Understanding the network.pdf - Back to Home

• Link aggregation or fat pipe technology—This is the aggregation
of multiple switch ports operating as a single interface. This
technology was originally developed by Kalpana (later acquired
by Cisco Systems under the name Fast EtherChannel). Link
aggregation for Ethernet is now IEEE standard 802.3ad.
• Virtual LANs (VLANs)—VLANs are manufactured Layer 2
broadcast domains. Using VLANs, it is possible to partition the
switch's ports into one or more logical, Layer 2 broadcast
domains. The practical result is the capability of the switch to
support multiple Layer 3 network transports (for example,
Layer 3 broadcast domains) on the same switch (and if need be,
on the same port). In other words, Layer 3 broadcast and
unicast are only sent to ports designated to receive them.
VLANs are created by either static or dynamic means, defining
certain ports on the switch to be members of particular VLANs
(Layer 2 broadcast domains). Cabletron's SecureFast, Cisco
Systems'ISL VLAN protocol, and the ATM Forum's LANE are all
variations of proprietary VLAN schemes. The IEEE 802.1q
standard is now the supported VLAN standard for most switch
manufacturers.
• Traffic prioritization—In addition to logical Layer 2 broadcast
domain partitioning, certain VLAN implementations provide
CoS-based forwarding. In contrast to the standard switch
queuing method which is known as first in, first out (FIFO), with
CoS forwarding, VLANs and physical ports can be set with a CoS
priority level. The CoS priority level definition, in conjunction
with multiple transmission queues (one for each CoS level,
defined on the switch), is then used to provide prioritized or
"weighted" packet delivery. The IEEE standard 802.1p defines
the Layer 2 traffic prioritization scheme used with 802.1q VLANs.
Along with 802.1q, there are several proprietary prioritization
schemes; Intel's High Priority Queue (HPQ) and 3COM's
Dynamic Access are two examples of proprietary-based
queuing.
• Full-duplex transmission—Full-duplex data transmission is not a
new concept to data networking. Until switching arrived,
however, it was not possible to achieve with LAN transmission
protocols. Full-duplex operation provides the capability to
simultaneously send and receive packets over the transmission
medium. Full-duplex operation is available with FDDI (as a
proprietary option only), 10BaseT, 100BaseTX and FX, Gigabit
Ethernet (covered under the IEEE 802.3x standard), and Token
Ring (which is defined as part of the IEEE 802.5r standard).