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Computer Networks (CSE-4711) Lecture-5. Instructor: Sazid Zaman Khan Lecturer, Department of Computer Science and Engineering, IIUC. Network Topology . Topology defines how the networked devices are connected with one another. Topology can be define on two levels: 1. Physical and
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Computer Networks (CSE-4711)Lecture-5 Instructor: SazidZaman Khan Lecturer, Department of Computer Science and Engineering, IIUC
Network Topology • Topology defines how the networked devices are connected with one another. Topology can be define on two levels: • 1. Physical and • 2. Logical • Physical topology: The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling.
Different types of topology • In the Bus topology, devices connect directly to a common backbone. • In a Ring topology, nodes are connected like a ring. • The Linear topology is just a number of nodes in series. Figure-1: Bus, ring and linear topology respectively from left
Different types of topology • The Star topology is where all nodes connect back to a central node. It’s common in the LAN environment, for instance where PCs connect back to an access switch. • In the Tree topology, nodes are connected like branches of a tree. Figure-2: Star and Tree topology respectively from left
Different types of topology • With full mesh topology, all nodes are connected directly to all other nodes. Although this provides the most direct path between endpoints, it is in reality not very practical. • Partial mesh topology is simply a subset of full mesh topology. • Hybrid topology is a combination of topologies that do not exhibit the characteristics of any standard topology. Figure-3: Full mesh topology
Network Topology • The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
Logical topology • Logical topology is the way information flows in the network. • A physical topology of a network is its shape and the logical topology is the shape of the data flow. Regardless of how the nodes are physically connected, there can be different ways by which data flows among the nodes. This is called the logical topology. Some examples are given below: • Client-Server : There can be a wide variety of physical connections between the client (who requests a web page to the web server) and server (the web server that stores the web page). But the logical path of data flow is from client to server or server to client.
Logical topology • Peer-to-Peer: Very small business networks and home networks are often peer-to-peer. This means that no server is involved at all. Each computer acts as both a client and a server. Typically, directory shares or folders are set up on each of the computers, and local accounts on the computers are used to provide some minimal security
Logical topology • VPN: If you have multiple locations to connect but do not want to pay for multiple dedicated links or even Frame Relay, you could just use the Internet. The only problem would be that the Internet isn't a very private space through which to send your business traffic. What you would really need is a way to traverse the Internet but keep your communication secure. A virtual private network (VPN) will do just that. A VPN is a private connection that is going through a public network, typically the Internet but sometimes just another untrusted network. The communication is made secure by encapsulating the IP traffic within another protocol called a tunneling protocol.
Logical topology • VLAN: With conventional networks using only routers for layer 3 and switches as layer 2, subnets are limited to the physical location in which they reside. This can be constricting to a network administrator if a department spans multiple locations and the administrator wants to manage and set security policies based on subnets related to departments. A virtual local area network(VLAN) is the solution to this problem. In a VLAN, switches are used to create layer 3 domains, also called subnets. These subnets can span multiple switches regardless of the location of the switch. This gives the network administrator the flexibility to design a logical network that does not have to conform to any physical limitations, such as the actual location of the clients. Administrators can manage the security of the entire subnet as if it were all in the same location, even if it isn't. Routers or layer 3 switches can be used to connect the separate layer 3 domains while still maintaining security.
Network devices • Hub: The hub is a hardware device that contains multiple, independent ports that match the cable type of the network. Most common hubs interconnect Category 3 or 5 twisted-pair cable with RJ-45 ends. Hubs offer an inexpensive option for transporting data between devices, but hubs don't offer any form of intelligence because they send the incoming data at one port to all other ports. This also means that they work on physical layer.Hubs can be active or passive: • An active hub or repeater strengthens and regenerates the incoming signals before sending the data on to its destination. • Passive hubs do nothing with the signal.
Network devices • Switches: Switches are a special type of hub that offers an additional layer of intelligence to basic, physical-layer repeater hubs. A switch must be able to read the MAC (Media Access Control address used by your network card) address of each frame it receives. This information allows switches to repeat incoming data frames only to the computer or computers to which a frame is addressed. This speeds up the network and reduces congestion.
Network devices • Bridges: A bridge is used to join two network segments together, it allows computers on either segment to access resources on the other. They can also be used to divide large networks into smaller segments. Bridges have all the features of repeaters, but can have more nodes, and since the network is divided, there is fewer computers competing for resources on each segment thus improving network performance. Bridges operate at both the Physical Layer and the MAC sublayer of the Data Link layer. Bridges read the MAC header of each frame to determine on which side of the bridge the destination device is located, the bridge then repeats the transmission to the segment where the device is located.
Networking devices • Routers: Routers Are networking devices used to extend or segment networks by forwarding packets from one logical network to another. Routers are most often used in large internetworks that use the TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the Internet using dedicated leased lines. Routers work at the network layer (layer 3, they can take out and read 3 envelopes of the letter example that I explained) of the Open Systems Interconnection (OSI) reference model for networking to move packets between networks using their logical addresses (which, in the case of TCP/IP, are the IP addresses of destination hosts on the network). Because routers operate at a higher OSI level than bridges do, they have better packet-routing and filtering capabilities and greater processing power, which results in routers costing more than bridges.
Networking devices • Gateways: A gateway is a device used to connect networks using different protocols. Gateways may work at different layers of the OSI model. Application Gateways can even operate in application layer for example an email gateway can translate internet messages to SMS messages.
Network devices • NICs (Network Interface Card): Network Interface Card, or NIC is a hardware card installed in your computer (your WLAN or Ethernet adapter) so it can communicate on a network. The network adapter provides one or more ports for the network cable to connect to, and it transmits and receives data onto the network cable.
Which device operate in which layer Figure-4: Devices and layers in which the operate
Broadcast domain • VLANs become important when you consider broadcasts. Broadcasts are frames sent to all devices on a switch, and in many cases, a normal and frequent function. A broadcast domain is the set of all devices that receive a broadcast. Small LANs are typically equivalent to a single broadcast domain. • Devices on a network generate significant broadcast traffic. Broadcasts normally occur when a device is trying to send data to another device, but doesn't know the MAC address of the destination device. A PC that knows the destination IP, but not the MAC associated with that IP, will send a broadcast. This type of broadcast is an ARP (Address Resolution Protocol) broadcast.
Firewalls • Firewalls are computer network devices or software which protect a network from other less-trusted networks. Figure-5: Devices and layers in which the operate
Virtual LAN • VLAN's allow a network manager to logically segment a LAN into different broadcast domains (see Figure2). Since this is a logical segmentation and not a physical one, workstations do not have to be physically located together. Users on different floors of the same building, or even in different buildings can now belong to the same LAN. Therefore, two finance department workers can be on different buildings but they will still be in the “Finance VLAN”. See figure-5 on next page
Virtual LAN Figure-6: Virtual LAN (VLAN)
