Руководство Пользователя для Netopia 3220-h
How Your Cayman 3220-H Works
Cayman 3220-H User’s Guide
C-2
December 2000
ATM uses fixed-length cells to transport data. When data, such as an
Ethernet packet, is passed to ATM, the data is segmented into a series
of small (53-byte) cells. Each ATM cell consists of 5 bytes of header
information (virtual path identifier, virtual circuit identifier, and CRC
checksum) and 48 bytes of data. Information in the header identifies
cells belonging to the same virtual channel, which is used to route
the cell to its intended destination.
Ethernet packet, is passed to ATM, the data is segmented into a series
of small (53-byte) cells. Each ATM cell consists of 5 bytes of header
information (virtual path identifier, virtual circuit identifier, and CRC
checksum) and 48 bytes of data. Information in the header identifies
cells belonging to the same virtual channel, which is used to route
the cell to its intended destination.
Each end-point on an ATM virtual circuit generates a constant stream
of cells to the circuit's other end-point. When there is no data to
transport, ATM sends a stream of empty cells from one end of a
virtual circuit to the other. When a user at one end-point sends a
message or file to a user at the other end, ATM incorporates the data
into the stream of cells. If several users want to transfer data
simultaneously, ATM uses multiplexing to let each user share the data
stream dynamically.
of cells to the circuit's other end-point. When there is no data to
transport, ATM sends a stream of empty cells from one end of a
virtual circuit to the other. When a user at one end-point sends a
message or file to a user at the other end, ATM incorporates the data
into the stream of cells. If several users want to transfer data
simultaneously, ATM uses multiplexing to let each user share the data
stream dynamically.
About Network
Address
Translation
Address
Translation
Network address translation (NAT) lets a Cayman 3220-H conceal the
topology of an Ethernet network connected to its LAN interface
from routers on networks connected to its WAN interface.
topology of an Ethernet network connected to its LAN interface
from routers on networks connected to its WAN interface.
When NAT is enabled, the Cayman 3220-H “proxies” for computers
on your network by pretending to be the originating host for
network communications from non-originating networks. The
Cayman 3220-H tracks which local hosts are communicating with
which remote hosts, and routes packets received from remote
networks to the correct computer on the LAN (Ethernet A) interface.
Sites communicating through an Internet service provider typically
enable NAT, since they often receive one IP address from the ISP.
on your network by pretending to be the originating host for
network communications from non-originating networks. The
Cayman 3220-H tracks which local hosts are communicating with
which remote hosts, and routes packets received from remote
networks to the correct computer on the LAN (Ethernet A) interface.
Sites communicating through an Internet service provider typically
enable NAT, since they often receive one IP address from the ISP.
When NAT is disabled, the Cayman 3220-H acts as a traditional
TCP/IP router. It uses RIP (Routing Information Protocol) to
advertise the networks connected to its Ethernet ports to the routers
on the other end of the network connection.
TCP/IP router. It uses RIP (Routing Information Protocol) to
advertise the networks connected to its Ethernet ports to the routers
on the other end of the network connection.