Information About Topology

Table Of Contents

Information About Topology

The SCE 2000 Platform

Information About Topology Considerations

Functionality

Number of links

Redundancy

Information About Link Continuity

Information About Asymmetric Routing Topology

Information About Physical Topologies

Information About Two Cascaded SCE 2000s For Dual Links

Information About Topology-Related Parameters

Information About Topology

This chapter describes the possible deployment topologies of the SCE 2000 .

The Cisco SCE solution offers a number of basic topology options that permit the user to tailor the SCE Platform to fit the needs of a particular installation. An understanding of the various issues and options is crucial to designing, deploying, and configuring the topology that best meets the requirements of the individual system.

• The SCE 2000 Platform

• Information About Topology Considerations

The SCE 2000 Platform

The SCE 2000 introduces a solution for dual links with load sharing and asymmetrical routing and support for fail-over between two SCE platforms.

The SCE 2000 supports wire speed processing of full-duplex 2-Gigabit Ethernet streams. The SCE 2000 can, therefore, be deployed in a multi-link environment, either in a single or dual SCE platform topology.

•single SCE 2000 topology — Provides increased network capacity and the ability to process both directions of a bi-directional flow, processing both the upstream and downstream paths of a flow, even if they traverse different links

•dual SCE 2000 topology (cascade) — cascaded SCE 2000 s provide high-availability and fail-over solution and maintain the line and service in case of SCE 2000 failure.

Information About Topology Considerations

There are several issues that must be considered in order to arrive at the optimum configuration of the topology-related parameters:

•Functionality — Will the system be used solely to monitor traffic flow, with report functionality only, or will it be used for traffic flow control, with enforcement as well as report functionality?

•Number of links — The SCE 2000 may be connected to one or two GBE links. This is relevant for both Inline and Receive-Only topologies.

•Redundancy — Must the system be designed to guarantee uninterrupted SCE 2000 functionality? If so, there must be a backup SCE 2000 Platform to assume operation in case of failure of the primary device.

•Link continuity — How should the SCE 2000 respond to platform failure with regard to link continuity? Should traffic flow continue even though the unit is not operating, or be halted until the platform is repaired/replaced?

These issues determine three important aspects of system deployment and configuration:

•How many SCE 2000 Platforms are needed and how will they be installed?

•Physical topology of the system — The actual physical placement of the SCE 2000 in the system.

•Topology-related configuration parameters — The correct values for each parameter must be ascertained before configuring the system to make sure that the system will function in the desired manner.

Functionality

The SCE 2000 can serve one of two general functions:

•Monitoring and Control — The SCE 2000 monitors and controls traffic flow. Decisions are enforced by the SCE 2000 depending on the results of the monitoring functions of the SCE 2000 and the configuration of the Service Control Application for Broadband or Mobile solution.

In order to perform control functions, the SCE 2000 must be physically installed as an inline installation and the connection mode must be "inline".

•Monitoring only — The SCE 2000 monitors traffic flow, but cannot control it.

Either an inline installation or an optical splitter installation may be used for monitoring only. In the latter case connection mode must be "receive-only".

Number of links

The SCE 2000 can be deployed in a single GBE link or in two GBE links. The two-link topology may implement load-sharing and the SCE 2000 in this case is able to process both directions of a bi-directional flow even if they split to both links.

Redundancy

When a high degree of reliability is desired, a second SCE 2000 Platform should be installed to provide backup operation capabilities. The combination of two SCE 2000 s guarantees uninterrupted functioning in case of a failure of one of the platforms. The two SCE 2000 s are cascaded, so that, although all processing is performed only in the active SCE 2000 , the standby SCE 2000 is constantly updated with all the necessary information so that it can instantly take over processing the traffic on the data links should the active SCE 2000 fail.

If only preservation of the network links is required, and uninterrupted functionality of the SCE 2000 is not required, a single SCE 2000 is sufficient.

Information About Link Continuity

The bypass mechanism of the SCE 2000 allows traffic to continue to flow, if desired, even if the device itself is not functioning.

Note that when the SCE 2000 is connected to the network through an optical splitter, a failure of the SCE 2000 does not affect the traffic flow, as the traffic continues to flow through the optical splitter.

• Bypass Mechanism

• Maintaining the Network Links vs Maintaining SCE 2000 Platform Functionality

Bypass Mechanism

The SCE 2000 includes a Network Interface Card with a bypass mechanism that is enabled upon SCE 2000 failure. In addition, when connected in-line it can also be enabled in normal operation to simultaneously bypass traffic flow to the other side and direct it internally for analysis. In this case it maintains "receive-only"-like monitoring functions, when control functionality is not required.

The bypass card supports the following four modes:

•Bypass — The bypass mechanism preserves the network link, but traffic is not processed for monitoring or for control.

•Forwarding — This is the normal operational mode, in which the SCE 2000 processes the traffic for monitoring and control purposes.

•Sniffing — The bypass mechanism preserves the network link, while in parallel allowing the SCE 2000 to process the traffic for monitoring only.

•Cutoff — There is no forwarding of traffic, and the physical link is forced down (cutoff functionality at layer 1).

Maintaining the Network Links vs Maintaining SCE 2000 Platform Functionality

When a single SCE 2000 is deployed, the user may decide that in case of a failure, maintaining the network link is more important than providing the SCE 2000 functionality. In this scenario, when the SCE 2000 detects a failure that requires a reboot process for recovering, it immediately switches to Bypass mode, allowing all traffic to bypass the SCE 2000 . The SCE 2000 stays in Bypass mode maintaining the network link, albeit without SCE 2000 processing, until the SCE 2000 fully recovers from the failure and is ready to resume normal functioning.

Alternatively, the user may decide that the SCE 2000 functionality is sufficiently crucial to require severing the link if the SCE 2000 platform fails. In this case, when the SCE 2000 detects a failure that requires a reboot process for recovering, it immediately switches to Cutoff mode, stopping all traffic flow. The SCE 2000 stays in Cutoff mode, halting all traffic, until it fully recovers from the failure and is ready to resume normal functioning. In Cutoff the physical interface is blocked, enabling the network device connected to the SCE 2000 to sense that the link is down.

Information About Asymmetric Routing Topology

• Asymmetric Routing Topology

• Asymmetric Routing and Other Service Control Capabilities

Asymmetric Routing Topology

In some Service Control deployments, asymmetrical routing occurs between potential service control insertion points. Asymmetrical routing can cause a situation in which the two directions of a bi-directional flow pass through different SCE platforms, resulting in each SCE platform seeing only one direction of the flow (either the inbound traffic or the outbound traffic).

This problem is typically solved by connecting the two SCE platforms in cascade mode (or through an MGSCP cluster), thereby making sure that both directions of a flow run through the same SCE platform. However, this is sometimes not feasible, due to the fact that the SCE platforms sharing the split flow are geographically remote (especially common upon peering insertion). In this type of scenario, the asymmetric routing solution enables the SCE platform to handle such traffic, allowing SCA BB to classify traffic based on a single direction and to apply basic reporting and global control features to uni-directional traffic.

Asymmetric Routing and Other Service Control Capabilities

Asymmetric routing can be combined with most other Service Control capabilities, however there are some exceptions.

Service Control capabilities that cannot be used in an asymmetric routing topology include the following:

•Subscriber redirect

•Subscriber notification

•Any kind of subscriber integration, including MPLS VPN. (Use subscriber-less mode or anonymous subscriber mode instead)

•Classical open flow mode , including the following:

–Flow-open-mode classical explicitly enabled (ROOT level configuration)

–VAS traffic forwarding mode enabled

–Analysis layer transport mode enabled (ROOT level configuration)

–`no TCP bypass-establishment' mode enabled (ROOT level configuration)

–A traffic rule is configured for certain flows to use the classical open flow mode (ROOT level configuration)

Information About Physical Topologies

Following are descriptions of a number of physical topologies that the SCE 2000 supports.

• Information About Inline SCE 2000 Topologies

• Single Link: Receive-only Topology

• Dual Link: Receive-Only Topology

Information About Inline SCE 2000 Topologies

A single SCE 2000 supports both single GBE link and dual GBE link topologies.

• Single Link: Inline Topology

• Dual link: Inline Installation

Single Link: Inline Topology

Typically, the SCE 2000 is connected in a full duplex GBE link between two devices (Router, BRAS, etc.). When the SCE 2000 is installed as an inline installation, it physically resides on the data link between the subscribers and the network.

Figure 3-1 Single SCE Platform Single Link: In-line Topology

When configuring the SCE 2000 , an inline installation is referred to as "inline" connection mode.

Dual link: Inline Installation

In this topology, one SCE 2000 is connected inline in two full duplex, GBE links.

In case the two links are load-shared, asymmetrical routing might occur, and some of the flows may be split, i.e. the upstream packets of the flow go on one link, and the downstream packets go on the other link.

When installed in this topology, the SCE 2000 completely overcomes this phenomenon, and provides its normal functionality as if asymmetrical routing were not occurring in the two links.

Figure 3-2 Single SCE Platform Dual Link Inline Topology

This topology supports both monitoring and control functionality, and is referred to as "inline" connection mode.

Single Link: Receive-only Topology

In this topology, an optical splitter resides physically on the GBE link between the subscribers and the network. The traffic passes through the optical splitter, which splits traffic to the SCE 2000 . The SCE 2000, therefore, only receives traffic and does not transmit.

Figure 3-3 Single SCE Platform Single Link: Receive-Only Topology

When configuring the SCE 2000, an optical splitter topology is referred to as "receive-only" connection mode.

Note that in an optical splitter topology, the SCE 2000 only enables traffic monitoring functionality.

Note When implementing receive-only topologies with a switch, the switch must support SPAN functionality that includes separation between ingress and egress traffic and multiple SPAN-ports destinations.

Dual Link: Receive-Only Topology

In this topology, one SCE 2000 is connected in receive-only mode to two full duplex, GBE links using optical splitters. If the two links are load-shared, asymmetrical routing might occur, and some of the flows may be split, i.e. the upstream packets of the flow go on one link, and the downstream packets go on the other link.

When installed in this topology, the SCE 2000 completely overcomes this phenomenon, and provides its normal monitoring functionality as if asymmetrical routing were not occurring in the two links.

This installation supports monitoring functionality only, and is configured as "receive-only" connection mode.

Figure 3-4 SCE Platform Dual Link Receive-Only Topology

Note When implementing receive-only topologies with a switch, the switch must support SPAN functionality that includes separation between ingress and egress traffic and multiple SPAN-ports destinations.

Information About Two Cascaded SCE 2000s For Dual Links

In this topology, two cascaded SCE 2000 s are used. This allows a fail-over solution, where in case of a failure of one SCE 2000 the functionality that the SCE 2000 provides is preserved by the redundant platform.

• Two Cascaded SCE 2000s: Inline Topology

Two Cascaded SCE 2000s: Inline Topology

This topology allows both control and monitoring functionality where redundancy is required and "inline" connection is used. The two SCE 2000 s are cascaded, so the primary SCE 2000 processes the traffic of the two links, while the secondary SCE 2000 only bypasses the traffic of its links to the primary SCE 2000 for processing, and then bypasses the processed traffic back to the link. The two SCE 2000 s also exchange keep-alive messages and subscriber state information.

In case the primary SCE 2000 fails, the two SCE 2000 s switch their roles, and this way fail-over is provided.

Figure 3-5 Two SCE Platforms: Dual Link Inline Topology

This fail-over solution preserves the SCE 2000 functionality and the network link:

•The two SCE 2000 s are simultaneously aware of the subscriber contexts, and subscriber states are constantly exchanged between them, such that if the primary SCE 2000 fails, the secondary can take over with minimum state loss.

•When one SCE 2000 fails (depending on the type of failure) its link traffic is still bypassed to the functioning SCE 2000 and processed there, so the traffic processing continues for both the links.

•The bypass of the traffic through the failed SCE 2000 is configurable, and the user may choose to always cutoff the line that goes through the failed SCE 2000 . In this case network redundancy protocols like HSRP are responsible for identifying the line cutoff and switching all the traffic to go through the functioning SCE 2000 .

Information About Topology-Related Parameters

Refer to the following sections to determine the correct values for all topology-related parameters before beginning run the initial setup of the SCE 2000 .

• SCE 2000 Configuration

• Connection Mode Parameter

• Physically Connected Links Parameter

• Priority

• On-Failure Mode Parameter

SCE 2000 Configuration

There are four topology-related parameters:

•Connection mode — Can be any one of the following, depending on the physical installation of the SCE 2000 (Refer to Connection Mode Parameter ):

–Inline — single SCE 2000 inline

–Receive-only — single SCE 2000 receive-only

–Inline-cascade — two SCE 2000 s inline

–Receive-only-cascade — two SCE 2000 s receive-only

•Physically-connected-links — In cascaded configurations, this parameter defines the number of the link connected to this SCE 2000 (Refer to Physically Connected Links Parameter ).

It is applicable only in a cascade topology.

•Priority — This parameter defines which is the primary SCE 2000 (Refer to Priority ).

It is applicable only in a cascade topology.

•On-failure — This parameter determines whether the system cuts the traffic or bypasses it when the SCE 2000 either has failed or is booting. It is not applicable to receive-only topologies (Refer to On-Failure Mode Parameter ).

Any of these parameters may be configured via either the setupcommand or the connection-modecommand.

Connection Mode Parameter

The connection mode parameter refers directly to the physical topology in which the SCE 2000 is installed. The connection mode depends on two factors:

•Inline/Receive-only :

–Inline — The SCE 2000 resides on the data link between the subscriber side and the network side, thus both receiving and transmitting packets.

–Receive-only — The SCE 2000 does not reside physically on the data link. Data is forwarded to the SCE 2000 via an external switch. The SCE 2000 itself receives only and does not transmit.

•Cascade — Indicates a two SCE 2000 topology where the SCE 2000 are connected via the cascade ports.

The connection mode parameter is determined by the physical deployment of the SCE 2000 , as follows:

•Single SCE 2000 inline installation = " Inline " connection mode.

•Single SCE 2000 optical splitter installation = " Receive-only " connection mode.

•Two SCE 2000 inline installation = " Inline-cascade " connection mode.

•Two SCE 2000 optical splitter installation = " Receive-only-cascade " connection mode.

Physically Connected Links Parameter

If the system consists of more than one device, this parameter defines which link is connected to this SCE 2000 . Currently the system supports a maximum of two links, which are designated link 0 and link 1.

Priority

In a cascade topology, the user must define the priority of each SCE 2000 .

•Primary — The Primary SCE 2000 is active by default

•Secondary — The Secondary SCE 2000 is the default standby.

Note that these defaults apply only when both devices are started together. However, if the primary SCE 2000 fails and then recovers, it will not revert to active status, but remains in standby status, while the secondary device remains active.

On-Failure Mode Parameter

As described in the section The Bypass Mechanism, the bypass card supports four different modes. The following two modes are possible when the SCE 2000 is not operational due to platform failure or boot:

•Bypass — The optical splitter forwards traffic with no intervention of the control application running in the SCE 2000 platform, but monitoring functions continue uninterrupted.

•Cutoff — There is no forwarding of traffic. The link is forced down, resulting in traffic cutoff at Layer1.

The Forwarding mode enables control of traffic flow and is not compatible with the non-operational status.

In a single SCE 2000 topology, the value of this parameter is determined by whether or not the link can be completely cut when the SCE 2000 fails, or whether traffic flow should continue across the link in spite of platform failure.

•Cutoff mode is required for the following:

–Redundant inline topology.

–Non-redundant inline topology if value-added services are crucial and are more important than maintaining connectivity.

•Bypass mode is required for the following:

–Non-redundant inline topology if connectivity is crucial.