What is Network Cabling?
REZA 04


   Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.
The following sections discuss the types of cables used in networks and other related topics.
  • Unshielded Twisted Pair (UTP) Cable
  • Shielded Twisted Pair (STP) Cable
  • Coaxial Cable
  • Fiber Optic Cable
  • Cable Installation Guides
  • Wireless LANs
  • Unshielded Twisted Pair (UTP) Cable
   Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1).
Fig.1. Unshielded twisted pair 


   The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging). 


Categories of Unshielded Twisted Pair
Category
Speed
Use
1
1 Mbps
Voice Only (Telephone Wire)
2
4 Mbps
LocalTalk & Telephone (Rarely used)
3
16 Mbps
10BaseT Ethernet
4
20 Mbps
Token Ring (Rarely used)
5
100 Mbps (2 pair)
100BaseT Ethernet
1000 Mbps (4 pair)
Gigabit Ethernet
5e
1,000 Mbps
Gigabit Ethernet
6
10,000 Mbps
 
 
 Gigabit Ethernet


Unshielded Twisted Pair Connector
   The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.


Fig. 2. RJ-45 connector 


Shielded Twisted Pair (STP) Cable 
    Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables.
Shielded twisted pair cable is available in three different configurations:
  1. Each pair of wires is individually shielded with foil.
  2. There is a foil or braid shield inside the jacket covering all wires (as a group).
  3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).
Coaxial Cable
  Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers. 


Fig. 3. Coaxial cable 

   Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial.
   Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in school networks, especially linear bus networks.
   Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install. 


Coaxial Cable Connectors
The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather screw, onto the cable. 


Fig. 4. BNC connector 

Fiber Optic Cable 
   Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.
   Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.
The center core of fiber cables is made from glass or plastic fibers (see fig 5). A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of teflon or PVC. 


Fig. 5. Fiber optic cable 

   There are two common types of fiber cables -- single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive. 

Specification
Cable Type
10BaseT
Unshielded Twisted Pair
10Base2
Thin Coaxial
10Base5
Thick Coaxial
100BaseT
Unshielded Twisted Pair
100BaseFX
Fiber Optic
100BaseBX
Single mode Fiber
100BaseSX
Multimode Fiber
1000BaseT
Unshielded Twisted Pair
1000BaseFX
Fiber Optic
1000BaseBX
Single mode Fiber
1000BaseSX
Multimode Fiber 


Wireless LANs

   More and more networks are operating without cables, in the wireless mode. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.
   Wireless networks are great for allowing laptop computers, portable devices, or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.
   The two most common types of infrared communications used in schools are line-of-sight and scattered broadcast. Line-of-sight communication means that there must be an unblocked direct line between the workstation and the transceiver. If a person walks within the line-of-sight while there is a transmission, the information would need to be sent again. This kind of obstruction can slow down the wireless network. Scattered infrared communication is a broadcast of infrared transmissions sent out in multiple directions that bounces off walls and ceilings until it eventually hits the receiver. Networking communications with laser are virtually the same as line-of-sight infrared networks.

Wireless standards and speeds
   The Wi-Fi Alliance is a global, non-profit organization that helps to ensure standards and interoperability for wireless networks, and wireless networks are often referred to as WiFi (Wireless Fidelity). The original Wi-Fi standard (IEEE 802.11) was adopted in 1997. Since then many variations have emerged (and will continue to emerge). Wi-Fi networks use the Ethernet protocol. 
Standard
Max Speed
Typical Range
802.11a
54 Mbps
150 feet
802.11b
11 Mbps
300 feet
802.11g
54 Mbps
300 feet
802.11n
100 Mbps
300+ feet


Wireless Security
  Wireless networks are much more susceptible to unauthorized use than cabled networks. Wireless network devices use radio waves to communicate with each other. The greatest vulnerability to the network is that rogue machines can "eves-drop" on the radio wave communications. Unencrypted information transmitted can be monitored by a third-party, which, with the right tools (free to download), could quickly gain access to your entire network, steal valuable passwords to local servers and online services, alter or destroy data, and/or access personal and confidential information stored in your network servers. To minimize the possibility of this, all modern access points and devices have configuration options to encrypt transmissions. These encryption methodologies are still evolving, as are the tools used by malicious hackers, so always use the strongest encryption available in your access point and connecting devices.
  

Encryption.
Enable the strongest encryption supported by the devices you will be connecting to the network. Use strong passwords (strong passwords are generally defined as passwords containing symbols, numbers, and mixed case letters, at least 14 characters long).
Isolation.
Use a wireless router that places all wireless connections on a subnet independent of the primary private network. This protects your private network data from pass-through internet traffic.
Hidden SSID.
Every access point has a Service Set IDentifier (SSID) that by default is broadcast to client devices so that the access point can be found. By disabling this feature, standard client connection software won't be able to "see" the access point. However, the eves-dropping programs discussed previously can easily find these access points, so this alone does little more than keep the access point name out of sight for casual wireless users.


Advantages of wireless networks:
  • Mobility - With a laptop computer or mobile device, access can be available throughout a school, at the mall, on an airplane, etc. More and more businesses are also offering free WiFi access ("Hot spots").
  • Fast setup - If your computer has a wireless adapter, locating a wireless network can be as simple as clicking "Connect to a Network" -- in some cases, you will connect automatically to networks within range.
  • Cost - Setting up a wireless network can be much more cost effective than buying and installing cables.
  • Expandability - Adding new computers to a wireless network is as easy as turning the computer on (as long as you do not exceed the maximum number of devices).


Disadvantages of wireless networks:
  • Security - Be careful. Be vigilant. Protect your sensitive data with backups, isolated private networks, strong encryption and passwords, and monitor network access traffic to and from your wireless network.
  • Interference - Because wireless networks use radio signals and similar techniques for transmission, they are susceptible to interference from lights and electronic devices.
  • Inconsistent connections - How many times have you hears "Wait a minute, I just lost my connection?" Because of the interference caused by electrical devices and/or items blocking the path of transmission, wireless connections are not nearly as stable as those through a dedicated cable.
  • Speed - The transmission speed of wireless networks is improving; however, faster options (such as gigabit Ethernet) are available via cables. If you are only using wireless for internet access, the actual internet connection for your home or school is generally slower than the wireless network devices, so that connection is the bottleneck. If you are also moving large amounts of data around a private network, a cabled connection will enable that work to proceed much faster.
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network topology , protocol and architecture
REZA 04
EXAMPLE OF TOPOLOGY

 

Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer.




A linear bus topology is a network topology consisting of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and LocalTalk networks use a linear bus topology.

Advantages of a linear bus topology
Disadvantages of a linear bus topology
·                     Easy to connect a computer or peripheral to a linear bus.
  • Requires less cable length than a star topology.
  • Entire network shuts down if there is a break in the main cable.
  • Terminators are required at both ends of the backbone cable.
  • Difficult to identify the problem if the entire network shuts down.
  • Not meant to be used as a stand-alone solution in a large building.



Star networks
-          one of the most common computer network topologies.
-          In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages.
-          This consists of a central node, to which all other nodes are connected; this central node provides a common connection point for all nodes through a hub.
-          An active star network has an active central node that usually has the means to prevent echo-related problems.
-          The star topology reduces the chance of network failure by connecting all of the systems to a central node.
-          It is also designed with each node (file servers, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator.
-          Data on a star network passes through the hub, switch, or concentrator before continuing to its destination.
-          The hub, switch, or concentrator manages and controls all functions of the network.
-           It also acts as a repeater for the data flow.
-          This configuration is common with twisted pair cable. However, it can also be used with coaxial cable or optical fibre cable.

Advantages

Disadvantages
  • Better performance: star topology prevents the passing of data packets through an excessive number of nodes. At most, 3 devices and 2 links are involved in any communication between any two devices. Although this topology places a huge overhead on the central hub, with adequate capacity, the hub can handle very high utilization by one device without affecting others.
  • Isolation of devices: Each device is inherently isolated by the link that connects it to the hub. This makes the isolation of individual devices straightforward and amounts to disconnecting each device from the others. This isolation also prevents any non-centralized failure from affecting the network.
  • Benefits from centralization: As the central hub is the bottleneck, increasing its capacity, or connecting additional devices to it, increases the size of the network very easily. Centralization also allows the inspection of traffic through the network. This facilitates analysis of the traffic and detection of suspicious behaviour
  • Easy to detect faults and to remove parts.
  • No disruptions to the network when connecting or removing devices.
  • High dependence of the system on the functioning of the central hub
  • Failure of the central hub renders the network inoperable



Tree

-          Tree topology is a combination of Bus and Star topology.

Advantage
Disadvantages
• Point-to-point wiring
for individual
segments.
• Overall length of each segment is
limited by the type of cabling
used.
• If the backbone line breaks, the
entire segment goes down
• More difficult to configure and
wire than other topologies.



FDDI (Fiber Distributed Data Interface)
• 100mbps
• normally implemented over fiber optic (fast-
Ethernet, UTP)
• dual redundancy built in by use of primary
and secondary ring
• automatic bypassing and isolation of faulty
nodes



Network Protocols
Network protocols like HTTP, TCP/IP, and SMTP provide a foundation that much of the Internet is built on. Find out more about these protocols and how they work. Network protocols defines a language of rules and conventions for communication between network devices.

What Is Packet Switching?
Packet switching is a method used by network protocols including IP and Frame Relay to deliver data across a computer network connection in individually delivered small pieces.

Introduction to MAC Addresses
In computer networking, the Media Access Control (MAC) address is just as important as an IP address. Learn more about how MAC addressing works on Ethernet, Wi-Fi and Bluetooth networks.

ARP - Address Resolution Protocol
ARP converts an IP address to its corresponding physical network address. ARP is a low-level protocol usually implemented in the device drivers of network operating systems. ARP is most commonly utilized on Ethernet networks.

PPPoE
PPPoE (Point-to-Point Protocol over Ethernet) is a network protocol sometimes used by broadband modems for connecting to DSL Internet service.

Spanning Tree Protocol
The Spanning Tree Protocol implements a standard algorithm to prevent redundant transmission of data along intermediate hops between a source and destination host.

NTP - Network Time Protocol
Network Time Protocol is a server based system to synchronize time of day clocks computer across the Internet.

SOCKS
SOCKS is an Internet protocol designed to allow clients to communicate with proxy servers (or VPN servers) through network firewalls.

UWB
Ultra-wideband - UWB - is a communication method used in wireless networking to achieve high bandwidth connections with low power utilization. Originally designed for use in commercial radar systems, UWB technology is gradually being adopted in consumer electronics and wireless personal area networks (PANs).

Network Management Protocol
SNMP is a standard TCP/IP protocol for network management. Network administrators use SNMP to monitor network availability and performance, and control devices to help recover from technical issues.

Ethereal Network Protocol Analyzer
Ethereal is a high quality utility program commonly used by students, researchers and some companies to monitor network traffic.

"Internet Core Protocols - The Definitive Guide"
This book features in-depth technical background on fundamental network protocols such as TCP, ICMP and ARP.


Network architecture  is  the design of a communications network. It is a framework for the specification of a network's physical components and their functional organization and configuration, its operational principles and procedures, as well as data formats used in its operation.


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