DETEWE OpenCom 510, User Manual

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Useful Information on Internet Access Configuration Examples
E-mail
One of the most important services
in the Internet is e-mail. E-mails are
buffered in individual e-mail ac-
counts on a mail server. Mail servers
are operated by ISPs for example.
With the OpenCom 510 you can set
up one or more e-mail accounts for
every user account configured on
the OpenCom 510. These e-mail ac-
counts are then checked at regular
intervals.
If there are new e-mails in an e-mail
account, and the OpenCom 510 has
been configured for this function,
the user specified in the
OpenCom 510 user account is noti-
fied of the new e-mail on his system
terminal. System telephones from
the OpenPhone 6x and 2x product
range can also display information
such as the sender or the subject of
the e-mail.
NAT
Network address translation (NAT) is
activated on accessing the Internet
(ISP). You require this feature in or-
der to translate internal IP addresses
to valid external IP addresses. This
has three important consequences
for Internet access:
■
Several workstations can share a
single Internet access. You do
not require a LAN access, only a
single account with the Internet
service provider.
■
The IP addresses used in the LAN
are translated into IP addresses
valid worldwide. So you require
no such addresses for your LAN.
■
Only TCP/IP connections trig-
gered from a workstation can be
established. Consequently, while
you can call up Web pages from
a workstation, you cannot install
a Web server visible in the Inter-
net on a workstation.
Certain protocols cannot be used
when NAT is being used. This affects
protocols with the following proper-
ties:
■
TCP/IP addresses are trans-
ported in the useful load, e.g.
NetBIOS over TCP/IP.
■
The protocol requires an active,
inward-directed connection es-
tablishment, e.g. ICQ.
■
The protocol will function with-
out TCP/UDP port numbers, e.g.
ICMP or IGMP.
The OpenCom 510 NAT has suitable
processes for ensuring the functions
of many important protocols af-
fected by these rules. These are the
protocols FTP (in “active” mode), Cu-
SeeMe (“videoconferencing”), IRC
(“chat”), ICMP errors (“traceroute”)
and ICMP echo (“ping”).