Page 14 - Handout Computer Network.

1.4 Overview of High-Speed and Dialup Connectivity

In the early 1960s, modems were introduced to provide data communications
connectivity for dumb terminals to a centrally based computer. Many companies rented
computer time because owning an onsite system was cost-prohibitive. The connection rate was
very slow— 300 bits per second (bps), which translates to about 30 characters per second. As
PCs became affordable in the 1970s, Bulletin Board Systems (BBSs) appeared, allowing users to
connect and post or read messages on a discussion board. Running at 300 bps was acceptable,
because this exceeds the speed at which most people can read or type. BBSs did not become
widely used until the early 1980s, and the transfer of files and graphics began to be desirable.
The 300-bps speed quickly became intolerable, and modem speeds started to increase. By the
1990s, modems were running at 9600 bps. They reached the current standard of 56 kbps (56,000
bps) by 1998. Inevitably, the high-speed services used in the corporate environment, such as
digital subscriber line (DSL) and cable modem access, migrated to the consumer market. These
services no longer required expensive equipment or a second phone line. They are also always-
on services and therefore provide instant access that does not require a connection to be
established for each session. This results in greater reliability and flexibility. It has also led to the
ease of Internet connection sharing and small office and home networks.

1.5 Testing Connectivity with Ping

Ping is a program that is useful for verifying a successful TCP/IP installation. It is named
after the sonar operation used to locate and determine the distance to an underwater object.
Ping stands for Packet Internet Groper. The ping command works by sending multiple IP packets
to a specified destination. Each packet sent is a request for a reply. The output response for a ping
contains the success ratio and round-trip time to the destination. From this information, you can
determine if there is connectivity to a destination. The ping command is used to test the NIC
transmit/receive function, the TCP/IP configuration, and network connectivity.
The following are some usages of the ping command:

• ping 127.0.0.1 (internal loopback test)—This verifies the operation of the TCP/IP stack and
NIC transmit/receive function.
• ping IP address of host computer—Verifies the TCP/IP address configuration for the local
host.

• ping default-gateway IP address—Verifies whether the router that connects the local
network to other networks can be accessed.

• ping remote destination IP address—Verifies connectivity to a remote host.

• https://www.youtube.com/watch?v=IIicPE38O-s&t=218s

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