Network Fundamentals and Protocols
Network Fundamentals
802.1 Standard
The 802.1 standard states that each network adapter (NIC) has a unique 48-bit physical address recorded in ROM. Thus, each computer connected to the network will have a different ID from the others.
Twisted Pair Cabling
The EIA 568B standard defines categories for differential, twisted pair cabling:
Category 5
It is the most widely used today. It uses 4 pairs of wires: 2 for transmitting data and the other two are either left free or are used to transmit voice. It can be used for 100BASE-T networks at 100 Mbps. The resistance of the wire is 100 Ohm.
Category 5e, 6, and 7
Used for 1000BASE-T Ethernet networks. Includes voice and video data transfer.
Crossover Cable
Used to transmit and receive signals correctly between similar devices. For Ethernet, pin 1 at one RJ-45 end connects to pin 3 at the other end, and pin 2 at one end connects to pin 6 on the other end. Crossover cables are used to connect devices like:
- Switch to switch
- Hub to hub
- Router to router
- PC to PC
Network Protocols
CSMA/CD Protocol
Each host “listens” to the medium to see if someone is transmitting information. If no one is sending information, the host sends its data (frame). The information travels across the cable, and all devices receive it. Each device checks the destination address.
Collision Detection
If two devices want to send data at the same time, a collision occurs. Devices detect a collision when what they hear on the medium is different from what they are sending. The device that detects the collision sends a congestion signal (JAM). All devices learn that there was a collision. A postponement algorithm (back-off) is initiated. The device that sent the data waits a random amount of time before attempting to resend the data. If there is a new collision, the random time is increased until it reaches a maximum (around 15 attempts).
The CSMA/CD protocol is currently only used in half-duplex systems.
Internet Protocol (IP)
It originated from UNIX. It is a protocol for transporting packets of information through connected networks. It is the basic inter-protocol for data transfer on the Internet.
TCP (Transmission Control Protocol)
Responsible for assembling the information packets that arrive.
UDP (User Datagram Protocol)
Enables the transmission of messages without requiring a connection or guaranteeing delivery. Used in transmissions that do not require secure transmission.
ARP (Address Resolution Protocol)
A protocol that supplements TCP/IP, used for resolving destination addresses.
IP Addressing Classes
Class A
For very large networks. First byte range: 1-126. Supports 126 different subnets.
Class B
For medium networks. First byte range: 128-191.
Class C
For small networks. First byte range: 192-223.
TCP/IP Protocol Utilities
ping [IP address or hostname]
Used to diagnose connectivity between two hosts. You specify an address, and four packets are sent. The recipient, if it exists and is connected, returns the packets. It is an “echo” utility.
ARP
View the local memory of correspondence between IP addresses and physical addresses. Normally used with
arp -a.ipconfig /all
Provides information about the IP configuration on the local computer.