1. Computer Engineering and Networks, College of Engineering, Majmaah University LAN TECHNOLOGIES Mohammed Saleem Bhat m.bhat@mu.edu.sa CEN-444 Networks Structure And Protocols

2. Computer Engineering and Networks, College of Engineering, Majmaah University Technology Options-Ethernet Ethernet Fast Ethernet Gigabit Ethernet 10 Gig Ethernet WLAN

3. Computer Engineering and Networks, College of Engineering, Majmaah University Media Access Ethernet and Wi-Fi are both “multi-access” technologies Broadcast medium, shared by many hosts Simultaneous transmissions will result in collisions Media Access Control (MAC) protocol required Rules on how to share medium The Data Link Layer is divided into two Part MAC Media Access Control) Sublayer and LLC (Logic Link Control) Sublayer

4. Computer Engineering and Networks, College of Engineering, Majmaah University 802.3 Ethernet Carrier-sense multiple access with collision detection (CSMA/CD). CS = carrier sense MA = multiple access CD = collision detection Base Ethernet standard is 10 Mbps. 100Mbps, 1Gbps, 10Gbps standards came later

5. Computer Engineering and Networks, College of Engineering, Majmaah University Ethernet CSMA/CD CSMA/CD (carrier sense multiple access with collision detection) media access protocol is used. Data is transmitted in the form of packets. Sense channel prior to actual packet transmission. Transmit packet only if channel is sensed idle; else, defer the transmission until channel becomes idle. After packet transmission is started, the node monitors its own transmission to see if the packet has experienced a collision. If the packet is observed to be undergoing a collision, the transmission is aborted and the packet is retransmitted after a random interval of time using Binary Exponential Backoff algorithm.

6. Computer Engineering and Networks, College of Engineering, Majmaah University Ethernet Address End nodes are identified by their Ethernet Addresses (MAC Address or Hardware Address) which is a unique 6 Byte address. MAC Address is represented in Hexa Decimal format e.g 00:05:5D:FE:10:0A The first 3 bytes identify a vendor (also called prefix) and the last 3 bytes are unique for every host or device

7. Computer Engineering and Networks, College of Engineering, Majmaah University Ethernet Frame Structure Preamble: 7 bytes with pattern 10101010 followed by one byte with pattern 10101011 Used to synchronize receiver, sender clock rates Addresses: 6 bytes, frame is received by all adapters on a LAN and dropped if address does not match Length: 2 bytes, length of Data field CRC: 4 bytes generated using CR-32, checked at receiver, if error is detected, the frame is simply dropped Data Payload: Maximum 1500 bytes, minimum 46 bytes If data is less than 46 bytes, pad with zeros to 46 bytes LAN Technologies Length

8. Computer Engineering and Networks, College of Engineering, Majmaah University Ethernet 10 Base 5 (Thicknet) (Bus Topology) 10 Base 2 (Thinnet) (Bus Topology) 10 Base T (UTP) (Star/Tree Topology) 10 Base FL (Fiber) (Star/Tree Topology) LAN Technologies

9. Computer Engineering and Networks, College of Engineering, Majmaah University 802.11 Wireless LAN Provides network connectivity over wireless media An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network The AP is connected to wired network and is equipped with antennae to provide wireless connectivity LAN Technologies Network connectivity to the legacy wired LAN Desktop with PCI 802.11 LAN card Laptop with PCMCIA 802.11 LAN card Access Point

10. Computer Engineering and Networks, College of Engineering, Majmaah University 802.11 Wireless LAN Range ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point To service larger areas, multiple APs may be installed with a 20-30% overlap A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off) Three flavors: 802.11b 802.11a 802.11g LAN Technologies

11. Computer Engineering and Networks, College of Engineering, Majmaah University Multiple Access with Collision Avoidance (MACA) Before every data transmission Sender sends a Request to Send (RTS) frame containing the length of the transmission Receiver respond with a Clear to Send (CTS) frame Sender sends data Receiver sends an ACK; now another sender can send data When sender doesn’t get a CTS back, it assumes collision LAN Technologies senderreceiver other node in sender’s range RTS CTS ACK data other node in receiver’s range

12. Computer Engineering and Networks, College of Engineering, Majmaah University WLAN : 802.11b The most popular 802.11 standard currently in deployment. Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band LAN Technologies

13. Computer Engineering and Networks, College of Engineering, Majmaah University WLAN : 802.11a Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band Incompatible with devices operating in 2.4GHz Supports Data rates up to 54 Mbps. LAN Technologies

14. Computer Engineering and Networks, College of Engineering, Majmaah University WLAN : 802.11g Supports data rates as high as 54 Mbps on the 2.4 GHz band Provides backward compatibility with 802.11b equipment LAN Technologies

15. Computer Engineering and Networks, College of Engineering, Majmaah University Repeater, HUB, Bridge & Switch REPEATER, HUB, BRIDGE AND SWITCH

16. Computer Engineering and Networks, College of Engineering, Majmaah University Repeater A repeater receives a signal, regenerates it, and passes it on. It can regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media. It operates at Physical Layer of OSI The Four Repeater Rule for 10-Mbps Ethernet should be used as a standard when extending LAN segments. This rule states that no more than four repeaters can be used between hosts on a LAN. This rule is used to limit latency added to frame travel by each repeater. Repeater, Hub, Bridge & Switch

17. Computer Engineering and Networks, College of Engineering, Majmaah University Hub Hubs are used to connect multiple nodes to a single physical device, which connects to the network. Hubs are actually multiport repeaters. Using a hub changes the network topology from a linear bus, to a star. With hubs, data arriving over the cables to a hub port is electrically repeated on all the other ports connected to the same network segment, except for the port on which the data was sent. Repeater, Hub, Bridge & Switch

18. Computer Engineering and Networks, College of Engineering, Majmaah University Bridge Bridges are used to logically separate network segments within the same network. They operate at the OSI data link layer (Layer 2) and are independent of higher- layer protocols. The function of the bridge is to make intelligent decisions about whether or not to pass signals on to the next segment of a network. When a bridge receives a frame on the network, the destination MAC address is looked up in the bridge table to determine whether to filter, flood, or copy the frame onto another segment Broadcast Packets are forwarded Repeater, Hub, Bridge & Switch

19. Computer Engineering and Networks, College of Engineering, Majmaah University Switch Switches are Multiport Bridges. Switches provide a unique network segment on each port, thereby separating collision domains. Today, network designers are replacing hubs in their wiring closets with switches to increase their network performance and bandwidth while protecting their existing wiring investments. Like bridges, switches learn certain information about the data packets that are received from various computers on the network. Switches use this information to build forwarding tables to determine the destination of data being sent by one computer to another computer on the network. Repeater, Hub, Bridge & Switch

20. Computer Engineering and Networks, College of Engineering, Majmaah University Switches: Dedicated Access Hosts have direct connection to switch Full Duplex: No collisions Switching: A-to-A’ and B-to-B’ simultaneously, no collisions Switches can be cascaded to expand the network Repeater, Hub, Bridge & Switch switch A A’ B B’ C C’