Chapter Seven

1
Chapter Seven

• WANs and Remote Connectivity

2
Objectives

• 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

3
WAN Essentials

• 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

4
WAN Essentials
Figure 7-1 Differences in LAN and WAN
connectivity
5
PSTN

• 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)

6
PSTN

• 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)

7
PSTN
Figure 7-2 A typical PSTN connection to the
Internet
8
X.25 and Frame Relay

• 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

Figure 7-3 A WAN using frame relay
9
X.25 and Frame Relay

• 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

10
ISDN (Integrated Services Digital Network)

• 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

11
BRI (Basic Rate Interface)

• A variety of ISDN using two 64-Kbps bearer (B)
  channels and one 16-Kbps data (D) channel, as
  indicated by the following notation
• 2BD
• Through bonding, the two 64-Kbps channels can be
  combined to achieve an effective throughput of
  128-Kbps

12
BRI (Basic Rate Interface)

• The Network Termination 1 (NT1) device connects
  twisted-pair wiring at customers 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

Figure 7-4 A BRI link
13
PRI (Primary Rate Interface)

• A variety of ISDN using 23 B channels and one
  64-Kbps D channel, as represented by the
  following notation
• 23BD
• PRI links use same kind of equipment as BRI
  links, but require the services of an extra
  network termination devicecalled a Network
  Termination 2 (NT2)to handle multiple ISDN lines

14
PRI (Primary Rate Interface)
Figure 7-5 A PRI link

• It is only feasible to use ISDN for the local
  loop portion of a WAN link

15
T-Carriers

• 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

16
Types of 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
• 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

17
Types of T-Carriers
Figure 7-1 Carrier specifications
18
T-Carrier Connectivity

• 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

Figure 7-6 A CSU/DSU connecting a T1
19
T-Carrier Connectivity

• Multiplexer
• Device that combines multiple voice or data
  channels on one line

Figure 7-7 Typical use of a multiplexer on a
T1-connected data network
20
T-Carrier Connectivity

• Routers and bridges
• On a typical T1-connected data network, terminal
  equipment will consist of bridges, routers or a
  combination of the two

Figure 7-8 A router on a T1-connected network
21
DSL

• 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

22
Types of DSL

• Term xDSL refers to all DSL varieties, of which
  at least eight currently exist
• DSL types can be divided into two categories
• Asymmetrical
• Symmetrical
• To understand the difference between these two
  categories, you must understand the concept of
  downstream and upstream data transmission

23
Types of DSL
Table 7-2 Comparison of DSL types
24
DSL Connectivity

• DSL connectivity, like ISDN, depends on the PSTN
• Inside carriers 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

Figure 7-9 A DSL connection
25
DSL Connectivity

• Once inside the customers home or office, the
  DSL line must pass through a DSL modem

Figure 7-10 A DSL modem
26
Cable

• 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

Figure 7-11 A cable modem
27
Cable

• 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 customers house
• Head-end
• Cable companys central office, which connects
  cable wiring to many nodes before it reaches
  customers sites

28
Cable
Figure 7-12 Cable infrastructure
29
SONET (Synchronous Optical Network)

• 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

Figure 7-13 SONET technology on a long-distance
WAN
30
SONET (Synchronous Optical Network)
Table 7-3 SONET OC levels
31
WAN ImplementationSpeed
Table 7-4a A comparison of WAN technology
transmission speeds
32
WAN ImplementationSpeed
Table 7-4b A comparison of WAN technology
transmission speeds
33
WAN ImplementationReliability

• WAN implementations can roughly be divided as
  follows
• Not very reliable, suited to individual or
  unimportant transmissions
• PSTN dial-up
• 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
• SONET

34
WAN ImplementationSecurity

• 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

35
WAN ImplementationVirtual Private Networks
(VPNs)

• VPNs are wide area networks logically defined
  over public transmission systems that serve an
  organizations users, but isolate that
  organizations traffic from other users on the
  same public lines

Figure 7-14 An example of a VPN
36
Remote Connectivity

• 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 users 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

37
Remote Connectivity

• 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

38
Dial-Up Networking

• Refers to the process of dialing into a LANs
  (private) access server or to an ISPs (public)
  access server to log onto a network

Figure 7-15 Choosing a network connection type
39
SLIP and PPP

• 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

40
Chapter Summary

• 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

41
Chapter Summary

• 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

42
Chapter Summary

• 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

43
Chapter Summary

• 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