Mitel MiVOICE BUSINESS, Инструкция по инженерии

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Network Configuration Specifics
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DHCP LEASE TIME
To allow users to move off the local subnet, or to let new users join a subnet, a method is needed
to give up an IP address and to obtain a new address. If a phone is disconnected, it obviously
cannot talk to the DHCP server, so another method is needed to free up unused addresses.
DHCP lease time clears out unused IP addresses and makes them available for new requests.
The timer can be set from a few minutes to months. The default is set to 8 hours , which keeps
the amount of checking to see if an IP address is still in use to a reasonable level while providing
adequate recovery time to free up any unused addresses.
The exact lease time to use depends upon the system requirements. If there are plenty of spare
addresses, then the lease can be extended. Some users will specify up to a week to allow a
system to maintain the same IP addresses over a long weekend when power is removed. If
addresses are less available, and phones are more mobile, shorter times are preferred.
3300 TFTP SERVER
The 3300 ICP internal TFTP server is used to provide the IP phones with application software.
This section provides information about the interaction that takes place between the IP phones
and the 3300 TFTP server.
The 3300 TFTP server can handle 400 sessions (this is configurable) simultaneously. If a
particular phone can’t get access to the TFTP server, it will try repeatedly for a number of
seconds, after which it will re-boot and start again.
Some time-out values of interest are:
• Phones will attempt to access the TFTP server three times before rebooting. Attempts to
access the TFTP server will be made at intervals of 15-30 seconds. This interval is random
to even out the loading on the TFTP server, and to avoid a situation where multiple sets
are attempting to access the TFTP server simultaneously.
• Inter-packet timeout can be up to four seconds. More reliable transmissions will cause the
inter-packet time to lessen and the transmission of acknowledgement packets and any
retries that might occur will speed up.
• Phones will attempt to complete the TFTP download in 20 minutes.
When a phone is setting up a TFTP session with the 3300 ICP's internal TFTP server or an
external TFTP server there is an "auto-negotiation" process that they go through to establish
the block size.
The devices will try to establish the block transfer size at 4096 bytes, then they try 2048 bytes,
then they try 1024 bytes and finally they try 512 bytes.
Note: It is possible to run out of IP addresses with permanent leases, so Mitel
recommends minimizing use of these addresses. For example, a laptop user who roams
from office to office plugs in the laptop, receives a permanent address, and then
disconnects the device. The IP address is never released by the user, and the address
is never handed out to another user because the lease never expires. Eventually the
server can run out of addresses.