Internetwork
Let's say an organization operates two offices, one located on the East Coast and the other on the West Coast. Each office is equipped with a Local Area Network (LAN) that enables all employees within the respective office to communicate with each other.
When a host in the west coast office sends a message to another host in the same office, the message is directed through the Local Area Network (LAN) of that office.
- The switch within the LAN is responsible for directing traffic to the same network. Switches operate at the Data Link layer (Layer 2) of the OSI model. It uses the MAC address of the destination host to forward the message directly to that host. The router blocks the message since it's not needed for intra-office communication.
On the other hand, when a host on the west coast sends a message to a host on the east
coast, router R1 routes the packet to router R2, and the packet reaches the destination.
- Routers operate at the Network layer (Layer 3) of the OSI model. Routers use IP (Internet Protocol) addresses to route packets between different networks(office's).
There is also Layer 3 Switches (Network Layer), also known as routing switches or multilayer switches, can perform both switching and routing functions. They use IP addresses to route traffic between different networks.
Protocol Layers are discussed later...
A heterogeneous network made of four WANs and three LANs
Switching
An internet is a switched network in which a switch connects at least two links together. A switch needs to forward data from a network to another network when required. The two most common types of switched networks are:- circuit-switched networks
- packet-switched networks.
Circuit-Switched Network
A specific, dedicated route (all intermediate switches and communication lines) through the network infrastructure along with a fixed bandwidth is reserved for the duration of a communication session. This type of network is traditionally associated with telephone systems but can also be used in other contexts.- This path remains active until the communication session ends.
- Until the session is expired no other device can use this preserved bandwidth.
- The capacity of the connection is reserved even if no data is being transmitted.
- Provides a consistent quality of service with minimal delay once the circuit is established.
Packet-Switched Network
A packet-switched network transmits data in small blocks called packets. Data is divided into packets, each of which is routed independently through the network. Packet-switched networks are better suited for bursty and unpredictable traffic patterns. This type of network is common in computer networking, including the Internet.- No dedicated path: packets may take different routes to reach the destination.
- Bandwidth is dynamically allocated and shared among multiple users
- Unused bandwidth is dynamically reallocated to other data packets.
- Quality of service can vary due to potential delays, packet loss, and the dynamic nature of routing.
A router in a packet-switched network has a queue that can store and forward the
packet. If packets arrive at one router when the thick line is already working at its full
capacity, the packets should be stored and forwarded in the order they arrived.
In computer networks, we mostly discuss packet-switched networks.
The Internet
An internet, with a lowercase 'i', refers to any two or more networks that can communicate with each other. The most prominent example of an internet is the Internet, with an uppercase 'I', which consists of thousands of interconnected networks.
More precisely "the Internet is a vast, global network of interconnected computer networks that communicate using standardized protocols, allowing devices and users worldwide to exchange data, access information, and connect with each other."
The Internet today
Backbones (Top Level)- At the top level, the backbones are large networks owned by some communication companies such as Sprint, Verizon. They serve as the main routes for data traffic across the Internet, connecting major data centers and regions worldwide. They are connected through complex switching systems called peering points, where different backbone networks exchange data. Also Known As: International ISPs.
Provider Networks (Second Level)
- Smaller networks that connect to the backbones to provide Internet services to lower-level networks and end-users. They Act as intermediaries, using the services of backbones for a fee to offer connectivity to customer networks and sometimes to other provider networks. They are connected to backbones and sometimes directly to other provider networks. Also Known As: National or regional ISPs.
Customer Networks (Edge Level)
- Customer Networks at the Edge Level consist of corporate networks, home networks, and individual users that utilize the services provided by provider networks. These networks are the end-users of the Internet's services, paying fees to provider networks for Internet connectivity and services.
Accessing the Internet
To access the Internet, users require a physical connection to an Internet Service Provider (ISP), usually established via a point-to-point Wide Area Network (WAN).
Using Telephone Networks
- Dial-Up Service: Uses a modem to convert data to voice. It's slow and ties up the phone line, suitable for small residences.
- DSL Service: Upgrades telephone lines for higher speeds, allowing simultaneous voice and data use.
Using Cable Networks
- Uses the infrastructure of cable TV services for Internet connectivity. Offers higher speeds, but speed can vary based on the number of users in the area.
Using Wireless Networks
- Uses wireless technology for Internet access. Combines wired and wireless connections within households or small businesses.
Direct Connection to the Internet
- Large organizations can become local ISPs by leasing a high-speed WAN and connecting to a regional ISP. This is suitable for entities like large universities with significant Internet needs.
INTERNET HISTORY
Early History
Pre-1960s: Telegraph and Telephone Networks
- Telegraph and Telephone: These were early forms of communication networks designed for constant-rate communication, enabling the exchange of encoded messages and voice signals. They were not suitable for handling bursty data, which is data transmitted at variable rates.
Packet-Switched Networks
1961: Birth of Packet-Switching Theory
- Leonard Kleinrock: At MIT, Kleinrock introduced the theory of packet switching, a method suitable for bursty traffic.
- Paul Baran and Donald Davies: Independently published related research on packet-switched networks.
1969: ARPANET
- Advanced Research Projects Agency Network (ARPANET): The Department of Defense's ARPA funded a project to connect computers across different institutions to share research and reduce redundancy.
- First Nodes: Four nodes were established at UCLA, UCSB, SRI, and the University of Utah, connected via Interface Message Processors (IMPs).
Evolution of the Internet
1972: Internetting Project
- Vint Cerf and Bob Kahn: Proposed linking diverse networks to enable communication between different systems, introducing the concept of gateways to transfer data across networks.
1973: TCP/IP
- Transmission Control Protocol (TCP): Cerf and Kahn outlined protocols for end-to-end data delivery, including error correction.
- Internet Protocol (IP): Split from TCP to handle routing of datagrams.
1977: First Internet Demonstration
- Three Networks: Successfully demonstrated communication across ARPANET, packet radio, and packet satellite networks.
1981: Berkeley UNIX and TCP/IP
- Integration: UC Berkeley included TCP/IP in the UNIX operating system, promoting its widespread adoption.
1983: TCP/IP Standardization
- Official Protocol: TCP/IP became the standard for ARPANET, which split into MILNET (military) and ARPANET (civilian).
Expansion and Commercialization
1981: CSNET
- Computer Science Network (CSNET): Sponsored by the National Science Foundation (NSF) for universities not connected to the Department of Defense, expanding academic access to networking.
1986: NSFNET
- National Science Foundation Network (NSFNET): Created to connect supercomputer centers with a backbone network, enhancing nationwide research connectivity.
1990: ARPANET Retirement
- Transition: ARPANET was decommissioned, with NSFNET taking over as the main backbone for Internet traffic.
1991: ANSNET
- Advanced Network & Services Network (ANSNET): Established by IBM, Merit, and Verizon to manage the increasing Internet traffic with a high-speed backbone.
The Modern Internet
1995: Commercialization
- NSFNET Decommission: NSFNET returned to a research network, and commercial ISPs took over the primary role in providing Internet connectivity to the public.
1990s-Present: Growth and Innovation
- Web Browsers and WWW: The development of web browsers like Mosaic and the World Wide Web by Tim Berners-Lee in the early 1990s revolutionized Internet usage, making it accessible to the general public.
- Broadband and Wireless: Advancements in broadband and wireless technologies have significantly increased Internet access speeds and availability.
- Social Media and Mobile Internet: The rise of social media platforms and the proliferation of smartphones have transformed how people interact, access information, and conduct business online.
