Extreme Networks ExtremeWare XOS Guide Manual page 467

O (continued)
OSI reference model
OSPF
P
packet
PDU
PIM-DM
PIM-SM
ping
ExtremeWare XOS 11.1 Concepts Guide
The 7-layer standard model for network architecture is the basis for
defining network protocol standards and the way that data passes
through the network. Each layer specifies particular network
functions; the highest layer is closest to the user, and the lowest layer
is closest to the media carrying the information. So, in a given message
between users, there will be a flow of data through each layer at one
end down through the layers in that computer and, at the other end,
when the message arrives, another flow of data up through the layers
in the receiving computer and ultimately to the end user or program.
This model is used worldwide for teaching and implementing
networking protocols.
Open Shortest Path First. This is an IGP. OSPF, a routing protocol for
TCP/IP networks, uses a link state routing algorithm that calculates
routes for packets based on a number of factors, including least hops,
speed of transmission lines, and congestion delays. You can also
configure certain cost metrics for the algorithm. This protocol is more
efficient and scalable than vector-distance routing protocols. OSPF
features include least-cost routing, ECMP routing, and load balancing.
Although OSPF requires CPU power and memory space, it results in
smaller, less frequent router table updates throughout the network.
This protocol is more efficient and scalable than vector-distance
routing protocols.
This is the unit of data sent across a network. Packet is a generic term
used to describe units of data at all levels of the protocol stack, but it
is most correctly used to describe application data units. The packet is
a group of bits, including data and control signals, arranged in a
specific format. It usually includes a header, with source and
destination data, and user data. The specific structure of the packet
depends on the protocol used.
Protocol data unit. A PDU is a message of a given protocol comprising
payload and protocol-specific control information, typically contained
in a header.
Protocol-Independent Multicast - Dense mode. PIM-DM is a multicast
protocol that uses Reverse Path Forwarding but does not require any
particular unicast protocol. It is used when recipients are in a
concentrated area.
Protocol-Independent Multicast - Sparse mode. PIM-SM is a multicast
protocol that defines a rendezvous point common to both sender and
receiver. Sender and receiver initiate communication at the
rendezvous point, and the flow begins over an optimized path. It is
used when recipients are in a sparse area.
Packet Internet Groper. Ping is the ICMP echo message and its reply
that tests network reachability of a device. Ping sends an echo packet
to the specified host, waits for a response, and reports success or
failure and statistics about its operation.
P
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