User's Manual

Table Of Contents
3 Detailed Description
26 APCD-LM043-4.0
Addressing of IP Packets
Figure 16 shows how the source and destination MAC and IP addresses are sent in IP
packets travelling between the end-user’s PC and the Internet network servers.
Figure 16 Addressing of IP Packets
As shown in Figure 16, if NAT is not enabled in the NAP Router, then the source and
destination IP addresses are maintained throughout the route between the end-user PC and
network servers. The source and destination MAC addresses, however, change whenever the
packet is passed through a router. This change of MAC addresses also takes place in the
CCU router application.
Internet to End-user Computer Data Transmission
1. Internet traffic comes through the gateway router, and possibly through backhaul and
Ethernet switches, to the CCU Ethernet port.
2. The CCU receives an IP packet through the CCU Ethernet port and checks the TCP
or UDP port number. If the port number appears in the CCU Port Filter Table,
described in Port Filter Table (CCU and EUM) on page 183, the packet is discarded.
3. The CCU reads the destination IP address. If the destination IP address is the same
as either the CCU Radio or Ethernet IP address, the packet is sent to the CCU
application.
4. The CCU checks the Routing Table, described in Routing Table (CCU and EUM) on
page 184. If the route to the destination is through the CCU Ethernet port, then the
packet is discarded, since it is not destined for a host in the CCU’s radio subnet.
Network Server
NAP Router
(no NAT)
EUM CCU BackhaulSwitch
End-user PC
Internet Router
(several)
Network Server IP Address
End-user PC IP Address
End-user PC MAC
Address
CCU Radio MAC
Address
Destination IP
Address
Source IP
Address
Destination
MAC Address
Source MAC
Address
AABB
Destination IP
Address
Source IP
Address
Destination
MAC Address
Source MAC
Address
Destination IP
Address
Source IP
Address
Destination
MAC Address
Source MAC
Address
Destination IP
Address
Source IP
Address
Destination
MAC Address
Source MAC
Address
NAP Router MAC
A
Address
CCU Ethernet MAC Address
Internet Router
MAC
A
Address
Network
Server MAC
Address
NAP Router
MAC
B
Address
Internet
Router MAC
B
Address
End-user PC IP Address
Network Server IP Address
CCU Radio MAC
Address
End-user PC MAC
Address
CCU Ethernet MAC Address
NAP Router MAC
A
Address
NAP Router
MAC
B
Address
Internet
Router MAC
B
Address
Internet Router
MAC
A
Address
Network
Server MAC
Address
End-user PC to Network Server
Network Server to End-user PC
Backhaul