DOCSIS IP-video Bypass Architecture (DIBA),
           an Architecture for IPTV over Cable
III. UNDERSTANDING DIBA                            functional, “synchronized” channel. The DOCSIS channels
Figure 5 shows a network such as might exist at an MSO,
showing both the backbone network and...
this point, an HTTP-get command will be sent to the video                       IPTV                                 Inter...
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DOCSIS IP-Video Bypass Architecture (DIBA), an Architecture ...

  1. 1. DOCSIS IP-video Bypass Architecture (DIBA), an Architecture for IPTV over Cable Gerald Joyce, Member, IEEE, Jeffrey Bao, Michael Patrick, Dave Flanagan system with both DOCSIS service and digital video. Both TV Abstract—As with other video service providers, the cable and VoD typically travel through the regional area network via industry is anticipating IP-video and IPTV, and plans to deliver IP packets. In the case of digital video, the IP headers are these over the DOCSIS™ (data over cable service interface removed at the MPEG EdgeQAM (E-QAM) modulator. The specification) protocol that cable modems use. The delivery of IP video services will lead to a tremendous increase in DOCSIS issue for conversion to IP-video and IPTV for cable is that traffic, higher IP bandwidth provisioning, and a lessening of the downstream DOCSIS bandwidth is several times more reliance on traditional, non-IP digital video. Indeed, DOCSIS 3.0 expensive than digital video carrier bandwidth, due to the was developed with multiple downstream channels to the cable complex processing within Cable Modem Termination System modems, in part, for the delivery of IP video services. The (CMTS). Modular CMTS separated the downstream modulators (EdgeQAMs) from the CMTS core to allow scaling of the number of downstream channels, mainly for IP video. However, there is an economic issue in play, namely that digital video bandwidth is TV Integrated still only a fraction of the cost of the IP / DOCSIS bandwidth that DOCSIS Channels CMTS would supplant it. The DOCSIS IP-video Bypass Architecture Local Edge Digital Video Carriers (DIBA) mitigates this problem by exploiting the repetitiveness of Network Router VOD MPEG video packets. IP-video is made to follow the same path as digital Server EQAM video, but still emerge with correct DOCSIS encapsulation. Digital Set-top DOCSIS CM DIBA promises IP-video at cost parity with digital video. TV IP TV Index Terms—IPTV, DOCSIS, DOCSIS bypass, cable, DIBA, Figure 1. A cable system showing the TV and VoD servers, RAN, Edge Router, CMTS, Cable Modem (CM), IPTV, Digital Set-top and TV. I. INTRODUCTION II. MODULAR CMTS FOR IP-VIDEO Cable operators are considering IP-video and IP Television DOCSIS 3.0 was introduced to accommodate IP-video and (IPTV) to supplement their current digital video delivery. IP- IPTV over cable by enabling multiple downstream carriers based video enables new video sources (the Internet) and new between a CMTS and a CM., laying the foundation for scaling video destinations (subscriber IPTV playback devices). the downstream bandwidth independently of the upstream Additionally, IPTV ‘socializes’ TV watching, and provides bandwidth. [4]. The DOCSIS Modular-CMTS (M-CMTS) video mobility between locations and devices. [1] IPTV architecture defined a common Edge-QAM (E-QAM) should also be considered as a delivery option of Video on architecture in which the E-QAMs are separate from the Demand (VoD), currently provided as digital video. If, at any CMTS core. [5] The CMTS core does much of the DOCSIS time, 50% of cable customers are consuming 10 Mbps each of downstream processing, but the final DOCSIS downstream digital video (far exceeding the average bandwidth consumed emerges from the E-QAM. A strategy of using M-CMTS to per subscriber for data services), then 2.5 Gbps could be provide IPTV VoD would call for deploying M-CMTS E- required for every 500 cable customers. This can be provided QAMs for DV-VoD first, and adding M-CMTS core capacity by 66 digital QAM channels in a conventional cable system. as needed to transition the digital video VoD to IPTV-VoD. The extent to which VoD is delivered as IPTV governs the However, the M-CMTS core capacity used for IPTV-VoD extent to which these QAM channels must be converted to IP would quickly exceed the CMTS capacity used for high speed carrying channel conforming to the Data over Cable Service data (HSD). A straightforward implementation of M-CMTS Interface Specification (DOCSIS) [2]. Figure 1. shows a cable for IPTV, therefore, will require many times the cost of M- CMTS core capacity as that currently used for HSD. Manuscript received August 15, 2008. Gerald Joyce (e-mail: This paper proposes a simple, almost obvious, alternative for, and Jeffrey Bao IPTV support with M-CMTS: IPTV should be tunneled ( are with the Motorola Applied Research and directly to the E-QAM, bypassing the M-CMTS core Technology Center, Michael Patrick (, and altogether. This technique is called the DOCSIS IPTV Bypass David Flanagan ( are with Motorola, Home and Network Mobility. Architecture (DIBA). 978-1-4244-2309-5/09/$25.00 ©2009 IEEE
  2. 2. III. UNDERSTANDING DIBA functional, “synchronized” channel. The DOCSIS channels from the DIBA EdgeQAM are the non-synchronized, non-fully A. The ‘Hairpin’ Cost MAC functional DOCSIS channels that are used for IP-video. IPTV is by definition an IP packet with video content from an There are two major features. First, instead of traveling from IP source to an IP destination address. In traditional IPTV, the the edge (or last-hop) router to the CMTS, the packets bypass server sends an IP packet to the destination address of a the CMTS and instead go to the DIBA Encapsulator/Edge- subscriber playback device, which we call generically an “IP QAM. Secondly, the DIBA EdgeQAM is modified to perform Set-Top Box” (IPSTB). With the M-CMTS architecture the necessary DOCSIS framing on the incoming, video bearing forwarding, the IPTV packet is routed through the M-CMTS IP packets. The IP-video exits the DIBA EdgeQAM as ‘un- core, as depicted in Figure 2. In a conventional M-CMTS synchronized’ DOCSIS channels, as mentioned above. The architecture without DIBA, therefore, the IPTV content is cable modem cannot distinguish these channels from forced to make two transits through the local switch that equivalent ‘un-synchronized’ channels from a CMTS or M- connects regional networks with the core CMTS. First, the CMTS DEPI EdgeQAM. The IP-video packets are forwarded video/IP travels to the M-CMTS core, then “hairpins” back from the CM to the IP-set top for decoding. through the local network on a DOCSIS External Physical Interface (DEPI) pseudo-wire to the DEPI E-QAM. If-and- DOCSIS Channels when IPTV becomes a significant fraction of overall IPTV Integrated CMTS Synchronized Downstream bandwidth delivered to a fiber node, this hairpin forwarding of Edge Local IPTV content will require significant expenditures by MSOs Network Router Other DOCSIS Downstreams for M-CMTS core and edge routing bandwidth. VOD DIBA Server Tunnel EQAM DOCSIS 3.0 CM DOCSIS Channels IP TV M-CMTS Figure 3. IP-video Path in the DIBA network. IPTV CORE Synchronized Downstream Edge Local Router Other DOCSIS Downstreams Figure 4 shows the encapsulation scheme for IP-video over Network VOD DEPI DIBA. The video exits the video server as Single Program Server EQAM Transport Stream (SPTS) video (comprised of 188 Byte video DOCSIS 3.0 CM frames) within UDP and IP, and addressed to the IP set-top IP TV box. On the last link to the Edge Router this payload will be within an Ethernet packet delivered to the Edge Router. The Figure 2. IPTV’s “hairpin” routing without DIBA Edge Router will inspect this packet based on IP addresses, UDP port numbers, and IP protocol. Those packets of the designated video flow will be forwarded over a tunnel (such as B. DIBA is Designed for Economy the Generic Routing Encapsulation tunnel) to the DIBA Edge- DIBA accomplishes the goals of the M-CMTS without the QAM, rather than to the CMTS. The Edge-QAM will add the unnecessary expense of the M-CMTS core processing. It also DOCSIS encapsulation of the MAC frame and the underlying works with integrated CMTSs. Operators can deploy MPEG2 Transport Stream format that DOCSIS uses. The independently scalable numbers of downstream channels cable modem will strip off the DOCSIS encapsulation and without changing the MAC domain or the number of upstream forward the IP-video to the IP set-top box. DOCSIS channels. These downstream channels are available for VoD/IP and switched-digital-video/IP. They can also lower the cost to deliver video over DOCSIS service to be competitive with today’s MPEG VoD. Video Edge Edge- IP Server Router QAM CM STB A DOCSIS 3.0 cable modem can receive multiple Home IP Metro Local DOCSIS downstream DOCSIS channels, but only one needs to be fully Network Network Network functional at the MAC layer. This primary or synchronized MPEG-2 (SPTS) MPEG-2 (SPTS) MPEG-2 (SPTS) MPEG-2 (SPTS) channel will convey the DOCSIS timestamps to the CMs; UDP (IP-STB) UDP (IP-STB) UDP (IP-STB) UDP (IP-STB) manage ranging to provide the proper time-base to the cable IP (IP-STB) IP (IP-STB) IP (IP-STB) IP (IP-STB) Ethernet Ethernet (IP-STB) modem; instruct the cable modems when to transmit upstream; (router) GRE tunnel Ethernet (IP-STB) IP (Edge-QAM) DOCSIS MAC deliver other MAC layer messages for cable modem MPEG2-TS registration, maintenance, etc. Ethernet (EdgeQAM) Figure 4 Encapsulation scheme for IP-video over DIBA. C. Video Encapsulation by DIBA Edge-QAMs Figure 3 shows an integrated CMTS deployed with DIBA. Here the DOCSIS channel from the Integrated CMTS is fully
  3. 3. IV. DIBA DEVELOPMENT NETWORK Figure 5 shows a network such as might exist at an MSO, showing both the backbone network and the DOCSIS network, VOD IPTV IMS-Core including CPE. Included is an IMS core (Interrogating, Proxy, Internet Server Server (I,P,S-CSCF) Serving - Call Session Control Functions), so as to enable IPTV session mobility, handoff, etc. On the access network side of the edge router are shown the standard components: PCMM & Policy Server [7, 8], the CMTS, Edge Resource Manager. Also shown is a DIBA application manager. The DOCSIS subnet on the CPE side of the CMTS is also shown. Since digital video is distributed via IP to the EdgeQAM, these PCMM Edge are also shown. Shown in red is the path for DIBA based IP- Edge- Policy Resource HDTV video. Again, the edge router forwards the video IP packets to Router Server Manager the DIBA EdgeQAM, bypassing the CMTS. If the video Tunnel network is viewed as IP subnets, the IP-video path seems to go IP Set-top ‘off’ IP network. This view is because the ‘non-synchronized’ CMTS DIBA App DIBA CM downstream DOCSIS channels from the DIBA are not fully Manager E-QAM MAC enabled. The Edge-QAM is performing DOCSIS encapsulation, but only for the special case of highly repetitive DOCSIS Subnet CM packets of certain IP-video flows. This is economical to do since DOCSIS is based on the ITU-T J.83, MPEG2 Transport stream that is used by digital video. The CMTS has instructed Figure 5. MSO IPTV network including backbone, local and DOCSIS the CM to treat this QAM carrier as a DOCSIS channel. So networks. The IP-video is tunneled from edge router to DIBA EdgeQAM, DIBA is leveraging the digital video origins of the DOCSIS bypassing the CMTS. DOCSIS encapsulation is performed by the DIBA physical/MAC layer. We have tested the critical elements of EdgeQAM. this network, including the DOCSIS network, DIBA bypass and DIBIA encapsulation engine, which forwarded 6. The DIBA application manager configures the edge router encapsulated packets over IP to a digital video Edge-QAM. so as to identify the IP packets that are to be bypassed, e.g., This encapsulation engine is the equivalent of DOCSIS based on the source and destination IP addresses; source and encapsulation in an Edge-QAM. The video flow was sent on a destination Port numbers; IP protocol type. Thus, instead of non-primary channel to a DOCSIS 3.0 modem. The modem being forwarded to the CMTS, packets of the new DIBA video forwarded the video flow to an IP set-top, which decoded the flow will be tunneled to the DIBA EdgeQAM, e.g., by a video without any problems. Generic Routing Encapsulation Tunnel. [6] 7. The DIBA App Manager signals OK back to the P-CSCF 8. The P-CSCF then forwards the SIP INVITE to the IPTV V. CONTROL PLANE: DIBA LEVERAGES STANDARD Server, which forwards it to the VoD server. PCMM AND CMTS FUNCTIONS 9. A SIP OK is sent from the VoD server back along this chain Most of the standard control plane functions of PCMM and to the IP set-top. The video flow begins. Modular-CMTS are retained. The set-up of a QoS enabled unicast IPTV session are as follows. [7, 8] VI. OVER-THE-TOP VIDEO 1. IPTV client requests IP video by way of a SIP invite, which While the network configurations considered so far all passes first to the Proxy-CSCF. The P-CSCF forwards the assume MSO controlled IPTV and IP-video servers, a good service request and QoS requirements to the DIBA application deal of IP video content will come from the internet. This manager. This information then passes to the PCMM policy could be broadcast, unicast or video file downloads. DIBA server, and finally to CMTS. offers a means of economically handling such over-the-top 2. CMTS checks authorization of CM for desired class of (OTT) traffic. service and if QoS can be supported. 3. The CMTS requests the necessary additional downstream Figure 6 shows an adaptation of DIBA for OTT IP-video. The channel capacity on a DIBA E-QAM from the Edge Resource subscriber will typically use a browser to select a video. A Manager. Domain Name Server request is sent for the IP address of the 4. The CMTS configures the CM for the appropriate DOCSIS actual video server providing that selection. A TCP session channel and video flow from the DIBA EdgeQAM will be set up from that video server to the IP set-top. These 5. CMTS makes available certain additional fields necessary session set-up communications will not pass over a DIBA for DIBA encapsulation by the Edge-QAM / Encapsulation bypass, but through the CMTS in the usual manner for data. Engine, e.g., the CPE MAC address. The CMTS signals OK The DIBA App Manager will interact with the IPTV Client to back to the Policy Server and DIBA Application Manager. obtain the IP address and port number of both the IPTV client and the internet based IP server. The DIBA App Manager will configure the edge router and Edge-QAM for the bypass. At
  4. 4. this point, an HTTP-get command will be sent to the video IPTV Internet Protocol Television server, and the resulting video flow will be delivered via the HSD High Speed Data DIBA bypass. M-CMTS Modular Cable Modem Termination System DIBA IPTV MPEG Moving Picture Experts App Client Manager Group Web Video MPEG2-TS MPEG2- Transport Stream Server DNS DNS DOCSIS MSO Multi System Operator Query CMTS Server 3.0 CM PCMM Packet Cable Multimedia t QoS Quality of Service ge p o tu ide SIP Session Initiation Protocol se P v Edge-Resource P T VoD Video on Demand TC HT Manager & REFERENCES Edge Edge-QAM [1] W. L. Er, P. Wong, Q. Fan, “Next Generation IPTV Services”, Internal Router Motorola Symposium, Singapore, 2008 Packet Inspection DOCSIS Encapsulation [2] Data-Over-Cable Service Interface Specifications, SP-RFIv1.1-I09- Bypass via Tunnel 020830, CableLabs, Louisville, Colorado, U.S.A Figure 6. Over-the-top video originating from the Internet and delivered via [3] M. Patrick, G. Joyce, “Delivering Economical IP Video over DOCSIS DIBA over a DOCSIS network by Bypassing the M-CMTS with DIBA”, Society of Cable Telecommunications Engineers 2007 Conference on Emerging Technology, Houston, TX, Jan, 2007. [4] Data-Over-Cable Service Interface Specifications DOCSIS 3.0, MAC and Upper Layer Protocols Interface Specification CM-SP-MULPIv3.0- VII. CONCLUSIONS I03-070223, CableLabs, Louisville, Colorado, U.S.A. [5] Data-Over-Cable Service Interface Specifications, Modular CMTS, IP-video and IPTV are challenges to cable companies in Downstream External PHY Interface Specification, CM-SP-DEPI-I02- that they would ordinarily cost more to deploy than does the 051209, CableLabs, Louisville, Colorado, U.S.A. legacy digital video. The reason for this is that, while digital [6] RFC2784 - Generic Routing Encapsulation (GRE), D. Farinacci, et al, March 2000 video is delivered over the backbone metro network via [7] PacketCable™ Technical Report, Multimedia Architecture Framework, Internet Protocol, it is transmitted by an inexpensive Edge- PKT-TR-MM-ARCH-V02-051221, CableLabs, Louisville, Colorado, QAM. IP-video has to, additionally, traverse a CMTS core. It U.S.A. is then transmitted by an internal modulator (of an integrated [8] PacketCable™ Multimedia Specifications, PcketCable Multimedia Web Service Interface Specification,PKT-SP-MM-WS-I02-080522, CMTS) or by an external Edge-QAM (as in the modular- CableLabs, Louisville, Colorado, U.S.A.. CMTS architecture). The DIBA approach is to configure an edge router to forward the IP-video packets not to the CMTS The authors can be reached at:, but directly to a less expensive DIBA Edge-QAM. For,, repetitive video packets, the DIBA Edge-QAM then does the DOCSIS encapsulation. In this way substantial cost reduction is achieved for IP-video and IPTV over cable. Acronyms Acronym Definition CMTS Cable Modem Termination System DEPI DOCSIS External Physical Interface DIBA DOCSIS IP-video Bypass Architecture DOCSIS™ Data over Cable Service Interface Specification, trademark of CableLabs E-QAM Edge-QAM IMS IP Multimedia Subsystem IP-STB IP-Set Top Box