NET 121b: Essentials of Networking
Chapter 7: Remote and WAN Connectivity
This chapter discusses devices that are used to connect one network
to another. The topics of this chapter are:
- Introduction to remote connectivity
- Installing and configuring a modem
- Remote Access Service (RAS) and remote access clients
- WAN connectivity
The chapter begins with a list of methods that can be used to connect
to a network from a remote location. Users should be cautioned that the
line speed of such a connection is usually much slower than they are used
to on their regular network workstation. Line speed is more properly referred
to as data transfer rate, which is measured in bits per second (bps).
Depending on the speed of the connection, speed may be measured in Kilobits
per second (Kbps) or Megabits per second (Mbps).
- Ordinary phone lines deliver a level of service called POTS: Plain
Old Telephone Service. You cannot expect line speed greater than
about 53 Kbps on such a line, and actual speeds are usually lower. POTS
lines require a user to have a modem.
Modems are called that because they take a digital signal from a
computer, and modulate that signal into an analog signal to pass
across a telephone line. On the other end of such a connection, the
receiving modem demodulates that signal, and turns it into a
digital signal for the receiving computer. (Analog signals have the
potential to represent an infinite number of values inside the top and
bottom of their ranges. Digital signals are restricted to specific values
within their ranges.)
You should be aware that modems usually connect to telephone jacks
using short patch cords with RJ-11 connectors on each end. (This was
not always so. Acoustic modems actually had rubber cups to accept
the mouthpiece and earpiece of a "standard" telephone receiver.)
RJ-11 plugs and jacks may have six connectors in them, but four is
more common. RJ stands for Registered Jack.
Communications over modems may be set up as half-duplex or full-duplex.
Both modes allow communications in both directions on the channel,
but on half-duplex connections the devices must take turns
being sender and receiver. On full-duplex connections, simultaneous
traffic is allowed each direction.
- An ISDN (Integrated Services Digital Network) line is
another alternative, in some locations. This service is not available
everywhere. In most cases, you must be within 18,000 feet of a telephone
company switch capable of delivering the service. ISDN provides digital
and analog services over standard telephone lines. It maps to Layers
1 and 2. It is composed of three types of channels:
- Channel A - 4 KHz analog channel for voice service. Most discussions
of ISDN service ignore this channel.
- Channel B - 64 Kbps digital channel for data.
- The user gets two B channels with Basic Rate Interface [BRI]
- The user gets 23 B channels with Primary Rate Interface [PRI]
in North America and Japan, 30 B channels in Europe and Australia.
- Channel D - 8 or 16 Kbps digital channel for signaling (overhead).
The user gets one D channel in both BRI and PRI configurations.
- Cable modems are popular. They are usually obtained from your
cable television provider, but they are also available over the counter
at electronics dealers. In either case, you need to subscribe to a cable
data service to use one. Connections are always on (unless service is
interrupted) and there is no dialing to the ISP. Line speed can vary
from 512 Kbps to 10 Mbps for downloads, and may reach 2 Mbps for uploads.
Cost is usually about the same as a monthly cable bill, in addition
to your monthly cable bill.
- xDSL (Digital Subscriber Line) variants are also available
in some locations. Prices vary, and you cannot connect to such a line
unless you are within a limited distance from a telephone company switch.
For those who can get such service, line speed can be about 1 Mbps upstream,
up to 8 Mbps downstream. The text indicates that 8 Mbps download speed
is a more common limit. Variants:
- ADSL (Asymmetric
Digital Subscriber Line) - download speed is faster than upload
speed, as noted above. Can use the same line for voice service:
the next two variants cannot.
- HDSL (High Bit Rate Digital Subscriber Line)
- upload and download speeds are typically the same, but more cables
are required to reach higher speeds
- SDSL (Symmetric Digital Subscriber Line) - upload
and download speeds will be about the same for this variant, up
to 2 Mbps
- Satellite service may be available to potential subscribers
in areas where there is no cable data service, and the location is too
far from telephone equipment for any option other than POTS to be available.
Requires a satellite dish, and service will be affected by weather.
- Wireless service has several variations
- Wi-Fi connectivity is built into most laptops,
and may be added to most that were built without it. Wi-Fi is service
limited to connecting to a network through a wireless access point
(called a hot spot). Typically, you must be within 100 feet of the
access point, and there must be no radio interference. A common
cause of interference is a cordless telephone operating on the same
frequency as the Wi-Fi system. (IEEE standards 802.11b and 802.11g
operate at 2.4 GHz, the same as many cordless phones, Bluetooth
devices, and some microwave ovens. 802.11a operates at 5 GHz.)
- Wireless modems are available from many cell
carriers. This is typically a card that plugs into a slot on a laptop
that makes a cell phone connection to a data service carrier. You
must, of course, be inside a working cell of the provider you contract
service with for this to work.
- Bluetooth devices communicate wirelessly on the
2.4 GHz frequency. Bluetooth is more limited in range: usually about
30 feet, sometimes less. This makes it more useful for communication
between close devices than for connecting to a network.
The text discusses installing and configuring a modem
for several pages. The installation instructions are
actually instructions to tell Windows about new hardware. They are to
be carried out after installing the actual modem hardware.
The instructions in the text are given for Windows 2000 or 2003 server,
but they can also be followed on a 2000 or XP workstation, once a modem
has been installed in the computer.
- Open Control Panel.
- Open Phone and Modem Options.
- If needed, enter information about your location.
- Click the Modems tab.
- Click Add to add a new modem.
- If you want Windows to detect the modem, Click Next;
otherwise, place a check in the box beside Don't detect my modem,
then click Next, and drill down to your modem's manufacturer, and its
- Finish as you would any hardware installation.
Configuration instructions for your modem follow, most
of which are self explanatory. For instance, you can double-click a location
to edit it. On the Edit Location screen, make settings on the General
tab that reflect your telephone environment, such as dialing 8 or 9 to
get an outside line, and setting the code to disable call waiting for
Remote Access Services
A Windows 2000 or 2003 server provides remote access through Routing
and Remote Access Service (RRAS). This service is configured
with the Routing and Remote Access console in the server's
Administrative Tools menu. RRAS is installed on the server by default,
but it must be configured by an administrator before
it can run. This state can be confirmed by starting the Routing and Remote
Access console, looking for a red arrow (pointing down)
on the icon for your server. This symbol tells you that the service is
down. After configuration, the symbol changes to green
arrow that points up.
Configuration choices include what protocols to support
for your remote users. There are two sets of protocols
- LAN protocols - the protocols your users will be
allowed to use on your LAN once they are connected to it. The choices
are TCP/IP, IPX/SPX, and AppleTalk
- dial-up protocols - the protocols that your server
will support for users attempting to connect to its modem. The choices
are Point-to-Point protocol (PPP) and Serial Line Interface Protocol
The LAN protocols are dictated by the kind of
network(s) your server provides access to. Most
networks use TCP/IP, older Novell networks
require IPX/SPX, and Macintosh networks
may require Appletalk.
Dial-up protocols are needed to communicate over a modem.
Again, the choice is simple: use PPP, if possible. PPP
is an improved version of SLIP. SLIP should only be used when needed to
connect with older equipment that does not support PPP. PPP provides access
to better services, such as allowing Multilink connection. Multilink lets
the server treat two dial-up connections from one user as one connection,
which increases the effective bandwidth of the user's connection. (Of
course, this requires the remote user and your server to have multiple
modems and phone lines.)
RRAS service can act as a Virtual Private Network interface
for your remote users. This is most effective when the users attach to
your server through the Internet. They contact the RRAS
service through a web address, authenticate with it, and are admitted
to your network as a local user. Authentication can be
handled two ways. The first way is for the RRAS server
to communicate with Active Directory (your Windows network
database of users and resources) to perform the authentication. The second
way is to configure the RRAS server to work with a Remote Authentication
Dail-In User Service (RADIUS) server. A RADIUS server can put
all the authentication work on one box, which can be dedicated to that
The text reminds us that dial-up connections will be much slower than
LAN connections. Users will be happier if they access data across slow
links, but run applications locally. Actually, this is true in any case.
Users experience better performance if applications are loaded on their
To create a remote access client to use a dial-up connection,
open Control Panel, open Network Connections, and click Create a New Connection.
If you do not see this choice, open the New Connection Wizard.
The text describes the security choices on the dial-up connection's properties.
You should be aware of the choices:
- EAP - Extensible Authentication Protocol extends the functionality
of PPP. It recogizes more devices and authentication methods than PPP
- PAP - Password Authentication Protocol provides support for
passwords and IDs, but is not considered to be secure.
- CHAP - Challenge Handshake Authentication Protocol is the
most secure protocol in the list. Each computer must be configured with
a secret key. This key is used with the device ID and a random value
to create a hash value that is sent to the other device which must match
the hash code with its own calculation in order for access to be granted.
- MS-CHAP - Microsoft Challenge Handshake Authentication Protocol
is similar to CHAP, but uses Window-based algorithms.
- SPAP - Shiva Password Authentication Protocol is a version
of PAP that is only for Shiva hardware.
The chapter ends with a discussion of data services that provide more
bandwidth than traditional dial-up connections. Wide Area Networks are
not the same as LANs. They are built with different protocols, different
hardware, and different methods. There are several kinds of wide bandwidth
data services available, which vary from country to country.
- T-carrier system: North America
- T1 - 1.544 Mbps, divided into 24 lines that are each 64 Kbps.
- T2 - not generally available; equivalent to four T1 lines: 6.312
- T3 - equivalent to 28 T1 lines; about 45 Mbps
- T4 - 274.176 Mbps
- E-carrier system: European market
- E1 - 2.048 Mbps
- E2 - 8.448 Mbps
- E3 - 34.368 Mbps
- E4 - 139.264 Mbps
- E5 - 565.149 Mbps
- J-carrier system: Japan
- J1 - 1.544 Mbps
- J1C - 3.152 Mbps
- J2 - 6.312 Mbps
- J3 - 32.064 Mbps
- J3C - 97.728 Mbps
- SONET and SDH -
Synchronous Optical NETwork (SONET) is a United States version of Synchronous
Digital Hierarchy (SDH)
- OC-1 - 51.84 Mbps
- OC-3 - 155.52 Mbps
- OC-12 - 622.08 Mbps
- OC-48 - 2488.32 Mbps
- OC-192 - 9953.28 Mbps
- OC-768 - 39813.12 Mbps