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This chapter introduces the Wide Area Network (WAN) Service Node, the Extended Services Processor (ESP), and PNNI routing. It includes the following sections:
The WAN Service Node provides Asynchronous Transfer Mode (ATM) and Frame Relay switched virtual circuits (SVCs), and soft permanent virtual circuits (SPVCs) across a Cisco WAN switching network. The network created out of WAN Service Nodes is enhanced for SVCs and also supports traditional ATM and Frame Relay permanent virtual circuits (PVCs), as illustrated in Figure 1-1. An additional feature of the WAN Service Node is its use of the Private Network-Network Interface (PNNI) routing protocol. Defined by the ATM Forum for ATM networks, PNNI provides a dynamic routing protocol, is responsive to changes in network resource availability, and will scale to large networks.
A network of WAN Service Nodes provides network interworking between Frame Relay and ATM networks, but there is no service interworking between ATM and Frame Relay customer premise equipment (CPE) SVCs. While Frame Relay SVCs will be connected across the WAN switching network, they have to be terminated on another Frame Relay device. Similarly, ATM SVCs are established only between ATM CPE-that is, end users. WAN Service Node resources, such as port virtual path identifier (VPI) range and bandwidth and trunk bandwidth, are partitioned between SVCs and PVCs. Resource partitioning provides a firewall between PVCs and SVCs so that problems with CPE or large all bursts do not affect the robustness and availability of PVC services.
Figure 1-2 illustrates the WAN Service Node in a typical cabinet.
The WAN Service Node consists of:
As shown in Figure 1-3, the MGX 8220 and ESP are co-located with and interface directly with the BPX switch.
The MGX 8220 provides a service access platform for connecting a wide range of services over narrowband and medium-band interfaces to both ATM and Frame Relay CPE. ATM CPE is interfaced to the WAN Service Node through an MGX 8220 ATM UNI service module (AUSM). Frame Relay CPE is interfaced to the WAN Service Node through an MGX 8220 Frame Relay service module (FRSM). The MGX 8220 maps all service traffic to and from ATM, based on standardized interworking methods. The aggregated CPE service traffic is sent and received over an ATM interface to the BPX switch, an ATM switch, shown as the BNM-to-BXM T3/OC-3 interface in Figure 1-3. The BPX switch is a Cisco standards-based high-capacity (19.2 Gigabit) broadband ATM switch that provides backbone ATM switching and delivery of a range of user services. Note that as shown in Figure 1-3, the BPX switch can also provide an ATM service interface (shown as the BXM to CPE) for higher speed ATM CPE. The BPX switch also provides the high-speed (T3/E3 and OC3) ATM trunks to other WAN Service Nodes or the network-to-network interface (NNI) to standards-based foreign ATM switches. The ESP provides the WAN Service Node with the ATM or Frame Relay signaling function. It interprets industry-standard signaling messages from ATM or Frame Relay CPE to provide the call setup and teardown for switched virtual circuits across the ATM network. In addition to SVC signaling, the ESP also performs PNNI routing, collects statistics, and processes alarms and billing records for the WAN Service Node.
The MGX 8220 is described in detail in the Cisco MGX 8220 Reference and MGX 8220 Command Supplement.The BPX switch is described in detail in the Cisco BPX 8620 Reference and BPX 8620 Installation manuals. The Cisco WAN Switching System Overview (formerly known as the System Manual) provides conceptual information and describes the services and overall features of Cisco WAN switching networks.
From the WAN Service Node's viewpoint, there are two types of external interfaces as shown in Figure 1-4:
Interim Inter-switch Protocol (IISP) is a static routing protocol defined by the ATM Forum to provide base level capability until the Private Network-Network Interface (PNNI) was specified. The IISP provides users with some level of multi-vendor switch interoperability based on the existing ATM Forum UNI 3.1 specifications. IISP assumes no exchange of routing information between switching systems. It uses a a fixed routing algorithm with static routes. Routing is done on a hop-by-hop basis by making a best match of the destination address in the call setup with address entries in the next hop routing table at a given switching system. Entries in the next hop routing table are configured by the user. IISP is described in more detail in Chapter 4.
Private Network-Network Interface (also known as Private Network to Node Interface) PNNI is a dynamic routing protocol defined by the ATM Forum. PNNI is a protocol specified for use between private ATM switches (for example, Cisco WAN Service Nodes), and between groups of private ATM switches. PNNI includes two categories of protocols:
PNNI is described in more detail in Chapter 4.
To support ATM and Frame Relay SVCs, the Cisco WAN Service Nodes essentially overlay a signaling network over a traditional (that is, PVC-based) network. This signaling network, indicated by the dashed lines in Figure 1-5, connects all of the WAN Service Nodes and extends to the CPE. The signaling plane establishes and maintains SVCs between the CPE, that is, end users, across a Cisco WAN switching ATM network.
The signaling plane is created out of two basic types of signaling channels:
The signaling VCCs are normally configured during the provisioning of UNI ports and NNI trunks.
There is an internal signaling VCC established between every UNI port on the WAN Service Node which will support ATM or Frame Relay SVCs and the ESP in the WAN Service Node.There are two types of UNI signaling channels supported by the WAN Service Node as shown in Figure 1-6.
There is also a signaling channel established between each adjacent pair of WAN Service Nodes. This NNI signaling channel shown in Figure 1-7 is configured for either IISP or PNNI protocol. During IISP configuration, one side of the NNI signaling connection is configured as the user side and a weight is assigned. In the figure, the thin line between the ESPs indicates the logical connection; the physical connection is configured through BPX switch 1 and BPX switch 2.
The growing need for higher speeds, more bandwidth, and a wide variety of voice and data services is transforming communications networks. Fast packet networking, known technically as cell relay or asynchronous transfer mode (ATM), is becoming the dominant switching technology underlying high-speed communications in LANs, private WANs, and public networks. ATM provides high transmission speeds, low delay, and efficient use of bandwidth.
ATM is a telecommunications concept defined by ANSI and ITU (formerly CCITT) standards for carrying a complete range of user traffic, including voice, data, and video. In ATM, information is packaged into 53-byte cells, of which 5 bytes are used for header information. The 53-byte fixed-length cell was chosen to provide effective performance for all types of traffic. Being well-defined by the various standards committees, ATM has been chosen to be the underlying transport mechanism of the Broadband Integrated Services Digital Network (B-ISDN). (Transport refers to the use of ATM switching and multiplexing techniques at the data-link layer [layer 2 of the OSI model] to convey user information from source to destination within a network.)
While B-ISDN is a definition for public networks, ATM can also be used within private networks.
The ATM standards define a delineation between the transport layer and the application layer. ATM protocol is independent of the transmission speed of the connection. Unlike most LAN protocols, ATM is connection-oriented. Before data transfer can occur, an end-to-end connection must be established. Once a connection is defined, ATM cells are self-routing in that each call contains a header with an address that indicates its destination. This saves processing time at intermediate nodes within the network, since routing is pre-determined.
Each ATM cell header contains two address fields, a Virtual Path Identifier (VPI) and a Virtual Connection Identifier (VCI). These two fields identify each connection across a single link in the network. ATM switches use either the VPI alone or the VPI and VCI fields to switch cells from the input port to an output port at each network node. In ATM terminology, a VPC is a Virtual Path Connection, and a VCC is a Virtual Channel Connection.
The Cisco WAN System Overview contains further information about traditional Cisco WAN switching ATM networks, including conceptual information about ATM connections.
ATM and Frame Relay standards groups have clearly defined permanent virtual circuits (PVCs). After being added to the network, PVCs remain relatively static. A virtual circuit only allocates a physical connection when there's data to send. The connection between two devices is set up at the start of transmission, or when the network is configured. A PVC is similar to a dedicated private line because the connection is set up on a permanent basis. While no bandwidth is allocated on a PVC link when setting up the connection, the operator tells the network about the characteristics of the desired circuit and sufficient network bandwidth is reserved.
Soft permanent virtual circuits (SPVCs) are PVCs which are routed using the Private Network-Network Interface (PNNI) routing protocol. The "permanent" qualifier indicates that the virtual connection is established administratively, through an operator's command, rather than on demand by signaling. A soft PVC is one where the establishment within the network is done by signaling (in this case, PNNI signaling), just as it is done for Frame Relay and ATM switched virtual circuits.
In the PNNI network, SPVC connections are established using the best available route. During a network failure, SPVC connections could be rerouted and the newly selected path many not be the optimal route. The ESP's SPVC feature provides for auto-grooming of SPVCs. Auto-grooming is a background management process that evaluates SPVC connections; if a better path for the connection is found, the SPVC will be released and rerouted to the optimized path.
Chapter 5, Soft Permanent Virtual Circuits, contains detailed information about SPVCs as they are implemented by the WAN Service Node.
With a switched virtual circuit, there must be some signaling mechanism to build a connection each time the user (ATM or Frame Relay CPE device) needs it. In addition, when the call is disconnected, there must be a mechanism for the orderly disconnection of the call, and the network's resources must be relinquished. During a disconnect, the Cisco WAN switching network sweeps through its connection tables and removes the connection.
ATM switched virtual circuits (SVCs) are ATM connections setup and maintained by a standardized signaling mechanism between ATM CPE (ATM end systems) across a Cisco WAN switching network. ATM SVCs are created on user demand and removed when the call is over, thus freeing up network resources.
Chapter 2 contains more detailed information about ATM SVCs.
The WAN Service Node with the Extended Services Processor capability will function as a point-to-multipoint SVC client when configured with a Cisco Lightstream LS1010 ATM Switch. (This combination of the WAN Service Node and the LS1010 thus supports LAN emulation [LANE]). For more information, see the section Point-to-Multipoint SVCs in Chapter 9.
Chapter 3 contains more detailed information about Frame Relay SVCs.
Because the BPX 8620 is an ATM switch, Frame Relay SVCs that are setup and established across the Cisco WAN switching network must be translated into an ATM format to be carried across the network. At the far end, where typically the connection is terminated on another Frame Relay CPE, the ATM cells have to be converted back to Frame Relay format. This is referred to as Network Interworking. Network Interworking can be performed between Frame Relay CPE and ATM CPE when the ATM CPE recognizes that it is connected to an interworking function (Frame Relay, in this case). The ATM CPE must then exercise the appropriate service specific convergence sublayer (SSCS). The SSCS will then convert the ATM cells to Frame Relay traffic.
In this release of the WAN Service Node, all Frame Relay SVC connections must be between Frame Relay CPE (Frame Relay end users) or ATM CPE that is aware that it is performing Network Interworking, and all ATM SVC connections must be between ATM CPE (ATM end users). In other words, Service Interworking between ATM and Frame Relay SVCs is not supported in this release. (ATM and Frame Relay Service Interworking for PVCs is supported by the WAN Service Node as part of Release 8.4, and Release 9.0.)
As described earlier, the Cisco WAN Service Node is composed of an integrated BPX 8620, MGX 8220, and ESP.
The Cisco BPX switch is described in detail in the Cisco BPX 8620 Installation Manual and the BPX 8620 Reference.
The WAN Service Node supports SVCs on the BPX cards listed in Table 1-1. (Note that the only the front cards are listed here and they must be mated with the appropriate backcard.)
| Model Number | Interface |
|---|---|
| BXM-155-8 | OC3/STM-1 |
| BXM-155-4 | OC3/STM-1 |
| BXM-T3-8 | T3 |
| BXM-E3-8 | E3 |
| BXM-T3-12 | T3 |
| BXM-E3-12 | E3 |
| BXM-T3-4 | T3 |
| BXM-E3-4 | T3 |
| BXM-T3-12E | T3 |
| BXM-E3-12E | E3 |
| BXM-155-8E | OC3/STM-1 |
| BXM-155-4E | OC3/STM-1 |
| BXM-622-2E | OC12/STM-4 |
| BXM-622E | OC12/STM-4 |
The WAN Service Node supports SVCs on the MGX 8220 cards listed in Table 1-2. (Note that the only the front cards are listed here and they must be mated with the appropriate backcard.) MGX 8220 cards do not support SPVC connections.
| Model Number | Interface |
|---|---|
| AX-BNM-155 | OC3/STM-1 |
| AS-BNM-DS3 | T3 |
| AX-FRSM-4T1 | T1 |
| AX-FRSM-4E1 | E1 |
| AS-AUSM-8E1 | E1 |
| AX-AUSM-8T1 | T1 |
The Extended Services Processor (ESP) is an adjunct processor shelf integrated into the WAN Service Node.
The basic ESP features include:
Available in either AC- or DC-powered models (ESP-AC or ESP-DC), the ESP is an orderable option for the BPX switch. The ESP can be configured in both non-redundant and redundant configurations. For the redundant configuration, two ESPs are installed in the WAN Service Node.
The ESP uses three main physical interfaces, as shown in Figure 1-8:
The ESP also provides the following application interfaces:
The ESP software includes the following components:
The WAN Service Node is typically configured through three Configuration Interfaces:
A single ESP controlling a WAN Service Node, such as is shown in Figure 1-8, operates in the StandAlone mode. In the StandAlone mode there is no redundancy for a failed ESP. During the initial installation of a ESP, it can be configured as either Primary or Secondary but must be configured to operate in StandAlone mode.
When a second ESP is added to a single ESP operating in StandAlone mode, you must change the operating mode of a StandAlone ESP to Active or Standby mode. Initial configuration procedures for StandAlone ESPs are covered in Chapter 7 in the section, Installing a Redundant ESP with an Existing StandAlone Unit.
As shown in Figure 1-9, ESPs can be installed in redundant pairs in the WAN Service Node. In a redundant pair, one ESP is active, that is it controls the switched services in the WAN Service Node, and the other ESP is standby. The redundant ESPs are known as peers. The ESPs will switch roles from active to standby and vice versa under the following conditions:
Each ESP determines its role by means of Role Resolution protocol, which exchanges messages between the two units at startup. Both the active ESP and the standby ESP monitor its role and connectivity, and if appropriate, automatically switchover (that is, switch roles from active to Out of Service and from standby to active) with the peer ESP.
The redundant ESPs need to synchronize their database so that when the active ESP has gone out of service, the standby unit can take over and resume the service. There are two types of update mechanisms for synchronizing ESP databases. These are the bulk and real-time updates. The bulk update is used to synchronize a standby ESP with an active unit whenever it is restarted. The real-time updates are those messages that are exchanged after ESPs are synchronized and while both the active and standby ESPs are communicating.
The WAN Service Node provides another form of ESP redundancy protection through the use of Y-cables. With Y-cables, the ESP ATM NIC can be connected to two BXM cards or two BXM ports, as shown in Figure 1-10. This prevents the failure of a BXM card or port from disabling the ESP.
Figure 1-10 illustrates only a single ESP-to-BXM redundancy option. There are four ESP-to-BXM redundancy options possible:
1 ) A single ESP with a Y-cable to redundant BXMs.
2 ) Two ESPs (a redundant pair), each attached to a single port on a single BXM.
3 ) Two ESPs (a redundant pair), each attached to a single port on two separate (redundant) BXMs.
4 ) Two ESPs (a redundant pair), each attached to different ports with Y-cables on two separate (redundant) BXMs.
Y-cables are for connecting the ESP's ATM Network Interface Card to redundant BXMs. They do not necessarily indicate that the ESP is connected in the redundant pair configuration (that is, an active and standby ESP). The section Fiber Optic Cable Assemblies in Appendix B contains further information about ESP Y cables.
As shown in Figure 1-10, the WAN Service Node could have an Ethernet LAN connection to a StrataView Plus Workstation. StrataView Plus discovers and monitors the ESP similarly to the way it does an MGX 8220 interface shelf. StrataView Plus discovers the existence of the ESP when it is added to the BPX switch with the addshelf command. After discovery, the ESP will be displayed on the StrataView Plus topology map as a shelf attached to the BPX switch.
StrataView Plus manages the WAN Service Node by providing:
In addition, StrataView Plus processes and logs the following traps reported by the ESP:
Active and Standby ESPs are viewed as separate entities. Alarms are supported by the Cisco Robust Trap Mechanism (RTM) using the SNMP Agent and the RTM MIB. StrataView Plus uses the RTM's keep-alive protocol to decide whether the ESP is reachable. Unreachable status will be propagated to both the StrataView Plus map and database. All ESP traps will be logged into the StrataView Plus event log and also forwarded to any manager registered to receive traps from StrataView Plus. Up to 8 Trap managers can be supported.
Before the WAN Service Node network can provide ATM or Frame Relay SVCs in response to a call from the CPE, the individual ESP Server Shelves must be both configured and provisioned. Although the distinction is not necessarily sharp, in this manual, configuration will refer to setting up the WAN Service Node for operation, such as configuring the line between the ESP ATM NIC and the BPX switch BXM card, and provisioning refers to allocating resources for end-user PVC or SVC connections. Provisioning is done primarily, but not exclusively, with the ESP Configuration Interface.
ESP configuration and provisioning includes:
Most of the WAN Service Node provisioning is done with the ESP Configuration Interface, which is described in detail in Chapter 7. Chapter 8 contains provisioning procedures.
ATM PVCs which terminate on BPX switch BXM cards on both ends of the connection can be migrated to SPVCs to take advantage of PNNI's routing flexibility. The migration process will convert the PVC into an SPVC with the same endpoint VPI, VCI.
This PVC migration is performed with a Migration Utility, which runs on a StrataView Plus workstation, and is described in Appendix I, PVC Migration Tool.
During provisioning, resources on all UNI ports (both ATM and Frame Relay) are partitioned between SVCs and PVCs. Partitioning is performed with the BPX switch and MGX 8220 command line interfaces. Partitioning information is retrieved from the BPX switch by reading the port and trunk tables in the BPX switch MIB and from MGX 8220 by reading the resource partitioning tables in the AUSM and FRSM MIBs.
The BPX switch line and routing or feeder trunk resources to be partitioned are:
MGX 8220 Feeder Trunk (BXM) resources partitioned are:
MGX 8220 AUSM port resources partitioned are:
MGX 8220 FRSM port resources partitioned are:
SVCs are excluded from any PVC management operations such as OAM, ATM-LMI (Annex G), Frame Relay LMI and ILMI. SVC status is not reported by any of these protocols and an SVC failure does not generate any OAM AIS flows.
Procedures for resource partitioning are provided in Chapter 9.
When a PVC is migrated to an SPVC, its endpoint identifier (that is, its VPI, VCI) must be maintained. (If this is not done the CPE must be reprovisioned with the new VPI, VCI values.) An existing PVC does not reside in the SVC portion of the resource partition, however. SPVCs do reside in the SVC portion of the resource partition.With static resource partitioning, all the connections on that card or port would have to be removed before the resource partition could be moved to include the PVC's endpoint identifier. Dynamic resource partitioning allows you to shift the resource partition without deleting existing connections. Dynamic resource partitioning is supported only on BXM cards.
There is a description of dynamic resource partitioning in Chapter 5 in the section Dynamic Resource Partitioning.
The WAN Service Node collects and stores usage information on a per-call basis. This point-to-point billing information can be used by customers, such as the service provider with a network of WAN Service Nodes, as the basis for billing its end customers.
Currently, the WAN Service Node stores the billing records in a binary file. This binary file can be converted to a flat file (ASCII format) with the tool described in Appendix C in the section Billing Tools.
The WAN Service Node collects the following billing data:
Note that only BXM, AUSM, and FRSM SVC connections keep cell and frame counts. (The ASI and BNI cards do not keep cell counts and are not supported in ESP Release 2.2 for SVC and SPVC connections.)
Billing and Call Detail Records are described in detail in Appendix C.
Cisco recommends that a modem be attached to the ESP to provide remote access for our Product Support and Technical Assistance Center (TAC). With an attached dial-in modem, Product Support can log in remotely and resolve potential problems.
Modem or telnet access are required during field trials of the WAN Service Node. There will have to be a modem attached (or telnet access provided) to every ESP in your network.
You can order the following modem through Cisco:
Modem Part Number: IPX-5941B
Description: IPX ISC V.34RQ Modem 28.8, Sync, Async, with Security
Appendix G provides additional information about connecting a modem to the ESP.
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