Lecture 07
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This document discusses different types of network transmission and interconnection devices. It describes unicast transmission as one-to-one communication, multicast as one-to-many communication, and broadcast as one-to-all communication. The document then discusses various network devices like hubs, switches, bridges, routers and gateways, explaining their functions and key differences. For example, it notes that switches perform buffering to prevent collisions, while hubs do not, and that bridges connect local area networks transparently while routers require IP address configuration.
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Lecture 07
- 2. Type of Transmission Unicast: Unicast is the term used to describe communication where a piece of information is sent from one point to another point. In this case there is just one sender, and one receiver Multicast: Multicast is the term used to describe communication where a piece of information is sent from one or more points to a set of other points. In this case there is may be one or more senders, and the information is distributed to a set of receivers (there may be no receivers, or any other number of receivers). Broadcast:Broadcast is the term used to describe communication where a piece of information is sent from one point to all other points. In this case there is just one sender, but the information is sent to all connected receivers.
- 4. Introduction There are many different devices for interconnecting networks •4 X.25 Network Ethernet Hub Ethernet Hub Hosts Hosts RouterBridge Token- ring Gateway
- 5. Hub Connects a group of Hosts, multiple LANs. It is physical layer device. Broadcast Collisions may occur if two hosts send data at same time.
- 7. Switch Switches add more intelligence to data transfer management. Multiple devices communicate simultaneously It is layer 2 device
- 8. Switches Token- ring Bridge •8 Bridge IP LLC 802.3 MAC 802.3 MAC 802.5 MAC LLC IP LLC 802.5 MACLAN LAN
- 9. Switch MAC Address Table
- 10. Switch MAC Address Table The following six steps describe the process used to populate the MAC address table on a switch 1. The switch receives a broadcast frame from PC1 on Port 1, as seen in Figure 2. The switch enters the source MAC address and the switch port that received the frame into the address table. •Port1:PC1 MAC Port2:Empty •Port3:Empty
- 11. Switch MAC Address Table 3. Because the destination address is a broadcast, the switch floods the frame to all ports, except the port on which it received the frame. 4. The destination device replies to the broadcast with a unicast frame addressed to PC1.
- 12. Switch MAC Address Table 5. The switch enters the source MAC address of PC2 and the port number of the switch port that received the frame into the address table. The destination address of the frame and its associated port are found in the MAC address table 6. The switch can now forward frames between source and destination devices without flooding, because it has entries in the address table that identify the associated ports
- 13. Router A router is a device that sends packets from one network to another network Routers receive packets, read their headers to find addressing information, and send them on to their correct destination on the network or Internet Routers can forward packets through an internetwork by maintaining routing information in a database called a routing table The routing table typically contains the address of all known networks and routing information about that network such as:
- 14. Router Interface Routing Path Next Hop Route Metric (Cost) Route Timeout Routers build and maintain their routing database by periodically sharing information with other routers. The exact format of these exchanges is based on the routing protocol. The routing protocol determines The information contained in the routing table How messages are routed from one network to another How topology changes (i.e. updates to the routing table) are communicated between routers Convergence is used to describe the condition when all routers have the same (or correct) routing information.
- 15. Router
- 16. External Components of a 2600 Router
- 17. Overview of Router Modes
- 19. Bridge, LAN switch, Ethernet switch There are different terms to refer to a data-link layer interconnection device: The term bridge was coined in the early 1980s. Today, the terms LAN switch or (in the context of Ethernet) Ethernet switch are used. Convention: Since many of the concepts, configuration commands, and protocols for LAN switches were developed in the 1980s, and commonly use the old term `bridge’, we will, with few exceptions, refer to LAN switches as bridges. •19
- 20. Ethernet Hubs vs. Ethernet Switches An Ethernet switch is a packet switch for Ethernet frames Buffering of frames prevents collisions. Each port is isolated and builds its own collision domain An Ethernet Hub does not perform buffering: Collisions occur if two frames arrive at the same time. •20 HighSpeed Backplane CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD Output Buffers Input Buffers CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD Hub Switch
- 21. Dual Speed Ethernet hub Dual-speed hubs operate at 10 Mbps and 100 Mbps per second Conceptually these hubs operate like two Ethernet hubs separated by a bridge •21 100 Mbps 100 Mbps 100 Mbps 100 Mbps 10 Mbps 10 Mbps 10 Mbps 10 Mbps Dual-Speed Ethernet Hub
- 22. Gateways The term “Gateway” is used with different meanings in different contexts “Gateway” is a generic term for routers (Level 3) “Gateway” is also used for a device that interconnects different Layer 3 networks and which performs translation of protocols (“Multi-protocol router”) •22 SNA Network IP Network X.25 Network Gateway Gateway Host Host
- 23. Bridges versus Routers An enterprise network (e.g., university network) with a large number of local area networks (LANs) can use routers or bridges 1980s: LANs interconnection via bridges Late 1980s and early 1990s: increasingly use of routers Since mid1990s: LAN switches replace most routers •23
- 24. A Routed Enterprise Network •24 Internet Router Hub FDDI FDDI
- 25. A Switched Enterprise Network •25 Internet Router Bridge/ Switch
- 26. Bridges versus Routers Routers Each host’s IP address must be configured If network is reconfigured, IP addresses may need to be reassigned Routing done via RIP or OSPF Each router manipulates packet header (e.g., reduces TTL field) Bridges/LAN switches MAC addresses of hosts are hardwired No network configuration needed Routing done by learning bridge algorithm spanning tree algorithm Bridges do not manipulate frames •26
- 27. Bridges •27 Overall design goal: Complete transparency “Plug-and-play” Self-configuring without hardware or software changes Bridges should not impact operation of existing LANs Three parts to understanding bridges: (1) Forwarding of Frames (2) Learning of Addresses (3) Spanning Tree Algorithm