WANs and Remote Connectivity

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WANs and Remote Connectivity

• Chapter Seven

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WAN Topologies

• Internet is largest WAN in existence
• Most WANs arise from need to connect buildings
• WANs and LANs similar in fundamental ways
• Differ at Layers 1 and 2 of OSI Model
• WANs typically send data over publicly available
  communications networks
• Network service providers (NSPs)
• Dedicated lines
• WAN link connection between WAN sites (points)
• Point-to-point connections

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WAN Topologies

• WAN topologies resemble LAN topologies
• Details differ because of
• Distance they must cover
• Larger number of users
• Heavy traffic
• WAN topologies connect sites via dedicated and,
  usually, high-speed links
• Requires special equipment
• Links not capable of carrying non-routable
  protocols

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WAN Essentials
Differences in LAN and WAN connectivity
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WAN Topologies (continued)

• Bus
• Similar to bus LAN topology
• Often best option for organizations with few
  sites and capability to use dedicated circuits
• Dedicated circuits make it possible to transmit
  data regularly and reliably
• Ring
• Similar to ring LAN topology
• Usually use two parallel paths for data
• Cannot be taken down by loss of one site
• Only practical for connecting few locations

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WAN Topologies (continued)
A bus topology WAN
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WAN Topologies (continued)
A ring topology WAN
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WAN Topologies (continued)

• Star
• Separate routes for data between any two sites
• Failure at central connection can bring down WAN
• Mesh
• Every site interconnected
• Fault-tolerant
• Full mesh WAN and partial mesh WAN
• Tiered
• Sites connected in star or ring formations
  interconnected at different levels
• Highly flexible and practical

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WAN Topologies (continued)
A star topology WAN
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WAN Topologies (continued)
Full mesh and partial mesh WANs
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WAN Topologies (continued)
A tiered topology WAN
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WAN Transmission Methods

• PSTN
• ISDN
• xDSL
• Cable
• T-Carriers

• FDDI
• X.25 and Frame Relay
• ATM
• SONET
• Satellite

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Public Switched Telephone Network (PSTN)

• Refers to the network of typical telephone lines
  that service most homes
• Also called plain old telephone service (POTS)
• Dial-up connection uses a PSTN or other line to
  access a remote server via modems at both the
  source and destination
• Modems convert digital signals of computer to
  analog phone signals and vice versa
• The place where two telephone systems meet is the
  point of presence (POP)

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Public Switched Telephone Network (PSTN)

• Public Switched Telephone Network (PSTN)
  comprises entire telephone system
• Traffic carried by fiber-optic and copper
  twisted-pair cable, microwave, and satellite
  connection
• Dial-up usually means connection using PSTN line
• Advantages Ubiquity, ease of use, low cost
• Disadvantages Low throughput, quality, marginal
  security

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Public Switched Telephone Network (PSTN)
Typical PSTN connection to the Internet
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Integrated Services Digital Network (ISDN)

• International standard for transmitting digital
  data over PSTN
• Specifies protocols at Physical, Data Link,
  Transport layers
• Handle signaling, framing, connection setup and
  termination, routing, flow control, error
  detection and correction
• Dial-up or dedicated connections
• Carries voice calls and data simultaneously on
  one line
• Established by the ITU
• All ISDN connections are based on two types of
  channels
• B channel is the bearer channel
• D channel is the data channel

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Basic Rate ISDN(BRI)

• Uses two B channels and one D channel, as
  indicated by the notion 2BD
• Through bonding, the two 64 Kbps B channels can
  be combined to achieve an effective throughput of
  128 Kbpsthe maximum amount of data a BRI
  connection can accommodate
• Network Termination 1 (NT1)
• Connects the incoming twisted-pair wiring with
  the customers ISDN terminal equipment (TE)
• A terminal adapter (TA) converts digital signals
  into analog signals for use with ISDN phones and
  other analog devices

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Physical Layer

• The Sync field consists of 9 Quaternaries (2 bits
  each) in the pattern 3 3 -3 -3 -3 3 -3 3 -3.
• (B1 B2 D) is 18 bits of data consisting of 8
  bits from the first B channel, 8 bits from the
  second B channel, and 2 bits of D channel data.
• The Maintenance field contains CRC information

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Data Link Layer

• SAPI (Service access point identifier), 6-bits
  packet mode C/R (Command/Response) bit indicates
  if the frame is a command or a response EA0
  (Address Extension) bit indicates whether this is
  the final octet of the address or not TEI
  (Terminal Endpoint Identifier) 7-bit device
  identifier unique IDs for each terminalEA1
  (Address Extension) bit, same as EA0

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Network Layer

• Protocol Discriminator (1 octet) - identifies the
  Layer 3 protocol.
• Length (1 octet) - indicates the length of the
  next field. Call Reference Value (CRV) (1 or 2
  octets) - used to uniquely identify each call on
  the user-network interface.
• Message Type (1 octet) - identifies the message
  type (i.e., SETUP, CONNECT, etc.).
• Mandatory and Optional Information Elements
  (variable length) - are options that are set
  depending on the Message Type.

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Network Layer
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Basic Rate ISDN(BRI)
BRI link
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Primary Rate ISDN(PRI)

• Uses 23 B channels and one 64 Kbps D channel as
  represented by the notion 23BD
• Network Termination 2 (NT2)
• Required on PRI to handle the multiple ISDN lines
  between the customers network termination
  connection and the local phone companys wires
• Local loop
• Part of a phone system that connects a customer
  site with a public carriers POP

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Primary Rate ISDN(PRI)
PRI link
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ISDN

• Advantages
• Higher speeds than basic analog
• Less expensive than dedicated leased lines
• Runs on existing copper wire
• Data and voice simultaneously sent
• Disadvantages
• Other technologies have supplanted
• More expensive for ISDN devices

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X.25 and Frame Relay

• X.25
• Analog packet switched LAN technology optimized
  for long-distance data transmission
• Protocols at the Physical, Data Link, and Network
  layers of the OSI Model.
• Provides excellent flow control and ensures data
  reliability over long distances by verifying the
  transmission at every node
• 2.048 Mbps
• Frame Relay
• Updated version of X.25 that relies on packet
  switching
• Protocols operate at the Data Link layer of the
  OSI Model and can support multiple different
  Network and Transport layer protocols
• Does not guarantee reliable delivery of data
• Leaves error correction for higher-layer
  protocols
• 45 Mbps

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X.25 and Frame Relay

• PVCs (permanent virtual circuits)
• Point-to-point communication over which data may
  follow any number of different paths
• X.25, Frame Relay, and some forms of ATM use PVCs
• Committed information rate (CIR)
• Guaranteed minimum amount of bandwidth selected
  when leasing a Frame Relay circuit

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Frame Relay

• Virtual Circuits
• Data Link Connection Identifier identifies
  virtual circuit connections
• switched virtual circuits (SVCs) are connections
  that are established when parties need to
  transmit, then terminated once the transmission
  is complete
• permanent virtual circuits (PVCs) are connections
  that are established before data needs to be
  transmitted and maintained after the transmission
  is complete and they are not dedicated,
  individual links
• With Frame Relay, pay only for bandwidth required
• Throughput sensitive to network traffic

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Frame Relay Connections

• PBX Public Branch Exchange
• Router Data Terminating Equipment

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Frame Relay Frame

• Flags---Delimits the beginning and end of the
  frame
• DLCI The 10-bit DLCI is the essence of the Frame
  Relay header.
• Extended Address (EA) The EA is used to indicate
  whether the byte in which the EA value is 1 is
  the last addressing field.
• Congestion Control This consists of the three
  bits that control the Frame Relay
  congestion-notification mechanisms.

• Data---Contains encapsulated upper-layer data.
• Frame Check Sequence---Ensures the integrity of
  transmitted data.

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T-Carriers

• Leased line that follows the standards for T1s,
  fractional T1s, T1Cs, T2s, T3s, and T4s
• Leased lines
• Permanent dedicated connections established
  through a public telecommunications carrier
• Billed to customers on a monthly basis

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T-Carriers

• Multiplexing divides a single channel into
  multiple channels for carrying voice, data,
  video, or other signals
• Time division multiplexing (TDM)
• Divides the channel into multiple time slots and
  assigns each data stream its own time slot to
  follow
• Multiplexers
• Provides the means of combining multiple voice
  and/or data channels on one line

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Multiplexing
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T-Carriers

• 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
• Fractional T1
• Arrangement allowing an organization to use only
  some channels on a T1 line, paying for what they
  use

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T-Carriers

• DS0 64Kbps 1/24 of T-1 1 Channel
• DS1 1.544Mbps 1 T-1 24 Channels
• DS1C 3.152 Mbps 2 T-1 48 Channels
• DS2 6.312 Mbps 4 T-1 96 Channels
• DS3 44.736 Mbps 28 T-1 672 Channels
• DS3C 89.472 Mbps 56 T-1 1344 Channels
• DS4 274.176 Mbps 168 T-1 4032 Channels

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T-Carrier Connectivity Devices

• 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
• Terminal equipment Switches, routers, or bridges
  (may be integrated with CSU/DSU)

CSU/DSU connecting a T1
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T-Carrier Connectivity

• Lines require connectivity hardware at customer
  site and local telecommunications providers
  switching facility
• Wiring
• UTP, STP, coaxial cable, microwave, or
  fiber-optic
• STP preferable to UTP (repeaters generally
  required)
• For multiple T1s, coaxial, microwave, or
  fiber-optic required
• For T3s, microwave or fiber-optic necessary

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T-Carrier Connectivity Devices
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Ciscos Implementation

• The wide area link must be a point-to-point full
  or fractional T1 or E1.
• Time-division multiplexing (TDM) Cross Connect
  Cisco MC3810s act transparently for the signaling
  channel this is a bit-in, bit-out situation. In
  other words, there are no bits appended, and
  therefore, MC3810 supports the PBX's use of the
  non-HDLC like signaling channel that is connected
  from the PBX to the MC3810 DVM.
• Multiple channels can be configured for a cross
  connect. There are PBXs in this topology, and
  they require more than one channel for signaling.

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Transmitting Over T1
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T-Carrier Connectivity Devices

• Routers and bridges

Router on a T1-connected network
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Digital Subscriber Lines(DSL)

• Uses advanced data modulation techniques to
  achieve extraordinary throughput over regular
  phone lines
• In data modulation, one signal alters the
  frequency, phase, or amplitude of another signal
• Phase refers to the progress of a wave through
  time

Phase differences
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Digital Subscriber Lines(DSL)

• Operates over PSTN
• Best suited to local loop
• Advanced data modulation techniques allow
  extraordinary throughput over telephone lines
• Physical layer functions
• Dedicated service
• Data connection in which the user does not have
  to dial-up and ISP
• Term xDSL refers to all DSL varieties, of which
  seven currently exist

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xDSL

• HDSL High Rate Digital Subscribers Line
• Two pairs, symmetric
• SDSL Single-Line DSL
• One wire pair, symmetric
• RADSL Rate Adaptive DSL
• One wire pair, asymmetric
• ADSL Asymmetric DSL
• one wire pair, asymmetric
• VDSL Very high data rate DSL
• asymmetric

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xDSL
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Digital Subscriber Lines(DSL)

• Asymmetrical (DSL, ADSL)
• Characteristic of a transmission technology that
  affords greater bandwidth in one direction than
  in the other direction
• Symmetrical (SDSL)
• Characteristic of a transmission technology that
  provides equal throughput for data traveling both
  upstream and downstream
• Suited to users who both upload and download
  significant amounts of data

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DSLAM
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Digital subscriber line access multiplexer

• The DSLAM at the central office connects the
  signals from the DSL modems and combines them
  into one signal using multiplexing. The DSLAM
  connects to the telecommunication providers
  backbone.

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Digital Subscriber Link (DSL)
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Another view of DSL Infrastructure
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xDSL

• Advantages
• High speed
• Standard copper wires
• Minimal costs
• Carry voice and data over the same line
• Disadvantages
• Limited length

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Cable

• Hybrid fiber-coax (HFC)
• Fiber cable, known as a head-end, connecting the
  cable companys office to a node location near
  the customer
• Coaxial cable, known as a cable drop, connecting
  the node to the customers house

Cable infrastructure
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Cable

• Based on coaxial cable wiring used for TV signals
• Asymmetrical
• Requires cable modem
• Hybrid fiber-coax (HFC) expensive fiber-optic
  link that can support high frequencies

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Hybrid Fiber-Coax (HFC)
Cable infrastructure
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SONET(Synchronous Optical Network)

• Can provide data transfer rates from 64 Kbps to
  2.4 Gbps using the same TDM technique used by
  T-carriers
• Known internationally as SDH (Synchronous Digital
  Hierarchy)
• Self-healing

SONET ring
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SONET Connectivity
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Synchronous Optical Network
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Synchronous Optical Network
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SONET(Synchronous Optical Network)
SONET Optical Carrier levels
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IEEE 802.16 (WiMAX) Internet Access

• Worldwide Interoperability for Microwave Access
  (WiMAX) IEEE 802.16a
• Frequency ranges between 2 and 11 GHz
• Up to 70 Mbps throughput
• Potential option for rural and outlying areas

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Satellite Internet Access

• Satellite Orbits
• Geosynchronous orbit satellites orbit earth at
  same rate as earth turns
• Uplink creation of communications channel for
  transmission from earth-based transmitter to
  orbiting satellite
• Transponder receives uplink signal, transmits it
  to earth-based receiver in a downlink
• Low earth orbiting (LEO) satellites cover smaller
  geographical area, require less power
• Medium earth orbiting (MEO) satellites

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Satellite Internet Access (continued)
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Satellite Internet Access (continued)

• Satellite frequencies
• L-band 1.5 to 2.7 GHz
• S-band 2.7 to 3.5 GHz
• C-band 3.4 to 6.7 GHz
• Ku-band 12 to 18 GHz
• Ka-band 18 to 40 GHz
• Satellite Internet services
• Dial return arrangement receive data via
  satellite downlink, send data via dial-up
  connection
• Satellite return arrangement send and receive
  data using satellite uplink and downlink

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Satellite Internet Access
Dial return satellite Internet service
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WAN Speed
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WAN Speed (continued)
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WAN Implementation

• Reliability of WAN technologies can be
• Not very reliable, suited for individual or
  unimportant transmissionsPSTN dial-up
• Sufficiently reliable, suited for day-to-day
  transmissionISDN, T1, fractional T1, T3, xDSL,
  cable, X.25, and Frame Relay
• Very reliable, suited to mission-critical
  applicationsFDDI, ATM, and SONET

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Security

• Issues to consider with security
• WAN security depends in part on the encryption
  measures each carrier provides for its lines
• Enforce password-based authorization for LAN and
  WAN access
• Develop, publish, and enforce a security policy
  for users in an organization
• Maintain restricted access to network equipment
  rooms and data centers

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Establishing Remote Connectivity

• Remote access methods
• Direct dial to the LAN
• Remote access server
• Provides central access point for multiple users
  to dial into a LAN or WAN
• Dialing directly into private networks or ISPs
  remote access server to log on to a network
• PSTN, X.25, or ISDN transmission methods
• Client must run dial-up software
• Comes with virtually every OS
• Credentials typically user name and password
• Authentication server compares credentials with
  database
• Remote Access Service (RAS) Microsofts dial-up
  networking software
• Remote node
• Computer dialed into a LANs remote access server

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Establishing Remote Connectivity

• Remote access methods (cont.)
• Direct dial to a workstation
• Remote control
• Internet/Web interface
• Remote Access Service (RAS)
• Simple dial-in server
• Routing and Remote Access service (RRAS)
  Microsofts remote access software
• Available with Windows Server 2003 NOS and
  Windows XP client OSs
• Enables Windows Server 2003 computer to accept
  multiple remote client connections
• Over any type of transmission path
• Enables server to act as a router
• Incorporates multiple security provisions

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Establishing Remote Connectivity
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Serial Line Internet Protocol (SLIP)

• Communications protocol enabling a workstation to
  connect to a server using a serial connection
• TCP/IP only
• Static IP addresses
• Supports only asynchronous transmission

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Point-to-Point Protocol (PPP)

• Communications protocol enabling a workstation to
  connect to a server using a serial connection
• Supports both asynchronous and synchronous
  transmission
• Carries many types of Network layer packets
  supports multiple network layer protocols
  TCP/IP, IPX/SPX
• Supports DHCP
• Performs error correction and data compression
• Supports encryption
• Encrypts password
• PPP over Ethernet (PPPoE) Standard for
  connecting home computers to ISP via DSL or
  broadband cable

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Remote Access Protocols
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Remote Control

• Allows remote user on client computer to control
  another computer (host) across a LAN or WAN
• Host must be configured to allow access
• Host may allow clients a variety of privileges
• Remote Desktop Software For Windows OSs
• Relies on Remote Desktop Protocol (RDP)
• Application Layer protocol
• Simple to configure
• Can run over any type of connection

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Terminal Services

• Popular method for gaining remote access to LANs
• Terminal server computer running specialized
  software allowing it to act as a host
• Supplies applications and resource sharing to
  remote clients
• Allows multiple simultaneous connections
• Optimized for fast processing and application
  handling
• Terminal services software Microsoft Terminal
  Services, Citrix Metaframe
• Thin client workstation using terminal services

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Web Portals

• A Web portal is simply a secure, Web-based
  interface to an application
• Any type of Internet connection is sufficient for
  using Web portals
• On the host side, a Web server supplies the
  application to multiple users upon request
• The use of Web portals calls for secure
  transmission protocols

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Virtual Private Networks (VPNs)

• Long-distance networks logically defined over
  public transmission systems that serve all of an
  organizations users, but isolate that traffic
  from other users on the same public lines. Uses
  encryption to secure data.

Example of a VPN
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Virtual Private Networks

• WANs logically defined over public transmission
  systems
• Traffic isolated from other traffic on same
  public lines
• Required software usually inexpensive
• Can be created by configuring special protocols
  on routers or firewalls connecting VPN sites
• Must consider interoperability and security
• Tunneling create virtual connection (tunnel)
  between two VPN nodes

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Virtual Private Networks

• Point-to-Point Tunneling Protocol (PPTP)
  encapsulates PPP so that any type of PPP data
  can traverse Internet masked as IP or IPX
  transmission
• Developed by Microsoft
• Supports encryption, authentication, and access
  services provided by Windows Server 2003 RRAS
• Uses Microsoft Point to Point Encryption (MPPE)
  to encrypt data
• Layer 2 Tunneling Protocol (L2TP) Similar to
  PPTP
• Accepted and used by multiple, different vendors
• Can connect VPN using mix of equipment types
• Uses IPSec for encryption