Design and Performance of 3G Wireless Networks and Wireless Lans
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The iWAG provides mobility services to mobile IP users and as a result, a mobile client can seamlessly access a 3G or 4G mobility network. Clients can access WiFi Internet public wireless , where ever possible. However, if WiFi is not available, the same clients can connect to the Internet service with a 3G or 4G mobility network. Service providers use a combination of WiFi and mobility offers to offload their mobility networks in the area of high-concentration service usage.
Contrary to Mobile IP approach, this functionality is implemented by the network, which is responsible to track the movements of the host and initiate the required mobility which signals on its behalf.
Comparison of wireless data standards
However, in case the mobility involves different network interfaces, the host needs modifications similar to Mobile IP in order to maintain the same IP address across different interfaces. The APN is the name for the settings your phone reads to set up a connection to the gateway between your carrier's cellular network and the public Internet. The IMSI is used to identify the user of a cellular network and is a unique identification associated with all cellular networks. It is stored as a 64 bit field and is sent by the phone to the network. This number includes a country code and a National Destination Code which identifies the subscriber's operator.
Step 1. Step 2.
Step 3. Step 4. Step 6. Step 7. The mobile device is automatically associated to the Service Set Identifier SSID broadcast by the access points to establish and maintain wireless connectivity. However, at least for the moment, no such mechanism exists. This is an active area of research, both in the industry and academia.
Design and Performance of 3G Wireless Networks and Wireless LANs
So how does the battery and power management affect networking performance? Signal power explained in Signal Power is one of the primary levers to achieve higher throughput. However, high transmit power consumes significant amounts of energy and hence may be throttled to achieve better battery life. Similarly, powering down the radio may also tear down the radio link to the radio tower altogether, which means that in the event of a new transmission, a series of control messages must be first exchanged to reestablish the radio context, which can add tens and even hundreds of milliseconds of latency.
Both throughput and latency performance are directly impacted by the power management profile of the device in use. In fact, and this is key, in 3G and 4G networks the radio power management is controlled by the RRC: not only does it tell you when to communicate, but it will also tell you the transmit power and when to cycle into different power states. The radio state of every LTE device is controlled by the radio tower currently servicing the user. The network operator can make modifications to the parameters that trigger the state transitions, but the state machine itself is the same across all LTE deployments.
The device is either idle, in which case it is only listening to control channel broadcasts, such as paging notifications of inbound traffic, or connected, in which case the network has an established context and resource assignment for the client. When in an idle state, the device cannot send or receive any data.
This negotiation can take several roundtrips to establish, and the 3GPP LTE specification allocates a target of milliseconds or less for this state transition. In LTE-Advanced, the target time was further reduced to 50 milliseconds. Once in a connected state, a network context is established between the radio tower and the LTE device, and data can be transferred. However, once either side completes the intended data transfer, how does the RRC know when to transition the device to a lower power state?
In the high-power state, the RRC creates a reservation for the device to receive and transmit data over the wireless interface and notifies the device for what these time-slots are, the transmit power that must be used, the modulation scheme, and a dozen other variables. Then, if the device has been idle for a configured period of time, it is transitioned to a Short DRX power state, where the network context is still maintained, but no specific radio resources are assigned.
In LTE, just as in most other modern wireless standards, there are shared uplink and downlink radio channels, the access to which is controlled by the RRC. When in a connected state, the RRC tells each and every device which timeslots are assigned to whom, which transmit power must be used, modulation, plus a dozen other variables. If the mobile device does not have an assignment for these resources by the RRC, then it cannot transmit or receive any user data. What happens if the network or the mobile device must transmit data when the radio is in one of Short or Long DRX dormant states?
The device and the RRC must first exchange control messages to negotiate when to transmit and when to listen to radio broadcasts. So what does this all mean in practice? In fact, one reason why LTE offers better performance is precisely due to the simplified architecture and improved performance of the RRC state transitions. In practice, this state was designed to handle non-interactive traffic, such as periodic polling and status checks done by many background applications. Each device maintains a buffer of data to be sent, and as long as the buffer does not exceed a network-configured threshold, typically anywhere from to 1, bytes, then the device can remain in the intermediate state.
Finally, if no data is transferred while in FACH for some period of time, another timer transitions the device down to the idle state. However, even though LTE offers a theoretically higher degree of power control, the radios themselves tend to consume more power in LTE devices; higher throughput comes at a cost of increased battery consumption. Hence, LTE devices still have a much higher power profile than their 3G predecessors. Individual power states aside, perhaps the biggest difference between the earlier-generation 3G networks and LTE is the latency of the state transitions.
Where LTE targets sub-hundred milliseconds for idle to connected states, the same transition from idle to DCH can take up to two seconds and require tens of control messages between the 3G device and the RRC!
Hence, all mobile applications should plan for multisecond RRC latency delays when accessing the network over a 3G interface. The growth curve for EV-DO networks may look comparatively flat, but even so, current industry projections show nearly half a billion CDMA powered wireless subscriptions by Not surprisingly, regardless of the differences in the standards, the fundamental limitations are the same in UMTS- and CDMA-based networks: battery power is a constraining resource, radios are expensive to operate, and network efficiency is an important goal.
This is definitely the simplest RRC state machine out of all the ones we have examined: the device is either in a high-power state, with allocated network resources, or it is idle. Further, all network transfers require a transition to a connected state, the latency for which is similar to that of HSPA networks: hundreds to thousands of milliseconds depending on the revision of the deployed infrastructure. There are no other intermediate states, and transitions back to idle are also controlled via carrier configured timeouts.
An important consequence of the timeout-driven radio state transitions, regardless of the generation or the underlying standard, is that it is very easy to construct network access patterns that can yield both poor user experience for interactive traffic and poor battery performance.
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In fact, all you have to do is wait long enough for the radio to transition to a lower-power state, and then trigger a network access to force an RRC transition! Next, we load an application that schedules an intermittent transfer, such as a real-time analytics beacon, on an second interval.
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The device may end up spending hundreds of milliseconds in data transfer and otherwise idle while in a high-power state. Worse, it would transition into the low-power state only to be woken up again a few hundred milliseconds later—worst-case scenario for latency and battery performance. Every radio transmission, no matter how small, forces a transition to a high-power state. The size of the actual data transfer does not influence the timer.
Further, the device may then also have to cycle through several more intermediate states before it can return back to idle. First, you have to pay the latency cost of the state transition, then the transfer happens, and finally the radio idles, wasting power, until all the timers fire and the device can return to the low-power state. Among these applications, Pandora serves as a great case study for the inefficiency of intermittent network transfers on mobile networks. Whenever a Pandora user plays a song, the entire music file is streamed by the application from the network in one shot, which is the correct behavior: burst as much data as you can, then turn off the radio for as long as possible.
However, following the music transfer, the application would conduct periodic audience measurements by sending intermittent analytics pings every 60 seconds. The net effect? The analytics beacons accounted for 0.
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By coalescing the analytics data into fewer requests, or by sending the audience data when the radio is already active, we can eliminate the unnecessary energy tails and almost double the power efficiency of the application! Now that we have familiarized ourselves with the RRC and device capabilities, it is useful to zoom out and consider the overall end-to-end architecture of a carrier network. Our goal here is not to become experts in the nomenclature and function of every component, of which there are dozens, but rather to highlight the components that have a direct impact on how the data flows through the carrier network and reasons why it may affect the performance of our applications.
The specific infrastructure and names of various logical and physical components within a carrier network depend on the generation and type of deployed network: EV-DO vs. HSPA vs.
LTE, and so on. Why LTE? First, it is the most likely architecture for new carrier deployments. Second, and even more importantly, one of the key features of LTE is its simplified architecture: fewer components and fewer dependencies also enable improved performance.
In fact, this is the component controlled and mediated by the Radio Resource Controller. Whenever a user has a stronger signal from a nearby cell, or if his current cell is overloaded, he may be handed off to a neighboring tower. However, while this sounds simple on paper, the hand-off procedure is also the reason for much of the additional complexity within every carrier network.
Comparison of wireless data standards - Wikipedia
If all users always remained in the same fixed position, and stayed within reach of a single tower, then a static routing topology would suffice. However, as we all know, that is simply not the case: users are mobile and must be migrated from tower to tower, and the migration process should not interrupt any voice or data traffic. Needless to say, this is a nontrivial problem. Of course, there is no magic: the radio access network must communicate with the core network to keep track of the location of every user.
Further, to handle the transparent handoff, it must also be able to dynamically update its existing tunnels and routes without interrupting any existing, user-initiated voice and data sessions. In LTE, a tower-to-tower handoff can be performed within hundreds of milliseconds, which will yield a slight pause in data delivery at the physical layer, but otherwise this procedure is completely transparent to the user and to all applications running on her device. In earlier-generation networks, this same process can take up to several seconds.
The core network must know the location of the user, but frequently it knows only the tracking area and not the specific tower currently servicing the user—as we will see, this has important implications on the latency of inbound data packets. In turn, the device is allowed to migrate between towers within the same tracking area with no overhead: if the device is in idle RRC state, no notifications are emitted by the device or the radio network, which saves energy on the mobile handset. Put simply, it is the piece that connects the radio network to the public Internet.
First, we have the packet gateway PGW , which is the public gateway that connects the mobile carrier to the public Internet. The PGW is the termination point for all external connections, regardless of the protocol. When a mobile device is connected to the carrier network, the IP address of the device is allocated and maintained by the PGW. Each device within the carrier network has an internal identifier, which is independent of the assigned IP address.
In turn, once a packet is received by the PGW, it is encapsulated and tunneled through the EPC to the radio access network. The fact that the device IP address is allocated and maintained by the PGW has a number of important implications. First, it means that a wireless device can be easily associated with multiple IP addresses. Conversely, if the IP addresses are at a premium, then multiple devices can share the same IP address but be allocated different ports for outgoing and incoming traffic: the PGW acts as a NAT. In fact, the latter case is quite common.
The same carrier IP address can be assigned to dozens, if not hundreds, of devices within its network.