8 Networking Techniques, Media and Devices
Manoj Kumar
I. Objectives
To learn about the various aspects of networking technology i.e network topologies, switching techniques, network devices and different type of network connections.
II. Learning Outcomes
On completion of this lesson, learners will attain knowledge about switching technologies such as circuit switching, packet switching, cell switching, network media used for transmissions. They would learn about the topologies for interconnection of computers such as Bus, Ring, Star, Mesh, Hybrid etc. Learner would be able to understand network devices such as Hub, Switches, Gateway and Routers, Modems are also introduced in this module.
III. Module Structure
1. Introduction
2. Network Topology
2.1 Bus Topology
2.2 ing Topology
2.3 Star Topology
2.4 Mesh Topology
2.5 Hybrid and Wireless Topology
3. Switching Techniques
3.1 Circuit Switching
3.2 Packet Switching
3.3 Cell Switching
4. Network Media
5. Network Devices
5.1 Network Interface Card (NIC)
5.2 Hub
5.3 Switch
5.4 Router/Gateway
6. Network Connection
6.1 Network Cabling
6.2 Wireless Network
7. Summary
8. References
1. Introduction
There is a saying in Hindi that “एकता म� ताकत एकता म� शिक्त” i.e. “Unity is strength and unity is power”. When an individual or a device works independently, the full potential of the entity is not utilized properly. While getting connected each other, the network of such entities gives maximum utilization of resources and power of sharing. In computers also, the interconnections of many computers can be created which is called Networking of computers. The interconnections of computers enable to share resources such as hardware, data and information with high reliability and speed. Between the computers, the data is passed as signals and the signal is interpreted as binary digits by the computers to enable the transmission of data. Prowess technological implementation is required with various networking techniques to create a dedicated and reliable network. Network inherits the socializing nature of human quality to share its resources among other connected computers. Since computer cannot move to make its own connection, various technological solutions are required to transmit data from one computer to another. It has to be connected each other with a media, switching of data or signals are required along with proper design of connections. This section will discuss about switching technologies such as Circuit Switching, Packet Switching, Cell Switching, Network media used for transmissions, such as Unshielded Twisted Pair (UTP) cables, Shielded Twisted Pair (STP) cables, Fiber cables and wireless media, Topologies for interconnection of computers such as Bus, Ring, Star, Mesh, Hybrid etc. Network devices such as Hub, Switches, Gateway and Routers, Modems, are also introduced in this module.
2. Network Topology
In order to interconnect computers, cable and other components, physical layout of the devices involved is to be prepared in advance. Such a layout of computers, cables, network device is called network topology and network may use one topology for the entire network or it may be also built using multiple topologies. Major topologies used in computer networking are Bus topology, Star Topology, Mesh topology, ring topology, hybrid topology and recently added wireless topology. Main computer which serves its resources to other computers is called server and individual computer which accepts the services is called clients. Servers and clients are commonly referred as Nodes. Topology is the design of connecting nodes in the network. Nodes can be desktop, workstation, printers, switches etc.
2.1 Bus Topology
This is the simple topology which uses a straight cable with terminator at both ends. All the nodes are connected to this linear cable. The signal generally originates from one node in bus topology and travels in both directions in the cable from the same computer. When the signal reaches at the end, the terminator observes the signal. Signals can also bounce back and return in the direction it came from. Though, bus topology is a good solution for standalone network, the signal bombs will create problems due to pollution of the signal traveling in both directions. The major disadvantage is if there is a single break, the network breaks down completely.
2.2 Ring Topology
All nodes are connected by a ring cable which do not have any start or end in termination as shown in the bus topology. Generally, ring topology is used as a redundancy purpose in establishing WAN (Wide Area Network) or MAN (Metropolitan Area Network). The Signal passes in one direction only in Ring topology and each computer is supposed to regenerate the signal so that it can travel in destination required. As seen in the bus topology, if one workstation fails, entire network fails.
2.3 Star Topology
Star topology is a robust technology where a central device is used for connecting nodes to the center. The cable will connect the nodes directly to the switch. Such connections of the nodes are central switch, which gives a design of a Star as given in the picture.
Star topology is most popular and widely used topology in implicating local area network using the Internet. Since each node is connected with the cable, it is easy to identify faults in the network. Star Topology requires more cable links than the bus topology and attributes more expenses than the bus topology. The disadvantage is, if the central switch fails the entire network will fail.
2.4 Mesh Topology
Mesh topology is an interconnection of all nodes in the network. Since one node is connected to many other nodes, the reliability of the network is very high with multiple paths to destination. Mesh topology is very expensive, hence not very popular.
Fig.4: Mesh Topology
2.5 Hybrid and Wireless Topology
Tree topology use one switch and all equipments will be connected in hierarchical structure. Hybrid Topology is a mixture of all the topologies. It can be Bus-Ring, Star-Ring, Bus-Star or combination of all. Recently, WiFi technology has been introduced for Wireless LAN and wireless topology is used to plan the layout of Access Points (APs) and wireless controllers. Details will be discussed later in Wireless network.
3. Switching Techniques
Once the network is created with many nodes, which are located in different places by connecting to other networks, to transmit the data across the network dedicated connections are required between end nodes. Generally, data is sent as packet or frames through a physical connection between the end points. Transmitting data across network is called switching technique. There are three types of switching techniques popularly used in networks.
3.1 Circuit Switching
Circuit switching is a technology used in telecommunication network in which two network nodes are connected by a dedicated communication Chanel called circuit. Circuit is to be establishing before starting the communication of data. A Circuit dedicates full bandwidth of Chanel for the entire duration of the communication process. Once circuit is established between two nodes through many intermediary nodes it will look like the nodes are physically connected. Delay in transmission is always constant in circuit due to the dedicated Chanel.
The disadvantage of circuit switching is that the numbers of users are restricted to use and circuit remains reserved. If it is not used by the reserved user the circuit remains ideal. For example hot lines, analog telephone network etc. Since these kind of circuits are giving low variance in latency, circuit switching is preferred for video and audio transmissions. Extra overhead and delay is impertinent due to the set up and tear down of the circuit.
3.2 Packet Switching
To overcome the limitation of circuit switching due to the low utilization of the circuit, packet switching is introduced. All transmitted data are fragmented as blocks called ‘Packets’. All packets are sending across network with numbers tagged to each packet. These fragmented packets are randomly sent across network. On arrival of the packets at the destination, the fragmented packets get reassembled to the original data. If any packet is lost in between, lost packets are requested again by the destination node.
Packet switching is established by setting up a limited number of dedicated connections of constant bit rate and constant delay between nodes. If traffic increases the delay also increases. The packet switching can be connection oriented or connectionless. The connectionless switching is called datagram switching which is commonly used by Ethernet, IP and UDP. Connection oriented switching used in X.25, frame relay, multi protocol label switching (MPLS used in BSNL) and TCP.
3.3 Cell Switching
Cell switching is high speed switching technology to overcome the speed problem faced in circuit and packet switching. Cell switching uses a connection- oriented packet switched network. Fixed sized cell (53 bytes in ATM) is used in cell switching to while packet switching technology uses for variable linked packets. This technique is also used in DSL and ISDN.
The disadvantage is, there is no flow control or error control. Cell switching can handle multiple data types such as voice, video and data. Cell switching combines the best features of circuit switching for guaranteed delivery and packet switching for efficiency.
4. Network Media
Physically the network is established in general by interconnecting nodes by using cables. Cable works as a media between two nodes. Light and air can also be used as media for transmission of data over the network. When light is used in the technology then it is called optical technology and when air is used it can be called as wireless. Bluetooth, WiFi, Wimax, VSAT etc use air as a media for signals and Infrared (IR), Radio Frequency (RF) and microwave signals are used for data transmission. Two simple nodes can be connected by using a cable in local network. A modem is used for connecting a computer with telephone, which can remotely connect another computer in distance place. Modem stands for MODulation and DEModulation which converts signal from analog to digital and vice- versa so that data can be sent on telephone network.
5. Network Devices
Cables and network devices are required to make physical connection between nodes. Nodes can be workstations, PCs, servers, laptops, printers or other network devices. Various cabling scheme will be discussed later in this module. Popular network devices used for building network are Network Interface Card (NIC) hubs, unmanaged switches, managed switches, layer 3 switches, routers, firewall appliances for security etc.
5.1 Network Interface Card (NIC)
All equipment which is expected to connect to a network requires a simple connection device called NICs. Generally PC comes out with inbuilt NIC with a RJ45 connector. Patch cord from a network device such as hub, switch etc., can be plugged directly into the NIC port. All network equipment and NICs will have a unique physical address globally called MAC (Media Access Control) address in hexadecimal form which is basic for Ethernet frame to locate a physical address in the segmented network.
5.2 Hub
Hubs are simple network device which work on broadcasting principle to connect segments of a LAN. All nodes connected to a central hub which has multiple ports will receive signals from all nodes and hub will then broadcast the signal to all nodes. Targeted recipient will receive the packets and others will discard the packets. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. Each and every packet travels to all nodes irrespective of its destination. This creates traffic as well as collision in the network. Though it was that simple network can be created with hubs, reliability and stability is very poor while using hubs.
Fig.7: Hub
5.3 Switch
Switch is a more dedicated device for the transmission of packets which filters and forwards packets between LAN segments. Switches are of two types based on its working nature. Simple switch operate at the data link layer (layer 2) and advanced one work on network layer (layer 3) of the OSI Reference Model. layer 3 switches are generally managed switches and a VLAN (Virtual LAN) segmentation can be done for each network segment.
Though Hub and switch looks similar, the functionality is different while dealing with packet transmission. Collision and heavy traffic can be managed with a switch. Hub is broadcasting device and switch is unicasting device because switches have memory element to store MAC address.
5.4 Router/Gateway
Router is an intelligent device that forwards data packets along the right network path. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP.s network.
Routers are required to interconnect different LAN segments located at gateway level. Routers use additional data like headers and a forwarding table to determine the best path for forwarding the packets. Routers also use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.
6. Network Connection
6.1 Network Cabling
There are different types of cables to connect to nodes depending upon the networking standards. The most popular one is twisted pair cables as used in electrical connection. Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted for the purpose of nullifying Electro Magnetic Interference (EMI) for better signal transmission. Twisted pair cables are covered with a shield. UTP cables are made of 25 pairs with color codes which are found in Ethernet. The cables are made of copper wires with colored insulation in a polyethylene jacket. These cables are used in data network for short and medium rage connections. Popular cable types are UTP (Unshielded Twisted Pair), STP (Shielded Twisted Pair) and S-FTP (Foil Shielded Twisted pair), S-STP (Braided shielding). Depending upon the bandwidth UTP can be classified as CAT-5 (100MHz) which are commonly used in old LANs, CAT-6 (250 MHz), CAT-7 (600 MHz). CAT 7 A (100 MHz) is the latest standard, which, supports applications of telephone, CCTV, Gigabit Data in the same cable.
For high speed and long distance network optical fiber cables are used which work on light principle. Fiber optical cable is made from hundreds of hair -like strands of glass to send pulses of light to carry data. An optical convertor at the end, converts the light signals into the electrical signals. Optical fiber consists of a core and a cladding layer for internal reflection of light. Fibers that support many prorogation paths are called multi- mode fibers, while those that support a single mode are called single- mode fibers. Multi mode fibers have a wider core diameter and used for short distance communication. Single mode fibers are used for long distance, transmission which is more than one kilometer. Two fiber cables are cleaved and then carefully spliced together with the cores. Multi mode fibers are identified by OM (Optical Mode) as out lines in ISO standards. OM 1 is having bandwidth at 850/300nm with 200/500 MHz, and OM 2 with 500 Mhz. OM 3 is having 2000 MHz designed for 10 GB/s transmission and OM 4 for 4700 MHz designed for 40 GB/s, and 100 GB/s transmission. OS 1 is a single- mode fibers designed for 1 to 10 GB at maximum distance of 2000 meters while OS 2 is designed for 5000 to 10000 meters.
6.2 Wireless Network
As mentioned earlier, cables are used for connecting nodes in a network. Air can be used as media instead of physical cables. Wireless equipment is used to get connected to network devices for data transmission in wireless networks. It is common to use a data card or USB modem to connect to the Internet. A USB modem can be procured from any popular ISP (Internet Service Provider) and it enables a PC or Laptop to communicate to their server for Internet services. For an organisation, VSAT (Very Small Aperture Terminal) antenna can be used to communicate with ISP through satellite. ISP maintains Mother Earth Stations (MES) to communicate with parabolic antenna receivers. VSAT is easy to install in any location which is geographically difficult for terrestrial connection. VSAT technology is very expensive and higher bandwidth cannot be achieved with low cost.
Radio frequency signal can also be used to create a local area network (LAN) and such a LAN is called Wireless LAN/WiFi network. An Access Point (AP) would work as a transmitter with its antenna to co communicate with the wireless receivers in PCs or Laptops. Now a days, laptop comes with default Wireless Facility called ‘WiFi’ or IEEE 802.11 n/g/. WiFi can also be used to communicate with mobile devices if WiFi is enabled in mobile device. Proper security like WPA, WPA2 etc, should be enabled in WiFi networks.
7. Summary
A robust network design should have proper network topology, feasible media, sophisticated and reliable network devices such as hub, switch, router, gateway etc. Aesthetically designing the network is an art and structured cabling with data centre aggregates in a common centre gives more flexibility in managing the network. Adoption of old standards and technology based on new requirement can levy upon market trends. Newer and newer technologies are introduced in market for better speed and reliability. Different products are also available with sophisticated and integrated solutions. Basic network for a simple organisation can be planned in different ways based on the various technologies and equipment discussed in this module. A well designed Tier-3/Tier2 Data centre can be built for sophisticated integrated network solutions. Established IT companies are known for creative design and implementation of Data Centre which holds all related equipments with high reliability and redundancy including ISPs and power requirements.
8. References
1. Building the State-of-the-Art IT Infrastructure for ICT enabled Higher Educational Institutions, Manoj Kumar K, INFLIBNET News Letter, Vol 20. N0.2 (April to June 2013), ISSN : 0971-9849
2. URL accessed on 1st April 2014.
3. http://www.cs.cornell.edu/skeshav/book/slides/switching/switching.pdfURL accessed on 15th Feb 2014.
4. http://www.cs.cornell.edu/skeshav/book/slides/switching/switching.pdfURL accessed on 15th Feb 2014.
- http://sadik.net/DIYProjects/category/cat5/ and http://www.automation- drive.com/cable-ethernet