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7000 Series L3 Managed Switch Reference Manual for Software v2.0
C-16 Glossary
Multicasting
To transmit a message to specific recipients across a network. A simple example of multicasting is sending
an e-mail message to a mailing list. Teleconferencing and videoconferencing also use multicasting, but
require more robust protocols and networks. Standards are being developed to support multicasting over a
TCP/IP network such as the Internet. These standards, IP Multicast and Mbone, will allow users to easily
join multicast groups. Note that multicasting refers to sending a message to a select group whereas
broadcasting refers to sending a message to everyone connected to a network. The terms multicast and
narrowcast are often used interchangeably, although narrowcast usually refers to the business model whereas
multicast refers to the actual technology used to transmit the data.
Multicast OSPF
With a MOSPF specification, an IP Multicast packet is routed based both on the packet's source and its
multicast destination (commonly referred to as source/destination routing). As it is routed, the multicast
packet follows a shortest path to each multicast destination. During packet forwarding, any commonality of
paths is exploited; when multiple hosts belong to a single multicast group, a multicast packet will be
replicated only when the paths to the separate hosts diverge. See “OSPF” on page 18 for more information.
Multiplexing
A function within a layer that interleaves the information from multiple connections into one connection.
Multi-Protocol Label Switching
An initiative that integrates Layer 2 information about network links (bandwidth, latency, utilization) into
Layer 3 (IP) within a particular autonomous system—or ISP—in order to simplify and improve IP-packet
exchange. MPLS gives network operators a great deal of flexibility to divert and route traffic around link
failures, congestion, and bottlenecks. From a QoS standpoint, ISPs will better be able to manage different
kinds of data streams based on priority and service plan. For instance, those who subscribe to a premium
service plan, or those who receive a lot of streaming media or high-bandwidth content can see minimal
latency and packet loss. When packets enter into a MPLS-based network, Label Edge Routers (LERs) give
them a label (identifier). These labels not only contain information based on the routing table entry (i.e.,
destination, bandwidth, delay, and other metrics), but also refer to the IP header field (source IP address),
Layer 4 socket number information, and differentiated service. Once this classification is complete and
mapped, different packets are assigned to corresponding Labeled Switch Paths (LSPs), where Label Switch
Routers (LSRs) place outgoing labels on the packets. With these LSPs, network operators can divert and
route traffic based on data-stream type and Internet-access customer.
MT-RJ connector
A type of fiber-optic cable jack that is similar in shape and concept to a standard telephone jack, enabling
duplex fiber-optic cables to be plugged into compatible devices as easily as plugging in a telephone cable.
MUX
See “Multiplexing” on page 16.