Lecture Slides On Networking

DS126111:FUNDAMENTALS OF COMPUTER NETWORKS

KIGALI INDEPENDENT UNIVERSITY-ULK

By:John Mpenzi BSc in CompEng & Msc in Software Engineering

IT

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CONTENT         

Communcation network Architecture Communication protocols Data security and integrity on network Data comm through network and network mngt Client-server computing Network concepts,components,protocols OSI Models and Layers LAN and WAN Technologies and Topologies etc

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Lesson 1: Networking Basic 

This lesson covers the very basics of networking. 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

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Networking History 

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Early networks

From a historical perspective, electronic communication has actually been around a long time, beginning with Samuel Morse and the telegraph. He sent the first telegraph message May 24, 1844 from Washington DC to Baltimore MD, 37 miles away. The message? “What hath God wrought?” or shaped Less than 25 years later, Alexander Graham Bell invented the telephone – beating out a competitor to the patent office only by a couple of hours on Valentine’s Day in 1867. This led to the development of the ultimate analog network – the telephone system. The first bit-oriented language device was developed by Emile Baudot – the printing telegraph. By bit-oriented we mean the device sent pulses of electricity which were either positive or had no voltage at all. These machines did not use Morse code. Baudot’s five-level code sent five pulses down the wire for each character transmitted. The machines did the encoding and decoding, eliminating the need for operators at both ends of the wires. For the first time, electronic messages could be sent by anyone 4

Telephone Network 

But it’s really the telephone network that has had the greatest impact on how businesses communicate and connect today. Until 1985, the Bell Telephone Company, now known as AT&T, owned the telephone network from end to end. It represented a phenomenal network, the largest then and still the largest today

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Developments in Communication 

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In 1966, an individual named “Carter” invented a special device that attached to a telephone receiver that would allow construction workers to talk over the telephone from a twoway radio. Bell telephone had a problem with this and sued – and eventually lost. As a result, in 1975, the Federal Communications Commission ruled that devices could attach to the phone system, if they met certain specifications. Those specifications were approved in 1977 and became known as FCC Part 68. In fact, years ago you could look at the underside of a telephone not manufactured by Bell, and see the “Part 68” stamp of approval. 6

1960's - 1970's Communication 

In the 1960’s and 1970’s, traditional computer communications centered around the mainframe host. The mainframe contained all the applications needed by the users, as well as file management, and even printing. This centralized computing environment used lowspeed access lines that tied terminals to the host. These large mainframes used digital signals – pulses of electricity or zeros and ones, what is called binary -- to pass information from the terminals to the host. The information processing in the host was also all digital. 7

Problems faced in communication This brought about a problem. The telephone industry wanted to use computers to switch calls faster and the computer industry wanted to connect remote users to the mainframe using the telephone service. But the telephone networks speak analog and computers speak digital. Let’s take a closer look at this problem. Digital signals are seen as one’s and zero’s. The signal is either on or off. Whereas analog signals are like audio tones – for example, the high-pitched squeal you hear when you accidentally call a fax machine. So, in order for the computer world to use the services of the telephone system, a conversion of the signal had to occur.

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The solution a modulator/demodulator or “modem.” The modem takes the digital signals from the computer and modulates or transforms the signal into analog format. In sending information from a desktop computer to a host using POTS or plain old telephone service, the modem takes the digital signals from the computer and modulates the signal into analog format to go through the telephone system. From the telephone system, the analog signal goes through another modem which converts the signal to digital format to be processed by the host computer. This helped solve some of the distance problems, at least to a certain extent. 9

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Birth of the personal computer

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The birth of the personal computer in 1981 really fueled the explosion of the networking marketplace. No longer were people dependent on a mainframe for applications, file storage, processing, or printing. The PC gave users incredible freedom and power.

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The Internet 1970's - 1980's 

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The 70’s and 80’s saw the beginnings of the Internet. The Internet as we know it today began as the ARPANET — The Advanced Research Projects Agency Network – built by a division of the Department of Defense essentially in the mid ‘60's through grant-funded research by universities and companies.. Many local area networks connected to the ARPANET with TCP/IP. TCP/IP was developed in 1974 and stands for Transmission Control Protocol / Internet Protocol. The ARPANET was shut down in 1990 due to newer network technology and the need for greater bandwidth on the backbone. In the late ‘70’s the NSFNET, the National Science Foundation Network was developed. This network relied on super computers in San Diego; Boulder; Champaign; Pittsburgh; Ithaca; and Princeton. Each of these six super computers had a microcomputer tied to it which spoke TCP/IP. The microcomputer really handled all of the access to the backbone of the Internet. Essentially this network was overloaded from the word "go".

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Further developments in networking lead to the design of the ANSNET -- Advanced Networks and Services Network. ANSNET was a joint effort by MCI, Merit and IBM specifically for commercial purposes. This large network was sold to AOL in 1995. The National Science Foundation then awarded contracts to four major network access providers: Pacific Bell in San Francisco, Ameritech in Chicago, MFS in Washington DC and Sprint in New York City. By the mid ‘80's the collection of networks began to be known as the “Internet” in university circles. TCP/IP remains the glue that holds it together. In January 1992 the Internet Society was formed – a misleading name since the Internet is really a place of anarchy. It is controlled by those who have the fastest lines and can give customers the greatest service today. The primary Internet-related applications used today include: Email, News retrieval, Remote Login, File Transfer and World Wide Web access and development. 12

1990's Global Internetworking 

With the growth and development of the Internet came the need for speed – and bandwidth. Companies want to take advantage of the ability to move information around the world quickly. This information comes in the form of voice, data and video – large files which increase the demands on the network. In the future, global internetworking will provide an environment for emerging applications that will require even greater amounts of bandwidth. If you doubt the future of global internetworking consider this – the Internet is doubling in size about every 11 months.

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LAN building 

In this section some of the basic elements needed to build local area networks (LANs) will be described.

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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 15

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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 industrywide special interest groups (SIGs) and standards committees such as the Institute of Electrical and Electronics Engineers (IEEE).

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Major characteristics of LANs 

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. 17

Components of LAN 

- Network operating system (NOS)

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

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Network interface card(NIC) -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 or intensifies 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. -The NIC also provides the physical connection between the computer and the transmission cable (also called “media”). 19

Wiring Hub -In order to have a network, you must have at least two devices that communicate with each other -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

-The computer system is also plugged into the hub, which facilitates communication between the two devices.

-In this simple model, it is a computer and a printer. The printer also has an NIC installed -which in turn is plugged into a wiring hub

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Cables or Transmission Media The wires connecting the various devices together are referred to as cables.

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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.

- 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.”

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Network Cabling 

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

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Transmission protocols determine how NIC cards take turns transmitting data onto the cable 

There are three primary cable types: - Twisted-pair (or copper) - Coaxial cable and - Fiber-optic cable

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Twisted-pair (or copper) 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.

-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 coaxialtype connections

- 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.

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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 twistedpair 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.

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Fiber-optic cable

-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 25

There are two types of fiber cable

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Single or mono-mode— -Multimode—Allows Allows only one mode (or multiple modes of light to wavelength) of light to propagate through the propagate through the fiber; is capable of higher fiber. Often used for bandwidth and greater workgroup distances than multimode. Often used for campus applications. Uses lightbackbones. Uses lasers as emitting diodes (LEDs) as the light generating method. Single mode is much more light generating device. expensive than multimodeMaximum cable length cable. Maximum cable is 2 km length is 100 km.

-Super servers,

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

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Throughput Needs....!!

-The throughput rate The examples on above

image 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 on how data is transmitted and the medium used for transmission.

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

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). 27

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Questions 

Qn1.Write short notes on the following: a) b) c) d) e) f) g) h)

LAN, its characteristics and why its implementation Discuss different types of soft wares and give examples Give different types of operating systems Discuss different types of LAN components Explain the term Network cabling Discuss different kinds of cabling What do you understand by the term Topology Explain different modes of Topologies

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LAN Topologies 

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.

-Bus and Tree topology -Star topology -Ring topology -

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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. 31

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.

-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.

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Ring topology

-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. -A ring topologies are most often organized in a closed-loop star

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LAN/WAN Devices    

Hub Bridges Switches Routers

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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 multi-port 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).

-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 base band, 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

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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.

Bridge functions:

-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

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. NB:When one station - Uses memory buffers to store frames during periods of heavy transmits, all other transmission, and forwards them stations must wait when the medium is ready

until the line is silent again before transmitting 36

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.”

-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

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Routers 

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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.

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Lesson 2: OSI Reference Model 

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This lesson covers the OSI reference model. It is sometimes also called ISO or 7 layer reference model. The model was developed by the International Standards Organization in the early 1980's. It describes the principles for interconnection of computer systems in an Open System Interconnection environment

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The Layered Model 

The concept of layered communication is essential to ensuring interoperability of all the pieces of a network

In this image, the goal is to get a message from Location A to Location B. The sender doesn’t know what language the receiver speaks – so the sender passes the message on to a translator.

The translator, while not concerned with the content of the message, will translate it into a language that may be globally understood by most, if not all translators – thus it doesn’t matter what language the final recipient speaks. In this example, the language is Dutch. The translator also indicates what the language type is, and then passes the message to an administrative assistant. 40

Upon closer study of the process employed to communicate, you will notice that communication took place at different layers. At layer 1, the administrative assistants communicated with each other. At layer 2, the translators communicated with each other. And, at layer 3 the sender was able to communicate with the recipient.

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Why a Layered Network Model.........?

3. -A layered network model does a number of things. •

It reduces the complexity of the problems from one large one to seven smaller ones

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It allows the standardization of interfaces among devices

It also facilitates modular engineering so engineers can work on one layer of the network model without being concerned with what happens at another layer

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Devices Function at Layers

-Each of these devices operates at a different level of the OSI Model -NIC cards receive information from upper level applications and properly package data for transmission on to the network media

-NIC cards live at the lower four layers of the OSI Model. -Hubs, whether

Ethernet live at the physical layer. They are only concerned with passing bits from one station to other connected stations on the network

-Bridges and switches on the other hand, will filter traffic and build bridging and switching tables in order to keep track of what device is connected to what port

Routers, or the technology of routing, lives at layer 3.

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A closer look at “Host& Media Layers”

Host Layers :-

Media Layers :-

The upper four layers, Application, Presentation, Session, and Transport, are responsible for accurate data delivery between computers. The tasks or functions of these upper four layers must “interoperate” with the upper four layers in the system being communicated with.

The lower three layers – Network, Data Link and Physical -- are called the media layers. The media layers are responsible for seeing that the information does indeed arrive at the destination for which it was intended

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Layer Functions

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Layers in a Peer-to-Peer Communications Network

In this exercise we package information and move it from Host A, across network lines to Host B. Each layer uses its own layer protocol to communicate with its peer layer in the other system. Each layer’s protocol exchanges information, called protocol data units (PDUs), between peer layers.

-This peer-layer protocol communication is achieved by using the services of the layers below it. The layer below any current or active layer provides its services to the current layer

-The transport layer will ensure that data is kept segmented or separated from one other data. -At the network layer we get packets that begin to be assembled. At the data link layer those packets become frames and then at the physical layer those frames go out on the wires from one host to the other host as bits

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Data Encapsulation

-This whole process of moving data from host A to host B is known as data encapsulation – the data is being wrapped in the appropriate protocol header so it can be properly received. Let’s say we compose an email that we wish to send from system A to system B. The application we are using is Eudora. We write the letter and then hit send. Now, the computer translates the numbers into ASCII and then into binary (1s and 0s). If the email is a long one, then it is broken up and mailed in pieces. This all happens by the time the data reaches the Transport layer.

-At the network layer, a network header is added to the data. This header contains information required to complete the transfer, such as source and destination logical addresses

-The packet from the network layer is then passed to the data link layer where a frame header and a frame trailer are added thus creating a data link frame.

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Layers 1 & 2: Physical & Data Link Layers

-Locating computer systems on an internet work is an essential component of any network system

-Every NIC card on the network has its own MAC address. In this example we have a computer with the MAC address 000.0C12.3456. The MAC address is a hexadecimal number so the numbers in this address here don’t go just from zero to nine, but go from zero to nine and then start at "A" and go through "F".

-Every type of device on a network has a MAC address

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Layer 3: Network Layer Network Layer: Path Determination

-Path determination occurs at Layer 3. The path determination function enables a router to evaluate the available paths to a destination and to establish the preferred handling of a packet

-Data can take different paths to get from a source to a destination.

-At layer 3, routers really help determine which path. The network administrator configures the router enabling it to make an intelligent decision as to where the router should send information through the cloud.

-The network layer sends packets from source network to destination network. After the router determines which path to use, it can proceed with switching the packet: taking the packet it accepted on one interface and forwarding it to another interface or port that reflects the best path to the packet’s destination.

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Addressing—Network and Node

-Each device in a local area network is given a logical address. The first part is the network number -The second part is a node number, in this example we have nodes 1, 2, and 3. The router uses the network number to forward information from one network to another.

-This host address derives automatically from information in hardware of the specific LAN device.

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Network Layer Protocol Operations

Take an example The message will exit Station X and travels through the corporate internal network until it gets to a point where it needs the services of an Internet service provider

-The message will bounce or jump through their network and eventually arrive at Mom’s Internet provider in Dearborn

-As information travels from Station X it reaches the network level where a network address is added to the packet.

At the data link layer, the information is encapsulated or summed up an Ethernet frame. Then it goes to the router – here it is Router A

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Multi-protocol Routing

-Routers are capable of understanding address information coming from many different types of networks and maintaining associated routing tables for several routed protocols concurrently

-As the router receives packets from the users on the networks using IP, it builds a routing table containing the addresses of the network of these IP users.

-Routing tables can contain address information from multiple protocol networks. -Each uses routing tables to determine paths

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Routed Versus Routing Protocol Routing protocol support a routed protocol by providing

Routed protocols - They are any network protocol suite that provides enough information in its network layer address to allow a packet to direct user traffic

mechanisms for sharing routing information. Routing protocol messages move between the routers. -A routing protocol allows the routers to communicate with other routers to update and maintain tables

-Routing protocol messages do not carry end-user traffic from network to network. -A routing protocol uses the routed protocol to pass information between routers

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Static Versus Dynamic Routes Routers must be aware of what links, or lines, on the network are up and running, which ones are overloaded, or which ones may even be down and unusable. There are two primary methods routers use to determine the best path to a destination: static and dynamic

Static knowledge is administered manually: a network administrator enters it into the router’s configuration

Dynamic knowledge works differently. After the network administrator enters configuration commands to start dynamic routing, route knowledge is updated automatically by a routing process whenever new topology information is received from the internetwork

Dynamic routing tends to reveal everything known about an internetwork. For security reasons, it might be appropriate to conceal parts of an internetwork. Static routing allows an internetwork administrator to specify what is advertised about restricted partitions.

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Layers 4–7: Transport, Session, Presentation, and Application Layers Transport Layer— Segments UpperLayer Applications

Transport Layer It also establishes the end-to-end connection, from your host to another host. As the transport layer sends its segments, it can also ensure data integrity. Essentially the transport layer opens up the connection from your system through a network and then through a wide area cloud to the receiving system at the other end

it segments upper layer application information. You might have more than one application running on your desktop at a time. You might be sending electronic mail open while transferring a file from the Web, and opening a terminal session. The transport layer helps keep straight all of the information coming from these different applications.

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Transport Layer— Establishes Connection

-Another function of the transport layer is to establish the connection from your system to another system -When you are

browsing the Web and double-click on a link your system tries to establish a connection with that host

-Once the connection has been established, there is some negotiation that happens between your system and the system that you are connected to in terms of how data will be transferred

-Once the negotiations are completed, data will begin to transfer. As soon as the data transfer is complete, the receiving station will send you the end message and your browser will say done.

-Essentially, the transport layer is responsible then for connecting and terminating sessions from your host to another host 56

Transport Layer— Sends Segments with Flow Control

Another important function of the transport layer is to send segments and maintain the sending and receiving of information with flow control.

When a connection is established, the host will begin to send frames to the receiver. When frames arrive too quickly for a host to process, it stores them in memory temporarily. If the frames are part of a small burst, this buffering solves the problem. If the traffic continues, the host or gateway eventually exhausts its memory and must discard additional frames that arrive.

Instead of losing data, the transport function can issue a not ready indicator to the sender. Acting like a stop sign, this indicator signals the sender to discontinue sending segment traffic to its peer After the receiver has processed sufficient segments that its buffers can handle additional segments, the receiver sends a ready transport indicator, which is like a go signal. When it receives this indicator, the sender can resume segment transmission. 57

Lesson 3: Introduction to TCP/IP TCP/IP is shorthand for a suite of protocols that run on top of IP IP-is the Internet Protocol, and TCP is the most important protocol that runs on top of IP. Any application that can communicat e over the Internet is using IP,

-Protocols that run on top of IP include: TCP, UDP and ICMP -TCP/IP protocols work together to break data into packets that can be routed efficiently by the network. In addition to the data, packets contain addressing, sequencing, and error checking information. This allows TCP/IP to accurately reconstruct the data at the other end.

Here’s an analogy of what TCP/IP does. Say you’re moving across the country. You pack your boxes and put your new address on them. The moving company picks them up, makes a list of the boxes, and ships them across the country using the most efficient route. That might even mean putting different boxes on different trucks. When the boxes arrive at your new home, you check the list to make sure everything has arrived (and in good shape), and then you unpack the boxes and “reassemble” your house.

A suite of protocols - Rules that dictate how packets of information are sent across - multiple networks - Addressing 58 - Error checking

IP -Every computer on the Internet has at least one address that uniquely identifies it from all other computers on the Internet (aptly called its IP address!).

-IP looks at the destination address to decide what to do next. If the destination is on the local network, IP delivers the packet directly

-When you send or

receive data—say an email message or web page—the message gets divided into little chunks called packets or data grams. -Each of these packets contains both the source IP address and the destination IP address.

-If the destination

is not on the local network, then IP passes the packet to a gateway— usually a router

-Computers usually have a single default gateway. Routers frequently have several gateways from which to choose. A packet may get passed through several gateways before reaching one that is on a local network with the destination.

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TCP/IP Transport Layer TCP/IP Applications - Application layer - File Transfer Protocol (FTP) - Remote Login (Telnet) - E-mail (SMTP) - Transport layer - Transport Control Protocol (TCP) - User Datagram Protocol (UDP)

-After TCP/IP was invented and deployed, the OSI layered network model was accepted as a standard. OSI neatly divides network protocols into seven layers; the bottom four layers are shown in this diagram. The idea was that TCP/IP was an interesting experiment, but that it would be replaced by protocols based on the OSI model

- Network layer - Internet Protocol (IP) - Data link & physical layer - LAN Ethernet, Token Ring, FDDI, etc. - WAN Serial lines, Frame Relay, X.25, etc

TCP is the most important of all the IP protocols. Most Internet applications you can think of use TCP, including: Telnet, HTTP (Web), POP & SMTP (email) and FTP (file transfer). 60

TCP Transmission Control Protocol TCP stands for Transmission Control Protocol. Here’s how it works: Every TCP connection is uniquely identified by four numbers: -TCP establishes a reliable connection between two applications over the network. This means that TCP guarantees accurate, sequential delivery of your data. If something goes wrong, TCP reports an error, so you always know whether your data arrived at the other end.

source IP address source port destination IP address destination port

-TCP packets also include a checksum to verify the integrity of the data. Packets that fail checksum get retransmitted

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UDP User Datagram Protocol Unreliable - Fast - Assumes application will retransmit on error - Often used in diskless workstations

-UDP is a fast, unreliable protocol that is suitable for some applications. Unreliable means there is no sequencing, no guaranteed delivery (no automatic retransmission of lost packets) and sometimes no checksums. Fast means there is no connection setup time, unlike TCP

ICMP Ping

-Ping is an example of a program that uses ICMP rather than TCP or UDP. Ping sends an ICMP echo request from one system to another, then waits for an ICMP echo reply. It is mostly used for testing.

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IPv4 Addressing -IPv4 addresses are 32 bits long and are usually written in “dot” notation. An example would be 192.1.1.17.

-The Internet is

actually a lot of small local networks connected together. Part of an IP address identifies which local network, and part of an IP address identifies a specific system or host on that local network.

-What part of an IP address is for the “network” and what part is for the “host” is determined by the class or the subnet

11000000

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IP Addressing—Three Classes -Class A: NET.HOST.HOST.HOST - Class B: NET.NET.HOST.HOST - Class C: NET.NET.NET.HOST

To summarize: -IPv4 addresses are 32 bits with a network part and a host part. -The network part of an address is used for routing packets over the Internet. The host part is used for final delivery on the local net.

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IP Addressing—Class A Here’s an example of a class A address. Any IPv4 address in which the first octet is less than 128 is by definition a class A address. This address is for host #222.135.17 on network #10, although the host is always referred to by its full address.

IP Addressing— Class B Here’s an example of a class B address. Any IPv4 address in which the first octet is between 128 and 191 is by definition a class B address

Example:10.222.135.17 - Network # 10 - Host # 222.135.17 - Range of class A network IDs: 1–126 - Number of available hosts: 16,777,214

- Network # 128.128 - Host # 141.245 - Range of class B network IDs: 128.1–191.254 - Number of available hosts: 65,534

Example: 128.128.141.245

IP Addressing—Class C Here’s an example of a class C address. Most IPv4 addresses in which the first octet is 192 or higher are class C addresses, but some of the higher ranges are reserved for multicast applications. Example: - 192.150.12.1 -Network # 192.150.12 -Host # 1 -Range of class C network IDs: 192.0.1–223.255.254 -Number of available hosts: 254

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example

140.179.220.200 Written in binary form: 140 .179 .220

.200

10001100.10110011.11011100.11001000  

We see the address in the decimal form Your computer sees it in the binary form

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Binary Octet: 

An octet is made up of eight “1”s and/or “0”s, representing the following values:

128

64

32

16

8

4

2

1

So the value of 140 (the first octet of our example) looks like this: 1

0

0

0

1

1

0

0

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Cont’d 1 0 0 0 128 + 0 + 0 + 0 +

1 1 0 0 8 + 4 + 0 + 0 = 140

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Lesson 4: LAN Basics covers the fundamentals of LAN technologies. We’ll look at Ethernet, Token Ring, and FDDI. For each one, we’ll look at the technology as well as its operations.

The most popular local area networking protocol today is Ethernet. Most network administrators building a network from scratch use Ethernet as a fundamental technology.

Token Ring technology is widely used in IBM networks.

FDDI networks are popular for campus LANs – and are usually built to support high bandwidth needs for backbone connectivity. 69

Ethernet Ethernet and IEEE 802.3 Ethernet was initially developed by Xerox. They were later joined by Digital Equipment Corporation (DEC) and Intel to define the Ethernet 1 specification in 1980. •There have been further revisions including the Ethernet standard (IEEE Standard 802.3) which defines rules for configuring Ethernet as well as specifying how elements in an Ethernet network interact with one another.

Ethernet is the most popular physical layer LAN technology because it strikes a good balance between speed, cost, and ease of installation. •These strong points, combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today

The Fast Ethernet standard (IEEE 802.3u) has been established for networks that need higher transmission speeds. It raises the Ethernet speed limit from 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure

Gigabit Ethernet is an extension of the IEEE 802.3 Ethernet standard. •It increases speed tenfold over Fast Ethernet, to 1000 Mbps, or 1 Gbps. 70

Benefits and background - Ethernet is the most popular physical layer LAN technology because it strikes a good balance between speed, cost, and ease of installation - Supports virtually all network protocols - Xerox initiated, then joined by DEC & Intel in 1980

Revisions of Ethernet specification - Fast Ethernet (IEEE 802.3u) raises speed from 10 Mbps to 100 Mbps - Gigabit Ethernet is an extension of IEEE 802.3 which increases speeds to 1000 Mbps, or 1 Gbps Ethernet Protocol Names

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Ethernet and Fast Ethernet Ethernet Operation

-This chart gives you an idea of the range of Ethernet protocols including their data rate, maximum segment length, and medium

-Ethernet has survived as an essential

media technology because of its tremendous flexibility and its relative simplicity to implement and understand

-Let’s say in our example here that station A is going to send information to station D. Station A will listen through its NIC card to the network. If no other users are using the network, station A will go ahead and send its message out on to the network. Stations B and C and D will all receive the communication.

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-At the data link layer it will inspect the MAC address. Upon inspection station D will see that the MAC address matches its own and then will process the information up through the rest of the layers of the seven layer model.

As for stations B & C, they too will pull this packet up to their data link layers and inspect the MAC addresses. Upon inspection they will see that there is no match between the data link layer MAC address for which it is intended and their own MAC address and will proceed to dump the packet.

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Ethernet Reliability

Ethernet is known as being a very reliable local area networking protocol. In this example, A is transmitting information and B also has information to transmit. Let’s say that A & B listen to the network, hear no traffic and broadcast at the same time. A collision occurs when these two packets crash into one another on the network. Both transmissions are corrupted and unusable.

-When a collision occurs on the network, the NIC card sensing the collision, in this case, station C sends out a jam signal that jams the entire network for a designated amount of time

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-Once the jam signal has been received and recognized by all of the stations on the network, stations A and D will both back off or pull back for different amounts of time before they try to retransmit. This type of technology is known as Carrier Sense Multiple Access With Collision Detection – CSMA/CD.

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High-Speed Ethernet Options

Fast Ethernet - Fast EtherChannel® - Gigabit Ethernet - Gigabit EtherChannel

-We’ve mentioned that Ethernet also has high speed options that are currently available. Fast Ethernet is used widely at this point and provides customers with 100 Mbps performance, a ten-fold increase. Fast EtherChannel is a Cisco value-added feature that provides bandwidth up to 800 Mbps. There is now a standard for Gigabit Ethernet as well and Cisco provides Gigabit Ethernet solutions with 1000 Mbps performance.

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What Is Fast Ether Channel? -Grouping of multiple Fast Ethernet interfaces into one logical transmission path

What Is Gigabit Ethernet? -In some cases, Fast Ether Channel technology may not be enough

-Scalable bandwidth up to 800+ Mbps - Using industrystandard Fast Ethernet - Load balancing across parallel links - Extendable to Gigabit Ethernet

-The rule of thumb today is to plan for 80 percent of the traffic going over the backbone -Gigabit networking is important to accommodate these evolving needs. Gigabit Ethernet builds on the Ethernet protocol but increases speed tenfold over Fast Ethernet, to 1000 Mbps, or 1 Gbps

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Summary Topologies - Summary - LAN technologies include Ethernet, Token Ring, and FDDI - Ethernet - Most widely used - Good balance between speed, cost, and ease of installation - 10 Mbps to 1000 Mbps - Token Ring - Primarily used with IBM networks - 4 Mbps to 16 Mbps - FDDI - Primarily used for corporate backbones - Supports longer distances - 100 Mbps

Assignment Go and read about Token Ring Architecture/technol ogies and FDDI Ref:1.Wesley 2.William stallings(Business data communication. Prepare for presentation

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Lesson 5: Understanding LAN Switching   

Shared LAN Technology LAN Switching Basics - Key Switching Technologies

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Shared LAN Technology

-As you can see indicated in the diagram on the left, Ethernet is fundamentally what we call a shared technology -All users of a given LAN segment are fighting for the same amount of bandwidth

-Frames, or packets, do in our network as we're trying to make transmissions on our Ethernet (frames fighting for the same bandwidth 80

Other Bandwidth Consumers

we basically have one transmitter that's trying to reach one receiver, which is by far the most common, or hopefully the most common form of communication in our network.

Another way to communicate is with a mechanism known as a broadcast. And that is when one transmitter is trying to reach all receivers in the network.So, as you can see in the diagram, in the middle, our server station is sending out one message, and it's being received by everyone on that particular segment.

And a multicast is when one transmitter is trying to reach, not everyone, but a subset or a group of the entire segment 81

Hub-Based LANs

Bridges Another way is to add bridges. In order to scale our networks we need to do something known as segmentation -And bridges provide a

Hubs are introduced into the network as a better way to scale our thin and thick Ethernet networks -Basically what we have is an individual desktop connection for each individual workstation or server in the network, and this allows us to centralize all of our cabling back to a wiring closet

certain level of segmentation in our network. And bridges do this by adding a certain amount of intelligence into the network Bridges operate at Layer 2, while hubs operate at Layer 1. So operating at Layer 2 gives us more intelligence in order to make an intelligent forwarding decision.

-bridges are more intelligent than a hub, because they can actually listen in, or eavesdrop on the traffic going through the bridge, they can look at source and destination addresses, and they can build a table that allows them to make intelligent forwarding decisions.

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Switches—Layer 2

switches to provide the most control in our network, at least at Layer 2 -So that when we look at our network we see that physically each station has its own cable into the network, well, conceptually we can think of this as each workstation having their own lane through the highway

-There’s -microsegmentation. That's a fancy way simply to say that each workstation gets its own dedicated segment through the network.

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Switches versus Hubs -If we compare that with a hub or with a bridge, we're limited on the number of simultaneous conversations we can have at a time -Remember, if two stations tried to communicate in a hubbed environment, that collisions -In a switched environment, not going to expect collisions because each workstation has its own dedicated path through the network.

-In terms of bandwidth, and scalability, is we have dramatically more bandwidth in the network. -Each station now will have a dedicated 10 megabits per second worth of bandwidth.

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The Need for Speed: Early Warning Signs -include increased delay on our file transfers

Typical Causes of Network Congestion

-print jobs that take a very long time to print out. (From the time we queue them from our workstation, till the time they actually get printed, if that's increasing, that's an indication that we may have some LAN congestion problems. )

-if we have too many users on a shared LAN segment. (Remember that shared LAN segments have a fixed amount of bandwidth )

-As we add users, proportionally, we're degrading the amount of bandwidth per user

-So we gonna get to a certain number of users and gonna be to be too much congestion, too many collisions, too many simultaneous conversations trying to occur all at the same time

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Network Traffic Impact from Centralization of Servers -Also, the way the traffic is distributed on our network can have an impact as well. A very common thing to do in many networks is to build what's known as a server farm -In a server farm effectively what we're doing is centralizing all of the resources on our network that need to be accessed by all of the workstations in our network.

-Servers are gradually moving into a central area (data center) versus being located throughout the company to: - Ensure company data integrity - Maintain the network and ensure operability - Maintain security - Perform configuration and administrative functions

-So what happens,

we cause congestion on those centralized segments within the network 86

Today’s LANs

Mostly switched resources; few shared - Routers provide scalability - Groups of users determined by physical location

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Chapter 6: WAN Basics In this chap, We gonna at ,what a WAN is, to talking about basic technology such as WAN devices , circuit and packet switching also cover transmission options from POTS (plain old telephone service) to Frame Relay, to leased lines etc

So, what is a WAN? A WAN is a data communications network that serves users across a broad geographic area and often uses transmission facilities provided by common carriers such as telephone companies -These providers are companies like MTN,Rwandatel, ISPA,Artel,KIST etc

- Telephone service is commonly referred to as plain old telephone service (POTS). - WAN technologies function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

Common WAN network components include WAN switches, access servers, modems, CSU/DSUs, and ISDN Terminals 88

WAN Devices

-A WAN switch is a multiport internetworking device used in carrier networks -operate at the data link layer of the OSI reference model. -These WAN switches can share bandwidth among allocated service priorities, recover from outages, and provide network design and management systems.

A modem is a device that interprets digital and analog signals, enabling data to be transmitted over voice-grade telephone lines. At the source, digital signals are converted to analog. At the destination, these analog signals are returned to their digit

-The CSU/DSU also provides signal timing for communication between these devices.

An access server is a concentration point for dial-in and dial-out connections. A channel service unit/digital service unit (CSU/DSU) is a digital interface device that adapts the physical interface on a data terminal equipment device (such as a terminal) to the interface of a data circuit terminating (DCE) device (such as a switch) in a switched-carrier network

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An ISDN terminal is a device used to connect ISDN Basic Rate Interface (BRI) connections to other interfaces, such as EIA/TIA232. - A terminal adapter is essentially an ISDN modem

WAN Terminating Equipment

The WAN physical layer describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE).

DTE is the attached device (the customer’s device). In this model, the services offered to the DTE are made available through a modem or channel service unit/data service unit (CSU/DSU).

-Typically, the DCE is

the service provider,

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CSU/DSU (Channel Service Unit / Data Service Unit) Device that connects the end-user equipment to the local digital telephone loop or to the service providers data transmission loop. -The DSU adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. -Also responsible for such functions as signal timing for synchronous serial Transmission

Circuit Switching

Circuit switching is a WAN switching method in which a dedicated physical circuit or path is established, maintained, and terminated through a carrier network for each communication session -circuit switching

operates much like a normal telephone call. Integrated Services Digital Network (ISDN) is an example of a circuit-switched WAN technology. 91

Packet Switching

Packet switching is a WAN switching method in which network devices share a single point-topoint link to transport packets from a source to a destination across a carrier network

Network devices share a point-to-point link to transport packets from a source to a destination across a carrier network Statistical multiplexing is used to enable devices to share these circuits or routes. Asynchronous Transfer Mode (ATM), Frame Relay, Switched Multi-megabit Data Service (SMDS), and X.25 are examples of packet-switched WAN technologies.

- Statistical multiplexing is used to enable devices to share these circuits

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WAN Virtual Circuits A virtual circuit is a logical circuit created to ensure reliable communication between two network devices. -Two types of virtual circuits exist: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs

- A logical circuit ensuring reliable communication between two devices - Switched virtual circuits (SVCs) - Dynamically established on demand - Torn down when transmission is complete - Used when data transmission is sporadic - Permanent virtual circuits (PVCs)

SVCs are dynamically established on demand and are torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic or periodic,or random. PVCs are permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time.

- Permanently established - Save bandwidth for cases where certain virtual circuits must exist all the time

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WAN Protocols -The OSI model provides a conceptual framework for communication between computers, but the model itself is not a method of communication.

Variety of Comm. Protocols LAN protocols: operate at the physical and data link layers and define communication over the various LAN media

-Actual communication is made possible by using communication protocols.

- WAN protocols: operate at the lowest three layers and define communication over the various wide-area media.

-A protocol implements the functions of one or more of the OSI layers.

- Network protocols: are the various upper-layer protocols in a given protocol suite. - Routing protocols: networklayer protocols responsible for path determination and traffic switching

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Cont’d

SDLC:Synchronous Data Link Control. SDLC is a bit-oriented, full-duplex serial protocol that has spawned or generated numerous similar protocols, including HDLC and LAPB. HDLC:High-Level Data Link Control. Bitoriented synchronous data link layer protocol developed by ISO. -Specifies a data encapsulation method on synchronous serial links using frame characters and checksums. LAPB:Link Access Procedure, Balanced. Data link layer protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from HDLC

PPP:Point-to-Point Protocol. Provides router-to-router and host-to-network X.25 PTP:Packet level protocol. Network layer protocol in the X.25 protocol stack. Defines how connections are maintained for remote terminal access ISDN:Integrated Services Digital Network. Communication protocol, offered by telephone companies, that permits telephone networks to carry data, voice Frame Relay:Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices.

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Transmission Options or WAN Services -A number of transmission options available today

POTS (Plain Old Telephone Service) Using Modem Dialup

Analog modems using basic telephone service are asynchronous transmissionbased, and have the following benefits: - Available everywhere - Easy to set up - Dial anywhere on demand - The lowest cost alternative of any widearea service 96

Integrated Services Digital Network (ISDN) -ISDN provides a highbandwidth, cost-effective solution for companies requiring light or sporadic or periodic high-speed access to either a central or branch office.

-ISDN ,is a digital service, that can transmit data, voice, and video over existing copper phone lines. -Instead of leasing a dedicated line for high-speed digital transmission, ISDN offers the option of dialup connectivity— incurring charges only when the line is active

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Types of ISDN Basic Rate Interface (BRI) and Primary Rate Interface (PRI).

NB: PRI can be used at your central site if you plan to have many ISDN dial-in clients.

BRI provides two “B” or bearer channels of 64 Kbps each and one additional signaling channel called the “D” or delta channel

PRI provides up to 23 bearer channels of 64 Kbps each and one D channel for signaling.

That’s 23 channels but with only one physical connection, which makes it an elegant or neat solution- there’s no wiring mess

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Leased Line -Leased lines are most cost-effective if a customer’s daily usage exceeds four to six hours. -Leased lines offer predictable throughput with bandwidth typically 56 Kbps to 1.544 Mbps. -They require one connection per physical interface (namely, a synchronous serial port). - One connection per physical interface - Bandwidth: 56 kbps–1.544 Mbps - T1/E1 and fractional T1/E1 - Cost effective at 4–6 hours daily usage - Dedicated connections with predictable throughput - Permanent - Cost varies by distance

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Frame Relay -Frame Relay frames travel over predetermined virtual circuit paths, are selfrouting and arrive at their destination in the correct order -Frame Relay is designed to handle the LAN-type bursty traffic efficiently. Frame Relay provides a standard interface to the wide-area network for bridges, routers ,LAN Devices etc

-The guaranteed bandwidth (known as committed information rate or CIR) is typically between 56 Kbps and 1.544 Mbps.

-A Frame Relay interface is designed to act like a widearea LAN- it relays or transmits data frames directly -cost is normally not distance-sensitive to their destinations at very high speeds.

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Connecting Offices with Frame Relay -Companies, that require office-to-office communications, usually choose between a dedicated leased-line connection or a packet-based service, such as Frame Relay or X.25. -As a rule, higher connect times make leased-line solutions more cost-effective. Like ISDN, Frame Relay requires only one physical connection to the Frame Relay network, but can support many Permanent Virtual Circuits, or PVCs.

Frame Relay service is often less expensive than leased lines, and the cost is based on: - The committed information rate (CIR), which can be exceeded up to the port speed when the capacity is available on your carrier’s network. -The number of permanent virtual circuits (PVCs) you require; a benefit to users who need reliable and dedicated connections to resources simultaneously. 101

X.25

-X.25 networks implement the internationally accepted ITU-T standard governing the operation of packet switching networks. -Transmission links are used only when needed -It performs error checking along each hop from source node to destination node. The bandwidth is typically between 9.6Kbps and 64Kbps.

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Digital Subscriber Line (xDSL) -Digital subscriber line (DSL) technology is a high-speed service that, like ISDN, operates over ordinary twisted-pair copper wires supplying phone service to businesses and homes in most areas

-Using special modems and dedicated - DSL is a pair of “modems” on each end of a copper wire pair - DSL converts ordinary phone lines into high-speed data conduits

equipment in the phone company's switching office, DSL offers faster data transmission than either analog modems or ISDN service, plus-in most cases-simultaneous voice communications over the same lines

-End-users don’t “buy” DSL, they “buy” services, such as high-speed Internet access, intranet, leased line, voice, VPN, and video on demand -Service is limited to certain geographical areas

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DSL Modem Technology -DSL has several flavors. ADSL delivers asymmetrical data rates (for example, data moves faster on the way to your PC than it does on the way out to Internet).

The type of service available to you will depend on the carriers operating in your area. Because DSL works over the existing telephone infrastructure, it should be easy to deploy over a wide area in a relatively short time

-Other DSL technologies deliver symmetrical data (same speed traveling in and out of your PC).

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How to choose Service? -Analog services are the least expensive type of service. ISDN costs somewhat more but improves performance over even the fastest current analog offerings -Leased lines are the costliest of these three options, but offer dedicated, digital service for more demanding situations. Which is right?

You’ll need to answer a few questions: - Will employees use the Internet frequently? - Will the Internet be used for conducting business (for example, inventory management, online catalog selling or account information or bidding on new jobs)? - Do you anticipate a large volume of traffic between branch offices of the business? - Is there a plan to use videoconferencing or video training between locations? - Who will use the main office’s connection to the Internet - individual employees at the central office, telecommuting workers dialing in from home, mobile workers dialing in from the road? 105

Cont’d The more times the answer is “yes”, the more likely that leased line services are required. It is also possible to mix and match services -For example, small branch offices or individual employees dialing in from home might connect to the central office using ISDN, while the main connection from the central office to the Internet can be a T1.

-It is important to understand that as the bandwidth increases, so do the charges, both from the ISP and the phone company. Keep in mind that rates for different kinds of connections vary from location to location.

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Compare the technology options, assuming all services are available - A leased-line service provides a dedicated connection with a fixed bandwidth at a flat rate. You pay the same monthly fee regardless how much or how little you use the connection. - A packet-switched service typically provides a permanent connection with specific, guaranteed bandwidth (Frame Relay). Temporary connections (such as X.25) may also be available. The cost of the line is typically a flat rate, plus an additional charge based on actual usage. - A circuit-switched service provides a temporary connection with variable bandwidth, with cost primarily based on actual usage.

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Wide-Area Network Requirements Minimize bandwidth costs - Maximize efficiency - Maximize performance - Support new/emerging applications - Maximize availability - Minimize management and maintenance Manage Bandwidth to Control Cost

Bandwidth-on-demand gives you the flexibility to add additional WAN bandwidth when it’s needed to accommodate heavy network loads such as file transfers

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Dial-on-Demand Routing -Interesting traffic might be defined as any traffic destined for the remote network, or only traffic related to a specific host address or service. -Dial-on-demand routing allows a router to automatically initiate and close a circuit-switched session -With dial-on-demand routing, the router dials up the WAN link only when it senses “interesting” traffic

-Equally important, dial-ondemand routing enables the router to take down the connection when it is no longer needed, ensuring that the user will not have unnecessary WAN usage charges

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Bandwidth-on-Demand Snapshot Routing

Snapshot routing -Bandwidth-on-demand works in a similar way. -When the router senses that the traffic level on the primary link has reached a certain—say, threshold or entrance when a user starts a large file transfer—it automatically dials up additional bandwidth through the PSTN to accommodate the increased load.

-this feature ensures that the remote router always has the most up-to-date routing information but only when needed. -Without Snapshot Routing, your ISDN connection would be dialed every 30 seconds

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IPX Protocol Spoofing -Protocol spoofing allows the user to improve performance while providing the ability to use lower line speeds over the WAN.

Compression -Compression reduces the space required to store data, thus reducing the bandwidth required to transmit

-The benefit of these compression algorithms is that users can utilize lower line speeds if needed to save costs -Compression also provides the ability to move more data over a link than it would normally bear

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- Dial Backup -When the software detects the loss of a signal from the primary line device or finds that the line protocol is down, it activates the secondary line to establish a new session and continue the job of transmitting traffic over the backup line. -Dial backup addresses a customer’s need for reliability and guaranteed uptime -Dial backup capability offers users protection against WAN downtime by allowing them to configure a backup serial line via a circuitswitched connection such as ISDN

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Chapter 7: Understanding Routing What Is Routing? -Routing is the process of finding a path to a destination host and of moving information across an internet work from a source to a destination -A router is a device that forwards packets from one network to another and determines the optimal path along which network traffic should be forwarded

-Routers forward packets from one network to another based on network layer information

Routers—Layer 3 It determines the appropriate network path to send the packet

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LAN-to-LAN Connectivity

This illustrates the flow of packets through a routed network using the example of an e-mail message being sent from system X to system Y

-The message exits system X and travel through an organization’s internal network until it gets to a point where it needs an Internet service provider 114

Read about the following   

Path determination Multi-protocol routing Routing table

Routing Tables -To aid the process of path determination, routing algorithms initialize and maintain routing tables, which contain route information -Routing Information-Include

-Destination/next hop associations tell a router that a particular destination is linked to a particular router representing the “next hop” on the way to the final destination

-Routers compare metrics to determine optimal routes. Metrics differ depending on the routing algorithm used. A metric is a standard of measurement, such as path length, that is used by routing algorithms to determine the optimal path to a destination.

-path desirability 115

Routing Algorithm Goals -Routing tables contain information used by software to select the best route. But how, specifically, are routing tables built? What is the specific nature of the information they contain? How do routing algorithms determine that one route is preferable to others?

Routing algorithms are based on the following design goals: -Optimality - the

capability of the routing algorithm to select the best route, depending on metrics e.g. hops and

-Simplicity and low overhead - efficient routing algorithm functionality with a minimum of software and utilization overhead

Robustness and stability –checks the unforeseen circumstances, such as hardware failures, high load conditions

Rapid convergence - Convergence is the

process of agreement, by all routers, on optimal routes. When a network event causes changes in router availability, recalculations are need to reestablish networks

delays

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Routing Metrics Routing algorithms have used many different metrics to determine the best route

Path length - The most common metric. The sum of either an assigned cost per network link or hop count, a metric specify the number of passes through network devices between source and destination. Reliability - dependability (bit-error rate) of each network link. Some network links might go down more often than others. Also, some links may be easier or faster to repair after a failure. Delay - The length of time required to move a packet from source to destination through the internet work. Depends on bandwidth of intermediate links, port queues at each router, network congestion, and physical distance. A common and useful metric. Bandwidth - available traffic capacity of a link. Load - Degree to which a network resource, such as a router, is busy (uses CPU utilization or packets processed per second). Communication cost - operating expenses of network links (private versus public lines). Now let’s talk a little about network addressing. 117

Network Addressing -Sub netting allows single routing entries to refer either to the larger block or to its individual constituents

Sub network Addressing -Sub networks or subnets are networks arbitrarily segmented by a network administrator in order to provide a multilevel, hierarchical routing structure while shielding the sub network from the addressing complexity of attached networks

-A subnet mask is a 32bit number that determines how an IP address is split into network and host portions, on a bitwise basis -For example, 131.108.0.0 is a standard Class B subnet mask; the first two bytes identify the network and the last two bytes identify the host.

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Cont’d -A subnet mask is a 32-bit address mask used in IP to indicate the bits of an IP address that are being used for the subnet address. Sometimes referred to simply as mask. The term mask derives from the fact that the non-host portions of the IP address bits are masked by 0’s to form the subnet mask.

Read about “Routing Algorithms Types” Static and Dynamic Routing Routing protocol evolutions Required to make individual presentations Deadline next class !!!

-Sub netting helps to organize the network, allows rules to be developed and applied to the network, and provides security and shielding

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Chap 8:Layer 3 Switching Assignment: Required to read the above chapter and answer the following questions Qn1. What Is Layer 3 Switching? Qn2. What is the Difference Between Layer 2 Switching, and Routing? Qn3.Discuss the advantages of layer 3 switches Qn4. Why Do We Need Layer 3 Switching?

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Chapter 9: Understanding Virtual LA

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Guidelines for exam preparation   

Chap1=Networking Basics Chap2=OSI Reference Model Chap4 and 6

Exam Structure !!!! Sections( A= 10marks and B=70 marks)=Exam Total 80%)( Section A-Multiple choices and B-Structured questions Assignments=20% 122

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