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As a result of receiving frequent queries from customers as to the overall
workings of the Internet and Web technology, we have compiled this basic
overview that provides broad definitions and/or explanations of the following:
Internet
The Internet is a vast worldwide network comprised of thousands of
smaller interconnected networks; this worldwide network evolved
from a project funded by the U.S. Defense Advanced Research
Projects Agency (DARPA). The Internet was originally created to help
researchers and scientists exchange information quickly and actually
prohibited use of the network for commercial purposes. Today, the Internet has grown dramatically and its users have
expanded from research institutions and scientific laboratories to
commercial businesses and consumers. The Internet now includes
many for-profit Internet Service Providers such as SBCIS. Along with
the increase in number of users on the Internet, the quantity of tools
that can be used on the Internet has also grown. Now these users on
the Internet can not only transfer files in electronic format, they can
send messages via electronic mail (e-mail), conduct research using
the vast resources of the Internet, hold real-time "talk" sessions with
others connected to the Internet, and much more. SBCIS receives its customers' network traffic and delivers it either to
the destination address or, as needed, to a Global Service Provider
who forwards it onto the ultimate destination. In turn, SBCIS receives
network traffic that is destined for its customers from Global Service
Providers and then delivers it to the appropriate location.
The SBCIS network is composed of multiple network hubs connected
by a high speed Internet backbone network. Each major network hub
runs on an FDDI LAN connecting routers and hosts that accept and
route Internet Protocol (IP) traffic and provide auxiliary services that
make accessing the Internet easier. Today, customers access the
SBCIS network by connecting to the closest major hub via
point-to-point DS1 (T-1), DS3, Dedicated ISDN, Frame Relay or ATM
Cell Relay. Each of these major hubs is connected directly to the
Internet through an Internet Global Service Provider. Domain Domain Name Service (DNS), though typically invisible to the
user, is the most fundamental tool associated with use of the
Internet. The Internet uses the IP protocol and all IP traffic must
have a source host address and a destination host address in the
form of 207.193.0.0. Unfortunately, these addresses are extremely
cumbersome and nearly impossible to remember. The function of DNS is to map the required IP addresses into more
user-friendly, easy-to-remember host names. For example, the IP
address of the SBCIS mail server could be 207.193.0.0, but its
associated host name is swbell.net. DNS allows users to document
the correlation between their IP addresses and host names. Each site
is responsible for documenting the correlation between their own IP
addresses and host names. This information is then propagated to
other DNS servers all over the world. Everyone on the Internet relies
on this mapping to easily access hosts and resources. Also since hosts at a specific site are associated with a specific IP
network address, all hosts at that site can be grouped together into
a single domain. In this way, many Internet sites can reuse a host
name such as "compass", as long as they each belong to different
domains. To clarify, compass.pacbell.net does not correspond to the
same IP address as compass.pacbell.com, since the domain
"pacbell.net" is associated with the 207.11.1.0 network and the
domain "pacbell.com" is associated with the 157.164.4.0 network. Of
course, two computers cannot have the same host name if they are
part of the same domain. One or more hosts running specialized software provide the DNS for a
particular site; these hosts are commonly referred to as name servers
or domain name servers. Customers are responsible for providing one
primary name server at their location or they can choose to use
SBCIS' optional Primary DNS service. As part of our basic service, SBCIS offers Dedicated Access
customers the option of using one of our name servers as a primary
or secondary name server, for one fully qualified domain per
customer. There is no additional charge for secondary DNS and a
nominal charge for primary DNS services. The advantage of such a
configuration is that if the primary name server fails, the SBCIS name
server can provide the required mapping between host names and IP
addresses. Without a secondary name server, the site would be virtually isolated
from the rest of the Internet. Remote users would find hosts at that
site to be unresponsive to their host names. Likewise, local users
trying to reach any host would be forced to manually enter the
destination IP address in place of its host name. Please note that not
providing DNS is NOT a security feature; it will not prevent your site
from receiving data since the IP addresses for your site can easily be
found or guessed.
Electronic mail (e-mail) is an electronic equivalent to a letter
delivered by the US Postal Service. However, in its electronic format,
mail can be delivered almost instantaneously around the world! The
Internet is equivalent to the US Postal Service delivery system and
like the US Postal Service there must be a mechanism for getting mail
in and out of the delivery system. With the US Postal Service, the
sender must take the letter to the nearest post office or mailbox.
Once a letter is delivered by the US Postal Service, the receiver must
go to their mailbox and retrieve their mail. Similarly, the sender of e-mail must have a way of both delivering and
receiving mail from the delivery system. This is accomplished through
the use of individual host e-mail software, mail servers, and mail
gateways. SBCIS Dedicated Access customers may provide their own e-mail host
software, server and gateway(s), or can choose to purchase these
services from SBCIS. If customers choose to provide their own e-mail,
we strongly recommend that the customer's e-mail system be Simple
Mail Transfer Protocol (SMTP) RFC-1123 compliant since this is the
predominant e-mail protocol used on the Internet. Each host must have an e-mail software package installed to
generate the actual e-mail messages. The host e-mail software must
be configured to forward messages to the local SMTP mail server for
delivery. The local SMTP mail server then determines where to send outgoing
messages by looking up the Mail Exchange (MX) record for the top
level domain portion of the destination e-mail address. For example, if
the destination address of an electronic mail message is
"help@pacbell.net", the latter portion of the address is pacbell.net.
The SMTP mail server (which may also be referred to as the "mail
server", "mail host", "mail spooler", or "mail relay") will check its DNS
to obtain the MX record for pacbell.net. The mail server would then
forward the e-mail message to the IP address indicated in the MX
record for pacbell.net. The mail server also accepts incoming mail addressed to its site and
delivers the mail to the individual hosts. The mail server may be
configured to "spool" incoming mail if an individual host is temporarily
unable to receive mail. The mail server stores the messages until the
host is again able to accept mail. A spooling facility requires that disk
space is reserved on the mail server for this purpose; the more mail a
site gets, the more disk space is required. A reasonable configuration is enough disk space to spool mail for the
entire site for three days. In some environments, a mail gateway is also necessary. A mail
gateway's function is to translate e-mail messages from a proprietary
format to a standard, SMTP-compliant format. For example, a mail
gateway might translate between Macintosh Quickmail and SMTP
Internet mail. If you are unsure which mail package your site is using,
contact your local system administrator. If you need assistance
setting up your e-mail system, you may contact your Internet
Application Manager for a list of integration partners. An electronic news feed provides access to the exchange of
information between Usenet news servers around the world. The
process of exchanging information between Usenet servers occurs
fairly frequently in order that updates and postings to Usenet news
groups can be propagated throughout the Internet. The function of Usenet news is to allow Internet users to exchange
ideas about particular subjects ranging from highly technical to
political to recreational. Many users find that Usenet news is a
valuable resource since specific questions or ideas can be posted to a
news group and a response is usually posted fairly rapidly. Internet
users tend to monitor news groups that are of specific interest to
them; therefore, the likelihood of getting valuable, free information is
quite high. Since Usenet is not administered by any one entity, news
groups may or may not be moderated. This means that some
newsgroups may be considered distasteful, offensive, or inappropriate
to certain users. SBCIS currently provides its customers an unrestricted Usenet news
feed which consists of ALL of the newsgroups it receives. It is the
customer's responsibility to filter out unwanted newsgroups. Customers who want to receive Usenet news must provide a high
performance host that can devote a large percentage of resources to
processing news. SBCIS recommends that dedicated access
customers set up their news server on a host with the following
minimal characteristics: Usenet news software must be installed and configured on the news
server. InterNetNews (INN) is a free software package that is the
defacto standard news server software. While there are other
commercially available news software packages, SBIS recommends
INN or Netscape News Server for its dedicated access customers.
This recommendation may change in the near future with the advent
of news server software incorporating Graphical User Interfaces
(GUIs) that make configuration and administration of the news server
much simpler. Each host also needs to have a newsreader installed.
Most Web browsers provide a newsreader (see Web Browser below). Please note that the configuration and administration of a news
server is a complicated issue, requiring a high level of systems
administration expertise. SBCIS can refer you to one of our
integration partners if you need assistance in setting up your news
server. A Web browser, such as Netscape Navigator, is a software
application that enables individual users to access the Internet with a
Graphical User Interface (GUI). These applications make it easy for
Internet users to do research, locate specific sites or services, and
conduct financial transactions and keep up on the news available on
the World Wide Web (www). Most Web browsers also provide
facilities for posting and reading Usenet news. Under an agreement
with Netscape Communications Corporation, SBCIS is authorized to
sell Netscape Navigator LAN Edition. More and more organizations are finding it valuable to have a
presence on the World Wide Web (WWW). Web servers function as
virtual storefronts to provide customer service, marketing,
advertisements and public relations information to Internet users.
Web servers may also be used to provide resources or proprietary
information to employees or key partners. A Web server can be easily
configured to record the number of hits or connections to each of its
Web pages; this information can be used to measure the interest
level of the content of the Web pages themselves. If you want to have a Web server on the Internet, SBIS recommends
that your server have at least the following characteristics: If the load on the Web server is too great, additional servers may be
set up to handle additional requests. Packet filters are typically implemented on the routers connecting a
site to the Internet. These filters are a set of criteria by which each
IP packet, sent or received from a particular interface, is judged. If
the packet meets the criteria, the router will process it. If the packet
does not meet the criteria, the router will discard it. Since each IP packet has a source and destination address, it is
possible to narrow down other Internet sites able to connect to your
network. However, since most Internet applications require two-way
transmission, such filtering will also decrease the number of sites your
users are able to access. Along with a source and destination address, IP packets utilizing TCP
and UDP protocols also contain a destination port number. The port
number determines what Internet service this packet is accessing.
For example, an IP packet with TCP port number 25 is destined for
the Sendmail port, the standard SMTP mail port on a UNIX machine.
Many sites choose to develop filter criteria based on the TCP port
number and the structure of the packet itself. Such filtering is
certainly more thorough than the simple source/address packet filter,
however, it requires an in-depth understanding of TCP/IP. Finally, filters can be created based on the location of particular bits
within each packet. Such filtering is quite valuable to those who have
mastered the intricacies of TCP/IP.
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