BITS 2513 – INTERNET TECHNOLOGY

LECTURE 3: INTERNET INFRASTRUCTURE

TOPICS

1. To connect to Internet:• Using a Telephone Line to

Connect to Internet• Using a Cable Modem, ISDN,

DSL or Satellite to Connect to the Internet

• Connecting a PC on a LAN to the Internet

2. Physically and Logically Dividing a Large Network

3. Routing on the Internet

Using a Telephone Line to Connect to Internet

Using a Telephone Line to Connect to the Internet• To establish a successful connection,

you need:– Modem to transmit data over the

telephone line and software that allows the operating system to interact with the modem

– Operating system utility that allows you to configure the modem to connect to a specific ISP

– TCP/IP protocol stack– ISP user information: Telephone

number, user ID, password, and other information needed to connect to an ISP

Using a Cable Modem, ISDN, DSL or Satellite to Connect to the

Internet

Modems: An Introduction

• The word modem comes from modulator/demodulator, which means to convert from analog to digital and digital to analog.

• A telephone line connects to a modem or telephone using either an RJ-11 or an older RJ-12 connector.

• A modem is responsible for managing communication between devices and can also be referred to as a Data Communications Equipment (DCE) device.

Modems: An Introduction (Continued)

• The computer or terminal that is using the DCE to communicate with another device is called the Data Terminal Equipment (DTE).

Installing a Modem and Its Drivers

• To connect to the Internet using a telephone line, you first must install and configure a modem, and then install the software that drives the modem.

• Modem divided into 2:- External Modem- Internal modem

Installing a Modem and Its Drivers – External Modem (Continued)• If the modem is an external

(modem) device, insert the modem to a serial port on the back of the computer using a serial cable.

• The port either can have 9 pins or 25 pins and is designed according to the serial port standard called the RS-232 standard or, more recently, the EIA/TIA-232 standard.

• Nowadays, modem are equipped with USB/ Ethernet ports for better and easier configurations.

Installing a Modem and Its Drivers Internal Modem (Continued)• If the modem is an internal

modem, the modem card is inserted in an expansion slot, typically a PCI slot, inside the computer and communicates with the CPU through lines connecting the slot to the CPU that are embedded on the motherboard.

• Nowadays, Internal modem are printed on the circuit board of the computer.

Creating a Dial-Up Connection• Dial-Up Networking

(DUN) is a process that enables a computer to use a modem and a telephone line to connect to a network, just as if that computer had a network card and network cables.

• The modem behaves just like a network card, providing the physical connection to the network and the firmware.

Configuring TCP/IP

• In Windows 7, Windows

Vista, Windows 2000 and

Windows XP, TCP/IP is

automatically installed when

a network card or modem is

added to a computer.

• In Windows 98, you must

install TCP/IP and bind it to the

modem.

The Role of TCP/IP in a Dial-Up Connection• The following list summarizes some of the

most important information about TCP/IP:– To ensure computers to be assign a

unique IP address. (IP address might be static or dynamic)

– To ensure computers to be assign a subnet mask. (This is to tell the TCP/IP whether the remote computer is on the same or different network)

– To provide a gateway for communications between computers and the Internet.

– To ensure computers can communicate with a domain name server . DNS is a computer to translate the domain name into IP address.

PPP and Multilink PPP• When a computer communicates with

another computer using only a single connection, the connection is said to be point-to-point.

• The dial-up connection is a point-to-point connection.

• Windows 98/2000/XP/Vista/ 7 also support Multilink PPP, which allows you to use two or more physical connections for a single, virtual, dial-up link called a multipoint connection.

• The protocol that makes a multipoint connection possible is PPP Multilink (MP), sometimes known as Point-to-Point Multilink, Multilink PPP, Multilink, or just MP.

Connection to the Internet via Cable, ISDN, DSL, or Satellite

• Connecting a single computer to an ISP via cable, ISDN, DSL, or satellite requires the same TCP/IP settings as a dial-up connection on a regular phone line.

• Cable modems, DSL, and LANs all use a network card in the computer for the physical connection.

• The network card provides a network port for a network cable.

• For cable modem service to the Internet, the other end of the network cable connects to a cable modem.

Connection Using - Cable Modems• The cable modem connects

to a regular TV coaxial cord, which then connects to a TV cable wall outlet.

• The cable modem also has an electrical connection to provide power to the box, as well as a connection to a network card in your computer.

Connection Using - Integrated Services Digital Network (ISDN) and DSL• ISDN requires a device, called

an NT1 (Network Terminator 1), that connects the ISDN and DSL systems; this device is located inside or outside your house where the telephone company’s responsibility ends.

• You also need another device called a TA (terminal adapter).

• A DSL connection uses a DSL converter box that is sometimes combined with a router as a single device so more than one computer can use the DSL line.

• Ex: Streamyx

Connecting to the Internet by Satellite

• The first thing the technician does is to find the best place for the satellite dish.

• After the satellite disk is mounted to the house, cables are wired through the house to the room containing the computer.

• Then, modems are connected to the computer, usually through a USB port.

Connecting a PC ona LAN to the Internet

Connecting a LAN to the Internet

Connecting the Gateway to the Internet

Connecting the Gateway to the Internet (Continued)

• The connection to the LAN always uses a network card, but the connection to the ISP could be a (i) network card, (ii) modem, or (iii) ISDN card.

• If the connection to the ISP is by way of a network card, the computer has two network cards installed.

• One card is bound to the protocol used by the LAN and the other card is bound to the protocol used by the ISP’s network, which is always TCP/IP.

Physically and Logically Dividing a Large Network

Physically and Logically Dividing a Large Network

• You can divide a network using two approaches: 1. You can physically divide the

network using hardware devices

2. You can logically divide the network using software settings

• The first approach is called segmenting the network; the second approach is called subnetting.

Bridges and Switches• Bridges and Switches are more

intelligent than hubs and make decisions involving whether to allow traffic to pass or where to route that traffic, reducing traffic on each segment and improving network performance.

• A routing table is a database stored within a router that is used to find the best network path on which to forward information.

• A network bridge keeps routing tables for each network to which it connects.

Bridges and Switches (Continued)• The tables start out empty and all

data packets that reach the bridge from one segment are passed on to the other segment connected to the bridge.

• Just like bridges, switches keep tables of the MAC addresses of all the devices connected to the switch.

• Switches use these tables to determine which path to use when sending packets.

• However, unlike a bridge, a switch passes a packet only to its destination segment instead of to all segments other than the one it came from.

Bridges and Switches (Continued)• Bridges and switches use MAC

addresses to subdivide a network into physical segments.

• However, all the segments are still logically a single network because each host is communicating with other hosts on other segments using the MAC address rather than the IP address.

• As far as a host is concerned, it is not aware that a bridge or a switch exists in the network.

Subnetting

• A large network can be logically

divided into two or more

networks based on IP addresses

rather than MAC addresses to

reduce congestion.

• Each division (of a network)

is called a subnet and the

process is called subnetting.

Subnet Masks• How does the host know if a

remote host is on the same network?

• An IP address is made up of the network ID and the host ID.

• The host is told what portion of the IP address identifies the network by an entry in the TCP/IP configuration settings.

• This entry is called the network mask, or subnet mask, and is used to define which portion of an IP address identifies the network and which portion identifies the host.

Subnet Masks (Continued)

• The network mask is a group of four 8-bit numbers separated by periods.

Subnet Masks (Continued)• If the network IDs had been different, the host

would not have attempted to resolve the IP address to the MAC address, but would have sent the data to the gateway to its network.

• A gateway is any device, typically a router, that provides access to another network.

• Subnet masks usually are not displayed as 32 bits separated by periods as they are in Table 6-1.

Selecting a Subnet Mask• A network engineer carefully selects a subnet mask based

on the number of subnets he needs and the number of hosts planned for each subnet.

• Table 6-3 shows several examples of subnet masks and explains the number of hosts and subnets that can use each subnet mask.

• Subnetting is necessary when a large company is using a Class A, B, or C license for its entire network and wants to use that one license over several networks to prevent network congestion.

Routing on the Internet

How Data Travels Across Interconnected Networks

• Figure 6-12 shows a simplified view of how networks work together to send data over the maze of many networks called the Internet.

• A router is a stateless device, meaning that it is unconcerned about the data that it is routing, but it is concerned about the destination address of that data.

• Networks are connected by routers, which belong to more than one network.

How Data Travels Across Interconnected Networks (Continued)

Routers

• Routers are responsible for helping data travel across interconnected networks.

• A router can forward data to the correct network in a way that is similar to a switch’s method.

• A router uses the most efficient path available to forward packets to their destination, which may be located across a great geographical distance.

Routers (Continued)

• A brouter, short for bridge and router, functions as both a bridge and a router.

• The device can forward routable protocols, including TCP/IP and IPX/SPX packets, and in these cases, is working as a router.

Routers (Continued)• Like switches, routers use

tables to determine the best route by which to send the data to its destination.

• When routers communicate with other routers to build routing tables and determine availability of routes, one of several protocols is used: RIP, OSPF, BGP, DVMRP, NLSP, or IGRP.

TCP/IP Routing

• Suppose a host computer wants to send data to another host.

• Remember that the host uses its subnet mask to decide if the destination host is on its own or another network.

• If the first host knows that the remote host is on its same network, it must discover the MAC address of the remote host.

TCP/IP Routing (Continued)

• If the sending host determines that the remote host is on a different network, it sends the data to the router, which is serving as the gateway to remote networks.

• When a packet arrives at a router, the router decides if the packet belongs to a host within its own local network or needs to be routed to a different network.

Routing Across Many Networks• For routing across

interconnected networks, each time a packet encounters a router, its TTL is reduced by one.

• If the router must send the packet over a network that cannot handle large packets, the router divides the packet into smaller packets.

Default Gateways

• Sometimes, a large network has

more than one router, as shown in

Figure 6-21and so the network has

more than one gateway to other

networks.

• The network in the upper-left of

the figure is 250.1.2 and has two

routers (D and E), each of which

also belongs to other networks.

Default Gateways (Continued)

Default Gateways (Continued)• Host E is designated as the

default gateway, meaning that hosts on the 250.1.2 network send packets addressed to other networks to this gateway first.

• The other router Host D, is called the alternate gateway and is used if communication to the default gateway fails.