2. Introduction to Computer Networks Introduction to Computer Networks

3. Connection Services This lesson examines connection service options. Many network connection choices are available, and each has advantages and disadvantages. We begin with simple telephone lines and move on to cover high- speed digital services.

4. Carriers All modem communication takes place over some kind of communication line or cable. Which type of cable it is, as well as who provides it and its related services, makes a difference in network performance and cost.All modem communication takes place over some kind of communication line or cable. Which type of cable it is, as well as who provides it and its related services, makes a difference in network performance and cost. Dial-Up Lines: Dial-up lines are common telephone lines. Some digital lines support data transmission speeds of up to 56 Kbps.Dial-Up Lines: Dial-up lines are common telephone lines. Some digital lines support data transmission speeds of up to 56 Kbps. Dedicated Lines: from 56 Kbps to 45 Mbps or more. (DSL)Dedicated Lines: from 56 Kbps to 45 Mbps or more. (DSL) Telephone LinesTelephone Lines

5. Remote Access Service (RAS) Most server-based network OS provide a service, called Remote Access Service (RAS).Most server-based network OS provide a service, called Remote Access Service (RAS). To establish a remote connection requires two services: RAS and a client service known as dial-up networking (DUN).To establish a remote connection requires two services: RAS and a client service known as dial-up networking (DUN).

6. RAS Connections The physical connection to a RAS server can be made using several different media. These include the following:The physical connection to a RAS server can be made using several different media. These include the following: Public Switched Telephone Network (PSTN)Public Switched Telephone Network (PSTN) X.25: This packet-switched network service can be used to make dial-up or direct connections.X.25: This packet-switched network service can be used to make dial-up or direct connections. Integrated Services Digital Network (ISDN)Integrated Services Digital Network (ISDN) Digital Subscriber’s Line (DSL)Digital Subscriber’s Line (DSL)

7. RAS Protocols RAS supports three connection protocols.RAS supports three connection protocols. Serial Line Interface protocol (SLIP): does not support dynamic IP addressing or the NetBEUI or IPX protocols, it cannot encrypt logon information, and it is supported only by RAS clients.Serial Line Interface protocol (SLIP): does not support dynamic IP addressing or the NetBEUI or IPX protocols, it cannot encrypt logon information, and it is supported only by RAS clients. Point-to-Point Protocol (PPP): supports TCP/IP, IPX, NetBEUI, compression and encrypted passwords.Point-to-Point Protocol (PPP): supports TCP/IP, IPX, NetBEUI, compression and encrypted passwords. Point-to-Point Tunneling Protocol (PPTP) is an essential part of VPN technology. PPTP provides secure transmission over TCP/IP networks because its connections are encrypted.Point-to-Point Tunneling Protocol (PPTP) is an essential part of VPN technology. PPTP provides secure transmission over TCP/IP networks because its connections are encrypted.

8. RAS and Security The actual methods by which RAS ensures security can vary with the operating system. RAS security functions include:The actual methods by which RAS ensures security can vary with the operating system. RAS security functions include: AuditingAuditing CallbackCallback Security hostSecurity host PPTP filteringPPTP filtering

9. Limitations of RAS Do not use RAS if you need a higher bandwidth than that provided by an asynchronous modem, or if you need a dedicated full-time connection.Do not use RAS if you need a higher bandwidth than that provided by an asynchronous modem, or if you need a dedicated full-time connection. Use RAS if you determine that your bandwidth requirements are not greater than 128 Kbps.Use RAS if you determine that your bandwidth requirements are not greater than 128 Kbps. if you do not require a full-time connection, if you do not require a full-time connection, or if you must keep system costs down.or if you must keep system costs down.

10. WAN Overview Most WANs are combinations of LANs and other types of communications components connected by communication links called "WAN links." WAN links can include:Most WANs are combinations of LANs and other types of communications components connected by communication links called "WAN links." WAN links can include: Packet-switching networks. Fiber-optic cable. Microwave transmitters. Satellite links. Cable television coaxial systems.Packet-switching networks. Fiber-optic cable. Microwave transmitters. Satellite links. Cable television coaxial systems.

11. WAN Transmission Technologies: Communication between LANs will involve one of the following transmission technologies:Communication between LANs will involve one of the following transmission technologies: AnalogAnalog DigitalDigital Packet switchingPacket switching

12. Analog Connectivity The same network that your telephone uses is available to computers.The same network that your telephone uses is available to computers. One name for this worldwide network is the Public Switched Telephone Network (PSTN).One name for this worldwide network is the Public Switched Telephone Network (PSTN). In the context of computing, the PSTN, offering voice-grade dial-up telephone lines, can be thought of as one large WAN link.In the context of computing, the PSTN, offering voice-grade dial-up telephone lines, can be thought of as one large WAN link.

13. Digital Connectivity Point-to-point digital circuits are dedicated circuits that are provided by several telecommunications carriers.Point-to-point digital circuits are dedicated circuits that are provided by several telecommunications carriers. Organizations requiring a faster, more secure transmission environment than that which analog lines provide can turn to digital data service (DDS) lines.Organizations requiring a faster, more secure transmission environment than that which analog lines provide can turn to digital data service (DDS) lines. Digital lines are available in several forms, including DDS, T1, T3, T4, and switched 56.Digital lines are available in several forms, including DDS, T1, T3, T4, and switched 56. DDS provides point-to-point synchronous communicationDDS provides point-to-point synchronous communication

14. Digital data service (DDS) DDS sends data from a bridge or router through a device called a Channel Service Unit/Data Service Unit (CSU/DSU).DDS sends data from a bridge or router through a device called a Channel Service Unit/Data Service Unit (CSU/DSU).

15. T1 Service T1 service is perhaps the most widely used type of digital line.T1 service is perhaps the most widely used type of digital line. It is a point-to-point transmission technology that uses two-wire pairs to transmit a full-duplex signal at a rate of 1.544 Mbps.It is a point-to-point transmission technology that uses two-wire pairs to transmit a full-duplex signal at a rate of 1.544 Mbps. Subscribers who do not need or cannot afford the bandwidth of an entire T1 line can subscribe to one or more T1 channels in 64 Kbps increments, known as Fractional T-1 (FT-1).Subscribers who do not need or cannot afford the bandwidth of an entire T1 line can subscribe to one or more T1 channels in 64 Kbps increments, known as Fractional T-1 (FT-1).

16. Digital Transmission Rates Signal Carrier T1-Chs Voice-Chs Data-RateSignal Carrier T1-Chs Voice-Chs Data-Rate DS-0 N/A N/A 1 64 K DS-1 T1 1 24 1.544 MB DS-2 T2 4 96 6.312 MB DS-3 T3 28 672 44.736 MB DS-4 T4 168 4032 274.760 MBDS-0 N/A N/A 1 64 K DS-1 T1 1 24 1.544 MB DS-2 T2 4 96 6.312 MB DS-3 T3 28 672 44.736 MB DS-4 T4 168 4032 274.760 MB T3 and Fractional T-3 leased line service provides voice and data-grade service from 6 Mbps to 45 Mbps. These offer the highest-capacity leased-line service commonly available.T3 and Fractional T-3 leased line service provides voice and data-grade service from 6 Mbps to 45 Mbps. These offer the highest-capacity leased-line service commonly available.

17. Packet-Switching Networks Because packet technology is fast, convenient, and reliable, it is used to transmit data over extensive areas such as across cities, states, or countries.Because packet technology is fast, convenient, and reliable, it is used to transmit data over extensive areas such as across cities, states, or countries.

18. Virtual Circuits Many packet-switching networks use virtual circuits.Many packet-switching networks use virtual circuits. These are circuits composed of a series of logical connections between the sending computer and the receiving computer.These are circuits composed of a series of logical connections between the sending computer and the receiving computer. The circuit is bandwidth allocated on demand, not an actual cable or permanent, physical link between two stations.The circuit is bandwidth allocated on demand, not an actual cable or permanent, physical link between two stations. Virtual circuits can last either as long as the conversation lasts (Switched Virtual Circuits (SVCs)), or as long as the two communicating computers are up and running (Permanent Virtual Circuits (PVCs))Virtual circuits can last either as long as the conversation lasts (Switched Virtual Circuits (SVCs)), or as long as the two communicating computers are up and running (Permanent Virtual Circuits (PVCs))

19. Sending Data Across a WAN WAN environments are becoming more popular to deliver the speed or bandwidth an organization needs.WAN environments are becoming more popular to deliver the speed or bandwidth an organization needs. X.25. Frame relay. Asynchronous Transfer Mode (ATM). Integrated Services Digital Network (ISDN). Fiber Distributed Data Interface (FDDI). Synchronous Optical Network (SONET). Switched Multimegabit Data Service (SMDS). Internet.X.25. Frame relay. Asynchronous Transfer Mode (ATM). Integrated Services Digital Network (ISDN). Fiber Distributed Data Interface (FDDI). Synchronous Optical Network (SONET). Switched Multimegabit Data Service (SMDS). Internet. These WAN technologies include: These WAN technologies include:

20. X.25 X.25 is a set of protocols incorporated in a packet- switching network.X.25 is a set of protocols incorporated in a packet- switching network. The early X.25 networks used telephone lines to transmit data.The early X.25 networks used telephone lines to transmit data.

21. Frame Relay Frame relay is an advanced fast-packet variable- length, digital, packet-switching technology.Frame relay is an advanced fast-packet variable- length, digital, packet-switching technology. This technology stripped away many X.25 accounting and checking functions that are not necessary in a reliable, secure, fiber-optic circuit environment.This technology stripped away many X.25 accounting and checking functions that are not necessary in a reliable, secure, fiber-optic circuit environment. Frame relay uses a point-to- point systemFrame relay uses a point-to- point system

22. Asynchronous Transfer Mode (ATM) ATM is an advanced implementation of packet switching that provides high-speed data transmission rates to send fixed-size packets (cells) over broadband and baseband LANs or WANs.ATM is an advanced implementation of packet switching that provides high-speed data transmission rates to send fixed-size packets (cells) over broadband and baseband LANs or WANs.

23. ATM Switches ATM switches act as multiplexers allowing multiple data input.ATM switches act as multiplexers allowing multiple data input. ATM can offer throughput rates from 155MB up to 1.2 gigabits per second.ATM can offer throughput rates from 155MB up to 1.2 gigabits per second.

24. Integrated Services Digital Network (ISDN) ISDN is an inter-LAN digital connectivity specification that accommodates voice, data.ISDN is an inter-LAN digital connectivity specification that accommodates voice, data. The 64 Kbps channels, B channels, can carry voice, data, or images. The slower 16 Kbps channel, the D channel, carries signaling and link management data. ISDN Basic Rate desktop service is called 2B+D.The 64 Kbps channels, B channels, can carry voice, data, or images. The slower 16 Kbps channel, the D channel, carries signaling and link management data. ISDN Basic Rate desktop service is called 2B+D. Primary Rate ISDN uses the entire bandwidth of a T1 link by providing 23 B channels at 64 Kbps and one D channel at 64 Kbps.Primary Rate ISDN uses the entire bandwidth of a T1 link by providing 23 B channels at 64 Kbps and one D channel at 64 Kbps.

25. Fiber Distributed Data Interface (FDDI) Fiber Distributed Data Interface (FDDI) is a specification that describes a high-speed (100 Mbps) token-ring network that uses fiber-optic media.Fiber Distributed Data Interface (FDDI) is a specification that describes a high-speed (100 Mbps) token-ring network that uses fiber-optic media. FDDI can be used for metropolitan area networks (MANs) to connect networks in the same city with a high-speed fiber-optic cable connection.FDDI can be used for metropolitan area networks (MANs) to connect networks in the same city with a high-speed fiber-optic cable connection. It is limited to a maximum ring length of 100 kilometers (62 miles), so FDDI is not really designed to be used as a WAN technology. It is limited to a maximum ring length of 100 kilometers (62 miles), so FDDI is not really designed to be used as a WAN technology.

26. FDDI FDDI uses the token-passing system in a dual-ring setting. Traffic usually flows on the primary ring.FDDI uses the token-passing system in a dual-ring setting. Traffic usually flows on the primary ring. If the primary ring fails, FDDI automatically reconfigures the network so that the data flows onto the secondary ring in the opposite direction.If the primary ring fails, FDDI automatically reconfigures the network so that the data flows onto the secondary ring in the opposite direction.

27. Synchronous Optical Network (SONET) SONET is a standard for optical transport that was formulated by the Exchange Carriers Standards Association (ECSA) for ANSI.SONET is a standard for optical transport that was formulated by the Exchange Carriers Standards Association (ECSA) for ANSI. SONET has also been incorporated into the Synchronous Digital Hierarchy recommendations of the CCITT (ITU).SONET has also been incorporated into the Synchronous Digital Hierarchy recommendations of the CCITT (ITU). SONET defines optical-carrier (OC) levels and electrical-equivalent synchronous transport signals (STSs) for the fiber optic-based transmission hierarchy. SONET defines optical-carrier (OC) levels and electrical-equivalent synchronous transport signals (STSs) for the fiber optic-based transmission hierarchy.

28. Synchronous Optical Network (SONET) SONET defines optical-carrier (OC) levels and electrical-equivalent synchronous transport signals (STSs) for the fiber optic-based transmission hierarchy. SONET defines optical-carrier (OC) levels and electrical-equivalent synchronous transport signals (STSs) for the fiber optic-based transmission hierarchy.

29. Switched Multimegabit Data Service (SMDS) SMDS) is a switching service provided by some local exchange carrier services.SMDS) is a switching service provided by some local exchange carrier services. Transmission speeds range from 1 Mbps to 34 Mbps with many-to-many connectivity. SMDS does not perform error checking or flow control; that is left up to the sites being connected.Transmission speeds range from 1 Mbps to 34 Mbps with many-to-many connectivity. SMDS does not perform error checking or flow control; that is left up to the sites being connected. SMDS uses the same fixed-length cell relay technology as ATM. SMDS is a dual-bus topology that forms a ring that is not closed. SMDS uses the same fixed-length cell relay technology as ATM. SMDS is a dual-bus topology that forms a ring that is not closed.

30. Internet Internet (Web) has become the most popular WAN connection for all LANs.Internet (Web) has become the most popular WAN connection for all LANs. The Internet is a network of networks, linking computers to computers sharing the TCP/IP protocols. The Internet is a network of networks, linking computers to computers sharing the TCP/IP protocols. A VPN solution provides today's companies the ability to interconnect different corporate network sites in a completely secure environment using the Internet. A VPN solution provides today's companies the ability to interconnect different corporate network sites in a completely secure environment using the Internet.