This section provides an overview of the 7750 SR services, service model and service entities used in conjunction with Triple Play services only to the relevant service types. Details about services, configurations, and CLI syntax can be found in the 7750 SR OS Services Guide.
Topics in this section include:
With 7750 SR OS, the architectural foundations of Alcatel-Lucent’s TPSDA established in previous releases is reinforced while its applicability is expanded to encompass many new deployment models and support Any Mode of Operation (AMO). Through these enhancements, TPSDA becomes more universally deployable and flexible in addressing the specifics of any provider’s network/rollout.
Figure 1 depicts TPSDA’s centralized, integrated element, service and subscriber management architecture.
All of the 7750 SR OS and Alcatel-Lucent’s 5750 SSC’s subscriber policy enforcement and management capabilities described in this section build upon Alcatel-Lucent’s TPSDA extensive capabilities and provide key capabilities in the following areas:
The TPSDA architecture (Figure 2), is based on two major network elements optimized for their respective roles, the Broadband Service Aggregator (BSA) and the Broadband Service Router (BSR). An important characteristic of BSAs and BSRs is that they effectively form a distributed virtual node with the BSAs performing subscriber-specific functions where the various functions scale, and the BSRs providing the routing intelligence where it is most cost-effective.
The connectivity between BSAs and BSRs is a Layer 2 forwarding model shown in Figure 2 above as a secure VPLS infrastructure. This refers to the fact that the BSA-BSR interconnections form a multipoint Ethernet network with security extensions to prevent unauthorized communication, denial of service, and theft of service. One of the advantages of using VPLS for this application is that VPLS instances can be automatically established over both ‘hub and spoke’ and ring topologies providing sub-50 ms resilience. Regardless of the fiber plant layout, VPLS enables a full mesh to be created between BSA and BSR nodes, ensuring efficient traffic distribution and resilience to node or fiber failure.
In the BSR to BSA downstream direction (Figure 3), IP services rely on IP layer classification of traffic from the network to queue traffic appropriately towards the BSA. Under extreme loading (only expected to occur under network fault conditions), lower priority data services and/or HSI traffic will be compromised in order to protect video and voice traffic. Classification of HSI traffic based on source network address or IEEE 802.1p marking allows the QoS information to be propagated to upstream or downstream nodes by network elements. Refer to
Table 3 for the descriptions.
In the upstream direction (BSA to BSR. Figure 4), traffic levels are substantially lower. Class-based queuing is used on the BSA network interface to ensure that video control traffic is propagated with a minimal and consistent delay, and that preferred data/HSI services receive better treatment for upstream/peering service traffic than the best effort Internet class of service.
Figure 6 displays a Layer 2 PE network (such as the 7450 ESS) aggregating traffic from DSLAMs (Alcatel-Lucent) to BRAS devices. The VPLS service is running in the PEs directly connected to the DSLAMs (VPLS PE1) while the PEs connected to the BRAS devices are running a point-to-point Layer 2 service (Epipe).
A service is a globally unique entity that refers to a type of connectivity service for either Internet or VPN connectivity. Each service is uniquely identified by a service ID within a service area. The 7750 SR service model uses logical service entities to construct a service. In the service model, logical service entities are provide a uniform, service-centric configuration, management, and billing model for service provisioning.
Services can provide Layer 2/bridged service or Layer3/IP routed connectivity between a service access point (SAP) on one 7750 SR router and another service access point (a SAP is where traffic enters and exits the service) on the same (local) or another 7750 SR router (distributed). A distributed service spans more than one router.
Distributed services use service distribution points (SDPs) to direct traffic to another 7750 SR through a service tunnel. SDPs are created on each participating 7750 SR, specifying the origination address (the 7750 SR router participating in the service communication) and the destination address of another SR-Series. SDPs are then bound to a specific customer service. Without the binding process, far-end 7750 SR devices are not able to participate in the service (there is no service without associating an SDP with a service).
The 7750 SR offers the following types of subscriber services which are described in more detail in the referenced chapters:
Common to all 7750 SR connectivity services are policies that are assigned to the service. Policies are defined at a global level and then applied to a service on the router. Policies are used to define 7750 SR service enhancements. The types of policies that are common to all 7750 SR connectivity services are:
The 7750 SR routers provide a comprehensive set of service-related counters. Accounting data can be collected on a per-service, per-forwarding class basis, which enables network operators to accurately measure network usage and bill each customer for each individual service using any of a number of different billing models.
In the 7750 SR service model, the 7750 SR service edge routers are deployed at the provider edge. Services are provisioned on 7750 SRs and transported across an IP and/or IP/MPLS provider core network in encapsulation tunnels created using Generic Router Encapsulation (GRE) or MPLS Label Switched Paths (LSPs).
Each subscriber service type is configured with at least one service access point (SAP). A SAP identifies the customer interface point for a service on an Alcatel-Lucent 7750 SR router (
Figure 9). The SAP configuration requires that slot, MDA, and port/channel information be specified. The slot, MDA, and port/channel parameters must be configured prior to provisioning a service (see the
Cards, MDAs, and Ports section of the 7750 SR OS Interface Configuration Guide).
A SAP is a local entity to the 7750 SR and is uniquely identified by:
Depending on the encapsulation, a physical port or channel can have more than one SAP associated with it. SAPs can only be created on ports or channels designated as “access” in the physical port configuration. SAPs cannot be created on ports designated as core-facing “network” ports as these ports have a different set of features enabled in software.
The encapsulation type is an access property of a service Ethernet port or SONET/SDH or TDM channel. The appropriate encapsulation type for the port or channel depends on the requirements to support multiple services on a single port/channel on the associated SAP and the capabilities of the downstream equipment connected to the port/channel. For example, a port can be tagged with IEEE 802.1Q (referred to as dot1q) encapsulation in which each individual tag can be identified with a service. A SAP is created on a given port or channel by identifying the service with a specific encapsulation ID.
A service distribution point (SDP) acts as a logical way to direct traffic from one 7750 SR to another 7750 SR through a uni-directional (one-way) service tunnel. The SDP terminates at the far-end 7750 SR which directs packets to the correct service egress SAPs on that device. A distributed service consists of a configuration with at least one SAP on a local node, one SAP on a remote node, and an SDP binding the service to the service tunnel.
An SDP from the local device to a far-end 7750 SR requires a return path SDP from the far-end 7750 SR back to the local 7750 SR. Each device must have an SDP defined for every remote router to which it wants to provide service. SDPs must be created first, before a distributed service can be configured.
To configure a distributed service from ALA-A to ALA-B, the SDP ID (4) (Figure 11) must be specified in the service creation process in order to “bind” the service to the tunnel (the SDP). Otherwise, service traffic is not directed to a far-end point and the far-end 7750 SR device(s) cannot participate in the service (there is no service).
The Alcatel-Lucent service model uses encapsulation tunnels through the core to interconnect 7750 SR service edge routers. An SDP is a logical way of referencing the entrance to an encapsulation tunnel.
Each SAP configuration includes a specific port/channel on which service traffic enters the 7750 SR from the customer side (also called the access side). Each port is configured with an encapsulation type. If a port is configured with an IEEE 802.1Q (referred to as dot1q) encapsulation, then a unique encapsulation value (ID) must be specified.
Virtual Private LAN Service (VPLS) as described in Internet Draft draft-ietf-ppvpn-vpls-ldp-01.txt, is a class of virtual private network service that allows the connection of multiple sites in a single bridged domain over a provider-managed IP/MPLS network. The customer sites in a VPLS instance appear to be on the same LAN, regardless of their location. VPLS uses an Ethernet interface on the customer-facing (access) side which simplifies the LAN/WAN boundary and allows for rapid and flexible service provisioning.
VPLS offers a balance between point-to-point Frame Relay service and outsourced routed services (VPRN). VPLS enables each customer to maintain control of their own routing strategies. All customer routers in the VPLS service are part of the same subnet (LAN) which simplifies the IP addressing plan, especially when compared to a mesh constructed from many separate point-to-point connections. The VPLS service management is simplified since the service is not aware of nor participates in the IP addressing and routing.
A VPLS service provides connectivity between two or more SAPs on one (which is considered a local service) or more (which is considered a distributed service) 7750 SR routers. The connection appears to be a bridged domain to the customer sites so protocols, including routing protocols, can traverse the VPLS service.
