Capacity Management in Multimedia Networks. Presented at SCTE Emerging Technologies 2005

Transcription

1 Capacity Management in Multimedia Networks Ben Ben Bekele Bekele Jason Jason Schnitzer Schnitzer Senior DOCSIS Engineer Chief OSS Architect Principal Cox Cox Communications YAS Broadband Applied Ventures Broadband Lake Lake Hearn Drive 1877 Broadway 1909 Broadway Atlanta, GA Boulder, Colorado Atlanta, GA Boulder, CO p: p: p: f: p: f: f: f: Presented at SCTE Emerging Technologies 2005 Updated November 5, 2004 Abstract PacketCable Multimedia (PCMM) technology introduces a new way for Cable to offer premium quality on-demand data service. Central to this service offering, the PCMM specification provides a system for the dynamic allocation of bandwidth and quality of service in the local access network. However, the PCMM standard does not consider the capacity management requirements necessary for these new services to function and scale in large operational networks. In order for Cox Communications and other MSOs to deliver this rich multimedia promise, a system must be in place working in concert with PCMM to provide control over capacity driven by business goals, operational policy, and network resource availability. Towards this end, the CAPacity MANagement (CAPMAN) program has been created in order to provide a structured approach to management of access network resources in a world of PCMM-based Voice, Video, and Data. This paper provides an overview of the CAPMAN approach to Capacity Management in emerging Cable Multimedia networks by proposing preliminary requirements and architecture compatible with the PCMM specification. While providing a brief overview of PCMM, it explores the CAPMAN methodology for the modeling and prediction of capacity requirements for new services. In addition, the paper presents a simple control system for capacity management policy based on multimedia service priority and available network resources. 11/19/2004 Page 1/10

2 PacketCable Multimedia - Business Drivers and Technology Why do MSOs need PCMM? SCTE Emerging Technologies 2005 The last few years have seen the rise in high-speed data service in MSO networks and with that an increased demand for high-bandwidth and advanced services. That demand has led to the recent deployment of PacketCable for Voice over IP (VoIP) service and operators seek new ways to provide new, reliable, high-bandwidth, low latency, On Demand -type services that will provide additional revenue using the existing access network. The key service platform for enabling Cable operators to realize this new revenue is PCMM. What are the services that can be deployed with PCMM? PCMM will allow MSOs to build an IP services platform that utilizes the current HFC and DOCSIS 1.1 infrastructure. Though the possibilities are limited only by the rate of innovation in the Internet creative community, these new service opportunities include: - Turbo Speed - On-Demand speed boost for a designated amount of time - Low Latency Gaming - Premium value video conferencing - SIP based VOIP - Video Streaming on Demand - Speed Preview to up-sell current service PCMM Technology PCMM uses the Dynamic Quality of Service (DQoS) technology introduced by PacketCable 1.0 for the deployment of VoIP [8]. From a system perspective, DQoS enables dynamic requests for bandwidth in the DOCSIS network by a client device whenever a client initiates a service. CMTS resources can be requested on the fly requiring that operators are aware of existing capacity and make decisions to allow the service to be granted by assessing current capacity. Since PCMM is protocol-agnostic in terms of the interaction between the Client Device and Application Manager (AM), the implementation of such a PCMM architecture allows cable operators to provide new On Demand services by simply adding another signaling module within the AM to support the new service. This allows the Client Device and AM to support a variety of application and signaling protocols (e.g., HTTP, SIP, H.323, DCS, NCS, etc.) and allow QoS resources to be requested via the policy server in a scalable, extensible and efficient manner. Currently, the CMTS accepts the request for resources from the policy server based on simplified admission control mechanisms. The CMTS acts as the Policy Enforcement Point (PEP) and the Policy Server acts as the Policy Decision Point (PDP). The CMTS can request (PULL) policy decisions from a Policy Server (PS) and decide to grant or reject a QoS request based on policy set at the PS. Conversely, the PS can signal (PUSH) 11/19/2004 Page 2/10

3 the policy to the CMTS. In this case, policy decision are made ahead of the QoS request based on a policy request from an Application Manager, which gets the request from a client device via any of the many possible signaling mechanisms. But setting static limits on CMTS resources based on pre-determined policies restricts the ability of Cable operators to deliver a robust multimedia service without negatively impacting existing best effort and Committed Information Rate (CIR) services. The dynamic nature of the Multimedia Service requires real-time knowledge of network resources and the ability to adapt dynamically the condition of the network. Business Drivers for PCMM CAPMAN Because these additional services will have to co-exist with the current Best Effort Data services and PacketCable VoIP services that operators are providing, a capacity management system that predicts multimedia capacity and manages the usage of network resources between the various competing services has to be implemented. This paper proposes a Dynamic CAPacity MANagement system (D-CAPMAN) in concert with the deployment of PCMM as it is added to the existing network DOCSIS infrastructure. This system will prevent overbuilding network capacity to accommodate new Multimedia services using a Dynamic Network Management System based on Dynamic Channel Change (DCC) and real time network capacity feedback. The key drivers for installing D-CAPMAN for Multimedia are: I. Optimization allows operators to launch PCMM without adding more capacity to their existing network, but instead allows them to use their network resources optimally. II. III. Service Assurance enables a PCMM client to always get the requested QoS by dynamically re-allocating bandwidth using schemes such as DCC or temporarily adapting network configuration to insure the optimal operation of the Multimedia service, thus providing continuous revenue generation by reducing churn. Targeted Upgrades for operations to analyze network resource consumption and to forecast the network capacity required based on current and future services provided. Proxied QoS Request Allocation In a single Phase resource reservation PCMM model [1], a client sends a service request to an AM. In turn, the AM sends a QoS request to a PS. The PS validates the QoS request against designated MSO policies and, if accepted, sends a Policy Set to the CMTS. The CMTS performs admission control on the requested QoS, based on the availability of resources at that instant, to satisfy the request, then installs the policy decision and establishes the requested service flow(s) with the requested QoS levels. A two-phase resource reservation model allows for the AM to request that QoS resources be 11/19/2004 Page 3/10

4 authorized and reserved. The CMTS waits until resources are available before committing the QoS resource. This will delay the service offering, which may create the potential for the customer to cancel his PCMM service if there is a long delay in the commit phase. In a proxied QoS request scenario, service flow create, delete and change commands sent to the CMTS are controlled by the application manager since the client device has no direct communication with the CMTS. Proxied QOS Resource Management Architecture Clent Device Service Request Application Manager Policy Request Cable Modem Policy Server Policy Set CMTS Single Phase or Two-Phase Resource Allocator Client QoS Request (Push Policy) Figure 1. Proxied Resource Allocation In this scenario, the client device sends an application-specific Service Request to the Application Manager. The AM sends a Policy Set to the PS after determining the QoS needs of the particular application. The PS validates the Policy Request against the MSO policy and, if valid, sends a Policy Set to the CMTS. The CMTS looks at the available Resource at that instant and performs admission control of the requested QoS by installing a policy authorization. The CMTS makes a decision to authorize the policy based on the QoS resource usage it has tracked. So the CMTS sets a hard policy to grant or deny the policy based on what it knows at that instant. This can be done using a single phase or a two-phase resource reservation model. 11/19/2004 Page 4/10

5 The difference in this scenario is that the client device communicates directly with the CMTS to add, change or delete resource reservations. Once the policy is set at the CMTS, the client can request QoS directly from the CMTS or dynamically modify the QoS as long as it is within the authorized envelope granted by the policy server. This allows for dynamic optimization of the required QoS based on the client device needs. This method is still handicapped by the fact that the CMTS can only make decisions to grant or deny bandwidth based on an instantaneous view of the QoS allocation and cannot make any other decisions to make bandwidth available to the service. Future PCMM Capacity Management Figure 2. Push Policy Resource Allocation As shown in the PCMM specification, the potential resource management issues that can arise from providing a variety of dynamic services has not been addressed. The PacketCable Multimedia Capacity Management platform that is proposed in this paper will address resource management in a dynamically changing network resource allocation scenario and how it will co-exist with the existing best effort data service. This paper will also address the metrics, models and tools that will be used to determine actual network capacity and ways to make additional capacity available to provide the QoS requested by PCMM clients in a timely manner. 11/19/2004 Page 5/10

6 COX DOCSIS ACCESS NETWORK CMTS/CM Elements Figure 3. Future PCMM Capacity Management PacketCable Multimedia - Capacity Management Requirement Why do MSOs need Capacity Management for PCMM? In short, PCMM provides a system and architecture that allows for the creation, customization, and management of new services (or applications) that are programmed dynamically into the CMTS. Though the technology described in the PCMM specification addresses interfaces and architecture [1], this work does not propose to provide an operational model to satisfy the practical concerns of deployment in a large scale cable network. From a cable operator s perspective, the goal of CAPMAN is clear - to satisfy the expectations of their subscribers while optimizing the use of DOCSIS network resources. Though simply stated, this goal has relatively complicated implications from a requirements perspective. The requirements of the CAPMAN system can be broken into three functional areas - I. Capacity Measurement of resource utilization. II. Capacity Modeling of requirements to ensure sufficient future resource availability. III. Capacity Control of admission to the DOCSIS resource domain. 11/19/2004 Page 6/10

7 Capacity Measurement The first requirement towards capacity management of PCMM is to define measurement metrics in the DOCSIS access segment for the observation of network behavior in the context of capacity resource availability. In DOCSIS parlance, this amounts to the collection of CMTS data that furnishes information regarding both the interface level (US, DS, MAC domain) and the service flow level (SFID) from the devices and access segment for which the PCMM traffic will traverse. As stated, PCMM looks to DOCSIS [2] as the underlying system for transport of packets in the access network. The DOCSIS OSS Specification [9] describes a number of Simple Network Management Protocol (SNMP) Management Information Base (MIB) modules and a data model for the collection of these monitoring metrics for the CMTS. The objects definitions for building D-CAPMAN measurement metrics are defined in both the Quality of Service (QoS) MIB [6] and the Radio Frequency (RF) MIB [7]. A second approach as an alternative to SNMP for the collection of CMTS measurements is IP Detail Record (IPDR). IPDR is mechanism for data access offering advantages in terms of scalability, stability, and reliability for the collection of Service Flow information from networks for applications in both usage measurement and capacity management. Capacity Modeling The second key functional requirement within CAPMAN for PCMM provides Cable operators with the ability to estimate the number of services that can be accommodated on a specific segment of the DOCSIS access network. A comprehensive capacity modeling method for multimedia networks is required to quantify the complex relationships between MSO business goals, multimedia offerings, QoS and the DOCSIS network infrastructure. Various approaches to network dimensioning have been proposed for packet-based multiservice environments including both DOCSIS and analogous radio access networks [3], [4]. Inputs: For each segment of the network, the following data is required as input to the capacity model: - CMTS Configuration. Capacity limits. Based on CMTS configuration and performance, the maximum burst rate of the channel (e.g. burst profiles, packet forwarding rates, effective bandwidth). - Capacity Utilization. Both from traffic measurement and from the provisioning system. 11/19/2004 Page 7/10

8 pkt-mm-3 SCTE Emerging Technologies Service Loading and Access Topology. The total load (by service) definition on the network. Subscriber density by specific service based on devices mapped to topology within the network. - Service Traffic Characterization. The behavior of each service type in terms of service flow specification (flowspec) and the associated packet size distribution behavior. - Service Activity Factor. For an access network during a specified time interval, such as the busy hour, the percentage of time that service (flow) activity is present. This provides the worst case for estimation of maximum utilization for a specific service. - Service Growth Rates. For a given market or system, the rate at which each service is expected to grow over a given amount of time. Output: The output of the multimedia capacity model describes the estimated utilization of the network as a percentage of overall upstream, downstream and media access control domain capacity. Application Manager mm-8 mm-7 Record Keeping Server pkt-mm-5 pkt-mm-4 MSO Managed IP Network Client Cable Modem pkt-mm-1 CMTS pkt-mm-2 Policy Server pkt-mm-6 mm-10 mm-9 MSO OSS/BSS MEASURE MODEL CONTROL Capacity Manager Figure 4. PCMM CAPMAN Architecture 11/19/2004 Page 8/10

9 Capacity Control The third and final functional requirement of CAPMAN for PCMM is Capacity Control. PCMM describes the roles of the Policy Server and CMTS as decision and enforcement points within the Resource Control Domain; the Policy Server serves as a Policy Decision Point (PDP) in relation to the CMTS in that the Policy Server implements MSO-defined authorizations and resource management features [1]. The specification goes on to describe the opportunity for the PS to base policy decisions on resource availability, but provides no specific guidance on the provisions for Capacity within this allowance; Policy decisions may be based on Parameters associated with the request or status of available resources. In the PCMM model, the PS is responsible for managing dynamic requests to the CMTS. As part of the signaling model, the PS forwards all requests including the traffic profile describing the QoS attributes (flowspec) of the service used to support the desired IP flow. This traffic profile can be expressed in a number of ways, but will always describe the same parameters of capacity describing data rate and volume. In turn, the CMTS is capable of accepting or denying a request based on a number reasons including congestion. Though this CMTS admission rejection mechanism is useful in times of high utilization, it only has an instantaneous view of network burst load and cannot anticipate future resource requirements or pending dynamic request. A larger window of time is needed for Capacity analysis and control. It is the role of the PS to make these decisions based on a longer term service level view of the network. The PS does so in concert with a CAPMAN control system. As illustrated in Figure 4, the role of the capacity manager within the resource domain is to provide the PS with capacity availability information within a specific segment of the network before admitting a flow request from the AM. Conclusion As Cable operators worldwide deploy PCMM on demand technology and services, a critical element of their success will be the management and optimization of access network resources. The CAPMAN project is under development to address the needs of the industry by working toward a systematic approach to the management of capacity for PCMM, Voice, Video, and Data services. 11/19/2004 Page 9/10

10 References [1] PacketCable Multimedia Specification, PKT-SP-MM-I , April 30, 2004, Cable Television Laboratories, Inc. [2] DOCSIS Radio Frequency Interface Specification, SP-RFIv1.1-I , July 2003, Cable Television Laboratories, Inc. [3] Come the Revolution Network Dimensioning, Service Costing, and Pricing in a Packet Switched Environment, G.Davies, M.Hardt, F.Kelly. [4] UMTS Radio Access Network Dimensioning, H.Ramzie, 1 st Quarter 2001, Alcatel Telecommunications Review. [5] Multimedia Traffic Engineering, The Bursty Model, January 8, 2002, John T. Chapman, Cisco. [6] Data Over Cable System Interface Specification - Quality of Service Management Information Base, Internet Draft, September 2004, M. Patrick, W.Murwin. [7] Radio Frequency (RF) Interface Management Information Base for DOCSIS 2.0 compliant RF interface, Internet Draft, July 2004, D.Raftus, E.Cardona. [8] PacketCable Dynamic Quality-of-Service Specification, PKT-SP-DQOS-I , July 2004, Cable Television Laboratories, Inc. [9] Data-Over-Cable Service Interface Specification, Operations Support System Interface Specification, DOCSIS 2.0. CM-SP-OSSIv2.0-I , July 2004, Cable Television Laboratories, Inc. 11/19/2004 Page 10/10