ND0801_Assignment_3_Protocols for P3
- 1. National Diploma Unit 08 Communication Technology Assignment 2 Support Material
- 2. Criteria Objectives in this Presentation • P2 explain the principles of signal theory • P3 describe communication protocols used and explain why they are important
- 3. What is Communications? Communications is an act of transporting messages from a source to a destination. A message consists of data that carries information and is sent through a communications medium (channel) from one device to another
- 4. Digital Basics signalstate A string of zero’s and ones form a stream of data that can be translated by a computer to process data and commands Digital signals are based on two states, Zero and One 1 0 1 0 1 0 1 Send Receive TX RX This is a trace you would see on an oscilloscope
- 5. Communication Protocols We are going to cover what a protocol is a and describe some common ones in digital communications A protocol is a set of rules to follow when two or more devices are communicating An analogy is that of a life of a telephone call. Both parties put their phones back in the ready to answer mode The phone rings The caller replies ‘Hi may I speak to John’The called person says ‘I am John’ The called person answers with a ‘Hello’ The conversation starts The conversation ends with a ‘goodbye’ usually from the caller
- 6. Protocol Exercise Now it is your turn to sort out the order of a transaction in a shop such as Argos ie. the protocol to follow when obtaining goods. Enter shop Select item and write down code and quantity on a slip Pay for the item Look at catalogue Go to the till and hand over slip Collect item Hand over the receipt to the Collection point when called Receive receipt and details of collection point 1 2 3 4 5 6 7 8
- 7. Protocol Exercise Answer Was that easy? Enter shop Select item and write down code and quantity on a slip Pay for the item Look at catalogue Go to the till and hand over slip Collect item Hand over the receipt to the Collection point when called Receive receipt and details of collection point 1 2 3 4 5 6 7 8
- 8. TCP/IP Next we are going to look at two protocols commonly used on a network such as the Internet These two protocols usually work together as a ‘Stack’ inside a computer. TCP stands for Transport Control Protocol and IP stands for Internet Protocol They have different roles •TCP creates and ensures that data transfer is reliable • IP ensures that data is addressed so that it can reach its proper destination Let’s have look at IP first
- 9. Internet Protocol (IP) We previously looked at a packet structure; Remember? Data IP Header Data is the user information broken up into chunks and given a layer 4 headers such as for TCP (we will look at that afterwards). The IP Header above contains information such as source and destination addresses. For simplification we shall only look at the addressing information A B Internet cloud Router Packets from computer A are destined for computer B
- 10. Internet Protocol Source Address Destination Address Data 211.410.11.3 202.20.10.1 Every network communication device will have an IP address allocated in the form of four groups of numbers. This called a dotted decimal format. Packets are labelled with the source and destination IP addresses so that they can be directed by a process known as routing and so that the receiver can return data to the sender forming a two way connection A B Router 202.20.10.1 211.410.11.3 Internet cloud
- 11. Transport Control Protocol (TCP) IP HeaderData We previously looked at a packet structure; this is how it is structured We will now look at the data part of that IP packet in which could contain a segment formatted for TCP: In order for data to be sent over an IP internetwork it has to be chopped up into segments first. This is done inside the computer by the TCP/IP stack. Data Data Seg 5Seg 1 Seg 2 Seg 3 Seg 4
- 12. TCP Process, Sequence Numbering Data Seg 5Seg 1 Seg 2 Seg 3 Seg 4 In this example a string of data is chopped up into five segments and each of these segments is given a sequence number. This forms part of the TCP formatting process. Segmented Data Seq 1 Segmented Data Seq 2 Segmented Data Seq 4 Segmented Data Seq 3 Segmented Data Seq 5
- 13. TCP Segment Format Simplified segment format based on TCP Each segment is also allocated source and destination port numbers Segmented Data Sequen- ce no Source Port Destination Port Ports are numbers together with ip addresses are used to set up many simultaneous communication sessions on a computer WWW Peer to Peer email Peer to Peer Email server Web Server End User Port 80 Port 110 Port 2124 Checksum
- 14. TCP Flow Control Each segment is also allocated flow control bytes called ACK and Window Simplified segment format based on TCP Segmented Data Sequ- ence no Source Port Destination Port Flow control Flow control together with the sequence numbering is used to ensure a reliable delivery of data by the acknowledgment of receipt of segments in the right order Now give me the next 5 segments email End User I am sending 5 segments Email ServerI have received the 5 segments I expected
- 15. TCP Flow Control Remember that when data is sent out to an internetwork it has an IP header to tell the network devices in the internetwork its destination. email End User I am sending 5 segments Email Server I have received only 3 of the 5 segments I expected Now give me the last 2 segments again Now what if the email server did not receive some of the segments properly TCP will confirm the number of segments received and ask for the last missing ones again. It will adjust the number of segments it requests to a smaller number until its satisfied that the errors are reduced. This is called ‘windowing’.
- 16. Wireless Technology in Use • Mobile Phones • Point to Point • Point to multipoint • Infrared • Laser • Blue Tooth • WIFI
- 17. Wireless communication • The increasing use of wireless networks in local area networks (LANs), access points, • infrared (line of sight, scatter and reflective), LASER, narrow band radio, spread-spectrum radio, point to point and extended LANs with wireless bridges, • the increased availability of mobile computing
- 18. Wireless Protocols We looked at two important protocols in some depth. This was to give you an idea of what is involved in data transfer over an internetwork such as the Internet. Next we will look at some wireless protocols because these are becoming more important. First of all a little lesson in radio basics…. WiFi GSM/GPRS UMTS Blue Tooth IrDA
- 19. Bluetooth • Low cost short range unlicensed radio standard for interconnecting devices • Constantly channel hops (swaps frequencies) for reliable connection • Uses the frequency band around 2.4GHz with up to 2 Mbit/s bit rate. Q:You know what LAN is. What is PAN? Notes
- 20. More on Bluetooth Serious flaws in Bluetooth security lead to disclosure of personal data There is a problem with security What is ‘bluejacking’ and ‘bluesnarfing’? The Viking! Task: Make a list of Bluetooth products that a company might find useful Can you name all of these items? Notes
- 21. Bluetooth Technical A short range network connecting devices such as computer peripherals and PDAs is said to be a “piconet”. Bluetooth is a standard for such a piconet which specifies radio access and frequency hopped single carrier modulation techniques which are similar in principle to those used by the original 1 Mb/s FHSS IEEE802.11 standard over wider distances. Bluetooth is not an IEEE standard and is not easily described in terms of the seven-layer OSI model. It operates in the 2.40-2.48 GHz band over ranges of about 10 metres .The band is divided into 79 channels each 1MHz wide and Bluetooth frequency hops its carrier with 1600 hops/second and a dwell time of 625 microseconds. There is a master unit controlling the hopping sequence used by each slave. All devices hop together. Frequency shift keying (FSK) modulation is used with a bandwidth efficiency of 1 bit/s per Hz to achieve 1Mb/s. Much of this capacity is consumed by a rather elaborate overhead of control information. The fact that Bluetooth uses the same 2.40-2.48 GHz frequency band as IEEE802.11b and that it is non-compatible with IEEE802.11 is a serious problem since Bluetooth is capable of wiping out IEEE802.11b communication over its short range. The IEEE 802.11 committees are considering this problem and most likely will propose a new standard to rival Bluetooth. Ref: 802.11 Wireless LAN Fundamentals, Pejman Roshan, Jonathan Leary, Cisco Press, 2003
- 22. Infrared Infrared Data Association IrDA Uses infrared for very short distance communications Speeds of up to 16Mbit/s with further developments to 100Mbit/s Look for some products using this standard: http://www.irda.org/ Q: What products could help an organisation? Notes:
- 23. Mobile Phone History • First introduced in the early 70’s • The heavy battery pack version lasted an hour at best A Invented by Martin Cooper in 1973 The long talk time version was very heavy! http://inventors.about.com/cs/inventorsalphabet/a/martin_cooper.htm
- 24. Mobile Phone History • Denoted now by the letter G for generation http://www.techweb.com/encyclopedia/defineterm.jhtml?term=cellulargenerations 1G: Analogue system. First mobile phones 1990’s Late1990’s Now 4G: The near future 2G: Changes to a digital system. More efficient and secure Q: What features does 3G give the user? 1970’s 2.5G: Adds email & internet access using Wireless Application Protocol (WAP)
- 25. UK Mobile Phone Operators • Yes there are five that actually own infrastructure, the rest are third party providers. What is infrastructure? Masts, switching centres and interconnects to the PSTN BT TowerMobile Mast installation Three standards in use GSM, Global System for Mobile communications GPRS, General Packet Radio Service and UMTS, Universal Mobile Telecommunications System Q: What does PSTN stand for? http://www.hillsfar.demon.co.uk/Site/Cellnet.html https://styx.uwaterloo.ca/~jscouria/GSM/trio.html http://www.webopedia.com/TERM/G/GPRS.html
- 26. Wireless Application Protocol (WAP) Web Server InternetWAP Gateway WAP provides an interface between Web services and mobile phones so that web pages can be downloaded and viewed. Antennae Array HTMLWML Ref: http://en.wikipedia.org/wiki/Wireless_Markup_Language
- 27. Wireless LANS Protocols Access Points Wireless Routers Print Server 802.11a 802.11b 802.11j 802.11g IEEE standards
- 28. Wireless LAN History A number of manufacturers approached the Institute of Electrical and Electronics Engineers (IEEE) in the USA. Having successfully launched the Ethernet standard under the 802.3 committee, they set up another committee with the designation 802.11, but it took until 1997 before a recommendation could be agreed. It allowed for data transfer at a rate of 2 Mbps using either frequency hopping or direct sequence spread spectrum. The standard was published in 1997 to enable development to start. Even at this early stage there were two variants, 802.11a (operating in the 5.8 GHz ISM band) and 802.11b (operating in the 2.4 GHz ISM band). These standards were ratified in December 1999 and January 2000 respectively. Ref: http://www.radio-electronics.com/info/wireless/overview/wireless_dev.php Further developments led to the 802.11g standard giving 54mbit/s in the 2.4 GHz band Q: Manufacturers claim 108Mbit/s bit rate on 802.11g systems. How does this happen? Notes
- 29. Wireless LAN Configurations A wireless access point allows remote devices such as laptops to access the network Q: Can you name these devices? Switch Modem Laptop Wireless Access Point Desktop ComputerTelephone Socket with filter Wireless Adaptor Network Cable
- 30. Wireless LAN Configuration Continued A wireless router allows remote devices such as laptops to access the network and has a router and modem inside with sometimes more than one Ethernet port Q: Where do you Definitely need a cable? Wireless Router Centrino Laptop Desktop Computer Wireless Adaptor Telephone Socket with filter Notes
- 31. Security Protocols Intro Wireless communications is a security risk because of the broadcast nature of the signal An example of how open wireless was before digital systems was its use in mobile communications by the emergency services. Channels could be monitored by using a device called a scanner that could tune to a wide range of frequencies and modulation schemes Recently the police has replaced the old analogue radio system with a digital one called TETRA that is very secure. Next to adopt the new radio system is the ambulance service.
- 32. Wireless LAN Security Protocols The two main protocols in use are WEP and WPA WEP: Wired Equivalency Privacy. As specified by IEEE 802.11b. Data that is to be sent and received wirelessly is encrypted using a combination of the data to be sent and a private and public key. The encryption method uses a cipher called RC4. WPA: Wi-Fi Protected Access, as specified by the Wi-Fi Alliance This also uses the RC4 cipher method in addition to another protocol called TKIP (Temporal Key Integrity Protocol) that provides a robust encryption method of the public key. This makes it harder for intrusion attacks to be successful. A cipher is a method of converting plain text into a code that is designed to only be read by the authenticated receiver. A key is a number from a very large range used as a base for the encryption process calculation (algorithm).
- 33. Wireless LAN Security Process For access to the wireless router a password is required from the laptop. This is encrypted and sent to the wireless router for authentication. If this is the only level of security used then a wireless connection is made and data will be transferred in encrypted form. Encrypted Password Acknowledgement Encrypted data flow using key and a cipher method
- 34. Setting up Wireless Security Task: Investigate and report how you would set up a wireless router for home use. To do this task: Make a list of software and hardware you will need and then describe the procedure you could take to install and set up a working wireless connection There are many wireless systems available for a home network. BT, Netgear, Dlink, Cisco, Belkin, 3-Com, Linksys, US Robotics are some makes. Q. Does a router need extra software on your PC to function?
- 35. References • http://www.kettering.edu/~drussell/Demos/rad2/mdq.html {good animation of waves} • http://en.wikipedia.org/wiki/Wifi#Wi-Fi:_How_it_works • http://en.wikipedia.org/wiki/Dipole_antenna#Folded_dipole • http://www.radio-electronics.com/info/wireless/index.php {good on Wireless technologies} • http://www.pulsewan.com/data_101.htm {Extensive information on data comms)