5.2. LAN technologies (Ethernet, token Ring, Gigabit Ethernet)
5.3. Large networks and wide areas
5.1. LAN topologies (bus, ring, star)
Local Area Network (LAN) is a data communication network connecting various terminals or computers within a building or limited geographical area. The connection among the devices could be wired or wireless. Ethernet, Token Ring and Wireless LAN using IEEE 802.11 are examples of standard LAN technologies.
LAN has the following Topologies
Star Topology
Bus Topology
Ring Topology
Mesh Topology
Hybrid Topology
You should consider four main factors when selecting a LAN technology:
Cost efficiency
Installed base
Maintainability
Performance 5.2. LAN technologies (Ethernet, token Ring, Gigabit Ethernet) IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD), also known as the Ethernet:
• 10 Mbit/s transmission speed and
• Bus topology (shared medium).
Ethernet is the most widely used LAN technology, which is defined under IEEE standards 802.3. The reason behind its wide usability is Ethernet is easy to understand, implement, maintain, and allows low-cost network implementation. Also, Ethernet offers flexibility in terms of topologies that are allowed. Ethernet operates in two layers of the OSI model, Physical Layer, and Data Link Layer. For Ethernet, the protocol data unit is Frame since we mainly deal with DLL. In order to handle collision, the Access control mechanism used in Ethernet is CSMA/CD.
Ethernet technology has evolved over the years, and today it is distinguished into the following types based on their speeds.
i. Fast Ethernet o 100 Mbit/s version of Ethernet, using CSMA/CD algorithm (recent addition to IEEE 802.3). o 10 times faster than “normal” Ethernet, and 10 times smaller (max. app. 200 m between stations). o Easy upgrade path from Ethernet, simply replace Ethernet hubs, adapters, and driver software! ii. Gigabit Ethernet o Gigabit Ethernet delivers a data rate of 1,000 Mbit/s (1 Gbit/s). iii. 10 Gigabit Ethernet o 10 Gigabit Ethernet is the recent generation and delivers a data rate of 10 Gbit/s (10,000 Mbit/s). It is generally used for backbones in high-end applications requiring high data rates. Token Ring: This technology was developed by IBM and it uses three-byte frames to connect computers. These three-byte frames are known as tokens, and they travel along servers or computers forming a logical structure of ring. The token ring network has data transfer rates of 4, 16, and 100 Mbps. These networks were largely used in corporate environments, but today are getting replaced by Ethernet. ARCNET: It stands for Attached Resource Computer Network, which was used for connecting microcomputers in the 1980s. It was mainly used for automation tasks in offices. This technology is nowadays used in industrial controls. FDDI: This stands for fiber distributed data interface and is another LAN technology in use today. It made use of fiber optic cables, and can transmit up to 100 Mbit/seconds. This LAN technology can deliver up to 200 kms, and it uses two rings. The first ring acts as a primary backup and second ring acts as a secondary backup. The primary ring has 100 Mbit/seconds capacity; the secondary ring can also carry another 100 Mbit/seconds, thereby adding to 200 Mbit/s.
5.3. Wide-area Networks (WANs)
WAN provides long-distance transmission of data, voice, image and information over large geographical areas that may comprise a country, continent or even the whole world.
In contrast to LANs, WANs may utilize public, leased or private communication devices, usually in combinations, and can therefore span an unlimited number of miles. A WAN that is wholly owned and used by a single company is often referred to as enterprise network.
When an enterprise grows to include branch offices, e-commerce services, or global operations, a single local-area network (LAN) is no longer sufficient to meet its business requirements. Wide- area network (WAN) access has become essential for larger businesses today.
A variety of WAN technologies meet the different needs of businesses, and there are many ways to scale the network. Adding WAN access introduces other considerations, such as network security and address management. Consequently, designing a WAN and choosing the correct carrier network services is not a simple matter.
WANs are networks that span a larger geographic area and usually require the services of a common carrier. Examples of WAN technologies and protocols include Frame Relay, ATM, and DSL. It is a data communications network that operates beyond the geographic scope of a LAN. Its use facilities provided by a service provider, or carrier, such as a telephone or cable company, to connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. WANs provide network capabilities to support a variety of mission-critical traffic such as voice, video, and data.
Here are the three major characteristics of WANs:
o WANs generally connect devices that are separated by a broader geographic area than can be served by a LAN. o WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers. o WANs use serial connections of various types to provide access to bandwidth over large geographic areas.
Why Are WANs Necessary?
LAN technologies provide both speed and cost efficiency for the transmission of data in organizations over relatively small geographic areas. However, other business needs require communication among remote sites, including the following:
o People in the regional or branch offices of an organization need to be able to
communicate and share resources with the central site. o Organizations often want to share information with other organizations across large distances. For example, software manufacturers routinely communicate product and promotion information to distributors that sell their products to end users. o Employees who frequently travel on company business need to access information that resides on their corporate networks.
In addition, home computer users need to send and receive data across increasingly larger distances. Here are some examples:
o It is now common in many households for consumers to communicate with
banks, stores, and a variety of providers of goods and services via computers. o Students do research for classes by accessing library catalogs and publications located in other parts of their country and in other parts of the world
WAN Connections and Technology
Though WANs cover a wide area, connections can be either wired or wireless. Wired WANs usually consist of broadband internet services and multiprotocol label switching (MPLS), which is a form of data-forwarding technology used to control traffic flow and speed up connection, while wireless WANs normally include 4G/5G and Long-Term Evolution (LTE) networks. Wired WAN Pros and Cons
The pros generally revolve around security. In wired network architecture, devices must be physically wired into the network, making it more difficult for cyber attackers to gain unauthorized access. Additionally, with a physical connection required, organizations can control the number of devices that have access to the network. With fewer devices accessing the network, the risk of malware potentially infecting the infrastructure is reduced.
The other benefit is speed. Unlike a wireless system that can be subject to outside interference, a wired network allows for a faster connection.
The cons involve hardware. The more cabled connections, the more wires to manage. Further, when using a cabled network, employees can only gain access when there is a physical connection available, limiting mobility.
Wireless WAN Pros and Cons
The benefits of a wireless WAN are the opposite. The workplace can be anywhere, giving employees flexibility. The cons include both risks, as wireless networks are generally more vulnerable to attacks, and speed, as wireless networks are often slower.
To reduce costs, an organization might lease its WAN infrastructure as a service from a third- party service provider. The WAN may operate over a dedicated, private channel, or in a hybrid scenario, have parts of it operating via a shared, public medium like the internet.
Types of WAN technologies
Asynchronous Transfer Mode (ATM)
It is a fast communication technique, which is cell-based architecture, rather than a frame-based
architecture. This telecommunication standard is defined by ITU and ANSI. It is used for transferring various types of signals in the network. One of the key advantages of ATM is that it requires no separate overlay networks for signal transmission. ATM can connect points in close and farther geographical locations.
Asynchronous transfer mode (ATM) technology can transfer voice, video and data through private and public networks. It is built on a cell-based architecture, rather than a frame-based architecture. Frame Relay
Frame Relay is a technology for transmitting data between LANs or endpoints of a WAN. It specifies the physical and data-link layers of digital telecommunications channels using a packet switching methodology.
Frame Relay packages data in frames and sends it through a shared Frame Relay network. Each frame contains all necessary information for routing it to its destination. Frame Relay's original purpose was to transport data across telecom carriers' ISDN [integrated services digital network] infrastructure, but it's used today in many other networking contexts.
DSL (Digital Subscriber line)
It is a family of technologies that are used to transmit digital data over telephone lines.
These DSL modem is a device used to connect a computer or router to a telephone line which provides the digital subscriber line service for connection to the internet.
DSL technology is a permanent connection technology that uses existing twisted pair telephone lines to transport data with high bandwidth and provides subscriber IP services. A DSL modem converts an Ethernet signal from the user device into a DSL signal, which is transmitted to the central office.
Several DSL subscriber lines are multiplexed into a single high capacity link using a DSL access multiplexer (DSLAM) at the provider's location. DSLAMs incorporate TDM technology for aggregation of several subscriber lines on a single medium, usually a T3 (DS3) connection. To achieve fast data rates, current DSL technologies use sophisticated coding and modulation techniques.
MPLS
Multi-protocol tag switching (MPLS) is a high-performance multi-protocol WAN technology
that directs data from one router to the next according to short path tags, rather than IP network addresses. MPLS has several characteristics that define it. It is multiprotocol, which means it has the ability to transport any content, including IPv4, IPv6, Ethernet, ATM, DSL and Frame Relay traffic. Use tags that tell the router what to do with a package. The tags identify the routes between remote routers instead of between terminals and while MPLS routes IPv4 and IPv6 packets effectively, everything else is switched. It is a service provider technology. Leased lines deliver bits between sites, and Frame Relay and WAN Ethernet deliver frames between sites. However, MPLS can deliver any type of package between sites.
WIMAX
Worldwide interoperability for microwave access (WiMAX) is a new technology that has just begun to be used. It is described in the IEEE 802.16 standard and a wireless MAN standard primarily for broadband internet access. WiMAX provides a high-speed broadband service with wireless access and provides extensive coverage such as a cellular telephone network, rather than small areas of Wi-Fi wireless coverage. It works similarly to Wi-Fi, but with higher speeds, over longer distances and for a greater number of users.
3G / 4G MOBILE DATA
Increasingly, cellular service is another wireless WAN technology used to connect users and remote locations where no other WAN access technology is available. Phones, tablet PCs, laptops and even some routers can communicate over the Internet using mobile data technology. These devices use radio waves to communicate through a mobile phone tower.
Some common terms of the mobile data industry include the following:
3G / 4G wireless: abbreviation for third and fourth generation cellular access. These technologies support wireless Internet access.
Long-term evolution (LTE) : refers to a newer and faster technology, which is
considered part of the fourth generation (4G) technology.
VPN TECHNOLOGY
When a remote worker or a worker in a remote office uses broadband services to access the corporate WAN through the Internet, security risks are generated. To address security issues, broadband services provide capabilities to use VPN connections to a VPN server , which is usually located on the corporate site. A VPN is an encrypted connection between private networks through a public network, such as the Internet. Instead of using a dedicated Layer 2 connection, such as a leased line, a VPN uses virtual connections called “VPN tunnels,” which are routed over the Internet from the company's private network to the site host or the remote employee.
VPN benefits include the following:
o Cost effective: VPNs allow organizations to use the global Internet to connect remote offices and users to the main corporate site, eliminating the need for dedicated WAN links and expensive modem banks. o Security: VPNs provide the maximum level of security through two advanced encryption and authentication protocols that protect data from unauthorized access. o Scalability: Because VPNs use the Internet infrastructure in ISPs and devices, it is easy to add new users. Companies can greatly increase capacity, without adding significant infrastructure. o Compatibility with broadband technology: Broadband service providers, such as DSL and cable, support VPN technology, so that mobile workers and remote employees can take advantage of their homes' high-speed Internet service to Access corporate networks.
