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

Figure C-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 C-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.

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

Table C-26. CAC Feature Evaluation Criteria

Evaluation Criteria	Description
Voice over X (VoX) supported	The voice technologies to which the CAC method applies, such as VoIP 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 cloud	The scope of visibility of the CAC feature. Some mechanisms work 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 endpoint	Different mechanisms involve different elements of the network. Several 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 duration of call	Whether the mechanism make a one-time decision before allowing the call, or whether it also protects the QoS of the call for the duration of the call by reserving the required resources.
Postdial delay	Whether the mechanism imposes an additional postdial delay because it requires extra messaging or processing during call setup.
Messaging network overhead	Whether the method uses additional messaging that must be provisioned in the network to gather the information necessary for the CAC decision.

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

Figure C-38. Voice Packet Structure

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

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

Table C-27. 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

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

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

Table C-28. 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 C-40 shows a typical VoIP network that can use the max-conn command to limit the number of calls between locations.

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

Table C-29. 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 C-41 shows a typical VoFR network that can use the frame-relay voice-bandwidth command to limit the number of calls between locations.

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

Table C-30. Trunk Conditioning CAC Evaluation Criteria111

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

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

Table C-31. 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 C-43 shows a VoIP network using Local Voice Busyout to provide CAC.

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

Table C-32. 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 C-44 shows a VoIP network using Advanced Voice Busyout to provide CAC.

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

Table C-33. Call Fallback Command

Call Fallback Command Keyword	Description	Default Value
cache-size x	Specifies the call fallback cache size for network traffic probe entries.	128
cache-timeout x	Specifies the time after which the cache entries of network conditions are purged.	600s
instantaneous-value-weight x	Specifies that the call fallback subsystem take an average from the last two cache entries for call requests.	66
jitter-probe num-packets x	Specifies the number of packets in a jitter probe used to determine network conditions.	15
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 SAA probes.	None
map subnet	Specifies that the call fallback router keep a cache table by subnet addresses of distances for several destination peers sitting behind the router.	None
probe-timeout x	Sets the timeout for an SAA probe for call fallback purposes.	30s
threshold delay x loss y	Specifies that the call fallback threshold use only packet delay and loss values.	None
icpif x	Specifies that the call fallback use the ICPIF threshold.	10

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

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

Table C-34. 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 CASalternate 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

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

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

Table C-35. 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

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

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

Table C-36. 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

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

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

Table C-37. 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

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

Table C-38. Gatekeeper Bandwidth Command

Command	Mode and Function
bandwidth {interzone | total | session} {default | zone zone-name} max-bandwidth	Specifies the gatekeeper zone bandwidth restrictions
bandwidth remote max-bandwidth	Specifies the total bandwidth for H.323 traffic between this gatekeeper and any other gatekeeper

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

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

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

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

Table C-39. 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 C-40 evaluates the gatekeeper zone bandwidth mechanism against the CAC evaluation criteria described earlier in this chapter.

Table C-40. 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 of call	None
Postdial delay	None
Messaging network overhead	Part of the gatekeeper RAS messaging

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

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

Table C-41 describes the available options for the acc-qos and req-qos commands.

Table C-41. 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.

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

Table C-42 summarizes the bandwidth RSVP allocates for calls using different Cisco IOS gateway codecs.

Table C-42. 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

Table C-43 lists the commands used to define and enable RSVP.

Table C-43. 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 | guaranteed-delay}	Specifies the desired quality of services requested to be used in reaching a specified VoIP dial peer
acc-qos {best-effort | controlled-load | guaranteed-delay}	Specifies the acceptable quality of service for any inbound and outbound call on a VoIP dial peer

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

Table C-44 lists the commands used to enable and define the DSBM in Example C-18.

Table C-44. 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 rate kbps	Configures the average rate, in kbps, for the DSBM candidate
ip rsvp dsbm non-resv-send-limit burst kilobytes	Configures the maximum burst size, in KB, for the DSBM candidate
ip rsvp dsbm non-resv-send-limit peak kbps	Configures the peak rate, in kbps, for the DSBM candidate

Table C-45 lists other RSVP commands that can be useful in monitoring and troubleshooting RSVP.

Table C-45. RSVP Monitoring and Troubleshooting Commands

Command	Mode and Function
show ip rsvp neighbor [interface-type interface-number]	Displays current RSVP neighbors
show ip rsvp request [interface-type interface-number]	Displays RSVP-related request information being requested upstream
show ip rsvp reservation [interface-type interface-number]	Displays RSVP-related receiver information currently 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 RSVPenabled interfaces on the router
show ip rsvp sender [interface-type interface-number]	Displays Resource Reservation Protocol (RSVP) PATH-related sender information currently in the database

Table C-46 evaluates the RSVP mechanism against the CAC evaluation criteria described earlier in this chapter.

Table C-46. 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 C-47 compares the strengths and weaknesses of the measurement-based and resource-based CAC mechanisms. With this information, you can determine the best method for your individual network.

Table C-47. Comparison of Measurement-Based and Resource Reservation-Based CAC Features

Criteria	Measurement-Based Techniques	Resource Reservation-Based Techniques
Network topology	Topology independent. The probe travels to a destination IP address without knowledge of nodes, hops, and bandwidth availability on individual links.	Topology aware. The bandwidth availability on every node and every link is taken into account.
Backbone transparency	Transparent. Probes are IP packets and can be sent over any network, including SP backbones and the Internet.	To be the truly end-to-end method that reservation techniques are intended to be, the feature must be configured on every interface along the path, which 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 contemplatedwith some compromise to the end-to-end nature of the method.
Postdial delay	An increase in postdial delay exists for the first call only. Information on the destination is cached after the first call, and a periodic probe is sent to the IP destination. Subsequent calls are allowed or denied based on the latest cached information.	An increase in postdial delay exists for every call, because the RSVP reservation must be established before the call setup can be completed.
Industry parity	Several vendors have "ping"-like CAC capabilities. For a customer familiar with this operation, measurement-based techniques are a good fit.	None.
CAC accuracy	The periodic sampling rate of probes can potentially admit calls when bandwidth is insufficient. Measurement-based techniques perform well in networks where traffic fluctuations are gradual.	When implemented on all nodes in the path, RSVP guarantees bandwidth for the call along the entire path for the entire duration of the call. This is the only technique that achieves this level of accuracy.
Protecting voice QoS after admission	The CAC decision is based on probe traffic statistics before the call is admitted. After admission, the call quality is determined by the effectiveness of other QoS mechanisms in the network.	A reservation is established per call before the call is admitted. The quality of the call is therefore unaffected by changes in network traffic conditions.
Network traffic overhead	Periodic probe traffic overhead to a cached number of IP destinations. Both the interval and the cache size can be controlled by the configuration.	RSVP messaging traffic overhead for every call.
Scalability	Sending probes to thousands of individual IP destinations may be impractical in a large network. Probes can be sent to the WAN edge devices, however, which proxy on behalf of many more destinations on a high-bandwidth campus network behind the edge. This provides considerable scalability, because the WAN is much more likely to be congested than the campus LAN.	Individual flow reservation is important on the small-bandwidth links around the edge of the network. However, individual reservations per call flow may not make sense on large-bandwidth links in the backbone such as an OC-12. Hybrid network topologies can solve this need, and additional upcoming RSVP tools in this space will provide further scalability.

Table C-48 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 C-48. 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
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 C-50 summarizes the voice technologies supported by the CAC methods discussed in this chapter.

Table C-49. Summary of Voice Technologies supported

Feature	VoIP H.323	VoIP SIP	VoIP MGCP	VoFR	VoATM	CM	H.323 Video
Physical DS0 limitation	Yes	Yes	Yes	Yes	Yes	No	No
Max-Connections	Yes	Yes	Yes	Yes	Yes	No	No
Voice-Bandwidth	No	No	No	Yes	No	No	No
Trunk conditioning	Yes	Yes	Yes	Yes	Yes	No	No
Local Voice Busyout	Yes	Yes	Yes	Yes	Yes	No	No
Advanced Voice Busyout	Yes	Yes	Yes	No	No	No	No
PSTN fallback	Yes	Yes	Yes	No	No	No	No
Resource availability indication	Yes	No	No	No	No	No	No
CallManager locations	Yes	No	Yes	Yes	Yes	Yes	No
Gatekeeper zone bandwidth	Yes	No	No	No	No	Yes	Yes
Resource Reservation Protocol	Yes	No	No	No	No	No	No