Phone Behavior During Times Of Network Congestion - Cisco 8800 Series Administration Manual

Phone Behavior During Times of Network Congestion

• You have enabled autoregistration in Cisco Unified Communications Manager
• The phone has not been added to the Cisco Unified Communications Manager database
• The phone is registering for the first time
Related Topics
Cisco Unified Communications Manager Documentation, on page xvii
Phone Behavior During Times of Network Congestion
Anything that degrades network performance can affect Cisco IP Phone voice and video quality, and in some
cases, can cause a call to drop. Sources of network degradation can include, but are not limited to, the following
activities:
• Administrative tasks, such as an internal port scan or security scan
• Attacks that occur on your network, such as a Denial of Service attack
Phone Behavior on a Network with Two Network Routers
The Cisco IP Phone 8800 Series uses a firewall to provide protection against cyber intrusions, such as a
man-in-the-middle attack. This firewall cannot be disabled. But it could stop traffic on a phone, if you configure
your network with two network routers in the same subnet and with IP redirect.
The phone firewall stops traffic because this network setup is similar to a man-in-the-middle attack. The phone
receives redirect packets for different destination IPs in a different subnet from the phone. The phone is on a
network with more than one router, and the default router sends traffic to a second router.
Look at the phone logs if you suspect the firewall is stopping traffic. Look for an error code 1 notification
from the operating system when it tried to establish a connection. One of the signatures is
sip_tcp_create_connection: socket connect failed cpr_errno: 1.
A network with two network routers in the same subnet and with IP redirect is not a common configuration.
If you are using this network setup, consider using only one router on a subnet. But if you require two network
routers on the same subnet, disable IP Redirect on the router and reboot the phone.
Cisco IP Phone 8800 Series Administration Guide for Cisco Unified Communications Manager
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