Network Devices : Routers

Nework Devices

See previous post Network Devices. now we will share about Routers.

Router

Routers

A router has two basic functions, path determination using a variety of metrics, and forwarding packets from one network to another.  Routing metrics can include load on the link between devices, delay, bandwidth, and reliability, or even hop count (i.e. the number of devices a packet must go through in order to reach its destination). 

In essence, routers will do all that bridges and switches will do, plus more.  Routers have the capability of looking deeper into the data frame and applying network services based on the destination IP address.  Destination and Source IP addresses are a part of the network header added to a packet encapsulation at the network layer.    

Network

Summary Network Devices :

n  LANs are designed to operate within
a limited geographic area

n  Key LAN components are computers, NOS, NICs, hubs, and cables

n  Common LAN topologies include
bus, tree, star, and ring

n  Common LAN/WAN devices are hubs, bridges, switches, and routers

Network Devices : Switches

Network Devices

see previous post network devices. Now, we will share about Switches.

Switches

Switches

Switches use bridging technology to forward traffic between ports.  They provide full dedicated transmission rates between two stations that are directly connected to the switch ports.  Switches also build and maintain address tables just like bridges do.  These address tables are known as “content addressable memory.” Let’s look at an example.

Replacing the two hubs and the bridge with an Ethernet switch provides the users with dedicated bandwidth.  Each station has a full 10Mbps “pipe” to the switch.  With a switch at the center of the network, combined with the 100Mbps links, users have greater access to the network. 

Given the size of the files and applications on this network, additional bandwidth for access to the sever or to the corporate intranet is possible by using a switch that has both 10Mbps and 100Mbps Fast Ethernet ports.  The 10Mbps links could be used to support all the desktop devices, including the printer, while the 100Mbps switch ports would be used for higher bandwidth needs.

Network Devices

Network Devices

In the previous post, we shared about network devices . this post will share to you about bridges,switches, and routers. happy reading..

Bridge

Bridges

Bridges improve network throughput and operate at a more intelligent level than do hubs.  A bridge is considered to be a store and forward device that uses unique hardware addresses to filter traffic that would otherwise travel from one segment to another.  A bridge performs the following functions:

•         Reads data frame headers and records source address/port (segment) pairs

•         Reads the destination address of incoming frames and uses recorded addresses to determine the appropriate outbound port for the frame.

•         Uses memory buffers to store frames during periods of heavy transmission, and forwards them when the medium is ready.

Let’s take a look at an example.

The bridge divides this Ethernet LAN into two segments, each connecting to a hub and then to a bridge port.  Stations 123-125 are on segment 1 and stations 126-128 are on segment 2. 

When station 124 transmits to station 125, the frame goes into the hub (who repeats it and sends it out all connected ports) and then on to the bridge.  The bridge will not forward the frame because it recognizes that stations 124 and 125 are on the same segment.  Only traffic between segments passes through the bridge.  In this example, a data frame from station 123, 124, or 125 to any station on segment 2 would be forwarded, and so would a message from any station on segment 2 to stations on segment 1. 

When one station transmits, all other stations must wait until the line is silent again before transmitting. In Ethernet, only one station can transmit at a time, or data frames will collide with each other, corrupting the data in both frames. 

Bridges will listen to the network and keep track of who they are hearing.  For instance, the bridge in this example will know that system 127 is on Segment 2, and that 125 is on segment 1.  The bridge may even have a port (perhaps out to the Internet) where it will send all packets that it cannot identify a destination for.  network devices : bridge. to be continued...

Network Device

Network Device

Let’s now take a look at some of the devices that move traffic around the network. 

The approach taken in this section will be simple.  As networking technology continues to evolve, the actual differences between networking devices is beginning to blur slightly.  Routers today are switching packets faster and yielding the performance of switches.  

Switches, on the other hand, are being designed with more intelligence and able to act more like routers.  Hubs, while traditionally not intelligent in terms of the amount of software they run, are now being designed with software that allows the hub to be “intelligent” acting more like a switch. 

In this section, we’ll keep these different types of product separate so that you can understand the basics.  Let’s start off with the hub.

Network Device Hub

Star topology networks generally have a hub in the center of the network that connects all of the devices together using cabling.  When bits hit a networking device, be they hubs, switches, or routers, the devices will strengthen the signal and then send it on its way. 

A hub is simple a multiport repeater.  There is usually no software to load, and no configuration required (i.e. network administrators don’t have to tell the device what to do). 

Hubs operate very much the same way as a repeater.  They amplify and propagate signals received out all ports, with the exception of the port from which the data arrived. For example, if system 125 wanted to print on the printer 128, the message would be sent to all systems on Segment 1, as well as across the hub  to all systems on Segment 2.  System 128 would see that the message is intended for it and would process it. 

Devices on the network are constantly listening for data.  When devices  sense a frame of information that is addressed (and we will talk more about addressing later) for it, then it will accept that information into memory found on the network interface card (NIC) and begin processing the data. 

In fairly small networks, hubs work very well.  However, in large networks the limitations of hubs creates problems for network managers.  In this example, Ethernet is the standard being used.  The network is also baseband, only one station can use the network at a time.  If the applications and files being used on this network are large, and there are more nodes on the network, contention for bandwidth will slow the responsiveness of the network down.

to be continued...

Local Area Network (LAN) Topology

Local Area Network (LAN) Topology

You may hear the word topology used with respect to networks. “Topology” refers to the physical arrangement of network components and media within an enterprise networking structure. There are four primary kinds of LAN topologies: bus, tree, star, and ring.

Networks

Bus topology is

•         A linear LAN architecture in which transmissions from network components propagate the length of the medium and are received by all other components.

•         The bus portion is the common physical signal path composed of wires or other media across which signals can be sent from one part of a network to another. Sometimes called a highway.

•         Ethernet/IEEE 802.3 networks commonly implement a bus topology

Tree topology is

•         Similar to bus topology, except that tree networks can contain branches with multiple nodes. As in bus topology, transmissions from one component propagate the length of the medium and are received by all other components.

The disadvantage of bus topology is that if the connection to any one user is broken, the entire network goes down, disrupting communication between all users. Because of this problem, bus topology is rarely used today.

The advantage of bus topology is that it requires less cabling (therefore, lower cost) than star topology.

Star topology is a LAN topology in which endpoints on a network are connected to a common central switch or hub by point-to-point links. Logical bus and ring topologies re often implemented physically in a star topology.

•         The benefit of star topology is that even if the connection to any one user is broken, the network stays functioning, and communication between the remaining users is not disrupted.

•         The disadvantage of star topology is that it requires more cabling (therefore, higher cost) than bus topology.

Star topology may be thought of as a bus in a box.    

Ring topology consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop.

•         Each station on the network connects to the network at a repeater.

•         While logically a ring, ring topologies are most often organized in a closed-loop star. A ring topology that is organized as a star implements a unidirectional closed-loop star, instead of point-to-point links.

•         One example of a ring topology is Token Ring.

Redundancy is used to avoid collapse of the entire ring in the event that a connection between two components fails.

Throughput and Bandwidth

Throughput and Bandwidth

Super servers, high-capacity workstations, and multimedia applications have also fueled the need for higher capacity bandwidths.

The examples on this slide shows that the need for throughput capacity grows as a result of a desire to transmit more voice, video, and graphics. The rate at which this information may be sent (transmission speed) is dependent how data is transmitted and the medium used for transmission. The “how” of this equation is satisfied by  a transmission protocol.

Each protocol runs at a different speed. Two terms are used to describe this speed: throughput rate and bandwidth.

The throughput rate is the rate of information arriving at, and possibly passing through, a particular point in a network.

In this post, the term bandwidth means the total capacity of a given network medium (twisted pair, coaxial, or fiber-optic cable) or protocol.

•         Bandwidth is also used to describe the difference between the highest and the lowest frequencies available for network signals. This quantity is measured in Megahertz (MHz).

•         The bandwidth of a given network medium or protocol is measured in bits per second (bps).

Some of the available bandwidth specified for a given medium or protocol is used up in overhead, including control characters. This overhead reduces the capacity available for transmitting data.

Cable Types for Network Connetions

Cable Types for Network Connetions

This post will give the details of the previous post Network Connetions.

Unshielded twisted-pair (UTP)

UTP

Unshielded twisted-pair (UTP) is a four-pair wire medium used in a variety of networks. UTP does not require the fixed spacing between connections that is necessary with coaxial-type connections. There are five types of UTP cabling commonly used as shown below:

•         Category 1:    Used for telephone communications. It is not suitable for transmitting data.

•         Category 2:    Capable of transmitting data at speeds up to 4 Mbps.

•         Category 3:    Used in 10BaseT networks and can transmit data at speeds up to 10 Mbps.

•         Category 4:    Used in Token Ring networks. Can transmit data at speeds up to 16 Mbps.

•         Category 5:    Can transmit data at speeds up to 100 Mbps.

Shielded twisted-pair (STP) is a two-pair wiring medium used in a variety of network  implementations. STP cabling has a layer of shielded insulation to reduce EMI. Token Ring runs on STP.

Using UTP and STP:

•         Speed is usually satisfactory for local-area distances.

•         These are the least expensive media for data communication. UTP is cheaper than STP.

•         Because most buildings are already wired with UTP, many transmission standards are adapted to use it to avoid costly re-wiring of an alternative cable type.

Coaxial cable

Coaxial Cable

Coaxial cable consists of a solid copper core surrounded by an insulator, a combination shield and ground wire, and an outer protective jacket.

The shielding on coaxial cable makes it less susceptible to interference from outside sources. It requires termination at each end of the cable, as well as a single ground connection.

Coax supports 10/100 Mbps and is relatively inexpensive, although more costly than UTP.

Coaxial can be cabled over longer distances than twisted-pair cable. For example, Ethernet can run at speed over approximately 100 m (300 feet) of twisted pair. Using coaxial cable increases this distance to 500 m.

Fiber-optic cable

Fiber Optics

Fiber-optic cable consists of glass fiber surrounded by shielding protection: a plastic shield, kevlar reinforcing, and an outer jacket. Fiber-optic cable is the most expensive of the three types discussed in this section, but it supports 100+ Mbps line speeds.

There are two types of fiber cable:

•         Single or mono-mode—Allows only one mode (or wavelength) of light to propagate through the fiber; is capable of higher bandwidth and greater distances than multimode. Often used for campus backbones. Uses lasers as the light generating method. Single mode is much more expensive than multimode cable. Maximum cable length is 100 km.

•         Multimode—Allows multiple modes of light to propagate through the fiber. Often used for workgroup applications. Uses light-emitting diodes (LEDs) as light generating device. Maximum cable length is 2 km.

Network Connetions

Network Connections

The wires connecting the various devices together are referred to as cables.

•         Cable prices range from inexpensive to very costly and can comprise of a significant cost of the network itself.

•         Cables are one example of transmission media. Media are various physical environments through which transmission signals pass. Common network media include twisted-pair, coaxial cable, fiber-optic cable, and the atmosphere (through which microwave, laser, and infrared transmission occurs). Another term for this is “physical media.”

•         Note that not all wiring hubs support all medium types.

Network Connections

The other component shown in this slide is the connector.

•         As their name implies, the connector is the physical location where the NIC card and the cabling connect.

•         Registered jack (RJ) connectors were originally used to connect telephone lines. RJ connectors are now used for telephone connections and for 10BaseT and other types of network connections. Different connectors are able support different speeds of transmission because of their design and the materials used in their manufacture.

•         RJ-11 connectors are used for telephones, faxes, and modems. RJ-45 connectors are used for NIC cards, 10BaseT cabling, and ISDN lines.

Cable is the actual physical path upon which an electrical signal travels as it moves from one component to another.

Transmission protocols determine how NIC cards take turns transmitting data onto the cable. Remember that we discussed how LAN cables (baseband) carry one signal, while WAN cables (broadband) carry multiple signals. There are three primary cable types:

•         Twisted-pair (or copper)

•         Coaxial cable and

•         Fiber-optic cable

the next post will inform you the details of cable types. see Network Operating System

Network Operating System

Network Operating System (OS)

Network

In order for computers to be able to communicate with each other, they must first have the networking software that tells them how to do so. Without the software, the system will function simply as a “standalone,” unable to utilize any of the resources on the network.

Network operating software may by installed by the factory, eliminating the need for you to purchase it, (for example AppleTalk), or you may install it yourself.

The computer shown here may be a workstation or a personal computer (PC).

Network Interface Card (NIC)

In addition to network operating software, each network device must also have a network interface card. These cards today are also referred to as adapters, as in “Ethernet adapter card” or “Token Ring adapter card.”

The NIC card amplifies electronic signals which are generally very weak within the computer system itself. The NIC is also responsible for packaging data for transmission, and for controlling access to the network cable. When the data is packaged properly, and the timing is right, the NIC will push the data stream onto the cable.

The NIC also provides the physical connection between the computer and the transmission cable (also called “media”). This connection is made through the connector port. Examples of transmission media are Ethernet, Token Ring, and FDDI.

Hub

Hub

In order to have a network, you must have at least two devices that communicate with each other. In this simple model, it is a computer and a printer. The printer also has an NIC installed (for example, an HP Jet Direct card), which in turn is plugged into a wiring hub. The computer system is also plugged into the hub, which facilitates communication between the two devices.

Additional components (such as a server, a few more PCs, and a scanner) may be connected to the hub. With this connection, all network components would have access to all other network components.

The benefit of building this network is that by sharing resources a company can afford higher quality components. For example, instead of providing an inkjet printer for every PC, a company may purchase a laser printer (which is faster, higher capacity, and higher quality than the inkjet) to attach to a network. Then, all computers on that network have access to the higher quality printer. Network Operating System.

Internet Networking Basics

Internet Networking Basics

Internet Networking Basics

Internet Network Basic. This blog covers the very basics of internetworking. We’ll start with a little history that describes how the networking industry evolved. We’ll then move on to a section that describes how a LAN is built: essentially the necessary components (like NIC cards and cables). We then cover LAN topologies. And finally we’ll discuss the key networking devices: hubs, bridges, switches, and routers.

This post is an overview only. It will familiarize you with much of the vocabulary you hear with regards to networking. Some of these concepts are covered in more detail in later post.

The term local-area network, or LAN, describes of all the devices that communicate together—printers, file server, computers, and perhaps even a host computer. However, the LAN is constrained by distance. The transmission technologies used in LAN applications do not operate at speed over long distances. LAN distances are in the range of 100 meters (m) to 3 kilometers (km). This range can change as new technologies emerge.

For systems from different manufacturers to interoperate—be it a printer, PC, and file server—they must be developed and manufactured according to industry-wide protocols and standards.

More details about protocols and standards will be given later, but for now, just keep in mind they represent rules that govern how devices on a network exchange information. These rules are developed by industry-wide special interest groups (SIGs) and standards committees such as the Institute of Electrical and Electronics Engineers (IEEE).

Local Area Network (LAN)

Most of the network administrator’s tasks deal with LANs. Major characteristics of LANs are:

•         The network operates within a building or floor of a building. The geographic scope for ever more powerful LAN desktop devices running more powerful applications is for less area per LAN.

•         LANs provide multiple connected desktop devices (usually PCs) with access to high-bandwidth media.

•         An enterprise purchases the media and connections used in the LAN; the enterprise can privately control the LAN as it chooses.

•         LANs rarely shut down or restrict access to connected workstations; local services are usually always available.

•         By definition, the LAN connects physically adjacent devices on the media.