sign in sign up
<<
Home , Gamer Network, Server (computing)

DOCSIS 1.1 – WHERE GAMING AND QUALITY OF SERVICE (QOS) INTERSECT

Kenneth Gould Time Warner Cable

Abstract [3], where are the opportunities for Multiple Service Operators (MSOs) to provide gaming Broadband on-line gaming is poised to be services that provide added value to their a key usage demand for residential high- customers and subsequently results in new speed data customers. With the recent revenue streams? releases of hugely multiplayer games such as Ultima Online and the availability of network The most obvious possibility is to simply enabled gaming consoles such as the use gaming to attract new high-speed data Microsoft and Playstation 2, there are customers to cable modem service. Every increasing opportunities for MSOs to cater to Xbox console is manufactured with an (and profit from) the demands of the Ethernet port that is the sole interface for broadband gamer. networked-based games. Xbox Live games are typically written for network play with the assumption that the bandwidth available will be less than 64Kbps upstream and VIDEO GAMING IS NOT A GAMBLE downstream. It is relatively easy to provide a DOCSIS configuration file for a cable Given the public launch of broadband- modem that limits its bandwidth enabled gaming consoles in the last year, consumption to 64Kbps. Likewise, the such as the Microsoft Xbox and Sony physical location of the Xbox relative to the Playstation 2 consoles, considerable interest physical location of a cable modem within in cable modem service has been generated the home is not a real problem given the within the gaming community. availability of wireless Ethernet bridges and wireless-equipped cable modems. This By January 7th, 2003, Microsoft opens up our potential pool of customers announced that more than 250,000 beyond households containing PCs. subscribers had signed up for the Xbox Live service that was launched on November 15th, The question is: Can MSOs offer this 2002 – this is twice as much as initial sales product without cannibalizing its existing projections [1]. With 21.5 million Sony high-speed data customer base? One Playstation 2 consoles shipped to North stumbling block is that while it is easy to America as of January 9th, 2003 [2], one can limit a cable modem service to 64Kbps, it is expect that quite a few owners will opt to far more difficult to limit a service to only purchase network adapters allowing for on- support console gaming. While the IANA line game-play over a cable modem. To a list of well-known port numbers describes lesser extent there is still demand for network both TCP and UDP ports 3074 as being the access from GameCube customers “Xbox port”[4], our observations have shown and the customers with the more aged that Xbox Live games use a wide variety of . ports, of which 3074 is merely the most used. This greatly limits an MSO’s ability to create As the console gaming industry is a multi- filters on a cable modem to allow Xbox billion dollar industry within North America traffic yet disable the customer’s ability to attach his PC to a “gaming cable modem” to maintained by the individual publishers. surf the web or run peer-to-peer applications. Regardless of the model for server Likewise, attempts to filter traffic based upon maintenance, the argument can be made that the MAC address of the console are fruitless co-locating the gaming servers within an given the end-user’s ability to change the MSO’s network can be a win-win situation Xbox’s MAC address at will. Similar for the publishers and the MSO. The MSO’s behavior is seen from Sony Playstation 2s. customers experience even lower network On a practical operations note, typically latency which should make the customer and ISPs like to sign up customers with the the publishers happy and the MSO benefits minimum of paperwork. Customers are by keeping more gaming traffic on their usually instructed to accept the ISP’s “Terms network and off of the backbone. and Conditions” electronically on a web page. This proves to be challenging for a Quality of Service Opportunities new gaming-only customer to complete using What value-add could an MSO possibly only a gaming console. bring to a gaming experience for which a

gamer might actually pay? After all, console It is worth pursuing the concept of gaming over a cable modem works well attracting new customers from households today. One differentiator for MSOs is the which either only contains gaming consoles ability to offer quality of service (QoS) or which contain both consoles and PCs but guarantees. While console gaming works have not yet opted for cable modem service, well today in a purely best effort data at a service tier whose bandwidth is less than environment, MSOs will soon be offering the typical residential high-speed data tier. many new services which will constrain how The MSO’s market trials are still in their much bandwidth is available for best effort infancy, and there is not yet enough statistical services. A perfect example is the offering of data to determine whether offering lower- Voice-over-IP (VoIP) in a DOCSIS 1.1- priced gaming tiers will cannibalize higher- enabled network. Assuming that the VoIP priced PC-centric tiers, but anecdotal traffic is being transmitted using the DOCSIS observations have so far indicated that Unsolicited Grant Service (UGS) traffic downgrading very seldom occurs. flows on the same upstream and downstream

channels as the traditional Best Effort Co-Location Opportunities services, then for each phone call being made Game publication is a multi-billion dollar through a CMTS, there is obviously less revenue generator for large game publishers bandwidth available for gaming. such as [5], and as a result, these publishers spend a great deal of time In a bandwidth constrained environment, and money to ensure that the servers on would gamers pay to possess a guaranteed which the games are hosted are highly amount of bandwidth and guaranteed latency available, scalable to the number of dedicated to console traffic? Probably. One customers playing, and well located within can argue that as new services are rolled out, the network to provide low-latency MSOs will also be rolling out more efficient gameplay. The Xbox gaming servers seem to equipment (higher modulation profiles, provide a consistent “feel” to the gameplay as DOCSIS 2.0, etc) that will offset any the servers for each title are managed by bandwidth constraints created by new Microsoft. The game servers for PS2 games services. The counter-argument is that this is are not maintained by Sony, but are unlikely given customers’ penchant for consuming all bandwidth available to them, a combination of DOCSIS 1.1 and DiffServ and even were it true, gamers may still be or MPLS. willing to pay a small fee just to achieve Dynamic QoS is typically used today in guaranteed low latency for their consoles. PacketCable-based voice over IP (VoIP) Gamers are constantly looking for an edge deployments. In this case bandwidth is over their on-line opponents and are reserved for voice calls “on the fly” between convinced that low latency gives them that the cable modem and the CMTS only when a edge. message is generated that indicates that a customer’s phone has gone off-hook. An QoS – Background extension to the voice-centric PacketCable specifications is a promising possibility for The DOCSIS 1.1 specifications created a future gaming services. The primary foundation upon which products with quality functions defined by the PacketCable VoIP of service requirements such as latency and specifications are QoS authorization and bandwidth can be built. There are essentially admission control, generation and capture of two mechanisms for defining quality of billing information, and security. These are service, “provisioned QoS” (pQoS) or all functions desirable in a QoS-aware “dynamic QoS” (dQoS). The parameters gaming environment. CableLabs has been dictating the pQoS settings are pre-defined in working on an extension of these the DOCSIS configuration file that the cable specifications, known as PacketCable modem receives at the time that it boots. The Multimedia [6], which expands the DOCSIS configuration file would typically residential voice-centric specifications to be a define a classifier that determines which general purpose platform for delivering many packets are affected by the defined quality of IP-based multimedia services that depend service rules. The packets that meet the upon QoS. Note that while the PacketCable classifier’s parameters make up a Multimedia framework is based upon the unidirectional stream of packets known as a VoIP PacketCable specifications, the “service flow”. For example, since the implementation of a VoIP PacketCable majority of Xbox gaming traffic is service is not a pre-requisite for PacketCable transmitted to and from port 3047, a classifier Multimedia-based gaming as gaming has no can be defined which places all UDP or TCP requirements for voice specific items such as packets transmitted to, or received on, port wiretapping, PSTN interconnects, etc. 3047 onto a particular service flow. That service flow has QoS parameters associated PacketCable Multimedia Architecture for with it, such as a scheduling type (e.g. real time polling vs. best effort) and latency Gaming requirements (e.g. sub 150ms). All other The easiest way to describe the traffic could default to a standard best effort PacketCable Multimedia Architecture is to service flow which would have a lower provide a diagram of the architecture and transmission scheduler priority. discuss the functionality and interaction of each of the components as it related to Obviously, the DOCSIS 1.1 specifications providing QoS for gaming applications. only handle reserving and allocating bandwidth within the DOCSIS domain, specifically between cable modems (CMs) and the cable modem termination server (CMTS). End to end QoS can be setup with Record Keeping Server CMTS

CMTS Policy Server

Cable Modem CMTS Policy Server

Gaming Console

Gaming Server

Figure 1 - PacketCable Multimedia CMTS Architecture for Gaming Figure 2 – A single policy server can serve Our assumption is that the gaming console multiple CMTSs. has no concept of its QoS requirements nor of the PacketCable signaling like that available to a VoIP MTA (multimedia Once instructed by the Policy Server of terminal ) to its desire for QoS the gaming console’s QoS requirements, the reservations. Instead, a gaming console CMTS creates service flows for an individual simply communicates with the gaming server cable modem’s gaming traffic with the as it does today. (e.g. Xbox’s MechAssault appropriate QoS characteristics. As an game causes the Xbox to communicate with option, the PacketCable Multimedia Xbox Live servers to set up a gaming session architecture also takes into account the desire between players). to track the actual usage of the QoS-based service flows for billing purposes. These The CMTS is the gatekeeper (referred to billing records are gathered and maintained as a Policy Enforcement Point or PEP) which on the Record Keeping Server. determines whether the resources are available to reserve bandwidth between the The gaming server and the policy server cable modem and itself. Thus, the gaming are expected to reside within the MSO server must communicate the console’s network and are considered trusted devices. bandwidth needs to the CMTS. It does so The gaming server must also take on the through an intermediary known as the Policy responsibility of authenticating the gaming Server. As there could be many different console and assuring that the consoles are applications all of which are contending for authorized to request gaming services. limited bandwidth resources, the Policy Server determines the relative priority of each request (based upon business rules) to determine which requests for QoS should actually be given to the CMTS. The Policy Server is also referred to as the Policy Decision Point (or “PDP”).

Messaging Protocols You will notice that there are a few things missing which simply fall outside of the Record Keeping Server PacketCable Multimedia domain, namely RADIUS RADIUS end-to-end network QoS setup including Policy Server to Policy Server DOCSIS COPS+ DSx communications. One can imagine that CMTS Policy Server Cable gamers desire low network latency on each Modem network segment over which their gaming Gaming Console COPS+ traffic travels. This can conceptually be Unspecified handled by DiffServ or MPLS – most MSOs Protocol Gaming Server would argue that their network backbones are over-engineered and that the DOCSIS

component is where the bandwidth is the Figure 3 – Messaging Protocols most valuable resource.

Obviously, there is also a messaging flow Most relevant gaming servers have the between the CMTS, Policy Server, Gaming ability to match gamers based upon their Server, and gaming console which indicates historical levels of quality of play (that is to the success or failure of the QoS say, based upon how good the player is at provisioning. The messaging between the performing the game), and also based upon gaming console and the gaming server is the latency of the gamer’s network outside of the PacketCable specifications. connections. Obviously, one goal of the The messaging from the gaming server to the PacketCable Multimedia framework can be Policy Server and from the Policy Server to to lower the latency of an individual gamer’s the CMTS is IETF’s COPS based. Any network connection to the CMTS. The game event messaging sent from the Policy Server servers would need to report the gamer’s or CMTS to the optional Record Keeping potential latency when matching up gamers Server is RADIUS based, and the rather than their pre-service-flow-setup CMTS/cable modem exchanges to establish latency. This could require some additional QoS-based service flows is based on communication between the gaming server DOCSIS DSx messaging. and the policy server and potentially inter- policy server or inter-gaming server This has been a greatly simplified communications. explanation of QoS allocation. Upstream and downstream service flows are handled by the The gaming consoles described above are CMTS in different manners. Upstream referred to in the PacketCable Multimedia transmissions are made on a contentious, Architecture Framework as “legacy” clients shared-access medium, where downstream as these consoles are unaware of the QoS traffic is handled by the CMTS as if it were a capabilities and signaling necessary for the traditional IP router. The specifics of the QoS negotiations within the framework. QoS parameters that are associated with upstream and downstream service flows A second type of can have some (these parameters are different) and the PacketCable awareness built-in – when a service flow scheduling types can be found in network-based game is started, the client can the VoIP-centric PacketCable 1.0 request QoS. The console can now signal to specifications. [7] the CMTS to add, change or delete bandwidth reservations, but the CMTS will implement a PacketCable Multimedia only accept the reservations if the gaming Architecture that would enable QoS server and policy server have authorized the guarantees for gaming consoles without console’s reservation. This is very similar to modification to those console or console the behavior of a VoIP MTA. This concept games. This architecture would require of building PacketCable awareness into a enhancements to the gaming servers to make console or console game will probably not the server applications capable of interacting receive much enthusiasm for implementation with the Policy Servers. by the game developers unless there is a We have seen that there are a lot of considerable client base that could make use customers playing games on our broadband of it. For that reason, we anticipate that networks, research shows that they are support for legacy clients must be well willing to spend vast quantities of money to implemented first. do so, and they have voted with their wallets to use today’s low-latency, high speed The third type of client is one which is connections - it is up to the MSOs to cement totally PacketCable aware and does not the relationship by providing a service which depend upon a gaming server to setup its is unobtainable from other providers. QoS. Instead the console is capable of transmitting its own bandwidth QoS requests References to the CMTS along with authorization [1]http://news.com.com/2110-1040- credentials. The CMTS passes the request 979556.html - “Xbox Live sign-ups beat onto the Policy Server which authenticates forecasts”, cnet.com and authorizes the consoles request. The [2]http://news.com.com/2100-1040- request message is then sent back to the 980966.html - “PlayStation 2 shipments top CMTS which will then setup the appropriate 50 million”, cnet.com service flows for that console. [3]http://www.idsa.com/IDSABooklet.pdf -

“Essential Facts about the and The details of the PacketCable ”, Interactive Digital Multimedia signaling message structures, Association (idsa.com) service flow scheduling types, service flow [4]http://www.iana.org/assignments/port- management, etc are outside of the scope of numbers - “Port Numbers”, Assigned this document, but should be publicly Numbers Authority (IANA.org) available in the CableLab’s PacketCable [5]http://www.business2.com/articles/mag/0, Multimedia Technical Report and 1640,45482,00.html – “Could This Be the Specifications by the time of the publication Next Disney?”, Business 2.0 (business2.com) of this document. [6]“PacketCable Multimedia Architecture

Framework PKT-TR-MM-ARCH-V01”, Summary Cable Laboratories Console gamers are able to use cable (cablelabs.com) modem connections today with good results. [7]“PacketCable™ Dynamic Quality-of- As MSOs deploy new services that consume Service Specification PKT-SP-DQOS-I05- more of the limited bandwidth available 021127” Cable Television Laboratories between the cable modems and cable modem (cablelabs.com) termination servers, the gamers’ user experience could become less attractive. One method to enhance the user experience is to