LocalTalk

LocalTalk is a network protocol that was developed by Apple Computer, Inc. for Macintosh computers. The method used by LocalTalk is called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). It is similar to CSMA/CD except that a computer signals its intent to transmit before it actually does so. LocalTalk adapters and special twisted pair cable can be used to connect a series of computers through the serial port. The Macintosh operating system allows the establishment of a peer-to-peer network without the need for additional software. With the addition of the server version of AppleShare software, a client/server network can be established. The LocalTalk protocol allows for linear bus, star, or tree topologies using twisted pair cable. A primary disadvantage of LocalTalk is speed. Its speed of transmission is only 230 Kbps.

Wireless LAN

Not all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.Wireless networks are great for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.

The two most common types of infrared communications used in schools are line-of-sight and scattered broadcast. Line-of-sight communication means that there must be an unblocked direct line between the workstation and the transceiver. If a person walks within the line-of-sight while there is a transmission, the information would need to be sent again. This kind of obstruction can slow down the wireless network.

Scattered infrared communication is a broadcast of infrared transmissions sent out in multiple directions that bounces off walls and ceilings until it eventually hits the receiver. Networking communications with laser are virtually the same as line-of-sight infrared networks.
Wireless LANs have several disadvantages. They provide poor security, and are susceptible to interference from lights and electronic devices. They are also slower than LANs using cabling.

Bluetooth Technology

First of all, I want to told you from where word “Bluetooth” came, it put on the name of a great Denmark king whose name was “Harald Bluetooth” a thousand years of ago. Now the question is, what is bluetooth technology, actually it is a technology which is used for low-power radio communications to wirelessly link phones, computers and other network devices over short distances. Initially it was developed for support of personal wireless devices including cell phones, PDAs, and wireless headsets.The signals that are transmitted through “Bluetooth” devices are short distance in nature, They diminishes after 10m(30 feet).The data transferred through Bluetooth devices is at a rate of less than 1Mbps.As I already told you “Bluetooth” devices works on the principle of radio communication systems, so it is not required that the two Bluetooth devices must be in line of sight of each other, they can be either in different rooms, as long as the received transmission is powerful enough.

Today,there are many bluetooth enabled devices exists such as phones, printers, modems and headsets etc. This technology is useful only when the Bluetooth enabled devices are present in low- bandwidth position. Today Bluetooth is mainly used in cell phones to transfer sound data, or text data with laptops, and from Bluetooth enabled devices.From the security point of view, the data transferred between blue tooth devices is encrypted through some custom algorithms so that it can be safely transmitted. Hence, we can say that data transferred through Bluetooth devices is secure.As, the work is going on the development of Bluetooth so that it can be made more faster,simpler in comparison to other wireless technology.

Understsnding FDDI topology

FDDI stands for Fiber Distributed Data Interface. The FDDI standard is ANSI X3T9.5 . The FDDI topology is ring with two counter rotating rings for reliability with no hubs. Cable type is fiber-optic. Connectors are specialized. The media access method is token passing. Multiple tokens may be used by the system. The maximum length is 100 kilometers. The maximum number of nodes on the network is 500. Speed is 100 Mbps. FDDI is normally used as a backbone to link other networks. A typical FDDI network can include servers, concentrators, and links to other networks. CDDI is a copper version of FDDI which uses category 5 cable. Obviously the distance is more limited than FDDI.

Devices called concentrators provide functions similar to hubs. Most concentrators use dual attachment station network cards but single attachment concentrators may be used to attach more workstations to the network.

FDDI token passing allows multiple frames to circulate around the ring at the same time. Priority levels of a data frame and token can be set to allow servers to send more data frames. Time sensitive data may also be given higher priority. The second ring in a FDDI network is a method of adjusting when there are breaks in the cable. The primary ring is normally used, but if the nearest downstream neighbor stops responding the data is sent on the secondary ring in attempt to reach the computer. Therefore a break in the cable will result in the secondary ring being used. There are two network cards which are:

1. Dual attachment stations (DAS) used for servers and concentrators are attached to both rings.
2. Single Attachment stations (SAS) attached to one ring and used to attach workstations to concentrators.
A router or switch can link an FDDI network to a local area network (LAN). Normally FDDI is used to link LANs together since it covers long distances.

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Destination and Next Hop Addresses

What is the relationship between the destination address in a datagram header and the address of the next hop to which the datagram is forwarded?The Destination IP address field in a datagram contains the address of the Ultimate destination.When a router receives a datagram,the router extracts the destination address D,and uses it to compute the address of the next router to which datagram should be sent,N.Although the datagram is sent directly to address N,the header in the datagram retains destination address D.All routes are computed using IP address.After computing the address of a next hop,N,IP software uses the address binding to translate N to an equivalent hardware address for transmission.

Physical Network Connection With Routers

The basic hardware component used to connect heterogeneous networks is a Router.Physically,routers resembles bridges that means each router is a special purpose hardware system dedicated to the task of interconnecting networks.Like a bridge,a contains a processor and memory as well as a separate I/O interface for each network to which it connects.The network treats a connection to a router, the same as the connection to any other computer.

The most important that you have to kept in your mind about router is that it is not only used to connect two similar technology,it can also be used to connect two different types of network technology. Router can connect two LAN's,a LAN and a WAN,or two WAN's.Furthermore,when a router connects two network in the same general category,the networks do not need to use the same technology.For ex:- A router can connect an Ethernet LAN to a frame relay network.Thus,each cloud represents an arbitrary network technology.On summarizing this whole,we can say that a router is a special purpose system dedicated to the task of interconnecting networks.A router can interconnect networks that use different technologies,including different media,physical addressing schemes or frame formats.

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Operating System Concepts
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