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 computers 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 todays 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.

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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.

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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
  dont 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

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DSL Service Types
Service Transmission Rate Link Length Applications
High-bit-rate Digital Subscriber Line (HDSL) 1.544 Mbps full-duplex (using two wire pairs) or 2.048 Mbps full-duplex (using three wire pairs) 12,000 to 15,000 feet Used by large networks as a substitute for T-1 leased line connections, LAN and private branch exchange (PBX) interconnections, or frame relay traffic aggregation
Symmetrical Digital Subscriber Line (SDSL) 1.544 Mbps full-duplex or 2.048 Mbps full-duplex (one wire pair) 10,000 feet Same as HDSL
Asymmetrical Digital Subscriber Line (ADSL) 1.544 to 8.448 Mbps downstream 16 Kbps to 640 Kbps upstream 10,000 to 18,000 feet Internet/intranet access, remote LAN access, virtual private networking, video on demand, Voice over IP
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DSL Service Types (Cont.)
Service Transmission Rate Link Length Applications
Rate-Adaptive Digital Subscriber Line (RADSL) 640 Kbps to 2.2 Mbps downstream 272 Kbps to 1.088 Mbps upstream 10,000 to 18,000 feet Same as ADSL, except that the transmission speed is dynamically adjusted to accommodate the link length and signal quality
ADSL Lite Up to 1 Mbps downstream up to 512 Kbps upstream 18,000 feet Internet/intranet access, remote LAN access, IP telephony, videoconferencing
Very high-bit-rate Digital Subscriber Line (VDSL) 12.96 to 51.84 Mbps downstream 1.6 to 2.3 Mbps upstream 1000 to 4500 feet Multimedia Internet access, high- definition television delivery
ISDN Digital Subscriber Line (IDSL) Up to 144 Kbps full-duplex 18,000 feet Internet/intranet access, remote LAN access, IP telephony, videoconferencing
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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

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CATV Connections
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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.

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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.

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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.

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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.

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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

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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

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The SLIP Frame
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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

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The PPP Frame
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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

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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.

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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.

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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.

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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.

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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 providers
  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

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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

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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.

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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.