Network Topology

Topology architecture is a form of physical connections to connect each node in a network. In the LAN system there are three main topologies are most often used: bus, star, and ring. Network Topology is then developed into a tree and mesh topology which is a combination of star, mesh, and bus. With the popularity of wireless technology today, the birth of new topology is also a wireless topology. The following topologies are defined:

    1. Bus Topology
    2. Topology Ring
    3. Topology Star
    4. Topology Tree
    5. Mesh topology (not uniformly)
    6. Topology Wireless (Wireless)

Bus Topology

Bus topology is often also referred to as the backbone topology, where there is a coaxial cable that is created and then several computers connected to the cable.

• Simply stated on a bus topology, a cable transmission media is created from end to end, then both ends closed with the "terminator" or terminating-resistance (usually in the form of electrical resistance around 60 ohms).
• At some point held the connection (tap) for each terminal.
• The realization of these taps can be "wired transceiver" when used "thick coax" as transmission media.
• Or a "BNC T-connector" when used "thin coax" as transmission media.
• Or a connector "RJ-45" and "hub" when used UTP cable.
• The transmission of data in the cable are "full duplex", and its "broadcast", all terminals can receive data transmission.

• A protocol will govern the transmission and reception of data, namely the Protocol Ethernet or CSMA / CD.
• The use of coaxial cable (10Base5 and 10Base2) has been standardized in IEEE 802.3, is as follows:

TABLE: Coaxial Cable Characteristic

	10Base5	10Base2
Rate Data	10 Mbps	10 Mbps
Long / segmen	500 m	185 m
Range Max	2500 m	1000 m
Tap / segmen	100	30
Disntance per Tap	2.5 m	0.5 m
Cable Diameter	1 cm	0.5 cm

• Seeing that on each segment (span) cable is finite it is necessary to "Repeater" to connect the cable segments.

Bus topology advantages are:

• Installation is relatively cheaper 
• Damage to a single client computer will not affect the communication between other clients 
• The cost is relatively cheaper

Bus topology weaknesses are:

• If the main cable (bus) or break the backbone of communication failure 
• If the main cable is very long it becomes difficult search problems 
• The possibility of data collision will occur (data collision) if many clients who send a message and this will reduce the speed of communication.

Topology Ring

Ring topology is often called a ring topology because of its shape like a circular cincing. All computers in the network needs to connect in a ring. The ring is almost the same function as concenrator on star topology which is the central gathering end of the cable from each computer connected.

• In more simpler ring topology is a string of media transmission from one terminal to another terminal to form a circle, where the transmission line is only "one way".

The three functions necessary in a ring topology: penyelipan data, acceptance data, and transfer data.

• Inserting data is the process where data is inserted into the transmission channel by the sender after a given address and additional bits.
• Reception of data is the process when the destination terminal has been taking data from the channel, that is by comparing the address on the packet data terminal with the address itself. If the address is the same then the data items copied.
• The transfer of data is the process whereby data items were taken back by the sender because there is no terminal accept it (perhaps due to wrong address.) If the data were not collected this data will then spin glittering channel. On a bus network that will not happen because the shipment will be absorbed by the "terminator".
• In virtually every terminal in the network ring is a "repeater", and able to perform all three functions of the ring topology.
• Systems that govern how data communications take place on the ring network is often called the token-ring.
• Possible problems that can arise in a ring network is:
  • Failure of a terminal / repeater will decide the communication to all terminals.
  • Installation of a new terminal cause disruption to the network, a new terminal should know and be connected with both terminals neighbors.

Topology Star

Called a star topology because of its shape like a star, a device called a concentrator can be a hub or switch into the center, where all the computers in a network connected to this concentrator.

• In a star topology the central terminal to act as regulator and controller of all communications that occurred. Other terminals perform a communication through this central terminal.
• Central control terminal can be a computer that functioned as a controller but can also be "HUB" or "MAU" (Multi Accsess Unit).
• There are two alternatives for the operation of the central node.
  • Central node operates in a "broadcast" that transmits data to all directions. In this operation, although physically appear as a star but in fact operate as logical bus. This alternative is using a HUB.
  • Central node operates as a "switch", the data items received by the node and then sent only to the terminal objective (is point-to-point), this akternatif using MAU as a controller.
• When using the HUB, the actual physical topology is star-shaped network but logically bertopologi Bus. When using the MAU is both physical and logical bertopologi Stars.
• Advantages of star topology :
  • As each component is connected directly to the central node then becomes easy management, communication failures easy to navigate.
  • Failure of one component / terminal does not affect other terminal communications.
• Disadvantages of topologi bintang:
  • The failure of central control (central node) cut off all communication
  • When used as the control center is the hub then the speed will be reduced in accordance with the addition of computers, the more slowly.

Topologi Tree

• Tree topology is the development or generalization of a bus topology. Transmission medium is a single cable branching but not a closed loop
• Tree topology starting from a point called the "headend". From the cable headend drawn into some branches, and in each branch to connect multiple terminals in a bus, or dicabang again to become complicated.
• There are two difficulties with this topology:
  • Because branching is needed a way to show where data is sent, or to whom the intended data transmission.
  • Need a mechanism to regulate the transmission of the terminal the terminal in the network.

Topologi Mesh

• Mesh topology is the topology that has no rules in connection. This topology is typically arise due to lack of initial planning when building a network.
• Because of irregular then becomes difficult to detect communication failures, and there is the possibility of wasteful in the use of transmission media.

Topologi Wireless

• Wireless networks become a trend as an alternative to cable networks, especially for the development of traditional LAN because it can reduce cabling costs and reducing cable relocation tasks if there is a change in the architecture of buildings and so on. This topology is known by various names, such as WLAN, WaveLAN, HotSpot, etc..
• The basic model of the wireless LAN is as follows:

• The smallest block of Wireless LAN is called Basic Service Set (BSS), which consists of a number of stations / terminals running the same protocol and compete in terms of access to the same shared media.
• A HUB can connect directly, or separate from a distribution system backbone via the access point (Access Point).
• MAC protocol can be fully distributed or controlled through a central coordination function within the access point.
• An Extended Service Set (ESS) consists of two or more BSs are connected through a distribution system.

• Interaction between a wireless LAN with other LAN type is described as follows:

• On a LAN can have a wired LAN backbone, such as "Ethernet"to support the servers, workstations, and one or more bridge / router to be connected with other networks. In addition there is the control module (CM), which acts as an interface for wireless LAN networks. CM includes both the function of bridge or router function for connecting a wireless LAN network. In addition there is Hub and also the user module (UM), which controls a number of stations wired LAN.
• The use of other wireless LAN technology is to connect LANs in nearby buildings.
• Terms of wireless LAN :
  • Completion rate: medium access control protocol should be used as efficient as possible by the wireless medium to maximize capacity.
  • Number of nodes: wireless LAN needs to support hundreds of nodes on multiple cells.
  • Connection to the LAN backbone: the control module (CM) must be capable of connecting a LAN to another LAN or an ad-hoc wireless network.
  • Service Area: area coverage for wireless LANs typically have a diameter of 100 to 300 meters.
  • Robustness and security of transmission: wireless LAN systems must be reliable and able to provide a security system especially wiretapping.
• Wireless LAN technology:
  • LAN infrared (IR): confined in a room because the IR can not penetrate opaque walls.
  • LAN radio waves: limited in a complex building, such as Bluetooth, WiFi, and HomeRF.
  • Spectrum LAN deployment: operating in ISM bands (industrial, scientific, medical) that do not require a license.
  • Narrowband microwave: to operate at microwave frequencies that are not included in the spread spectrum.