D-Link DCS-930L Wireless N Network Camera - Csci6433.org

bloatdecorumSoftware and s/w Development

Oct 30, 2013 (3 years and 10 months ago)

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1

CSCI 233

Internet Protocols

Class 8

David C. Roberts

Agenda


An Interesting Internet
Product


Remote Login Applications
--
TELNET


File Transfer Applications

FTP, NFS


Mail Applications

SMTP, POP, IMAP

2

New Product


Scanning Internet Camera


Pans, zooms, produces Internet video


Connects directly to the Internet


Doesn’t need a server

3

4

5

D
-
Link DCS
-
930L Wireless N Network Camera

The D
-
Link DCS
-
930L Wireless N Network Camera comes with
everything you need to quickly add a surveillance camera to your home
or small office network. It works right out of the box. Simply connect
the cables, plug in the camera, run the short installation wizard and
setup is complete. To view what the D
-
Link DCS
-
930L Wireless N
Network Camera is seeing, simply log on to mydlink.com, choose your
device, and start viewing
-

there is no need to configure your router to
open up ports or remember hard
-
to
-
memorize Internet addresses.
Order the D
-
Link DCS
-
930L Wireless N Network Camera today!

What It Can Do

6

DDNS


What is DDNS?


How do you think it works?

7

DDNS


Runs as DDNS server


Works
with dynamic IP addresses


Software is added to host machine to provide IP address to
DDNS at startup


DDNS service maps DDNS name to dynamic IP address

8

Uses of The Product


Monitor any space; just connect it to the Internet


Control, monitor the camera from anywhere you have Web
access


Shows the power, capability of the dumb network that is
available everywhere

9

AND NOW. ON TO TELNET

10

Remote Login


TELNET

is one of the Internet’s oldest protocols

defined in
the 1960s


Each computer used to have a terminal wired to it to control it


Hard to control a large complex of computers, and lots more
terminals than desired


TELNET allows user to establish login session on remote
machine and execute commands


Client
-
server
model can provide services to multiple machines


Using TCP, interactive use of remote machines can also be
provided

11

TELNET Protocol


TELNET establishes TCP connection, passes
keystrokes from user’s keyboard to the remote
computer, brings back output to the user’s
screen


Services:


Network virtual terminal

standard interface


Client and server negotiate options


Both ends of connection treated symmetrically

12

TELNET Virtual Server (NVT)


TELNET client translates from user terminal format into NVT
format


Server translates NVT into local OS requirements


13

TELNET Client and Server

14

TELNET NVT Control
Characters

15

Some TELNET
Commands

16

Current Uses


Today TELNET is used mostly within an installation for control
of computer systems


Largely replaced for general use by end users for remote
access to desktops


However, it’s the foundation of my ISP’s business!

17

Summary


High
-
level services provide important functionality to TCP/IP


TELNET is one of those services


TELNET provides a remote control console


Implemented across many operating systems

18

Methods for File Sharing


Remote file access


File transfer


Peer to peer

19

File Transfer Protocol


File transfer


Interactive access


Format specification


Authentication control

20

Process Model


Server allows concurrent access by multiple
clients, using TCP/IP


Control and data transfer connections are (often)
separate


Client and server usually each have separate processes
for control, data transfer


Data transfer processes and connections are created
and dropped as needed, but control connection
persists during a session


21

FTP Client and Server

22

FTP Port Number Assignment


Client uses random, locally determined port to
connect to server


Client connects to port 21 at the server (a well
-
known port)


Client gets (another) unused local port number,
connects to port 20 at server for data transfer
connection


TELNET network virtual terminal protocol is used
for the control connection; but only basic NVT
definition.

23

FTP Session Establishment

24

Modes


Active mode: client sends the server the IP
address and port number on which client will
listen, and server initiates TCP connection.


Passive mode: (used if client is behind firewall
and unable to accept incoming TCP connections)
client sends a PASV command to the server and
receives an IP address and port number in
return. The client uses these to open the data
connection to the server.

25

Active Connection

26

Passive Connection

27

Representations


ASCII mode: for text. Data converted from the sending host's
character representation to 8
-
bit ASCII before transmission,
and to the receiving host's character representation.
Inappropriate for files that contain data other than plain text.


Image (aka Binary) mode:
sending
machine sends each file
byte for byte, and
recipient
stores the
byte stream
as
received.


EBCDIC
mode: use for plain text between hosts using
IBM’s
EBCDIC
character set. This mode is otherwise like ASCII mode.


Local
mode: Allows two computers with identical setups to
send data in a proprietary format without the need to convert
it to ASCII

28

Trivial File Transfer Protocol


Inexpensive, unsophisticated service


Simple file transfer, no authentication


Runs over any unreliable packet system


Sending side sends 512 byte file, waits for ACK for each block,
then sends next one


First packet specifies the transfer


Block of less than 512 octets indicates end of file

29

Question: Why would anyone use TFTP when there is also FTP?

NFS

Network File System


Originally developed by Sun Microsystems


Allows computer to access a remotely stored file over an IP
network or the Internet


30

NFS Implementation

31

How NFS Fits

32

Peer to Peer

33

Peer to Peer File Sharing


No notion of clients and servers


“peer” nodes function as both client and server to one
another


Foldershare

uses peer
-
to
-
peer protocols

34

Peer to peer

Client
-
server

Types of Peer to Peer Networks


Structured
:


Peers are organized following specific criteria and algorithms, which lead to
overlays with specific topologies and properties. They typically use distributed
hash table
-
based (DHT) indexing.


Unstructured
:


No algorithm for organization or optimization of network connections



P
ure peer
-
to
-
peer systems: entire network consists solely of equipotent peers. There is
only one routing layer, as there are no preferred nodes with any special infrastructure
function.


Hybrid peer
-
to
-
peer systems: may have infrastructure nodes to exist, often called
supernodes.


Centralized peer
-
to
-
peer systems: central server is used for indexing functions and to
bootstrap the entire system. Connections between peers are not determined by any
algorithm.

First prominent and popular peer
-
to
-
peer file sharing system,
Napster, was centralized. Gnutella and
Freenet

are decentralized.
model.
Kazaa

is hybrid.

35

Advantages of Peer to Peer


No single point of computer failure


No single point of network failure


No traffic congestion at servers


No need for high
-
capacity server


Uses available capacity of client machines

36

Disadvantages of Peer to Peer


Near
-
simultaneous updates of the same file can cause lots of
network traffic


No guarantee of timeliness

37

Summary


Forms of access to remote files:


Whole
-
file copying


Shared on
-
line access


FTP uses whole
-
file copying, allows users to list
directories as well as transfer files in either
direction


TFTP provides a simple means for file
transfer


NFS provides file system emulation


Peer to peer provides file transfer without
servers, but with potential timeliness problems

38

Electronic Mail

Email allows users to send memos across the Internet.


Notes can be short or quite large


Notes can have multiple attachments


Must work when remote machine is unreachable

39

Actors in the Email System


Post Office


SMTP servers move email between each other


SMTP servers store email for delivery to end users


Users


POP clients pick up email from SMTP servers


POP clients hand outgoing mail to SMTP servers

40

Delayed Delivery

41

Sender and receiver do not need to be connected to
the server at the same time

Alias Expansion, Mail
Forwarding

42

Internetworking and Email


TCP/IP internet makes universal delivery service
possible


Mail systems built on TCP/IP are inherently
reliable because of end
-
to
-
end delivery


Alternatively, mail gateways are used


Allow mail transfer between different systems


When gateway has a message, sender discards it

43

Question: Is email through a gateway better or worse than a direct
SMTP transfer?

TCP/IP Email Standards


Format and computer interaction are specified separately


Format: header, blank line, body


Body unspecified


Header is key word, colon, value


Some keywords required, others optional


Header is readable

44

Email Addresses



local
-
part @ domain
-
name



domain
-
name:
name of mail destination


local
-
part:
address of a mailbox at destination

Note: when gateways are employed, mail addresses are site
-
dependent

45

SMTP


Simple Mail Transport Protocol


Focuses on how mail delivery system passes messages from
one machine to a server on another machine


Does not specify anything about user interface


Does not specify how mail is stored


46

Assured Delivery


SMTP server forms TCP/IP connection with
receiving server


Once receiving server has put message into safe
store, then it acknowledges and sender discards
message


If SMTP can’t transfer message on the first try, it
keeps trying


After several days of failure, SMTP reports failure
to deliver.

47

SMTP Highlights


All communications is readable ASCII text


Transcript of interactions is readable


Each message is acknowledged separately


Addresses of the form local
-
part@domain
-
name


48

Example Transfer

S: 220 Beta.GOV SMPT ready

C: HELO Alpha.EDU

S: 20 Beta.GOV

C: MAIL FROM:
Smith@Alpha.EDU

S: 250 OK

C: RCPT TO:
Green@Beta.GOV

550 No such user here

RCPT TO:
Brown@Beta.GOV

250 OK

C: DATA

S: 354 Start mail input;end with <CR><LF>.<CR><LF>

C: ..sends body of mail message

C: <CR><LF>.<CR><LF>

S: 250 OK

C: QUIT

S: 221 Beta.GOV Service closing transmission channel

49

Client establishes connection

Sent by server

Sent by client

Mail Retrieval and Mailbox
Manipulation


POP3

Post Office Protocol


POP3 client creates TCP connection to POP3
server on mailbox computer


Mailbox computer runs two servers:


SMTP to place mail into user mailboxes


POP3 server to allow user to extract messages from
user mailbox


POP3 retrieves messages, deletes from user
mailbox


Two servers must coordinate use of the user
mailbox


50

MIME Extension for Non
-
ASCII
Data

MIME

Multipurpose Internet Mail Extensions


Defined to allow transmission of non
-
ASCII data
through mail


MIME allows arbitrary data to be encoded in
ASCII, transmitted as standard email message


MIME message tells recipient type of data, type
of encoding used


Data type and subtype is specified


MIME information is in 822 mail header

51

MIME Content Types

52

MIME Example

From:
bill@acollege.edu

To:
john@example.com

MIME
-
Version: 1/0

Content
-
Type: image/gif

Content
-
Transfer Encoding: base64


….data for the image….

53

Mail Retrieval, Mailbox
Protocols


Post Office Protocol

client login with userid/password


Client can then retrieve, delete messages


Server computer must run two servers: POP and SMTP


POP and SMTP must coordinate use of mailbox

54

Internet Message Access Protocol


POP stores messages offline; not compatible with the use of
multiple computers


IMAP allows message access, manipulation from multiple
computers


Platform
-
independent access to mail

55

Question: How does server resource usage of IMAP compare with POP?

Summary


Email is a very important Internet service


Separate standards are used for message format and
transfer


SMTP

how a mail system on one machine transfers to a
server on another


POP3

how a user can retrieve contents of a mailbox


IMAP

user protocol for use from multiple computers


MIME allows arbitrary data to be exchanged using SMTP

56

Thank you!