Telecommunications Networking II
Topic 24
Internet Wrap-up
Dr. Stewart D. Personick
Drexel University
Copyright 2002, S.D. Personick. All Rights Reserved.
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Ref: the New Yorker magazine
Copyright 2002, S.D. Personick. All Rights Reserved.
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On the Internet …
• Arfie wants to send a copy of this New Yorker
cartoon to his friend Fuzzball
• Arfie works at the Laboratory for Canine
Sciences (LCS) at MIT
• Arfie’s Internet address is Arfie@lcs.mit.edu
• Arfie has Fuzzball’s business card:
Copyright 2002, S.D. Personick. All Rights Reserved.
3
Fuzzball
fb@eecs.berkeley.edu
Copyright 2002, S.D. Personick. All Rights Reserved.
4
On the Internet...
• Arfie uses his scanner to “capture” the
cartoon as a bit-mapped image:
3 inches x 4 inches using 600 x 600 dpi
scanning;
1 byte per dot (pixel) =>
3 x 4 x 600 x 600 x 1 byte = 4.32 MB
Copyright 2002, S.D. Personick. All Rights Reserved.
5
On the Internet...
• Arfie will be sending this file to Fuzzball
• Arfie “brings up” his mail application; enters
Fuzzball’s domain and user name:
fb@eecs.berkeley.edu; attaches the 4.32 MB
file; enters a subject line and a brief plain text
note; and pushes the “send button”
Copyright 2002, S.D. Personick. All Rights Reserved.
6
On the Internet...
• Arfie’s host computer needs to translate
fb@eecs.berkeley.edu into a 4-byte IP a
address
• It sends a query to Arfie’s domain name
server asking for this translation. This query is
sent using UDP (transport layer protocol)
inside of an IP datagram…inside (initially) an
Ethernet frame
Copyright 2002, S.D. Personick. All Rights Reserved.
7
DNS Query
Ethernet
Frame
UDP Header
DNS query
IP Header
Copyright 2002, S.D. Personick. All Rights Reserved.
8
On the Internet...
• Arfie’s local DNS server at MIT doesn’t have
a cached translation for
fb@eecs.berkeley.edu….so
• Arfie’s host computer sends a query to .edu
to find out where the eecs.berkeley.edu DNS
server is
• It then sends a query to the
eecs.berkeley.edu DNS server, at it’s IP
address, to find out what the IP address of
fb@eecs.berkeley.edu’s mail server is
Copyright 2002, S.D. Personick. All Rights Reserved.
9
On the Internet...
• Arfie’s host then opens up a TCP connection
to Fuzzball’s mail server; and proceeds to
send a sequence of TCP segments
• Each TCP segment contains a piece of the
~13MB message. Arfie’s connection into the
Internet, at layer 1-2 consists of an wireless
802.11b link terminating on a 10Mbps
Ethernet, leading into a 155 Mbps access line
to MIT’s Internet service provider
Copyright 2002, S.D. Personick. All Rights Reserved.
10
Arfie
MIT
Cambridge MA
Wireless
Port
Router
802.11b
10 Mbps Ethernet
155 Mbps
100 Mbps Ethernet
The propagation delay
between MIT and
Berkeley averages .03
seconds (~ 2.5 speed of
light delay)
Backbone of the
Internet
Router
155 Mbps
eecs.berkeley.edu
mail server
Berkeley CA
Copyright 2002, S.D. Personick. All Rights Reserved.
11
On the Internet
• Limitations on the speed with which this
message can be sent are:
-The data rate on Arfie’s 802.11b wireless
connection
-Congestion on Arfie’s 10Mbps Ethernet
-Congestion elsewhere in the path between
Arfie’s computer and Fuzzball’s mail server
-TCP window size (flow control) limitations
Copyright 2002, S.D. Personick. All Rights Reserved.
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