What is LAN network (Local area network)
A network that connects a relatively small number of machines in a relatively close geographical area. A local area network (LAN network) is usually privately owned and links the devices in a single office, building, or campus. Depending on the needs of an organization and the type of technology used, a LAN network can be as simple as two PCs and a printer in someone’s home office; or it can extend throughout a company and include audio and video peripherals.
Currently, local area network (LAN) size is limited to a few kilometers. Local area network (LANs) are designed to allow resources to be shared between personal computers or workstations. The resources to be shared can include hardware (e.g., a printer), software (e.g., an application program), or data. A common example of a LAN, found in many business environments, links a work group of task-related computers, for example, engineering workstations or accounting PCs. One of the computers may be given a large capacity disk drive and may become a server to clients. Software can be stored on this central server and used as needed by the whole group.
In this example, the size of the LAN may be determined by licensing restrictions on the number of users per copy of software, or by restrictions on the number of users licensed to access the operating system. In addition to size, LANs are distinguished from other types of networks by their transmission media and topology.
In general, a given LAN will use only one type of transmission medium. The most common LAN topologies are bus, ring, and star. Early LANs (local area network) had data rates in the 4 to 16 megabits per second (Mbps) range. Today, however, speeds are normally 100 or 1000 Mbps.
LAN (local area network) TECHNOLOGIES
- Fast Ethernet
- Gigabit Ethernet
- 10 Gig Ethernet
- Ethernet and Wi-Fi are both “multi-access” technologies
- Broadcast medium, shared by many hosts
- Simultaneous transmissions will result in collisions
- Media Access Control (MAC) protocol required
- Rules on how to share medium
- The Data Link Layer is divided into two Part MAC Media Access Control) Sublayer and LLC (Logic Link Control) Sublayer
- Carrier-sense multiple access with collision detection (CSMA/CD).
- CS = carrier sense
- MA = multiple access
- CD = collision detection
- Base Ethernet standard is 10 Mbps.
- 100Mbps, 1Gbps, 10Gbps standards came later
- CSMA/CD (carrier sense multiple access with collision detection) media access protocol is used.
- Data is transmitted in the form of packets.
- Sense channel prior to actual packet transmission.
- Transmit packet only if channel is sensed idle; else, defer the transmission until channel becomes idle.
- After packet transmission is started, the node monitors its own transmission to see if the packet has experienced a collision.
- If the packet is observed to be undergoing a collision, the transmission is aborted and the packet is retransmitted after a random interval of time using Binary Exponential Back off algorithm.
- End nodes are identified by their Ethernet Addresses (MAC Address or Hardware Address) which is a unique 6 Byte address.
- MAC Address is represented in Hex Decimal format e.g. 00:05:5D:FE:10:0A
- The first 3 bytes identify a vendor (also called prefix) and the last 3 bytes are unique for every host or device
- 100 Mbps bandwidth
- Uses same CSMA/CD media access protocol and packet format as in Ethernet.
- 100BaseTX (UTP) and 100BaseFX (Fiber) standards
- Physical media :-
- 100 BaseTX – UTP Cat 5e
- 100 BaseFX – Multimode / Singlemode Fiber
- Full Duplex/Half Duplex operations.
- Provision for Auto-Negotiation of media speed:
10 Mbps or 100Mbps (popularly available for copper media only).
- Maximum Segment Length
- 100 Base TX – 100 m
- 100 Base FX – 2 Km (Multimode Fiber)
- 100 Base FX – 20 km (Singlemode Fiber)
- 1 Gbps bandwidth.
- Uses same CSMA/CD media access protocol as in Ethernet and is backward compatible (10/100/100 modules are available).
- 1000BaseT (UTP), 1000BaseSX (Multimode Fiber) and 1000BaseLX (Multimode/Singlemode Fiber) standards.
- Maximum Segment Length
- 1000 Base T – 100m (Cat 5e/6)
- 1000 Base SX – 275 m (Multimode Fiber)
- 1000 Base LX – 512 m (Multimode Fiber)
- 1000 Base LX – 20 Km (Singlemode Fiber)
- 1000 Base LH – 80 Km (Singlemode Fiber)
10 Gig Ethernet
- 10 Gbps bandwidth.
- Uses same CSMA/CD media access protocol as in Ethernet.
- Propositioned for Metro-Ethernet
- Maximum Segment Length
- 1000 Base-T – Not available
- 10GBase-LR – 10 Km (Singlemode Fiber)
- 10GBase-ER – 40 Km (Singlemode Fiber)
802.11 Wireless LAN
- Provides network connectivity over wireless media
- An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network
- The AP is connected to wired network and is equipped with antennae to provide wireless connectivity
- Range ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point
- To service larger areas, multiple APs may be installed with a 20-30% overlap
- A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off)
- Three flavors:
Multiple Access with Collision Avoidance (MACA)
- Before every data transmission
- Sender sends a Request to Send (RTS) frame containing the length of the transmission
- Receiver respond with a Clear to Send (CTS) frame
- Sender sends data
- Receiver sends an ACK; now another sender can send data
- When sender doesn’t get a CTS back, it assumes collision
WLAN : 802.11b
- The most popular 802.11 standard currently in deployment.
- Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band
WLAN : 802.11a
- Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band
- Incompatible with devices operating in 2.4GHz
- Supports Data rates up to 54 Mbps.
WLAN : 802.11g
- Supports data rates as high as 54 Mbps on the 2.4 GHz band
- Provides backward compatibility with 802.11b equipment
Basic Elements of LAN Data Communication
- Sender – A device that is used to send or transmit messages to another device is called sender or transmitter or source.
- Medium – A path through which data is transmitted (or sent) from one location to another location, called transmission medium.
- Receiver – A device that is used to receive messages from another device is called receiver or sink.
Communication Devices used in LAN (Local Area Network)
- Network Interface Card
- Hub & Switch
- A repeater receives a signal, regenerates it, and passes it on.
- It can regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media.
- It operates at Physical Layer of OSI
- The Four Repeater Rule for 10-Mbps Ethernet should be used as a standard when extending LAN segments.
- This rule states that no more than four repeaters can be used between hosts on a LAN.
- This rule is used to limit latency added to frame travel by each repeater.
- Hubs are used to connect multiple nodes to a single physical device, which connects to the network.
- Hubs are actually multiport repeaters.
- Using a hub changes the network topology from a linear bus, to a star.
- With hubs, data arriving over the cables to a hub port is electrically repeated on all the other ports connected to the same network segment, except for the port on which the data was sent.
- Switches are Multiport Bridges.
- Switches provide a unique network segment on each port, thereby separating collision domains.
- Today, network designers are replacing hubs in their wiring closets with switches to increase their network performance and bandwidth while protecting their existing wiring investments.
- Like bridges, switches learn certain information about the data packets that are received from various computers on the network.
- Switches use this information to build forwarding tables to determine the destination of data being sent by one computer to another computer on the network.
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