 Similar to the quality of service, which is provided in LTE and LTEA networks in the 3GPP based next generation networks. In mobile Ymax, particularly Ymax 2.0, quality of service is a very important consideration. We are going to understand in this module what are the types and the variants which are recommended in mobile Ymax 2.0. The IEEE A-2.16E standard has certain quality of service recommendations which are based on the user traffic types aka service flows. Depending upon the elastic traffic, real-time and non-real-time traffic, these service flows can be provisioned either in a contention-based environment or contention-free environment. When it comes to contention, it means some kind of resource shortage is assumed. There is no prior strict admission control so the contention-based traffic is treated like best effort. The contention-free service flows are the ones which are provided a guaranteed service in terms of delay bounds, packet loss and so forth. We have to begin with some basic kinds of contention-free services including unsolicited grant service, real-time polling service and so forth. We are going to look at these in detail because each one has its own implications in what kind of traffic it can handle and how good it is suited for that kind of traffic. Then we have the non-real-time traffic. It can be provisioned through non-real-time polling service. Since it is related to non-real-time traffic such as email, web browsing and file transfer, so it can be incorporated either as a contention-based service or a contention-free service. For contention-free service, the base station that is homey node B in LTEA, here we have the base station and advanced base station if you recall and then we have the mobile stations and advanced mobile stations. So here for contention-free service, the base station periodically polls the mobile station and the mobile station actually asks for a certain reservation. On the contrary, if it is contention-based service for non-real-time, the base station allocates a certain bandwidth upon bandwidth request. It is known as BWREC or the bandwidth request which is made by the mobile station, so the bandwidth is allocated. But compared to contention-free, this bandwidth might get shared as more number of users appear on the network. So let's look at the service flows which offer quality of service-based services to mobile YMAX 2.0 users. As we just shortly discussed, we have the polling service in real-time, non-real-time polling service. We have the best effort, then we have the unsolicited grant service. The unsolicited grant service is quite interesting because it relates to the real-time traffic which is known by a unique behavior that is it has fixed packet sizes. So this emulates some kind of TDM-like behavior. So if we are transmitting VoIP in fixed-sized packets, then unsolicited grant service is going to be the best. The polling service for real-time is highly suited for the variable packet sizes for voiceover IP which includes now silence suppression. Silence suppression actually means that the packets are not containing any wasteful information. The only thing that is included is the audio or the voice of the speaker. Then IPTV is also suited for real-time polling service. There is a variation or modification to the real-time polling service known as extended real-time polling service. Again, it is for variable-sized packets but these variable-sized packets actually have both active and silent intervals. It means that we have the active intervals when the user activity or user audio is on along with the silent intervals. This kind of traffic is suited for multimedia traffic. Multimedia streaming service actually is the one which is used by different online movie stores and video content sites such as Netflix, YouTube, etc. Then we have the non-real-time polling service. As we said, it is related to elastic traffic so it is delay tolerant. Then we have West Effort. We've already discussed it. An interesting service flow which is recommended in IEEE 802.16M is adaptive granting and polling service. We might look at it in more detail. It is very flexible because as the name suggests it is adaptive both in terms of the time allocation, packet size allocation and the inter-packet delay. It is suited for some interactive environments such as online video games, voice over IP which is for instance SIP based voice over IP service with adaptive rates. Adaptive rates means that multiple rates can be adjusted. Higher rates, lower rates, moderate rates and then certain delay sensitive TCP based services. For instance, we have the TCP based service like FTP. FTP is not delay sensitive but we can think about a file transfer which needs to be carried out within a certain time period anyways. For that adaptive granting and polling can be a service provided in YMAX 2.0 networks.