E-MAIL DIAL: Controlling Costs

To
control e-mail dial costs, Motorola has designed Instant
Access Mail-Watch to monitor and control ISDN call charges
associated with ISP-based e-mail services. It is claimed to
deliver significant cost savings in multi-user LAN
environments while at the same time requiring no additional
configuration of the client PCs. And it is a feature
embedded totally within the instant access router; is
totally transparent to the user, and requires no additional
software or hardware.

Application
Scenario

In
a typical e-mail service for small businesses and remote
offices (Figure 1), the office location may consist of a
number of e-mail clients. In this scenario, each PC will
independently poll for e-mail after a set interval using
Post Office Protocol version 3 (POP3). The polling interval
is configurable and may be anywhere from every minute to,
perhaps, once per day. The basic steps in the mail transfer
are summarized in figure 2.

This
sequence appears quite efficient, because the connection is
only open long enough for the exchange to take place.
However, a complication is introduced with the "minimum
call duration" setting on the router. Most services
assume a fixed fee or "minimum call charge" for
the first three to five minutes (the connection
establishment tariff). Closing and re-opening calls inside
this "minimum call duration" has the effect of
creating more "call minutes" than were actually
used hence inflating the monthly charge.

After the expiry of
the "minimum call duration", most ISDN service
operators charge in fixed time segments. The idle timer
ensures that the connection is closed after no data has been
exchanged for the time set. So the actual steps would be
more accurately represented as:

E-mail client (PC) sends a poll to the mail server over the LAN

E-mail client (PC)
sends a poll to the mail server over the LAN

The time elapsed
between steps 3 (end of response) and 5 (closing of
connection) and between the poll and response represents
wasted "bandwidth"–time when the ISDN call is
open but no data is being exchanged. If this wasted
bandwidth could be exploited by other clients, then
significant savings could be realized.

Polling frequently,
raises the dial connection to the Internet equally
frequently resulting in a high ISDN call charge. For a
single client, reducing the polling interval will reduce the
call charges but this may be of little use with multiple
clients because the clients are not synchronized. 

The fundamental issue
preventing this is that there is no means to synchronize the
polling between individual clients on the LAN.

Conventional
Solutions

Using
conventional technology, it is possible to install an
additional PC on the LAN to act as the mail server. This
machine polls the Internet or head office-based server at a
site-based polling interval and retrieves mail on behalf of
all the clients. It does this independently of the client
polls. E-mail clients are then set to poll the local mail
server at a more frequent rate. The local server will
respond to the local polls in accordance with whether any
mail messages have been retrieved or not.

This solves the immediate problem

This solves the
immediate problem of synchronizing the polls but has a
number of disadvantages like additional expense,
configuration and support expertise, etc. 

The
MailWatch Solution

This
is a solution that not only synchronizes client polling to a
combined site polling rate, but achieves this without any
reconfiguration of local devices. The principles of the
MailWatch operation enable:

• The clients to be
  configured to poll a central mail server at the ISP in
  the normal way.

• The router to be
  configured with a "forwarding window". This is
  the time window during which client polls will be
  permitted to open an ISDN connection to the Internet.

• If a poll is
  received during this window, then it is simply relayed
  to the server in the normal manner.

• If a poll is
  received outside of this window, then the router
  intercepts the poll and responds with a "no
  messages present" reply to the client, causing the
  client to believe that it has successfully polled the
  server.

• If a client has
  e-mail to send, this request will be permitted to open
  the connection whether within the window or not. This
  instance is typically far less frequent than normal
  polling.

In this way, local
clients can be set to poll frequently to check e-mail but
only the polls falling in a polling window will pass over
the link. The window can be configured to repeat on a
regular basis throughout the day and can be adjusted to take
account of special needs at certain times and days of the
week.

By configuring the
MailWatch service on the router, the end user or managed
service vendor can minimize costs for the user associated
with dial-based e-mail services. Because the feature is
configured on the router, no additional cost is incurred for
additional hardware and software and no additional support
is required. The user is also protected against PC users on
the LAN inadvertently misconfiguring e-mail clients.
Teleworkers and mobile workers can gain access to their
e-mail from all locations since the e-mail server remains in
the backbone of the ISP network. No office dial-in service
is required. An advanced feature of MailWatch permits
"first time polling" to be passed through to the
ISP mail server at any time, independent of the
"forwarding window". This allows a user to come
into the office, collect e-mail and then go on to the next
meeting. From this point, they are synchronized with the
other clients.

Courtesy : Motorola