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An ordered group of data and control signals transmitted through a network, as a subset of a larger message.

Parity Bit

An additional non-information bit added to a group of bits to ensure that the total number of l bits in the character is even or odd.

Physical Layer

Layer 1 of the OSI model. The layer concerned with electrical, mechanical, and handshaking procedures over the interface connecting a device to the transmission medium.


Protocol Independent Multicast
PIM is a multicast routing protocol that runs over an existing unicast infrastructure. Unicast routing protocols include RIP and OSPF. PIM is called “protocol independent” because it can use the route information that any routing protocol enters into the multicast Routing Information Base (RIB)


Plain Old Telephone Service
The analog dial tone-type telephone networks and services in place worldwide with transmission rates up to 52 kbps. In contrast, telephone services based on digital communications lines, such as ISDN, have higher speeds and bandwidths. POTS networks are also called public switched telephone networks (PSTNs).


Also called CoS (class of service), classifies traffic into categories such as high, medium, and low. The lower the priority, the more “drop eligible” is a packet. E-mail and Web traffic are often placed in the lowest categories. When the network gets busy, prioritization ensures critical or high-rated traffic is passed first, and packets from the lowest categories may be dropped.


A formal set of conventions governing the formatting and relative timing of message exchange between two communicating systems.