Example Network: The Internet, X.25, Frame Relay, Ethernet, VoIP, NGN and MPLS, xDSL.

Internet

The Internet is the global system where different computer networks are connected and use the Internet protocol suite (TCP/IP) to link billions of devices worldwide. The Internet carries a wide range and variety of information resources and services. The Internet also has enabled and accelerated new forms of personal interactions through instant messaging, Internet forums, and social networking. The Internet has no centralized governance(not exact protocol or standards) in either technological implementation or policies for access and usage; each constituent network sets its own policies. Only the overreaching definitions of the two principal name spaces on the Internet, the Internet Protocol address space and the Domain Name System (DNS), are provided by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN).

X.25

X.25 is an ITU-T standard protocol which defines the way in which packets travel in a packet switched wide area network (WAN) communication. An X.25 WAN consists of packet-switching exchange (PSE) nodes and different types of networking hardware, plain old telephone service connections or ISDN connections as physical links. X.25 network handles the combination of packets at the source device, delivery, and then dis-assembly at the destination. X.25 packet delivery technology includes error checking and retransmission logic should delivery failures occur along with the switching and network layer routing. It also supports multiple simultaneous conversations by multiplexing packets and using virtual communication channels.

Frame Relay

Frame Relay is a standardized technology used in wide area network that specifies the communication in physical and logical link layers of digital telecommunications channels using a packet switching methodology. It is designed in a way to reduce cost in data transmission for intermittent traffic between local area networks (LANs) and between endpoints in wide area networks (WANs).

Ethernet

Ethernet is a computer networking technologies used in LANs and MANs. It is the most widely used for local area network (LAN) technology. Ethernet is a link layer protocol in the TCP/IP stack, describing how networked devices should format data for efficient transmission between other network devices on the same network segment, and how to put that data out on the network connection.

VoIP

VoIP is a voice over an Internet Protocol (IP) based network. VoIP is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Voice signals are converted to packets of data, which are transmitted on shared, public lines, hence avoiding the tolls of the traditional, public switched telephone network (PSTN). Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service.

NGN

A Next Generation Networks (NGN) is a packet-based network able to provide Telecommunication Services to users and able to make use of multiple broadbands, QoS-enabled transport technologies and in which service-related functions are independent of the underlying transport-related technologies.

MPLS

Multiprotocol Label Switching (MPLS) is a protocol for speeding up and shaping network traffic flows. MPLS allows most packets to be forwarded at Layer 2 (the switching level) rather than having to be passed up to Layer 3 (the routing level).

xDSL

Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.
In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access. The bit rate of consumer DSL services typically ranges from 256 kbit/s to over 100 Mbit/s in the direction of the customer (downstream), depending on DSL technology, line conditions, and service-level implementation.
xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for upstream traffic, and from 32 Kbps to over 1 Mbps for downstream traffic.

References:

1. A.S. Tanenbaum, “Computer Networks”, 3rd Edition, Prentice Hall India, 1997.
2. W. Stallings, “Data and Computer Communication”, Macmillan Press, 1989.
3. Kurose Ross, “Computer Networking: A top-down approach”, 2nd Edition, Pearson Education
4. Larry L. Peterson, Bruce S. Davie, “Computer Networks: A Systems Approach”, 3rd Edition, Morgan Kaufmann Publishers