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MAKERERE UNIVERSITY College of Computing and Information Sciences School of Computing and Informatics Technology MAKERERE UNIVERSITY College of Computing and Information Sciences School of Computing and Informatics Technology BIT 1102: COMMUNICATIONS TECHNOLOGY AND THE INTERNET 6. LAN ACCESS METHODS/NETWORK PROTOCOLS

Network Protocol 2 Just like Human beings communicate using languages such as English, French Network Protocol 2 Just like Human beings communicate using languages such as English, French or Swahili, Computers / Nodes on a network need to follow a standard in order to transmit to each other. So, a network protocol can be defined as a set of rules (a language) governing devices communicating on a network. BIT 1102: Communications Technology & the Internet

Network Protocol 3 It is a formal description of digital message formats and the Network Protocol 3 It is a formal description of digital message formats and the rules for exchanging those messages in or between computing systems and in telecommunications. BIT 1102: Communications Technology & the Internet

What’s a protocol? 4 . Hi TCP connection req Hi TCP connection response Got What’s a protocol? 4 . Hi TCP connection req Hi TCP connection response Got the time? 2: 00 pm time Qn: Other human protocols? BIT 1102: Communications Technology & the Internet

Who develops these Standards? 5 Several international bodies are dedicated to developing acceptable standards Who develops these Standards? 5 Several international bodies are dedicated to developing acceptable standards for communicating on the network. These include, IEEE: Institute of Electrical and Electronic Engineers (www. ieee. org) IETF = Internet Engineering Task Force (www. ietf. org) ITU: International Tele Communications Union(www. itu. int). ANSI= American National Standards Institute(www. ansi. org). BIT 1102: Communications Technology & the Internet

Network protocols 6 There are many protocols currently in use for various purposes such Network protocols 6 There are many protocols currently in use for various purposes such as: LAN access methods Ethernet Token ring TCP IP SMTP and many more. BIT 1102: Communications Technology & the Internet

Access Control Methods 7 A LAN Access method describes how the devices access the Access Control Methods 7 A LAN Access method describes how the devices access the network and share the transmission facilities Two primary access control methods exist for computers to communicate with each other over the network Token based access Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Other methods will be explored in computer Networks BIT 1102: Communications Technology & the Internet

Ethernet 8 Ethernet is one of the most common and widely used network protocols Ethernet 8 Ethernet is one of the most common and widely used network protocols that uses methods known as 1. Carrier Sense Multiple Access with Collusion Detection (CSMA/CD). 2. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). BIT 1102: Communications Technology & the Internet

Carrier Sense Multiple Access(CSMA) 9 Multiple Access Any of the network devices can transmit Carrier Sense Multiple Access(CSMA) 9 Multiple Access Any of the network devices can transmit data onto the network at will; there is no central controller A broadcast network where all stations see all frames, regardless of whether they represent an intended destination Each station must examine received frames to determine if the station is a destination. If so, the frame is passed to a higher protocol layer for appropriate processing. Carrier Sense Before sending data, stations listen to the network to see if it is already in use. If in use, the station wishing to transmit waits, otherwise it transmits BIT 1102: Communications Technology & the Internet

CSMA/CD 10 In this method, the computer “listens” to the network before transmitting. If CSMA/CD 10 In this method, the computer “listens” to the network before transmitting. If the network is clear, the computer / node sends the transmission. Sometimes when using CSMA/CD, two computers may begin transmitting at the same time. When this occurs, there is data collision and both computers back off and wait for a random time to re-transmit. The delay however is minimal and does not greatly affect the network speed. BIT 1102: Communications Technology & the Internet

Ethernet cont’d 11 Ethernet protocol runs on topologies such as Bus, tree and star. Ethernet cont’d 11 Ethernet protocol runs on topologies such as Bus, tree and star. Fiber optic, Coaxial, wireless and twisted pair are the main channels supported by Ethernet at speeds of 10 Mps. (Fast Ethernet and Gigabit Ethernet transmit at 100 Mps and 1000 Mps respectively) BIT 1102: Communications Technology & the Internet

ii) Carrier Sense Multiple Access with Collision Avoidance 12 Unlike CSMA/CD, Carrier Sense Multiple ii) Carrier Sense Multiple Access with Collision Avoidance 12 Unlike CSMA/CD, Carrier Sense Multiple access with Collision Avoidance (CSMA/CA) involves listening in to the network in order to “avoid” collisions. In CSMA/CA, before any actual transmission occurs, the sender must broadcast an intension to transmit, and only transmits when the network is clear. If the network is busy, the sending computer withdraws the transmission and re-broadcasts after a pre defined interval. BIT 1102: Communications Technology & the Internet

ii) Carrier Sense Multiple Access with Collision Avoidance 13 1. Sender send a request-to-send ii) Carrier Sense Multiple Access with Collision Avoidance 13 1. Sender send a request-to-send (RTS) frame to receiver and indicates the time needed to complete data transmission 2. Receiver send clear-to-send (CTS) frame, indicates time to complete data transmission and reserves channel for the sender 3. Sender transmits the data and receiver responds with an ACK frame, ensuring reliable transmission 4. RTS and CTS frames let other stations know of the data transmission so that collision is avoided BIT 1102: Communications Technology & the Internet

CSMA/CA cont’d 14 Local talk protocol developed by Macintosh computers is an example of CSMA/CA cont’d 14 Local talk protocol developed by Macintosh computers is an example of a protocol that uses CSMA/CA is also used on networks where by the medium of transmission does not allow for collision detection. In wireless LANs, for example, not all stations may be able to detect each other so CSMA/CD is not an option. CSMA/CA transmits at lower speeds of about 230 kb/s BIT 1102: Communications Technology & the Internet

Token Ring 15 How does Token work? BIT 1102: Communications Technology & the Internet Token Ring 15 How does Token work? BIT 1102: Communications Technology & the Internet Ring protocol

Token ring Explained 16 Developed by IBM, this protocol uses a special electronic frame Token ring Explained 16 Developed by IBM, this protocol uses a special electronic frame known as a token which is passed from computers connected together in a logical “ring”. If a computer has data to transmit, the data is attached to the token which is passed round the “ring” until it reaches the destination. At this point, the receiving computer captures the data and releases the empty token. If the token arrives at a computer without anything to transmit, it simply proceeds to the next computer. BIT 1102: Communications Technology & the Internet

Token Ring cont’d 17 Though once popular, the token ring protocol has lost popularity Token Ring cont’d 17 Though once popular, the token ring protocol has lost popularity to the Ethernet protocol and is rarely used currently. Defined under IEEE 802. 5. Token ring Networks Transmit between 4 Mbps to 1 GBps over twisted pair or fiber optic cable BIT 1102: Communications Technology & the Internet

FDDI 18 Developed by the ANSI, Fibre Distributed Data Interface (FDDI) is a network FDDI 18 Developed by the ANSI, Fibre Distributed Data Interface (FDDI) is a network protocol that enables transmission over long distances. (It generally connects two or more LANs) at high speeds, mainly over fiber optic cable. FDDI uses Dual Ring topology using a Token mechanism as discussed (see token ring) The “Dual” ring topology refers to two rings, one of which will operate if there’s no problem on the network. If there’s failure on the primary ring, transmission then moves to the backup ring. BIT 1102: Communications Technology & the Internet

Fiber-Distributed Data Interface (FDDI) 19 FDDI provides a standard for data transmission in a Fiber-Distributed Data Interface (FDDI) 19 FDDI provides a standard for data transmission in a local area network that can extend in range up to 200 kilometers (124 miles). In addition to covering large geographical areas, FDDI local area networks can support thousands of users. As a standard underlying medium it uses optical fiber (though it can use copper cable, in which case one can refer to CDDI). BIT 1102: Communications Technology & the Internet

Asynchronous Transfer Mode (ATM) 20 A highly complex network protocol that involves the transmission Asynchronous Transfer Mode (ATM) 20 A highly complex network protocol that involves the transmission of all data in packets of a fixed size (53 Bytes). ATM protocols are connection-oriented ie transmission only starts when the channel is known to be free. While ATM is wide spread in WANs, it has generally failed to gain popularity as a LAN protocol. The MFA (Frame Relay Alliance) Forum (formerly ATM Forum) is a Consortium regulating this protocol (mfaforum. org) BIT 1102: Communications Technology & the Internet

Internet Protocol (IP) 21 Internet protocol (IP): IP is used to transfer data from Internet Protocol (IP) 21 Internet protocol (IP): IP is used to transfer data from one computer to another on a Network. IP is able to achieve this based on an IP address, which is a Unique number assigned (Either manually or automatically) to each computer on the Network. IPV 4 (version 4) in most use currently. IPV 6 is being migrated to in many organizations as well. BIT 1102: Communications Technology & the Internet

Transport Control Protocol (TCP) 22 While IP is only concerned with delivering data packets, Transport Control Protocol (TCP) 22 While IP is only concerned with delivering data packets, the Transmission Control Protocol (TCP) ensures reliable and accurate delivery of the data packets across the network. TCP and IP together (TCP/IP) form the basic communication “language” or protocol used on the Internet. BIT 1102: Communications Technology & the Internet

Other Common protocols 23 Simple Mail Transfer Protocol (SMTP): This protocol is used in Other Common protocols 23 Simple Mail Transfer Protocol (SMTP): This protocol is used in sending and receiving of Electronic mails (e-mail). Dynamic Host Configuration protocol: This protocol is used to automatically assign IP addresses to “hosts” or work stations on a network. A DHCP server is normally configured to perform this task. BIT 1102: Communications Technology & the Internet

Other Common protocols cont’d 24 Hyper Text Transfer Protocol (HTTP): This is a protocol Other Common protocols cont’d 24 Hyper Text Transfer Protocol (HTTP): This is a protocol used for exchanging information on the World wide Web (www) Its standards development has been coordinated by the IETF and the W 3 C (World Wide Web Consortium) Secure Socket Layer (SSL) protocol: The predecessor to Transport Layer Security(TLS) , SSL is concerned with the security of a message being relayed over a network e. g. the internet (Security to be covered in a later chapter) BIT 1102: Communications Technology & the Internet

Other Common protocols cont’d 25 The File Transfer Protocol (FTP): Is used widely on Other Common protocols cont’d 25 The File Transfer Protocol (FTP): Is used widely on the Internet for transferring files to and from a remote host. FTP is commonly used for uploading pages to a Web site and for providing online file archives. BIT 1102: Communications Technology & the Internet

26 Thank you BIT 1102: Communications Technology & the Internet 26 Thank you BIT 1102: Communications Technology & the Internet