User's Manual Part 1

3: Detailed Description
APCD-LM043-8.0 (DRAFT C) 53
direction. While the LMS4000 900 MHz Radio Network may be able to support this level,
either as a guaranteed grade of service class parameter or on a best effort basis, VoIP
applications result in a high per packet overhead on the radio channel. This overhead and the
requirement for low latency mean the VoIP call occupies about 10% of the available bandwidth
for the duration of the call. It obviously does not take very many VoIP users to significantly
affect system performance. Also, unless this grade of service guarantee is given, the quality of
the call may be affected as other users become associated, increasing the polling interval
beyond 20 ms. Since the grade of service applies to an EUM and not to an individual service,
a VoIP user would have to be given a very high grade of service, to the possible detriment of
other end users.
3.7 CCU and EUM Feature Description
This section describes the following CCU and EUM features:
• DHCP Relay on page 53
• Port Filtering on page 54
• SNTP/UTC Time Clock on page 55
• Customer List on page 56
• SNMP Support on page 56
3.7.1 DHCP Relay
NOTE: DHCP Relay is needed only in Routed mode, and is not required
in Switched Ethernet or Through Only mode.
IP address information for CCUs and EUMs are manually entered. In the case of end-user
PCs, IP addresses can be entered manually or obtained automatically from a DHCP server, if
CCU DHCP relay is enabled.
Once DHCP Relay is enabled in the CCU, DHCP requests from the end-user’s computer pass
transparently through the CCU and EUM to the operator’s DHCP server. Since the IP address
assigned to the end-user’s computer must be on the same subnet as the CCU radio port, the
operator needs to preassign an appropriate block of IP addresses in the DHCP server.
TIP: It is helpful to assign meaningful names, such as the
customer name, to customer computers or home network routers.
Then, if a DHCP server is implemented, the address leases pool
includes this name with the client IP address, facilitating easier
identification.