1 Overview
1.2 Technology Overview
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multicast address. If set to one, this means this is a /transient/ multicast address,
meaning that it is not permanently assigned.
The flags bit are followed by another four-bit field that is used to define the scope
of the multicast address. This field allows multicast addresses to be global to the
entire Internet or restricted to smaller zones such as a specific organization or link.
The remaining bits define the multicast group ID. Under IPv6, multicast addresses
can be scoped to the local node, link, site, and so on. IPv6 routers do not forward a
multicast packet beyond the scope of the packet address.
For detailed information on IPv6 multicast addresses, see RFC 2375 and RFC 4291.
For information on assigned multicast addresses, see the IANA online database at:
http://www.iana.org/assignments/ipv6-multicast-addresses
Although IP multicasting is not a link-layer feature, it does require some support
from the underlying network interface driver. You must be able to configure the
network interface to know which multicast groups (addresses) are of interest to it.
When packets addressed to those groups arrive on the interface, the driver passes
the packet up to IP. Otherwise, the driver ignores the packet. All END drivers
currently shipped with the Wind River Network Stack support this ability.
The mechanics by which an application adds its host to a multicast group and
transmits or receives multicast data are usually handled using a UDP socket
connection. For an example of how to manage a multicast send and receive, see
Examples of Host Send and Receive, p.169.
1.2.11 Management Information Base (MIB-II)
A management information base is a virtual database that defines management
information, or variables, that can be used by a management protocol such as
SNMP to manage devices in a communications network. MIB-II is the second
generation management information base.
A MIB consists of a collection of objects used to manage entities such as routers and
switches. Objects in a MIB are defined using a subset of Abstract Symbol Notation
One (ASN.1) called the “Structure of Management Information Version 2.” The
database is hierarchical, and entries are addressed through object identifiers.
For further information on MIB-II, see RFC 1213, Management Information Base
for Network Management of TCP/IP-based internets: MIB-II, RFC 1155, Structure
and Identification of Management Information for TCP/IP-based Internets, and
RFC 1157, A Simple Network Management Protocol (SNMP).
1.2.12 Robust Header Compression (ROHC)
IP-based cellular phones and handheld computers communicate over cellular
links. For cellular phone systems, it is important to use the scarce radio resources
in an efficient way. A sufficient number of users per cell is crucial, otherwise
deployment costs are prohibitive.
When Internet protocol is used over cellular links for interactive voice
conversations, the large header overhead may pose a problem. In common
IP/UDP/RTP packets, the header information attached to each packet can be
significantly higher than the transmitted payload. For instance, an IPv4 packet