Introduction
Local area Network (LAN) use one of the following physical layout designs. These designs are referred to as 'topologies'.LANs are the high speed, low-error data netorks that span a relatively small geographic area. they connect workstations,peripherals,terminals, and other devices in a single building or other geographically limited area.
The application in use, such as multimedia, database updates, e-mail, or file and print
sharing, generally determines the type of data transmission.
LAN transmissions fit into one of three categories:
• Unicast
• Multicast
• Broadcast
Unicast
With unicast transmissions, a single packet is sent from the source to a destination on a
network. The source-node addresses the packet by using the network address of the
destination node. The packet is then forwarded to the destination network and the network
passes the packet to its final destination.
With a multicast transmission, a single data packet is copied and forwarded to a specific
subset of nodes on the network. The source node addresses the packet by using a multicast
address. For example, the TCP/IP suite uses 224.0.0.0 to 239.255.255.255. The packet is
then sent to the network, which makes copies of the packet and sends a copy to each
segment with a node that is part of the multicast address. Figure 2-2 is an example of a
multicast network
Broadcast
Broadcasts are found in LAN environments. Broadcasts do not traverse a WAN unless the
Layer 3 edge-routing device is configured with a helper address (or the like) to direct these
broadcasts to a specified network address. This Layer 3 routing device acts as an interface
between the local-area network (LAN) and the wide-area network (WAN)..
NOTE: Broadcasts will traverse a WAN if the WAN is bridged.
LAN Addressing
LAN (or any internetwork) addresses identify individual or groups of devices. Addressing
schemes vary depending on the protocol family and OSI layer.
Types: 1.Point to point
2.Bus
3.Ring
4.Star
5.Mesh
6.Hybrid
1.Point To Point
In networking, the Point-to-Point Protocol (PPP) is a data link protocol commonly used in establishing a direct connection between two networking nodes. It can provide connection authentication, transmission encryption, and compression.
2.Bus
For the bus, all stations attach, through appropriate hardware interfacing known as a tap, directly to a linear transmission medium, or bus. Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the bus.
Ethernet (IEEE 802.3) best represents this topology
Figure:
3.Ring
In the ring topology, the network consists of a set of repeaters joined by point-topoint links in a closed loop. The repeater is a comparatively simple device, capable of receiving data on one link and transmitting them, bit by bit, on the other link as fast as they are received, with no buffering at the repeater.
Because each NIC in a LAN-attached station is a repeater, each LAN station will repeat any signal that is on the network, regardless of whether it is destined for that particular station. If a LAN-attached station’s NIC fails to perform this repeater function, the entire network could come down. The NIC controller is capable of recognizing and handling the defective repeater and can pull itself off the ring, allowing the ring to stabilize and continue operating.
Figure:
In the star LAN topology, each station is directly connected to a common central node. Typically, each station attaches to a central node, referred to as the star coupler, via two point-to-point links, one for transmission and one for reception. In general, there are two alternatives for the operation of the central node.Several different cable types can be used for this point-to-point link, such as shielded twisted-pair (STP), unshielded twisted-pair (UTP), and fiber-optic cabling. Wireless media can also be used for communications links
Figure:.
Mesh networking is regarded as a valuable enhancement to Today's access point based WLAN and WPAN. This project investigates different aspects of WPAN mesh networking techniques to provide capabilities of self-organization, self-healing, energy saving and dynamic adaptation to changing environment for both high-rate and low-rate WPANs specified in IEEE 802.1.5.3 and 802.15.4 standards respectively.
6.Hybrid
Switches and hubs are simple methods for creating small workgroup LANs. By using structured wiring methods, it is easy to connect hubs and switches to create larger LANs.The hybrid topology combines more than one type of topology.When a bus line joins two hubs of different topologies, the configuration is called a star bus.The bus line is used to transfer the data between the star topologies.
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