higher computing network protocols, the osi model and ip addresses
TRANSCRIPT
Higher Computing
Network Protocols, the OSI model and IP addresses
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
Application Layer Protocols
• Remote access – Telnet
• File Transfer – FTP
• Information Access – HTTP HTTPS
• Email – SMTP and POP3
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
Telnet
FTPOpen hostname
Connected to hostname
220-Microsoft FTP Service
User (hostname):
anonymous
331 Annonymous access allowed, send identity (e-mail name) as password
Password:
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
20480 bytes received in 0.00 Seconds 20480000.00Kbytes/sec.
quit
FTP GUI front-end
HTTP
GET index.htm HTTP/1.0
HTTP/1.1 200 OK
Server: Microsoft-IIS/4.0
Date: Wed, 27 Feb 2002 10:07:15 GMT
Content-Type: text/html
Accept-Ranges: bytes
Last-Modified: Fri, 28 Apr 2000 14:34:33 GMT
ETag: "982f13df1eb1bf1:2f4d"
Content-Length: 558
<html>
<head>
<meta name="description" content="Main Page.">
HTTP Front-end
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
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 [email protected]
250 <[email protected]>, Sender accepted
rcpt to:[email protected]
250 <[email protected]>, Recipient ok
data
354 Enter mail, end with <CRLF>.<CRLF>
POP3 SMTP front-end
Ports
• FTP – 21 and 20
• Telnet – 23
• SMTP – 25
• POP3 –110
• HTTP – 80 and 8080
Lower level protocols
• Transmission Control protocol –TCP
• Internet Protocol – IP
• User Datagram Protocol UDP
TCP
Transmission Control Protocol: Sending
Breaks data to be transmitted into packetsEach packet is given a header which contains:
a sequence numberThe sender and recipient IP address
If an acknowledgement is not received then the packet is retransmitted
TCP
Transmission Control Protocol: Receiving
Reassembles packets received according to sequence number
Sends an acknowledgement
Waits for any missing packets
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
UDP
• User Datagram Protocol
• Like TCP but does not ask for re-delivery of lost packets
• Used for:– network troubleshooting – audio or video streaming
OSI Network LayersOpen Systems Interconnection
7
6
5
4
3
2
1
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
• 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
7: Application Layer
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
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)
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
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
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)
1: Physical Layer
• Provides a Physical Connection
Examples are:
• Cat5 Ethernet Cable, Fibre optic cable, Wireless
Mapping TCP/IP to OSI
ISO/OSI model Internet Architecture ModelProtocols / Standards
Application Layer
Application Layer
Telnet, FTP, POP3, SMTP, DNS
Presentation Layer
Session Layer
Transport Layer Transport Layer TCP, UDP
Network Layer Internet Layer IP, ICMP
Data Link Network Layer
SLIP, PPP, Ethernet, Token Ring (FDDI), ATMPhysical Layer
Network Identities
• For any network protocol every computer (host) must have a unique identity.
• Computer Name
• Ethernet – MAC address
• TCP/IP – IP address
Application
Network
Data Link
Physical
Application
Network
Data Link
Physical
File
Packet (IP Address)
Frame (MAC Address)
Data (10110111)
Application
Network
Data Link
Physical
Application
Network
Data Link
Physical
Router
Identifies packets by IP address
Application
Network
Data Link
Physical
Application
Network
Data Link
Physical
Switch
Identifies frames by MAC address
Application
Network
Data Link
Physical Layer
Application
Network
Data Link
HUB
Repeats frames
Physical Layer
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
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
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
Classes of IP Address
Class A:16 million addresses per block
Class B: 65000 addresses per block
Class C: 254 addresses per block
Class D Multicast
Class E Broadcast (Experimental)
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
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)
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.
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
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.
2013 SQA paper Q31
(i) Presentation layer
(ii) Network layer
(iii) Class B (Class C only has 254)
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.
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
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.
2012 SQA paper Q31
(a) 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
(b)A MAC address uniquely identifies the network card on the network.
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.
2011 SQA paper Q23
(i) The network is Class C The first octet is between 192 and 223. The first three octets are identical for each IP address
(ii) The second octet is different to the original which indicates a different network
(iii)The fourth octet is over 255
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.
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.