 In our earlier module, we looked at the packet cable network specifications and the docsys specifications as the two most noteworthy aspects of the overall cable network architecture. So we shall continue with docsys here. We'll define what is docsys, what are the variants and how each variant differs in terms of the data rate that it offers. So docsys as we earlier had defined is formally transmission of data over cable and how different interfaces should be defined for providing various kinds of services. So these are the guidelines, these are the instructions, the specifications which are all part of the docsys. The docsys primarily deals with the transmission of data, that is data of different services from the cable provider to the user when a user needs it. So it means a user makes a query or configures a certain kind of service through an application and then correspondingly that particular network is invoked and using that network this user is provisioned that kind of service. So it has two most important parts. We have the user equipment also known as the customer premises equipment which is nothing but a simple modem that is connected to the coaxial cable that reaches your home. Then we have the operator. The operator or the network side is dealing with two aspects. Number one, it is dealing with the electrical aspects of the transmission of signals over coaxial cable and if it is a mix of coaxial cable and fiber deployment because after the emergence of fiber optic people integrated the coaxial cable with fiber optic cable to extend the coverage. Of course, one is the electrical transmission medium, the other one is an optical medium. So some kind of translation as in electro optic and optoelectric translation needs to be performed. So the operator side that is the I would say the ISP side is responsible for the hybrid fiber coaxial network management. Then since we are talking about cable modem which is a pretty intelligent device that takes data from all the user devices in the residence converts them into packetized transmission. So it sends it to the operator side. The CMTS the termination system that receives or terminates the traffic coming from the cable modem is the scope of the operator. So DOCSES specifications deal with the design with the modes in which the cable modem and CMTS can communicate the electrical specifications and all that. Now the DOCSES started off with providing very native and basic services. So DOCSES 1.0 specifications was the first version of the provisioning of packetized voice video data over the cable. So DOCSES 1.0 number one provides different services and since each service may be provided to the user through a certain kind of device. For instance, if we talk about telephony then IP phones was once a dedicated hardware device which was present present in user premises. So it means that this is one device then we have a computer for browsing for surfing. So depending upon the user requirements different kinds of devices would be there on the user residence. So all these devices are connected to the cable modem centrally. So cable modem is the central device like a gateway or if you recall the Wi-Fi. It is kind of the Wi-Fi router or Wi-Fi access point. So using the cable modem configuration and cable modem parameter control the cable operator that is the ISP may control the internet access by changing the bitrate or a certain package to a user. So it means that in DOCSES 1.0 the service provider that is the cable service provider can offer different kinds of packages for instance 512 kbps, 1mb connection, 2mb connection and all that. So it means that the ISP had the control over what data rate should be provided to the end user. In the second variant of it quality of service was incorporated. Incorporating quality of service was really necessary because DOCSES 1.0 was providing different kinds of services but these services were competing with each other. Some of these services are delay tolerant, throughput tolerant and don't need much reliability. But some of these services need stringent support and stringent preferential treatment like high priority, higher throughput and low packet loss. So QS actually was added in 1.1. Of course throughput and delay are the most important considerations which were addressed here. The QS is implemented through the incorporation of parameter change like in DOCSES 1.0 different kinds of bandwidths or packages like 1mb, 2mb could be offered to the user. Likewise here also different configuration parameters can be used to provide different kinds of quality of service for different types of data and services that a user needs. So this allows a user to determine what kinds of services can a user subscribe to through different kinds of service level agreements like bronze, silver, gold, platinum, diamond like that. So using this different interesting business models can emerge. For instance a corporate or a multinational corporation could subscribe to the best quality of service because it could afford. So it means a package with higher cost could be provided to that corporate. Likewise for a retail customer like an individual home subscriber a very low QS based service could be configured. So it means this kind of service configuration and service graduation was incorporated in 1.1. In DOCSES 2.0 since at that time all fiber networks had started to emerge. I mean the packet cable service was meant for utilizing the coaxial cable. So it means the primary focus was coaxial cable and coaxial cable integrated with fiber is the HFC the hybrid fiber coax. So meanwhile all fiber networks also started to emerge. So it means service providers with no legacy would deploy all fiber solutions naturally all fiber solutions have much higher bandwidth. They may not have much coverage because the coaxial cable has been there for quite much time. So the goal was in DOCSES 2.0 to increase the data rate especially the upstream traffic. Because as we studied in original cable based services the emphasis was on downstream upstream was not much of a consideration. But slowly upstream started gaining importance because certain services like symmetric services like video conferencing needed DOCSES to upgrade to higher upstream. And then in DOCSES 3.0 support came in for IP version 6 which is highly NGN suitable because NGN assumes the underlying core to be IP based and preferably IPv6 based. Support for IPTV also came in then the concept of channel bonding was introduced that is more than one frequency could be used to provide data rates up to 170 megabits per second. It's a very high data rate from an individual subscriber point of view and on the upstream 127 120 megabits per second. So DOCSES 3.0 not only increased the features but it will also increase the data rate. This is the overall picture of how the different variants of DOCSES have increasing data rates both on the upstream and downstream. An interesting thing to observe here is that there are two variants of it the DOCSES per se which is a US based specification and Euro DOCSES primarily for Europe. Now since in US the TV channel bandwidth is 6 MHz and in Europe the TV channel bandwidth is 8 MHz so you see naturally in Euro DOCSES the data rate is relatively higher as compared to DOCSES per se. But the upstream traffic was restricted to same both in DOCSES and Euro DOCSES.