CHAPTER 11

                In this chapter, it is mentioned network devices depends on two types of software for their operation. It is the operating system and the configuration. IOS is the operating system of network devices. It is like what we knew as operating system of a computer. Just like an operating system of a computer, it is also the system software for Cisco devices. It is accessible via CLI (Command Line Interface). And there are also different ways to access the CLI environment such as console, Telnet, and AUX port. And that’s all about operating system for network devices. Here’s the configuration. As what I have read, configuration is created by an administrator in order to provide the specific functionality of a specific Cisco device. A configuration file is of two types: 1) the running configuration file; and the 2) startup configuration file.

                Cisco IOS is also designed as a modal operating system, meaning, there are different modes of operation. And this chapter also showed the CLI hierarchical structure of the modes. Modes are identified in the command-line prompt which is unique to that mode. And several examples of commonly used modes are described in this chapter. Basic IOS command structures are also shown in this chapter as an example. Applying basic configurations using Cisco IOS are also discussed. And there are also testing done to verify its connectivity of the network.

KEY TERMS:

1.       IOS

-          Internetwork Operating System.

-          It provides basic routing and switching functions, it provides reliable and secure access to networked resources and it also provide network scalability. It also facilitates the basic operation of the device’s hardware components.

2.       Configuration files

-          Contains the Cisco IOS software commands used to customize the functionality of a Cisco device.

3.       Startup Configuration files

-          Is used during system startup to configure the device. The startup-config files are loaded into the RAM each time the router is reloaded or started. Once the configuration files is loaded into the RAM, it is then considered as the running config.

4.       Running Configuration Files

-          It is modified when the network administrator performs device configuration. Changes to the running config will immediately affect the operation of the Cisco device. Changes made in the running config must be saved before the device is powered down because unsaved changes will be lost if the device will be turned off since it is in RAM.

5.       Ping command

-          It is an effective way to test connectivity.

-          It provides a method for checking the protocol stack and IPv4 address configuration on a host.

CHAPTER 10

This chapter discussed about Planning and Cabling Network. I’ve learned that in order to have a well planned functioning network, one must consider the different factors in choosing a device. These includes: the cost, ports/interfaces, speed, its expandability, its manageability, and its additional features and services. And because there are several types of media, such as UTP, Fiber Optics, and Wireless, there are also some factors to consider in choosing a media, these includes: its cabling length, its cost, adequate bandwidth, ease of installation, and is susceptible to EMI/RFI. I’ve learned that when connecting different types of devices, we shall use straight-through cable, and crossover cable when connecting same types of devices.

                It is also discussed here in this chapter the different end devices that requires IP addresses such as computers (for users and administrator), servers, IP cameras, printers, and IP phones; also network devices that requires IP address: router LAN interfaces and router WAN (serial) interfaces; and lastly are the network devices that requires IP address for management: switches and wireless access points.

                Designing an addressing scheme of the internetwork and assign ranges of network devices, router interface, and hosts are also learned here in this chapter. And in interconnecting devices, I’ve also learned the corresponding interfaces or ports of every Cisco devices, switches, and routers. For the LAN interface is the Ethernet, WAN interface is the serial, console interface for initial configuration of Cisco router or switch, and the Auxiliary interface is for remote management of the router.

                And in making LAN connections,  several cables are used such as UTP straight-through cables, UTP crossover cables, and others. When connecting different types of devices, use straight-through cable. And when connecting the same type of device, use a cross over cable.

                And in making WAN connections, there are also several connectors such as DSL (Digital Subscriber Line), physical serial cables, etc.

                Counting subnet is also reviewed in this chapter, but in this chapter, it is discussed that determining the total number of host is useful to develop its addressing scheme. And the ways for calculating addresses in the network is fully instructed in this chapter.

KEY TERMS:

1.       DCE       

-          Data Communication Equipment.

-          It provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices.

-          Some of its examples are modems and interface cards.

2.       DTE

-          Data Terminal Equipment.

-          It is the interface between the router and the DCE. It also controls data coming inbound or outbound.

3.       EMI       

-           interference in a radio receiver or other electrical circuit by electromagnet radiation

        emitted from an external source.

4.       MDI      

-          Medium Independent Interface.

-          It is the pinout order on an NIC card of a PC. It is also known as an uplink port for hubs or switches.

5.       MDIX

-          Media Independent Interface Crossover.

-          It is the pinout of switch or hub in which the input pins on side correspond with the output pins on the other side.

CHAPTER 9

                In this chapter, I have learned that Ethernet was designed for multiple hosts/computers which are interconnected within a shared topology, be accommodated. I’ve also learned that Ethernet technology’s foundation came from Alohanet in 1970 in Hawaii.  But in 1980, the first Ethernet standard was published. And in 1985, the IEEE (Institute of Electrical and Electronics Engineers) standards committee published standards for LANs. And this standard was 802.2 and 802.3, but the original standard was 802.3. the Ethernet divided the Data Link Layer into two sublayers: a) LLC (Logical Link Control); and b) MAC (Media Access Control). The 802.2 works in the upper sublayer (LLC) of the Data Link Layer, and the 802.3 works in the lower sublayer (MAC)of the Data Link Layer together with the Physical layer or the Layer 1.

                Ethernet’s frame has also several fields, the Preamble and Start Frame Delimiter, The Destination MAC Address, Source MAC Address, Length/ Type, Data and Pad, and Frame Check Sequence.

                CSMA/CD (Carrier Sense Multiple Access with Collision Detection was the first version of Ethernet’s media access method. When problems occurred during the attempts of multiple devices over a shared physical medium attempted to communicate, CSMA/CD manages that problem.

                I’ve also learned what is ARP or the Address Resolution Protocol. ARP is used by a host when it wants to have the MAC address of the other host. Then the requesting host sends ARP request into the network. Then the host in the network that has the IP address in the request then sends a reply with its MAC address.

KEY TERMS:

1.       IEEE

-          means Institute of Electrical and Electronics Engineers.

-          They are the one who published standards for the LAN’s/Ethernet.

2.       CSMA/CD

-          Means Carrier Sense Multiple Access with Collision Detection

-          It managed the problems that result when multiple computers attempt to communicate within a shared physical medium.

-          It controls the access to the shared media. It also detects collisions and frames are retransmitted.

3.       LLC

-          Means Logical Link Control

-          It is the upper sublayer of the Data Link layer. It makes the connection between the upper layers and it frames the network packet. It also identify the Network layer protocol and remains relatively independent of the physical equipment.

4.       MAC

-          Means Media Access Control

-          It is the lower sublayer of the Data Link layer. It gets data to the media. It has two primary responsibilities: 1) Data Encapsulation, which includes Frame delimiting, Addressing, Error Detection; 2) Media Access Control, which control the frame placement on and off the media and media recovery.

5.       MAN

-          Means Metropolitan Ares Network

-          A LAN applied across a city from being connected to single buildings, and then extended to between buildings.  

CHAPTER 8 – OSI PHYSICAL LAYER

          The discussion in this chapter (Chapter 8) is all about the OSI model’s layer 1 which is the Physical Layer and describes its purpose and functions. Before knowing deeper about the Physical Layer, let us recall that the upper layers of the OSI layers protocol prepare data from the human network for transmission from its source to its destination. The upper layers of the OSI model are implemented in software and the Physical layer is implemented in hardware. All communication from the human network becomes binary digits, which are transported individually across the Physical media.

          The Physical layer has three fundamental functions: a) physical components, includes the electronic hardware devices, media connectors that carry the signals to represent the bits; b) encoding, a method of converting data bits into a predefined code; c) signaling, the method of representing the bits.

          This chapter described also the standards of the Physical layer. These standards are defined by the organizations such as ISO, IEEE, ITU, ANSI, and etc. It also discussed about some kinds of copper media connectors such as coaxial cable, unshielded twisted-pair (UTP) cable, and RJ-45 connections, and also the safety accompanying the copper media in dealing with electrical hazards and fire hazards.

          To fully understand this chapter, here are some important points that are related to this OSI model’s Physical layer:

THE PHYSICAL LAYER
          The Physical layer consists of hardware in the form electronic circuitry, media, and connectors. And the function of the Physical layer protocol is to control how data is placed on the communication media. So, the Physical layer encodes the bits into the signals for a particular medium and it must also distinguish where one frame ends and where the next frame begins or else the devices on the media will not recognize whether it fully received the frame and not be able to reconstruct that frame. The Physical layer represents each of the bits in the frame as a signal.

THE MEDIA
          A media is a physical medium in which data is transferred. And the three basic forms of network media on which data is transferred are: copper cable, fiber, and wireless. And let us always remember that the media does not carry the frame as a single entity, in fact, the media carries signals one at a time to represent that bits that make up the frame.


THE BIT TIME
          The time that takes for a bit to be transmitted from a network adapter that is operating at some predefined standard speed.

THE SIGNALING METHODS or THE TWO WAYS TO ENCODE BITS AS VOLTAGES
          The nature of the signal representing the bits on the media depends on the signaling method that is used. The signaling method must have a standard agreement so that the receiver can detect the signals and decode them so that the communication between the media will not fail. One example of signaling is the NRZ (Non Return to Zero), in here, the bit stream is transmitted as a series of voltage values and these values includes the 0 which represents a low voltage and the 1 represents the high voltage. When there are long strings of 1s or 0s are being transmitted then the receiving nodes can not resynchronize the bit times with the transmitting nodes.
Another example of the signaling method is the Manchester Encoding. Manchester Encoding is different from NRZ. Unlike NRZ which only represents bits as voltages high or low, Manchester Encoding represents voltage transitions. In other words, 1 represents the transition bits from low voltage to high voltage, and 0 represents the transition from high voltage to a low voltage.

THE CODE GROUP
          A code group is a consecutive sequence of code bits that are interpreted and mapped as data bit patterns. It is often used as an intermediary encoding technique for higher speed LAN technologies. It is also a set of encoded symbols. Symbols on the other hand, is an encoding techniques that use bit patterns. Reducing bit level error, limiting the effective energy transmitted into the media, helping to distinguish data bits from control bits, and better media error detection are the advantages of using code groups.

THE DATA CARRYING CAPACITY
          Bandwidth is the amount of data that can be transmitted in a certain amount of time. It is usually expressed in bits per second (bps), either kilobits per second (kbps) or megabits per second (mbps) in digital bandwidth. Throughput is the measure of the transfer of bits across the media over a given period of time. Goodput is used to measure the transfer of usable data in a given period of time.


          In general, the Layer 1 of the OSI model is responsible for the physical interconnection of devices across the network. The Physical layer protocol encoded the bits and decodes it at the destination after transmission. To transmit data, bits are represented as signals using signaling methods over the different media. And there are the standards considered for the Physical layer, and these standards are defined by different organizations.

A Smile

A smile is better than pills
To ease all the everyday strife;
It perks up your heart and your spirit
So you can cope with everyday life.

It takes more muscles to frown
Than to flash a smile to the world;
It helps heal a broken heart
Like a waving banner unfurled.

It shows people you still have hope
That a better tomorrow will bring,
That no matter how bad the winter,
You still have the promise of spring.

So, smile when your heart is heavy,
It's the only thing you can do,
Frowning won't change the problem,
But smiling will your spirits renew.

~ Mary Eileen Butera ~