The Home Location Register

Published Date: 02 Nov 2017

Adam Hughes

Table of Contents

Comparison

Infrastructure

3G

This part of the report will look at the pieces that make up the 3G network topology. There are many components that make up 3G mobile networks. 3G networks are split up into two parts: the core network, and the services that run on the network such as SMS. 3GUMTS networks should provide a minimum data rate of 200kbit/s. Carriers often advertise higher speeds than this. The higher data rates have allowed for more bandwidth intensive applications to be developed on mobile platforms.

Core Network

Figure - http://de.academic.ru/pictures/dewiki/117/umts_network_architecture.pngThe core network facilitates things like user authentication, controlling phone calls and connecting to exterior networks(3GPP). A lot of the infrastructure of a UMTS network is shared with GSM. 3G UMTS contains circuit switched parts with dedicated resources to handle voice calls. The Radio Network Controller subsystems control aspects like encryption of data, and resource management. It also controls the NodeB that are connected to it.http://de.academic.ru/pictures/dewiki/117/umts_network_architecture.png

The core network is made up of 5 Major components some of which can be shared with a 4G or GSM network.

Serving GPRS Support Node (SGSN)

In 3G UMTS networks the role of the Serving GRPS Support Node is to send and receive packets between the mobile network and an external, packet switched network such as the internet, or an ISDN network. The SGSN is a very central part of the core network. It connects to the HLR, EIR, UTRAN and MSC. It used to keep track of the bandwidth that the customers of the network use so that they can be billed accordingly.

Mobile Switching Centre (MSC)

The Mobile Switching Centre plays a very central role in a UMTS network. It was carried over from previous generation networks, and connects to a lot of the other components that make up the network.

The MSC connects to a thing called the HLR. The HLR is a database that contains data about every SIM card that the mobile operator has issued, it was brought over from previous generation networks. It also connects to the UTRAN. The UTRAN subsystem handles all of the radio communications with 3G phones and devices.

The MSC also provides the ability for a user to move around while still being connected to the mobile network. The MSC will detect when they are starting to go out of range of the base stations they control and will handle the handover of the user from one base station to another, or from one MSC to another. The MSC is used to keep track of which resources users consume on the network so that they can be billed accordingly.

Home Location Register (HLR) [1] 

The HLR is essentially a database that is maintained by a mobile network operator. It contains all the information that a network needs to let users use all of its services. It contains things like their SIM number, location and what services they are allowed to use.

When a user leaves the area defined as their home area their details get sent to a similar database called a VLR that is in the region that they have moved (or roamed) into. User’s details are only in the VLR for the time that they are outside their home area. A home area is defined by the network operator.

Visitor Location Register (VLR) [2] 

The Visitor Location Register is a database similar to the HLR. When a user leaves the area that is served by their HLR and enter an area served by a VLR of another area their details are requested by the VLR and stored for the duration of the time they are in the VLR's area. The home area for a HLR is defined by the mobile operator. The VLR will temporarily store all the details that a network needs to allow a user to use its services. The purpose of having a VLR is to reduce the number of times a MSC needs to request details about a subscriber from another MSC/HLR.

Media Gateway (MGW)

The media gateway is a device that connects the UMTS network to other networks that use different transport layer protocols than the UMTS network. Its main function is to transcode the communications between the two or more networks it is connecting. The MGW connects to the MSC and RNC in the core network.

UTRAN

The UTRAN subsystem is the part of the network that users connect to. It is made up of two components, the NodeBs which is the radio transceivers, and RNCs that control the NodeBs. It allows the communication between users and the core network.

RNC

One of the parts of the UTRAN subsystem is an RNC. Each RNC is responsible for controlling one or more Node Bs. the RNC is partly responsible for tracking where users are within the UMTS network they are connected to so that calls and SMS messages can be sent to the correct person. They are also responsible for managing the radio resources for the Node Bs that they are in control of. The RNC is the first part of the network where a users data is encrypted or decrypted to keep the data secure as it travels over the network, and to prevent eavesdropping. They connect to the CS core of the network through the SSGN and MGW

Node B

The node B is a radio transmitter, receiver and antenna that allow subscribers mobile devices connect to the network. The geographical area that they are able to serve is called a cell. The Node Bs use Wideband Code Division Multiple Access to allow multiple users to use the same cell. They are also responsible for handling errors in the transmissions and modulating and demodulating the signals. [3] 

As more users connect to the Node B it creates more noise for the Node B. The signals from the other users that are connected to the same node B appear as noise because when CDM is used you need the code to make sense of the signals, and without the code the signals of all the users appear as noise. The Node B decreases its cell size to limit the number of users that can connect to it, therefore reducing the amount of noise in that cell. Having cells that grow and shrink depending on their size means that the placement of Node Bs needs to be carefully planned to ensure that there is even and reliable coverage.

WCDMA in UMTS networks

WCDMA is a technique to allow multiple users to use the same radio resources at the same time and in the same space as other users. Each user’s communications with the node B is split up by a code. When the radio signal is received it is decoded using the same code that it was coded with. All the other signals will appear as noise when decoding a signal. WCDMA has multiple channels of 5 MHz each allowing it to carry over 100 phone calls at the same time [4] , and user data at 2Mbpsd though higher data rates are achievable today due to further developments and new techniques. [5] 

In Europe and many countries in the Middle East, Africa, Australia and Asia WCDMA is used on 1920-1980 MHz for the Uplink and on 2110-2170 MHz for the downlink3. But in North America the frequencies used are: 1710-1755 MHz for the Uplink and 2110-2155 for the downlink3. This means that some phones that use WCDMA will work in Europe and most of the rest of the world, but not in North America. WCDMA makes it harder for somebody to intercept the communication and make any sense of it as they would need the code that the data was coded with. The radio part of the network is probably where the data is the least secure as anybody within range of it can hear or capture it.

Power Control

It is very important for a transmission using WCDMA to not be too over powering or loud compared to the other transmissions that are in the same physical area, or going to the same cell tower. This is because the other signals in the same area will appear as noise and will drown out the other radio signals. There is a mechanism to control the power of the radio transmissions on the user’s equipment. Multiple power control messages are sent to the user’s equipment and an algorithm is used to determine if the signal needs to be more or less powerful [6] . 5 control messages are sent to the user equipment and it makes a decision based on the result of the algorithm that is used. The purpose of this is to maintain a steady Signal to Noise Ratio (SNR) and to make sure that no signals are lost due to one signal being too strong.

The algorithm that is used is:

If Estimated SNR > Target SNR Then:

Power control message = down

If Estimated SNR < Target SNR Then:

Power control message = up

If all 5 of the Power Control Messages are down then the power of the radio signal on the users equipment is decreased by 1 decibel. If all 5 of the messages are "up" the transmit power is increased by 1 decibel 3. The power control also makes WCDMA more protective of the environment as there will be less radiation.

4G

This section of the report will outline the differences between the 3G UMTS network equipment and a 4G LTE network. The biggest advantage to consumers with a 4G LTE network is the massive improvement in speeds. There are a couple of big differences between the 3G UMTS architecture and a 4G LTE network. The first is that the 4G network uses IP and is packet switched compared to the 3G UMTS architecture that has both packet switched and circuit switched elements. LTE networks seem to be built around data services, but voice is still the most important for mobile users. There are multiple methods to deliver voice calls to a LTE user.

The main considerations and aims described in the Release 8 document that describes the next generation networks are: Reducing the latency of the network, higher data rates for users, a higher capacity network with lower operation costs, and a flexible way to deploy new technologies onto the network [7] .

Additions and changes to the core network

This part of the report will be about the differences and additions to the LTE network compared to the UMTS network.

ENode B

The function of the ENode B is very much the same as the Node B from the UMTs network apart from there is no RNC to control it. It does almost the same job with some changes. All communications from the ENode B to the core network are entirely IP and packet based. The removal of the RNC allows for a lower latency for users when using the network which will help improve the experience of using time critical data applications over a mobile network.

Another change of the radio aspect of LTE is that it uses two multiple access techniques compared to UMTS that use just one. OFDMA is used for the downlink, and SCFDMA is used for the uplink. The ENode B connects to the MME and the S-GW in the core network.

PDN GW

The Packet Data Network Gateway is the point of entry and exit for traffic that goes to external packet switched networks such as the internet. The other functions of the PDN GW include billing users for data used, packet screening and a place for lawful traffic interception. [8] Its function is similar to the SGSN from the UMTS architecture.

Mobility Management Entity (MME)

The MME plays a very critical role in the LTE architecture. A network can have multiple MMEs to help with load balancing, or to split up the network intro geographical locations. It is much like the MSC in the UMTS architecture.

One of the roles of the MME is to authenticate users when they attach to the network, and assign them a Packet Data Gateway, and Quality of Service parameters. The authentication is done by retrieving their details from the HSS and making sure that they are allowed to use the LTE network they are connecting to. The Quality of Service ensures that time critical traffic gets to its destination without much delay, and to give a good service to all of the users by prioritizing certain traffic. Another function of the MME is to track the location of the UE in the part of the network that it is responsible for. When the UE is going out of the area of control for the MME it is handed over to another MME. The MME connects to the eNodeB and provides a place for lawful interception of the radio signals.

HSS

The Home Subscriber Server or HSS is very similar to the HLR in the UMTS architecture. It stores details on how a user is identified, what they can do on the network and the subscribers location, authentication and authorization details, the quality of service profile for the user. It is the main database for information about a user on an LTE network.

Orthogonal Frequency-Division Multiple Access

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6295726

OFDMA is used on the downlink of LTE networks. It is a technique that has been proven to work in 802.11n wireless networks, on DSL connections and also network communications over power cables in homes. A slightly modified version is used on the uplink for LTE. It is called Single Carrier FDMA.

Another reason that this technique was chosen over other techniques was because it works well over multiple bandwidths and frequencies. This is great because it solves the problems of not all countries using the same frequencies for LTE. Some countries could have restrictions on what frequencies they can allocate to LTE.

OFDMA works by taking a bandwidth and splitting it up into smaller channels, typically 10MHz each. Frames are transmitted on each of these channels, the frames last for 10ms each and are made up of ten 1ms sub frames. Two further smaller slots are make up the sub frames each lasting 0.5ms. The user equipment is allocated a slot and can use it to send data over the network. [9] 

Services

Lots of services in 3G networks relied on the circuit switched core of the network. LTE is entirely packet and IP based, this means that network operators are going to have to come up with a new way to implement these services. Below is a small table showing the services from 3G networks and how they are going to be implemented into an evolved packet switched network.

The transition solution is a temporary solution for the services to be ready earlier with less development for when operators offer their LTE networks to customers. On the right hand side is the solution that will eventually replace the transition solution as the mobile operators start to expand their LTE architecture.

Legacy Services

Transition Solution

Final Solution

Circuit Switched Voice

CS Fallback

IMS VoIP

SMS

SMS over SGs (used to be called SMS over CS)

SMS over IP

Supplementary Services

CS Fallback

Multimedia Telephony

Emergency Calls w Location Support

CS Emergency Calls

IMS Emergency Calls with Location Support

Source: http://www.3gpp.org/Dispelling-LTE-Myths

Voice calls on LTE networks

4G LTE networks have been designed as an entirely packet switched network. In other mobile networks like UMTS and GSM there are circuit switched parts of the network to handle all voice calls. In LTE there is no circuit switched part of the network which means that voice calls are going to have to be handled in a new way. Voice over LTE or One Voice is the chosen long term standard for delivering voice calls over LTE networks.

CSFB (Circuit Switched Fallback)

In an LTE network there is no circuit switched part of the network to give dedicated resources to voice calls. CSFB allows for circuit switched services such as voice calls and SMS to be delivered over the LTE network. CSFB is a short term solution for solving the problem of delivering circuit switched services on LTE, the long term solution for voice is Voice over LTE, and for SMS the long term solution is SMS over IP. CSFB is a technique where a user is handed over to a circuit switched network when they receive a voice call or SMS message, and when their call ends they are handed back over to the LTE network. [10] 11

A downside to this approach and a reason why it would not work as a long term solution is that a user cannot use applications on their phone while they are on the circuit switched network.

VoLTE (Voice over LTE)

Voice over LTE is the chosen long term solution to delivering voice calls on the LTE networks. The voice calls are packetized and flow across the network as regular data.

When using this solution there is no need to maintain the current circuit switched network that is used for voice communications on mobile devices which results in a lower operating cost for network operators as they just need to maintain a simpler IP based network. The voice quality over LTE can also be improved as a higher data rate is available.

Security

3G

This part of the report will look at the security aspects of the 3G network.

Authentication and radio signals

A unique identifier on the SIM card that is placed inside the user equipment is used to identify a user so that they can authenticate to a network. The SIM number is sent to the HLR which makes sure that the user is allowed to connect to the network, and that the user is allowed to use the services offered by the network [12] .

When a user has authenticated with the network a Cipher Key is generated and stored in the core network. There is a single encryption algorithm that is defined in the 3GPP 99 [13] standards for UTRAN based 3GPP networks. All signals from the UE to the RNC are encrypted using the algorithm in the 3GPP 99 standard, and the cipher key that was generated when a user authenticated.

The encryption along with the CDMA based multiple access technique ensures that the data that is being transmitted from the users equipment to the cell tower is secure. The wireless part of the network is where the users data is most at risk, so it is important that steps are taken to try and mitigate these risks.

Core network security

The core network of the UMTS architecture also has its security risks. Social engineering could be used to get an employee or somebody that has access to the network to do something that would help an attacker compromise the network. An attacker could also launch a denial of service attack against the key components of the network through compromised mobile devices. I have also found a couple of news articles about false base stations being set up [14] 15to trick mobile phones into connecting to them. Once a mobile phone has connected to the false base station the data can be intercepted and read by the attackers.

Typical real world speeds

The typical speeds for a 4G connection have been reported to be between 12mbps up to a maximum of 40mbps. [16] 17

The typical speeds that I have experienced with my own phone using HSPA+ have been between 1mbps and 15mbps download speed. My tests shown in the image below where done on the 3 mobile network on a Google Nexus 4.

Which is best for the given scenario?

This part of the report will be a quick overview of the 4G LTE network and 3G UMTS discussing the advantages and disadvantages of each and evaluating which one would suit the given scenario the best.

4G advantages

The biggest advantage to the new LTE network over the older UMTS network from a consumers point of view is the massively increased download rate. The improved download speeds and latencies will allow for more demanding applications to be made portable. Although I don't think that the company described in the scenario would benefit from this if they are just updating a central server with GPS coordinates and other less data intensive applications.

Another advantage of adopting the LTE technology into the vehicles in the fleet for the given scenario is that

going to become the standard

better voice quality

4G disadvantages:

I think that the two biggest disadvantages of the LTE network go hand in hand. At the moment in the UK there is only a single provider that can provide the service. The cost of LTE data compared to data on a UMTS network is very high, I think that the price will fall as more providers start offering 4G contracts to consumers and the providers become more and more competitive.

Another disadvantage is that the company would need to buy new equipment to use the 4G network in their vehicles. At the moment there is a limited selection of mobile phones that support LTE. They are more costly compared to other phones, but again I think that they will become cheaper over time as 4G becomes more and more common.

Advantage of 3G

cheap

devices are common and cheap

It has more choice of networks

better price

3G disadvantages:

slow data rates

not reliable

Devices for LTE are expensive, there are not many of them

Majority of phones sold today use UMTS

Cost of LTE data is expensive -- there are no competitors against EE yet

4G faster data transfers, lower latency but more expensive

Issues associated with each system

3G

slow data rates

cheap

devices readily available

coverage is great

Network performance with each system

Cost

Will they actually need the extra speed?

4G much faster than 3G

Coverage from EE is great with either system

http://www.networkworld.com/news/2007/052107-special-focus-4g.html

http://www.krio.me/security-in-4g-and-other-mobile-networks/

http://www.javvin.com/wireless/VLR.html

http://searchnetworking.techtarget.com/definition/Home-Location-Register

http://en.wikipedia.org/wiki/Home_Location_Register#Home_location_register_.28HLR.29

www.elektroda.pl/rtvforum/download.php?id=338749

http://en.wikipedia.org/wiki/Home_Location_Register#Home_location_register_.28HLR.29

http://www.althos.com/tutorial/GSM-tutorial-mobile-switching-center-MSC.html

http://searchnetworking.techtarget.com/definition/Home-Location-Register

http://www.gartner.com/it-glossary/vlr-visitor-location-register/

http://www.argospress.com/Resources/cdma/cdmvisitolocatiregist.htm

http://www.umtsworld.com/technology/ran/ran.htm

http://en.wikipedia.org/wiki/Media_gateway

http://www.umtsworld.com/technology/ran/ran.htm

http://www.umtsworld.com/technology/ran/ran.htm

http://www.umtsworld.com/technology/overview.htm#a5

http://www.scribd.com/doc/17298925/the-UMTS-Architecture

http://www.3gpp.org/Technologies/Keywords-Acronyms/article/ims