Peer-to-Peer Networks

There is no dedicated servers or hierarchy among the computers. This is recommended for 10 or fewer users. No central administration and little security.

Server-Based Networks

For more than 10 users. There is centralized administration. There are specialized servers : File and print servers, Application servers, Mail servers, Fax servers, and Communication servers.

With Server-Based Networks, you have security, backup ability redundancy, high number of users. Also client computer hardware can be limited to the needs of the user because clients do not need the additional RAM and disk storage needed to provide server services.

Topology

It refers to the arrangement or physical layout of computers, cables, and other components on the network. All network designs stem from three basic topologies:

• Bus
• Star
• Ring

The Bus is a passive topology. Computers on a bus only listen for data being sent on the network. They are not responsible for moving data from one computer to the next. If one computer fails, it does not affect the rest of the network.

The star network offers centralized resources and management. However, because each computer is connected to a central point, this topology requires a great deal of cable in a large network. Also, if the contral point fails, the entire network goes down. If one computer, or the cable that connects it to the hub, fails on a star network, only the failed computer will not be able to send or receive network data. The rest of the network continues to function normally.

Hubs - Most hubs are active in that they regenerate and retransmit the signals the same way a repeater does. Because hubs usually have eight to twele ports for network computers to connect to, they are sometimes called multiport repeaters. Active hubs require electrical power to run.

A break or umplugged cable takes down only the unplugged computer using a hub.

Network Cabling - the Physical Media

• Coaxial
• Twisted-pair (Unshielded twisted-pair and Shielded twisted-pair)
• Fiber-optic

1. Coaxial cable - There are two types of coaxial cable: thin (thinnet) and thick (thicknet)

The BNC terminator - closes each end of the bus cable to absorb stray signals. Without BNC terminators, a bus network will not function.

Use coaxial cable if you need:

• A medium that will transmit voice, video, and data.
• To transmit data longer distances than less expensive cabling can transmit.
• A familiar technology that offers reasonable data security.

2. Twisted-Pair Cable

It consists of two insulated strands of copper wire twisted around each other.

Unshielded Twisted-Pair (UTP)

UTP using the 10BaseT specification is the most popular type of twisted-pair cable and is fast becoming the most popular LAN cabling. The maximum cable length segment is 100 meters or about 328 feet.

One potential problem with all types of cabling is crosstalk. Crosstalk occurs when signals from one line mix into another line. Shielding is used to reduce crosstalk.

Shielded Twisted-Pair (STP)

STP uses a woven copper braid jacket which is a higher-quality, more protective jacket than UTP has. STP also uses a foil wrap between and around the wire pairs, and internal twisting of the pairs. This gives STP excellent shielding to protect the transmitted data from outside interference.

Twisted-pair uses RJ-45 telephone connectors to connect to a computer.

3. Fiber-Optic Cable

Optical fivers carry digital data signals in the form of modulated pulses of light. This is a relatively safe way to send data because no electical impulses are carried over the fiber-optic cable.

Use fiber-optics cable if you:

• Need to transmit data at very high speeds over long distances in a very secure media. (2 km)

Do not use fiber-optic cable if you:

• Are under a tight budget. (Pricing is very high)
• Do not have the expertise available to preperly install it and connect devices to it. Fiber optic cable is increasingly easier to work with. Polishing and teminating techniques require fewer parts and less expertise.

Signal Transmission

Wireless Transmission

Wireless LANs use four techniques for transmitting data:

1. Infrared
2. Laser
3. Narrow-band (single-frequency) radio
4. Spread-spectrum radio

Mobile Computing

Wireless, mobile networks involve telephone carriers and public services to trasmit and receive signals using:

• Packet-radio communication
• Cellular networks
• Satellite stations

Network Performance

Bus mastering - With bus mastering, the network adapter card takes temporary control of the computer's bus, by-passes the computer's CPU, and moves data directly to the computer's system memory. This speeds up computer operations by freeing the computer's precessor to concentrate on other tasks. These cards are expensive, but they can improve network performance by 20 to 70 percent.

The OSI Model (Open Systems Interconnection reference model)

It provides a description of how network hardware and software work together in a layered fashion to make communications possible. It also helps with troubleshooting by providing a frame of reference that describes how components are supposed to function.

OSI layers

Layer 7 - Application Layer

Serves as the window for application processes to access network services. This layer represents the services that directly support user applications, such as software for file transfers, for database access, and for e-mail.

Layer 6 - Presentation Layer

Determines the format used to exchange data among networked computers. It can be called the network's translator. It is responsible for protocol conversion translating the data, encrypting the data, changing or converting the character set, and expanding graphics commands. Also manages data compression to reduce the number of bits that need to be transmitted.

Layer 5 - Session Layer

Allows two applications on different computers to establish, use, and end a connection called a session. This layer performs name recognition and the functions, such as security, needed to allow two applications to communicate over the network.

Layer 4 - Transport Layer

Ensures that packets are delivered error free, in sequence, and with no losses or duplications. It repackages messages, dividing long messages into several packets and collecting small packets together in one package.

Layer 3 - Network Layer

Is responsible for addressing messages and translating logical addresses and names into physical addresses. This layer also determines the route from the source to the destination computer. It determines which path the data should take based on network conditions, priority of service, and other factors.

Layer 2 - Data Link Layer

Sends data frames from the Network layer to the Physical layer. On the receiving end, it packages raw bits from the Physical layer into data frames. Data Link layer is responsible for providing the error-free transfer of these frames from one computer to another through the Physical layer. This allows the Network layer to assume virtually error-free transfer of these frames from one computer to another through the Physical layer.

Layer 1 - Physical Layer

Transmits the unstructured raw bit stream over a physical medium (such as the network cable). The Physical layer relates the electrical, optical, mechanical, and functional interfaces to the cable. It also carries the signals that transmit data generated by all of the higher layers. This layer defines how the cable is attached to the network adapter card.

The Role of Drivers

A driver is a software that enables a computer to work with a particular device. Although a device might be installed on a computer, the computer's operating system cannot communicate with the device until the driver for that device has been installed and configured. It is the software driver that tells the computer how to drive or work with the device so that the device performs properly.

The Binding Process

It allows a great deal of flexibility in setting up a network. Protocols and network adapter cards can be mixed and matched on an as-needed basis. For example, two protocol stacks, such as IPX/SPX and TCP/IP, can be bound to one network adapter card. If there is more than one network adapter card in the computer, one protocol stack can be bound to eithere or both network adapter cards.

Application Protocols

Network Protocols

Network Major Access Methods

Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)

With CSMA/CD, each computer on the network, including clients and servers, checks the cable for network traffic. If there is data on the cable, no other computer may transmit until the data has reached its destination and the cable is free again.

Token Passing

In token passing, a special type of packet called a token circulates around a cable ring from computer to computer. When any computer on the ring wants to send data across the network, it must wait for a free token. When a free token is detected, the computer may take control of it.

Demand Priority

This access method is based on the fact that repeaters and end nodes are the two components that make up all 100VG-AnyLAN networks. The repeaters manage network access by doing round-robin searches for requests to send from all nodes on the network. The repeater, or hub, is responsible for noting all addresses, links and end nodes and verifying that they are all functioning. According to the 100VG-AnyLAN definition an end node could be a computer, bridge, router, or switch.