Ethernet cables can be wired in three different ways. The two main ways are straight through and Cross over. The third type is called as Rolled. Straight through cables are generally used to connect different types of equipment; for example, a computer and a hub. Crossover cables are generally used to connect similar types of equipment like a computer to another computer. Inside the UTP cable there are 8 physical wires. The 8 wires are arranged in pairs: one pair is used to send information and other pair is used to receive information. For computers to communicate, the sending pair of one computer has to be connected to receiving pair of another computer. So crossover cables are required.
T568B Termination
T568A Termination
RJ45 Jack
Straight-through Cable
The straight- through cable is used to connect:
Host to switch or hub
Router to switch or hub
Straight through Cable
Straight Through Cable
In the above figure you can see only 1,2,3 and 6 pins are used. Connect pin 1 to pin 1,2 to 2,3 to 3 and 6 to 6. Remember this would be an Ethernet cable and it will not work with voice, Token Ring, and ISDN.
Crossover cable
The Crossover cable be used to connect:
Switch to switch
Hub to hub
Host to host
Hub to switch
Router direct to host
Same four wires are used in the cable as in the straight-through cable but different pins are connected together. In the following figure, can see how four wires are used in crossover Ethernet cable. And notice that instead of connecting 1to1, 2to2 etc, pins 1 is connected 3, pin 2 is connected to 6 on each side of the cable.
Crossover cable pinouts
Two pairs crossed, two pairs uncrossed
Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, may require that the "non-data" pairs 1 and 4 (pins 4, 5, 7 and 8) remain un-crossed.
T568A - All Four Pairs Crossed
T568B - All Four Pairs Crossed
Rolled cable
Roll Over or Console Cable
Rolled cables are not used to connect any Ethernet connections together, but rolled Ethernet cable can be used to connect a host to a router console serial communication port. Rolled cable is also used to connect PC running Hyper- Terminal to the Cisco hardware. Eight wires are used in rolled cable to connect serial devices, although not all eight are used to send information just as in Ethernet networking. Figure below shows eight cables used in a rolled cable.
In a network, a machine has to be connected to at least other machine, through metal cabling, fiber-optic cabling or radio waves. Even new technologies such as radio based networks and infrared light based networks produce new ways of connecting two devices to each other, but least expensive and most popular medium for networking is still copper wires.
Cables use copper wires to transmit electrical signals or fiber optic to transfer optical light signals. Cabling is also called as wiring because copper wire is used in greater part in the network cables. Electrical signal, which is transmitted through cable, generate magnetic field and radio frequency interfaces. When cables are used, the electrical signal emits radiation, which may interfere with other signals. When this happens it is called as cross talk. In order to overcome this, metallic wires are manufactured in such a way that it reduces the effects of radiation and interference. The wires, which are close to one another, can interfere with the transmission, changing the electrical signal and can cause bit error. Because of interference, cables produce emission and are susceptible to nearby cables. The popular way to reduce these effects of emission is to send the information, through a pair of wires and to twist the pair of wires together, Using an opposite current on each wire generates magnetic field but in opposite
direction. So by twisting the wires, the two magnetic fields cancel each other. Another popular way to reduce emissions of copper cables is to shield the wires by some material which blocks electromagnetic radiation. Shielding the wires makes the cables less flexible and increases material and manufacturing costs. In this lesson, you will learn some of the cable type, its uses and features.
Cabling types
A wide range of cabling types has been used to connect Ethernet systems. Network uses three types of cables: coaxial, twisted and fiber optic cables. Twisted pair is similar to telephone cable. It consists of pairs of cables twisted around each other to reduce electrical interference. For high speed and high secure systems, Fiber optic cables are used. However, it is less commonly used, as the cable is expensive and more difficult to install.
Unshielded Twisted Pair (UTP) Cable
Shielded Twisted Pair (STP) Cable
Coaxial Cable
Fiber Optic Cable
Twisted Pair Cables:
Twisted pair cable is a type of cable, which consists of two independently insulated wires around one another. The use of twisted pairs helps to reduce crosstalk and electromagnetic induction. High quality twisted pair cables have 1to 3 twists per inch. Twisted pair cables is the ordinary copper wire which is used to connect most of the home and business computers to Telephone company. Each wire in twisted pair cables has color plastic insulation attached to it. Twisted-pair cables are lighter, thinner, more flexible and easier to install than coaxial and fiber-optic cabled. There are two types of twisted pairs: Unshielded twisted pair and shielded twisted pair.
Shielded Twisted pair (STP):
The twisted pair in STP are individually wrapped in a foil shield and enclosed in an outer braided wire shield. The shielding is designed to minimize electromagnetic radiation and susceptibility to crosstalk. Each pair is surrounded by insulating material, with another insulator covering all pairs together. The extra material makes the cable white bulky and cause lack of flexibility. Shielded twisted pair cables are commonly used on networks using Token Ring topology.
Unshielded Twisted Pair (UTP):
Unshielded Twisted pair cable is the most popular of all the cable types. UTP cables are used not only for networking but also for traditional telephone (UTP) cable consists of four pairs of wires inside the jacket. Each wire has some colored plastic insulation attached to it. As copper wire is smaller in diameter, it may break easily. So, a thin plastic insulation provides more strength to each individual wire. Each pair has different twists per inch, which helps to eliminate interference from adjacent pairs or from other electrical devices.
Unshielded Twisted pairs standards
A great many different cabling standards exist. EIA/TIA (Electronic Industries Association / Telecommunications Information Association) standard 568A is one of several standard that specify “Categories” of unshielded twisted pair cabling systems in terms of data rates that they can carry. Under UTP type of cables for Ethernet wiring, the categories number. For computer networks the most common are category5, category5e and category6
CATI (category1) is typically used for telephone wire. This type of wire is not capable of supporting network traffic and it is twisted. CATI is not suitable to use with Ethernet. Only telephone companies who provide ISDN use it. There fore, the wiring between the customer’s site and Phone Company’s network use CATI cable.
CAT2 is used most commonly used for token ring networks, supporting speeds up to 4 Mbps. For higher speeds (100 Mbps) CAT5 cables are suitable. CAT3, CAT4 andCAT5 cables are generally 4 pairs of twisted copper wires. CAT5 has more twists per inch than CAT3, therefore it can run at higher speeds and greater lengths. CAT3 and CAT4 are also used for token ring networks. Category5e is a new standard that will specify transmission performance, which exceeds CAT5. Like CAT5, it consists of unshielded twisted pair with 100-ohm impudence and electrical characteristics supporting at frequencies up to 100MHz. CAT6 wire was originally designed to support multi gigabyte Ethernet. It is similar to CAT5 but contains a physical separator between the four pairs to further reduce electromagnetic interference. CAT7 is a proposed standard that aims to support transmission at frequencies up to 600MHz over 100 ohm twisted pair.
Most common cable categories
Category
Bandwidth
Applications
Notes
Cat1
0.4 MHz
Telephone and modem lines
Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat2
? MHz
Older terminal systems, e.g. IBM 3270
Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat3
16MHz
10BASE-T and 100BASE-T4 Ethernet
Described in EIA/TIA-568. Unsuitable for speeds above 16 Mbit/s.
Cat4
20MHz
16 Mbit/s Token Ring
Cat5
100MHz
100BASE-TX & 1000BASE-T Ethernet
Cat5e
100MHz
100BASE-TX & 1000BASE-T Ethernet
Enhanced Cat5. Practically the same as Cat5, but with better testing standards so Gigabit Ethernet works reliably.
Cat6
250MHz
1000BASE-T Ethernet
Most commonly installed cable in Finland according to the 2002 standard. SFS-EN 50173-1
Cat6e
250MHz (500MHz according to some)
10GBASE-T (under development) Ethernet
Not a standard; a cable maker's own label.
Cat6a
500MHz
10GBASE-T (under development) Ethernet
Standard under development (ISO/IEC 11801:2002 Amendment 2).
Cat7
600MHz
No applications yet.
Four pairs, U/FTP (shielded pairs). Standard under development.
Cat7a
1200MHz
Telephone, CATV, 1000BASE-T in the same cable.
Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.
Cat8
1200MHz
Under development, no applications yet.
Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.
Coaxial cable
Coaxial cable is a type of communication transmission cable in which solid center conductor is surrounded by an insulating medium, which is surrounded by tubular outer conductor (foil). The entire assembly is then surrounded with an insulating and protective outer layer. Coaxial cables are capable of carrying many data, voice and video conversations simultaneously. The two type of coaxial cabling used with Ethernet are.
Thicket
Thinnet
Thicket
Thicket coaxial is used with Ethernet 10BASE5 network, which supports a 100Mbps transmission rata and consists of 500 meter segment length. Thick Ethernet consists of mark at every 2.5 meters, which indicates proper placement of 10Base5 transceivers used to connect stations to the network Transceiver placed at any multiple of 2.5 meters intervals minimizes signal reflection, which may spoil the transmission quality in the cable. Vampire tap is used to connect to the segment. Vampire tap is piece of metal, which is cylindrical in shape when tap is closed. When tap is closed around the cable, it is pushed through the shielding to provide the metal in the vampire tap to touch the copper wire inside the cable.
Thinnet
Thinnet coaxial cable is used with Ethernet 10 Base2 networks. Compared to thicknet cables, thicknet are cheaper, Lighter, flexible and easier to install. It consists of 185 meter maximum segment Length. 10Base2 transceiver is connected to the thinnet cable segment through “BNC (British Naval Connector) T” connector. To connect to computer, one end of T connector plugs directly into Ethernet card in the computer station, another end is plugged into cable from upstream cable, and another cable attached to next device downstream.
10Base5 and 10Base2 Connectors
Transceiver is a term formed by combining the terms transmitter and receiver. Instead of Ethernet card, it consists of electronics that send and receive signal on the Ethernet cable. Disadvantages of coaxial cable includes that are more expensive, heavier and relatively inflexible. Also, when it is used for Ethernet, a single break in cable causes the failure of entire segment.
Fiber-Optic Cable
An optical fiber breakout cable
A multi-fiber cable
Fiber-optic cabling is a technology in which the electrical signal is converted into optical signal that is transmitted through a thin glass fiber and it is converted back into electrical signal. The figure below shows the components of a fiber-optic cable.
Fiber-optic cable is made from fiberglass and it does not break easily. The plastic and Kevlar coating provides more strength to the fiber glass. Kevlar is the material that most of bullet proof vests is made of.
Fiber-optic cable consists of two concentric layers of high-purity silica glass- the core and the cladding. The “core” is the inner part of an optical fiber through which light is transmitted. The “cladding” is the material in the middle layer. The light stays confined to the core because the cladding has lower refractive index than the core, which means that when light hits the outer wall, it is reflected back to core. The outer protective layer serves to protect core and cladding from damage.
The devices such as Ethernet switches, which are at the end of the cable, generate optical light signal. These signals travel through the optical fiber in the canter of cable. Electricity is not used across the cable; only light is transmitted.
The main idea of network is to help all organization increase its productivity by connecting all the computer or networks. Connection between networks has helped organization in many ways in spite of variation in time, location and type of computer or devices.
By being a part of network, a company can access information, processes and ways of doing business changes. It is very important for every organization to manage a corporate inter-network that helps to optimize its resources.
Network is characterized based on group employees in the following ways
Main Office : It is the location where all computers are connected to a LAN. It is a data center where all information related to company is centralized. Main office might contain thousands of employees who depend on networks to do their work.
The other areas of office where require access to the resources at main office and each other are
Branch Office : These are smaller groups of employees and they are connected through LAN. Even through some of the data's are stored in the branch office, most of the time they access the data from the main office. How frequently they access the data from the main office determines the type of WAN connection. It can be permanent of dial up connection.
Telecommuters : Employees who access the resources from the outside are telecommuters.
Mobile users : Some of the employees work from different locations and they require connection to the network. When they work at main or branch office, they connect to LAN. When they work outside the office, they use dial-up service to connect to the network.
In order to understand what types of equipment and services to install in your network, it is very important to understand the user and the business needs, then you can subdevide the network into smaller components,
Corporate Networking Strategy :
Three Layer Hierarchial Network Model :
To properly build an inter-network, a three layered hierarchical model is used to organize traffic flow. Hierarchical model also simplifies the task required for two computers to communicate and divides it into three layers. Each layer is focused on a specific function, as mentioned below:
Access layer provides work-group/user access to the network
Distribution provides policy based connectivity
Core or backbone layer provides optimal transport between sites.
Figure show various aspects of hierarchical model.
Access Layer :
This layer includes hubs and switches. Access layers is also called as Desktop Layer because it focus on connecting client nodes, such as workstations on the network. This layer ensures that packets are delivered to end user computers. Access Layers has ability to expand or contract collision domains using repeater, hub or switch. Switches in access layer are not high-powered device such as those found at the core layer. Rather it is advanced version of a hub. Access layer controls work-group access to the locally available resources. Traffic that flows to and from the local resources is restricted between resources, switches and users. In most of the network, access to the services such as database, centralized storage is denied. In this case the request or traffic will be sent to next layer distribution layer. At the access layer, user can
Enable MAC address filtering : it is possible to program a switch to allow only certain systems to access the connected LANs.
Create separate collision domain: A switch can create separate collision domain for each connected node to improve performance.
Share bandwidth : Allows the same network connection to handle all data. Allows moving data from one network to another to perform load balancing.
Note : A collision domain describes a portion of a network where any communication sent by a node is received by any other node on the network. In broadcast domain any part or any node of a network can broadcast to any node of the network
Distribution Layer: Distribution layer is also referred as Work-group layer. Usually routing between access layer and core layer is handled by distribution layer. It also provides policy based connectivity; it can read the packet and prioritize the delivery based on the set by user. Functions of distribution layer include
Packet filtering : Distribution layer processes the packets and transmit data packets based on the source and destination information to create network borders.
Access layer aggregation point : distribution layer serves the aggregation point for access layer switches.
Distribution layer serves as the boundary for broadcast and multi-cast domains.
performs queuing of packet and provides security service.
It determines the fastest way in which the request can be forwarded to the server. When the path is selected the request will be sent to core layer.
Core Layer : Core layer is considered as backbone of the network and includes the high-end switches and high-speed cables such as fiber cables. This layer of the network does not route traffic at the LAN. In addition, no packet manipulation is done by the devices in the layer. Rather, this layer is concerned with speed and ensures reliable delivery of packet. Usually, the traffic is being transmitted to and from services common to all users. These services are known as global or enterprise services. Example of these services includes email, Internet access and video conferencing. When the user access to enterprise service, then distribution chooses the best path and forwards the request to core layer. Core layer provides the rapid transmit of request to the enterprise service.
