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Also, refer to the Cisco WAN Switching Command Reference publications.
Refer to Release Notes for additional supported features.
Cisco BPX 8600 series wide-area switches offer a variety of service interfaces for data, video, and voice traffic, and support numerous connectivity options to address a broad range of diverse needs. Network interface options include broadband (T3/E3 to OC-12/STM-4) and narrowband (64 Kbps to n x T1/E1) via leased lines or public ATM services. Additionally, the BPX switch provides a cost-effective solution by offering a wide range of port densities via the MGX 8220 and MGX 8800 edge concentrators. Proven in the world's largest networks, the Cisco BPX 8620, 8650, and 8680 help you to anticipate and meet market demands while eliminating technology risk.
The Cisco BPX® 8600 series wide-area switches are standards-based high-capacity broadband ATM switches that provide backbone ATM switching, IP+ATM services including Multiprotocol Label Switching (MPLS) with trunk and CPU hot standby redundancy. The BPX 8600 series deliver a wide range of other user services (see Figure 1-1).
The BPX 8600 Series includes:
The Cisco BPX 8620 switch is a scalable, standards-compliant unit, fully compatible with:
The BPX multishelf architecture integrates both IP and ATM services, thereby enabling you to deploy the industry's widest range of value-added services. This architecture offer low-cost entry points for small sites up to unprecedented port density and scalability for the very largest sites. Finally, it supports both broadband services and narrowband services within a single platform.
The architecture supports both the broadband BPX switch and up to 16 edge concentrator shelves. This scalability results in full utilization of broadband trunks and allows the BPX switch to be expanded incrementally to handle an almost unlimited number of subscribers.
The edge concentrators terminate traffic from a variety of interfaces, such as IP, Frame Relay, ATM, and circuit emulation, and adapt non-ATM traffic into ATM cells. This traffic is aggregated and sent to the BPX switch where it is switched on high-speed ATM links. This aggregation on a single platform maximizes the density of broadband and narrowband ports. High-density aggregation of low-speed services also optimizes the efficiency of the high-speed switching matrix and broadband card slots.
The multishelf view is a "logical" view. Physically, the edge concentrator shelves may be co-located with the BPX switch or they may be located remotely. The connection between a shelf and the BPX switch is a high-speed, optionally redundant ATM link.
The BPX switch consists of the BPX shelf with fifteen card slots that may be co-located with the MGX 8220 or MGX 8800 and Service Expansion Shelf (SES) as required.
Three of the slots on the BPX switch shelf are reserved for common equipment cards. The other twelve are general purpose slots used for network interface cards or service interface cards. The cards are provided in sets, consisting of a front card and its associated back card.
The BPX shelf can be mounted in a rack enclosure that provides mounting for a co-located SES and the MGX 8220 or MGX 8800 interface shelves.
The BPX® 8650 is an IP+ATM switch that provides ATM-based broadband services and integrates Cisco IOS® software via Cisco 7200 series routers to deliver Multiprotocol Label Switching (MPLS) services.
The BPX 8650 provides these core Internet requirements:
The BPX 8650 supports:
The BPX 8680 universal service switch is a scalable IP+ATM WAN edge switch that combines the benefits of Cisco IOS® IP with the extensive queuing, buffering, scalability, and quality-of-service (QoS) capabilities provided by the BPX 8600 and MGX 8800 series platforms.
The BPX 8680 switch incorporates a modular, multishelf architecture that scales from small sites to very large sites and enables service providers to meet the rapidly growing demand for IP applications while cost-effectively delivering today's services.
The BPX 8680 consists of one or more MGX 8850s connected as feeders to a BPX 8620. Designed for very large installations, the BPX 8680 can scale to 16,000 DS1s by adding up to 16 MGX 8850 concentrator shelves while still being managed as a single node.
The BPX 8680-IP scalable Layer 2/Layer 3 WAN solution integrating the proven multiservice switching technology of the Cisco BPX 8650 switch with the flexibility and scalability of the Cisco MGX 8850. The MGX 8850 switch serves as an edge concentrator to the BPX 8650, which employs the BPX 8600 series switch modular, multishelf architecture to enable scalability. The BPX 8650 switch includes a Cisco 7204 label switch controller (LSC) and supports multiprotocol label switching (MPLS) for New World integrated infrastructures.
With Release 9.3.0, the BPX switch software supports a number of new features:
These older hardware components and technologies will be supported for five years from the time they are discontinued:
With the BCC-4 card, the BPX switch employs a non-blocking crosspoint switch matrix for cell switching that can operate at up to 19.2 Gbps peak. The switch matrix can establish up to 20 million point-to-point connections per second between ports.
The BXM cards support egress at up to 1600 Mbps and ingress at up to 800 Mbps. The enhanced egress rate enhance operations such as multicast.
Access to and from the crosspoint switch matrix on the BCC is through multiport network and user access cards. It is designed to easily meet current requirements with scalability to higher capacity for future growth.
A BPX switch shelf is a self-contained chassis that may be rack-mounted in a standard 19-inch rack or open enclosure.
All control functions, switching matrix, backplane connections, and power supplies are redundant, and non-disruptive diagnostics continuously monitor system operation to detect any system or transmission failure. Hot-standby hardware and alternate routing capability combine to provide maximum system availability.
Many network locations have increasing bandwidth requirements due to emerging applications and the confluence of voice, data, and video digital communications. To meet these requirements, you can overlay your existing narrowband networks with a backbone of BPX switches to utilize the high-speed connectivity of the BPX switch operating at up to 19.2 Gbps with its T3/E3/OC-3/OC-12 network and service interfaces.
The BPX switch service interfaces include BXM ports on the BPX switch and service ports on MGX 8220 shelves. The MGX 8220 shelves may be co-located in the same cabinet as the BPX switch, providing economical port concentration for T1/E1 Frame Relay, T1/E1 ATM, CES, and FUNI connections.
The BPX 8650 MPLS switch combines a BPX switch with a separate MPLS controller (Cisco Series 7200 router). By integrating the switching and routing functions, MPLS combines the reachability, scalability, and flexibility provided by the router function with the traffic engineering optimizing capabilities of the switch.
Multiprotocol Label Switching (MPLS) is a high-performance method for forwarding packets (frames) through a network. It enables routers at the edge of a network to apply simple labels to packets (frames). ATM switches or existing routers in the network core can switch packets according to the labels with minimal lookup overhead.
MPLS integrates the performance and traffic management capabilities of Data Link Layer 2 with the scalability and flexibility of Network Layer 3 routing. It is applicable to networks using any Layer 2 switching, but has particular advantages when applied to ATM networks. It integrates IP routing with ATM switching to offer scalable IP-over-ATM networks.
In contrast to label switching, conventional Layer 3 IP routing is based on the exchange of network reachability information. As a packet traverses the network, each router extracts all the information relevant to forwarding from the Layer 3 header. This information is then used as an index for a routing table lookup to determine the packet's next hop. This is repeated at each router across a network. At each hop in the network, the optimal forwarding of a packet must be again determined.
The information in IP packets, such as IP Precedence information and information on Virtual Private Network membership, is usually not considered when forwarding packets. Thus, to get maximum forwarding performance, typically only the destination address is considered. However, because other fields could be relevant, a complex header analysis must be done at each router that the packet meets.
The main concept of MPLS is to include a label on each packet.
Packets or cells are assigned short, fixed length labels. Switching entities perform table lookups based on these simple labels to determine where data should be forwarded.
The label summarizes essential information about routing the packet:
With Label Switching the complete analysis of the Layer 3 header is performed only once: at the edge label switch router (LSR) which is located at each edge of the network. At this location, the Layer 3 header is mapped into a fixed length label, called a label.
At each router across the network, only the label need be examined in the incoming cell or packet in order to send the cell or packet on its way across the network. At the other end of the network, an edge LSR swaps the label out for the appropriate header data linked to that label.
A key result of this arrangement is that forwarding decisions based on some or all of these different sources of information can be achieved by means of a single table lookup from a fixed-length label. For this reason, label switching makes it feasible for routers and switches to make forwarding decisions based upon multiple destination addresses.
Label switching integrates switching and routing functions, combining the reachability information provided by the router function, plus the traffic engineering benefits achieved by the optimizing capabilities of switches.
For multiservice networks, the BPX 8650 switch provides ATM, Frame Relay, and IP Internet service all on a single platform in a highly scalable way. Support of all these services on a common platform provides operational cost savings and simplifies provisioning for multiservice providers.
Cisco's MPLS solution is described in detail in the Cisco MPLS Controller Software Configuration Guide.
Private Network to Network Interface (PNNI) is a link-state routing protocol that provides standards-based dynamic ATM routing with QoS support as defined by the ATM Forum. PNNI supports aggregation for private ATM addresses and links between switches, and can scale the network and its performance by configuring PNNI peer groups and hierarchical levels.
A key feature of the PNNI hierarchy mechanism is its ability to automatically configure itself in networks in which the address structure reflects the topology. It is responsive to changes in network resources and availability.
PNNI is available on the BPX switch when an optional Cisco Service Expansion Shelf (SES) PNNI is installed. This controller is connected locally to a BPX 8600 series switch to provide PNNI signaling and routing for the establishment of ATM and Frame Relay switched virtual circuits (SVCs) and Soft Permanent Virtual Circuits (SPVCs) over a BPX 8600 wide area network. The network created with BPX SES PNNI nodes also supports traditional ATM and Frame Relay permanent virtual circuits (PVCs) in a separately partitioned AutoRoute network.
ATM SVCs are ATM connections that are established and maintained by a standardized signaling mechanism between ATM CPE (ATM end systems) across a Cisco WAN switching network. ATM SVCs are set up in accordance with user demand and removed when calls are completed, thus freeing up network resources.
BPX SES PNNI node resources, such as port virtual path identifier (VPI) range and bandwidth and trunk bandwidth, are partitioned between SVCs/SVPCs and PVCs. Resource partitioning provides a firewall between PVCs and SVCs/SVPs so that problems with CPE or large bursts do not affect the robustness and availability of PVC services. Bursty data for either PVCs or SVCs/SPVCs can always use any unused link bandwidth, regardless of partitioning.
For a brief description of the SES PNNI, see Service Expansion Shelf PNNI. Refer to the Cisco SES PNNI Controller Software Configuration Guide for detailed information abut the SES.
For further information about PNNI and the SES, refer to the Cisco SES PNNI Controller Software Configuration Guide.
This section is a brief description of the BPX switch's support for Virtual Private Networks (VPN). For additional information, refer to the Cisco MPLS Controller Software Configuration Guide.
Conventional VPNs that use dedicated lease lines or Frame Relay Private Virtual Circuits (PVC) and a meshed network (Figure 1-2) provide many advantages, but typically have been limited in efficiency and flexibility.
Instead of using dedicated leased lines or Frame Relay PVCs, and so on, for a VPN, an IP virtual private network uses the open connectionless architecture of the Internet for transporting data as shown in Figure 1-2.
An IP virtual private network offers these benefits:
MPLS virtual private networks combine the advantages of IP flexibility and connectionless operation with the QoS and performance features of ATM (Figure 1-3).
The MPLS VPNs provide the same benefits as a plain IP Virtual Network plus:
Interworking lets you retain your existing services and migrate to the higher bandwidth capabilities provided by BPX switch networks, as your needs expand. Frame Relay to ATM Interworking enables Frame Relay traffic to be connected across high-speed ATM trunks using ATM-standard Network and Service Interworking.
Two types of Frame Relay to ATM interworking are supported:
Part A of Figure 1-4 shows typical Frame Relay to network interworking. In this example, a Frame Relay connection is transported across an ATM network, and the interworking function is performed by both ends of the ATM network.
These are typical configurations:
Part B of Figure 1-4 shows a form of network interworking where the interworking function is performed by only one end of the ATM network, and the CPE connected to the other end of the network must itself perform the appropriate service-specific convergence sublayer function.
These are sample configurations:
Network Interworking is supported by the FRM, UFM-C, and UFM-U on the IGX switch, and the FRSM on the MGX 8220. The Frame Relay Service Specific Convergence Sublayer (FR-SSCS) of AAL5 is used to provide protocol conversion and mapping.
Figure 1-5 shows a typical example of Service Interworking. Service Interworking is supported by the FRSM on the MGX 8220 and the UFM-C and UFM-U on the IGX switch. Translation between the Frame Relay and ATM protocols is performed in accordance with RFC 1490 and RFC 1483.
Unlike Network Interworking, in a Service Interworking connection between an ATM port and a Frame Relay port, the ATM device does not need to be aware that it is connected to an interworking function.
The Frame Relay service user does not implement any ATM specific procedures. Also, the ATM service user does not need to provide any Frame Relay specific functions. All translational (mapping functions) are performed by the intermediate interworking function.
This is a typical configuration for service interworking:
Networks may be configured as:
By allowing CPE connections to connect to a nonrouting node (interface shelf), a tiered network is able to grow in size beyond that which would be possible with only routing nodes comprising the network.
Starting with Release 8.5, tiered networks support both BPX switch routing hubs and IGX switch routing hubs. Voice and data connections originating and terminating on IGX switch interface shelves (feeders) are routed across the routing network via their associated IGX switch routing hubs.
Tiered networks support multiservice connections, including Frame Relay, circuit data, voice, and ATM. By allowing the customer's equipment to connect to a nonrouting node (interface shelf), a tiered network is able to grow in size beyond that which would be possible with only routing nodes.
Intermediate routing nodes must be IGX switches. IGX switch interface shelves are the only interface shelves that can be connected to an IGX switch routing hub. With this addition, a tiered network provides a multiservice capability (Frame Relay, circuit data, voice, and ATM).
In a tiered network, interface shelves at the access layer (edge) of the network are connected to routing nodes via feeder trunks (Figure 1-6).
The routing hubs route the interface shelf connections across the core layer of the network.The interface shelves do not need to maintain network topology nor connection routing information. This task is left to their routing hubs.
This architecture provides an expanded network consisting of a number of nonrouting nodes (interface shelves) at the edge of the network that are connected to the network by their routing hubs.
T1/E1 Frame Relay connections originating at IGX switch interface shelves and T1/E1 Frame Relay, T1/E1 ATM, CES, and FUNI connections originating at MGX 8220 interface shelves are routed across the routing network via their associated BPX switch routing hubs.
These requirements apply to BPX switch routing hubs and their associated interface shelves:
Tiered networks with BPX routing hubs have the capability of adding interface shelves/feeders (nonrouting nodes) to an IGX/BPX routing network (Figure 1-7). Interface shelves allow the network to support additional connections without adding additional routing nodes.
The MGX 8220 or MGX 8800 and IGX 8400 nodes configured as interface shelves are connected to BPX routing hubs.
The MGX 8220 and MGX 8800 support frame T1/E1, X.21 and HSSI Frame Relay, ATM T1/E1, and CES, and are designed to support additional interfaces in the future.
These requirements apply to BPX routing hubs and their associated interface shelves:
Annex G | A bidirectional protocol, defined in Recommendation Q.2931. It is used for monitoring the status of connections across a UNI interface. Tiered Networks use the Annex G protocol to pass connection status information between a hub node and attached interface shelf. |
BPX Routing Hub | A BPX node in the routing network that has attached interface shelves. Also referred to as a hub node or BPX hub. |
MGX 8220 Interface Shelf | A standards-based service interface shelf that connects to a BPX routing hub, aggregates and concentrates traffic, and performs ATM adaptation for transport over broadband ATM networks. |
MGX 8800 Interface Shelf | A standards-based service interface shelf that connects to a BPX routing hub, aggregates and concentrates traffic, and performs ATM adaptation for transport over broadband ATM networks. |
IGX Interface Shelf | A special configuration of an IGX switch that is connected as a shelf to an IGX routing hub. An IGX interface shelf is sometimes referred to as an IGX A/F or feeder. The IGX interface shelf does not perform routing functions nor keep track of network topology. |
IGX Routing Hub | An IGX node in the routing network that has attached IGX interface shelves. Also referred to as a hub node or IGX hub. |
Feeder Trunk | Refers to a trunk that interconnects an interface shelf with the routing network via a BPX routing hub. A feeder trunk is sometimes referred to as an interface shelf trunk. |
IGX/AF | Another name for the IGX interface shelf. |
Routing Network | The portion of the tiered network that performs automatic routing between connection endpoints. |
VPI | Virtual Path Identifier. |
VCI | Virtual Connection Identifier. |
Converting an IGX node to an interface shelf requires reconfiguring connections on the node because no upgrade path is provided in changing a routing node to an interface shelf.
A BPX node, acting as a Hub Node, is not restricted from providing any other feature normally available on BPX nodes. A BPX Hub supports up to 16 interface shelves.
Connections within tiered networks consist of distinct segments within each tier. A routing segment traverses the routing network, and an interface shelf segment provides connectivity to the interface shelf end-point. Each of these segments are added, configured and deleted independently of the other segments.
Use the Cisco WAN Manager Connection Manager to configure and control these individual segments as a single end-to-end connection.
Interface shelves are attached to the routing network via a BPX routing hub using a BXM trunk (T3/E3 or OC-3) or BNI trunk (T3/E3). The connection segments within the routing network are terminated on the BNI feeder trunks.
All Frame Relay connection types that can terminate on the BPX are supported on the BNI feeder trunk (Vbr, Cbr, Abr, and ATF types). No check is made by the routing network to validate whether the connection segment type being added to a BNI feeder trunk is actually supported by the attached interface shelf.
Co-locating Routing Hubs and Interface Shelves
The trunk between an interface shelf and the routing network is a single point of failure, therefore, the interface shelves should be co-located with their associated hub node. Card level redundancy is supported by the Y-Cable redundancy for the BXM, BNI, AIT, and BTM.
Communication between CPE devices and the routing network is provided in accordance with Annex G of Recommendation Q.2931. This is a bidirectional protocol for monitoring the status of connections across a UNI interface. (Note: the feeder trunk uses the STI cell format to provide the ForeSight rate controlled congestion management feature.)
Communication includes the real-time notification of the addition or deletion of a connection segment and the ability to pass the availability (active state) or unavailability (inactive state) of the connections crossing this interface.
A proprietary extension to the Annex G protocol is implemented that supports the exchange of node information between an interface shelf and the routing network. This information is used to support the IP Relay feature and the Robust Update feature used by network management.
Network Management access to the interface shelves is through the IP Relay mechanism supported by the SNMP and TFTP projects or by direct attachment to the interface shelf. The IP Relay mechanism relays traffic from the routing network to the attached interface shelves. No IP Relay support is provided from the interface shelves into the routing network.
The BPX routing hub is the source of the network clock for its associated feeder nodes. Feeders synchronize their time and date to match their routing hub.
Robust Object and Alarm Updates are sent to a network manager that has subscribed to the Robust Updates feature. Object Updates are generated whenever an interface shelf is added or removed from the hub node and when the interface shelf name or IP Address is modified on the interface shelf. Alarm Updates are generated whenever the alarm state of the interface shelf changes between Unreachable, Major, Minor, and OK alarm states.
An interface shelf is displayed as a unique icon in the Cisco WAN Manager topology displays. The colors of the icon and connecting trunks indicate the alarm state of each.
Channel statistics are supported by FRP, FRM, ASI, and MGX 8220 endpoints. BNIs, AITs, and BTMs do not support channel statistics. Trunk Statistics are supported for the feeder trunk and are identical to the existing BNI trunk statistics.
Where greater bandwidths are not needed, the Inverse Multiplexing ATM (IMA) feature provides a low-cost trunk between two BPX switches.
The IMA feature allows BPX switches to be connected to one another over any of the eight T1 or E1 trunks provided by an IMATM module on an MGX 8220 shelf. A BNI or BXM port on each BPX switch is directly connected to an IMATM module in an MGX 8220 by a T3 or E3 trunk. The IMATM modules are then linked together by any of the eight T1 or E1 trunks.
Refer to the Cisco MGX 8220 Reference and the Cisco WAN Switching Command Reference publications for further information.
A virtual trunk may be defined as a "trunk over a public ATM service." The trunk really doesn't exist as a physical line in the network. Rather, an additional level of reference, called a virtual trunk number, is used to differentiate the virtual trunks found within a physical trunk port.
Figure 1-8 shows four Cisco WAN switching networks, each connected to a Public ATM Network via a physical line. The Public ATM Network is shown linking all four of these subnetworks to every other one with a full meshed network of virtual trunks. In this example, each physical line is configured with three virtual trunks.
The BPX switch provides ATM standard traffic and congestion management per ATM Forum TM 4.0 using BXM cards.
The Traffic Control functions include:
In addition to these standard functions, the BPX switch provides advanced traffic and congestion management features including:
Advanced Class of Service (CoS) management provides per-VC queueing and per-VC scheduling. CoS management provides fairness between connections and firewalls between connections. Firewalls prevent a single non-compliant connection from affecting the QoS of compliant connections. The non-compliant connection simply overflows its own buffer.
The cells received by a port are not automatically transmitted by that port out to the network trunks at the port access rate. Each VC is assigned its own ingress queue that buffers the connection at the entry to the network. With Abr with VSVD or with Optimized Bandwidth Management (ForeSight), the service rate can be adjusted up and down depending on network congestion.
Network queues buffer the data at the trunk interfaces throughout the network according to the connection's Class of Service. Service classes are defined by standards-based QoS. Classes can consist of the five service classes defined in the ATM standards as well as multiple sub-classes to each of these classes. Classes can range from constant bit rate services with minimal cell delay variation to variable bit rates with less stringent cell delay.
When cells are received from the network for transmission out a port, egress queues at that port provide additional buffering based on the Service Class of the connection.
CoS management provides an effective means of managing the Quality of Service defined for various types of traffic. It permits network operators to segregate traffic to provide more control over the way that network capacity is divided among users. This is especially important when there are multiple user services on one network. The BPX switch provides separate queues for each traffic class.
Rather than limiting the user to the five broad classes of service defined by the ATM standards committees, CoS management can provide up to 16 classes of service (service subclasses) that you can further define and assign to connections. Some of the COS parameters that may be assigned include:
With Automatic Routing Management (formerly referred to as AutoRoute), connections in Cisco WAN switching networks are added if there is sufficient bandwidth across the network and are automatically routed when they are added.
You need enter only the endpoints of the connection at one end of the connection and the IGX switch and BPX switch software automatically set up a route based on a sophisticated routing algorithm. This feature is called Automatic Routing Management. It is a standard feature on the IGX and BPX switches.
System software automatically sets up the most direct route after considering the network topology and status, the amount of spare bandwidth on each trunk, as well as any routing restrictions entered by the user (for example, avoid satellite links). This avoids having to manually enter a routing table at each node in the network. Automatic Routing Management simplifies adding connections, speeds rerouting around network failures, and provides higher connection reliability.
You can selectively enable cost-based route selection as the route selection per node. With this feature, a trunk cost is assigned to each trunk (physical and virtual) in the network. The routing algorithm then chooses the lowest-cost route to the destination node. The lowest cost routes are stored in a cache to reduce the computation time for on-demand routing.
Cost-based routing can be enabled or disabled at anytime. There can be a mixture of cost-based and hop-based nodes in a network.
The "Cost-Based Connection Routing" section, contains more detailed information about cost-based AutoRoute.
Priority bumping allows BPX and IGX switch connections classified as more important (via COS value) to "bump" (that is, set aside) existing connections of lesser importance. While the Automatic Routing Management feature is capable of automatically redirecting all failed connections onto other paths, priority bumping lets you prioritize and sustain more important connections when network resources are diminished to a point that all connections cannot be sustained. Network resources are reclaimed for the more important connections by bumping (derouting) the traffic on less important connections.
Priority bumping is triggered by insufficient resources (such as bandwidth), resulting from any number events, including changes to the network made by using the commands addcon, upcon, cnfcon, cnnfcos, cnfpref, cnftrk, and deltrk. Other triggers include trunk line/card failure, node failure, and communication failure. The most prominent event is a trunk failure.
For information on setting up Priority Bumping, see "Specifying Priority Bumping" in Chapter 10 of the Cisco WAN Switching Command Reference.
The Concurrent Routing feature is introduced in Switching Software Release 9.3.30 for the BPX and IGX platforms. Concurrent Routing (CR) allows multiple routing requests to be processed simultaneously on a node. For example, a node can initiate (master) one or more routes while simultaneously accepting other routes that pass through it (via) or terminate at it (slave).
If CR is not enabled on a node, routing requests received while a connection is being routed will be rejected or "blocked". As a result, only one bundle at a time can be routed on a node if CR isn't enabled This "blocking" algorithm underutilizes the switch's computational power. Blocked routing is illustrated in Figure 1-9 below.
CR allows the switch's processor to be more effectively utilized by allowing multiple routes to be in progress concurrently. The result is better overall reroute performance. CR is illustrated in Figure 1-10 below.
Performance improvement will not be realized for individual or topologically disjoint reroutes. The key performance metric that will be improved by CR is network settling time. Network settling time is defined by the longest settling time for any single node, assuming all of the nodes start routing at the same time. The number of nodes and connections in the network, network topology and other configurable routing parameters all effect network settling time.
The CR Feature provides the following functions:
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Note The extent to which CR reduces network settling time will vary with network topology, traffic conditions and the number of CR enabled nodes in the network. |
CR cannot be enabled until all of the nodes in a network have been upgraded to SWSW release 9.3.30. Once all of the nodes in a network have been upgraded to SWSW release 9.3.30, CR can be enabled on any node in that network. It is not necessary for CR to be enabled on every node in a network for CR to take place on those nodes that are CR enabled.
The maximum number of concurrent routes that can be configured on a node is 8. Allowing more than 8 concurrent routes would have diminishing returns, because processor utilization would become excessive. A node will continue to master new route requests (provided route candidates exist), or serve as a via or slave for new routes, unless doing so would exceed the route concurrency level that is configured on the node.
CR has the potential to dramatically reduce CPU idle time. To preserve enough CPU time for users to interact effectively with a node, even during periods of extensive rerouting, a mechanism has been implemented to limit (throttle) route concurrency. When CPU utilization exceeds a defined threshold (throttle level), new route activity is temporarily suspended to preserve node responsiveness. Throttling continues until CPU utilization drops below a second threshold (resume level), which is less than or equal to the throttle level. Allowing the resume level to be less than the throttle level provides for a hysteresis mechanism to avoid oscillation around the throttling point. The default CPU throttling values for master, via and slave routes are set at 80% of CPU capacity for throttling and 60% of CPU capacity to resume new route activity. Separate throttle and resume points can be set for master, via, and slave routes to allow tailoring of route behavior, however, these settings can only be changed with Cisco-level commands.
If a node masters two or more routes that share the same via and slave nodes, these routes will have overlaping paths. Due to messaging protocol limitations, a node is only able to master concurrent routes that do not have overlaping paths. The Path Blocking algorithm checks each master route candidate that a node might initiate to see if it overlaps with another active route mastered by that node. If there will be any overlaping, the candidate is rejected and candidate selection continues. Path Blocking is node specific, but the degree to which it will limit concurrent master routes on a node is a function of network topology. If a node is only serving as a via and/or a slave, it cannot be path blocked.
Priority Bumping (PB) is a computationally-intensive process which allows switch connections classified as more important (based on CoS value) to "bump" connections of lesser importance. CR may be restricted if the PB feature is enabled on a network. Both PB and CR are processor intensive. To avoid excessive processor utilization, no new route requests will be initiated or accepted on the nodes an active PB route traverses, until it has completed.
The CR feature does not alter the AutoRoute messaging protocol. AutoRouting is enabled by default on nodes that are not CR enabled. When Auto Routing is enabled on a node a backoff mechanism may be triggered to prevent excessive collisions. When the backoff mechanism is triggered the node will be temporarily unavaliable as a candidate for CR. This mechanism is conceptually similar to the Path Blocking algorithm described above.
Once all of the nodes on a network have been upgraded to Release 9.3.30, CR can be enabled on any node by using the cnfcmparm command to set the route concurrency level to an integer value greater than 1 but no greater than 8. Once CR has been enabled on a node, it operates automatically. CR can be turned off on a node by specifying a concurrency level of 1. See table 1-1 and example 1-1 below.
CLI command | Parameter | Description |
|---|---|---|
cnfcmparm | Routing concurrency level | This is a nodal parameter. It specifies the amount total number of routes that can be simultaneously in progress on the node. |
The dsprrst command continues to be used to display routing statistics in SWSW release 9.3.30, however, when CR is enabled, the semantics of some statististics are altered slightly.
Three new statistics have been added to the display to show the number of times CPU throttling/resumption has occurred for master, via, and slave routes, respectively. These statistics will be shown on the first page of reroute statistics as shown in the example below.
Note that the CR performance gain is not reflected in the basic dsprrst display. The basic statistics show the CPU real-time performance, whereas CR enhances routing concurrency in the network. To correct this deficiency, a new option to the dsprrst command is added to display nodal settling time measurements. A settling time measurement is initiated whenever candidate selection successfully locates a candidate for routing. The settling time measurement ends when candidate selection fails to find a candidate to route and no routes are currently active. In addition to the start and end time of the measurement, the following statistics are kept:
These statistics allow the following quantities to be derived:
At any time, the last 10 settling time measurements (including the active measurement, if any) are displayed using the new option. Nodal settling time history is cleared whenever reroute statistics are cleared. This new screen is shown in the second example, below.
The BPX/IGX switch networks provide a choice of two dynamic rate based congestion control methods, Abr with VSVD and Optimized Bandwidth Management (ForeSight). This section describes Standard Abr with VSVD.
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Note Abr with VSVD is an optional feature that must be purchased and enabled on a single node for the entire network. |
When an ATM connection is configured between BXM cards for Standard Abr with VSVD per ATM Forum TM 4.0, Resource Management (RM) cells are used to carry congestion control feedback information back to the connection's source from the connection's destination.
The Abr sources periodically interleave RM cells into the data they are transmitting. These RM cells are called forward RM cells because they travel in the same direction as the data. At the destination these cells are turned around and sent back to the source as backward RM cells.
The RM cells contain fields to increase or decrease the rate (the CI and NI fields) or set it at a particular value (the explicit rate ER field). The intervening switches may adjust these fields according to network conditions. When the source receives an RM cell, it must adjust its rate in response to the setting of these fields.
When spare capacity exists with the network, Abr with VSVD permits the extra bandwidth to be allocated to active virtual circuits.
The BPX/IGX switch networks provide a choice of two dynamic rate-based congestion control methods, Abr with VSVD and Cisco's Optimized Bandwidth Management (ForeSight). This section describes Optimized Bandwidth Management (ForeSight).
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Note Optimized Bandwidth Management (ForeSight) is an optional feature that must be purchased and enabled on a single node for the entire network. |
Optimized Bandwidth Management (ForeSight) may be used for congestion control across BPX/IGX switches for connections that have one or both endpoints terminating on cards other than BXM. The ForeSight feature is a dynamic closed-loop, rate-based congestion management feature that yields bandwidth savings compared to non-ForeSight equipped trunks when transmitting bursty data across cell-based networks.
ForeSight permits users to burst above their committed information rate for extended periods of time when there is unused network bandwidth available. This enables users to maximize the use of network bandwidth while offering superior congestion avoidance by actively monitoring the state of shared trunks carrying Frame Relay traffic within the network.
ForeSight monitors each path in the forward direction to detect any point where congestion may occur and returns the information back to the entry to the network. When spare capacity exists with the network, ForeSight permits the extra bandwidth to be allocated to active virtual circuits. Each PVC is treated fairly by allocating the extra bandwidth based on each PVC's committed bandwidth parameter.
If the network reaches full utilization, ForeSight detects this and quickly acts to reduce the extra bandwidth allocated to the active PVCs. ForeSight reacts quickly to network loading in order to prevent dropped packets. Periodically, each node automatically measures the delay experienced along a Frame Relay PVC. This delay factor is used in calculating the ForeSight algorithm.
With basic Frame Relay service, only a single rate parameter can be specified for each PVC. With ForeSight, the virtual circuit rate can be specified based on a minimum, maximum, and initial transmission rate for more flexibility in defining the Frame Relay circuits.
ForeSight provides effective congestion management for PVC's traversing broadband ATM as well. ForeSight operates at the cell-relay level that lies below the Frame Relay services provided by the IGX switch. With the queue sizes utilized in the BPX switch, the bandwidth savings is approximately the same as experienced with lower speed trunks. When the cost of these lines is considered, the savings offered by ForeSight can be significant.
BPX switches provide one high-speed and two low-speed data interfaces for data collection and network management:
Each BPX switch can be configured to use optional low-speed modems for inward access by the Cisco Technical Response Team for network troubleshooting assistance or to autodial Customer Service to report alarms remotely. If desired, another option is remote monitoring or control of customer premise equipment through a window on the Cisco WAN Manager workstation.
A Cisco WAN Manager NMS workstation connects via the Ethernet to the LAN port on the BPX and provides network management via SNMP. Statistics are collected by Cisco WAN Manager using the TFTP protocol.
You can also use the Cisco WAN Manager's Connection Manager to manage:
Network Management software includes these applications:
For further information on network management, refer to the Cisco WAN Manager Operations publication.
Cisco WAN Manager is a single unified management platform utilizing HP OpenView® to manage BPX, IGX, and SES devices. It provides a standards-based multiprotocol management architecture. Regardless of the size or configuration of your network, Cisco WAN Manager collects extensive service statistics, tracks resource performance, and provides powerful remote diagnostic and control functions for WAN maintenance.
Online help screens, graphical displays, and easy command line mnemonics make Cisco WAN Manager user-friendly. Plentiful hard disk storage is provided to allow accumulating time of day statistics on many network parameters simultaneously. The data is accumulated by the node's controller card and transmitted to the Cisco WAN Manager workstation where it is stored, processed, and displayed on a large color monitor.
Cisco WAN Manager connects to the network over an Ethernet LAN connection. With Ethernet, you can establish Cisco WAN Manager connectivity to remote nodes via Frame Relay over TCP/IP to the LAN connector on the local node, or via in-band ILMI.
Cisco WAN Manager provides in-band management of network elements via SNMP agent interfaces and MIBs embedded in each node and interface shelf. The SNMP agent allows a user to manage a StrataCom network or sub-network from any SNMP-based integrated network management system (INMS).
Network interfaces connect the BPX switch to other BPX or IGX switches to form a wide-area network. The BPX switch provides these trunk interfaces:
The T3 physical interface utilizes DS3 C-bit parity and the 53-byte ATM physical layer cell relay transmission using the Physical Layer Convergence Protocol.
The E3 physical interface uses G.804 for cell delineation and HDB3 line coding.
The BXM-622 cards support these physical interfaces:
The BPX switch supports network interfaces up to 622 Mbps and provides the architecture to support higher broadband network interfaces as the need arises.
Optional redundancy is on a one-to-one basis. The physical interface can operate either in a normal or looped clock mode. As an option, the node synchronization can be obtained from the DS3 extracted clock for any selected network trunk.
The BXM T3/E3 card supports the standard T3/E3 interfaces.
The BXM-155 cards support SMF, SMFLR, and MMF physical interfaces.
The BXM-622 cards support SMF and SMFLR physical interfaces.
The BXM cards support cell relay connections that are compliant with both the physical layer and ATM layer standards.
The MGX 8220 interfaces to a BNI or BXM card on the BPX, via a T3, E3, or OC-3 interface. The MGX 8220 provides a concentrator for T1 or E1 Frame Relay and ATM connections to the BPX switch with the ability to apply Optimized Bandwidth Management (ForeSight) across a connection from end-to-end. The MGX 8220 also supports CES and FUNI (Frame-based UNI over ATM) connections.
The BPX Switch system manager can configure alarm thresholds for all statistical type error conditions. Thresholds are configurable for conditions such as frame errors, out of frame, bipolar errors, dropped cells, and cell header errors. When an alarm threshold is exceeded, the NMS screen displays an alarm message.
Graphical displays of collected statistics information, a feature of the Cisco WAN Manager NMS, are a useful tool for monitoring network usage. Statistics collected on network operation fall into four general categories:
These statistics are collected in real-time throughout the network and forwarded to the WAN Manager workstation for logging and display. The link from the node to the Cisco WAN Manager workstation uses a protocol to acknowledge receipt of each statistics data packet.
Refer to the Cisco WAN Manager Operations publication, for more details on statistics and statistical alarms.
A BPX service switch network provides network-wide, intelligent clock synchronization. It uses a fault-tolerant network synchronization architecture recommended for Integrated Services Digital Network (ISDN). The BPX switch internal clock operates as a Stratum 3 clock per ANSI T1.101.
Because the BPX switch is designed to be part of a larger communications network, it is capable of synchronizing to higher-level network clocks as well as providing synchronization to lower-level devices. You can configure any network access input to synchronize the node. Any external T1 or E1 input can also be configured to synchronize network timing.
A clock output allows synchronizing an adjacent IGX switch or other network device to the BPX switch and the network. In nodes equipped with optional redundancy, the standby hardware is locked to the active hardware to minimize system disruption during system switchovers.
You can configure the BPX Service Node to select clock from these sources:
The Cisco WAN switching cell relay system software shares most core system software, as well as a library of applications, between platforms. System software provides basic management and control capabilities to each node.
BPX node system software manages its own configuration, fault-isolation, failure recovery, and other resources. Because no remote resources are involved, this ensures rapid response to local problems. This distributed network control, rather than centralized control, provides increased reliability.
Software among multiple nodes cooperates to perform network-wide functions such as trunk and connection management. This multiprocessor approach ensures rapid response with no single point of failure. System software applications provide advanced features that you can install and configure as required.
Some of the many software features are:
The routing software supports the establishment, removal and rerouting of end-to-end channel connections. There are three routing modes:
The system software uses these criteria when it establishes an automatic route for a connection:
When a node reroutes a connection, it uses these criteria and also looks at the priority that has been assigned and any user-configured routing restrictions. The node analyzes trunk loading to determine the number of cells or packets the network can successfully deliver. Within these loading limits, the node can calculate the maximum combination allowed on a network trunk of each type of connection: synchronous data, ATM traffic, Frame Relay data, multimedia data, voice, and compressed voice.
Network-wide T3, E3, OC-3, or OC-12 connections are supported between BPX switches terminating ATM user devices on the BPX switch UNI ports. These connections are routed using the virtual path and/or virtual circuit addressing fields in the ATM cell header.
Narrowband connections can be routed over high-speed ATM backbone networks built on BPX broadband switches. FastPacket addresses are translated into ATM cell addresses that are then used to route the connections between BPX switches, and to ATM networks with mixed vendor ATM switches. Routing algorithms select broadband links only, avoiding narrowband nodes that could create a choke point.
The rerouting mechanism ensures that connections are presorted in order of cell loading when they are added. Each routing group contains connections with loading in a particular range. The group containing the connections with the largest cell loadings is rerouted first, and subsequent groups are then rerouted on down to the last group that contains connections with the smallest cell loadings.
There are three configurable parameters for configuring the rerouting groups:
You configure the three routing group parameters by using the cnfcmparm command.
For example, there might be 10 groups, with the starting load size of the first group at 50, and the incremental load size of each succeeding group being 10 cells. Then group 0 would contain all connections requiring 0-59 cell load units, group 1 would contain all connections requiring from 60-69 cell load units, on up through group 9 which would contain all connections requiring 140 or more cell load units.
| Routing Group | Connection Cell Loading |
|---|---|
0 | 0-59 |
1 | 60-69 |
2 | 70-79 |
3 | 80-89 |
4 | 90-99 |
5 | 101-109 |
6 | 110-119 |
7 | 120-129 |
8 | 130-139 |
9 | 140 and up |
In standard AutoRoute, the path with the fewest number of hops to the destination node is chosen as the best route. Cost-based route selection uses an administrative trunk cost routing metric. The path with the lowest total trunk cost is chosen as the best route.
Here is a short description of the major functional elements of Cost-Based Route Selection.
You use these switch software Command Line Interface (CLI) commands for cost-based route selection:
The Cisco WAN Switching Command Reference contains detailed information about the use of BPX switch commands.
Cisco WAN switching cell relay networks use a fault-tolerant network synchronization method of the type recommended for Integrated Services Digital Network (ISDN). You can select any circuit line, trunk, or an external clock input to provide a primary network clock. Any line can be configured as a secondary clock source in the event that the primary clock source fails.
All nodes are equipped with a redundant, high-stability internal oscillator that meets Stratum 3 (BPX) or Stratum 4 requirements. Each node keeps a map of the network's clocking hierarchy. The network clock source is automatically switched in the event of failure of a clock source.
There is less likelihood of a loss of data resulting from re-frames that occur during a clock switchover or other momentary disruption of network clocking with cell-based networks than there is with traditional TDM networks. Data is held in buffers and packets are not sent until a trunk has regained frame synchronism to prevent loss of data.
The increasing use of Virtual Trunks in Wide Area Networks has led to the development of the Virtual Trunk Clock Source Synchronization feature (VTCSS) in SWSW release 9.3.30. VTCSS operates transparently making network synchronization to a single ATM service provider clock source possible.(1)
When a virtual trunk port (VTP) is configured as a network clock source in pre-9.3.30 SWSW releases, the first virtual trunk (VT) interfaced on that VTP becomes the clock source by default. If the first VT fails, the clock source is automatically switched to the next available clock source (2) exclusive of the VTP that the failed VT was interfaced with.
With the VTCSS feature, if the first VT on a clock configured VTP fails, the clock source is switched to the next VT interfaced on that VTP. If the second VT fails the clock source is switched to the next VT interfaced on the same VTP and so on. As a result, the clock source remains associated with the physical interface (clock configured VTP) as long as there are one or more active VTs interfaced on it.(3)
The VTCSS feature is here is no configuration
1. May not allow all nodes in the network to synch. to the same clock source...may just allow a network to achieve a higher degree of clock synchronization than was previously possible.
2.As defined by the network system software.
3. If one VT on a VTP is configured: pass synch = yes, that VTP can't be a clock source in the first place. Do I need to mention that in the scope of this doc?
4. Do I need to mention the debug on/off flag, or is this beyond the scope of the BPX Installation & Configuration Guide?
as the clock source., even though the physical interface of the Virtual interface is active and there are other active VT's available to switch to.
In Wide Area Networks, the clock synchronization from a public ATM service provider helps to have glitch free, data transfer between the IGX/BPX and the service provider, if we can derive the clock out of the VT's successfully. Therefore if the physical interface can derive the clock from the ATM cloud, irrespective of any Virtual Interface failures, the nodes in a network can achieve a higher degree of clock synchronization.
This feature enables the association of the Virtual trunk clock source with the physical interface and therefore enables the use of Virtual Trunks as clock sources for all of the virtual interfaces available on the trunk port.
This project is aimed at associating the network clock source with the physical interface, rather than the virtual interface, since the physical interface is the one which drives/derives the clock. Therefore, if a VT fails, the clock source should not be switched to another physical interface or internal clock source, if there is another healthy (clock configurable) active interface up and running. This implies that if at least one virtual trunk interface is up without any failure, the physical interface will still be a sustainable clock source. So irrespective of the virtual trunk failure, the clock source should always be associated with the physical interface port, where the virtual trunk is activated.
Background and Justification
The requirement of supporting the Virtual Trunk clocking, arises from the marketing requirement of network synchronization using a single clock source of public ATM service provider, irrespective of single VT failures in a multiple VT scenario. The present switch software implementation associates the VT clock source with the first logical trunk interface (VI), and therefore a failure of the first VT interface, will cause a switching of the clock source to the next available interface. This project is aimed at allowing the network clock source to be always associated with the physical interface, since the physical interface is the one which drives/derives the clock.
Configuration
The clock synchronization from a public ATM service provider helps to have a glitch free, data transfer between the IGX/BPX and the service provider, if we can derive the clock out of the VT's successfully. Therefore, if the physical interface can derive the clock from the ATM cloud, irrespective of the Virtual Interface failures, the nodes in a network can achieve a higher degree of clock synchronization. There is no special configuration required with the addition of this feature
Overview
The VT clock source synchronization will allow the network to synchronize and provide stable clocking for all nodes throughout the attached nodes in the cloud.
The summary of functions which will be implemented in Release 9.3 for the support of enhanced VT clocking includes:
1. When a VT port is configured for clock source, the first virtual trunk interface on the trunk port will be internally marked as the clock source. Unlike the current implementation, if the first interface on the trunk port fails, or becomes unusable as clock source, the node will search for the next active virtual interface (which will be usable as a clock source) and mark that interface as the clock source. Therefore this VT search mechanism, allows the clock source of the node to be associated with the physical trunk port rather than virtual interface.
2. The clock selection mechanism, within the same trunk port(slot.port) will be transparent to the user. An event will be generated to indicate the switching of the clock source from one VI to another on the same trunk port, if the debug flag on/off3 is enabled. This debug flag will be defaulted to `disabled'.This event log is confined only to the local node and can be enabled through a debug on/off flag. The present clock switch event logs (local and remote node) will be modified, to remove the virtual interface number.
3. There is no switching of the interface clock occurs, if a clock source VT fails, and there is another active (OK state) interface available on the same interface port and therefore the interface clock source is not failed. However, the new selected VI has to be suitable for configuring as a clock source. With this implementation, the permanent association of the clock source to the first virtual interface of the VT port will be removed and a selection criteria will be applied to associate the clock source to the next available virtual interface on the trunk port.
4. When one VT (the first interface) on the trunk port, configured for the clock source fails, the selection algorithm will look for one clock source configurable virtual interface on the same trunk port. The clock switch to the next source occurs only if there were no clock configurable VIs detected. The suitability of an interface to be a clock source is determined by the clock test.
5. When a virtual trunk, which is configured as a clock source is deleted/deactivated from the node, the clock switch (to the next available source) occurs only if the physical trunk port containing the VT has no other usable virtual trunks.
6. If all of the Virtual Trunks on a trunk port are failed, even though the physical interface may be configurable as clock source, the clock selection criteria will not select the trunk port, for the clock source, since there are no more usable logical trunks available.
7. If the VT port is configured as a clock source, the clock routing/selection algorithm will be triggered at the highest number node only if all the virtual interfaces of a virtual trunk port are not clock source configurable. The current implementation triggers the selection, when a trunk status change occurs only on the first VI of the VT port, independent of the logical trunk number.
8. The clock source switch will occur only if all the VIs on a VT port are failed (the trunk port is now not a sustainable clock) and the message to the trunk card will be issued to de-configure the clock. This is because there is no need to send in the configuration message to the card as long as trunk port is not changing. Therefore between logical trunk selections on the same port, the clock switch will not happen to the next source (or internal, if no source is available).
9. The VT search occurs only on the local node and the VT search is transparent to the other nodes in the n/w, including highest numbered node. If the VT search does not find one suitable clock then the node may trigger a network wide selection or routing as appropriate, depending on the clock routing topology.
The association of the Virtual trunk clock source to the physical interface allows the use of Virtual Trunks as clock source for all of the virtual interfaces available on the trunk port, since the physical interface is the one which drives/derives the clock. Therefore if a VT, configured as a clock source fails, the clock source should not be switched to another physical interface or internal clock source, unless there is no clock configurable active interface up and running. So irrespective of the virtual trunk failure, the clock source should always be associated with the physical interface port, where the virtual trunk is activated.
Feature Summary:
This feature provides an indirect association of the clock source to the physical trunk port rather than the individual virtual interfaces of a virtual trunk port. A clock switch from a configured clock source occurs when a failure is detected by the clock test (diagnostics) running in the back ground. The clocks will be selected in the order of their configuration and the routing of the clock occurs through the topology table defined or derived by the highest number node in the network.The details of the clock synchronization is given in the following section (5.3.1).
A Virtual trunk port can be configured for a clock source, if that physical trunk port (all of the VIs) does not pass the clock sync to route the clock through the other nodes in the network. The default configuration for the VT's for the clock routing is (pass sync) No, where as the non-virtual trunks are always defaulted as clock routing trunks(pass sync = yes). A trunk can be configured as a clock source, only if it is not a clock routing trunk (pass sync = no) and therefore the VT ports that are configured for clock sources cannot route the clock through. Also, the configuration of a virtual trunk, as clock routing as yes or no (pass sync) will affect all the VI's on the trunk port, since the clock routing attribute is a characteristic of the physical interface.
For the software implementation, the default association of clock source internally to the first VI on the trunk port, when the clock source is configured on the port will continue in the same way as now. Therefore if we first configure a VT port, for clock, the first virtual trunk will be selected for our internal reference, which helps us in implementing the local clock switching, transparently to the user. The logical trunk association is for the implementation reference, since a logical trunk is the way of connecting the trunk port interface in switch software.
The use of the trunk port as clock source with all of the VTs in failed state, may not be a real customer scenario and therefore such a configuration is not supported. Also the current switch software implementation of virtual trunks does not provide an accurate status for the detection of the physical interface failures, when all the virtual interfaces are failed.The failure of a clock source can be due to some of the alarm conditions and is determined by the clock diagnostics.
Features:
The VT clocking feature allows the mapping of clock source to one of the suitable logical trunk out of all of the active VIs of a VT port. The following additional features will be provided, if a VT port is configured for clock source:
The event log will indicate the clock switch to the physical interface (slot.port) as in the case of a regular trunk.
If all the VIs fail on physical trunk port, even though this would be configurable as a clock source, the interface will be taken out of service and removed from the list of selectable sources.
The VI failure and clock switching within the same interface port will be transparent to the other nodes in the network.
All of the VIs in a trunk port can trigger the nw clock selection depending on the topology
A debug flag can turn on the event logging, whenever a clock switch occurs between the VIs of a trunk port. The default value for this flag is `Disabled'
The normal trunk failures continue to cause clock source switches as they do currently and there is no effect on regular trunks (non-virtual trunks) with the introduction of this feature.
If the first virtual interface is failed, at a time when the clock source is configured at a node, the node will behave in the same as currently, and the clock source will be marked for the first interface. Because of the failure the clock source will not be switched to the new configured interface, but when the clock diagnostics reports the failure, the VT search will look for the next interface on the port and attach the source.
When the first interface comes back up, the interface will not be switched back, unless there is a failure and no alternate VI is available.
The VT search occurs in the cyclic order starting at the current interface and runs through max VI's. In IGX the maximum number of Virtual Interfaces is 15 and in BPX the maximum number of VIs is 31 on a trunk port.
No impact on the Release 9.3 Virtual Ports feature, with the introduction of this feature
Limitations:
The following is a known limitation of the VT clock sources:
Even though the VTs can be configured to pass the clock sync (pass sync = yes), and therefore route the clock through Virtual Trunks (through the cloud), the stability of the clock is determined by the entry and exit points in the cloud. This is a current system limitation.
Functional Description and Feature Usage:
The clock source selection algorithm will be modified to indirectly map the clock source to the active physical interface rather than the first virtual interface, by a logical assignment of the VIs to the clock source, according to the VI failure. The behavior of the present UI configuration for the cnfclksrc command will not be changed, it continues to take the virtual trunk port interface, in the slot.port format. The feature will be provided for both IGX and BPX virtual trunks.Following the clock source failure and recovery detection, the clock source will get re-attached, but without sending any message to the card to de-configure and later re-configure. Therefore NO switching to internal source and back will occur between clock switches within the same port. Since the re-attachment is within the same trunk port in the case of VT, the logical trunk interface is referred only for the fault detection, since switch software always require a reference by logical trunk.
Cisco WAN hardware and software components are designed to provide a switch availability in excess of 99.99 percent. Network availability will be impacted by link failure, which has a higher probability of occurrence than equipment failure.
Because of this, Cisco WAN network switches are designed so that connections are automatically rerouted around network trunk failures, often before users detect a problem. System faults are detected and corrective action taken often before they become service affecting. This section describes some of the features that contribute to network availability.
System availability is a primary requirement with the BPX switch. The designed availability factor of a BPX switch is (99.99 percent) based on a node equipped with optional redundancy and a network designed with alternate routing available. The system software, as well as firmware for each individual system module, incorporates various diagnostic and self-test routines to monitor the node for proper operation and availability of backup hardware.
For protection against hardware failure, a BPX switch shelf can be equipped with the following redundancy options:
If redundancy is provided for a BPX switch, when a hardware failure occurs, a hot-standby module is automatically switched into service, replacing the failed module. All cards are hot-pluggable, so replacing a failed card in a redundant system can be performed without disrupting service.
Since the power supplies share the power load, redundant supplies are not idle. All power supplies are active; if one fails, then the others pick up its load. The power supply subsystem is sized so that if any one supply fails, the node will continue to be supplied with adequate power to maintain normal operation of the node. The node monitors each power supply voltage output and measures cabinet temperature to be displayed on the NMS terminal or other system terminal.
Each BPX switch shelf within the network runs continuous background diagnostics to verify the proper operation of all active and standby cards, backplane control, data, and clock lines, cabinet temperature, and power supplies. These background tests are transparent to normal network operation.
Each card in the node has front-panel LEDs to indicate active, failed, or standby status.
Each power supply has green LEDs to indicate proper voltage input and output.
An Alarm, Status, and Monitor card collects all the node hardware status conditions and reports it using front panel LED indicators and alarm closures. Indicators are provided for major alarm, minor alarm, ACO, power supply status, and alarm history. Alarm relay contact closures for major and minor alarms are available from each node through a 15-pin D-type connector for forwarding to a site alarm system.
BPX switches are completely compatible with the network status and alarm display provided by the Cisco WAN Manager NMS workstation. In addition to providing network management capabilities, it displays major and minor alarm status on its topology screen for all nodes in a network.
The Cisco WAN Manager NMS also provides a maintenance log capability with configurable filtering of the maintenance log output by node name, start time, end time, alarm type, and user-specified search string.
Posted: Fri Jul 27 17:11:30 PDT 2001
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