2. Introduction to Computer Networks Introduction to Computer Networks

3. Elements of Network Connectivity This lesson explores the devices and technologies available to expand networks beyond the scope of simple local area networks.

4. Connectivity Devices Devices used to expand LANs include modems, repeaters, bridges, routers, brouters, and gateways.Devices used to expand LANs include modems, repeaters, bridges, routers, brouters, and gateways. Modem Technology: Modems convert digital signals to analog waves, and vice versa.Modem Technology: Modems convert digital signals to analog waves, and vice versa.

5. Modem Hardware Modems are known as data communications equipment (DCE) and share the following characteristics:Modems are known as data communications equipment (DCE) and share the following characteristics: A serial (RS-232) communications interfaceA serial (RS-232) communications interface An RJ-11 telephone-line interface (a four- wire telephone plug)An RJ-11 telephone-line interface (a four- wire telephone plug)

6. Modem Standards Some of the common industry standards for modems include:Some of the common industry standards for modems include: Hayes-Compatible: manufacturers currently offer modems with speeds of 56,600 bps or more.Hayes-Compatible: manufacturers currently offer modems with speeds of 56,600 bps or more. International Standards: the International Telecommunications Union (ITU) has developed standards for modems.International Standards: the International Telecommunications Union (ITU) has developed standards for modems. These specifications, known as the V series, include a number that indicates the standard.These specifications, known as the V series, include a number that indicates the standard.

7. ITU Modem Standards V.22bis 2400 1984 V.32 9600 1984 V.32bi 14,400 1991 V.34 28,800 1994 V.42 57,600 1995 V.90 56,600 1998V.22bis 2400 1984 V.32 9600 1984 V.32bi 14,400 1991 V.34 28,800 1994 V.42 57,600 1995 V.90 56,600 1998 Several of the newer modems feature industry standards, such as V.42bis/MNP5 data compression, and have transmission speeds of 57,600 bps; and some modems go up to 76,800 bps.Several of the newer modems feature industry standards, such as V.42bis/MNP5 data compression, and have transmission speeds of 57,600 bps; and some modems go up to 76,800 bps.

8. Types of Modems There are different types of modems because different types of communication environments require different methods of sending data.There are different types of modems because different types of communication environments require different methods of sending data. These environments can be divided roughly into two areas related to the timing of communications:These environments can be divided roughly into two areas related to the timing of communications: Asynchronous Asynchronous Synchronous Synchronous

9. Asynchronous Communication (Async) Async was developed in order to make use of common telephone lines.Async was developed in order to make use of common telephone lines. Communication is not synchronized: There is no clocking method to coordinate the transmission between the sender and the receiver.Communication is not synchronized: There is no clocking method to coordinate the transmission between the sender and the receiver. Speed can be up to 28.8K bps. However, the data compression can boost the rate to 115.2K.Speed can be up to 28.8K bps. However, the data compression can boost the rate to 115.2K.

10. Synchronous Communication Synchronous communication relies on a timing scheme to transmit bits in block known as frames.Synchronous communication relies on a timing scheme to transmit bits in block known as frames. Special characters are used to synchronize and check its accuracy periodically.Special characters are used to synchronize and check its accuracy periodically.

11. Synchronous protocols Synchronous protocols perform a number of jobs that asynchronous protocols do not.Synchronous protocols perform a number of jobs that asynchronous protocols do not. Format data into blocks.Format data into blocks. Add control information.Add control information. Check the information to provide error control.Check the information to provide error control. The primary protocols in synchronous communication are:The primary protocols in synchronous communication are: Synchronous Data Link Control (SDLC), High- level Data Link Control (HDLC), Binary Synchronous Communications Protocol (bisync).Synchronous Data Link Control (SDLC), High- level Data Link Control (HDLC), Binary Synchronous Communications Protocol (bisync).

12. Asymmetric Digital Subscriber Line (ADSL) This technology converts existing twisted-pair telephone lines into access paths for multimedia and high-speed data communications.This technology converts existing twisted-pair telephone lines into access paths for multimedia and high-speed data communications. These new connections can transmit more than 8 Mbps to the subscriber and up to 1 Mbps from the subscriber.These new connections can transmit more than 8 Mbps to the subscriber and up to 1 Mbps from the subscriber. The technology requires special hardware, including an ADSL modem on each end of the connection.The technology requires special hardware, including an ADSL modem on each end of the connection. It also requires broadband cabling, which is not available in every locations, and there is a limit to the connection length.It also requires broadband cabling, which is not available in every locations, and there is a limit to the connection length.

13. Expanding a Network Using Components Hubs.Hubs. Bridges.Bridges. Routers.Routers. There are components that can be installed to increase the size of the network within its existing environment. These components include:There are components that can be installed to increase the size of the network within its existing environment. These components include: Gateways.Gateways. Repeaters.Repeaters.

14. Hubs Connecting or adding hubs to a LAN can effectively increase the number of workstations.Connecting or adding hubs to a LAN can effectively increase the number of workstations. Uplink crossover cables are wired differently than standard patch cables.Uplink crossover cables are wired differently than standard patch cables. This method of growing a LAN is popular, but does come with many design limitations.This method of growing a LAN is popular, but does come with many design limitations.

15. Repeaters Repeaters regenerate weakened signalsRepeaters regenerate weakened signals Repeaters do not translate or filter signals.Repeaters do not translate or filter signals. A repeater cannot connect segments using different access methods.A repeater cannot connect segments using different access methods.

16. Implementing a repeater Use a repeater to:Use a repeater to: Connect segments of similar or dissimilar media,Connect segments of similar or dissimilar media, To increase the distance transmitted.To increase the distance transmitted. Pass all traffic in both directions.Pass all traffic in both directions. Connect in the most cost-effective manner.Connect in the most cost-effective manner. Do not use a repeater when:Do not use a repeater when: There is heavy network traffic.There is heavy network traffic. Segments are using different access methods.Segments are using different access methods. Data filtering is needed.Data filtering is needed.

17. Bridges Bridges use routing table to segment network traffics, and make each segment more efficient.Bridges use routing table to segment network traffics, and make each segment more efficient.

18. Remote Bridges Because bridges can expand and segment networks, they are often used in large networks that have widely dispersed segments.Because bridges can expand and segment networks, they are often used in large networks that have widely dispersed segments.

19. Spanning tree algorithm (STA) Because remote LAN segments can be joined over telephone lines, it is possible for multiple LANs to be joined by more than one path.Because remote LAN segments can be joined over telephone lines, it is possible for multiple LANs to be joined by more than one path. STA can sense the existence of more than one route, determine which would be the most efficient, and then configure the bridge to use that one.STA can sense the existence of more than one route, determine which would be the most efficient, and then configure the bridge to use that one. In this situation, it is possible that data might get into a continuous loop. To handle this possibility, the 802.1 Network Management Committee of IEEE has implemented the spanning tree algorithm (STA). In this situation, it is possible that data might get into a continuous loop. To handle this possibility, the 802.1 Network Management Committee of IEEE has implemented the spanning tree algorithm (STA).

20. Routers Router works in an environment that consists of several network segments with differing protocols and architecturesRouter works in an environment that consists of several network segments with differing protocols and architectures Routers work at the network layer of the OSI reference model, it can exchange protocol-specific information between separate networks.Routers work at the network layer of the OSI reference model, it can exchange protocol-specific information between separate networks. Router is a device that not only knows the address of each segment, but can also determine the best path for sending data and filtering broadcast traffic.Router is a device that not only knows the address of each segment, but can also determine the best path for sending data and filtering broadcast traffic.

21. Routing Algorithms OSPF ("open shortest path first") is a link-state routing algorithm. Link-state algorithms control the routing process and allow routers to respond quickly to changes in the network. NetWare Link Services Protocol (NLSP) is a link-state algorithm to be used with IPX.OSPF ("open shortest path first") is a link-state routing algorithm. Link-state algorithms control the routing process and allow routers to respond quickly to changes in the network. NetWare Link Services Protocol (NLSP) is a link-state algorithm to be used with IPX. RIP (Routing Information Protocol) uses distance-vector algorithms to determine routes. Transmission Control Protocol/Internet Protocol (TCP/IP) and IPX support RIP.RIP (Routing Information Protocol) uses distance-vector algorithms to determine routes. Transmission Control Protocol/Internet Protocol (TCP/IP) and IPX support RIP.

22. Types of Routers Static Routers.Static Routers. Dynamic Routers.Dynamic Routers. Static routers require an administrator to manually set up and configure the routing table and to specify each route.Static routers require an administrator to manually set up and configure the routing table and to specify each route. Dynamic routers discover routes automatically and examine information from other routers to make decisions about how to send data across the network.Dynamic routers discover routes automatically and examine information from other routers to make decisions about how to send data across the network.

23. Distinguishing Between Bridges and Routers Bridges work at the data-link layer MAC sublayer, and routers work at the network layerBridges work at the data-link layer MAC sublayer, and routers work at the network layer

24. Brouters A brouter can act as a router for one protocol and as a bridge for all the others.A brouter can act as a router for one protocol and as a bridge for all the others. Route selected routable protocols.Route selected routable protocols. Brouters can:Brouters can: Bridge nonroutable protocols.Bridge nonroutable protocols. Deliver more cost-effective and more manageable internetworking than separate bridges and routers.Deliver more cost-effective and more manageable internetworking than separate bridges and routers.

25. Gateways Gateways enable communication between different architectures and environments.Gateways enable communication between different architectures and environments. Communication protocols.Communication protocols. A gateway links two systems that do not use the same:A gateway links two systems that do not use the same: Data-formatting structures.Data-formatting structures. Languages.Languages. Architecture.Architecture.

26. How Gateways Work Gateways are task- specific, typically perform protocol conversion at the application layer.Gateways are task- specific, typically perform protocol conversion at the application layer.