Desigining Real World Network.

                            

Ethernet:

Ethernet is the most popular physical network architecture in use today. First conceived in the 1960s at the University of Hawaii as the ALOHA network. In 1972 Robert Metcalfe and David Boffs at Xerox PARC implemented the network architecture and signaling scheme and in 1975 they introduced the first Ethernet product. Ethernet is a bus or star bus based technology that uses baseband signaling and CSMA/CD to arbitrate network access.

How Ethernet Works:

• Ethernet arbitrates access to the network with the CSMA/CD media access method.
• Only one workstation can use the network at a time.
• Workstations send signals (packets) across the network.
• When a collision takes place, the stations transmitting the packets stop transmitting and wait a random period of time before retransmitting.

10Mbps Ethernet:

Four commonly used 10Mbps Ethernet cabling systems are:

• 10Base5 or thicknet, which uses thick coaxial cable.
• 10Base2 or thinnet, which uses thin coaxial cable.
• 10BaseT, which uses UTP cable.
• 10BaseFL, which uses optical fiber.

10Base5 (Thicknet) Ethernet:

Specifications:

• Maximum segment length                            500 m
• Maximum taps                                             100
• Maximum segments                                      5
• Maximum segments with node                     3
• Maximum distance between taps                  2.5 m
• Maximum repeaters                                      4
• Maximum overall length with repeater          2.5 kms
• Maximum AUI drop cable length                  50m

Thicknet cable has the following disadvantages:

• Large size
• High cost
• Connection method
• Very few advantages comparing today’s network but it is still reliable.

10Base2 (Thinnet) Ethernet:

Specifications:

• Maximum segment length                            185 m
• Maximum segments                                     5
• Maximum segments with node                     3
• Maximum repeaters                                     4
• Maximum overall length with repeater        925 m
• Maximum devices per segment                    30

Disadvantages of Thinnet:

• High cost compared to UTP cable.
• Bus configuration makes the network unreliable.

Advantages:

• It was economical solution since longtime, so it is used in many existing installation

10BaseT Ethernet:

Specifications:

• Maximum segment length                           100 m
• Maximum segments                                    1024
• Maximum segments with node                    1024
• Maximum nodes per segment                      2
• Maximum hubs in a chain                            4
• Maximum nodes per network                     1024

Advantages:

• UTP costs less and is more flexible than 10Base5 or 10Base2 cabling.
• 10BaseT is easy to troubleshoot.
• It is possible to isolate a device that is causing problems.

10BaseFL Ethernet:

Specifications:

• Maximum segment length              2000 m
• Maximum segments                       1024
• Maximum segments with node      1024
• Maximum nodes per segment        2
• Maximum hubs in a chain             4
• Maximum nodes per network       1024

100Mbps Ethernet:

For some applications, a 10Mbps data rate is not enough.

Two competing standards of 100Mbps:

• 100VG-AnyLAN.
• 100baseT Ethernet or Fast Ethernet.

100VG-AnyLAN has thefollowing advantages:

• It is faster
• It supports both Ethernet and Token Ring packets
• It uses a demand priority access method
• Hubs can filter individually addressed frames for enhanced privacy 

Network Protocols For computer Networking

Network Protocols:

Protocols are the agreed upon ways in which computers exchange information.

Protocols that work together to provide a layer or layers of the Open System Interconnection model are known as protocol stack or suite.

Standard protocol stacks:

•  The ISO/OSI protocol suite
•  IBM System Network Architecture (SNA)
•  Digital DECnet                    ,  AppleTalk
•  Novell NetWare       , TCP/IP

A protocol is a set of basic steps that both parties must perform in the right way.

 For one computer to send a message to another computer, first computer must perform the following steps:

1. Break the data into small section called packets
2. Add addressing information to the packets identifying the destination computer
3. Deliver the data to the network card for transmission over the network

The receiving computer must perform the same steps but in opposite order:

1. Accept the data from the network adapter card.
2. Remove the transmitting information that was added by the transmitting computer.
3. Reassemble the packets of data into the original message.

 Networks primarily send and receive the small chunks of data called packets.

Packet structure: Packets have the following components:

1. A source address specifying the sending computer.
2. A destination address.
3. Instructions that tell the computer how to pass the data along.
4. Reassembly information for when the packet is part of a longer message.
5. The data to be transmitted to the remote computer.
6. Error-checking information to ensure that the data arrives intact.

 The components are combined into three sections:

•  Header: Includes alert signal to indicate that the data is being transmitted, source and destination addresses and clock information to synchronize the transmission.
•  Data: The actual data being sent. This can vary from 48 bytes to 4K.
• Trailer: The contents of the trailer varies among network types, but it typically includes a CRC. CRC helps the network determine whether a packet has been damaged in transmission

Microsoft-Supplied Network Protocol:

• NetBEUI
• NWLink
• TCP/IP
• NetBEUI

NetBEUI: It stands for NetBIOS Extended User Interface. Microsoft included NetBEUI 3.0 with Windows NT. (Originally it is developed by IBM)

Advantages of NetBEUI:

• High speed on small network
• Ability to handle more than 254 sessions
• Better performance over slow serial links than previous versions
• Ease of implementation
• Self-tuning features
• Good error protection
• Small memory overhead

Disadvantages of NetBEUI:

• It cannot be routed between networks
• Few tools for NetBEUI such as protocol analyzer
• It offers very little cross-platform support

NWLink:

NWLink is Microsoft’s implementation of Novell’s IPX/SPX protocol stack, used in Novell NetWare.