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The RSVP-ATM QoS Interworking feature provides the ability to do the following:
This feature is supported on Cisco 7500 series routers with a VIP2-50 and Enhanced ATM port adapter (PA-A3). The hardware provides the traffic shaping required by the feature and satisfies the OC-3 rate performance requirement.
For complete conceptual information, see the section "RSVP-ATM QoS Interworking" in the chapter "Signalling Overview" in this book.
For a complete description of the RSVP-ATM QoS Interworking commands in this chapter, refer to the Cisco IOS Quality of Service Solutions Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index, or search online.
To configure RSVP-ATM QoS Interworking, perform the tasks in the following sections. The tasks in the first five sections are required; the remaining tasks are optional.
For information on how to configure these features, refer to the Cisco IOS Switching Services Configuration Guide and the Cisco IOS Switching Services Command Reference.
The RSVP-ATM QoS Interworking feature does not support RSVP with multicast.
See the end of this chapter for the section "RSVP-ATM QoS Interworking Configuration Examples."
RSVP allows end systems or hosts on either side of a router network to establish a reserved-bandwidth path between them to predetermine and ensure QoS for their data transmission. By default, RSVP is disabled so that it is backward compatible with systems that do not implement RSVP.
To enable RSVP on an interface and restrict the total amount of bandwidth that can be reserved for RSVP as well as the amount that can be reserved for a single RSVP reservation or flow, use the following command in global configuration mode:
Command | Purpose |
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ip rsvp bandwidth [interface-kbps] [single-flow-kbps] |
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For RSVP over ATM, reservations are needed primarily between routers across the ATM backbone. To limit the number of locations where reservations are made, enable RSVP selectively only at subinterfaces corresponding to router-to-router connections across the backbone network. Preventing reservations being made between the host and the router both limits VC usage and reduces load on the router.
The default maximum bandwidth is up to 75 percent of the bandwidth available on the interface. By default, the amount reservable by a flow can be up to the entire reservable bandwidth.
On subinterfaces, the more restrictive of the available bandwidths of the physical interface and the subinterface is applied.
Command | Purpose |
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ip rsvp svc-required |
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To ensure defined QoS, SVCs created in response to RSVP reservation requests are established having QoS profiles consistent with the mapped RSVP flowspecs.
The SCR of an ATM SVC is equal to the RSVP reservation rate; the MBS of an ATM SVC is equal to the RSVP burst size. RSVP attempts to compensate for the cell tax when establishing the reservation so that the requested bandwidth is actually available for IP data traffic.
The sustained cell rate formula is given by the following equation:
ratm = rrsvp * (53/48) * (MPS + DLE + (MPS + DLE) % 48)/MPS
The formula terms used in the equation (and subsequent equations) are described in Table 9, followed by an explanation of how the formula was derived.
| Term | Definition |
ratm | ATM rate (SCR). |
rrsvp | RSVP rate. |
MPS | Minimum IP packet size, including the IP headers (300 bytes minimum). |
DLE | Data-link encapsulation overhead. For RSVP ATM SVCs, AAL5 SNAP encapsulation is used, which imposes a 5-byte encapsulation header on each PDU. |
% | Modulus operator. It yields the integer remainder from an integer division operation. For example, 57 % 53 results in 4. |
CPS | Cell payload size. The total number of bytes in all the payloads of all the cells required to send a single packet with encapsulation. |
UCO | Unused cell overhead (0 to 47). |
COMP | Compensation factor. CPS divided by MPS. |
There are two reasons for converting from RSVP rate to the ATM cell rate:
Because a portion of the last cell is unused, it is possible that a certain IP packet size requires more ATM cell layer bytes.
MPS + DLE is the length of the data packet that needs to be segmented into a number of fixed-length (48-byte payload) pieces that would then be put into a cell and sent.
Because the CPS needs to be greater than or equal to MPS + DLE, CPS must be larger than MPS.
CPS can be calculated by the following expression:
CPS = ceil((MPS + DLE)/48) * 48
where ceil(x) is the ceiling operator that returns the smallest integer greater than or equal to the real number x. Upon expanding the implementation of the ceil(x) operator, the above expression can be arithmetically transformed into the following equation:
CPS = MPS + DLE + (MPS + DLE) % 48
where (MPS + DLE) % 48 yields the integer remainder when MPS + DLE is divided by 48. Because (MPS + DLE) % 48 is equal to the UCO, the equation for CPS can be rewritten as follows:
CPS = MPS + DLE + UCO
Because the IP bit rate was calculated by considering only the IP data and header (that is, packets of length MPS or larger), the IP bit rate (rrsvp) needs to be multiplied by COMP. From Table 9 we see that COMP = CPS/MPS. Thus:
ATM cell payload bit rate = rrsvp * COMP = rrsvp * CPS/MPS
When expanded, the ATM cell payload bit rate is given by the equation:
ATM cell payload bit rate = rrsvp * (MPS + DLE + UCO)/MPS
Each ATM cell has a 5-byte header and a 48-byte payload, resulting in a 53-byte cell. Because the entire cell needs to be accounted for (not just the payload), we need to multiply the above equation by a compensation factor of 53/48. This yields the desired equation:
ratm = rrsvp * (53/48) * (MPS + DLE + UCO)/MPS
Thus, the SCR of the SVC created to carry the RSVP flow is calculated by the following formula:
ratm = rrsvp * (53/48) * (MPS + DLE + (MPS + DLE) % 48)/MPS
The ATM PCR is derived using the same formula as the cell rate formula. It is either based on the maximum line rate of the ATM interface or on a configured maximum.
The maximum burst size of the SVC is derived by the following formula:
ratm = rrsvp * (MPS + DLE + UCO)/(MPS * 48)
Note that the actual PCR, SCR, and MBS will be slightly larger than these formulas indicate.
See the task "Limiting the Peak Rate Applied to the PCR for SVCs" for information on setting the PCR of the ATM SVC.
Each new RSVP reservation causes establishment of a new SVC. If an existing reservation is refreshed, no new signalling is needed. If the reservation is not refreshed and it times out, the SVC is torn down. If the reservation is refreshed but the RSVP flowspec has changed, the existing SVC is torn down and a new one with the correct QoS parameters is established.
To set a limit on the PCR of reservations for all new RSVP SVCs established on the current interface or any of its subinterfaces, use the following command in interface configuration mode:
Command | Purpose |
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ip rsvp atm-peak-rate-limit limit |
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To configure DWRED with per-VC DWRED enabled as a drop policy at the interface level for a specific DWRED group, use the following command in interface configuration mode:
Command | Purpose |
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random-detect [attach group-name] |
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The per SVC-DWRED drop policy ensures that packets that match reservations and conform to the appropriate token bucket have the highest priority. Attaching DWRED group definitions to the interface to support per-VC DWRED drop policy ensures that if packets must be dropped, then best-effort packets are dropped first and not those that conform to the appropriate QoS determined by the RSVP's token bucket. This drop policy meets the loss requirements of controlled load called for by the Controlled Load Service class.
To meet the loss goals of controlled load, it is necessary to ensure that if packets must be dropped, best-effort packets are dropped first. Given that packets matching reservations and conforming to the appropriate token bucket will have the highest precedence, per-SVC DWRED is used as the drop policy.
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Note In order to use per-SVC DWRED, dCEF must be configured on the router. For information on how to configure dCEF, refer to the Cisco IOS Switching Services Configuration Guide and the Cisco IOS Switching Services Command Reference. |
Command | Purpose |
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show ip rsvp atm-peak-rate-limit [interface] |
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show ip rsvp interface [interface-type interface-number] | |
show ip rsvp {precedence | tos} [interface] |
The following example configures two Cisco 7500 series routers that connect over an ATM core network through a PVC and multiple SVCs. As depicted in Figure 14, Router A is connected to the ATM core network downstream; upstream it is connected across an Ethernet connection to the RSVP sender host system. Router B is connected upstream to the ATM core network and downstream across an Ethernet connection to the RSVP receiver host.
The example configuration shows three PVCs, two of which are required by ATM. One of the PVCs is used for RSVP-ATM Interworking. It is used for transmission of best-effort traffic and control traffic such as routing and RSVP messages. The ATM SVCs are established in response to reservation request messages in order to service those requests.
Router A
The following portion of the example configures Router A in global configuration mode. It enables CEF and the NetFlow feature accelerate feature, both of which must be turned on before the RSVP-ATM QoS Interworking feature can be enabled at the interface configuration level.
RouterA# config terminal RouterA(config)# ip routing RouterA(config)# ip cef RouterA(config)# ip flow-cache feature-accelerate
The following segment of the configuration for Router A configures the ATM2/1/0 interface. The ip route-cache flow command enables NetFlow on the interface. The interface must be configured with this command before the RSVP-ATM QoS Interworking feature can be enabled. If you do not enter the ip route-cache flow command before the ip rsvp-required command, a warning is issued requesting that you change the order of the commands.
The ip rsvp bandwidth command enables RSVP on the interface with default values for bandwidth allocation to RSVP. The ip rsvp svc-required command enables establishment of an SVC to service each new RSVP reservation on the interface. The ip rsvp tos and ip rsvp precedence commands configure conform and exceed values to be used for setting the ToS and IP Precedence bits of packets that either conform to or exceed the RSVP flowspec. (Note that once set, the ToS and IP Precedence bit values remain for the duration of the packet.)
RouterA(config)# interface ATM2/1/0 RouterA(config-if)# no shut RouterA(config-if)# ip address 145.5.5.1 255.255.255.0 RouterA(config-if)# no ip proxy RouterA(config-if)# no ip redirects RouterA(config-if)# ip route-cache RouterA(config-if)# ip mroute-cache RouterA(config-if)# ip route-cache flow RouterA(config-if)# no ip mroute-cache RouterA(config-if)# ip route-cache cef RouterA(config-if)# atm pvc 1 0 5 qsaal RouterA(config-if)# atm pvc 2 0 16 ilmi RouterA(config-if)# atm esi-address 111111111151.00 RouterA(config-if)# pvc pvc12 0/51 RouterA(config-if-atm-vc)# inarp 5 RouterA(config-if-atm-vc)# broadcast RouterA(config-if-atm-vc)# exit RouterA(config-if)# ip rsvp bandwidth RouterA(config-if)# ip rsvp svc-required RouterA(config-if)# ip rsvp tos conform 4 RouterA(config-if)# ip rsvp precedence conform 3 exceed 2
The following portion of the configuration configures the Ethernet interface named Ethernet0/1 on Router A that is used for the connection between the sender host and Router A. RSVP is enabled on the interface with default bandwidth allocations.
RouterA(config)# interface Ethernet0/1 RouterA(config-if)# ip address 145.1.1.1 255.255.255.0 RouterA(config-if)# no ip proxy RouterA(config-if)# no ip redirects RouterA(config-if)# no shut RouterA(config-if)# ip route-cache RouterA(config-if)# ip mroute-cache RouterA(config-if)# ip route-cache flow RouterA(config-if)# no ip mroute-cache RouterA(config-if)# ip route-cache cef RouterA(config-if)# fair RouterA(config-if)# ip rsvp bandwidth
The following section displays configuration for Router A after the preceding commands were used to configure it:
RouterA# write terminal Current configuration: ! version 12.0 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname RouterA boot system tftp rsp-jv-mz 171.69.209.28 enable password ! ip subnet-zero ip flow-cache feature-accelerate ip cef interface Ethernet0/1 ip address 145.1.1.1 255.255.255.0 no ip redirects no ip directed-broadcast no ip proxy-arp ip rsvp bandwidth 7500 7500 no ip route-cache cef no ip mroute-cache fair-queue 64 256 1000 ! interface ATM2/1/0 ip address 145.5.5.1 255.255.255.0 no ip redirects no ip directed-broadcast no ip proxy-arp ip rsvp bandwidth 112320 112320 ip rsvp svc-required ip route-cache flow
ip rsvp tos conform 4
ip rsvp precedence conform 3 exceed 2 no ip route-cache cef no ip route-cache distributed no ip mroute-cache atm pvc 1 0 5 qsaal atm pvc 2 0 16 ilmi atm esi-address 111111111151.00 pvc pvc12 0/51 inarp 5 broadcast !
Router B
Router B is configured similarly to Router A. In the following global configuration portion of the example, Router B is configured so that CEF and the NetFlow feature accelerate feature are enabled, both of which must be turned on before the RSVP-ATM QoS Interworking feature can be enabled.
RouterB# config terminal RouterB(config)# ip routing RouterB(config)# ip cef RouterB(config)# ip flow-cache feature-accelerate
The following segment of the configuration for Router B configures the interface named ATM3/0/0. The ip rsvp bandwidth command enables RSVP and the ip route-cache flow command enables NetFlow on the interface. The ip rsvp svc-required command enables the RSVP-ATM QoS Interworking feature, allowing for the establishment of an SVC to service each new RSVP reservation on the interface.
RouterB(config)# interface ATM3/0/0 RouterB(config-if)# atm pvc 1 0 5 qsaal RouterB(config-if)# atm pvc 2 0 16 ilmi RouterB(config-if)# atm esi-address 111111111152.00 RouterB(config-if)# pvc pvc12 0/52 RouterB(config-if-atm-vc)# inarp 5 RouterB(config-if-atm-vc)# broadcast RouterB(config-if-atm-vc)# exit RouterB(config-if)# ip rsvp bandwidth RouterB(config-if)# ip route-cache flow RouterB(config-if)# ip rsvp svc-required
The following portion of the configuration configures the Ethernet interface on Router B. This interface is used for the connection between the receiver host and Router B. RSVP is enabled on the interface.
RouterB(config)# interface Ethernet0/2 RouterB(config-if)# no shut RouterB(config-if)# ip address 145.4.4.2 255.255.255.0 RouterB(config-if)# no ip proxy RouterB(config-if)# no ip redirects RouterB(config-if)# ip route-cache RouterB(config-if)# ip mroute-cache RouterB(config-if)# ip route-cache flow RouterB(config-if)# no ip mroute-cache RouterB(config-if)# ip route-cache cef RouterB(config-if)# fair RouterB(config-if)# ip rsvp bandwidth RouterB(config-if)# end RouterB(config)# ip routing RouterB(config)# router eigrp 17 RouterB(config-router)# network 145.5.5.0 RouterB(config-router)# network 145.4.4.0
The following section displays configuration for Router B after the preceding commands were used to configure it:
RouterB# write terminal Current configuration: ! version 12.0 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname RouterB ! ! boot system tftp rsp-jv-mz 171.69.209.28 enable password ! ip subnet-zero ip flow-cache feature-accelerate ip cef distributed interface Ethernet0/2 ip address 145.4.4.2 255.255.255.0 no ip redirects no ip directed-broadcast no ip proxy-arp ip rsvp bandwidth 7500 7500 ip route-cache flow no ip mroute-cache fair-queue 64 256 1000 ! interface ATM3/0/0 ip address 145.5.5.2 255.255.255.0 no ip redirects no ip directed-broadcast no ip proxy-arp ip rsvp bandwidth 112320 112320 ip rsvp svc-required
ip route-cache flow no ip route-cache cef no ip route-cache distributed no ip mroute-cache atm pvc 1 0 5 qsaal atm pvc 2 0 16 ilmi atm esi-address 111111111152.00 pvc pvc12 0/52 inarp 5 broadcast !
Posted: Mon Aug 21 21:32:59 PDT 2000
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