what operations does a router perform on an email message

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Request for Question Clarification by seizer-ga on 20 Aug 2002 16:43 PDT

Could you elaborate on your question a little, please? Routers don't
deal directly with email messages, so if you could put your question
in context, I might be able to explain a little more about what's
going on. Thanks!

Dear mskrissy,

I think this University of Sutherland article on network connections
will help to explain the relationship between email and routers...

http://www.cet.sunderland.ac.uk/~cs0rwa/ITE/Lecture7.htm

One of the most important keys to understanding networks is to
understand the concept (not necessarily the detail) of the ISO 7 layer
model. In the various diagrams of the aforementioned paper there is a
stack referred to as the ISO 7 layer model. The layers are:
application, presentation, session, transport, network, datalink and
physical. Communication occurs vertically up and down the stacks
within a device (computer or router), but internetwork communication
is performed mainly below the network layer. ie email application
programs do not talk directly with each other, but rely upon lower
layers for the interconnection.

The top and the bottom layers are very easy to remember, the layers in
between are somewhat murkier, but some can be related to different
network functions of your operating system:

The email program is considered to be on the top layer as an
application - it "communicates" with text that you can see and bits
that you don't.
The network card of your computer is considered on the bottom layer of
the stack it's primary means of communication can be considered to be
via physical voltage levels.

A router is in the "middle" at layer 3 and communicates using IP
addresses with which you are probably familiar. Without routers the
internet would collapse as packets would not know how to hop from your
computer to others on the internet to reach their final destination.

For example, after you select send in your email program your computer
sends some packets with an address 216.239.33.101 to its nearest
router. The router recognises this as an address outside your local
network (because it has thus previously been configured) and directs
the packet to an adjacent router "moving away from your computer"
towards the internet site. Thus packets containing your email data
will hop from router to router (or other device) until it reaches its
destination address. The destination computer will then be responsible
for "moving" the packet back up the layers to the receiving email
program.

________

This Lucent paper tracks an email through the layers in more detail,
please see p2 of document and further into the document provide more
details as to various router operations:
http://www.lucent.com/certification/pdf/study001.pdf

Google Search Strategy:
"operation of a router" OSI application
 OSI " email example" router
_________

I meant my text to provide a simplified explanation, while the links
go to greater depth. If you would like further clarification, please
select the button.

Regards,

could have been more technical but good resource links were given