Specifications

DOCSIS 1.1 for Cisco uBR905 and Cisco uBR925 Cable Access Routers and Cisco CVA122 Cable Voice Adapters
Information About DOCSIS 1.1 Support
6
Cisco IOS Release 12.2(15)CZ
– Unsolicited grants (UGS)—Constant bit rate (CBR) traffic, such as voice, that is characterized
by fixed-size packets at fixed intervals.
– Unsolicited grants with activity detection (USG-AD)—Combination of UGS and RTPS, to
accommodate real-time traffic that might have periods of inactivity (such as voice using silence
suppression). The service flow uses UGS fixed grants while active, but switches to RTPS polling
during periods of inactivity to avoid wasting unused bandwidth.
• Service flows for Voice-over-IP (VoIP) calls can be flexibly created using the following methods:
– Dynamic quality-of-service (DQoS)—The router is initialized with a primary upstream service
flow and a primary downstream service flow. When a VoIP call is made, the router sends a
request for a UGS service flow with a Dynamic Service Addition Request (DSA-REQ) message.
After the call, the router deletes the service flow using a Dynamic Service Deletion Request
message (DSD-REQ) message.
– Provisioned quality-of-service (PQoS)—The router is initialized with a primary upstream
service flow, a primary downstream service flow, and two secondary upstream service flows that
are reserved for VoIP calls. The router keeps the secondary flows in the admitted state until a
VoIP call is made. The router then activates the appropriate flow with a Dynamic Service
Change Request (DSC-REQ) message with a classifier for UGS service that specifies the IP
parameters needed for the voice call. After the call, the router deletes the classifier and
deactivates the service flow by sending another DSC-REQ message.
Note If the CMTS does not support DOCSIS 1.1 dynamic services, the router can also use the
previous DOCSIS 1.0+ mechanisms to create VoIP calls.
• Enhanced time-slot scheduling mechanisms to support guaranteed delay and jitter-sensitive traffic
on the shared multiple access upstream link.
• Payload header suppression (PHS) conserves link-layer bandwidth by suppressing unnecessary
packet headers on both upstream and downstream traffic flows.
• Layer 2 fragmentation on the upstream prevents large data packets from affecting real-time traffic,
such as voice and video. Large data packets are fragmented and then transmitted in the time slots
that are available between the time slots used for the real-time traffic.
• Concatenation allows a cable modem to send multiple MAC frames in the same time slot, as opposed
to making an individual grant request for each frame. This avoids wasting upstream bandwidth when
sending a number of very small packets, such as TCP acknowledgement packets.
• Advanced authentication and security through X.509 digital certificates and Triple Data Encryption
Standard (3DES) dual public key encryption.
• Support for IP multicast encryption and for Internet Group Management Protocol (IGMP) groups.
• Secure software download allows a service provider to remotely upgrade a cable modem’s software,
without risk of interception or alteration.
• SNMPv3 Support, which includes:
– DES 56-bit encryption.
– Authentication based on the HMAC-MD5 or HMAC-SHA algorithms that ensures that each
packet is from a valid source.
– An improved security model that provides for a larger number of security levels, with a greater
granularity in determining per-user access.
– MIBs are updated as required for DOCSIS 1.1 support.