# Local Area Network

## Summary


Local Area Network (LAN) is a computer network used for connecting computers within a limited geographical area such as offices, schools and buildings. Interconnected LANs dispersed over a wider area is called a Wide Area Network (WAN).

A LAN consists of cables, switches, routers, and bridges that together enable devices to connect and communicate with one another. Devices connected in a LAN have shared access to the interconnecting medium. When the medium is made of physical wires or cables, we called it **Wired LAN**. If the medium is radio waves we called it **Wireless LAN (WLAN)**.

The most common technology used for wired LANs is Ethernet. For wireless LANs, IEEE 802.11 standards are used and their commercialized technology is called Wi-Fi.

## Discussion

### What are the characteristics of a LAN?

LAN is a low-cost and effective network type capable of connecting multiple devices on a single transmission medium so that every device in the network can communicate with one another. 

LAN coverage is over a limited extent, from meters to a few kilometres. The quality of data transmission in LAN is comparatively higher than other network types due to the shorter coverage area. Switches or routers are used to construct a LAN network most of the time. This ensures higher data transmission speeds and reliability. 

Setting up a LAN network can be done at low costs. If there's a need for expansion, it can be done quickly. 


### What are the different LAN types?

Based on the communication mode, LAN can be generally classified into two types: 

    + **Client-Server LAN**: In this mode, only a single central server is used to connect with multiple clients through wired or wireless medium. If a client device needs to send a packet to another client, communication happens via the central server.
    + **Peer-to-Peer LAN**: In this mode, there's no need for a central server. Clients can communicate with each other directly. Sending a file is easier and faster, thus enabling higher speeds.

### What's the difference between Wireless LAN and Ethernet LAN?

Wireless LAN as the name suggests uses radio waves to transmit data whereas Ethernet uses wires to transmit data. Data transfer or communication through Ethernet LAN is more stable and faster, though both have their benefits. 

The particular Radio Frequency (RF) spectrum used in WLAN determines the coverage. Signal propagation and hence radio coverage are affected by walls, metal objects and even people. Coverage can be increased with wireless repeaters, bridges and access points. Data rates are steadily increasing for WLAN with the recent Wi-Fi 6 release (Feb 2021) that supports a maximum throughput speed of 9.6Gbps across multiple channels with 75% lower latency. 

Ethernet LAN primarily uses electrical signals to transmit data through cables. It has less interference than WLAN. Unshielded Twisted Pair (UTP) cables are commonly used to establish Ethernet connections. 10 Gigabit Ethernet (10GbE) is the latest standard that can offer a maximum throughput speed of 10Gbps. 


### Could you describe some limitations of LANs?

LAN networks are only suitable for transmission over a limited distance. The cost of installation rises as the coverage area expands.

LAN requires security to avoid threats from malware and viruses. Since computers are interconnected, any security breach can impact the entire network. Apart from securing devices physically, LAN security can be compromised by misconfigurations including weak passwords and improper allocation of devices. Obviously WLANs are easier to attack because physical access to network devices is not required. However, even in wired LANs, physical access to LAN sockets in hallways and reception areas can pose risks. It becomes important to keep the entire network under a policy guideline to avoid possible threats.


### What type of devices are commonly found on a LAN?

A LAN has many types of devices:   

    + **Host**: End device (client or server) that can send and receive data.
    + **Repeater**: Operates at the physical layer. Receives data on one port, boosts the signal and sends it out on another port.
    + **Hub**: Essentially a multi-port repeater. All devices connected to the hub belong to the same LAN segment. A packet coming on one port is forwarded to all other ports. More devices connected to a single hub will result in packet collisions and drop in throughput.
    + **Bridge**: Connects two or more LANs in the network. Isolates its ports to accommodate more devices. Bridges forward frames between different LAN segments by looking at MAC addresses. It works at physical and data link layers.
    + **Switch**: Similar to a bridge but more sophisticated. Whereas a bridge typically implements functionality in hardware, a switch does it in software.
    + **Router**: A layer 3 or network layer device. It routes packets by looking at IP addresses. Essential for connecting to the Internet.
    + **Gateway**: Interconnects to another network type, either LAN or WAN, by translating between their protocols.

### How does Virtual LAN differ from a normal LAN?

Virtual LAN (VLAN) increases the capabilities of a normal LAN. It's a logical way of separating traffic between multiple logical or virtual networks that exists physically on the same network. VLANs are mostly used by organizations with a large number of devices.

In a normal LAN, a broadcast message reaches all nodes whether they need it or not. In a VLAN, only a subset of nodes that belong to that VLAN (aka broadcast domain) will receive the broadcasted packet. Thus, VLANs mitigate packet flooding and network congestion. 

VLANs minimize security risks by reducing the number of hosts that receive a packet. Moreover, hosts that hold sensitive information can be on a separate VLAN. VLANs enable flexible network configuration, such as, grouping hosts by department rather than physical location. VLANs can be easily reconfigured just by changing port configurations. 

Implementation of VLAN will be cost-effective as it's built using switches. Routers are needed only for sending data outside the LAN.  


### Could you describe the different types of LAN topologies?

Topology in networking refers to the way of devices are interconnected. Some major LAN topologies are: 

    + **Bus Topology**: Also known as the backbone network. Simplest and widely used network design that needs only a single cable for connectivity. A device known as a terminator is placed at both ends to avoid signals reflecting back to each other.
    + **Star Topology**: A central device acts as a hub and connects to all other devices. Data on the network passes through devices in between before reaching the destination.
    + **Ring Topology**: Nodes are arranged in a ring topology. Data passes through each node before reaching the destination. Traffic can be bidirectional and the chances of packet collisions are less. Broken network links affect bi-directional communication.
    + **Mesh Topology**: Nodes are connected to each other in point-to-point configuration. Each node has multiple paths to reach another node. If one path fails, an alternate path is used, making this topology more fault-tolerant.

### What are the different data transmission methods used in LANs?

In communications, data can be transmitted in a few ways: 

    + **Unicast**: It's a one-to-one data transmission method that typically uses a connection-oriented protocol such as TCP (Transmission Control Protocol). A web server that transmits or streams data to a single user via a unique connection is an example of unicast.
    + **Multicast**: It's a one-to-many data transmission method that uses a connectionless protocol such as UDP (User Datagram Protocol). A simple example is an email addressed to a specific group of recipients.
    + **Broadcast**: It's a one-to-all data transmission method. Data originates from a single point and is sent to all users simultaneously. Cable TV is an example of a broadcast network.In LAN, unicasting is predominant with many applications using it (FTP, HTTP, Telnet). Multicasting is implicit in the way a hub operates. VLAN is also multicasting in some sense. Explicit multicasting is possible via the IGMP protocol. Broadcasting is usually employed when a node wants to discover something, such as in ARP and DHCP protocols. 


### How does a LAN interface with a WAN?

Routers connect LAN devices to WAN and then the wider internet. Most wireless routers come with two types of physical ports labelled as LAN and WAN. A WAN port is mostly connected to a modem that makes the router capable of accessing the internet. LAN port can be used to connect with devices that don't have Wi-Fi support. For secure communications, the LAN and WAN ports are internally separated by a firewall. Devices connected via WAN ports can't access the LAN devices unless port forwarding is configured. 

One of the essential operations done by a router is called **Network Address Translation (NAT)**. NAT is designed to conserve IP addresses. Rather than give every device in the world a unique IP address, LAN devices have unregistered IP addresses that are valid only within that LAN. Router acts as an intermediary and presents to the internet a single public IP address. Router translates between internal private addresses and the public address. 


### Could you describe some recent advancements in LAN technology?

LAN has seen significant development since its inception in the 1970s and has grown exponentially with changing demands and needs of users. Availability of next-generation WLAN cloud services, 5G, IoT, smart buildings, and cabling trends are transforming the industry. 

**Single-Pair Ethernet (SPE)** has become the trend for being faster and cost-effective. It provides transmission speeds up to 1Gbps with a single pair of twisted copper wires rather than the classic four-pair cables or RJ45 connectors. 

**All over IP** is an approach to building automation with IP alone. It's an integrated approach that brings together Ethernet/IP cabling, Power over Ethernet (PoE), and WLAN. Since all devices understand IP, there's no need for protocol translation in between. Such standardization improves reliability and availability.  

Adoption of Passive Optical LAN (POLAN) cable has changed the fundamental LAN architecture by replacing copper cables with single-mode fiber optic cables, providing higher bandwidth and numerous other advantages. 

## Milestones

1972

Dr. Robert M. "Bob" Metcalfe and his colleagues at Xerox PARC develop the first experimental Ethernet network called **Alto Aloha Network** for connecting with Altos, a personal workstation. 

May  
1973

Metcalfe renames Alto Aloha Network to **Ethernet**. He clarifies that this network can support any device. In a memo titled *Alto Ethernet* he gives a schematic representation in which personal computers can connect to a printer via a coaxial cable. 

1974

Cambridge University initiates the **Cambridge RING Project** for communication of devices through the *Laboratory* within the campus. Information flows on twisted pair cables between the printers and computers. 

Jul  
1976

David Boggs and Bob Metcalfe publish a paper titled *Ethernet: Distributed Packet Switching for Local Computer Networks*. The same year Ethernet becomes an open networking standard funded by three companies Xerox, DEC and Intel. 

Dec  
1977

The **first commercial LAN** is installed by Datapoint Corp. at Chase Manhattan Bank in New York. It uses the Attached Resource Computer (ARC) network using a token ring scheme for Ethernet. 

Dec  
1984

The Institute of Electrical and Electronics Engineers (IEEE) publishes the standard **IEEE 802.3** that specifies the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method, which is essential for the working of a LAN. 

1991

Kalpana Corporation launches a new device called **LAN switch**. Each port can run at full capacity simultaneously, something not possible with hubs. This is later called an Ethernet switch and it provides high-throughput communications. 

1995

**Fast Ethernet (FE)** is introduced with transmission speed up to 100Mbps to meet the increasing the needs of users. It's specified by the IEEE 802.3u standard. 

1997

First version of **Wireless Local Area Network (WLAN)** standards IEEE 802.11 is published with two raw data rates of 1 or 2Mbps. 

Jun  
2003

**Power over Ethernet (PoE)** is defined by the IEEE 802.3af and 802.3at standards. It can pass electric power along with data on twisted pair Ethernet cable. PoE can provide 48 volts over a 4-wire or 8-wire twisted pair. It's useful at locations without a power outlet.

Dec  
2013

In WLAN, the standard IEEE 802.11ac is defined. It operates at the 5GHz band with support for MU-MIMO (Multi-User MIMO). This allows access points to communicate with multiple devices simultaneously. 

Dec  
2017

**400GbE Ethernet** interface is approved by IEEE under the IEEE 802.3bs standard. It can transmit data up to 400Gbps, which is four times faster than 100Gbps standard while also consuming less power. 

Feb  
2021

The IEEE 802.11ax standard or **Wi-Fi 6** is launched. It provides more speed and greater stability on a higher bandwidth channel than its predecessors. MU-MIMO in Wi-Fi 6 can work in both 2.4GHz and 5GHz bands.