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626 Chapter 8: Call Admission Control and QoS Signaling

Foundation Summary

The “Foundation Summary” is a collection of tables and ﬁgures that provide a convenient review of many key concepts in this chapter. For those of you already comfortable with the topics in this chapter, this summary could help you recall a few details. For those of you who just read this chapter, this review should help solidify some key facts. For any of you doing your ﬁnal prep before the exam, these tables and ﬁgures are a convenient way to review the day before the exam.

Figure 8-35 shows the effect of a VoIP network without the use of CAC.

Figure 8-35 VoIP Network Without CAC

IP Network Supports 2 Calls Max!

	Call 1
	Call 2
R1	IP Network	R2
R1		R2

Call 3

The Third Call Degrades Voice Quality for All Calls

Figure 8-36 shows how CAC can be used in a legacy VoIP network to redirect a call to the PSTN in the even that sufﬁcient resources are not available to carry the call on the data network.

Figure 8-36 Legacy VoIP Network with CAC

IP Network Supports 2 Calls Max!

	Call 1
	Call 2
R1	IP Network	R2
R1		R2

PSTN

Call 3

CAC Reroutes the Third Call Through the PSTN

Foundation Summary 627

Figure 8-37 shows how CAC can be used in an IP telephony network to redirect a call to the PSTN in the event that sufﬁcient resources are not available to carry the call on the data network.

Figure 8-37 IP Telephony Network with CAC

	IP Network Supports 2 Calls Max!
Host Site		Call 1	Remote Site
		Call 2
IP	R1	IP Network	R2	IP
IP	R1		R2	IP
Host Phone A				Remote
				Phone A
IP	SW1	PSTN	SW2	IP
Host Phone B		PSTN		IP
				Remote
		Call 3		Phone B
		Call 3
IP		CAC Reroutes the Third Call
Host Phone C		CAC Reroutes the Third Call		IP
		Through the PSTN		IP
		Through the PSTN		Remote
				Remote
				Phone C
CallManager	CallManager
Publisher	Subscriber

Table 8-26 illustrates a few of the possible G.711 and G.729 bandwidth requirements.

Table 8-26 Bandwidth Requirements

	Payload				Packets
	per	IP/UDP/RTP	L2 Header	L2 Header	per	Bandwidth
Codec	Packet	Header Size	Type	Size	Second	per Call

G.711	160 bytes	40 bytes	Ethernet	14 bytes	50 pps	85.6 kbps

G.711	240 bytes	40 bytes	Ethernet	14 bytes	33 pps	77.6 kbps

G.711	160 bytes	40 bytes	MLPPP/FR	6 bytes	50 pps	82.4 kbps

G.711	160 bytes	2 bytes (cRTP)	MLPPP/FR	6 bytes	50 pps	67.2 kbps

G.729	20 bytes	40 bytes	Ethernet	14 bytes	50 pps	29.6 kbps

G.729	20 bytes	40 bytes	MLPPP/FR	6 bytes	50 pps	26.4 kbps

G.729	30 bytes	40 bytes	MLPPP/FR	6 bytes	33 pps	20 kbps

G.729	20 bytes	2 bytes (cRTP)	MLPPP/FR	6 bytes	50 pps	11.2 kbps

*For DQOS test takers: These numbers are extracted from the DQOS course, so you can study those numbers. Note, however, that the numbers in the table and following examples do not include the L2 trailer overhead.

628 Chapter 8: Call Admission Control and QoS Signaling

Figure 8-38 illustrates the packet structure of the layer 2 and IP/UDP/RTP headers and the payload for a voice packet.

Figure 8-38 Voice Packet Structure

Layer 2	IP	UDP	RTP	Payload of Speech Samples
Variable				Variable Size Based on Codec
Size	20	8	12	Selection and Number of
Based on	Bytes	Bytes	Bytes	Speech Samples Included
Layer 2
Protocol

Table 8-27 describes the criteria that is used to evaluate the different CAC tools.

Table 8-27 CAC Feature Evaluation Criteria

Evaluation Criteria	Description

Voice over X (VoX)	The voice technologies to which the CAC method applies, such as VoIP
supported	and VoFR. Some methods apply to a single technology, whereas other
	methods apply to multiple technologies.

Toll bypass or IP telephony	Whether the method is suitable for use only between voice gateways
	connected to the PSTN or a PBX (toll bypass), or will the method
	function with IP Phone endpoints (IP telephony).

Platforms and releases	The Cisco IOS platforms this feature is available on, and the software
	release in which it was introduced.

PBX trunk types supported	Some CAC features have a dependency on the PSTN or PBX trunk type
	used in the connection, or act differently with CCS trunks versus CAS
	trunks.

End-to-end, local, or IP	The scope of visibility of the CAC feature. Some mechanisms work
cloud	locally on the originating gateway only, others consider the cloud
	between the source and destination nodes, some consider the destination
	POTS interface, and some work end to end.

Per call, interface, or	Different mechanisms involve different elements of the network. Several
endpoint	CAC methods work per call, but some work per interface and some work
	per endpoint or IP destination.

Topology awareness	Whether the CAC mechanism takes into account the topology of the
	network, and therefore provides protection for the links and nodes in the
	topology.

Guarantees QoS for	Whether the mechanism make a one-time decision before allowing the
duration of call	call, or whether it also protects the QoS of the call for the duration of the
	call by reserving the required resources.

		Foundation Summary 629

Table 8-27 CAC Feature Evaluation Criteria (Continued)

	Evaluation Criteria	Description

	Postdial delay	Whether the mechanism imposes an additional postdial delay because it
		requires extra messaging or processing during call setup.

	Messaging network	Whether the method uses additional messaging that must be provisioned
	overhead	in the network to gather the information necessary for the CAC decision.

Figure 8-39 illustrates a network using physical DS0 limitation to provide CAC.

Figure 8-39 VoIP Physical DS0 Limitation

Six Physical Connections Between Each PBX and Router

R1	IP Network
	R2

IP Network Designed to Handle up to Six G.729 Calls

Table 8-28 evaluates the physical DS0 limitation mechanism against the CAC evaluation criteria described earlier in this chapter.

Table 8-28 DS0 Limitation CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	Independent of the VoX technology used

Toll bypass or IP Telephony	Toll bypass only

Platforms and releases	All voice gateways and all Cisco IOS releases

PBX trunk types supported	All

End to end, local, or IP cloud	Local

Per call, interface, or endpoint	Per DS0/trunk (per call)

Topology awareness	None

Guarantees QoS for duration of call	None

Postdial delay	None

Messaging network overhead	None

630 Chapter 8: Call Admission Control and QoS Signaling

Figure 8-40 shows a typical VoIP network that can use the max-conn command to limit the number of calls between locations.

Figure 8-40 Max-Connections Multi-Site

				Remote Site 1
			512 kbps	4 Fax Machines
			Circuit	Extensions 12xx
				10 Telephones
	Host Site			Extensions 12xx
	Host Site
				Remote Site 2
PSTN	T1 PRI
PSTN
			512 kbps	4 Fax Machines
	T1 Circuit	IP WAN	Circuit	Extensions 13xx
		IP WAN
				10 Telephones
	T1 PRI			Extensions 13xx
	T1 PRI
PBX				Remote Site 3
Extensions 5xxx
				4 Fax Machines
				Extensions 14xx
			512 kbps
			Circuit
				10 Telephones
				Extensions 14xx

Table 8-29 evaluates the Max-Connections mechanism against the CAC evaluation criteria described earlier in this chapter.

		Foundation Summary 631

Table 8-29 Max-Connections CAC Evaluation Criteria

	Evaluation Criteria	Value

	VoX supported	All VoX that use dial peers

	Toll bypass or IP telephony	Toll bypass only

	Platforms and releases	All voice gateways and all Cisco IOS releases

	PBX trunk types supported	All

	End to end, local, or IP cloud	Local

	Per call, interface, or endpoint	Per dial peer

	Topology awareness	None

	Guarantees QoS for duration of call	None

	Postdial delay	None

	Messaging network overhead	None

Figure 8-41 shows a typical VoFR network that can use the frame-relay voice-bandwidth command to limit the number of calls between locations.

Figure 8-41 Voice over Frame Relay (VoFR)

Host Site				Remote Site
	256 kbps		256 kbps	4 Fax Machines
	256 kbps	Frame	256 kbps	Extensions 12xx
T1 PRI	Circuit	Frame	Circuit	Extensions 12xx
T1 PRI	Circuit	Relay	Circuit
		Relay
PBX
Extensions 5xxx
				10 Telephones
				Extensions 12xx

Table 8-30 evaluates the VoFR Voice-Bandwidth mechanism against the CAC evaluation criteria described earlier in this chapter.

632 Chapter 8: Call Admission Control and QoS Signaling

Table 8-30 VoFR Voice-Bandwidth CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	VoFR

Toll bypass or IP telephony	Toll bypass only

Platforms and releases	Cisco 2600s, 3600s, 3810, and 7200 router; Cisco IOS
	Release 12.0(4)T

PBX trunk types supported	All

End to end, local, or IP cloud	Local

Per call, interface, or endpoint	Per call, per PVC

Topology awareness	None

Guarantees QoS for duration of call	None

Postdial delay	None

Messaging network overhead	None

Figure 8-42 shows a VoIP network using the connection trunk command to emulate a circuit switched network.

Figure 8-42 Trunk Conditioning

Host Site	Connection	Remote Site
	Connection
	Trunk
PSTN		PSTN
256 kbps		256 kbps
Circuit	Frame Relay	Circuit
	Frame Relay
T1 PRI
PBX		PBX

Table 8-31 evaluates the trunk conditioning mechanism against the CAC evaluation criteria described earlier in this chapter.

		Foundation Summary 633

Table 8-31 Trunk Conditioning CAC Evaluation Criteria

	Evaluation Criteria	Value

	VoX supported	VoIP/H.323, VoFR, VoATM (connection trunk conﬁgurations
		only)

	Toll bypass or IP telephony	Toll bypass applications only

	Platforms and Releases	Cisco 2600 and 3600 series routers, and Cisco MC3810
		multiaccess concentrators; Cisco IOS Release 12.1(3)T

	PBX trunk types supported	Analog and CAS

	End to end, local, or IP cloud	Local

	Per call, interface, or endpoint	Per telephony interface

	Topology awareness	None

	Guarantees QoS for duration of call	None

	Postdial delay	None

	Messaging network overhead	None; uses preexisting connection trunk keepalives

Figure 8-43 shows a VoIP network using Local Voice Busyout to provide CAC.

Figure 8-43 Local Voice Busyout

R1	IP Network	R2
R1		R2
	Interface Failure

SW1

CallManager

Table 8-32 evaluates the Local Voice Busyout mechanism against the CAC evaluation criteria described earlier in this chapter.

634 Chapter 8: Call Admission Control and QoS Signaling

Table 8-32 Local Voice Busyout CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	All

Toll bypass or IP telephony	Trunking (calls originating from PBX and terminating to IP
	telephony destinations)

Platforms and releases	Cisco 2600 and 3600 series routers, MC3810 multiaccess
	concentrators; Cisco IOS Release 12.1(2)T

PBX trunk types supported	Analog and CAS

End-to-end, local, or IP cloud	Local

Per call, interface, or endpoint	Per WAN, LAN, and telephony interface

Topology awareness	None

Guarantees QoS for duration of call	None

Postdial delay	None

Messaging network overhead	None

Figure 8-44 shows a VoIP network using Advanced Voice Busyout to provide CAC.

Figure 8-44 Advanced Voice Busyout

		SAA Probe sent across the IP network.
		SAA Probe responds. Congestions detected
		across the WAN; ICPIF or delay/loss
Busy-Out This Trunk		exceeded threshold.

R1	IP Network	R2
R1		R2
SW1		SW2
IP		IP
CallManager		CallManager

Table 8-33 evaluates the AVBO mechanism against the CAC evaluation criteria described earlier in this chapter.

		Foundation Summary 635

Table 8-33 Advanced Voice Busyout CAC Evaluation Criteria

	Evaluation Criteria	Value

	VoX supported	VoIP only

	Toll bypass or IP telephony	Toll bypass (calls originating from PBX and terminating to IP
		telephony destinations)

	Platforms and releases	2600s, 3600sand MC3810 with Release 12.1(3)T
		All router platforms with Release 12.2 Mainline

	PBX trunk types supported	Analog and CAS

	End to end, local, or IP cloud	IP cloud

	Per call, interface, or endpoint	Per IP destination

	Topology awareness	None

	Guarantees QoS for duration of call	None

	Postdial delay	None

	Messaging network overhead	Periodic SAA probes

Figure 8-45 shows a VoIP network using PSTN fallback to provide CAC.

Figure 8-45 PSTN Fallback

SAA Probe sent across the IP network.

PSTN

SAA Probe response. Congestions detected

across the WAN; ICPIF or delay/loss

exceeded threshold.

IP Network

SW1

SW2

Possible Destinations for Redirection:

•Alternate IP Destinations

•Gateway Connection to PSTN

• Hairpin Call to PBX

(CAS and Analog)

• Reject Call to PBX (ISDN)

CallManager

• Reorder Tone

636 Chapter 8: Call Admission Control and QoS Signaling

Table 8-34 lists the options and default values of the call fallback command.

Table 8-34 Call Fallback Command

Call Fallback Command		Default
Keyword	Description	Value

cache-size x	Speciﬁes the call fallback cache size for network trafﬁc	128
	probe entries.

cache-timeout x	Speciﬁes the time after which the cache entries of	600s
	network conditions are purged.

instantaneous-value-weight x	Speciﬁes that the call fallback subsystem take an average	66
	from the last two cache entries for call requests.

jitter-probe num-packets x	Speciﬁes the number of packets in a jitter probe used to	15
	determine network conditions.

jitter-probe precedence x	Speciﬁes the priority of the jitter-probe transmission.	2

jitter-probe priority-queue	Assigns a priority queue for jitter-probe transmissions.	Off

key-chain	Speciﬁes MD5 authentication for sending and receiving	None
	SAA probes.

map subnet	Speciﬁes that the call fallback router keep a cache table	None
	by subnet addresses of distances for several destination
	peers sitting behind the router.

probe-timeout x	Sets the timeout for an SAA probe for call fallback	30s
	purposes.

threshold delay x loss y	Speciﬁes that the call fallback threshold use only packet	None
	delay and loss values.

icpif x	Speciﬁes that the call fallback use the ICPIF threshold.	10

Figure 8-46 illustrates the call setup process for PSTN fallback.

Foundation Summary 637

Figure 8-46 PSTN Fallback Call Setup

Call Setup

1Scenario

Call Setup

2Scenario Call Reject / Hairpin

Call Setup 3Scenario

R1	IP Network	R2

Cache entry for IP address found; CAC values are acceptable.

Call Setup

Cache entry for IP address found; CAC values not acceptable and no secondary dial-peer exists.

Cache entry for IP address not found.

SAA Probe

SAA Response

Call Setup

Table 8-35 evaluates the PSTN fallback mechanism against the CAC evaluation criteria described earlier in this chapter.

638 Chapter 8: Call Admission Control and QoS Signaling

Table 8-35 PSTN Fallback CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	VoIP only

Toll bypass or IP telephony	Toll bypass; however, calls originating from a PBX and
	terminating to IP telephony destinations can be protected

Platforms and releases	Cisco 2600/3600, MC3810: Release 12.1.(3)T
	AS5300: Release 12.2.(2)T
	7200/7500 support SAA responder

PBX trunk types supported	All PBX/PSTN trunk signaling types (analog, digital CAS
	and CCS)
	For analog and digital CAS—alternate IP destination,
	hairpin
	For digital CCS, reject the call to the PBX or PSTN for
	rerouting

End to end, local, or IP cloud	IP cloud

Per call, interface, or endpoint	Per active/cached IP destination

Topology awareness	None

Guarantees QoS for duration of call	None

Postdial delay	Only for ﬁrst call that initiates probe

Messaging network overhead	Periodic SAA probes

Foundation Summary 639

Figure 8-47 illustrates how a CAC decision is made with resource availability indication (RAI).

Figure 8-47 RAI Conﬁguration

100%
High Water Mark	Gateway Sends RAI Unavailable
	Message to Gatekeeper
Low Water Mark	Gateway Sends RAI Available
Low Water Mark	Message to Gatekeeper
0%

Table 8-36 evaluates the RAI mechanism against the CAC evaluation criteria described earlier in this chapter.

Table 8-36 RAI CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	VoIP only

Toll bypass or IP telephony	Toll bypass
	Potentially IP telephony, but CM does not yet support RAI

Platforms and releases	Cisco AS5300 access server: Cisco IOS Release 12.0(5)T
	Cisco 2600 and 3600 series routers T1/E1: Cisco IOS
	Release 12.1(3)T

PBX trunk types supported	All

End to end, local, or IP cloud	Local at the terminating gateway (DSP and DS0 resources;
	algorithm platform dependent)

Per call, interface, or endpoint	Per gateway

Topology awareness	None

Guarantees QoS for duration of call	None

Postdial delay	None

Messaging network overhead	Occasional RAI toggle between gateway and gatekeeper

640 Chapter 8: Call Admission Control and QoS Signaling

Figure 8-48 illustrates a typical CallManager centralized call-processing model using locations to provide CAC.

Figure 8-48 CallManager Centralized Call-Processing Model with Regions and Locations Deﬁned

					Location: Atlanta
				256 kbps	Region: A
				256 kbps
				Circuit
						IP
	Host Site
					Catalyst	IP
	T1 PRI		768 kbps		Switch
PSTN	T1 PRI
PSTN					Location: San Jose
			Circuit	IP WAN	Location: San Jose
				IP WAN	Region: B
				256 kbps	Region: B
				Circuit
IP
IP						IP
IP
		Catalyst			Catalyst	IP
		Switch			Catalyst
IP		Switch			Switch
IP					Switch
					Location: Dallas
					Region: C
CallManager		CallManager		256 kbps
CallManager		CallManager		Circuit
Publisher		Subscriber		Circuit
Publisher		Subscriber
						IP
					Catalyst	IP
					Switch	IP
					Switch

Table 8-37 shows the amount of bandwidth that will be subtracted, per call, from the total allotted bandwidth for a conﬁgured region.

Table 8-37 Location-Based CAC Resource Calculations

Codec	Bandwidth Reserved

G.711	80 kbps

G.729	24 kbps

G.723	24 kbps

GSM	29 kbps

Wideband	272 kbps

Foundation Summary 641

Table 8-38 evaluates location-based CAC against the CAC evaluation criteria described earlier in this chapter.

Table 8-38 Location-Based CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	VoIP only

Toll bypass or IP telephony	IP Telephony only

Platforms and releases	CallManager 3.0
	(AAR was added in CallManager release 3.3.)

PBX trunk types supported	None

End to end, local, or IP cloud	End-to-end between originating and terminating location,
	although locations have no knowledge of the network topology
	in between

Per call, interface, or endpoint	Per call

Topology awareness	None

Guarantees QoS for duration of call	None

Postdial delay	None

Messaging network overhead	None

Figure 8-49 shows a single-zone gatekeeper-controlled VoIP network with two gateways that illustrates gatekeeper CAC in its simplest form.

Figure 8-49 Simple Single-Zone Topology

Gatekeeper

R1	IP Network	R2

Call 1 Is Allowed

Call 2 Is Allowed

Call 3 Is Denied

642 Chapter 8: Call Admission Control and QoS Signaling

Figure 8-50 shows a more complex enterprise multizone multigatekeeper-controlled VoIP network.

Figure 8-50 Complex Enterprise Multizone Topology

Zone 1 to Any Zone Limited to 128 kbps

HQ-Gatekeeper

Internal Zone HQ Traffic Is Unlimited

Zone HQ to Zone 1 Limited to 128 kbps

Zone HQ to Zone 2 Limited to 256 kbps

Headquarters	20
Headquarters
Zone HQ

Site 1-Gatekeeper

Remote Site 1

Zone 1

Site 2-Gatekeeper	5

Remote Site 2

Zone 2

Zone 2 to Zone 1 Limited to 128 kbps

Zone 2 to Zone HQ Limited to 256 kbps

Figure 8-51 shows a pair of CallManager clusters using a gatekeeper to provide CAC between the clusters.

Foundation Summary 643

Figure 8-51 Gatekeeper in a CallManager Topology
	CallManager		CallManager
	Cluster A			Cluster B
	R1	IP Network	R1
	R1		R1
IP	SW1		SW1	IP
x1111		PSTN		x2111

	Can I Make a Call? (ARQ)
CallManager			CallManager
CallManager			CallManager
Zone 1			Zone 2

		Yes You Can (ACF) or
		No You Cannot (ARJ)

Call Is Placed if Allowed

Gatekeeper

Tables 8-39 and 8-40 list the gatekeeper commands and options used to conﬁgure gatekeeper zone bandwidth.

Table 8-39 Gatekeeper Bandwidth Command

Command	Mode and Function

bandwidth {interzone \| total \| session}	Speciﬁes the gatekeeper zone bandwidth restrictions
{default \| zone zone-name} max-
bandwidth

bandwidth remote max-bandwidth	Speciﬁes the total bandwidth for H.323 trafﬁc between
	this gatekeeper and any other gatekeeper

644 Chapter 8: Call Admission Control and QoS Signaling

Table 8-40 Gatekeeper Bandwidth Command Options

Bandwidth
Command
Options	Function

interzone	Speciﬁes the total amount of bandwidth for H.323 trafﬁc from the zone to any
	other zone.

total	Speciﬁes the total amount of bandwidth for H.323 trafﬁc allowed in the zone.

session	Speciﬁes the maximum bandwidth allowed for a session in the zone.

default	Speciﬁes the default value for all zones.

zone
zone-name	Names the particular zone.

max-bandwidth	Maximum bandwidth. For interzone and total, the range is from 1 to 10,000,000
	kbps. For session, the range is from 1 to 5000 kbps.

Table 8-41 evaluates the gatekeeper zone bandwidth mechanism against the CAC evaluation criteria described earlier in this chapter.

Table 8-41 Gatekeeper Zone Bandwidth CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	VoIP/H.323 only

Toll bypass or IP telephony	Toll bypass and IP telephony
	(Some caveats exist if both the CallManager and Cisco IOS gateways
	are used in the same zone.)

Platforms and releases	Cisco IOS gateways since Release 11.3
	(CM has recent changes in E.164 registration, and bandwidth
	requested per call.)

PBX trunk types supported	All

End to end, local, or IP cloud	End-to-end between originating gateway and terminating gateway,
	although not aware of the network topology in between

Per call, interface, or endpoint	Per call

Topology awareness	None

Guarantees QoS for duration	None
of call

Postdial delay	None

Messaging network overhead	Part of the gatekeeper RAS messaging

Foundation Summary 645

Figure 8-52 shows the ﬂow of RSVP path and resv messages through the network.

Figure 8-52 RSVP Path and Resv Messages

		PATH Messages
	R2		R3

		RESV Messages
R1				R4

Data Flow

Sending

Receiving

Application

Figure 8-53 shows a call ﬂow of the H.323 call setup messages and the RSVP reservation messages.

646 Chapter 8: Call Admission Control and QoS Signaling

Figure 8-53 RSVP Call Setup for an H.323 Voice Call

Call Setup

IP Network

H.225

FastStart

Setup

H.225 Call

Proceeding

RSVP

PATH

Message

RSVP

RESV

Message

RSVP

PATH

Message

RSVP

RESV

Message

RSVP

Reservation

Confirm

H.225

Alerting

Connect

Call Setup

Table 8-42 describes the available options for the acc-qos and req-qos commands.

Table 8-42 acc-qos and req-qos Command Options

acc-qos and req-qos
Command Options	Function

best-effort	Indicates that RSVP makes no bandwidth reservation.

controlled-load	Indicates that RSVP guarantees a single level of preferential service,
	presumed to correlate to a delay boundary. The controlled-load service
	uses admission (or capacity) control to ensure that preferential service is
	received even when the bandwidth is overloaded.

guaranteed-delay	Indicates that RSVP reserves bandwidth and guarantees a minimum bit
	rate and preferential queuing if the bandwidth reserved is not exceeded.

This table was derived from the following: www.cisco.com/en/US/partner/products/sw/iosswrel/ps1834/products_feature_guide09186a008008045c.html.

Foundation Summary 647

Table 8-18 summarizes the results of nine call setup scenarios based on the QoS levels that can be conﬁgured in the VoIP dial peers at the originating and terminating gateways.

Figure 8-54 illustrates how RSVP uses the priority queue in LLQ for packets matching the voice-like proﬁle.

Figure 8-54 RSVP Packet-Classiﬁcation Criteria

			Egress Interface / PVC
				Queueing (LLQ)
		Voice Conforming, Admitted Flows

				Priority
				Priority
Unclassified				Queue
Unclassified
Flows		Non-Voice Conforming, Admitted Flows
Flows	RSVP			Reserved


				Queues
	Classification			Queues
	Classification


				Class 1
				Class 1


				Class 2
		Non-Admitted Flows, Voice Signaling


		Traffic, PATH and RESV Messages		Default
				Default
				Queue

Table 8-43 summarizes the bandwidth RSVP allocates for calls using different Cisco IOS gateway codecs.

Table 8-43 RSVP Bandwidth Reservations for Voice Codecs

Codec		Bandwidth Reserved per Call in LLQ

G.711	(A-law and µ-law)	80 kbps

G.723.1 and G.723.1A (5.3 kbps)		22 kbps

G.723.1 and G.723.1A (6.3 kbps)		23 kbps

G.726	(16 kbps)	32 kbps

G.726	(24 kbps)	40 kbps

G.726	(32 kbps)	48 kbps

G.728		32 kbps

G.729	(all versions)	24 kbps

648 Chapter 8: Call Admission Control and QoS Signaling

Table 8-44 lists the commands used to deﬁne and enable RSVP.

Table 8-44 RSVP Proﬁle, req-qos and acc-qos Commands

Command	Mode and Function

ip rsvp pq-proﬁle	Speciﬁes the criteria for determining which ﬂows go into the
	priority queue

req-qos {best-effort \| controlled-load \|	Speciﬁes the desired quality of services requested to be used
guaranteed-delay}	in reaching a speciﬁed VoIP dial peer

acc-qos {best-effort \| controlled-load \|	Speciﬁes the acceptable quality of service for any inbound
guaranteed-delay}	and outbound call on a VoIP dial peer

Figure 8-55 shows a managed segment in a Layer 2 domain that interconnects a group of routers.

Figure 8-55 DSBM Managed Subnet

DSBM Client

DSBM

DSBM Client

Ethernet

DSBM Client

Foundation Summary 649

Table 8-45 lists the commands used to enable and deﬁne the DSBM in Example 8-18.

Table 8-45 SBM Commands

Command	Mode and Function

ip rsvp bandwidth	Enables RSVP on an interface

ip rsvp dsbm candidate [priority]	Conﬁgures the interface to participate as a contender in the
	DSBM dynamic election process, whose winner is based on the
	highest priority

ip rsvp dsbm non-resv-send-limit	Conﬁgures the average rate, in kbps, for the DSBM candidate
rate kbps

ip rsvp dsbm non-resv-send-limit	Conﬁgures the maximum burst size, in KB, for the DSBM
burst kilobytes	candidate

ip rsvp dsbm non-resv-send-limit	Conﬁgures the peak rate, in kbps, for the DSBM candidate
peak kbps

Table 8-46 lists other RSVP commands that can be useful in monitoring and troubleshooting RSVP.

Table 8-46 RSVP Monitoring and Troubleshooting Commands

Command	Mode and Function

show ip rsvp neighbor [interface-type	Displays current RSVP neighbors
interface-number]

show ip rsvp request [interface-type	Displays RSVP-related request information being
interface-number]	requested upstream

show ip rsvp reservation [interface-type	Displays RSVP-related receiver information currently
interface-number]	in the database

show ip rsvp sbm [detail] [interface-name]	Displays information about a SBM conﬁgured for a
	speciﬁc RSVP-enabled interface or for all RSVP-
	enabled interfaces on the router

show ip rsvp sender [interface-type	Displays Resource Reservation Protocol (RSVP)
interface-number]	PATH-related sender information currently in the
	database

650 Chapter 8: Call Admission Control and QoS Signaling

Table 8-47 evaluates the RSVP mechanism against the CAC evaluation criteria described earlier in this chapter.

Table 8-47 RSVP CAC Evaluation Criteria

Evaluation Criteria	Value

VoX supported	VoIP/H.323 only

Toll bypass or IP telephony	Currently trunking only

Platforms and releases	Cisco IOS gateways in Release 12.1(5)T and 12.2

PBX trunk types supported	All

End to end, local, or IP cloud	End to end between originating gateway and terminating
	gatekeeper (provided all intermediate nodes are RSVP
	conﬁgured)
	Could be used at WAN edge with DiffServ backbone

Per call, interface, or endpoint	Per call

Topology awareness	Yes

Guarantees QoS for duration of call	Yes

Postdial delay	Yes

Messaging network overhead	Path/resv and periodic keepalives

There is little overlap between local CAC mechanisms and those that look ahead to the rest of the network to determine nonlocal conditions. It is easy to understand why the distinct local and nonlocal mechanisms are useful. However, there is considerable overlap between the measurement techniques and the resource reservation techniques of the two nonlocal, lookahead CAC mechanisms. For this reason, there is debate over which is the better method.

Table 8-48 compares the strengths and weaknesses of the measurement-based and resourcebased CAC mechanisms. With this information, you can determine the best method for your individual network.

Foundation Summary 651

Table 8-48 Comparison of Measurement-Based and Resource Reservation-Based CAC Features

	Measurement-Based	Resource Reservation-Based
Criteria	Techniques	Techniques

Network topology	Topology independent.	Topology aware.
	The probe travels to a destination IP	The bandwidth availability on every
	address without knowledge of nodes,	node and every link is taken into
	hops, and bandwidth availability on	account.
	individual links.

Backbone	Transparent.	To be the truly end-to-end method that
transparency	Probes are IP packets and can be sent	reservation techniques are intended to
	Probes are IP packets and can be sent	be, the feature must be conﬁgured on
	over any network, including SP	be, the feature must be conﬁgured on
	over any network, including SP	every interface along the path, which
	backbones and the Internet.	every interface along the path, which
	backbones and the Internet.	means the customer owns the WAN
		means the customer owns the WAN
		backbone, and all nodes run code that
		implement the feature. Owning the
		entire backbone is impractical in some
		cases, so hybrid topologies may be
		contemplated—with some
		compromise to the end-to-end nature
		of the method.

Postdial delay	An increase in postdial delay exists	An increase in postdial delay exists for
	for the ﬁrst call only. Information on	every call, because the RSVP
	the destination is cached after the ﬁrst	reservation must be established before
	call, and a periodic probe is sent to the	the call setup can be completed.
	IP destination. Subsequent calls are
	allowed or denied based on the latest
	cached information.

Industry parity	Several vendors have “ping”-like	None.
	CAC capabilities. For a customer
	familiar with this operation,
	measurement-based techniques are a
	good ﬁt.

CAC accuracy	The periodic sampling rate of probes	When implemented on all nodes in the
	can potentially admit calls when	path, RSVP guarantees bandwidth for
	bandwidth is insufﬁcient.	the call along the entire path for the
	Measurement-based techniques	entire duration of the call. This is the
	perform well in networks where trafﬁc	only technique that achieves this level
	ﬂuctuations are gradual.	of accuracy.

continues

652 Chapter 8: Call Admission Control and QoS Signaling

Table 8-48 Comparison of Measurement-Based and Resource Reservation-Based CAC Features (Continued)

	Measurement-Based	Resource Reservation-Based
Criteria	Techniques	Techniques

Protecting voice	The CAC decision is based on probe	A reservation is established per call
QoS after	trafﬁc statistics before the call is	before the call is admitted. The quality
admission	admitted. After admission, the call	of the call is therefore unaffected by
	quality is determined by the	changes in network trafﬁc conditions.
	effectiveness of other QoS
	mechanisms in the network.

Network trafﬁc	Periodic probe trafﬁc overhead to a	RSVP messaging trafﬁc overhead for
overhead	cached number of IP destinations.	every call.
	Both the interval and the cache size
	can be controlled by the conﬁguration.

Scalability	Sending probes to thousands of	Individual ﬂow reservation is
	individual IP destinations may be	important on the small-bandwidth
	impractical in a large network. Probes	links around the edge of the network.
	can be sent to the WAN edge devices,	However, individual reservations per
	however, which proxy on behalf of	call ﬂow may not make sense on large-
	many more destinations on a high-	bandwidth links in the backbone such
	bandwidth campus network behind	as an OC-12. Hybrid network
	the edge. This provides considerable	topologies can solve this need, and
	scalability, because the WAN is much	additional upcoming RSVP tools in
	more likely to be congested than the	this space will provide further
	campus LAN.	scalability.

Table 8-49 summarizes the 11 different voice CAC mechanisms that have been discussed in chapter. It also lists the ﬁrst Cisco IOS release in which the feature became available.

Table 8-49 Summary of CAC Features

Type	CAC Feature	SW Release

Local

	Physical DS0 limitation	SW independent

	Max-Connections on the dial peer	11.3

	VoFR Voice-Bandwidth	12.0.(4)T

	Trunk conditioning	12.1.(2)T

	Local Voice Busyout (LVBO)	12.1.(2)T

Measurement based

	Advanced Voice Busyout (AVBO)	12.1.(3)T

	PSTN fallback	12.1.(3)T

Foundation Summary 653

Table 8-49 Summary of CAC Features (Continued)

Type

CAC Feature

SW Release

Resource based

Resource calculation

Resource availability indication

12.0.(5)T (AS5300)

12.1.(3)T (2600/3600)

CallManager location-based CAC

CallManager 3.0

AAR was added in CallManager

release 3.3

Gatekeeper zone bandwidth

11.(3) (local zone)

12.1.(5)T (interzone)

Resource reservation

Resource Reservation Protocol

12.1.(5)T

Table 8-50 summarizes the voice technologies supported by the CAC methods discussed in this

chapter.

Table 8-50 Summary of Voice Technologies supported

VoIP

H.323

Feature

H.323

SIP

MGCP

VoFR

VoATM

Video

Physical DS0 limitation

Yes

Max-Connections

Yes

Voice-Bandwidth

Yes

Trunk conditioning

Yes

Local Voice Busyout

Yes

Advanced Voice Busyout

Yes

PSTN fallback

Yes

Resource availability

Yes

indication

CallManager locations

Yes

Gatekeeper zone

Yes

bandwidth

Resource Reservation

Yes

Protocol

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