Create Dynamic Service Flows (UGS) on CMTS with Test Command

Introduction

This document describes the procedure and commands to create dynamic service flows on a Cable Modem Termination System (CMTS). For example, Unsolicited Grant Service (UGS) used in voice calls.

Prerequisites

Requirement

Cisco recommends that you have knowledge of these topics:

• CMTS
• DOCSIS

Components Used

This document is not restricted to specific software and hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Background Information

In order to create a dynamic service flow (whatever the type), either the CMTS or the Cable Modem (CM) need to send a Dynamic Service Add (DSA) message. 

The DSA message contains two things:

• The Service Flow (SF) itself.
• The associated classifier(s).

The DSA message is a TLV encoded message which uses the same TLV definitions like the ones used for the CM.

Message sequence from PacketCable Multimedia (PCMM) specification:

Create The Flows

In order to create the flow, you need to send a DSA per service flow that you want to create (you could potentially merge the 2 messages into a single message as well, but split them makes them easier to understand).

Note: the commands used here are for cBR8 platform. The uBR10k uses the same command syntax, but without the docsis keyword in the test commands

Upstream Direction

Example:

test cable docsis dsa c005.c22c.dc5b message 1823010200040601060F010610040000037F130200E8160101150400000320140400004E20160f01010203020004090605040a305879

Decode of the TLVs

1. Service Flow TLV.

The Upstream SF TLV is TLV 24 (0x18): 

1823010200040601060F010610040000037F130200E8160101150400000320140400004E20

Decode: 

1823             TLV 0x18 (24)        - Len 35 - Upstream Service Flow (0x23 = 35)
01020004         TLV 0x18.1 (24.1)    - Len 02 - Upstream Service Flow ID     - value 0004
060106           TLV 0x18.6 (24.6)    - Len 01 - QoS Parameter set type       - value 06 -> Admitted and Active bit set
0F0106           TLV 0x18.F (24.15)   - Len 01 - Service flow scheduling type - value 06 -> UGS
10040000037F     TLV 0x18.10(24.16)   - Len 04 - Request Transmit policy      - value 0x0000037F
130200E8         TLV 0x18.13(24.19)   - Len 02 - Number of bytes              - value 0xe8 -> 232 bytes
160101           TLV 0x18.16(24.22)   - Len 01 - Number of grants per interval- value 1
150400000320     TLV 0x18.15(24.21)   - Len 04 - Tolerated Grant Jitter       - value 0x320  -> 800
140400004E20     TLV 0x18.14(24.20)   - Len 04 - Nominal Grant interval       - value 0x4e20 -> 20000

2. Classifier TLV.

The classifier used in this example is a simple IP packet classifier only. Other types of classifier exist (Protocol, UDP/TCP, etc.).

The Upstream Classifier TLV is TLV 22 (0x16):

160f01010203020004090605040a305879

Decode:

160f           TLV 0x16   (22)      - Len 15 - Upstream Classifier
010102         TLV 0x16.1 (22.1)    - Len 01 - Classifier reference - Unique classifier ID - value 0x02
03020004       TLV 0x16.2 (22.2)    - Len 02 - Service flow reference                      - value 0004 -> MUST match the SFID above
0906           TLV 0x16.9 (22.9)    - Len 06 - IPv4 packet classifier encoding
05040a305879   TLV 0x16.9.5(22.9.5) - Len 04 - Destination IPv4 classifier                 - value 0a305879  10.48.88.121

It corresponds to this service flow/classifier on the CM configuration file: 

Main
{
	UsServiceFlow
	{
		UsServiceFlowRef 4;
		QosParamSetType 6;
		SchedulingType 6;
		RequestOrTxPolicy 0x0000037f;
		UnsolicitedGrantSize 232;
		GrantsPerInterval 1;
		ToleratedGrantJitter 800;
		NominalGrantInterval 20000;
	}
	UsPacketClass
	{
		ClassifierRef 2;
		ServiceFlowRef 4;
		IpPacketClassifier
		{
			IpDstAddr 10.48.88.121;
		}
	}
}

Downstream Direction

Example:

test cable docsis dsa c005.c22c.dc5b message 191A010200990601060701050804000154A00A04000154A00B0200DA170f01010203020099090603040a305879

Decode of the TLVs

1. Service Flow TLV.

The Downstream Service Flow TLV is TLV 25 (0x19):

191A010200990601060701050804000154A00A04000154A00B0200DA

Decode:

191A           TLV 0x19   (25)      - Len 1A (26)   - Downstream Service Flow definition
01020099       TLV 0x19.1 (25.1)    - Len 02        - Downstream Service Flow ID   - value 0x99      
060106         TLV 0x19.6 (25.6)    - Len 01        - QoS Parameter set type       - value 06 -> Admitted and Active bit set
070105         TLV 0x19.7 (25.7)    - Len 01        - Traffic Priority             - value 05 -> Prio 5
0804000154A0   TLV 0x19.8 (25.8)    - Len 04        - Max Sustain Rate             - value 0x154a0 = 87200 bps
0A04000154A0   TLV 0x19.A (25.10)   - Len 04        - Min Reserved Rate            - value 0x154a0 = 87200 bps
0B0200DA       TLV 0x19.B (25.11)   - Len 02        - Assumed Min Rvd Rate packet size - value 0xda = 218

2. Classifier TLV.

This is also a plain IPv4 classifier. A more complex classifier can also be created.

The Downstream Classifer TLV is TLV 23 (0x17):

170f01010203020099090603040a305879

Decode:

170f          TLV 0x17    (23)      - Len 15 - Downstream Classifier
010102        TLV 0x17.1  (23.1)    - Len 01 - Downstream Classifier Reference        - value 0x02
03020099      TLV 0x17.3  (23.3)    - Len 02 - Downstream Service Flow ID reference   - value 0x99 -> MUST match SFID above
0906          TLV 0x17.9  (23.9)    - Len 06 - IPv4 classifier
03040a305879  TLV 0x17.9.3(23.9.3)  - Len 04 - Source IPv4 Address                    - value 0x0a305879 -> 10.48.88.121

It correspods to this service flow/classifier on the CM configuration file:

Main
{
	DsServiceFlow
	{
		DsServiceFlowRef 153;
		QosParamSetType 6;
		TrafficPriority 5;
		MaxRateSustained 87200;
		MinReservedRate 87200;
		MinResPacketSize 218;
	}
	DsPacketClass
	{
		ClassifierRef 2;
		ServiceFlowRef 153;
		IpPacketClassifier
		{
			IpSrcAddr 10.48.88.121;
		}
	}
}

Delete the Flows

Dynamic service flows can be deleted with a Dynamic-Service-Delete (DSD) message. The procedure is identical to delete both US SF and DS SF.

test cable docsis dsd <mac> <service-flow-id>

Example:

acdc-cbr8-2#show cable modem 2cab.a40c.5598 service-flow

SUMMARY:
MAC Address    IP Address      Host          MAC               Prim  Num Primary        DS
                               Interface     State             Sid   CPE Downstream     RfId
2cab.a40c.5598 172.54.0.4      C1/0/2/UB     w-online          27    0   In1/0/2:7      8711


Sfid  Dir Curr  Sid   Sched  Prio MaxSusRate  MaxBrst     MinRsvRate  Throughput
          State       Type
17    US  act   27    BE     5    1024        3044        0           929
18    DS  act   N/A   N/A    3    300000000   24600       0           887

--> Before : 2SFs only

acdc-cbr8-2#test cable docsis dsa 2cab.a40c.5598 message 1823010200040601060F010610040000037F130200E8160101150400000320140400004E20160f01010203020004090605040a305879

--> UGS SF

acdc-cbr8-2#test cable docsis dsa 2cab.a40c.5598 message 191A010200990601060701050804000154A00A04000154A00B0200DA170f01010203020099090603040a305879

--> DS SF

acdc-cbr8-2#show cable modem 2cab.a40c.5598 service-flow
Load for five secs: 10%/1%; one minute: 9%; five minutes: 10%
Time source is NTP, 10:54:57.426 CET Thu Nov 22 2018


SUMMARY:
MAC Address    IP Address      Host          MAC               Prim  Num Primary        DS
                               Interface     State             Sid   CPE Downstream     RfId
2cab.a40c.5598 172.54.0.4      C1/0/2/UB     w-online          27    0   In1/0/2:7      8711


Sfid  Dir Curr  Sid   Sched  Prio MaxSusRate  MaxBrst     MinRsvRate  Throughput
          State       Type
17    US  act   27    BE     5    1024        3044        0           896
57    US  act   43    UGS    0    0           0           0           0
18    DS  act   N/A   N/A    3    300000000   24600       0           0
58    DS  act   N/A   N/A    5    87200       3044        87200       0

--> Now Both UGS and DS voice flows are created (and throughput would be seen as soon as packets match the classifier.)

Related Information

• PacketCable Multimedia Specification
• Technical Support & Documentation - Cisco Systems