Introduction to Network Fundamentals
Read this introduction to the basic terms and technologies we will cover in this course, as well as a brief review of how the Internet and computer networks evolved over time.
The Growth of Computers
- A processor in a video game of today is 10,000 times faster than the ENIAC computer (1947)
- A Nintendo game today has more processing power than a 1976 Cray supercomputer
- Greeting cards contain more computer power than all computer before 1950
- Chips in some video cameras are more powerful than an IBM 360
- Computer power, bandwidth and number of hosts double every 12-18 months
- Moore’s Law: processor speed double every 18 months
The Growth of Networks
- From Time Magazine, July 27, 1998:
- Number of years it took for radio to reach 50 million domestic listeners:
- 40
- Number of years it took for television and cable to reach 50 million domestic viewers:
- 13
- Number of year it took to the World Wide Web to get 50 million domestic users:
- 4
Brief History of Computers and Networks
- Before 1950: Early Computers
- Expensive, cumbersome, taking a huge amount of space and operated only by experts
- Late 1950’s and 60’s: Batch Processing
- Smaller, more affordable computers
- Users would have to physically carry their work (e.g. punched cards), to the computer
- Single user only
- 1960’s: Interactive Processing Through Timesharing
- Terminals with no processing power connected directly to the computer
- Multiple users simultaneously
- 1970’s: Minicomputers and Microcomputers
- Own processing capacity, yet less expensive and more flexible than traditional mainframes
- 1980’s: Personal Computers, Distributed Systems, Networks.
Brief History of Computers and Networks
- 1960’s: Interactive Processing Through Timesharing
- Terminals with no processing power connected directly to the computer
- Multiple users simultaneously
- 1970’s: Minicomputers and Microcomputers
- Own processing capacity, yet less expensive and more flexible than traditional mainframes
- 1980’s: Personal Computers, Distributed Systems, Networks.
Chronology of the Internet Evolution
- 1964: Paul Baran wrote reports outlining packet networks
- 1969: First ARPANET nodes operational
- First two important applications: Telnet and FTP
- 1972: Distributed e-mail invented
- 1973: First non-US computer linked to ARPANET
- 1975: ARPANET transitioned to Defense Communications Agency
- 1980: TCP/IP experimentation begins
- 1981: New host added every 20 days
- 1983: TCP/IP switchover complete
- 1986: NSFnet backbone created
- 1990: ARPANET Retired
- 1991: Gopher introduced
- 1991: WWW invented
- 1992: Mosaic Introduced
- 1995: Internet Backbone privatized
- 1998: Number of registered domain name exceeds 2 million
- 2000: Number of indexable web pages exceed 1 billion
Uses of Computer Networks
- Business Applications
- Home Applications
- Mobile Users
Networks vs Distributed Systems
- Network:
- An interconnected collection of autonomous computers, where users are completely aware of the network existence.
- Users must explicitly generate a change.
- Distributed System:
- An interconnected collection of autonomous computers, where all computers operate as a single, large virtual computer system.
- The existence of multiple computers is transparent to users.
- A distributed system is a software system built on top of a network. Example: WWW
Network Classification
- Local Area Networks
- Metropolitan Area Networks
- Wide Area Networks
- Wireless Networks
- Home Networks
- Internetworks
Network Classification
Classification of interconnected processors by scale
Type of Network Links (transmission technology)
- Broadcast links
- Many machines sharing a common link.
- Point-to-point links
- Two machines sharing a single connection link.
Switching Techniques: Circuit Switching
- A physical path between sender and receiver is established. The path remains active until the “call” is completed.
- Can involve a long set-up time while the common carrier searches for the free path.
- No data is transmitted while the circuit is established.
- Example of Connection-Oriented service. Modeled after the telephone system.
- Advantages
- Low overhead (only small circuit ID needed)
- Packets arrive in sequence
- QoS easier to implement
- Disadvantages:
- Long set up times (high idle time)
- Non-resilient in case of router failure
Switching Techniques: Packet Switching
- The source node divides the data into packets and transmits the packets. Each packet has a header that includes the address of the destination node, as well as a sequence number, indicating the position of the packet in the message.
- The source node transmit to the first switching node in the network
- The switching node sends the packet to another node (or to the destination) based on the packet address. The process is repeated until the packet gets to the final destination.
- The destination node uses the sequence numbers to reassemble the packets in correct order.
- Example of connectionless service, modeled after the Postal System. Also known as Datagram packet switching
Datagram Packet Switching
- Advantages:
- No setup times (minimum idleness)
- Flexibility in the face of congestion
- More robust in the event of router failures
- Disadvantages:
- High Overhead
- More processing power at each node (larger addresses, per packet routing).
- More processing at end node (packets arrive out of order)
- Jitter (variation in packet delay)
Switching Techniques
- Virtual Call Switching:
- The first packet determines the route that all packets will follow.
- Combination of Circuit Switching and time-division multiplexing.
- Packets from different sources will be interleaved in transmission
- When you have multiple circuits in one wire, each circuit is called a virtual circuit.
The Concept of Layering: Divide and Conquer
- Divide the Network functions into logical layers.
- Each layer is composed of software and/or hardware modules that perform related network services.
- Each layer uses the services provided by the layer immediately underneath.
- Data to be transmitted must pass down through the layers of the source node to the communication medium (i.e. physical link).
- The data travels across the physical link and up through the layers of the destination node to the user. This is called end-to-end communications.
- More about Layering later in this course.
Network Architecture
- Each layer deals with messages (packets).
- Messages are generally limited to a maximum size.
- Each message contains a control or header information used to synchronize with the remote peer. The header contains “instructions” that tell the remote peer what to do with the message.
- Each message contains a data portion that contains arbitrary data.
- When layer N accepts data from layer N+1, it encapsulates the entire layer N+1 message in the data portion the layer N packet.
- When the remote peer receives a message, it strips of the header information and passes only the data to the next higher layer.
Connection-Oriented and Connectionless Services
Six different types of service.
Networks vs Distributed Systems
- Network:
- An interconnected collection of autonomous computers, where users are completely aware of the network existence.
- Users must explicitly generate a change.
- Distributed System:
- An interconnected collection of autonomous computers, where all computers operate as a single, large virtual computer system.
- The existence of multiple computers is transparent to users.
- A distributed system is a software system built on top of a network. Example: WWW
Source: Eladio R. Cortes Ramos This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License.
Last modified: Monday, August 24, 2020, 8:28 PM