Network Hardware

Local Area Networks LANs consist of Transmission media and network nodes. The network nodes fall into two major classes: Data terminal equipment (DTE) —Devices that are either the source or the destination of data frames. DTEs are typically devices such as PCs, workstations, file servers, or print servers. Data communication equipment (DCE)— Intermediate network devices that receive and forward frames across the network. DCEs may be either standalone devices such as repeaters, hubs, switches, and routers, or communications interface units such as network interface cards (NIC) and modems.

Network Interface Cards A network interface card (NIC) is a device that connects a client computer, server, printer or other component to a network. The NIC provides two important services: - it connects a computer physically to the network. - it converts information on the computer to ( and from) electrical signals of appropriate shape and transmission speed for your network.

Network Interface Cards NICs can be an expansion card (the most popular implementation) or built in to the motherboard of the computer. The NIC connects to the network via a small receptacle called a port. - For wired networks, you insert the network cable into this port. - For wireless networks, the port includes a transmitter/ receiver that sends/receives radio signals.

Network Interface Cards All NIC on your network must conform to a common physical and data link level protocol in order for their electrical signals to be compatible (and therefore to exchange information successfully). For example, if you are running a 10BaseT Ethernet network, then all of your computers, printers, and servers must contain 10BaseT Ethernet network interfaces. Some NICs accommodate more than one physical or data link protocol—for example, combinations of 10BaseT and 100BaseTX protocols (most network interfaces automatically sense the appropriate speed).

Network Interface Cards A NIC typically has at least two LEDs that indicate certain conditions: Link light—This LED indicates whether a network connection exists between the card and the network. Activity light—This LED indicates network activity. Under normal conditions, the light should flicker sporadically and often. Constant flickering may indicate a very busy network or a problem somewhere on the network that is worth investigating. Speed light—This LED indicates that the interface is connected at a certain speed.

Network Interface Cards Each NIC is associated with a unique address called its media access control (MAC) address. The MAC address helps route information within your local area network and is used by interconnecting devices such as switches. On Ethernet networks, each NIC receives a unique MAC address when it is manufactured. When the network interface is installed into a slot or onto the motherboard of a computer or printer, the interface MAC address becomes the address for the computer or printer. The MAC address is just one of several network addresses assigned to each network computer, server, or peripheral. Another network address is the device's Internet (IP) address. This address helps route information between networks, and is used by interconnecting devices called routers.

Hubs If the network includes more than two computers or peripherals  You should use a hub or a switch on your Ethernet LAN network. The basic function of a hub is to take data from one of the connected devices, optionally amplifies signal, and forward it to all the other ports on the hub. This method of operation is inefficient because, in most cases, the data is intended for only one of the connected devices. Hubs are also called concentrators or repeaters. Hub can be passive hub or active hub (regenerates the signal before it forwards it ). Hub are used on 10BaseT and 100BaseTX Ethernet networks.

Hubs A hub does not perform any processing on the data that it forwards, nor does it perform any error checking. Hubs come in various sizes, the most common being 12-port or 24-port. In a more complex network, many hubs can be interconnected. In addition to ports for connecting computers, hub has a port designated as an uplink port that enables the hub to be connected to another hub to create larger networks.

Hubs Like network interfaces, hubs must be compatible with the physical and data link protocol that you use. For example, if you are running a 10BaseT Ethernet network, then all hub connections to this network must also use this protocol.

Repeaters Repeater Simplest connectivity device regenerating signals Operates at Physical layer Has no means to interpret data  cannot direct data to their destination. It cannot improve or correct a bad or erroneous signal; it merely repeat it Limited scope One input port, one output port Receives and repeats single data stream Hub is a repeater with more than one output port Suitable only for bus topology networks Extend network inexpensively Rarely used on modern networks Limitations; other devices decreasing costs 11

Bridges Connects two network segments Analyze incoming frames and decide where to send Based on frame’s MAC address Operate at Data Link layer Bridges look like repeaters, single input port and single output port They differ from repeaters in that they can interpret physical addressing information Advantages over repeaters and hubs Protocol independence Add length beyond maximum segments limits Improve network performance because they can be programmed to filter out certain types of frames ( e.g. broadcast frame) 12

Disadvantage compared to repeaters and hubs Longer to transmit data Filtering database (forwarding table) Used in decision making Filter or forward 13 Figure 6-15 A bridge’s use of a filtering database

Bridges (cont’d.) New bridge installation Learn network Discover destination packet addresses Record in filtering database Destination node’s MAC address Associated port All network nodes discovered over time Today bridges nearly extinct Improved router and switch speed, functionality Lowered router and switch cost 14

Switches Switches are connectivity devices that subdivide network Smaller logical pieces, segments Operates at Data Link layer (traditional switchesl) Operate at layers 3 and 4 (advanced and modern switches) Interpret MAC address information Switches vary greatly in size and function Most switches have at least the following omponents Internal processor, operating system, memory, several ports 15

Multiport switch advantages over bridge Better bandwidth use, more cost-efficient Each port acts like a bridge Each device effectively receives own dedicated channel Ethernet perspective Dedicated channel represents collision domain 16 Figure 6-16 Switches

Installing a Switch Follow manufacturer’s guidelines General steps (assume Cat 5 or better UTP) Verify switch placement Make sure the switch is situated where you are going to keep it after all the cables are connected Turn on switch before connecting any cables to the switch’s ports, plug it in and turn it on. Also, when connecting a node to a switch, the node should not be turned on. Verify lights, self power tests The switch’s power light should illuminate. Most switches perform self-tests when turned on, and blinking lights indicate that these tests are in progress. Wait until the tests are completed (as indicated by a steady, green power light). 17

Installing a Switch (cont’d.) Configure (if necessary) If you are using a small, inexpensive switch, you might not have to configure it and you can skip to next step. However, you might need to assign an IP address to the switch, change the administrator password, or set up management functions. Configuring a switch usually requires connecting it to a PC and then running a configuration utility from a CD-ROM that came with the switch. Refer to your switch’s instructions to find out how to configure it. Connect NIC to a switch port (repeat for all nodes) Using a straight-through patch cable, connect the node’s NIC to one of the switch’s ports If you intend to connect this switch to another connectivity device, do not connect patch cables from nodes to the uplink port or to the port adjacent to the uplink port. On most hubs and switches, the uplink port is directly wired to its adjacent port inside the device. 18

Installing a Switch (cont’d.) After all nodes connected, turn on nodes After all the nodes have been connected to the switch, if you do not plan to connect the switch to another connectivity device, you can turn on the nodes. After the nodes connect to the network through the newly installed switch, check to verify that the switch’s link and traffic lights for each port act as they should, according to the switch’s documentation. Then make sure the nodes can access the network as planned. Connect switch to larger network (optional) To connect the switch to a larger network, you can insert one end of a crossover patch cable into the switch’s uplink port, then insert the other end of the cable into a data port on the other connectivity device. Alternately, you can insert one end of a straight-through cable into one of the switch’s data ports, then insert the other end of the straight-through cable into another device’s data port. If you are connecting one switch’s uplink port to another switch’s uplink port, you must use a crossover cable. After connecting the switch to another device, the switch senses the activity on its uplink port, evidenced by its blinking traffic light. 19

Installing a Switch (cont’d.) 20 Figure 6-17 Connecting a workstation to a switch Figure 6-18 A switch on a small network

Switching Methods Switches differ in how they interpret incoming frames and determine what to do with the frames Four switching modes exist Two basic methods discussed Cut-Through Mode Store-and-Forward Mode 21

Cut-Through Mode Switch reads frame’s header Forwarding decision made before receiving entire packet Uses frame header: first 14 bytes contains destination MAC address Cannot verify data integrity using frame check sequence Cannot detect corrupt packets  may increase the number of errors found on the network by propagating flawed packets Advantage Speed Disadvantage Data buffering (switch flooded with traffic) Best use Small workgroups in which speed is important Low number of devices 22

Store-and-Forward Mode Switch reads entire data frame into memory Checks for accuracy before transmitting information Advantage over cut-through mode Transmit data more accurately Disadvantage over cut-through mode More time consuming Best use Larger LAN environments because they do not propagate data errors. Can transfer data between segments running different transmission speeds 23

Content and Multilayer Switches Layer 3 switch (routing switch) Interprets Layer 3 data Layer 4 switch Interprets Layer 4 data Content switch (application switch) Interprets Layer 4 through Layer 7 data Advantages Advanced filtering, statistics keeping, security functions 24

Content and Multilayer Switches (cont’d.) Disadvantages No agreed upon standard Layer 3 and Layer 4 switch features vary widely Distinguishing between Layer 3 and Layer 4 switch Manufacturer dependent Higher-layer switches Three times Layer 2 switches Used in backbone 25