Introduction to Networking and Ethernet

       Introduction to Network and Protocol 

1.Network

Α network is simply defined as something that connects things together for a specific purpose. The term network is used in a variety of contexts, including telephone, television, computer, or even people networks.
A computer network connects two or more devices together to share a nearly limitless range of information and services, such as  Documents,  Email and messaging, Websites, Databases etc.

A computer network connects two or more devices together to share information and services. Multiple networks connected together form an internetwork.  

2.Protocols

Protocols are rules that govern how devices communicate and share information across a network. Multiple protocols often work together to facilitate end-to-end network communication, forming protocol suites or stacks. Examples of protocols include: 

IP – Internet Protocol
HTTP - Hyper Text Transfer Protocol
SMTP – Simple Mail Transfer Protocol 

FTP - File Transfer Protocol
POP3 - Post Office Protocol
Telnet - Telecommunication Network

3.Types of Network

The two most common categories of networks are LAN and WAN

1. LANs (Local Area Networks)

2. WANs (Wide Area Networks) 

3. MAN (Metropolitan Area Network) 

4. SAN (Storage Area Network)

5. VPN (Virtual Private Network) 

LAN- A LAN is generally a high-speed network that covers a small geographic area, usually contained within a single building or campus. A LAN is usually under the administrative control of a single organization. Ethernet is the most common LAN technology.

WAN - A WAN can be defined one of two ways. The book definition of a WAN is a network that spans large geographical locations, usually to connect multiple LANs. This is a general definition, and not always accurate

MAN - A MAN (Metropolitan Area Network) is another category of network, though the term is not prevalently used. A MAN is defined as a network that connects LAN’s across a city-wide geographic area.

An internetwork is a general term describing multiple networks connected together. The Internet is the largest and most well-known internetwork.  

SAN - Some networks are categorized by their function, as opposed to their size. A SAN (Storage Area Network) provides systems with high-speed, lossless access to high-capacity storage devices.

VPN - A VPN (Virtual Private Network) allows for information to be securely sent across a public or unsecure network, such as the Internet. Common uses of a VPN are to connect branch offices or remote users to a main office.

4.Network Topologies

Topology - A topology refers to a network’s physical and logical layout. A network’s physical topology refers to the actual layout of the computer cables and other network devices. A network’s logical topology refers to the way in which the network appears to the devices that use it.

Several topologies are in use on networks today. Some of the more common topologies are the bus, ring, star, mesh, and wireless.

(i) Multiprotocol Label Switching (MPLS)
(ii) Point-to-point
(iii) Point-to-multipoint
(iv) Ring
(v) Star
(vi) Mesh
(vii) Bus
(viii) Hybrid

4.1-Bus Topology
A bus topology uses a trunk or backbone to connect all the computers on the network, Systems connect to this backbone using T  connectors or taps (known as a vampire tap, if you must pierce the wire). To  avoid signal reflection, a physical bus topology requires that each end of the physical bus be terminated, with one end also being grounded. A hub or switch is not needed in this installation.   

Advantage

a) Compared to other topologies, a bus is cheap and easy to implement.

b) Requires less cable than other topologies

c) Does not use any specialized  network equipment.

Disadvantage

a) Network disruption might occur when computers are added or removed.

b) Because all systems on the network connect to a single backbone, a break in the cable prevents all systems from accessing the network.

c) Difficult to troubleshoot.

4.2-Ring Topology  

The ring topology is actually a logical ring, meaning that the data travels in a circular fashion from one computer to another on the network. It is not a physical ring topology. Figure 1.4 shows the logical layout of a ring network. 
A hub or switch is not needed in this installation either. In a true ring topology, if a single computer or section of cable fails, the signal is interrupted. The entire network becomes inaccessible. Network disruption can also occur when computers are added to or removed from the network, making it an impractical network design in environments where the network changes often.  

4.3-Star Topology  

In the star topology, all computers and other network devices connect to a central device called a hub or switch. Each connected device requires a single cable to be connected to the hub, creating a point-to-point connection between the device and the hub.  

Using a separate cable to connect to the hub or switch allows the network to be expanded without disruption. A break in any single cable does not cause the entire network to fail. 

The star topology is the most widely implemented network design in use today, but it is not without shortcomings. Because all devices connect to a centralized hub or switch, this creates a single point of failure for the network. If the hub or switch fails, any device connected to it cannot access the network. Because of the number of cables required and the need for network  devices, the cost of a star network is often higher than other topologies. 

Advantages

1. Star networks easily expanded without disruption to the network.

2. Cable failure affects only a single user.

3. Easy to troubleshoot and implement.

Disadvantage

1. Requires more cable than most of the other topologies.

2. A central connecting device enables a single point of failure.

3.Requires additional networking equipment to create the network layout.

4.4-Mesh Topology 

The wired mesh topology  incorporates a unique network design in which each computer on the network connects to every other, creating a  point-to-point connection between every device on the network. The purpose of the mesh design is to provide a high level of redundancy. If one network cable fails, the data always has an alternative path to get to its destination each node can act as a relay.  

The wiring for a mesh network can be complicated. Furthermore, the cabling costs associated with the mesh topology can be high, and troubleshooting a failed cable can be tricky. Because of this, the mesh topology is not the first choice for many wired networks but is more popular with servers or routers.  

A variation on a true mesh topology is the hybrid mesh. It creates a redundant point-to-point network connection between only specific network devices (such as the servers). The hybrid mesh is most often seen in WAN implementations but can be used in any network.  

Advantage

1. Provides redundant paths between LAN topologies.

2. The network can be expanded without disruption to current users.

Disadvantage

1. Requires more cable than the other devices

2. Complicated implementation

4.5-Hybrid Topologies  

As we might expect, topology designs are not black-and-white. Many topologies found in large networking environments are a hybrid of physical topologies. An example of a hybrid topology is the star bus—a combination of the star topology and the bus topology. Figure 1.11 shows how this might look in a network implementation.  

5.Infrastructure Wireless Topology 

The infrastructure wireless topology is commonly used to extend a wired LAN to include wireless devices. Wireless devices communicate with the wired LAN through a base station known as an access point (AP) or wireless access point. The AP forms a bridge between a wireless and wired LAN, and all transmissions between wireless stations, or between a system and a wired network client, go through the AP. APs are not mobile and must stay connected to the wired network; therefore, they become part of the wired network infrastructure (thus the name). In infrastructure wireless networks, there might be several access points providing wireless coverage for a large area or only a single access point for a

small area, such as a single home or small building.

6.Ad Hoc Wireless Topology  

In a wireless ad hoc topology, devices communicate directly between themselves without using an access point. This peer-to-peer network design is commonly used to connect a small number of computers or wireless devices. For example, an ad hoc wireless network may be set up temporarily between laptops in a boardroom or to connect systems in a home instead of using a wired solution. The ad hoc wireless design provides a quick method to share files and resources between a small number of systems. Figure 1.7 shows an ad hoc wireless network, and Figure 1.8 shows the infrastructure network using the AP.  

 

        Ethernet Technologies 

1.Ethernet

Ethernet is a family of technologies that provides data-link and physical specifications for controlling access to a shared network medium. It has emerged as the dominant technology used in LAN networking.

Ethernet was originally developed by Xerox in the 1970s, and operated at 2.94Mbps. The technology was standardized as Ethernet Version 1 by a consortium of three companies - DEC, Intel, and Xerox, collectively referred to as DIX - and further refined as Ethernet II in 1982.  

In the mid 1980s, the Institute of Electrical and Electronic Engineers (IEEE) published a formal standard for Ethernet, defined as the IEEE 802.3 standard. The original 802.3 Ethernet operated at 10Mbps, and successfully supplanted competing LAN technologies, such as Token Ring.  

2.Ethernet Cable Types

Ethernet can be deployed over three types of cabling:

i) Coaxial cabling – almost entirely deprecated in Ethernet networking

ii) Twisted-pair cabling

iii) Fiber optic cabling 

 

Coaxial cable - Coaxial cable, often abbreviated as coax, consists of a single wire surrounded by insulation, a metallic shield, and a plastic sheath. The shield helps protect against electromagnetic interference (EMI), which can cause attenuation, a reduction of the strength and quality of a signal. EMI can be generated by a variety of sources, such as florescent light ballasts, microwaves, cell phones, and radio transmitters. Coax is commonly used to deploy cable television to homes and businesses. 

Two types of coax were used historically in Ethernet networks: 

(a) Thinnet

(b)  Thicknet

Twisted-pair cable -  Twisted-pair cable consists of two or four pairs of copper wires in a plastic sheath. Wires in a pair twist around each other to reduce crosstalk, a form of EMI that occurs when the signal from one wire bleeds or interferes with a signal on another wire. Twisted-pair is the most common Ethernet cable.

Twisted-pair cabling can be either shielded or unshielded. Shielded twisted pair is more resistant to external EMI; however, all forms of twisted-pair suffer from greater signal attenuation than coax cable. 

Fiber optic -  While coax and twisted-pair cabling carry electronic signals, fiber optics uses light to transmit a signal. Ethernet supports two fiber specifications: 

1.Singlemode fiber – consists of a very small glass core, allowing only a single ray or mode of light to travel across it. This greatly reduces the attenuation and dispersion of the light signal, supporting high
bandwidth over very long distances, often measured in kilometers.

2. Multimode fiber – consists of a larger core, allowing multiple modes of light to traverse it. Multimode suffers from greater dispersion than singlemode, resulting in shorter supported distances.

 

3.Types of Communication

Half-Duplex - two-way communication, but not simultaneous

Full-Duplex - simultaneous two-way communication 

Simplex  - one-way communication

 

4.Types of Cable

1. Straight-through cable -  A straight-through cable is often referred to as a patch cable.  A straight-through cable is used to connect any device to a hub or switch, except for another hub or switch.  The hub or switch provides the crossover (or MDIX) function to connect transmit pins to receive pins. 

A straight-through cable is used in the following circumstances: 

a) From a host to a hub – MDI to MDIX

b) From a host to a switch - MDI to MDIX

c) From a router to a hub - MDI to MDIX

d) From a router to a switch - MDI to MDIX  

Pin#   Connector 1                  Connector 2         Pin#  

1         Orange White               Orange White           1
2              Orange                        Orange                   2
3        Green White                 Green White              3

4              Blue                           Blue                        4
5          Blue White                  Blue White               5

6              Green                          Green                    6
7        Brown White                Brown White            7

8              Brown                          Brown                  8

2. Crossover cable - A crossover cable is often required to uplink a hub to another hub, or to uplink a switch to another switch. This is because the crossover is performed twice, once on each hub or switch (MDIX to MDIX), negating the crossover. 

Pin#   Connector 1                  Connector 2         Pin#  

1         Orange White               Green White            1
2              Orange                        Green                    2
3        Green White                 Orange White            3

4              Blue                           Blue                        4
5          Blue White                  Blue White               5

6              Green                          Orange                  6
7        Brown White                Brown White            7

8              Brown                          Brown                  8

 

3. Rollover cable  -  A rollover cable is used to connect a workstation or laptop into a Cisco device’s console or auxiliary port, for management purposes. A rollover cable is often referred to as a console cable, and its sheathing is usually flat and light-blue in color. 

Pin#   Connector 1                  Connector 2         Pin#  

1         Orange White                     Brown                1
2              Orange                      Brown White          2
3        Green White                        Green                 3

4              Blue                         Blue White              4
5          Blue White                         Blue                  5

6              Green                      Green White            6
7        Brown White                      Orange               7

8              Brown                    Orange White           8

 

Rollover cables can be used to configure Cisco routers, switches, and firewalls.  

 

Power over Ethernet (PoE) 

Power over Ethernet (PoE) allows both data and power to be sent across the same twisted-pair cable, eliminating the need to provide separate power connections. This is especially useful in areas where installing separate power might be expensive or difficult.  

PoE was originally formalized as 802.3af, which can provide roughly 13W of power to a device. 802.3at further enhanced PoE, supporting 25W or more power to a device.  

PoE can be used to power many devices, including:

1. Voice over IP (VoIP) phones

2. Security cameras

3. Wireless access points

4. Thin clients   

PoE was originally formalized as 802.3af, which can provide roughly 13W of power to a device. 802.3at further enhanced PoE, supporting 25W or  more power to a device.