1 Chapter Overview Using Remote Connections SLIP and PPP WAN Technologies.
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Transcript of 1 Chapter Overview Using Remote Connections SLIP and PPP WAN Technologies.
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Chapter Overview
Using Remote Connections SLIP and PPP WAN Technologies
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Types of Remote Network Connections
Computer to Internet service provider (ISP)
Computer to private network Computer to computer Network to network
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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 Works with asynchronous 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
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 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.
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.
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Virtual Private Network (VPN) Communications The remote user connects to the Internet by
using a modem to dial in to a local ISP. The network is permanently connected to the
Internet and has a server that is configured to receive incoming VPN connections.
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 conduit.
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Point-to-Point Tunneling Protocol (PPTP) Encapsulation
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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.
The Basic Rate Interface (BRI) provides two 64-Kbps B channels and one 16-Kbps D channel.
The Primary Rate Interface (PRI) 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 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
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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
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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.
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.
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 dead2. Link establishment3. Authentication4. Link quality monitoring5. Network layer protocol configuration6. Link open7. 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. 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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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.
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. 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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SONET Optical Carrier (OC) Levels
OC Level Data Transmission Rate (in Mbps)
OC1 51.84
OC3 155.52
OC6 311.04
OC9 466.56
OC12 622.08
OC18 933.12
OC24 1244.16
OC36 1866.24
OC48 2488.32
OC96 4976.640
OC192 9953.280
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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 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.
SONET is a fiber optic telecommunications network standard consisting of a series of optical carrier levels.
ATM is a switched, connection-oriented service that was designed for use on both LANs and WANs.