CSC 96b Building and Managing Web Sites with Microsoft Technologies

1
CSC 96bBuilding and Managing Web Sites with
Microsoft Technologies

• Week 2 Lecture
• Networking Protocols

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Client/Server Architecture

• Servers
• Provide content to clients
• A machine (box) provides many services
• Example web/e-mail server at a company
• Clients
• Use/Request content provided by servers
• Clients rely on programs to front end the
  services
• Example browsers (IE, Netscape, Opera)

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Three Layer Model for Client/Server

• An idealized model for what client server is
• User Interface
• Business Logic
• Storage
• Client server is that idealized model it can be
  implemented any number of ways
• Example http//www.ciwmb.ca.gov/calmax/

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Client/Server Servers

• Typically servers are fixed resources. If they
  are on the Internet they have the same fixed IP
  address.
• Servers run operating systems such as Windows NT
  or Linux designed to be multitasking and to run
  unattended for long periods.
• Server hardware is different from PCs or Macs.
  Server hardware is designed to support multiple
  users and to be on all the time.
• Many sites use redundant server hardware so that
  the services they provide are available all of
  the time.

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Client/Server Clients

• In addition to web browsers, there are many
  different types of clients
• FTP software
• Video/Audio player browser add-ons
• Internet Telephony Applications
• News service feeds
• Custom applications that connect to databases
  over the internet.

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Networking

• "Networking is the / in client/server"
• - Pablo Fung.

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The ISO OSI Model (1974)

• ISO International Standards Organization
• Home Page (English) http//www.hike.te.chiba-u.ac.
  jp/ikeda/ISO/home.html
• OSI Open Systems Interconnection
• Presents an abstract 7 layer model of networking
  generally. All successful network schemes
  implement all or part of this model.
• The Internet would not exist except for the work
  of pioneers who built on this standard.

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ISO OSI Model
From (in part) Atlantic Technology Group
http//www.atlantic-tech.com/osimodel.htm
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Layers 1 2 The "Wiring".

• Notice that all of the different "models" the
  Internet -- Microsoft Networking, Novell, etc. --
  are all built on the same two layers.
• As a matter of implementation this is actually
  true. You can switch freely between different low
  level protocols and wiring schemes if your
  hardware and O/S supports it. (Slots to put cards
  in. Drivers to run the cards.)
• This means vendors can build better and faster
  hardware that existing systems can take advantage
  of. For example, we are experimenting with 100mps
  Ethernet upgrades, we swap out the card, add a
  new driver, plug in the wire to a 100mps hub, and
  we're ready.

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Layers 3 and 4 TCP/IP

• For the Internet, will be dealing with
  "Transmission Control Protocol/Internet Protocol"
  (TCP/IP)
• TCP/IP protocol is the glue that links the
  computer networks of the Internet, regardless of
  their hardware and software configurations.
• TCP/IP is a set of rules for
• A transport for carrying data
• Rules for how transport occurs
• Methods to insure that data arrives error free
• TCP/IP is open and non-proprietary

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IP Protocol

• Handles addressing and basic transport
• Each machine on a particular network must be
  assigned a unique IP address
• IP address is 4 smaller numbers separated by
  periods. Each number between 0 - 255 (hence each
  takes one byte)
• Examples
• 207.46.131.137 is a server at Microsoft
• 12.16.135.5 is Valtara.com
• 205.225.229.1
• Use PING to discover IP addresses.
• IP Address in America are handed out by American
  Registry for Internet Numbers (ARIN).
  http//www.arin.net/

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Limited Numbers

• Since each machine on a network has to have a
  unique IP address this would tend to limit the
  number of machines on a network such as the
  internet. And in fact the amount free numbers is
  running out. However
• Some of the 1st folks on the internet (Arpanet)
  have lots of unused numbers they could/do
  rent/sell.
• Proxy technology helps by allowing one scheme of
  numbers on one side of the proxy and another
  single number to the outside. Thus conserving
  numbers needed by an organization to connect all
  of its machines to the world. ISPs work this way.
• A new IP scheme is coming with a bigger range of
  numbers.
• Typically, you will not get IP numbers from ARIN
  directly -- rather you will contract with an ISP
  or TelCo for them.

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IP Addresses

• IP Addresses are divided into classes (A,B, or C)
  depending on the value of the first 3 bytes.
• Network address identifies a network in the
  Internet.
• Host Address identifies a computer within a
  network
• Subnet masks may be used to further divide a
  network address. Many networks dont use
  subnetting, but all addresses have default subnet
  address.

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Transmitting IP Packets

• Transmitted data broken into small chunks units
  called packets.
• Each packet contains data, source IP address, and
  destination IP address.
• Network devices called Routers forward packets
  from one network to another using routing tables
• Routing tables contain hard-coded and/or cached
  possible paths from one network to another.
• Packets routed through Internet until reach
  destination. The route may not be direct, and no
  delivery or accuracy guarantees.

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TCP Network Protocol

• TCP establishes an initial handshake between
  computers and allows retransmission of lost
  packets.
• TCP includes a port number with packets
  specifying the intended network service.
• Destination services listen for packets with that
  port number and process them.
• Depending on what service transmission protocol
  is used, sender may not wait for a response from
  the receiver (e.g., UDP).

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Ports o Call

• One of the things that makes TCP/IP really work
  as a protocol is PORTS.
• A port is simply the number of the desired
  service. For example
• Web server service usually responds on port 80
  (sometimes 8080).
• FTP is found on ports 20 21.
• News is usually on 119.
• These are called Well known ports
• If someone invents another service that needs a
  port they can pick an unused one and register it
  with the IANA. (Internet Assigned Numbers
  Authority http//www.iana.org/ ).

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TCP/IP Summary

• TCP/IP is the main protocol now used in
  internetworking. Even Novell is switching to it
  from IPX.
• Each machine on the internet has a unique IP
  address.
• The different services are said to run on ports.
• When a message is sent by TCP/IP it includes the
  IP of the sender and receiver and the targeted
  port number.
• What carries messages is largely irrelevant
  because of the wide spread acceptance of the OSI
  model.
• Its flexibility is what allows people to create
  new types of content (such as telephony and
  multimedia).

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DNS - Domain Name Service

• TCP/IP manages routing packets to destinations
  using IP Addresses, but these numbers are not
  human-friendly
• Domain Name Service is used to translate a
  human-friendly domain name to the computer IP
  address.
• E.g., DNS translates the domain Microsoft.com
  to the IP address 207.46.131.137
• DNS is a critical service for the Web

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Domain Name Services (Continued)

• The Internet is sprinkled with DNS Servers who
  maintain a list of domain names/ IP addresses.
• These machines are maintained by universities,
  ISPs, and telecommunications providers.
• also called Telcos or Telcoms
• All DNS servers build listings from downloads or
  cached lookups from the root DNS servers.
• The InterNIC (http//internic.net/) organization
  oversees the top level domains of .org, .gov,
  and .com, etc.

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Domain Name Services (Continued)
13 Root Server Authorities Top Level domain
servers (the ending suffixes) (com, net, fr, uk,
org, gov, etc) Second Level Domain. The level
under the top level domains for example the
Microsoft in Microsoft.com
DNS Cache servers located at internet
providers, government agencies, Telcos and
others. This organization forms a tree of DNS
lookups, so when a new domain is registered with
InterNIC, it propagates down the DNS tree until
it reaches local DSN caches.
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DNS (Continued)

• When you are using a browser and get a message
  Cannot open server xyz.com this is what has
  happed. Your computer could not translate xyz.com
  into an IP address.
• The WhoIs service (e.g like the site at
  http//www.whois.net/) will tell you who owns a
  particular domain name.

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Problems with TCP/IP and DNS

• Running out of address
• Only so many possible numbers.
• Who decides who gets to use what name?
• InterNIC, and other name space providers.
• Squatting
• People who grab names of companies and then wait
  for the companies to offer them at lot of money
  for the name.
• To change your IP address, you (or your ISP) will
  notify the InterNIC or other authorities to
  update the root DNS server. However, it can take
  time for the change to propagate through the
  entire Internet. This is less of a problem then
  it used to be as most Internet services do not
  cache the actual IP address.

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Protocols above TCP/IP

• OSI Layers 5-7 contain the high level protocols
  for exchanging information (content) as opposed
  to messages (packets) like TCP/IP.
• Typically even the simplest service (email, web,
  etc) relies on several protocols stacked on top
  of each other in order to get the job done.
• Protocols are thus divided into ones dealing with
  the mechanics of information exchange and those
  having to do with content and content formatting.
• Common high level internet protocols FTP, SMTP,
  HTTP.

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HTTP - Hyper-Text Transfer Protocol

• The whole point of this class.
• Each click on a lta href...gt link generates a
  request to the server to transfer the next page
  to the client.
• HTTP protocol passes client/server configuration
  information and other data back and forth.
• The protocol has gone through many evolutions
  (see Lecture 1) so that it covers forms, embedded
  objects and other extensions.

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FTP - File Transfer Protocol

• FTP is an
• Application (a user interface like WS-FTP) OSI
  layer 7
• Service runs on a server (box) OSI Layer 7
• Transport protocol OSI Layer 4
• FTP is used heavily by webmasters
• Many place downloadables on FTP servers,
  especially executable files.

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Other important protocols

• SMTP - Simple Mail Transfer Protocol
• The main mechanism for mail exchange. The
  internal format of which is usually MIME.
• NNTP - Network News Transport Protocol
• Protocol used for serving and reading rules
• IRC - Internet Relay Chat
• NFS, NIS, etc. - Network File System

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How does information get from A to B An e-mail
example
1. Sender composes a mail message in e-mail
program providing an address xyz_at_pdq.com.
2. E-mail program stores message until it is
picked up by the mailer service
3. E-mail service grabs the message from the
message store and adds SMTP information to it. If
the mail service knows the IP address for
PDQ.COM it supplies it.
4. SMTP passes the message though various layers
to TCP/IP which splits it into packets and sends
it. Using DNS to translate PDQ.COM into an IP
address if necessary. If it doesnt know the IP
address it passes it on to another machine it
knows the IP address of (designated as a gateway
(like your ISPs computer(s))) in the hope that
it knows what IP address PDQ.COM is. If no
address is ever found the message is bounced
back to the sender and passed to the mailer to
tell the user it couldnt be mailed to.
5. If a receiving computer is found, that
computers TCP/IP assembles the message and
decides it isdestined for the mail service and
passes it along. The mail service puts the
message into its mail store where it waits for
the receiver.
6. Receiver opens e-mail program and finds
assembled message waiting.
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Internet Engineering Task Force

• http//www.ietf.org/
• This is the place where scientists, engineers and
  companies form working groups to develop
  proposals for standards for lots of different
  computing areas, but particularly the Internet.
• Proposals are numbered RFC . RFC stands for
  Request For Comment.
• They have no power to compel companies or people
  to follow the standards.
• An overall desire for profit through
  interoperability drives companies to adopt and
  support the work of the IETF members.
• In the end it is the market place that decides
  which proposed standards will be widely adopted.
  Lots of them never go anywhere because vendors
  don't make stuff using the standard.

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References

• International Standards Organization Home Page
  (English) http//www.hike.te.chiba-u.ac.jp/ikeda/I
  SO/home.html
• Good ISO OSI Model http//www.atlantic-tech.com/o
  simodel.htm
• For more about TCP http//www.ee.siue.edu/rwalden
  /networking/tcp.html The CMP article on DNS
  http//www.networkcomputing.com/unixworld/pcunix/0
  04.html
• The "Home" of DNS, InterNIC http//rs.internic.ne
  t/rs-internic.html
• Way more then you ever wanted to know about how
  it all works ftp//rs.internic.net/rfc/rfc1035.txt
  and http//www.ietf.org/
• Home of internet addressing for America
  http//www.arin.org