Troubleshooting guide

CHAPTER
5-1
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
5
Troubleshooting DOCSIS Networks
DOCSIS provides the bandwidth and latency guarantees needed to provide toll-quality voice, data
services, and multimedia applications across a shared HFC network. It is designed to be backward
compatible, enabling DOCSIS 1.0 and 1.1 modems to operate in the same spectrum on the same network.
This chapter discusses:
• DOCSIS 1.0+, page 5-1
• Understanding Initialization States, page 5-3
• Radio Frequency (RF) Issues, page 5-9
• Troubleshooting RF Problems, page 5-10
• Measuring RF Signals, page 5-11
• Troubleshooting Slow Peformance, page 5-17
DOCSIS 1.0+
The Cisco uBR7246Vxr CMTS supports DOCSIS 1.0+ starting from IOS release 12.1(01)T.
DOCSIS 1.0+ is DOCSIS 1.0 with some special QoS extensions for supporting realtime
Voice/Fax/Video on the local access network. However, these features are only activated when a
DOCSIS 1.0+ MTA solicits these services via new dynamic MAC messages.
The DOCSIS 1.0+ services include the following:
• Two MTA-initiated dynamic MAC messages, DSA and DSD. These messages allow dynamic SIDs
to be created/destroyed at run-time on a per Voice/Fax call basis.
• Unsolicited Grant Service (CBR-scheduling) on the upstream. This helps to provide a high quality
QoS channel for the upstream constant bit rate (CBR) Voice/Fax packets from the MTA.
• For any given MTA, the ability to provide separate downstream rates based on the IP-precedence
value in the packet. This helps in separating Voice/Signaling/Data traffic going to the same MTA for
rate-shaping purposes.
Following is an example of how DOCSIS 1.0+ features are applied in an interaction between the uBR
and the MTA.
• The MTA downloads theconfig file at the time of registration, and sends the provisioning
information to the DOCSIS 1.0+ CMTS.