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Title: Higher Computing Network Protocols, the OSI model and IP addresses


1
Higher ComputingNetwork Protocols, the OSI
model and IP addresses
2
What is a protocol?
  • A set of rules agreed upon in order to
    communicate successfully. These might include
  • Data format
  • Transfer speed
  • Handshaking
  • Flow Control

3
Application Layer Protocols
  • Remote access Telnet
  • File Transfer FTP
  • Information Access HTTP HTTPS
  • Email SMTP and POP3

4
Application Layer Protocols
  • Telnet used to make a remote connection to
    computer
  • FTP connect (password required) upload and
    download files remains connected
  • HTTP connect to web server, retrieve file, then
    disconnect
  • POP3 download mail from mail server password
    required
  • SMTP upload mail to mail server originally no
    password required

5
Telnet
6
FTP
  • Open hostname
  • Connected to hostname
  • 220-Microsoft FTP Service
  • User (hostname)
  • anonymous
  • 331 Annonymous access allowed, send identity
    (e-mail name) as password
  • Password
  • username_at_school.mail
  • 230 Anonymous user logged in.
  •  
  • cd remote folder
  • 250 CWD command successful.
  •  
  • Get filename.doc
  • 200 PORT command successful.
  • 150 Opening ASCII mode data connection for
    searchrep.doc(20480 bytes).
  • 226 transfer complete

7
FTP GUI front-end
8
HTTP
  • GET index.htm HTTP/1.0
  • HTTP/1.1 200 OK
  • Server Microsoft-IIS/4.0
  • Date Wed, 27 Feb 2002 100715 GMT
  • Content-Type text/html
  • Accept-Ranges bytes
  • Last-Modified Fri, 28 Apr 2000 143433 GMT
  • ETag "982f13df1eb1bf12f4d"
  • Content-Length 558
  • lthtmlgt
  • ltheadgt
  • ltmeta name"description" content"Main Page."gt

9
HTTP Front-end
10
POP3
  • OK khs.mail POP service ready 1 MDaemon v2.7
    SP5 R
  •  
  • user username
  • OK username recipient ok
  •  
  • pass password
  • OK username's mailbox has 1 total messages (813
    octets).
  •  
  • list
  • OK 1 813

11
SMTP
  • 220 khs.mail ESMTP service ready 1 MDaemon v2.7
    SP5 R
  •  
  • helo username
  • 250 khs.mail Hello ianking, pleased to meet you
  •  
  • mail from username_at_khs.mail
  • 250 ltusername_at_khs.mailgt, Sender accepted
  •  
  • rcpt tosomeone_at_khs.mail
  • 250 ltsomeone_at_khs.mailgt, Recipient ok
  •  
  • data
  • 354 Enter mail, end with ltCRLFgt.ltCRLFgt

12
POP3 SMTP front-end
13
Ports
  • FTP 21 and 20
  • Telnet 23
  • SMTP 25
  • POP3 110
  • HTTP 80 and 8080

14
Lower level protocols
  • Transmission Control protocol TCP
  • Internet Protocol IP
  • User Datagram Protocol UDP

15
TCP
  • Transmission Control Protocol Sending
  • Breaks data to be transmitted into packets
  • Each packet is given a header which contains
  • a sequence number
  • The sender and recipient IP address
  • If an acknowledgement is not received then the
    packet is retransmitted

16
TCP
  • Transmission Control Protocol Receiving
  • Reassembles packets received according to
    sequence number
  • Sends an acknowledgement
  • Waits for any missing packets

17
IP
  • Internet Protocol
  • Adds a header to each packet (or datagram) for
    routing using sender and recipient IP
  • IP does not always know the final destination of
    a packet only the IP address of the next router
    along the line
  • Packets may take different routes and take
    different lengths of time to be delivered

18
UDP
  • User Datagram Protocol
  • Like TCP but does not ask for re-delivery of lost
    packets
  • Used for
  • network troubleshooting
  • audio or video streaming

19
OSI Network Layers Open Systems Interconnection
7 6 5 4 3 2 1
20
Transparency and Independence
  • Each layer has a specific task to perform.
  • Functions which are similar are grouped together
    within layers.
  • Each layer only knows about its immediately
    adjacent layers. A layer uses the services of the
    layer below and provides services to the layer
    above
  • The internal design of a layer is independent of
    the functions it provides

21
7 Application Layer
  • Provides a set of interfaces for applications to
    obtain access to networked services
  • This layer can be replaced with
  • Email client, Internet Browser, Web server, Mail
    server etc.
  • Protocols HTTP, SMTP, POP3, FTP, NNTP etc

22
6 Presentation Layer
  • Handles data format information for networked
    communications. This is done by converting data
    into a standardised format that can be understood
    by both sides
  • This layer deals with
  • Encryption and data conversion

23
5 Session Layer
  • The Session layer permits two parties to hold
    on-going communications called a Session across a
    network.
  • .
  • This layer is responsible for
  • Starting or stopping a communication session,
    managing logon and password authentication. The
    Domain Name Service (DNS)

24
4 Transport Layer
  • Ensures delivery of entire file or message using
    packet sequencing and packet acknowledgement
  • This layer deals with
  • Error detection and correction
  • Protocols TCP, UDP

25
3 Network Layer
  • Routes data to different LANs or WANs based on
    network address
  • This layer deals with
  • Packet Routing, IP forwarding
  • Protocols IP, ICMP

26
2 Data Link Layer
  • Transmits packets from node to node based on its
    station address
  • This layer deals with
  • synchronisation, putting data into frames along
    with error checking data
  • Protocol Ethernet (CSMACD)

27
1 Physical Layer
  • Provides a Physical Connection
  • Examples are
  • Cat5 Ethernet Cable, Fibre optic cable, Wireless

28
Mapping TCP/IP to OSI
29
Network Identities
  • For any network protocol every computer (host)
    must have a unique identity.
  • Computer Name
  • Ethernet MAC address
  • TCP/IP IP address

30
Application
Application
File
Network
Packet (IP Address)
Network
Frame (MAC Address)
Data Link
Data Link
Physical
Data (10110111)
Physical
31
Router Identifies packets by IP address
Application
Application
Network
Network
Data Link
Data Link
Physical
Physical
32
Switch Identifies frames by MAC address
Application
Application
Network
Network
Data Link
Data Link
Physical
Physical
33
HUB Repeats frames
Application
Application
Network
Network
Data Link
Data Link
Physical Layer
Physical Layer
34
IP addresses and DNS
  • Every computer on the Internet must have a unique
    IP address to identify it.
  • An IP address consists of four 8-bit numbers
    called octets
  • Since these numbers are not easy to remember,
    domain names are used as a more user friendly way
    of identifying machines
  • The Domain Name Service (DNS) translates Domain
    names into IP addresses

35
IP Addresses
  • four 8 bit numbers (octets) which can range from
  • 00000000 to 11111111 ie. 0 to 255
  • eg. 192.168.0 1
  • 11000000 10101000 00000000 00000001

36
Classes of IP Address
Class A nnn.hhh.hhh.hhh 1st octet 1 to
126 Class B nnn.nnn.hhh.hhh 1st octet 128 to
191 Class C nnn.nnn.nnn.hhh 1st octet 192
to 223 Class D nnn.hhh.hhh.hhh 1st octet
224 to 239 Class E nnn.hhh.hhh.hhh 1st octet
240 to 255 n network h host
37
Classes of IP Address
  • Class A16 million addresses per block
  • Class B 65000 addresses per block
  • Class C 254 addresses per block
  • Class D Multicast
  • Class E Broadcast (Experimental)

38
Private IP addresses (inside a LAN)
  • Class A 10.0.0.0 to 10.255.255.255
  • Class B 172.16.0.0 to 172.31.255.255
  • Class C 192.168.0.0 to 192.168.255.255
  • Used with a proxy server and Network Address
    Translation (NAT)
  • Localhost 127.0.0.1

39
Static and Dynamic IP addressing
  • Static fixed IP address
  • Dynamic IP address allocated by a server (DHCP
    server on a LAN, or provided by your ISP on a WAN)

40
2013 SQA paper Q 29
  • The hospital network uses TCP/IP to transfer
    files across the network.
  • (i) State three operations of the TCP part of
    this protocol.
  • (ii) State two operations of the IP part of this
    protocol.
  • (iii) Name one other common protocol that could
    be used to transfer files across the hospital
    network.

41
2013 SQA paper Q 29
  • (i) TCP splits the file into packets, adding
    header information which includes sender and
    receiver IP addresses and sequence number,
    reassembling the packets at the receiving end and
    acknowledging their arrival
  • (ii) IP adds its own address header and routes
    the packets around the network
  • (iii) HTTP or FTP could be used

42
2013 SQA paper Q31
  • A local tax office has 300 computers connected
    together in a Local Area Network with access to
    the Internet.
  • (a) The network conforms to the Open Systems
    interconnection (OSI) model.
  • (i) State which layer of the OSI model carries
    out encryption.
  • (ii) State which layer of the OSI model carries
    out routing.
  • (b) Explain which class of IP address is most
    appropriate for the tax office to use to network
    their computers.

43
2013 SQA paper Q31
  • Presentation layer
  • Network layer
  • Class B (Class C only has 254)

44
2012 SQA paper Q28
  • It is important that computer networks are
    designed to agreed standards, such as the Open
    Systems Interconnection (OSI).
  • (i) State the name of the layer of the OSI model
    at which a router functions.
  • (ii) State the name of the layer of the OSI model
    that carries out data encryption.
  • (b) TCP/IP is a set of protocols used in network
    communication. State the actions carried out by
    the IP part when transmitting data over a network.

45
2012 SQA paper Q28
  • (i) a router functions at the Network layer
  • (ii) Data encryption is done at the Presentation
    layer
  • (iii) IP adds its own address header and routes
    the packets around the network

46
2012 SQA paper Q31
  • A sports centre has a local area network of 10
    computers and 2 printers.
  • (a) Explain why class A IP addressing is not
    suitable for this network.
  • (b) A network interface card is required to
    provide a physical link to the local area
    network. The network interface card contains a
    MAC address. Describe the purpose of a MAC
    address.

47
2012 SQA paper Q31
  1. Class A allows 16,777,214 addresses (2 24- 2) A
    small network would use class C (with 254
    addresses) Only 12 IP addresses are needed
  2. A MAC address uniquely identifies the network
    card on the network.

48
2011 SQA paper Q23
  • The IP addresses for some of the devices on the
    network are as follows
  • Computer 1 198.169.120.100 File Server
    198.169.120.103
  • Computer 2 198.169.120.101 Router
    198.169.120.104
  • Computer 3 198.169.120.102 Printer
    198.169.120.105
  • (i) State the class of IP address used within
    this network. Justify your answer.
  • A new computer is added to the network. It is
    allocated the IP address
  • 198.198.120.278
  • (ii) State one reason why the second octet is
    invalid.
  • (iii) State one reason why the fourth octet is
    invalid.

49
2011 SQA paper Q23
  1. The network is Class C The first octet is
    between 192 and 223. The first three octets are
    identical for each IP address
  2. The second octet is different to the original
    which indicates a different network
  3. The fourth octet is over 255

50
2010 SQA paper Q25
  • The network conforms to the Open Systems
    Interconnection (OSI) model.
  • Two layers of the OSI model are the Session layer
    and the Network layer.
  • (i) State one task carried out at the Session
    layer.
  • (ii) Name a networking device that operates at
    the Network layer.

51
2010 SQA paper Q25
  • (i) The session layer manages starting and
    stopping the connection, manages logon and
    password authentication. This is the layer where
    the the Domain Name Service (DNS) operates.
  • (ii) A router operates at the network layer.
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