Transcript Chapter 12 Remote Network Access

Chapter 12
Remote Network Access

Using Remote Connections
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SLIP and PPP

WAN Technologies
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Types of Remote Network
Connections
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Computer to Internet service provider (ISP)
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Computer to private network
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Computer to computer
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Network to network
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Public Switched Telephone Network
(PSTN)
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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
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Modems
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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.
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Modem Communications
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Configuring a Modem
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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.
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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.
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Configuring a Modem
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Serial ports use a chip called a universal
asynchronous receiver-transmitter (UART) to
manage communications.
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For today’s high-speed modems, you should
always use a 16550 UART.
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Virtual Private Network (VPN)
Communications
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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.
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Virtual Private Network (VPN)
Communications
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The remote computer and the network server
establish a secured connection across the
Internet.
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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)
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Point-to-Point Tunneling Protocol
(PPTP) Encapsulation
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Integrated Services Digital Network
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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
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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
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DSL Service
Asymmetrical service – It runs at a different
upstream and downstream speed
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Provides higher transmission rates by utilizing
high frequencies that standard telephone services
don’t use
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You can use the telephone line for a DSL
connection and for voice traffic at the same time
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Most Common
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HDSL – phone companies, large corporations
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ADSL – Regular users
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DSL Service Types
Service
Transmission Rate
Link
Length
Applications
High-bit-rate
1.544 Mbps full-duplex (using
Digital Subscriber two wire pairs) or 2.048 Mbps
Line (HDSL)
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
1.544 Mbps full-duplex or 2.048
Digital Subscriber Mbps full-duplex (one wire pair)
Line (SDSL)
10,000 feet
Same as HDSL
Asymmetrical
1.544 to 8.448 Mbps
Digital Subscriber downstream; 16 Kbps to 640
Line (ADSL)
Kbps upstream
10,000 to
18,000 feet
Internet/intranet access,
remote LAN access,
virtual private
networking, video on
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demand, Voice over IP
DSL Service Types (Cont.)
Service
Transmission Rate
Link
Length
Applications
Rate-Adaptive
640 Kbps to 2.2
Digital Subscriber Mbps downstream;
Line (RADSL)
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
18,000
feet
Internet/intranet access, remote
LAN access, IP telephony,
videoconferencing
Very high-bit-rate 12.96 to 51.84 Mbps
Digital Subscriber downstream; 1.6 to
Line (VDSL)
2.3 Mbps upstream
1000 to
4500 feet
Multimedia Internet access, highdefinition television delivery
ISDN Digital
Subscriber Line
(IDSL)
18,000
feet
Internet/intranet access, remote LAN
access, IP telephony,
videoconferencing
Up to 1 Mbps
downstream; up to
512 Kbps upstream
Up to 144 Kbps
full-duplex
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ADSL Connections
ADSL Termination
Unit Remote or DSL
Modem
DSL Access
Multiplexer
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CATV Networks
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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
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Provide Internet access only
Usually downstream only
Require a dial-up connection for upstream
traffic
Not suitable for private network connections
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Thin Client Computing
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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.
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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
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Thin client computing uses a specialized protocol,
such as Independent Computing Architecture (ICA),
developed by Cyrix Systems, Inc.
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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
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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
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Host and remote software.
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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
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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
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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
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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
Link dead
2. Link establishment
3. Authentication
4. Link quality monitoring
5. Network layer protocol configuration
6. Link open
7. Link termination
1.
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WAN Characteristics
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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
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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 datalink 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
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WAN technologies
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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.
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Leased Lines
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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.
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The European equivalent of a T-1 is the E-1, which
runs at 2.048 Mbps.
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Leased Lines
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Leased line services are split into 64-Kbps
channels.
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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
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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
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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.
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Frame Relay
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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).
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ATM
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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
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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
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Using remote connections
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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 longdistance telephone connections.
SLIP and PPP
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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. 41
Chapter Summary (Cont.)
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WAN technologies
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Leased lines are dedicated, permanent, point-topoint 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.
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