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M-CMTS & DOCSIS 3.0 Standards at High Speed
« on: November 23, 2011, 06:54:00 am »
Author : Sadhana Pal, Gyan Prakash, Aradhana Jyotsana, Vivek Birla
International Journal of Scientific & Engineering Research Volume 2, Issue 10, October-2011
ISSN 2229-5518
Download Full Paper : PDF

 There are many challenges to cable operators. The main challenge that operators face to provide a Connected Life experience is lack of available bandwidth. Operators need to deliver more downstream and upstream band width to provide a fat pipe to and from the home. DOCSIS 3.0 is one of the best solutions to deliver higher band width. DOCSIS 3.0 addresses the bandwidth crunch in both the upstream and downstream directions. Another challenge is to deliver Higher Bandwidth at a Reduced Cost per Bit. While the need for bandwidth is enormous, operators have to be able to deliver next generation, high-bandwidth services at a reduced cost in order to stay competitive in the marketplace. The modular M-CMTS and I-CMTS solutions provide the building blocks to enable operators to offer highly competitive, high-bandwidth services at a reduced cost per bit. By using M-CMTS and deploying U-EQAM modulators, operators now can easily migrate to a high-bandwidth service to the home and enjoy greatly reduced capital expenditures (CapEx).

Keywords: DOCSIS 3.0, M-CMTS, Speed, Bandwidth

DOCSIS 3.0 is series of specifications that define the third generation of high speed data over cable systems. DOCSIS 3.0 provides a number of enhancements to the existing DOCSIS standard, most notably, channel bonding, support for IPv6, and support for IPTV. Channel bonding provides cable operators with a flexible way to significantly increase downstream speeds to a minimum of 160 Mbps, and upstream throughput up to a minimum rate of 120 Mbps to customers. DOCSIS3.0 addresses the following service goals-increasing channel capacity, enhancing the network security, expanding addressability of network elements and deploying new service offerings.

MSOs can leverage existing M-CMTS architecture to allow them to meet customer demands for higher bandwidth with DOCSIS3.0 edge-QAMs and channel bonding features. This architecture separates the downstream physical layer processing from the core CMTS and moves it to Harmonic's NSG 9000 universal edge- QAM, improving downstream data rates and significantly reducing costs. The NSG 9000 supports both wideband M-CMTS and M-CMTS solutions delivered using existing cable modems. The NSGs are already deployed in over 10 M-CMTS systems around the world including North America, Asia and Europe.

M-CMTS architecture:
The M-CMTS architecture includes a DOCSIS Timing server to maintain a consistent timing reference
between the M-CMTS core and EQAM, as well as to mitigate the propagation delay differences of
these two components. The DOCSIS Timing Interface (DTI) runs between the DTI Server and the
M-CMTS and EQAM devices.
The M-CMTS architecture was created to accomplish the following:
•   Allow operators to deploy independently scalable numbers of downstream DOCSIS channels without changing the MAC (media access control) domain or the number of upstream DOCSIS channels.
•   Lower the cost to deliver video over DOCSIS service to be competitive with current MPEG VOD (video on demand) by implementing a new generation of downstream-only cards on existing CMTS units. Current CMTS line cards combine downstream & upstream channels, forcing operators to add one upstream channel for every downstream channel they deploy; M-CMTS architecture removes this necessity. The architecture of M-CMTS is shown in figure1.

The connection to the DOCSIS Timing Server is usually implemented via a CAT5e cable.  It is also strongly recommended that each CMTS be connected to a second DOCSIS Timing Server for redundancy and find two RJ-45 ports for the DTI Server connection.

Figure 1. Architecture of M-CMTS

DOCSIS 3.0 specialized interface card for communicating between the M-CMTS core and EQAM.  This card will typically have a GBIC interface so that it can be configured with either copper or (CAT5e) or optical (multi-mode fiber) between the CMTS chassis and the EQAM.  There are multiple ports because CMTS will likely be transferring more traffic in the downstream than one gigabit Ethernet port can handle.  From a configuration standpoint, once the wideband interface card is added, all of the DOCSIS 3.0 downstream channels bonding commands are enabled in the DOCSIS 3.0 IOS that is installed in the system.  It is at this point that configuration of the downstream bonding groups to their respective MAC address in the EQAM occur. Once properly configured, the CMTS core will be bound to the EQAM over the physical connection between the wideband card and EQAM.  Downstream data is transmitted over the primary (CMTS) downstream channel and over the bonded EQAM channels as defined in the CMTS running configuration.  The link between the CMTS wideband card and the EQAM uses a DOCSIS 3.0 protocol called Downstream External-Phy Interface (DEPI).  DEPI is based upon the L2TPv3 protocol, which in layman’s terms is a very good protocol for transmitting multiple streams of IP data over the same physical media.  The reason this is important in the DOCSIS 3.0 network is because the DEPI must be able to manage not just data, but also video while managing QoS.

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