VPN Router 1750 bandwidth is very slow with poor quality voice

Network Setup

Internet———> Firewall———> HP Switch —–>Contivity 1750(Main host) ——> 4 Contivity 1100s——–> Network

All the Contivity 1100s are connected via Point-Point T1 Line to Contivity 1750 (Main host).

In the network,Contivity 1100s are connected via Point-Point T1 Line to Contivity 1750 (Main host) and the users are experiencing very slow and poor bandwidth. Some IP phones were getting disconnected intermittently or were experiencing slow speech path over the T1s with the traffic conditioning and Quality of Service (QOS) configured. If there was any FTP files sent over some of these T1s, the response was also slow.


The sniffer traces and logs were examined and could not find anything unusual.  Next the port statistics for the WAN interfaces were examined and we noticed on the remote and apex site that there were some large Cyclical Redundancy Check (CRC) errors and giant frame errors on several connections. It was discussed that the  patch cable was to be replaced at one of the sites where the large CRC errors were taking place. After this change was made, throughput was around 784 kbps.

It was discussed that the throughput was still too high and so this needed to be reduced. What was configured was a rate of 384 Kbps on the QOS>interfaces>traffic conditioning EF (Expedited Forwarding). This parameter was changed from 384 to 684 and bandwidth increased to desired rate.

See the document Configuring Firewalls, Filters, NAT, and QoS for the Contivity Secure IP Services Gateway, 315896-E for more information about configuring the bandwidth management and QOS recommendations. This document can be found online at https://support.nortel.com/go/main.jsp?cscat=DOCDETAIL&DocumentOID=568569.000000&searched=315896-E

Several contivities were showing some CRC errors on the port statistics. The cables were changed out and the errors were not seen anymore. Also the QoS needed some adjustments. What had been configured was the diffServ for traffic conditioning was set to low, and therefore the bandwidth was very low – the rates were set at 384 Kbps per second. Once we changed the rate to 684 Kbps per second, the bandwidth increased.

Affected products: 

VPN Router 1000 VPN Router 1100 V06_00.310
VPN Router 1000 VPN Router 1750 V06_00.310

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