Data Network Connectivity 11

Objectives In this chapter, you will learn to: Explain how NICs operate List the most common types of NICs Describe the purpose and operation of hubs and repeaters Describe the purpose and operation of bridges and switches Explain how routers connect dissimilar networks Identify other Layer 3 connectivity devices and understand their uses Describe how remote users can connect to a LAN or WAN via a modem Identify the components necessary for access and carrier network connectivity

Network Interface Cards (NICs) Devices that act as transceivers for workstations, servers, connectivity devices, and peripherals on a network. Transmit data in a format that other network nodes can interpret. Receive and interpret encoded data from the network. Assemble data frames during transmission and disassemble data frames during reception.

Adapter Card NICs A circuit board used to connect a device to the system board. Expansion slots - openings with multiple electrical contacts into which the adapter can be inserted. Bus - the circuit that is used by the system board to transmit data to the computer’s components.

Adapter Card NICs

PC Card NICs

USB NICs

Hubs

Bridges

Transparent bridging - a bridge begins polling a network to learn about its physical topology as soon as it is installed on the network. Spanning tree algorithm - a routine that can detect circular traffic patterns and modify the way multiple bridges work together, thus eliminating such patterns. Source-route bridging - a bridge polls the network to determine which path is best for a packet to travel from point A to point B. Translational bridging - the bridge not only forwards packets, but also translates packets between one logical topology and another.

Data Switches

Advantages Switches offer greater security because they isolate one device’s traffic from another. They provide separate channels for every device Disadvantages Switches can become overwhelmed by continuous, heavy traffic. In that event, they cannot prevent data loss. On a fully switched network, in which every node uses its own port on the switch and therefore provides separate data channel, devices cannot detect collisions.

Routers

Functions: Filter out broadcast transmissions to alleviate network congestion Prevent certain types of traffic from getting to a network, enabling customized segregation and security Support simultaneous local and remote connectivity Provide higher network fault tolerance through redundant components, such as power supplies or network interfaces Monitor network traffic and issue statistics to a database Diagnose internal or other connectivity problems and trigger alarms

Routers Static routing - a technique in which a network administrator programs a router to use specific paths between nodes. Dynamic routing - automatically calculates the best path between two nodes and accumulates this information in a routing table.

Routers

Routing Protocols Best path - the most efficient route from one node on a network to another. Routing protocols - to determine the best path, routers communicate with each other through routing protocols. Convergence time - the time it takes for a router to recognize a best path in the event of a change or outage. Bandwidth overhead - the burden placed on the underlying network to support the routing protocol.

Routing Protocols Routing Information Protocol (RIP) for IP and IPX - factors in only the number of of hops between nodes when determining a path from one point to another. Open Shortest Path First (OSPF) for IP - uses more complex algorithm for determining best paths. Enhanced Interior Gateway Routing Protocol (EIGRP) for IP, IPX, and AppleTalk - offers the benefits of supporting multiple protocols and limiting unnecessary network traffic between routers. Border Gateway Protocol (BGP) for IP - the routing protocol for Internet backbones.

Firewalls

Gateways Combinations of networking hardware and software that connects at least two dissimilar kinds of networks. Operate at multiple layers of the OSI model Can run on servers, workstations, or mainframe computers

Gateway Categories: gateway - translates messages from one type of system to another. Internet gateway - allows and manages access between LANs and the Internet. LAN gateway - allows segments of a LAN running different protocols, network access methods, or transmission types to communicate with each other. Voice/data gateway - allows a data network to issue data signals over a voice network. Wireless gateway - integrates a wireline network with a wireless network.

Gateway

Remote Connection Methods Direct dial to a remote access server - the client uses a dial-in software supplied with its operating system to connect to a remote access server on the LAN. Direct dial to a host workstation - the remote client uses a dial-in software supplied with its operating system to connect to a workstation that is directly attached to the LAN. Connect via the Internet - the client first connects to the Internet then connects to a private network.

Remote Connection Methods

How Modems Work Data compression: to obtain higher throughput, modems compress the data they receive from a computer before transmitting it. Data Transfer Rates: V.90 defines 56 Kbps, asymmetrical transmission in which one of the modems is assumed to be using a digital line. V.92 improves upon V.90 by increasing the upstream transmission rate to a maximum of 48 Kbps. V.92 also accomplishes faster session negotiation because modems using this standard keep a record of previous connections.

Flow Control and Buffering Software flow control (Xon/Xoff) - flow control information is issued over the same channel as the data being sent. Hardware flow control - separates flow control information from the data being sent. Buffer - a logically defined area of a computer’s memory where data is temporarily stored until it is requested by software, or until it is cleared. Buffering - the process of issuing data to a buffer.

Asynchronous and Synchronous communication Asynchronous - refers to a communications method in which data being transmitted and received by nodes does not have to conform to any predetermined timing schemes. Synchronous - refers to a communications method in which data is transmitted in a continuous stream of bits.

Modem Types Adapter card - modems can exist as an adapter card that connects to a computer’s bus. Serial port - traditionally, external modems connected to a computer via the serial port, which accepts a 22-pin, RS 232 data connector. PC Card - an excellent alternative for laptop users. USB - an excellent option for both desktop and laptop computer users.

Adapter Card

Serial Port

PC Card

USB

Virtual Private Networks

Digital Loop Carrier (DLC) A technique for delivering digital signals to a high volume of LEC subscribers over a combination of new and old local loop infrastructure. Uses multiplexing to consolidate multiple subscriber lines into fewer, high-capacity digital connections that lead to the LEC’s central office. The point at which lines are combined is called the remote subscriber terminal. Central office terminal - separates individual subscriber lines into their original circuits.

Digital Loop Carrier (DLC)

Access Nodes The point at which a user’s traffic enters or exits a carrier’s network. Digital cross-connect system (DCS) - a device that directly connects multiple digital lines with other digital lines. Integrated access devices (IADs) - integrate a number of functions into one device.

Access Nodes

Summary NICs enable workstations and other nodes to connect to a network. Gateways are combinations of software and hardware that connect dissimilar networks or systems. A virtual private network (VPN) allows an organization to carve a private WAN over public transmission facilities.