CN - Module 3- Network Media Types

Network Media Types

This post will explain about the four network media types:

• Coaxial Cable
• Twisted Pair
• UTP& SDP
• Straight-through, crossover & rollover cable
• Fiebr-optic cable
• Wireless Technologies
• 802.11, 802.11b, 802.11g, 802.11n

Coaxial Cable

A solid-core copper wire runs down the middle of the cable. Around that solid-core copper wire is a layer of insulation, and covering that insulation is braided wire and metal foil, which shields against electromagnetic interference. A final layer of insulation covers the braided wire. 

The bandwidth for coaxial cable is 10 Mbps (Mega bits per second). Type of Cable used to wire Local Area Networks (LAN) these days is Twisted Pair cable. It is extremely difficult to find a live business network using coaxial cable.

The Twisted Pair

Twisted-pair cable is the most common type of cabling you can see in today's Local Area Networks (LAN) networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk. Crosstalk is the undesired signal noise generated by the Electro-Magnetic fields of the adjacent wires.

When a wire is carrying a current, the current creates a magnetic field around the wire. This field can interfere with signals on nearby wires. To eliminate this, pairs of wires carry signals in opposite directions, so that the two magnetic fields also occur in opposite directions and cancel each other out. This process is known as cancellation.

There are five  types of Twisted pair cables:

UTP & STP

STP and UTP are the short form for Shielded Twisted Pair and Unshielded Twisted Pair respectively.

Unshielded twisted-pair (UTP) cable is the most common networking media. Unshielded twisted-pair (UTP) consists of four pairs of thin, copper wires covered in color-coded plastic insulation that are twisted together. The wire pairs are then covered with a plastic outer jacket. UTP cables are of small diameter and it doesn’t need grounding.  Since there is no shielding for UTP cabling, it relies only on the cancellation to avoid noise. 

Colors used for Twisted Pair wires are Orange, Orange-White, Blue, Blue-White, Green, Green-White, Brown and Brown-White. Following image shows a dissected Unshielded Twisted Pair cable.

Shielded twisted pair is a special kind of copper telephone wiring used in some business installations. An outer covering or shield is added to the ordinary twisted pair telephone wires; the shield functions as a ground.

When talking about cable pinouts we often get questions as to the difference in Straight-through, Crossover, and Rollover wiring of cables and the intended use for each type of cable. These terms are referring to the way the cables are wired (which pin on one end is connected to which pin on the other end).

Straight-through Wired Cable

Straight-Through refers to cables that have the pin assignments on each end of the cable. In other words Pin 1 connector A goes to Pin 1 on connector B, Pin 2 to Pin 2 ect. Straight-Through wired cables are most commonly used to connect a host to client. When we talk about cat5e patch cables, the Straight-Through wired cat5e patch cable is used to connect computers, printers and other network client devices to the router switch or hub (the host device in this instance).

Crossover cable

Crossover wired cables (commonly called crossover cables) are very much like Straight-Through cables with the exception that TX and RX lines are crossed (they are at oposite positions on either end of the cable. Using the 568-B standard as an example below you will see that Pin 1 on connector A goes to Pin 3 on connector B. Pin 2 on connector A goes to Pin 6 on connector B ect. Crossover cables are most commonly used to connect two hosts directly. Examples would be connecting a computer directly to another computer, connecting a switch directly to another switch, or connecting a router to a router.Note: While in the past when connecting two host devices directly a crossover cable was required. Now days most devices have auto sensing technology that detects the cable and device and crosses pairs when needed.

Rollover cable

Rollover wired cables most commonly called rollover cables, have opposite Pin assignments on each end of the cable or in other words it is "rolled over". Pin 1 of connector A would be connected to Pin 8 of connector B. Pin 2 of connector A would be connected to Pin 7 of connector B and so on. Rollover cables, sometimes referred to as Yost cables are most commonly used to connect to a devices console port to make programming changes to the device. Unlike crossover and straight-wired cables, rollover cables are not intended to carry data but instead create an interface with the device.

Fiber-Optic cable

Optical Fiber cables use optical fibers that carry digital data signals in the form of modulated pulses of light. An optical fiber consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, known as the cladding. There are two fibers per cable—one to transmit and one to receive. The core also can be an optical-quality clear plastic, and the cladding can be made up of gel that reflects signals back into the fiber to reduce signal loss.

There are two types of fiber optic cable: Single Mode Fibre (SMF) and Multi Mode Fibre (MMF).

1. Single Mode Fibre (SMF) uses a single ray of light to carry transmission over long distances.

2. Multi Mode Fibre (MMF) uses multiple rays of light simultaneously with each ray of light running at a different reflection angle to carry the transmission over short distances.

Wireless Technologies

802.11, 802.11b, 802.11b. 802.1g, 802.11n are a few of the of the wireless standards collectively known as WiFi technologies.

802.11

In 1997, the Institute of Electrical and Electronics Engineers (IEEE) created the first WLAN standard. They called it 802.11 after the name of the group formed to oversee its development. Unfortunately, 802.11 only supported a maximum network bandwidth of 2Mbps - too slow for most applications.

802.11b

IEEE expanded on the original 802.11 standard in July 1999, creating the 802.11bspecification. 802.11b supports bandwidth up to 11 Mbps, comparable to traditional Ethernet.

802.11b uses the same unregulated radio signaling frequency (2.4 GHz) as the original 802.11 standard. Vendors often prefer using these frequencies to lower their production costs. Being unregulated, 802.11b gear can incur interference from microwave ovens,cordless phones, and other appliances using the same 2.4 GHz range. However, by installing 802.11b gear a reasonable distance from other appliances, interference can easily be avoided.

• Pros of 802.11b - lowest cost; signal range is good and not easily obstructed
• Cons of 802.11b - slowest maximum speed; home appliances may interfere on the unregulated frequency band

802.11g

In 2002 and 2003, WLAN products supporting a newer standard called 802.11g emerged on the market. 802.11g attempts to combine the best of both 802.11a and 802.11b. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 Ghz frequency for greater range. 802.11g is backwards compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa.

• Pros of 802.11g - fast maximum speed; signal range is good and not easily obstructed
• Cons of 802.11g - costs more than 802.11b; appliances may interfere on the unregulated signal frequency

802.11n

802.11n (also sometimes known as "Wireless N") was designed to improve on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one. Industry standards groups ratified 802.11n in 2009 with specifications providing for up to 300 Mbps of network bandwidth. 802.11n also offers somewhat better range over earlier Wi-Fi standards due to its increased signal intensity, and it is backward-compatible with 802.11b/g gear.

• Pros of 802.11n - fastest maximum speed and best signal range; more resistant to signal interference from outside sources
• Cons of 802.11n - standard is not yet finalized; costs more than 802.11g; the use of multiple signals may greatly interfere with nearby 802.11b/g based networks.

Referrences:

• http://www.omnisecu.com/basic-networking/common-network-cable-types.php
• http://searchnetworking.techtarget.com/definition/shielded-twisted-pair
• http://compnetworking.about.com/cs/wireless80211/a/aa80211standard.htm
• http://www.webopedia.com/TERM/8/802_11.html

Computer Network - OSI vs TCP/IP

The Open System Interconnect (OSI) Model

Layer 7— The application layer: This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions). It represents the services that directly support applications such as software for file transfers, database access, email, and network games.

Layer 6—The presentation layer: This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). This layer also manages security issues by providing services such as data encryption and compression. It’s sometimes called the syntax layer.

Layer 5—The session layer: This layer allows applications on different computers to establish, use, and end a session/connection. This layer establishes dialog control between the two computers in a session, regulating which side transmits, and when and how long it transmits.

Layer 4—The transport layer: This layer handles error recognition and recovery, manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.

Layer 3—The network layer: This layer handles the routing of the data, addresses messages and translates logical addresses and names into physical addresses. It also determines the route from the source to the destination computer and manages traffic problems (flow control), such as switching, routing, and controlling the congestion of data packets.

Layer 2—The data-link layer: This layer package raw bit from the Physical layer into frames (logical, structures packets for data). It is responsible for transferring frames from one computer to another, without errors. After sending a frame, it waits for an acknowledgment from the receiving computer.

Layer 1—The physical layer: This layer transmits bits from one computer to another and regulates the transmission of a stream of bits over a physical medium. This layer defines how the cable is attached to the network adapter and what transmission technique is used to send data over the cable.

Protocol

TCP/IP Model

1. Application layer

This is the top layer of TCP/IP protocol suite. This layer includes applications or processes that use transport layer protocols to deliver the data to destination computers.  Some of the popular application layer protocols are :

• HTTP (Hypertext transfer protocol)
• FTP (File transfer protocol)
• SMTP (Simple mail transfer protocol)
• SNMP (Simple network management protocol) etc

2. Transport Layer

This layer provides backbone to data flow between two hosts. This layer receives data from the application layer above it. There are many protocols that work at this layer but the two most commonly used protocols at transport layer are TCP and UDP.

3. Network Layer

This layer is also known as Internet layer. The main purpose of this layer is to organize or handle the movement of data on network. By movement of data, we generally mean routing of data over the network. The main protocol used at this layer is IP. While ICMP(used by popular ‘ping’ command) and IGMP are also used at this layer.

4. Data Link Layer

This layer is also known as network interface layer. This layer normally consists of device drivers in the OS and the network interface card attached to the system. Both the device drivers and the network interface card take care of the communication details with the media being used to transfer the data over the network. In most of the cases, this media is in the form of cables. Some of the famous protocols that are used at this layer include ARP(Address resolution protocol), PPP(Point to point protocol) etc.

Comparison of OSI Reference Model and TCP/IP Reference Model

Following are some major differences between OSI Reference Model and TCP/IP Reference Model, with diagrammatic comparison below.

OSI(Open System Interconnection)	TCP/IP(Transmission Control Protocol / Internet Protocol)
1. OSI provides layer functioning and also defines functions of all the layers.	1. TCP/IP model is more based on protocols and protocols are not flexible with other layers.
2. In OSI model the transport layer guarantees the delivery of packets	2. In TCP/IP model the transport layer does not guarantees delivery of packets.
3. Follows horizontal approach	3. Follows vertical approach.
4. OSI model has a separate presentation layer	4. TCP/IP does not have a separate presentation layer
5. OSI is a general model.	5. TCP/IP model cannot be used in any other application.
6. Network layer of OSI model provide both connection oriented and connectionless service.	6. The Network layer in TCP/IP model provides connectionless service.
7. OSI model has a problem of fitting the protocols in the model	7. TCP/IP model does not fit any protocol
8. Protocols are hidden in OSI model and are easily replaced as the technology changes.	8. In TCP/IP replacing protocol is not easy.
9. OSI model defines services, interfaces and protocols very clearly and makes clear distinction between them.	9. In TCP/IP it is not clearly separated its services, interfaces and protocols.
10. It has 7 layers	10. It has 4 layers

Referrences:

• http://www.cisco1900router.com/what-is-ios-model-the-overall-explanation-of-ios-7-layers.html
• http://www.thegeekstuff.com/2011/11/tcp-ip-fundamentals/
• http://www.studytonight.com/computer-networks/comparison-osi-tcp-model