Network Protocols

1

• Network Protocols

2
Objectives

• At the completion of this lecture you should be
  able to
• explain what protocols are
• describe the basics of a packet switched network
• differentiate between IP, TCP and DNS
• use the FTP protocol
• use the Telnet protocol
• Understand the historical nature Gopher protocol
• explain the difference between WWW, FTP, Telnet
  and HTTP

3
What is a protocol?

• Protocol in general
• - an acceptable way of behaving.
• - driving on the left hand side of the road
• - how to participate in a tutorial discussion.
• Protocols are critical and there must be
  agreement on them.
• A network protocol
• Is the set of very detailed rules, sequences,
  message formats, and procedures that computer
  systems use and understand when exchanging data
  with each other

4
Examples of Protocols

• File Transfer Protocol (FTP)
• Telnet
• Hypertext Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• Gopher
• WWW (World Wide Web)

5
Packet Switched Network

• Network
• a collection of connected computers
• A switched network
• computers connected via multiple links - data is
  switched from one machine to the next until it
  reaches its destination.
• Packet Switched Network (PSN)
• message is broken into chunks called packets
• packets sent - but not necessarily via the same
  route.

6
TCP/IP

• Transmission Control Protocol/Internet Protocol
  (TCP/IP)
• ARPANET was converted to use TCP/IP which allowed
  the formation of the Internet
• It is a group of protocols that allows networked
  computers to communicate with each other
• It doesn't matter whether
• they are part of the same network or are attached
  to separate networks.
• one computer is a mainframe and the other a
  Macintosh.
• TCP/IP is a platform-independent standard that
  bridges the gap between dissimilar computers,
  operating systems, and networks

7
More on TCP/IP

• So TCP/IP allows two computers to exchange data.
  This is achieved as follows
• When two or more networks are involved they are
  physically connected by devices called IP
  routers. A router is a computer that transfers
  packets of data from one network to another.
• TCP/IP software makes everything seem like one
  big network. That is, TCP/IP has the affect of
  allowing two separate networks to communicate as
  though they were part of the same physical
  network.

8
What is the family of TCP/IP protocols?

• Some of the common TCP/IP application protocols
  include
• File Transfer Protocol (FTP),
• Telnet,
• Domain Name System (DNS),
• Simple Mail Transfer Protocol (SMTP),
• Multipurpose Internet Mail Extensions (MIME),
• X Window System,
• Dynamic Host Configuration Protocol (DHCP).

9

• SO HOW DOES TCP/IP WORK?

10
Firstly the Internet Protocol (IP)

• Allows for data to be sent over the Internet
  occurs in packets contains from 1 - 1500 bytes of
  data
• each packet is given a destination IP address
• An IP address is an unique identifier for a
  particular computer on the Internet
• The addresses include four eight-bit octets,
  which are often written in decimal format for
  simplicity. To illustrate this, it is easy to see
  that the following address 10000111.10100101.00100
  011.11110000 is more easily written and
  understood as 135.165.35.240

11
More on IP

• It is a connectionless protocol meaning that all
  packets are sent on a "best effort" basis.
• There is no guarantee that the packets will get
  to the destination in the order they that were
  sent, or even at all.
• Therefore the problems are
• packets may get lost
• packets may arrive out of sequence
• the message may be longer than 1500 bytes
• Answer .
• Another protocol .

12
The second protocol Transmission Control
Protocol (TCP)

• ensures a sent message is sent without any loss
  of data or any mix up of the order of the data
• will request re-transmission of lost or damaged
  packets.
• How does it do this?
• a long message is broken up into many IP packets
• each packet have a number allocated to it
• there is error checking
• damaged or missed packets may be asked for again

13
Domain Name System

• Every computer on the internet has a unique
  address (like a unique phone number) called an IP
  address
• 137.66.125.5 - such numbers are difficult to
  remember
• Domain Naming Service (DNS), an Internet protocol
  and distributed database, provides more English
  like names for IP addresses.
• DNS names are easy to understand, for example
  www.microsoft.com equates to 198.105.232.6

14
DNS Who controls it?

• Translating the name into the IP address is
  called resolving the domain name.
• ICANN is the global non-profit, private sector
  body responsible for ensuring the operability of
  DNS. It overseas the distribution of unique IP
  addresses.
• So how does DNS work when you enter a domain name
  into your browser?
• DNS - divides each IP address into top-level
  domains, sub-domains, sub-sub-domains etc a bit
  like a hierarchical type diagram.

15
How does DNS work?

• At the heart of DNS are 13 special computers
  distributed around the world containing the same
  information these are called root servers
  maintained by ICANN.
• These root servers contain the IP addresses of
  all the Top Level Domains (TLD) registries. A TLD
  registry contains all the information about every
  top level domain names for example, .edu.au,
  .org, .com.uk etc are examples of TLD.
• There are also thousands of other computers
  scattered around the world typically located
  with ISPs or other network suppliers called
  Domain Name Resolvers. They are used to resolve
  the remaining parts of the domain name.

16
Resolving a domain name ..

• So you enter a URL (e.g. www.csu.edu.au)
• This request is sent to a local resolver (e.g. at
  tgp.com.au)
• This local resolver splits the request and knows
  where to find the edu.au register and therefore
  sends the whole URL to one of the 13 root
  servers.
• The register responds with the IP address for
  csu.edu.au
• Then the local resolver queries the csu.edu.au
  register to find the final IP address for
  www.csu.edu.au

17
Root server
EDU
COM
ORG
GOV
CSU
ANU
MONASH
CSUSAP
18
Structure of Internet host names

• Example http//lorenz.mur.csu.edu.au
• The process is to read backwards
• au Australia
• edu - educational institution
• csu - name of the institution
• mur - a physical location indication Murray
• lorenz - actual machine name

19
Naming Conventions for DNS

• As you are aware DNS is made up of a sequence of
  labels separated by periods (.). Also note
• Each label has a maximum of 63 characters
• Total name can only be 255 characters.
• The organisation that owns a domain name is
  responsible for its local DNS server it
  provides the mapping between the hostname and the
  IP

20
Allocation of DNS

• In Australia this is administered by APNIC Asia
  Pacific Network Information Center
• It is one of four Regional Internet Registries in
  the world
• Is charged with ensuring the fair distribution
  and responsible management of IP addresses
• Executive of seven members to oversea its
  operations with 62 countries across the region.
• http//www.apnic.net

21
Top level domain names

• Examples of these include edu, com, gov, net,
  org, mil
• Latest top level domain names (introduced in
  2000)
• Biz business
• Info for all users
• Coop cooperatives
• Aero air-transport industry
• Museum museums
• Name for individuals launched January 2004
• Pro - professionals

22
Rules for allocating second level domain names

• Must be a distinct name (e.g. csu)
• Cannot be a place
• Is not a generic product e.g. pizza, car,
  restaurant etc.
• Is not a generic name describing an organisation
  or an industry e.g. bank, pharmacy, tennis etc.

23
So how do I register a domain name?

• Domain names ending in .aero, .biz, .com, .coop,
  .info, .museum, .name, .org or .pro are
  registered through registrars refer to
  http//www.internic.net/regist.html
• once registered your details are sent to other
  computers with your specific details

24
What is File Transfer Protocol (FTP)

• protocol that allows for the transfer of files
  across the Internet.
• both computers need to run FTP - one acts as a
  server (remote), the other as a client (local).
• mainly shareware type of files.
• usually stored in ZIP format or self-extracting
  EXE
• disadvantage must know the name of the file you
  are after

25
How can I FTP?

• Steps to FTP
• 1. log on to machine e.g. to csusap
• 2. Connect to a another remote machine by either
• a. anonymous FTP - very common - but can only
  access files in the pub directory.
• login name anonymous password ltyour email
  addressgt e.g. jatkinson_at_csu.edu.au
• Anonymous FTP allows users to enter public data
  archives and download file

26
How can I FTP?

• b. log in as yourself - this requires you to have
  an account on that machine i.e. username and
  password.
• This is what you do on CSUSAP
• Typically these machines are UNIX boxes

27
Pictorial explanation of FTP
get file1.txt
Computer B
Computer A
file2.txt
put file2.txt
file1.txt
Computer B has established an FTP session with
Computer A and issues the get and put statement
Both Computer A and Computer B have FTP running
28
FTP

• Basic commands with FTPing
• ftpgtopen csusap.csu.edu.au - establishes FTP
  session
• ftpgtls -l (List Long) equivalent to dir on the
  remote machine
• ftpgtcd . Changes to a new directory on the
  remote machine
• ftpgtquit (or perhaps exit) - terminates an FTP
  session

29
Which FTP program do I use?

• A number are available
• WINQVT - traditionally used on Windows 3.1
• Unix ftp - activated through Start, Run, ftp
• CuteFTP - excellent, windows based, easy to use
• WS-FTP - an FAQ exists for it on the ITC125 site
• Tucows - excellent repository for FTP programs
  (www.tucows.com)
• Web browser - e.g. Netscape/Explorer to retrieve
  files

30

• Another practical example of how to use WS-FTP

31
FTP - summary

• The FTP protocol is responsible for allowing the
  transfer of files from one computer to another
  (and vice versa). To do this
• The FTP program must be running on both
  connecting machines.
• You need to login to the remote machine to
  establish the formal link to allow transfer to
  occur.
• There are two types of FTP connection anonymous
  (where you connect to a public transfer area) and
  personal (where you login to your FTP space).
• You can upload and/or download files to the
  connection machine

32
What is the Telnet protocol

• Telnet is a protocol that allows for one machine
  to connect to another computer on the Internet.
• Basically one computer utilising the resources on
  another computer local machine a dumb terminal
• is still based on TCP/IP
• some 40 Request for Comments (RFCs) specify the
  nature of the Telnet protocol
• Why have a telnet session?
• a local machine can access remote computer
  hardware
• reduces organisations hardware costs
• still used to connect to library servers.

33
ITC125 The Information Super Highway
Telnet protocol
Computer B
Computer A
program S program Y
Computer B has established a telnet session with
Computer A and can now access the programs and
resources on Computer A
Both Computer A and Computer B have telnet
running
34
Historical information interest only .

• Gopher - only develop in 1992
• - returns a series of menus (which you search
  through) - these point to other menus
• - Gopher will go and locate the information for
  you
• - no longer popular because of the WWW.
• Wide Area Information Service (WAIS)
• - basically an indexing tool for information on
  your server

35
WWW

• World Wide Web (WWW)
• a protocol that uses hypertext links
• accessed by using a browser
• Uniform Resource Locator (URL) - a specific
  address to a particular resource.
  protocol//host/directory/resource
• Examples
• http//csu.edu.au/images/csu.gif
• ftp//ftp.monash.edu.au/pub/win95/update.txt
• telnet//csusap.csu.edu.au
• newsauscomputing

36
Other Web based protocols - HTTP

• 'HyperText Transfer Protocol' is the primary
  protocol of the World Wide Web (WWW)
• When a Web browser connects to a Web server, it
  uses HTTP to request Web pages
• A Web browser is an Internet client application,
  and the Web server is an Internet server
  application
• HTTP has the ability to transfer Web pages,
  graphics, and any other type of media that is
  used on the Web.

37
Please note ..

• Extensible HyperText Markup Language (XHTML) is
  not an Internet protocol
• It is a means to format of Web pages
• It consists of a set of tags and internal
  commands that are embedded inside Web pages to
  control the appearance and layout of Web pages,
  as well as links to other Web pages