Chapter 12 Remote Network Access

1. Chapter 12Remote Network Access • Using Remote Connections • SLIP and PPP • WAN Technologies

2. Types of Remote Network Connections • Computer to Internet service provider (ISP) • Computer to private network • Computer to computer • Network to network

3. Public Switched Telephone Network (PSTN) • Technical name for the standard voice telephone system • Also known as the Plain Old Telephone Service (POTS) • Analog, circuit-switched network (p.8) • Works with modems to transmit data between computers at almost any location • Typically uses copper-based, twisted-pair cable with RJ-11 jacks

4. Modems • A modem (modulator/demodulator) is required to convert a computer’s digital signals to the analog signals used by the PSTN. • At the other end of the connection, another modem converts the analog signals back to digital.

5. Modem Communications

6. Configuring a Modem • Most modems support the Plug and Play standard. • Modems typically need an interrupt request (IRQ) and an input/output (I/O) port to communicate with the computer. • For external modems, the IRQ and I/O port are assigned to the serial port. • For internal modems, you configure the device itself to use specific hardware resources.

7. Configuring a Modem • Serial ports use a chip called a universal asynchronous receiver-transmitter (UART) to manage communications. • For today’s high-speed modems, you should always use a 16550 UART.

8. Virtual Private Network (VPN) Communications • The remote user connects to the Internet by using a modem to dial in to a local ISP. Instead of Dialing directly to the Network (imagine the cost!!!). • The network is permanently connected to the Internet and has a server that is configured to receive incoming VPN connections.

9. Virtual Private Network (VPN) Communications • The remote computer and the network server establish a secured connection across the Internet. • This technique is called tunneling, because the connection runs across the Internet inside a secure medium. • This connection makes used of the PPTP (Point-to-Point Tunneling Protocol)

10. Point-to-Point Tunneling Protocol (PPTP) Encapsulation

11. Integrated Services Digital Network • Integrated Services Digital Network (ISDN) is a high-speed digital dial-up service that uses the standard PSTN infrastructure. • It is used primarily for Internet connections, but it also supports special devices such as ISDN telephones and fax machines.

12. Integrated Services Digital Network • The Basic Rate Interface (BRI) provides two 64-Kbps B channels and one 16-Kbps D channel. • The Primary Rate Interface (PRI) – higher grade service - provides 23 64-Kbps B channels and one 64-Kbps D channel. • For computer connections, ISDN requires a Network Terminator 1 (NT-1) and a terminal adapter.

13. ISDN Connections

14. DSL Service • Asymmetrical service – It runs at a different upstream and downstream speed • Provides higher transmission rates by utilizing high frequencies that standard telephone services don’t use • You can use the telephone line for a DSL connection and for voice traffic at the same time • Most Common • HDSL – phone companies, large corporations • ADSL – Regular users

15. DSL Service Types

16. DSL Service Types (Cont.)

17. ADSL Connections ADSL Termination Unit Remote or DSL Modem DSL Access Multiplexer

18. CATV Networks • Broadband networks owned by cable television companies • Provide Internet access through the same cable used for television signals • Run at 512 Kbps or more • Bandwidth shared with other users in the area • Asymmetrical transmissions • Provide Internet connections only

19. CATV Connections

20. Satellite Connections • Provide Internet access only • Usually downstream only • Require a dial-up connection for upstream traffic • Not suitable for private network connections

21. Thin Client Computing • Thin client computing is a terminal client program running on a computer or dedicated network client device that communicates with a terminal server elsewhere on the network. • The client provides the interface to the operating system and nothing more. • The actual operating system and all applications run on the terminal server.

22. Thin Client Computing • Thin client computing uses a specialized protocol, such as Independent Computing Architecture (ICA), developed by Cyrix Systems, Inc. • ICA carries keystrokes, mouse actions, and screen updates between the client and the server, so that the applications appear to be running locally.

23. Remote Connection Requirements • Common protocols. The two computers to be connected must share common protocols at the data-link layer and above. • TCP/IP configuration. The Internet Protocol (IP) address and other configuration parameters must be appropriate for the network.

24. Remote Connection Requirements • Host and remote software. • The remote computer must run a client program that can use the physical layer to establish a connection. • The host computer must run a program that can respond to connection requests and provide network access. • Security. The host computer and the other systems on the network must have security mechanisms that control access to network resources.

25. SLIP and PPP Characteristics • Open Systems Interconnection (OSI) data-link layer and TCP/IP link layer protocols • End-to-end protocols • No physical layer specifications

26. SLIP • Stands for Serial Line Internet Protocol • Simple protocol used for transmissions over serial connections • Provides no error detection, network layer protocol identification, or security • Transmits an IP datagram and follows it with a single End Delimiter byte • Rarely used today because Point-to-Point Protocol (PPP) has replaced it

27. The SLIP Frame

28. PPP • Stands for Point-to-Point Protocol • Used for dial-up Internet connections and other wide area network (WAN) technologies • More complex than SLIP • Provides additional services that SLIP lacks, such as IP address exchange, multiplexing of network layer protocols, and authentication • Uses a 5-byte header

29. The PPP Frame

30. Phases of the PPP Connection Establishment Procedure 1. Link dead 2. Link establishment 3. Authentication 4. Link quality monitoring 5. Network layer protocol configuration 6. Link open 7. Link termination

31. WAN Characteristics • WANs typically connect networks at different locations. • WANs are point-to-point links that do not use a shared medium. • WANs can use PSTN, ISDN, or DSL connections.

32. WAN Characteristics • To connect local area networks (LANs) at remote locations, you install a router at each site and connect them with a WAN link. • Most WAN connections use PPP at the data-link layer. • WAN links usually involve a third-party service provider, which often makes high-speed WANs slower than LANs.

33. WAN Technologies • WAN technologies • Leased lines are dedicated, permanent, point-to-point connections between two sites that are provided by telephone carriers. • Frame relay is a service that uses a cloud of virtual circuits to provide flexible amounts of bandwidth between sites. • ATM is a switched, connection-oriented service that was designed for use on both LANs and WANs.

34. Leased Lines • A leased line is a permanent analog or digital telephone connection between two locations that provides a predetermined amount of bandwidth. • The most common leased line in the US is the T-1, which runs at 1.544 Mbps. • The European equivalent of a T-1 is the E-1, which runs at 2.048 Mbps.

35. Leased Lines • Leased line services are split into 64-Kbps channels. • You can use each channel as an individual 64-Kbps link, or combine them into a single data pipe. • Leasing part of a T-1 (in 64-Kbps increments) is called fractional T-1 service. • A T-3 connection runs at 44.736 Mbps and an E-3 runs at 34.368 Mbps.

36. Installing a Leased Line • A telephone service provider furnishes a link between two sites, running at a specific bandwidth. • Prices are based on the amount of the bandwidth and the distance spanned. • Each end of a leased line must be connected to a channel service unit/data service unit(CSU/DSU). • To use the line, you connect the CSU/DSU to your network, using a router.

37. Frame Relay • Frame relay provides bandwidth similar to that of a leased line, but with greater flexibility. • Speeds range from 56 Kbps to the equivalent of a T-3. • Frame relay links are not locked into a specific speed.

38. Frame Relay • Each site is connected to the service provider’s network, called a cloud. • The two sites are linked by a dynamic connection through the cloud. • Each site requires a hardware device called a frame relay assembler/disassembler (FRAD).

39. ATM • Stands for Asynchronous Transfer Mode • Originally designed to carry voice, data, and video traffic on both LANs and WANs • Uses fixed-length, 53-byte frames called cells • Provides a connection-oriented, full-duplex, point-to-point service between devices

40. ATM • Uses no broadcast transmissions • Data relayed between networks by switches, not routers • Speeds: range from a 25.6-Mbps service, intended for desktop LAN connections, to 2.46 Gbps

41. Chapter Summary • Using remote connections • Stand-alone computers become remote clients when they connect to a distant network by using any one of several different technologies. • PSTN connections use modems and standard telephone lines to transmit data. They are relatively slow but also flexible and universal. • VPNs are secure tunnels through the Internet that enable remote computers to communicate with their networks without using long-distance telephone connections. • SLIP and PPP • SLIP is a simple protocol that enables two systems connected through their serial ports to exchange messages with very little control overhead. • PPP is a more complicated end-to-end protocol that enables two systems to negotiate the use of optional features such as authentication protocols and multiple network layer protocols.

42. Chapter Summary(Cont.) • WAN technologies • Leased lines are dedicated, permanent, point-to-point connections between two sites that are provided by telephone carriers. • Frame relay is a service that uses a cloud of virtual circuits to provide flexible amounts of bandwidth between sites. • ATM is a switched, connection-oriented service that was designed for use on both LANs and WANs.