Aggregation Loss Bandwidth in the Last Mile Residential Internet

Transcription

1 2014 UKSim-AMSS 16th International Conference on Computer Modelling and Simulation Aggregation Loss Bandwidth in the Last Mile Residential Internet Christopher Windmill School of Science and Technology Nottingham Trent University Nottingham, Nottinghamshire Abstract Aggregation Loss Bandwidth (ALB) within the last mile internet accounts for significant unusable bandwidth under current Internet Service Provider (ISP) centric routing strategies. Using a Hierarchical Network Topographical Routing (HNTR) scheme we show that this ALB can be exposed to the network and applications. A video streaming system is used as a case study to show the potential efficiency and monetary gains that can be made from exploiting this resource with minimal changes to the existing network infrastructure. This paper demonstrates the massive unused potential of the last mile Internet for video streaming services if a distributed management and billing architecture is introduced to the traditional Internet model. Keywords-Routing; Internet; Networking; Video Streaming; Future Internet. I. INTRODUCTION Under most current UK Internet structures all routing is carried out in an Internet Service Provider (ISP) centric manner [1]. All data must flow through an ISP controlled management point and often through multiple such points if the end-user s ISP does not control both the distribution and last-mile networks. Due to the inherent scaling issues with any:any (fully meshed) networks and the high costs associated with network infrastructure most UK ISPs are oversubscribed by a factor of at least 10, and more generally by a factor of approximately 50 [2]. This leads to a tiered implementation with aggregation points (AP) which provide a bandwidth scaling factor between the bandwidth upstream and downstream of the AP [3]. The first of these aggregation points within the UK Internet typically occurs at street cabinet level aggregating approximately 50 users and the second at the BT exchange / handover facility potentially aggregating multiples of these 50:1 feeds. This structure innately introduces large scale bandwidth drops that cannot be utilized in an ISP-centric Internet as data flow into an AP is limited to the aggregated bandwidth value (ABV). This difference the raw bandwidth under the AP and the ABV the aggregation loss bandwidth (ALB) introduces a network resource which can be exploited to deliver high quality on demand content. This work looks at the positioning of video caching and streaming systems [4] [5] above and below the APs [6] to show that this ALB can be utilized to significantly improve streaming volume, or alternatively stream quality [7]. Using the ALB the paper then considers the value of this lost bandwidth against i) the cost of renting similar bandwidth from BT, and ii) the cost this guaranteed bandwidth would cost under a BT Quality of Service (QoS) cost model.. II. MOTIVATION AND CONTEXT The growth of Internet bandwidth within the UK has shown a distinctly exponential growth for the last years, however, this growth has been levelling off [8] [9]. This growth can be divided into three major components: urban, suburban, and rural, with urban growth being the fastest due to fiber deployments with a growing divide between the urban and rural sustained bandwidths as shown in Fig.1. The usage of this bandwidth represents more of a chicken and egg problem as adoption of new technology tends to be slow until it reaches a ubiquitous state whereupon the usage increases dramatically [10]. Video streaming represents one of these technologies with catchup services having a slow uptake which is increasing as services such as Sky OnDemand makes use of on demand streaming to record content in advance of its next broadcast slot. Streaming video is becoming a hidden service as settop boxes [11] become more intelligent in their use of multiple content sources to improve the user experience. Figure 1. UK Internet bandwidth growth since 2009 using OFCOM residential broadband survey data showing exponential growth pattern and levelling off of urban bandwdith towards 40Mbps. Streaming has already been shown to be capable of disrupting the UK Internet with both the 2010 World Cup, and 2012 London Olympics viewers suffering delays and /14 $ IEEE DOI /UKSim

2 quality degradation. UK networks saw spikes of between 18 and 100% in traffic flow for these events with large portions of the populace still using broadcast TV solutions [12] [13]. While multicast and other technologies may offer solutions [14] these represent significant business and management issues and have been discarded previously due to these difficulties. Considering any solution we must further consider the potential requirements and characteristics of future video solutions [15]. In Table 1 the growth pattern of streaming media and stored media is considered with stored media representing higher quality (effectively lossless for H.264 codecs) bandwidth requirements. Typically we will see bits per pixel for streaming quality video and 2-3 bits per pixel for storage quality video [16] thus as video resolutions increase we will see somewhat linear increases in bandwidth requirements until an improved codec arrives. Further to this table we must consider factors such as 3D which under many current set-top box systems is implemented as a double frame concatenating the left and right frames leading to a virtual doubling of bandwidth requirements. This solution represents a sensible workaround for the limited processing capacity of existing boxes yet leads to additional bandwidth usage. III. NETWORK AND SIMULATION STRUCTURE The network structure used to simulate the ALB usage is a simplified model of the last mile / transit network of the UK Internet. Two potential aggregation layers are considered under the IP streaming model between the street level cabinet level and the transit network. For the Hierarchical Network Topographical Routing [1] (HNTR) model as routing is not centralized - the video server is considered to be below the first aggregation layer rather than above. This model, shown in Fig. 2, while not accurate in terms of video server positioning within the network aims to look at the bandwidth usage rather than protocol management or streaming parameters such as delay and jitter and so is a reasonable approximation to show the benefits of ALB usage. TABLE I. VIDEO BANDWIDTH FOR STORED AND STREAMING MEDIA Video Bandwidth (Mbps) Name Resolution Stored Media H.264 Streaming H p 320x p 480x p 729x p 1280x i 1920x p 1920x K Cinema 2048x p 3860x K Cinema 4096x p 7680x K Cinema 8192x Figure 2. Simulation network structure, representing a multi-layer IP network with two aggregation layers and video streaming sources position at these points as ALB simulation does not consider delay and jitter which higher placement will alter. A. Hierarchical Network Topographical Routing The traditional Internet Protocol (IP) based Internet can be considered ISP centric in that data must be routed through a centralized routing point such as an Internet Service Provider (ISP). Under the best case scenario this results in a single point of inflexion in the network, however, with the multi-tiered network within the UK provided by the BT wholesale network this can result in 2-3 points of inflexion in any given routing path. Combining these inflexion points with the APs at multiple levels of the network required to support an any:any network with a full speed last mile results in unusable bandwidth in the lower levels of the network. While many solutions have looked at peer-to-peer video streaming systems [17] and even the use of set-top-boxes [18] in the provision of these services they do not work around the bandwidth loss and limited upload speeds typically available in the UK. HNTR is a hierarchical tree-mesh based exclusive-or based routing network designed direct node to node routing to avoid adding inflexion points to the routing path and therefore to allow the usage ALB as routing can be localized as in a local area network. 462

3 B. Aggregation Loss Bandwidth Aggregation loss bandwidth (ALB) is the natural result of a network which aggregates multiple connections into a single upstream connection which has a fractional bandwidth of the layer below. As the traditional Internet provision model was based around a burst transmission communication style this aggregation allows each end point host to appear to receive the full upstream bandwidth without provisioning the network to support any:any bandwidth. This means that at each level there is effectively an unusable bandwidth as shown in (1). Bandwidth Host * #Hosts - Bandwidth Upstream (1) This bandwidth remains unusable in any system which forces traffic to traverse this aggregation point and under the current routing system all traffic must cross these boundaries in order to be logged / billed and managed / routed. Making use of this bandwidth requires significant changes to the design of the network to support either unmetered usage or a distributed management structure. IV. VIDEO STREAMING USE CASE In order to demonstrate the potential of ALB as a resource we consider unicast streaming from a single source which is capable of saturating the network. Video streams are considered to vary around 4Mbps representing a reasonable quality 720p video, or a low quality 1080p stream. This kind of streaming service represents a similar quality / service level to that provided by services such as Sky On Demand or Cisco s Content Connect [19] platform as examples of potential two / one layer aggregation systems respectively. Nodes request streams until their own bandwidth is saturated with the system as a whole eventually saturating available bandwidth. For the average 2013 bandwidth of approximately 10-15Mbps this represents 2-3 streams to per household to saturate the connection. These 2-3 streams represent a reasonable test load as the average Sky household maintains an average number of active set-top boxes above one and further ties into the increasing multidevice trends amongst younger system users. A. Comparison of Internal / External Bandwidth usages In Fig. 3 we breakdown the results of this testing by testing with both internal traffic which remains below the AP and external traffic which flows through the AP. In Fig. 3a, under the centralized IP structure, the single aggregation point results in there being no difference between internal traffic and external traffic with the overall bandwidth capped at the AP upstream bandwidth limit. In contrast under the HNTR solution in Fig. 3b there is a linear relationship between internal bandwidth usage which approaches and plateaus at the AP downstream bandwidth per host limit. Fig. 3c represents the aggregation of Fig.3a and 3b showing that for larger over subscription ratios virtually all available bandwidth under the first AP is ALB. B. Multi-user Stream Support The results as shown in Fig. 3 show that under the current Internet structure there is significant ALB which can be exploited however doesn t give a good overview of how this bandwidth can be exploited under a real world streaming system with multiple concurrent users per stream (multicast) and number of independent streams. Fig. 4a shows a system attempting to stream unicast streams from above an AP into the last mile. As can be seen the AP enforces unicast under the current network and so falls off symmetrically across number of streams and concurrent users as the system cannot multicast or exploit concurrency. In contrast, the HNTR system in Fig. 4b, being below the AP, can both exploit the ALB as well as concurrency and multicast to enable a user per stream independent curve based purely on the number of discrete streams. a) b) c) Figure 3. Usable system bandwidth (total system bandwidth aggregation loss bandwidth) at first aggregation point (cabinet level / Access Network) showing a) traditional ISP centric routing system, b) HNTR routing system with last mile inflexion, c) combined graph showing potential bandwidth gains at this level. 463

4 a) b) Figure 4. Aggregation loss bandwidth usage for streaming video system positioning the cache a) above or b) below first aggregation layer V..EVALUATING OF COST SAVINGS As the Internet is not just a theoretical test bed but rather a combination of commercial and research networks it is important to place the value of the ALB in a real world context. There are two logical ways to value ALB, either an upper bound as bandwidth which would need to be provisioned to provide a similar service, or as a lower bound as pre-existing bandwidth with QoS requirements to represent the lack of competition. It is likely most fair to value ALB somewhere between these as part of the chicken and egg problem the bandwidth would likely not be provisioned under an existing system, however, if it exists it would add to user satisfaction with the system. Fig. 5 shows the cost of provisioning additional bandwidth at peak to support additional streams. Fig. 5a considers the cost of streaming from a variety of locations in the network which BT prices separates into the access network, metro, and core and the multicast vs unicast streaming costs. Fig. 5b places this in the context of a real world streaming solution providing video on demand streams at a variety of time intervals (delayed start videos) such that groups of users become synchronized by adverts in order to exploit the constant nature of Fig. 4b. As can be seen the cost of adding a single 3Mbps stream approaches nearly 10,000 including all end to end costs and therefore a streaming system pushed below this point could become efficient at a break-even point of around 3 streams per last mile block. Fig. 6 places this in the lower bound context of QoS assured bandwidth which reflects a scenario whereby the bandwidth provided is already available to the system however is normally under competition. As can be seen for the same 3Mbps stream this provides a lower bound towards 2-30 per hour per stream. Given a streaming period of 4 hours per day in a 30 day month this gives a monthly cost per stream of 2-3,000. Fig.7 then places the upper and lower bound on the same graph in order to define an operating region for ALB to provide profitability to the system. VI. CONCLUSIONS This paper has introduced the concept of ALB as an unused resource within the traditional IP based ISP-centric network and has characterized this as a potentially beneficial resource. A simple streaming media model was implemented to test and verify the use of ALB and to demonstrate the large gains in usability and concurrency that exploiting ALB can bring. To place this in a real world context cost models were generated which place the potential breakeven point of a pre-aggregation point streaming system as low as 3 additional concurrent users. VII. FUTURE WORK From the work presented in this paper we aim to further develop the simulation of the video streaming network to further show the benefits of ALB in terms of more traditional network parameters such as delay and jitter. An improved bottom up streaming system using settop boxes will be demonstrated to remove the requirement for an independent streaming system thus reducing the break-even point towards zero as well as making the capability of the streaming system to saturate the network more realistic and viable. 464

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