Local Area Networks (LAN)

• Generally
  • Controlled by a single end-node organization.
  • Single building to single campus.
  • Higher speed.
  • The organization owns all of the equipment.
  • Hard to tell where the network ends and the computer begins.
  • Consider the following
    • Network card within a PC
    • Networked printer.
    • Network Attached Storage
    • A Second choice
    • Or perhaps this one
    • "Pricing for the FAS6000 series goes as follows: The FAS6030 has an entry price of $131,600, while the bigger FAS6070 costs $196,225. This price includes a single storage controller, iSCSI protocol software and a single disk shelf with electronically switched Fibre Channel hubs. One raw terabyte of storage in the form of 14 x 72GB/10Krpm FC disk drives is included, as well as the cabling required to connect the controller and disk shelf." (from here)
• The book trys to justify price/performance of LANS, but this, I believe, is out of date.
• The also differentiate between:
  • The PC network.
  • The fast network connecting servers in your machine room.
  • The storage area network. (SAN)
• SAN
  • This consists of network attached storage devices.
  • Normally they are connected with Fiber Channel internally
  • This is used for backup, and replication.
  • They appear to speak a form of SCSI protocol over this network.
  • Connected with ethernet externally.
  • There is no computer between these devices and the network.
  • They appear to the attached computer as a directly attached hard drive.
  • This is not the same as the network attached storage above, which is essentially a computer running nfs/smb/... .

Topologies and Choices of Transmission Media

• The topology is the way machines are physically hooked to the network.
• A bus topology places many machines on a shared media.
  • The signal is placed on the bus by the transmitter and sent to all attached devices.
  • There is a problem with bus contention.
  • You must indicate who the message is for.
  • As we have discussed before, this is cheap
    • A shared single wire
    • A limited number of ports on the networking hardware
  • but expensive.
    • shared network -> lower throughput
  • Notice this is still in use.
  • But perhaps not at the lan level.
• A tree is a bus with forks.
  • There can be no loops.
  • If we put a layer 2 switch at each of the branches, they are semi-independent.
  • This has all of the problems of a bus
  • But can be longer an accommodate more nodes.
• In both a bus and a tree
  • Machines are generally attached via a transceiver.
  • This is not an active element of the network, more like a tap.
  • Machines are not able to "remove" packets from the net.
  • Transmission must be in the form of packets, not circuits.
  • All machines have unique addresses.
  • All packets contain these addresses.
• Ring topology
  • Each station is attached via a repeater.
  • In this case, the repeater can remove a packet from the net.
  • A ring of machines is built.
  • Data is sent in one direction around the ring.
  • When it reaches the sender, it is removed.
• Star topology
  • Each node is directly connected to a network device.
  • These devices may be in a number of configurations, including a tree.
  • This is mostly the choice of today.
  • It requires a bunch of wires.
  • Normally all pulled to a central location
  • Or to wiring closets, which are then pulled to a central location.
• Transmission Medium
  • Coax
  • Twisted pair
    • Cat 3
    • Cat 5
    • Cat 6 and up.
  • Fiber
    • Multimode
    • Singlemode