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This chapter summarizes hardware options for implementing redundant DSL network environments. The following sections are included:
Cisco Customer Premise Equipment (CPE) associated with DSL deployments are summarized as follows:
Table 3-1 outlines relevant attributes and briefly describes the application of each of these devices.
Table 3-1 Details of Various Cisco ATU-R Devices
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1 2 Binary 1 Quaternary. An amplitude modulation technique used for ISDN and High bit rate Digital Subscriber Loop (HDSL) service in the United States. This is defined in the 1988 ANSI specification T1.601. 2B1Q has four levels of amplitude (voltage) to encode 2 bits. Each voltage level is called a quaternary. Because of the four voltage levels, each level translates to 2 b/Hz. 2 Foreign Exchange Station interface This interface is an RJ-11 connector that allows connection for basic telephone equipment, keysets, and PBXs. It supplies ring, voltage, and dial tone. |
Reliable twisted-pair lines from the customer premise xDSL router (such as a 6xx) to the central office (CO) are terminated at plain old telephone system (POTS) splitters. No redundancy is available in this path and lines are maintained by the local Telco provider.
For SOHO redundancy can be implemented here by using two DSL lines, using one to backup the other.
The Cisco 61xx/62xx Series products provide end-to-end service, carrying data between a DSL subscriber's home or office, a telephone central office (CO), and various networks. The Cisco 6100 Series with the NI-1 system sends and receives subscriber data over existing copper telephone lines, concentrating all traffic onto a single high-speed trunk for transport to the Internet or a corporate intranet. A Cisco 6130 it can be subtended to seven (12 using NI-2) systems while in 6260 it can be subtended to 12 systems.
Network Interface 1 (NI-1) consists of three modules:
The DS3 STM host module manages subscribers that are sent from a subtended Cisco 6100/6130 chassis and installed in slot 9 of a subtending host chassis.
The NI-1 module provides a high-speed connection for aggregated data traffic from the xTU-C modules
The system controller module is the central processing and control system for the main access Cisco 6100/6130. The system controller module contains all software required to perform the provisioning, monitoring, control, status, management, alarm reporting, etc.
Table 3-2 summarizes physical system slot allocation for NI-1.
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Note The secondary slots are not supported at this time. |
Network Interface 2 (NI-2) consists of the Network Interface module.
The NI-2 module provides a high-speed connection for aggregated data traffic from the xTU-C modules
Table 3-3 summarizes physical system slot allocation for NI-1.
The Cisco 6400 UAC uses an eight-slot, modular chassis supporting half-height and full-height cards, slot redundancy, and dual, fault-tolerant, load-sharing AC or DC power supplies. This section summarizes the functions of the following Cisco 6400 modules:
The central slots (slot 0A and 0B) in the Cisco 6400 are dedicated to redundant, field-replaceable node switch processor (NSP) modules that support both the 5-Gbps shared memory and the fully nonblocking switch fabric.
The NSP also supports the feature card and high performance Reduced Instruction Set (RISC) processor that provides the central intelligence for the device. The NSP supports a wide variety of desktop, backbone, and wide-area interfaces.
The remaining slots support up to eight hot-swappable carrier modules for node router processors (NRPs) or half-height node line cards (NLCs). NRPs and NLCs can be configured for redundant operation. As a result, you can have up to four redundant pairs of NRPs or any combination of NRPs and NLCs. The NRPs are fully functional router modules capable of terminating PPP sessions uploaded from your OC-12, OC-3, or DS3 node line cards.
Table 3-4 summarized slot assignment for Cisco 6400 NSP, NRP, and NLC modules.
Table 3-4 Cisco 6400 Slot Usage
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Details regarding Cisco 6400 software and hardware implementation are available at the following location:
The Cisco 6400 node switch processor (NSP) provides ATM switching functionality. The NSP uses permanent virtual circuits (PVCs) or permanent virtual paths (PVPs) to direct ATM cells between the NRP and ATM interface. The NSP also controls and monitors the Cisco 6400 system, including component NLCs and NRPs.
Redundancy need not be explicitly specified between NSPs using the slot identification, because only NSPs can be installed in slot 0. If two NSPs are installed in the Cisco 6400, they automatically act as a redundant pair. Use the main-cpu submode command to specify synchronization between the NSPs.
It is possible to force a switch-over of NSP from the active NSP to the secondary NSP. This may be needed if the current running NSP requires removal.
The synchronization between dual NSP's is enabled automatically by default. Use the main-cpu submode command to customize that behavior.
The NRP receives traffic from NLC interface ports via the NSP ATM switch. The NRP reassembles the ATM cells into packets, processes (routes, bridges, etc.) the packets, segments the packets, and sends them back to the NSP for transmission out of another NLC interface. The Cisco 6400 can contain multiple NRP modules, configured to operate independently or as redundant pairs (1+1).
NRP redundancy is achieved by redundant slot configuration in the NSP. The following configuration example illustrates creating a redundant NRP:
To ensure that the configuration is consistent between redundant NSPs or NRPs, you can configure automatic synchronization between the two devices. Possible options include: synchronizing just the startup configuration, synchronizing the boot variables, synchronizing the configuration register, or synchronizing all three configurations.
A secondary NSP/NRP is suspended during initialization and monitors primary for failure. Primary and secondary NSPs communicate via shared backplane signals for synchronization. On failure, the secondary resumes its suspended boot sequence and takes over as master.
Node line cards (NLCs) provide ATM interfaces for the Cisco 6400 system. There are three types of NLC available for the Cisco 6400, each offering a different interface type (OC-12, OC-3). NLC interfaces are controlled by the NSP.
NLC redundancy can be configured between two half-height line cards in adjacent subslots. When subslot redundancy is configured, all ports on the two subslot cards are redundant. The following configuration example illustrates creating a redundant NLC:
The Cisco 6400 supports 1+1, linear, unidirectional, non-reverting SONET APS (automatic protection switching) operation on its redundant NLC ports. In this 1+1 architecture, there is one working interface (circuit) and one protect interface, and the same payload from the transmitting end is sent to both the receiving ends. The receiving end decides which interface to use. The line overhead (LOH) bytes (K1 and K2) in the SONET frame indicate both status and action.
The protect interface provides communication between the process controlling the working interface and the process controlling the protect interface. With this protocol, interfaces can be switched to the protection channel because of a signal failure, loss of signal, loss of frame, automatically initiated switchover, or manual intervention. In unidirectional mode, the transmit and receive channels are switched independently.
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Note Currently, DS3 line card redundancy is not supported on the chassis. 1+1 linear, non-reverting, unidirectional APS is specific to optical interfaces (OC-3/OC-12 in the Cisco 6400). Cisco's APS is based upon the GR-253-Core Specification. |
Cisco 6400 supports dual, fault-tolerant, load-sharing AC or DC power supplies.
The latest Cisco IOS software release supporting the redundancy features for the Cisco 6400 can be found at CCO at the following link:
Table 3-5 summarizes Cisco 6400 software support of redundancy.
Important points that must be considered before implementing redundancy in 6400:
A redundant chassis solution is useful in the NAP or NSP where multiple Cisco 6400s are used to aggregate traffic. This approach is useful in the absence of software and hardware supported mechanism that would otherwise provide box level redundancy. The Cisco 6400 uses an eight-slot, modular chassis featuring the option of half-height and full-height card and slot redundancy (NSP, NRP, and NLC redundancy), along with dual, fault-tolerant, load-sharing AC or DC power supplies. The approach described in this section can be used to provide box-level high availability.
The redundant Cisco 6400 should be ready to act as backup for any of the active 6400, in terms of both software and hardware configuration. The backup aggregation switch will have no ATM or DS3 links coming to the DSLAMs. As a result, the switch will be functionally ready except there will be no incoming user calls.
In the case of a chassis failure the backup 6400 can be used to handle the calls of the failed chassis until it recovers. Human intervention is required to move the ATM or DS3 link from the failed chassis to the backup 6400. The Fast Ethernet or ATM uplinks to the ISP/Internet must also be moved.
This method can be used to provide physical backup for the 6400s.
Choosing to deploy a redundant chassis implementation requires planning and resource commitment. Before committing to a redundant chassis solution, be sure to assess factors that might influence the success and supportability of your solutions. Examples of assessment criterion include the following considerations:
Two important advantages can be attributed to a redundant chassis solutions:
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Note In the absence of a backup system the failed 6400 would have been immediately rebooted to establish network connectivity. |
Figure 3-1 illustrates an example redundant chassis network topology. Optional design solutions are summarized in the sections that follow this illustration:
Given the network topology as illustrated in Figure 3-1, this discussion of a redundant chassis approach focuses on how the chassis redundancy can be used to backup a Cisco 6400. The Cisco 6400 currently handles up to 14,000 simultaneous user calls. The approach can be applied to achieve higher availability for the DSLAM (61xx/62xx).
Before the redundant chassis is considered make sure the NRP and NSP within the box are redundant and configured for fail-over. Figure 3-2 illustrates a sample hardware configuration for a Cisco 6400 utilizing NRP/NSP/NLC redundancy features.
To further define the approach adopted for Design I supporting the network illustrated in Figure 3-1, consider the following slot pairings (active/backup) for the Cisco 6400 listed as 6400-1:
The associated NRPs and NSPs have the same hardware and software configurations including the same size flash and DRAM. Configurations between the two adjacent components will auto-sync unless explicitly specified by the no auto-sync command. Subslot redundancy association is between subslot 7/0 and subslot 8/0.
One can accomplish the associations suggested here with the following configurations on the NSP:
The other Cisco 6400s in Figure 3-1 (6400-2 and 6400-3) are similarly configured such that NSP, NRP, and NLC are supported with redundant backups.
In the example illustrated in Figure 3-1, The redundant chassis can provide a backup solution for all the three Cisco 6400s (6400-1, 6400-2, and 6400-3). As a result, the backup Cisco 6400 system must have the physical configurations associated with each of the operational Cisco 6400s. Table 3-6 how the configuration mapping should be done.
Table 3-6 Redundancy Design I Configuration Management Chart
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| 1 The virtual path identifiers/virtual channel identifiers (VPIs/VCIs) used are unique across all three 6400s (6400-1, 6400-2, 6400-3). |
As illustrated in Figure 3-1, the incoming interface (the link from the DSLAM) is A8/0/0 in each of the Cisco 6400s. Each of the Cisco 6400s, including the backup system, has a link to the local management LAN. The local management LAN includes the AAA server, SSG Server and the DHCP Server (if DHCP services on the NRP are not used).
Because each system has a link to the ISPs/Internet, the backup system will have the current routing/forwarding tables.
In this design, no changes are required in the NRP configurations. For example, the Cisco IOS configuration from 6400-1 NRP-SLOT-3 is copied to 6400-Backup NRP-SLOT-2.
However, the NSP in the Cisco 6400-Backup system must be configured so that it combines the configurations of the NSPs of each active Cisco 6400.
The following NSP configurations on the active Cisco 6400s and the backup Cisco 6400 illustrate how this redundant chassis design is implemented:
1. Relevant Cisco IOS configuration fragment for 6400-1 NSP-0A:
2. Relevant Cisco IOS configuration fragment for 6400-2 NSP-0A:
3. Relevant Cisco IOS configuration fragment for 6400-3 NSP-0A:
4. Relevant Cisco IOS configuration fragment for 6400-Backup NSP-0A:
Having the setup complete as discussed in "Design I Backup Chassis Setup Considerations", assume a failure occurs. The following notes summarize actions and considerations associated with recovering from a failure of one of the active Cisco 6400 UACs in the example network presented in Figure 3-1:
Keeping the same logical topology as illustrated in Figure 3-1, a second possible design approach is to have the software configurations of the active chassis stored in the backup Cisco 6400.
This is useful when all the active chassis are fully loaded without NRP redundancy.
The running configurations from the active Cisco 6400s must be copied to the backup system and saved in flash as defined in Table 3-7.
In this way the backup system can be used to replace any of the active 6400 by just switching to that system's configurations.
Table 3-7 Redundancy Design II Configuration Management Chart
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While these two design approaches both provide redundancy solutions for the hypothetical network arrangement illustrated in Figure 3-1, each makes certain assumptions about the active UACs. These assumptions influence the way the redundancy solutions are implemented.
Design I assumes that half the NRP, NSP, and NLC slots (as illustrated in Figure 3-2) of each active Cisco 6400 systems are used as backup slots. As a result, each active Cisco 6400 includes four NRPs, two NSPs, and two NLCs.
In contrast, Design II assumes that all the NRP slots in each of the active Cisco 6400s is operational with two redundant NSPs and NLCs. The only NRP backup modules in Design II reside in the backup Cisco 6400 system (6400-Backup).
In both designs, the redundant chassis (6400-Backup) includes six NRPs, one NSP, and one NLC.
In Design I, each active module is backed up by two specific modules:
In Design II, the backup environment differs, as follows:
From an operational perspective, the chief result is that Design I provides a higher level of inherent redundancy, while Design II provides for more total concurrent access connections.
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Note Assuming two additional incoming ATM lines are added to the backup Cisco 6400 in Figure 3-1, Design I can be made to accommodate up to three concurrent Cisco 6400 UAC failures. Design II can only accommodate one complete UAC failure at a time. |
Posted: Fri Aug 22 13:55:41 PDT 2003
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