same end points may take different routes
• Multiple letters of different end points are carried jointly through intermediate hops

After understanding the basic principles of computer and postal networks, let us compare them now.

There are lot of things common between computer and postal networks and they are given below:

• Communication happens through small envelopes/packets
• Each home/computer requires Unique postal/IP address
• Intermediate Networks needed
• End-End path needed for both (road/air/rail, wired/wireless links)
• No reservation of End-End path ( shared by multiple letters/packets)
• Signaling information sent along with data in each envelope/packet (Postal address/IP address)
• Next Hop Routing used in both
• Envelopes/Packets between same end points may take different intermediate paths
• Both are best-effort delivery mechanisms

While there are lot of things in common, there are still a few differences between a computer network and a postal network. They are given below:

• While postal networks use a physical envelope to carry information, computer networks use electronic packet data to carry information.
• While postal networks use road, rail, air with their respective vehicles like van, train, plane as information carriers, computer networks use wired/wireless telecommunication links with electromagnetic/optical signals to carry information.

Since the common things are much more than the differences, it can be concluded that computer networks and postal networks have similar basic principles of operation.

Comparison of Computer Networks with Telephone Networks

While telephone networks and computer networks have some things in common, they have a lot of differences between them.

Before we compare and contrast them, a brief overview of the principle of operation of a telephone network is given below:

• Telephone networks use circuit switching, wherein a dedicated circuit or a path is reserved for a call, end to end from the caller to the called party. This circuit is reserved for the entire duration of the call and is used to carry the signals of the actual telephonic conversation. No other call can share this end to end dedicated circuit, till the call is completed.
• A separate signalling protocol is used for setting up and tearing down the dedicated circuit during call establishment and call disconnection respectively. Also the signalling protocol uses a separate path (out-of-band signalling), that is different from the data circuit path.

The diagram given below illustrates a typical telephone call initiated from Chennai (India) to Connecticut (USA).

A sample telephone conversation using circuit switching

• As seen in the diagram, an end to end dedicated path is first established and reserved between Chennai and Connecticut (via. Mumbai and New York intermediate exchanges) for the entire duration of the call. The dedicated path is shown in red colour. 

As we already know, Computer networks use packet switching and next hop routing as its basic principle of operation.

The common things between telephone and computer networks are given below:

• End Nodes & Intermediate Nodes are Electronic Devices
• Actual node to node Communication is using electrical voltages & Currents
• Use Telecommunication Links
• Intermediate Networks with routing intelligence needed
• End-End Telecommunication (physical) Path Needed
• Each end node requires Unique number/address

The differences between telephone and computer networks are given in the table below:

• As seen in the table above, while telephone networks use circuit switching, with dedicated signalling and data channels, computer networks use packet switching with no end to end path reservation.
• So computer networks utilize the underlying telecommunication links in a better manner, as it permits packets from multiple senders to simultaneoulsy share the same link.