Saturday, 19 March 2011

Straight-through vs crossover cables

(wire 1<-> wire 3, wire 2<-> wire 6):
Considering the devices grouped in two categories: 1-switches / hubs / bridges, 2-workstations / servers / routers
If changing category, use a straight through cable, else use a crossover cable.  (or use straight-through when one of the port is marked with an X)

Ethernet Auto-Negotiation: determines the link speed and duplex status.
Ethernet Frames:
Ethernet II – uses a two-byte type field instead of the length.
802.3 – cannot identify the upper-layer protocol
802.2 (802.3 with LLC information in the data field of the header) – able to identify the upper layer protocol
SNAP – Subnetwork Access Protocol – used in AppleTalk and Cisco Discovery Protocol)

Half-Duplex: contention net using CSMA/CD (Carrier Sense Multiple Access/Collision Detection) and a backoff algorithm when collision occur.
Full-Duplex: two communication paths are required and compatible full-duplex NICs. Loopback and collision detection must be disabled.  Sets up a
point-to-point connection with the remote device. There are no collisions on a Full-Duplex link.

Ring LAN:
Token Ring: standard created by IBM and reflected in IEEE 802.5 with speeds of 4 or 16 Mbps.  Stations cannot transmits until they have the token,
which they can reserve using the Reservation Bits.
FDDI (Fiber Distributed Data Interface): token-passing ANSI standard providing LAN speed of up to 200 Mbps if dual rings are active. Only LAN
topology that is both physical and logical ring.
MSAU: MultiStation Access Unit, the controller of the token ring LAN, for up to 8 stations.
NAUN: Nearsest Active Upstream Neighbour
Active Monitor: one station on the ring always ensures there is only ever one token on the ring.
Beaconing: process by which a station attempts to determine a network failure.

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