中医药学高级丛书—中医儿科学_部分4.pdf

IP over WDM. Kevin H. Liu
Copyright  2002 John Wiley & Sons, Ltd.
ISBN: 0-470-84417-5
8
Other IP/WDM Specific Issues
† IP/WDM munication
† IP/work and service management
† TCP over works
IP/WDM munication
munication is required in some applications such as video conferencing,
where packets are delivered to a specified subgroup work hosts. A well-known,
in-use multicast backbone is the MBone, whereby a work is imposed over
the through tunnelling implemented by the multicast-enhanced routers to
forward multicast datagrams. In works, an optical signal can split into
multiple light paths/branches in the physical layer and this splitting can be regarded
as physical layer multicasting. However, wavelength splitting degrades optical signal
quality, so to achieve certain QoS parameter settings, the splitting is constrained by
several factors. IP multicasting support over IP/works is related to the type
of WDM switch, for example, switched WDM or reconfigurable WDM, and the IP
and WDM working architectures, . overlayed or peer-to-peer.
IP Multicasting
In conventional works, multicast is desirable to support munication
because it not only reduces host or server processing load, but also saves bandwidth
by work loading.
Figure presents parison between unicasting and multicasting a packet.
Using unicasting, the server has to send four identical packets to four other hosts.
Hence, four packets are inserted into work. Using multicasting, the server
inserts only one packet into work and routers forward this packet only to
multicasting members. The multicast group is identified by a multicast address.
Unlike a unicast IP address that uniquely identifies a single IP host, a multicast IP
address identifies an arbitrary group of IP hosts that have joined the group. In IPv4,
class D addresses, spanning from through , are reserved
340 OTHER IP/WDM SPECIFIC ISSUES
Figure IP unicasting