Mesh Topology

Mesh Network is a network where all the nodes are connected to each other and is a complete network. In a Mesh Network every node is connected to other nodes on the network through hops. Some are connected through single hops and some may be connected with more than one hope. While the data is traveling on the Mesh Network it is automatically configured to reach the destination by taking the shortest route which means the least number of hops. Data travels by hopping from one node to another and then reaches the destination node in a Mesh Topology Network.

An example of a Mesh Network is the Mobile Adhoc Network or MANet. The entire Mesh Network is continuously connected. Being completely connected does not mean that Mesh Network is dependant on each and every node of the network. Even if one node fails in the Mesh Network the network finds an alternate route to transfer the data. It is called the self healing technology where it receives data one way or the other.

The Mesh Network is based on a very sensible concept and has lesser chances of a network breakdown. There are so many possible combinations of routes and hops a data transfer can take that it will reach the destination one way or the other. It is highly unlikely that all the nodes in a single Mesh Network will break down at any given point of time.

Wireless Mesh Networks
Wireless Mesh Networks work based on the radio frequencies and was originally developed by the army to be able to communicate. The reliability factor is high in any kind of Mesh Network. There are three types of wireless Mesh Topologies.

• Fixed Wireless Connections
• Peer to Peer or Adhoc Networks
• Node to Node

Fixed Mesh Networks
The fixed Mesh Networks will work only in the specified location and they are not mobile networks. They are meant to be used in a limited surrounding with boundaries. The location of nodes in affixed Mesh Network is all pre determined and they are not interchangeable.

The fixed Mesh Network does not work on line of sight like the other types of Mesh Networks. The total number of hops in a fixed Mesh Network is usually fixed and also short. There may not be many nodes as this kind of Mesh Networks exist within an office or building. More often than not the data travels ion a specific direction.

Peer to Peer Mobile Networks
In a peer to peer mobile network the individual devices connect to each other using the Mesh Network. The peer does not require connecting to the main node and they can still communicate from one device to another device by taking the shortest possible data transfer route. However many experts believe that in the peer to peer Mesh Networks the problems with scalability in terms of time taken for data transfer is questionable. The device has to know to transmit the data in the most optimal path and the entire data transfer or depends on this single factor. If the device is incapable then the whole purpose of using it in a peer to peer connection is lost.

Tree Topology

Among all the Network Topologies we can derive that the Tree Topology is a combination of the bus and the Star Topology. The tree like structure allows you to have many servers on the network and you can branch out the network in many ways. This is particularly helpful for colleges, universities and schools so that each of the branches can identify the relevant systems in their own network and yet connect to the big network in some way.
A Tree Structure suits best when the network is widely spread and vastly divided into many branches. Like any other topologies, the Tree Topology has its advantages and disadvantages. A Tree Network may not suit small networks and it may be a waste of cable to use it for small networks. Tree Topology has some limitations and the configuration should suit those limitations.

Tree Network topology Benefits
• A Tree Topology is supported by many network vendors ad even hardware vendors.
• A point to point connection is possible with Tree Networks.
• All the computers have access to the larger and their immediate networks.
• Best topology for branched out networks.
Tree Topology Limitations
• In a Network Topology the length of the network depends on the type of cable that is being used.
• The Tree Topology network is entirely dependant on the trunk which is the main backbone of the network. If that has to fail then the entire network would fail.
• Since the Tree Topology network is big it is difficult to configure and can get complicated after a certain point.
The Tree Topology follows a hierarchical pattern where each level is connected to the next higher level in a symmetrical pattern. Each level in the hierarchy follows a certain pattern in connecting the nodes. Like the top most level might have only one node or two nodes and the following level in the hierarchy might have few more nodes which work on the point to point connectivity and the third level also has asymmetrical node to node pattern and each of these levels are connected to the root level in the hierarchy. Think of a tree that branches out in various directions and all these branches need the roots and the tree trunk to survive. A Tree Structured network is very similar to this and that is why it is called the Tree Topology.

Tree Topology Features
• There will be at least three levels of hierarchy in the Tree Network Topology and they all work based on the root node.
• The Tree Topology has two kinds of topology integral in it, the star and the linear way of connecting to nodes.
• The Tree Topology functions by taking into account the total number of nodes present in the network. It does not matter how many nodes are there on each level. Nodes can be added to any level of the hierarchy and there are no limitations a far as the total number of nodes do not exceed.
• The higher levels in the hierarchy are expected to perform more functions than the lower levels in the network.

bab:6

Kelas hari bincang tentang 10 jenis talian; talian sewa,talian persendirian ,talian khas,fixed line,Wimax,Digital Multimedia Broadcasting,WiFi,ZigBee,Wibree dan 3G. Selain itu, sisitem kom satellite ialah satu objek yang dicipta o manusia. jenis satelit ialah Geosynchronous-Earth Orbit(GEO),Low-Earth Orbit(LEO) dan Medium-Earth Orbit(MEO). Jenis- jenis satellite ialah Anti-satellite weapons, Astronomical satellite, Biosatellite, Navigational satellite, Reconnaisance satellite , Earth observation satellite, Space station, Tether satellites dan weather satellites. Aplikasi transmisi satellite ialah anolog broadcasting,digital broadcasting, voice communication, vidoe conferencing, mobile wireless, tracking and monitoring , global desitioning system(GPS) ,Internet access dan Wide Area Network. Kebaikannya ialah can reach a large geographical area, high bandwicth and cheaper over long distances. kelemahannya ialah cost yang tinggi, propagation delay ang susceptible to noise and interference.

BAB: KomUniKasi DaTa

Komunikasi data ialah satu keadaan dimanadata telah siap diproses oleh sesebuah kom akan dihantar kepada kom/perkakasan mlli media kom yang tertentu. tranmisi data: kom mesej,salaruan kom dan isyarat penghantaran.. Bentuk transmisi data terbahagi kpd 2 iaitu penghantaran selari dan bersiri..Mod penghantaran ialah simplex,sesetengah duplex dan duplex penuh. media penghantaran terbahagi kepada penghantaran berpadu dan tidak berpadu..media penghantaran berpadu ialah wayar terpuih,kabel koaxial dan gentian optik. Media penghantaran tanpa wayar pula ialah pengahantaran infra merah,siaran penghantaran, bluetooth,gelombang mikro dan satelit.konsep asas rangkaian terdiri drpd saling hub. kom2x dan terminal 2x bg membentuk laluan kpd data.. kompenan perkakasan ialah stesenkerja,pelayan dan routers. Pentadbir rangkaian berfungsi ialah pemasangan,penjagaan,beri sokongan,berkom dgn pengguna dan mengatasi sbg masalah dalam rangkaian. kelebihan ialah mengurangkan kos,berkongsi aplikasi,berkongsi sumber maklumat,pemusatan dalam pengurusan data dan penghubung kpd pengguna. kelemaham pula hilang hak pengguna sendiri, kekurangan kebebasan peribadi,ancaman keselamatan dan pengurangan produktiviti. rangkaian kawasan setempat(LAN) miliki individu y menawarkan saluran kom dlm kelajuan y tinggi untuk menghbgkan peralatan pemprosesan mak dlm geo y terhad.. Jenis-jenis (LAN) ialah pear-to-pear network,client-server network dan topologilan. protokol ialah satu set undang2x y membenarkan sistem kom y berbeza berkomunikasi. Wi-Fi ialah singkatan bg wireless fiderity,berkelajauan tinggi dan digunakan dalam jarak yang luas.

bentuk tranmisi data (penghantaran bersiri)

Also known as a star bus topology, tree topology is one of the most common types of network setups that is similar to a bus topology and a star topology. A tree topology connects multiple star networks to other star networks. Below is a visual example of a simple computer setup on a network using the star topology.In the above example picture if the main cable or trunk between each of the two star topology networks failed, those networks would be unable to communicate with each other. However, computers on the same star topology would still be able to communicate with each other.A type of network setup where each of the computers and network devices are interconnected with one another, allowing for most transmissions to be distributed, even if one of the connections go down. This type of topology is not commonly used for most computer networks as it is difficult and expensive to have redundant connection to every computer. However, this type of topology is commonly used for wireless networks. Below is a visual example of a simple computer setup on a network using a mesh topology.

Tak Segerak

Dikenali sebagai protokol mula-akhir. Protokol jenis ini selalunya digunakan pada terminal dungu (dumb terminal dan selalunya tidak mempunyai penimbal untuk menyimpan aksara tersebut. Penghantaran data dilakukan dengan menghantar satu bit tambahan pada permulaan (bit mula) dan akhir data (bit akhir). Bit mula akan memaklumkan kepada penerima bahawa selepas bit tersebut akan ada bit-bit data yang berbentuk aksara akan dihantar, kemudian diikuti oleh satu bit pariti dan kemudian bit akhir. Bit akhir menandakan berakhirnya penghantaran data tersebut.Bit mula menggunakan bit 0, bit akhir menggunakan bit 1 dan bit pariti pula bergantung kepada keadaan pengecaman ralat. Rajah menunjukkan penghantaran aksara menggunakan kaedah penghantaran data tak segerak.Dengan menggunakan protokol tak segerak setiap bit mesti disetkan untuk menghantar dan menerima data melalui kadar data yang diberikan. Kadar data ini diukur dalam unit bit per saat (bps). Bila peranti protokol tak segerak menghantar data, ia dimulakan dengan bit mula yang akan sentiasa 0, diikuti dengan 8 bit data dalam bait ( 7 bit [aksara] dan 1 bit pariti) dan kemudian bit 1 yang menunjukkan bit akhir. Jumlah kesemua bit yang akan dihantar ialah 10 bit. Rajah 1.10 di atas menunjukkan bahawa aksara A dihantar dengan diikuti aksara B daripada terminal dungu ke komputer perumah dengan menggunakan kod ASCII. Masa melahu (idle) akan wujud antara satu aksara dengan aksara yang lain semasa berlakunya penghantaran data.Kaedah penghantaran data jenis ini tidak sesuai digunakan untuk penghantaran data yang banyak, sedangkan kebanyakkan aplikasi komputer memerlukan penghantaran data yang banyak. Untuk mengatasi masalah ini kaedah protokol segerak lebih sesuai digunakan.

Protokol Segerak

Kaedah segerak boleh digunakan untuk membuat penyegerakan menghantar satu blok data (banyak aksara) yang besar. Kaedah ini tidak menggunakan bit mula-akhir, tiada masa melahu (idle) antara satu aksara dengan aksara yang lain.Kaedah segerak menggunakan beberapa aksara dipermulaan blok data yang hendak dihantar. Aksara ini dinamakan SYN. Ia mempunyai corak bit khas seperti 10101010. Corak bit ini akan memberitahu penerima bahawa ada satu blok aksara yang akan tiba selepas itu. Pada bahagian penghantar, satu bingkai (frame) akan dibentuk terlebih dahulu sebelum membuat penghantaran data. Dalam bingkai tersebut, beberapa aksara SYN dan aksara kawalan lain akan dimasukkan. 10 aksara kawalan diperlukan untuk untuk satu blok penghantaran. .Selain daripada itu kita juga boleh menggunakan aksara SYN untuk membuat penyegerakan, ada juga yang menggunakan isyarat jam pada talian berasingan. Apa yang dimaksudkan dengan talian berasingan ialah saluran/wayar yang berbeza digunakan untuk menghantar maklumat dan menghantar data. Isyarat jam akan dihantar bersama setiap bit data yang dihantar. Bila penerima menerima isyarat jam dari talian berkenaan, penerima akan membaca data dari talian penghantaran data.