The document discusses various topics related to creating larger computer networks, including modems, digital telephone lines, remote access, and protocols like PPTP. Modems are primarily used to transfer files between computers by uploading and downloading. Digital telephone lines like DSL and cable modems provide higher speed data transmission compared to standard analog lines. Remote access allows employees to securely access a corporate network from outside using protocols like PPTP, which creates private "tunnels" within public networks like the Internet.

1. UNIT 8: UNDERSTANDING
LARGER NETWORKS

2. OUTLINE
8.1 Modems Technology Carriers
8.1.1 Telephone lines
8.1.2 Remote access
8.1.3 Point-to-point tunnelling protocol
8.2 Creating Larger network
8.2.1 LAN expansion
8.2.2 Repeaters, Bridges, Routers
8.2.3 Gateway
8.2.4 Wide area Networks (WAN) transmission
8.2.5 Digital connectivity
8.2.6 Packet switching networks

3. Data Communications over Standard Telephone
Lines - Uses for a Modem
Modems are primarily used for file transfer, or sending files to a remote
computer
• Sending a file to another computer is called
uploading.
• Receiving a file from another computer is called downloading.

4. Data Communications over Standard Telephone
Lines - Uses for a Modem
Modems are primarily used for file transfer, or sending files to a remote
computer
• Sending a file to another computer is called
uploading.
• Receiving a file from another computer is called downloading.

6. Data Communications over Standard Telephone
Lines - Uses for a Modem
• Modems are primarily used for file transfer, or sending files to a remote
computer
• Sending a file to another computer is called
uploading.
• Receiving a file from another computer is called downloading.

7. Internal
Modem External
Modem

8. Data Communications over Standard Telephone
Lines - Uses for a Modem
Modems are primarily used for file transfer, or sending files to a remote
computer
• Sending a file to another computer is called
uploading.
• Receiving a file from another computer is called downloading.

9. Using Digital Telephone Lines
• Telephone companies are now installing digital
telephone lines, which are dedicated to transmitting
data in digital format.
• Digital phone lines transmit data at much higher
speeds than standard analog phone lines.
• Often, data travels across analog lines and digital
lines. In such cases, data may need to be converted
from one format to another multiple times before
reaching its destination.

11. Using Digital Telephone Lines - Common Dioital
Services
The most commonly used digital telephone services are:
• ISDN, T1, and T3
• DSL
• ATM
• Cable Modem

12. Using Digital Telephone Lines —
ISDN, T1, and T3
• Integrated Services Digital Network (ISDN) is a system
that replaces analog phone services with digital services.
• Basic rate ISDN (BRI) offers three channels on one
phone line: two for data and one for control. BRI
transmits data up to 128 Kbps.
• Primary rate ISDN (PRI) offers 24 channels at
transmission speeds up to 1.544 Mbps. This is T1
service.
• Using even more channels, T3 service offers up to 672
channels and speeds up to 44.736 Mbps.

13. Using Digital Telephone Lines -
DSL Technologies
• Digital Subscriber Line (DSL) service is outpacing
ISDN services.
• Standard DSL offers speeds of 52 Mbps using
standard phone lines.
• Several types of DSL service are available, reaching
transmission speeds up to 51.84 Mbps.

14. Using Digital Telephone Lines - ATM
• Asynchronous transfer mode (ATM) digital service is
offered as a high-bandwidth, efficient means for
transferring multimedia content, data, and voice over
phone lines.
• Some types of ATM service can reach transmission
speeds of 10,000 Mbps.

15. Using Digital Telephone Lines -
Cable Modem Connections
• Cable modems allow users to connect their PCs to
the Internet via the local cable television system.
• Cable companies offer Internet service by
combining television and data signals and
distributing them over the cable system.
• Cable modem service can achieve speeds of 27 Mbps.

17. Networks in the Home
• Because more homes now have multiple computers,
home networks are gaining in popularity. Home
networks offer the same advantages to home users as
to a business.
• Home networks are typically based on existing
telephone or wireless technologies.
• Popular PC operating systems, such as Windows and
the Mac OS, provide simple networking tools that
are adequate for running a home network.

18. •With a remote access
connection, employees can
access the corporate remote
access server and log in to the
network with their regular
user account.
•Employees can then use all
the resources that would be
available from the office
desktop computer.
What is Remote Access?

19. Remote access
• Remote access is the ability to communicate with a
computer or network that is located some distance
away over a dial-up connection.

20. Remote Access Service (RAS):
It is considered to be a WAN connection. It is built into
Windows NT that enables Users to log into an NT-based
LAN using a Modem.
Remote Access
Server
Remote Access
Server

21. Type 1: Dial-up Remote Access
A dial-up remote access connection comprises remote access clients, a remote access server
(RAS), and some telecommunication infrastructure (typically, an analog phone line). A
remote client uses the telecommunication infrastructure to create a temporary physical or
virtual circuit to a port on the RAS. After the circuit is created, the connection parameters
are set. If RAS and remote access clients are not located in a local telecommunication
boundary, incremental long distance charges are incurred. Even though it has limited
scalability, this solution is good for corporations that have a low requirement for remote
access.
Type 2: VPN Remote Access
A VPN remote access connection between a user and the enterprise data center consists of
a VPN client, a VPN device or server, and the Internet. When a client accesses the Internet
through a local ISP, a virtual point-to-point connection is created with a RAS acting as the
VPN server. Once this connection is created, the parameters for the VPN connection can be
set and a VPN tunnel established with the VPN device or server to access enterprise
resources. In this case, the client is not required to dial long distance.

22. RAS Supported Connection Type:
1. Public Switched Telephone Network (PSTN)
2. Integrated Service Digital Network (ISDN)
3. X.25
4. Asynchronous Transfer Mode (ATM) over
Asymmetric Digital Subscriber Line (ADSL)
6.VPN Connection
5. Digital Links and V.90

23. Public Switched Telephone Network
(PSTN):

24. Integrated Services Digital Network
(ISDN):

25. X.25

26. Asynchronous Transfer Mode (ATM)
over Asymmetric Digital Subscriber
Line (ADSL)

27. Digital Links and V.90:

28. VPN Connection For RAS:

29. RAS Supporting Clients:
1. TCP/IP Clients using PPP
2. LAN Manager
3. DOS RAS
4. Windows for Workgroups
5. Windows 95/98
6.Windows NT 3.1 and above
7. Windows 2000/Xp

30. Required RAS Server Components:
1. Modem
or
2. ISDN Interface
or
3. X.25 PAD 4. ATM

31. Networking:

32. Routing And Remote Access Server
(RRAS):

33. RAS Supported Connection
Protocols:
1. Point to Point Protocol (PPP)
2. Serial Line Internet Protocol (SLIP)
3. Compressed SLIP (CSLIP)
4. Point to Point Multilink Protocol (PPMP)
5. Microsoft RAS or AsyBEUI
6. Callback Control Protocol (CBCP)

34. Point to Point Protocol (PPP):
PPP (Point-to-Point Protocol) is designed for simple links
which transport packets between two peers. These links
provide full-duplex simultaneous bi-directional operation
and are assumed to deliver packets in order. PPP provides
a common solution for the easy connection of a wide
variety of hosts, bridges and routers.

35. Serial Line Internet Protocol (SLIP):
The Serial Line Internet Protocol is an encapsulation of the
Internet Protocol designed to work over Serial Ports and
Modem Connections. SLIP has been largely replaced by
the Point to Point Protocol. SLIP will only support
transport of IP Packets.

36. Compressed SLIP (CSLIP):
CSLIP is essentially for data compression of the SLIP Protocol.
It reduce packet overhead drastically. It requires CSLIP
support on both the Client and Server ends. This may also be
used with PPP and called CPPP.

37. Point to Point Multilink Protocol:
Point to Point Multilink Protocol is a variation on the PPP
that makes it possible to deploy multiple Physical Layer
Connections and have them perceived as a single data link
layer Connection by the upper layer protocols. It is
typically used as a bandwidth-on-demand technique. Or
combines bandwidth from several physical connections
into one logical connection.

38. Microsoft RAS or AsyBEUI:
It was not technically possible for an AsyBEUI client to "bridge" to
IPX/SPX and talk NCPs to a NetWare server for resource sharing.
Then AsyBEUI make the RAS server would pick up the traffic and
send it to the IPX/SPX stack using its NetBIOS interface capability.
This allowed you to use IPX/SPX as the protocol between two
Windows NT machines.
Or AsyBEUI Client can now bridge to IPX/SPX and talk to Server.

39. Callback Control Protocol (CBCP):
It allows the server to negotiate with the Client to call the
Client back to establish the connection. CBCP negotiates the
use of callback where the remote access server, after
authenticating the remote access client, terminates the
physical connection, waits a specified amount of time, and
then calls the remote access client back at either a static or
dynamically configured phone number. Common CBCP
options include the phone number being used by the
remote access server to call the remote access client back.

40. Point-to-Point Tunnelling Protocol
(PPTP)
• The Point-to-Point Tunnelling Protocol (PPTP) is a
collection of communication protocols that control the
safe implementation of virtual private networks (VPN),
which enable businesses to extend their own private
networks across the public Internet via "tunnels."

41. • A big corporation with offices worldwide can use PPTP to
construct a large local area network (LAN) – basically a VPN -
by using the architecture of a Wide Area Network (WAN), such
as the network of a public Internet Service Provider (ISP) or
telco. This is less expensive than setting out network
infrastructure across such long distances.
• Through the construction of a VPN across TCP/IP-based
networks, such as the Internet, PPTP allows for the safe flow of
data from a remote client to a server in a private company
network. It enables distant users to securely access business
networks through the Internet, as if they were physically present
on the network.
• PPTP is an expansion of the point-to-point protocol that is
currently in use on the Internet, and it was suggested as a
standard by Microsoft and its allies.

42. Advantages of PPTP
• Reduces hardware costs by separating ISDN cards and
modems from RAS servers, resulting in fewer devices to buy
and run.
• Instead of maintaining many hardware configurations,
administrators merely have to handle the Remote Access
Server (RAS) and the user accounts.
• A PPTP connection is encrypted and secured via the Internet,
and it may be used with other networking protocols such as IP,
IPX, and NetBIOS Extended User Interface (NetBEUI).

43. Disadvantages of PPTP
• When PPTP is used on insecure networks, it frequently encounters performance
difficulties. Connecting employees and sharing papers will not be a problem as long as
there is no sensitive data.
• The security standards of PPTP protocols are rather poor, as they only provide 128-bit
encryption. Even while this improves security to some level, advanced hacking techniques
may still readily obtain the information. It is for this reason that at least 256-bit encryption
is usually suggested.
• As it lacks data origin verification and data integrity, PPTP is known to be less
dependable. As a result, you can't be confident that the data provided is genuine and
hasn't been tampered with. It also fails to check the source of the information. As a result,
the trustworthiness of sensitive information exchanged through this protocol must be
questioned.
• Firewalls that identify and prohibit PPTP protocols are frequently imposed by Internet
Service Providers (ISPs). This is a precautionary measure.
• The NSA may have cracked PPTP, according to certain claims. It should be noted that
this is simply a hypothesis that has yet to be confirmed.

44. • Ways to stretch or expand network capabilities
—Physically expanding to support additional computers
—Segmenting the network into smaller pieces to filter
and manage network traffic
—Extending the network to connect separate LANs
—Connecting two or more disjointed networking
environments
• Many devices can accomplish these tasks
—Repeaters, bridges, switches, routers, and gateways
Creating Larger Networks

45. Creating Larger Networks
1. Repeaters
2. Bridges
3. Switches
4. Routers
5. Gateways

47. Repeaters
• Simplest connectivity device regenerating signals
• Operates at Physical layer
• Has no means to interpret data
• Limited scope
• One input port, one output port
• Receives and repeats single data stream
• Suitable for bus topology networks
• Extend network inexpensively
• Rarely used on modern networks
• Limitations; other devices decreasing costs

49. 1.2. Bridges
• Bridges can: limit traffic on each segment; reduce
bottlenecks; connect different network architectures;
and forward frames between segments
• Transparent bridges build a bridging table as they
receive frames
• Source-routing bridges (token ring networks) rely
on the frame's source to include path information

50. Bridges
• Connects two network segments
• Analyze incoming frames and decide where to send
• Based on frame’s MAC address
• Operate at Data Link layer
• Single input port and single output port
• Interpret physical addressing information
• Advantages over repeaters and hubs
• Protocol independence
• Add length beyond maximum segments limits
• Improve network performance

52. 1.3. Switches
• A switch is really a high-speed multiport bridge, an
intelligent device that maintains a switching table
and keeps track of which hardware addresses are
located on which network segments
• Can dedicate bandwidth to each port on the switch

55. 1.4. Routers

56. Routing Tables
• Routing can be static or dynamic
• A router chooses best path for packet in two ways
—Using a distance-vector algorithm
—Using a link-state algorithm

57. Router A's routing table

59. 1.5. Gateways
• Gateway: translates information between two
dissimilar network architectures or data formats
—Often connects PCs to mainframe computers
• Other types are found in smaller networks
—When packets arrive at gateway, the SW strips the
networking information, leaving only the raw data
• It then translates the data into the new format and
sends it back down the OSI layers using the
destination system's networking protocols
—Operates at Application, Network, or Session layer
—Harder to install, slower, and more expensive

60. 2. Wide Area Network (WAN)
Transmission Technologies
1. Analog Connectivity
2. Digital Connectivity
3. Packet-Switching Networks

61. • WANs are often constructed by linking LANs
—Connections established using communication
devices with communication lines from ISP or telco
—Special communication links to construct WANs
• Packet-switching networks
• Fiber-optic cable
• Microwave transmitters
• Satellite links
• Cable television coax systems
—Most organizations lease WAN links
—Technologies: analog, digital, packet switching

62. 2.1. Analog Connectivity

63. • One way to improve the quality of a PSTN
connection is to lease a dedicated line or circuit
—Line conditioning improves overall signal quality and
reduces interference and noise
• When deciding between a dial-up or dedicated
PSTN connection, consider a number of factors
Length of connection time required
—Cost of service and usage levels
—Availability of dedicated circuits, conditioning, or other
quality improvements
—Assessment of the need for a 24-7 connection

64. 2.1.1. Modems in Network Communications
• A modem is a device for making an analog
connection between computers over a telephone
line, effectively making a WAN connection between
computers or networks
—Modulates/demodulates signals

66. 2.1.2. Types of Modems
• Types of modems: asynchronous and synchronous
—Type used depends on phone lines and requirements
—When continuous network connections are needed,
digital technologies such as DSL or cable modems
offer higher bandwidth and better communication
capabilities at little or no extra cost

69. • Because synchronous modems have so little
overhead in terms of error checking, they are much
faster than asynchronous modems
• Synchronous modems were not designed for use
over regular phone lines
—Found in dedicated, leased-line environments

70. Figure 13-8
Guide to Networking Essentials, Fifth Edition 70
Synchronous modems send synchronization bits yerio‹licaIIy

71. 2.2. Digital Connectivity
• Because computers and LANs transmit data
digitally, using digital techniques to connect LANs
over long distances to form a WAN makes more
sense than using digital-to-analog conversion
• Digital Data Service (DDS) lines are direct or
point-to-point synchronous communication links
with 2.4, 4.8, 9.6, or 56 Kbps transmission rates
—E.g., ISDN, T1, T3, and switched 56K
• DDS uses a communication device called Channel
Service UniVData Service Unit (CSU/DSU)

73. 2.2.1. Digital Modems
• The interface for ISDN is sometimes called a digital
• modem
—Consists of network termination (NT) device and terminal adapter
(TA) equipment
• Cable TV operators and telcos that offer digital connections for SOHO
also use the term modem
—Technically, both uses of term “modem” are incorrect
• Some CATV systems do indeed use analog signaling, so the term
“cable modem” is correct in these cases

74. • Cable modems transmit signals to/from Internet
points of presence using broadband CATV network
—Provide shared media access bandwidth
—Security was a concern in early networks (users
could eavesdrop other communication sessions)
• DSL uses the same twisted-pair phone lines that
deliver voice services
—Connections are not shared (guaranteed bandwidth)
—Disadvantage: distance limitation between the user's
location and the nearest central office
—Most common types: ADSL and SDSL

75. 2.2.2. T1
75
Guide to Networking Essentials, Fifth Edition
• T1 is a DDS technology that uses two two-wire
pairs to transmit full-duplex data signals at a
maximum rate of 1.544 Mbps
—Digital link that organizations purchase or lease
—Subscribing to one or more channels instead of an
entire T1 is possible with fractional T1
—In some countries, the E1 technology is used
• Multiplexing enables several communication
streams to travel simultaneously over the same
cable segment
Can increase DS-1 rates up to DS-4 speeds

77. 2.2.3. T3
• A T3 line has 28 T1s or 672 channels and supports
a data rate of 44.736 Mbps
• Many large service providers offer both T3 and
fractional T3 leased lines with transmission rates of
6 Mbps and up
• A single T3 commonly replaces several T1 lines

78. 2.2.4. Switched 56K
• Switched 56K leased lines are older, digital, point-
to-point communication links offered by local and
long-distance telcos
—They offered the best alternative to PSTN
connections, particularly given their on-demand
structure
—Acircuit was not dedicated to a single customer; on-
demand pathways established for users
—Lease terms were based on per-minute use charges
—Today, used when multiple 56 Kbps channels are
aggregated for frame relay services or when other
specialized dedicated digital leased lines are needed

79. 2.2.5. Integrated Services Digital Network
• Digital communications technology developed in
1984 to replace the analog telephone system
• Available in many metropolitan areas of the United
States, as well as most of Western Europe
• Defines single-channel links of 64 Kbps
• Enjoys some popularity in WANs as a backup line
• Available in two formats or rates
—Basic Rate Interface (BRI): 128 Kbps
—Primary Rate Interface (PRI): same bandwidth as T1
• B-ISDN supports much higher data rates

80. 2.3. Packet-Switching Networks
• Fast, efficient, and highly reliable technology
—Breaks data into packets before transmiring them
• E.g., the Internet
—Data delivery doesn't depend on any single pathway
• Packets may take different routes
—Packets may need to be rearranged on delivery
—Packets are small
• If a packet fails to arrive at destination, retransmission
request can be serviced with minimal time loss
• Reduces the time each switch or host needs to
receive, analyze, and retransmit packets

81. 2.3.1. Virtual Circuits
• Many packet-switching networks use virtual
circuits to provide temporarily “dedicated”
pathways between two points
—Created after devices at both ends of the connection
agree on bandwidth requirements and request a
pathway
—Incorporate communication parameters that govern
receipt acknowledgements, flow control, and error
control
—Two types: switched (SVCs) and permanent (PVCs)

82. 2.3.2. X.25
• Developed in the mid-1970s, the X.25 specification
provided an interface between public packet-
switching networks and their customers
—Used most often to connect remote terminals with
centralized mainframes
—SVC network
—Originally, used POTS lines as communication links
• Error checking and retransmission schemes improved
success of transmissions but dampened speed
—Usually associated with public data networks
(PDNs) instead of public or private networks

84. 3. WAN Implementation Basics
1. Customer Equipment
2. Provider Equipment
3. Going the Last Mile
4. Remote Access Networking

85. • You have already learned some terms for the
technologies that make WANs work, such as
POTS, ISDN, and frame relay
• This section discusses how WANs are
implemented

86. 3.1. Customer Equipment
• Customer: organization building the WAN
• The equipment at the customer site that's usually
the responsibility of the customer is called the CPE
—Customer might own or lease the equipment from
the provider
—Usually includes devices such as routers, modems
(analog), and CSU/DSUs (digital)
• Demarcation point: point at which the CPE ends
and the provider's responsibility begins
—Junction where the physical WAN connection is made
from the customer to the telco or ISP (the provider)

87. 3.2. Provider Equipment
• Provider location nearest the customer site is oRen
referred to as the central ofiice (CO)
—Acable runs from the customer site demarcation
point to the CO of the WAN service provider
• Usually copper or fiber-optic; provider's responsibility
• For a wireless connection to the provider, a wireless
transmitter is usually mounted on customer's building
• The connection betweenthe demarcation point and
the CO is called the local loop or last mile
—The equipment specific to the WAN technology
• usually resides at the CO

90. 3.4.1. Serial Line Internet Protocol (SLIP)
• Serial Line Internet Protocol (SLIP): older
protocol used primarily by PCs to connect to the
Internet via a modem
—Data Link layer protocol that provides connectivity
across telephone lines and no error correction
—Relies on hardware for error checking and correction
—Supports connections only for TCP/IP and requires
no addressing because a connection is made only
between two machines
—Compressed SLIP (CSLIP) supports compression
—Not used much in today's environment

91. 3.4.2. Point-to-Point Protocol (PPP)
• PPP provides a more dynamic connection between
computers than SLIP
—Provides both Physical and Data Link layer services
• Effectively turns a modem into a NIC
—Supports multiple protocols (e.g., IP, IPX, NetBEUI)
—Inherently supports compression and error checking
—Supports dynamic assignment of IP addresses
• Can assign a block of addresses to RRAS modems
—Has replaced SLIP as the remote protocol of choice
for TCP/IP connections
• The only dial-up connections that RRAS supports
require PPP (or a direct Internet connection for VPNs)