CptS 302: Network Hardware

Ethernet
- Started as Ph.D. thesis (Bob Metcalfe) at MIT
  - Originally 3 Mb/s
  - Moved to 10 Mb/s quickly
- Developed into a product by Xerox, DEC, & Intel
- Protocol compared to "a polite dinner party"
  - CSMA/CD
    - Carrier Sense -- devices can tell when another is talking
    - Multiple Access -- any device can talk at any time
    - Collision Detection -- devices can tell when they talk at the same time as someone else
  - The basic idea is that any device on the ethernet is free to speak at any time
    - If two (or more?) devices talk at the same time, a collision occurs
    - Both devices wait for a slightly random delay (to prevent them from retrying at the same time)
    - Conventional wisdom says that ethernet can sustain only about 30% of the "rated" speed
  - Branching bus with no loops
    - The basic ethernet configuration is a bus, with a branch to each device
      - This is most obvious in thicknet, a little less so in thinnet, hard to tell in 10baseT or 100baseT
    - No loops means there is only one path for a signal to take
      - Loops in an ethernet will cause big trouble
- Unshielded Twisted Pair
  - The preferred medium for ethernet
  - Inexpensive wiring
  - Easy to install and debug
  - Each link is independent, so bad connections don't take down the network
  - Cables come rated by "category"
    - Category 3 supports 10 Mb/s
    - Category 5 supports 100 Mb/s
    - Categories 5e and 6 support 1 Gb/s
- Connecting Ethernets
  - Layer 1 -- Hubs
    - Also called "repeater" or "concentrator"
    - Retransmits ethernet frames
    - Does not interpret or act on content
    - Maximum of 4 hubs may be in any path on a 10 Mb/s ethernet, 2 hubs for 100 Mb/s, and 1 hub for 10 Mb/s
  - Layer 2 -- Switches
    - Do examine addresses
    - Regenerate packets
      - Not subject to repeater limits
    - "Learn" what addresses are on what port
    - Only send packets to ports that need them
    - Greatly reduce traffic on the network
      - And thus, greatly improve performance
    - Many can connect ports into "virtual LANs" or VLANs
  - Layer 3 -- Routers
    - Connect 2 or more networks
    - Look at address on Layer 3 (e.g. IP, Appletalk, NetBEUI)
    - Can route between different network types (ethernet, FDDI, ATM)
    - A Unix computer can be a router, but a dedicated router will probably be more reliable and perform better
FDDI
- Fiber Distributed Data Interface
- Dual token ring
- Fiber optic cable
- 100 Mb/s
ATM
- Asynchronous Transfer Mode
- Divides data into 53-byte chunks (called "cells")
- Can guarantee throughput
- The WSU backbone is ATM

Network Hardware

LAN/WAN/MAN

LANs

WANs and Wiring