Which Technologies Are Used in a Local Area Network

We are talking about the infrastructure we need to carry data.

Ethernet

• Most common infrastructure in LANs
• Outlined by the IEEE 802.3 standard.
• Commonly used with UTP (8 wires)/RJ45s (8 pins)
• When upgrading network speed, make sure all the devices can perform at that speed.
• We are talking about bits not bytes (8 bits) when discussing speed.

Ethernet Speeds

Networks Classifications

• Each different specification indications a:
  • Distance,
  • Medium, and
  • Speed
• When looking at the name 10 Base T, lets look at the number
  • 10 – tells us we are running at 10 Mbps, so we need a Cat 3. The “T” indicates we are using an ethernet cable (twisted pair)
• 100 Base X is really a category of several standards.
• 10 Base G is a collection of several Gigabit standards and is also known as the IEEE 802.3z standard and runs over copper or fiber.

LAN traffic is different from WAN network traffic in that WAN traffic is more organized and point to point, while on LAN’s you get a lot more broadcasts

Broadcast Domains

• Sends to all devices on the network.
  • ARP/DHCP discover request
• Cannot pass through a router.
  • Broadcast domain includes the network and the internally facing NIC of the router.
• Broadcast storm
  • A loop that occurs due to a misconfiguration of devices.
  • Can shut down network as broadcast propagates around switches

Collision Domains

• Occurs when two devices try to transmit simultaneously.
  • Collision windows are milliseconds long
• Data on the same line collides and corrupts packets
  • When  a collision occurs, the packets don’t just disappear as the sending devices have ways of rectifying the situation.
• Collision domain vs Broadcast domain.
  • Areas of the network where a broadcast message propagates
  • Collision domain are the links where collisions can occur within a broadcast domain.  Occurs when switch tries to talk to computer at the same time.  If we were using hubs rather than switches, the collision domain would be much larger as hubs send packets to everyone.
  • The ethernet standard, IEEE 802.3, has outlined ways of avoiding collisions.

CSMA/CD

Stands for “Carrier Sense Multiple Access Collision Detection” and is a reactive measure.  Can often result in transmitting a lot of data

• Carrier Sense
  • Nodes detect collision
• Multiple access
  • Multiple devices attempt to talk simultaneously
  • Some topologies do not provide simultaneous access to the network.  Ring technology requires tokens for access and are not multiple access.  Bus and Mesh are multiple access networks
  • Would not use this technology in a ring network
• Collision detection
  • When a collision is detected, the devices that sent the packets have a random interval of time for how long they wait before resending the packets.

CSMA/CA

Stands for “Carrier Sense Multiple Access Collision Avoidance” and is a proactive measure

• Carrier sense
  • Nodes detect collision
• Multiple access
  • Multiple devices attempt to talk simultaneously
  • Some topologies do not provide simultaneous access to the network.  Ring technology requires tokens for access and are not multiple access.  Bus and Mesh are multiple access networks
  • Would not use this technology in a ring network
• Collision avoidance
  • NIC send an alert, a small packet, to the network, notifying it that we are about to transmit.
  • When the computer realizes there is no collision, it sends the data.
  • If another device sends an alert as well and there is an alert message collision, both devices go through the random waiting period before resending the alert message.

Ethernet Bonding

• Combining multiple NICs
  • A single NIC could be a point of failure
  • Add a second NIC card and attach it to a port
  • Server can use both cards
• Increased Bandwidth/Redundancies
• Useful for servers.
• Good for maintaining uptime.