Client/Server -- When there's an imbalance between machines. One machine
serves as the client which receives its information from the other machine or the server.
Peer to Peer -- When all the machines are equal.
TCP/IP -- Transmission Control Protocal Internet Protocal; If you have a
TCP/IP then it doesn't matter what network or system you're on, your machine can talk to
any other machine. It bridges the gap between dissimilar computers, operating systems, and
networks. It's the protocal that drives the Internet. There are several subprotocals of
TCP/IP:
Communication Protocols
-- Protocols are rules established to govern the way data are transmitted in a computer network. Protocols fall into two general classifications: asynchronous and synchronous. In asynchronous transmission, data are transmitted at irregular intervals on as needed basis. This kind of transmission begins and ends each message with start/stop bits. In a synchronous transmission, the source and destination operate in synchronization to enable high-speed data transfer. Start/stop bits are not required in synchronous transmission. Communication protocols are defined in layers: physical and subsequent. The physical layer is how the networks connected to each other physically (wires). Subsequent layers describe how messages are packaged for transmission, how are they routed through the network and how are the messages displayed.The Seven Layer OSI Model
Application layer - determines how network
applications link to the network operating system. E-mail is an example.
Presentation layer - determines how an application will format
data sent across the network.
Session layer - controls the flow of data between applications
running on network PCs.
Network layer - establishes, maintains, and terminates the
connection between two stations. This layer is responsible for routing data between
networks.
Data-link layer - manages data flow into and out of network nodes,
detecting network errors as they occur.
Physical layer - consists of the physical connection between the
terminals (i.e wires).
Network Basic Input/Output System - This is the software layer
that links network operating system to the hardware.
There are two basic approaches to data-layer protocol design: packet-switched and
circuit-switched. The packet-switched is most popular in LANs because of its reliability
and simplicity. The most widely know is the packet-switched transmission control protocol/
Internet protocol(TCP/IP). TCP/IP protocol was developed by the defense department . It'
It is used for connecting different computer platforms. Circuit switched approaches are
usually used with WAN. ATM (the asynchronous transfer mode) protocol is a hybrid between
circuit- and packet-switched methods. The ATM divides data into small packets and then
routes these packets over a virtual circuit. A virtual circuit is a point-to-point
connection that may send data over different physical links during communication. Its
virtual because the user never knows that the packets are routed over different links. One
computer can't communicate with another unless they use the same protocol.
Mainframe - PC Communication -- Mainframes are important as the central
repositories of data. Channels access the mainframes. They are little computers that see
which disk the information is on so the mainframe doesn't have to handle it. Terminals
(PCs) access that channels. The terminals did no proccessing. The PC was the first smart
terminal. You have to run emulation software so it will appear to the controller as one of
the dumb terminals. There are many different layers of emulation software.
Physical Connection Between Mainframes and PCs
Synchronous - This connection uses a timing signal. The two machines set their
clocks to the same time. It's very fast because there's no extra overhead. It's hard to
synchronize over long distances.
Asynchronous - No timing signal is used. You know that the new byte begins
by inserting stop bits. The settings on a communication package determines the number of
stop bits. You use parity bits to determine if the receiver got the package. The problem
is that PCs use 8 bits and mainframes use 7. To fix this problem, a program called Kermit
is used. It's a very slow protocol.
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