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Computer NetworkingInternetworking devices2NICHubsBridgesSwitchesRoutersNetwork Interface Card (NIC)Every computer and most devices (e.g. a network printer) is connected to network through an NIC. In most desktop computers, this is an Ethernet card (10 or 100 Mbps) that is plugged into a slot on the computer motherboard.4 HubsAs seen earlier, a hub interconnects two or more workstations into a local area network. A simple interconnecting device that requires no overhead to operate.When a workstation transmits to a hub, the hub immediately resends the data frame out all connecting links.A hub can be managed or unmanaged. A managed hub possesses enough processing power that it can be managed from a remote location.Hubs continue to become smarter. Some call any interconnection device in a LAN a hub!Hubs5Hubs, also called concentrators, expand one Ethernet connection into many. For example, a four-port hub connects up to four machines (or other network devices) via UTP cables. The hub provides a star connection for the four ports. Many hubs contain a single BNC connector as well to connect the hub to existing 10Base-2 network wiring. The hub also can be connected via one of its ports. One port is designed to operate in either Straight-Through or Crossover mode, selected by a switch on the hub. A hub is similar to a repeater, except it broadcasts data received by any port to all other ports on the hub. Most hubs contain a small amount of intelligence as well, examining received packets and checking them for integrity. If a bad packet arrives or the hub determines that a port is unreliable, it will shut down the line until the error condition disappears. Because of its slight delay when processing a packet, the number of hubs that may be connected in series is also limited. Several hubs can be used to connect five Ethernet segments within the accepted limits. Because each UTP cable may be as long as 100 m, the maximum distance between nodes is 500 m (the network diameter).HubsA hub is the place where data converges from one or more directions and is forwarded out in one or more directions.Seen in local area networks6Nowadays you see hubs with switches; but basically the hub is the place where data comes together while the switch determines how and where data is forwarded from the place where data comes together.Hubs connecting segments7

8 BridgesA bridge can be used to connect two similar LANs, such as two CSMA/CD LANs.A bridge can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN.The bridge examines the destination address in a frame and either forwards this frame onto the next LAN or does not.The bridge examines the source address in a frame and places this address in a routing table, to be used for future routing decisions.BridgeA bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring).A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).9bridge In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs). In bridging networks, computer or node addresses have no specific relationship to location. For this reason, messages are sent out to every address on the network and accepted only by the intended destination node. Bridges learn which addresses are on which network and develop a learning table so that subsequent messages can be forwarded to the right network.

Bridging networks are generally always interconnected local area networks since broadcasting every message to all possible destinations would flood a larger network with unnecessary traffic. For this reason, router networks such as the Internet use a scheme that assigns addresses to nodes so that a message or packet can be forwarded only in one general direction rather than forwarded in all directions.

A bridge works at the data-link (physical network) level of a network, copying a data frame from one network to the next network along the communications path.

A bridge is sometimes combined with a router in a product called a brouter.

RoutersA router is a device or a software in a computer that determines the next network point to which a packet should be forwarded toward its destination.Allow different networks to communicate with each otherA router creates and maintain a table of the available routes and their conditions and uses this information along with distance and cost algorithms to determine the best route for a given packet.A packet will travel through a number of network points with routers before arriving at its destination.11A bridge interconnecting two dissimilar LANs

12Bridge interconnecting two identical LANs

Bridges vs Routers13Bridge: A bridge is a device that connects two segments of the same network. The two networks being connected can be alike or dissimilar. Unlike routers, bridges are protocol-independent. They simply forward packets without analyzing and re-routing messages. Router: A router is a device that connects two distinct networks. Routers are similar to bridges, but provide additional functionality, such as the ability to filter messages and forward them to different places based on various criteria. The Internet uses routers extensively to forward packets from one host to another. Based on these definitions we can see that key difference between a bridge and router is that a bridge does not look at protocols and a router does. A bridge does not look at traffic for the purpose of allowing or disallowing it, and it does not decide what to do with certain types of traffic; it simply moves data from one network to another. Whereas a router examines protocols and decides what to do with each packet based on defined criteria.14 SwitchesA switch is a combination of a hub and a bridge. It can interconnect two or more workstations, but like a bridge, it observes traffic flow and learns.When a frame arrives at a switch, the switch examines the destination address and forwards the frame out the one necessary connection.

Workstations that connect to a hub are on a shared segment.Workstations that connect to a switch are on a switched segment.

SwitchesAllow different nodes of a network to communicate directly with each other.Allow several users to send information over a network at the same time without slowing each other down.

GatewaysA gateway is a network point that acts as an entrance to another network. On the internet, in terms of routing, the network consists of gateway nodes and host nodes. Host nodes are computer of network users and the computers that serve contents (such as Web pages).Gateway nodes are computers that control traffic within your companys network or at your local internet service provider (ISP)What is the difference between?Bridge: device to interconnect two LANs that use the SAME logical link control protocol but may use different medium access control protocols.Router: device to interconnect SIMILAR networks, e.g. similar protocols and workstations and serversGateway: device to interconnect DISSIMILAR protocols and servers, and Macintosh and IBM LANs and equipment1819Workstations connected to a shared segment of a LAN

20SwitchesMajor role: isolating traffic patterns and providing multiple access. This design is usually done by the network manager.Switches are easy to install and have components that are hot-swappable.

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A Switch with Two Servers Allowing Simultaneous Access to Each Server22A server with two NICs and two connections to a switch

23A pair of remote bridges and switch combinationdesigned to isolate network traffic

24Switch providing multiple access to an e-mail server

25Full duplex connection of workstations to a LAN switch

26Computer NetworksA computer network is a system for communicating between two or more computers and associated devices. It is an interconnection of computers for the purposes of sharing information and resources.A popular example of a computer network is the internet, which allows millions of users to share information

An example of a network27RouterInternet

SegmentNodeHub

HubBridgeNetwork Topologies28Bus TopologyEach node is connected one after the other (like christmas lights)Nodes communicate with each other along the same path called the backbone

29Ring TopologyThe ring network is like a bus network, but the end of the network is connected to the first nodeNodes in the network use tokens to communicate with each other

Backbone30Star TopologyEach node is connected to a device in the center of the network called a hubThe hub simply passes the signal arriving from any node to the other nodes in the networkThe hub does not route the data

Hub31Branching Tree Topology

Network Protocols32Network protocols are layered such that each one relies on the protocols that underlie itSometimes referred to as a protocol stack

Figure 15.6 Layering of key network protocolsTCP/IP33Transmission Control Protocol (TCP)Software that breaks messages into packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destinationInternet Protocol (IP)Software that deals with the routing of packets through the maze of interconnected networks to their final destinationTCP/IP34User Datagram Protocol (DP)An alternative to TCP that is faster but less reliablePingA program used to test whether a particular network computer is active and reachableTracerouteA program that shows the route a packet takes across the Internet

High-Level Protocols35Other protocols build on TCP/IP protocol suiteSimple Mail Transfer Protocol (SMTP) used to specify transfer of electronic mailFile Transfer Protocol (FTP) allows a user to transfer files to and from another computerTelnet used to log onto one computer from anotherHyper Text Transfer Protocol (http) allows exchange of Web documentsWhich of these have you used?High-Level Protocols36Figure 15.7 Some protocols and the ports they use

PortA numericdesignationthat corresponds to a particularhigh-levelprotocolMIME Types37MIME typeA standard for defining the format of files that are included as email attachments or on websitesWhat does MIME stand for?

Protocols

TCP/IP41User Datagram Protocol (DP)An alternative to TCP that is faster but less reliablePingA program used to test whether a particular network computer is active and reachableTracerouteA program that shows the route a packet takes across the Internet

High-Level Protocols42Other protocols build on TCP/IP protocol suiteSimple Mail Transfer Protocol (SMTP) used to specify transfer of electronic mailFile Transfer Protocol (FTP) allows a user to transfer files to and from another computerTelnet used to log onto one computer from anotherHyper Text Transfer Protocol (http) allows exchange of Web documentsWhich of these have you used?Associated TCP/IP Protocols & ServicesHTTPThis protocol, the core of the World Wide Web, facilitates retrieval and transfer of hypertext (mixed media) documents. Stands for the HyperText Transfer protocolTelnetA remote terminal emulation protocol that enables clients to log on to remote hosts on the network.SNMPUsed to remotely manage network devices. Stands for the Simple Network Management Protocol. DNSProvides meaningful names like achilles.mycorp.com for computers to replace numerical addresses like 123.45.67.89. Stands for the Domain Name System.SLIP/ PPPSLIP (Serial Line Internet Protocol) and PPP (Point to Point Protocol) encapsulate the IP packets so that they can be sent over a dial up phone connection to an access providers modem.High-Level Protocols44Figure 15.7 Some protocols and the ports they use

PortA numericdesignationthat corresponds to a particularhigh-levelprotocolMIME Types45MIME typeA standard for defining the format of files that are included as email attachments or on websitesWhat does MIME stand for?TYPES OF NETWORKSLAN LOCAL AREA NETWORK IS A SMALL GEOGRAPHICAL AREA SUCH AS OUR SCHOOL BOARD.MAN METROPOLITAN AREA NETWORK IS A NETWORK OVER A LARGER GEOGRAPHICAL AREA SUCH AS THE PROVINCIAL GOVERNMENT.WAN WIDE AREA NETWORK IS A NETWORK USED OVER AN EXTREMELY LARGE GEOGRAPHICAL AREA SUCH AS THE FEDERAL GOVERNMENT.Basics of Networking47ersonal area network (PAN) is a computer network designed for communication between computer devices (including telephones and personal digital assistants close to one person). The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves or for connecting to a higher level network and the Internet.Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.

ersonal area network (PAN) is a computer network designed for communication between computer devices (including telephones and personal digital assistants close to one person). The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves or for connecting to a higher level network and the Internet.Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.

PAN PERSONAL AREA NETWORK Personal area network (PAN) is a computer network designed for communication between computer devices (including telephones and personal digital assistants close to one person). The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves or for connecting to a higher level network and the Internet. Personal area networks may be wired with computer buses such as USB and FireWire.Firewalls48Firewall A gateway machine and its software that protects a network by filtering the traffic it allowsAccess control policyA set of rules established by an organization that specify what types of network communication are permitted and denied

Have your messages ever beenreturned undelivered, blocked by a firewall?Firewalls49

Figure 15.8 A firewall protecting a LANNetwork Addresses50Hostname A name made up of words separated by dots that uniquely identifies a computer on the InternetIP addressAn address made up of four one-byte numeric values separated by dots that uniquely identifies a computer on the InternetIs there a correspondence between the parts of a hostname and an IP address?Network Addresses51

Class A: first byte network address and three bytes for host numberClass B: first two bytes for network address and two bytes for host numberClass C: first three bytes for network address and one byte for host numberFigure 15.9 An IP address is stored in four bytesWhere does the host number come from?Domain Name System52Host numberThe part of the IP address that specifies a particular host on the network Yes, but what is it?Domain nameThe part of a hostname that specifies a specific organization or groupTop-level domain (TLD)The last section of a Domain name that specifies the type of organization or its country of origin

Domain Name System53matisse.csc.villanova.eduComputernameDomain nameTLDDomain Name System54Figure 15.10 Top-level domains, including some relatively new ones

Domain Name System55Organizations based in countries other than the United States use a top-level domain that corresponds to their two-letter country codesFigure 15.11Some of the top-level domain names based on country codes

Do you emailsomeonein anothercountry? Domain Name System56Domain name system (DNS) A distributed system for managing hostname resolutionDomain name serverA computer that attempts to translate a hostname into an IP addressShould the tables containing hostname/IP mappings be sorted or unsorted? Why? FTP - File Transfer ProtocolFTP provides a standard system for sending and receiving files over IP networks.

HTTP ProtocolWeb browsers and servers use the Hypertext Transfer Protocol (HTTP) protocol to communicate.Electronic Mail ProtocolsSeveral network protocols were developed specifically to support electronic mail over the Internet.

SOAP - Simple Object Access ProtocolSOAP defines a standard way to encode objects within network packets using XML.

DHCPThe Dynamic Host Configuration Protocol (DHCP) supports automatic address assignment and improved configuration management of IP networks.

IPv6 - Internet Protocol version 6IPv6 promises to relieve the current IP address shortage, and this new version of the protocol may also increase performance and improve administration capabilities.

PPPoEThe Point to Point Protocol over Ethernet (PPPoE) standard helps access providers manage their broadband service delivery, and it can also improve the ease of use for DSL and cable modem customers.