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- WANs and Remote Connectivity
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- Identify network applications that require WAN technology
- Describe a variety of WAN transmission and connection methods
- Identify criteria for selecting an appropriate WAN topology,
transmission method, and operating system
- Understand the hardware and software requirements for connecting to a
network via modem
- Install and configure simple remote connectivity for a telecommunicating
client
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- WAN link
- Connection between one WAN site and another site
- A WAN link is typically described as point-to-point
- Dedicated line
- Continuously available link that is leased through another carrier
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- Public Switched Telephone Network
- Refers to the network of typical telephone lines and carrier equipment
that service most homes
- Also called plain old telephone service (POTS)
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- A dial-up connection uses a PSTN
or other line to access remote servers via modems at both the source and
destination
- The Federal Communications Commission (FCC) sets standards and policy
for telecommunications transmission equipment in the United States
- The place where two telephone systems meet is the point of presence (POP)
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- X.25
- Analog, packet-switched LAN technology optimized for long-distance data
transmission
- Frame Relay
- Updated, digital version of X.25 that also relies on packet switching
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- SVCs (switched virtual circuits)
- Connections established when parties need to transmit, then dismantled
once the transmission is complete
- PVCs (private virtual circuits)
- Connections established before data needs to be transmitted and
maintained after transmission is complete
- CIR (committed information rate)
- Guaranteed minimum amount of bandwidth selected when leasing a frame
relay circuit
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- International standard for transmitting data over digital lines
- Established by the ITU
- All ISDN connections are based on two types of channels:
- The B channel is the “bearer” channel
- The D channel is the “data” channel
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- A variety of ISDN using two 64-Kbps bearer (B) channels and one 16-Kbps
data (D) channel, as indicated by the following notation:
- Through bonding, the two 64-Kbps channels can be combined to achieve an
effective throughput of 128-Kbps
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- The Network Termination 1 (NT1) device connects twisted-pair wiring at
customer’s building with ISDN terminal equipment (TE) via RJ-11 or RJ-45
data jacks
- A terminal adapter (TA) converts digital signals into analog signals for
use with ISDN phones and other analog devices
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- A variety of ISDN using 23 B channels and one 64-Kbps D channel, as
represented by the following notation:
- PRI links use same kind of equipment as BRI links, but require the
services of an extra network termination device—called a Network
Termination 2 (NT2)—to handle multiple ISDN lines
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- It is only feasible to use ISDN for the local loop portion of a WAN link
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- Broadband
- Group of network connection types or transmission technologies
generally capable of exceeding 1.544 Mbps throughput
- T-carriers
- Term for any kind of leased line that follows the standards for T1s,
fractional T1s, T1Cs, T2s, T3s, or T4s
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- The most common T-carrier implementations are T1 and T3
- Signal level
- ANSI standard for T-carrier technology that refers to its Physical
layer electrical signaling characteristics
- DSO (digital signal, level 0)
- Equivalent of one data or voice channel
- Fractional T1
- Arrangement allowing an organization to use only some channels on a T1
line, paying for what they use
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- Wiring
- Can use unshielded or shielded twisted-pair copper wiring
- CSU/DSU (Channel Service Unit/Data Service Unit)
- CSU provides termination for the digital signal and ensures connection
integrity through error correction and line monitoring
- DSU converts the digital signal used by bridges, routers, and
multiplexers into the digital signal sent via the cabling
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- Multiplexer
- Device that combines multiple voice or data channels on one line
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- Routers and bridges
- On a typical T1-connected data network, terminal equipment will consist
of bridges, routers or a combination of the two
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- Digital Subscriber Lines
- Uses advanced data modulation techniques to achieve extraordinary
throughput over regular phone lines
- Like ISDN, DSL can span only limited distances without the help of
repeaters
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- Term xDSL refers to all DSL varieties, of which at least eight currently
exist
- DSL types can be divided into two categories:
- To understand the difference between these two categories, you must
understand the concept of downstream and upstream data transmission
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- DSL connectivity, like ISDN, depends on the PSTN
- Inside carrier’s POP, a device called a DSL access multiplexer (DSLAM)
aggregates multiple DSL subscriber lines and connects them to a larger
carrier or to the Internet backbone
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- Once inside the customer’s home or office, the DSL line must pass
through a DSL modem
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- Cable connections require that the customer use a special cable modem, a
device that modulates and demodulates signals for transmission and
reception via cable wiring
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- Hybrid fiber-coax (HFC)
- Very expensive fiber-optic link that can support high frequencies
- HFC upgrades to existing cable wiring are required before current TV
cable systems can serve as WAN links
- Cable drop
- Fiber-optic or coaxial cable connecting a neighborhood cable node to a
customer’s house
- Head-end
- Cable company’s central office, which connects cable wiring to many
nodes before it reaches customers’ sites
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- Can provide data transfer rates from 64 Kbps to 39.8 Gbps using the same
TDM technique used by T-carriers
- Known internationally as SDH (Synchronous Digital Hierarchy)
- SONET is self-healing
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- WAN implementations can roughly be divided as follows:
- Not very reliable, suited to individual or unimportant transmissions:
- Sufficiently reliable, suited for day-to-day transmissions:
- ISDN, T1, fractional T1, T3, DSL, cable, X.25, and frame relay
- Very reliable, suited to mission-critical applications:
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- Among other things, consider the following issues:
- WAN security depends in part on the encryption measures each carrier
provides for its lines
- Enforce password-based authorization for LAN and WAN access and teach
users how to choose difficult-to-decrypt passwords
- Take the time to develop, publish, and enforce a security policy for
users in your organization
- Maintain restricted access to network equipment rooms and data centers
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- VPNs are wide area networks logically defined over public transmission
systems that serve an organization’s users, but isolate that
organization’s traffic from other users on the same public lines
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- Remote access methods:
- Direct dial to the LAN
- The computer dialing into the LAN becomes a remote node on the network
- Direct dial to a workstation
- Software running on both remote user’s computer and LAN computer
allows remote user to “take over” the LAN workstation, a solution
known as remote control
- Internet/Web interface
- Through a browser, a user at home or on the road connects to a LAN
whose files are made visible to the Web through Web server software
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- ICA (Independent Computing Architecture) client
- Remote access client developed by Citrix Systems, Inc.
- Enables remote users to use virtually any LAN application over any type
of connection, public or private
- Remote Access Service (RAS)
- One of the simplest dial-in servers
- This software is included with Windows 2000 Server
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- Refers to the process of dialing into a LAN’s (private) access server or
to an ISP’s (public) access server to log onto a network
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- Serial Line Internet Protocol (SLIP)
- Communications protocol enabling a workstation to connect to a server
using a serial connection
- Can carry only IP packets
- Supports only asynchronous transmission
- Point-to-Point Protocol
- Communications protocol enabling a workstation to connect to a server
using a serial connection
- Can carry many different types of Network layer packets
- Supports both asynchronous and synchronous transmission
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- WANs are distinguished from LANs by the fact that the former networks
traverse a wider geographical area
- One WAN transmission method, PSTN, relies on the network of telephone
lines that typically service homes
- X.25 is an analog packet-switched technology optimized for long-distance
data transmission
- Frame Relay is an updated, digital version of X.25
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- Another WAN transmission method, ISDN, is an international standard
established by the ITU for transmitting data over digital lines
- Two types of ISDN connections are commonly used in North America are BRI
and PRI
- Another WAN transmission method is digital subscriber line (DSL)
- Cable is another option for high bandwidth local loop WAN transmission
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- T-carrier technology uses time division multiplexing (TDM) to divide a
single channel into multiple channels for carrying voice, data, video,
or other signals
- SONET can provide data transfer rates from 64 Kbps to 39.8 Gbps using
the same TDM technique employed by T-carriers
- When installing or upgrading a WAN, consider its ability to integrate
with your present LAN or WAN equipment, transmission speed required,
security needed, geographical distance the WAN must span, growth, and
cost
- VPNs represent one way to construct a WAN from existing public
transmission systems
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- Three ways remote users connect to LANs:
- Direct dial to the LAN
- Direct dial to a workstation
- An Internet connection with a Web interface
- SLIP and PPP are communications protocols enabling a workstation to
connect to a server using a serial connection
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