Showing posts with label Network Architecture. Show all posts
Showing posts with label Network Architecture. Show all posts

Saturday, 4 July 2020

An Introduction to Vehicle to Everything (V2X) and Cellular V2X (C-V2X)


We made an introductory tutorial explaining vehicle to everything. There are 2 different favours of V2X as shown in this tweet below


One is based on IEEE 802.11p (802.11bd in future). It is known by different names, DSRC, ITS-G5, etc. The other is the cellular V2X or C-V2X. It started as basic D2D but has evolved over the time. The slides and video are embedded below but this topic will need revisiting with more details.







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Tuesday, 9 June 2020

5G Roaming with SEPP (Security Edge Protection Proxy)

SEPP (Security Edge Protection Proxy) is part of the roaming security architecture as shown in the figure above. Ericsson's article, "An overview of the 3GPP 5G security standard" describes the use of SEPP as follows:

The use of SBA has also pushed for protection at higher protocol layers (i.e. transport and application), in addition to protection of the communication between core network entities at the internet protocol (IP) layer (typically by IPsec). Therefore, the 5G core network functions support state-of-the-art security protocols like TLS 1.2 and 1.3 to protect the communication at the transport layer and the OAuth 2.0 framework at the application layer to ensure that only authorized network functions are granted access to a service offered by another function.

The improvement provided by 3GPP SA3 to the interconnect security (i.e. security between different operator networks) consists of three building blocks:

  • Firstly, a new network function called security edge protection proxy (SEPP) was introduced in the 5G architecture (as shown in figure 2). All signaling traffic across operator networks is expected to transit through these security proxies
  • Secondly, authentication between SEPPs is required. This enables effective filtering of traffic coming from the interconnect
  • Thirdly, a new application layer security solution on the N32 interface between the SEPPs was designed to provide protection of sensitive data attributes while still allowing mediation services throughout the interconnect

The main components of SBA security are authentication and transport protection between network functions using TLS, authorization framework using OAuth2, and improved interconnect security using a new security protocol designed by 3GPP.

NG.113 5G Roaming Guidelines v2.0 clarifies:

4.2 Inter PLMN (N32) Interface

The Inter-PLMN specification 3GPP TS 29.573 has been produced by 3GPP to specify the protocol definitions and message flows, and also the APIs for the procedures on the PLMN (Public Land Mobile Network) interconnection interface (i.e. N32)

As stated in 3GPP TS 29.573 the N32 interface is used between the SEPPs of a VPLMN and a HPLMN in roaming scenarios. Furthermore, 3GPP has specified N32 to be considered as two separate interfaces: N32-c and N32-f.

N32-c is the Control Plane interface between the SEPPs for performing the initial handshake and negotiating the parameters to be applied for the actual N32 message forwarding. See section 4.2.2 of 3GPP TS 29.573.

Once the initial HTTP/2 handshake is completed the N32-c connection is torn down. This connection is End-to-End between SEPPs and does not involve IPX to intercept the HTTP/2 connection; although the IPX may be involved for IP level routing.

N32-f is the Forwarding interface between the SEPPs, that is used for forwarding the communication between the Network Function (NF) service consumer and the NF service producer after applying the application level security protection. See section 4.2.3 of 3GPP TS 29.573.

N32-f can provide Application Level Security (ALS) as specified in 3GPP TS 33.501 between SEPPs, if negotiated using N32-c. ALS provides the following protection functionalities: -

  • Message protection of the information exchanged between NF service consumer and producer
  • Forwarding of the application layer protected message from a SEPP in one PLMN to another PLMN by way of using IPX providers on the path. The IPX providers on the path may involve the insertion of content modification instructions which the receiving SEPP applies after verifying the integrity of such modification instructions.

The HTTP/2 connection used on N32-f is long lived; and when a SEPP establishes a connection towards another PLMN via IPX, the HTTP/2 connection from a SEPP terminates at the next hop IPX.

N32-f makes use of the HTTP/2 connection management requirements specified in 3GPP TS 29.500. Confidentiality protection shall apply to all IE’s for the JOSE protected message forwarding procedure, such that hop-by-hop security between SEPP and the IPXs should be established using an IPSec or TLS VPN.

If an IPX is not in the path between SEPPs, then an IPSec of Transport Layer Security, TLS VPN will be established directly.

Note: N32-f shall use “http” connections generated by a SEPP, and not “https”

The SEPP will act as a non-transparent Proxy for the NF’s when service based interfaces are used across PLMNs, however inside IPX service providers, an HTTP proxy may also be used to modify information elements (IE’s) inside the HTTP/2 request and response messages.

Acting in a similar manner to the IPX Diameter Proxy used in EPC roaming, the HTTP/2 Proxy can be used for inspection of messages, and modification of parameters. 


The picture in the tweet above shows how SEPP will play a role in Local Break Out (LBO) roaming as well as Home Routed (HR) roaming.

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Saturday, 4 April 2020

5G eXtended Reality (5G-XR) in 5G System (5GS)


We have been meaning to make a tutorial on augmented reality (AR), virtual reality (VR), mixed reality (MR) and extended reality (XR) for a while but we have only managed to do it. Embedded below is video and slides for the tutorial and also a playlist of different use cases on XR from around the world.

If you are not familiar with the 5G Service Based Architecture (SBA) and 5G Core (5GC), best to check this earlier tutorial before going further. A lot of comments are generally around Wi-Fi instead of 5G being used for indoors and we completely agree. 3GPP 5G architecture is designed to cater for any access in addition to 5G access. We have explained it here and here. This guest post also nicely explains Network Convergence of Mobile, Broadband and Wi-Fi.





XR use cases playlist



A lot of info on this topic is from Qualcomm, GSMA, 3GPP and 5G Americas whitepaper, all of them in the links in the slides.


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Wednesday, 1 April 2020

A Look into 5G Virtual/Open RAN - Part 2


In the first blog post of this series the different virtual RAN functions, interfaces and protocols have been discussed. Now it is time to have a look at a set of procedures that are required for the establishment of an UE connection in virtual 5G RAN.

The Big Picture

In 5G standalone RAN the crucial elements for user plane payload transport of an UE connection are  GTP/IP transport tunnels and a dedicated radio bearer on the radio interface.

When looking at the 5G RAN there are two of such tunnels: one on NG-U (aka N3) that is controlled by NGAP, and one on F1-U that is controlled by F1AP - see figure 1.

On behalf  of these two tunnels payload data can be transported between the 5G core network User Plane Function (UPF) to the gNB Distributed Unit (gNB-DU) and vice versa. For the transport over the 5G RAN fronthaul (realized e.g. as eCPRI) and across the radio interface a dedicated radio bearer (DRB) for the user plane transport must be configured by the gNB Central Unit for the Control Plane (gNB-CU CP).

As in LTE it is the RRC protocol that establishes this DRB. However, due to the virtualization the different protocol layers for the air interface are also distributed and the gNB-DU is in charge of all the lower layer PHY/RLC/MAC parameters (e.g the c-RNTI), while the gNB-CU CP assigns higher layer parameters of PDCP and RRC like the DRB-ID. Since only the gNB-CU CP can send downlink RRC messages to the UE the lower layer parameters from the DU first need to be sent in uplink direction to the gNB-CU CP.

Beside this parameter exchange the F1AP is also responsible for the tunnel management of the F1-U Tunnel.

The downlink tunnel endpoint information is provided by the gNB-DU using F1AP, but the uplink tunnel endpoint terminates at the gNB-CU UP and thus, its endpoint parameters are received by the gNB-CU CP when it exchanges information with the gNB-CU UP on behalf of the E1AP protocol.

Figure 1: Network Functions, Protocols and Parameters involved in Setup of User Plane Data Transmission Resources
(click on the image to see full size)
A similar situation we see for the NG-U tunnel that is controlled by NGAP, the protocol for communication between gNB-CU CP and the Access and Mobility Management Function (AMF) in the 5G core. Neither the gNB-CU CP nor hte AMF have direct access to the NG-U tunnel endpoints. Hence, E1AP is used again to transmit the downlink tunnel parameters to the gNB-CU CP while the uplink tunnel endpoint parameters must be sent by the UPF to the Session Management Function (SMF) using the Packet Forwarding Control Protocol (PFCP) and later by the SMF to the AMF over the service-based interface where the tunnel endpoint parameters are embedded in a JavaScript Object Notation (JSON) container.

By the way, JSON is a quite generic format for exchanging and storing different kind of data. Between the AMF and the SMF JSON is used to transport Non-Access Stratum Session Management messages (defined in 3GPP 24.501).

The Ladder Diagram

Having the Big Picture in mind it is now easier to look at the ladder diagram with the individual RAN messages for UE connection setup - shown in Figure 2.

It looks complicated, because the F1AP messages carry RRC plus NAS messages in uplink and downlink direction, but when understanding the underlying logic it is easy.

Figure 2: 5G VRAN Successful UE Connection Setup
(click on the image to see full size)

The very first step (in the figure: step 0) is the random access procedure executed on the MAC layer involving the UE and the gNB-DU.

After successful random access the UE sends the NR RRC Setup Request message. This is the Initial UL RRC Message transported by the F1AP from the gNB-DU to the gNB-CU CP. Actually the F1AP carries PDCP transport blocks and inside the PDCP the NR RRC messages are found, but to keep it simple I do not show the PDCP header in the ladder diagram.

Beside RRC Setup Request there are also some other initial NR RRC messages and RRC response messages possible (see step 1 and 2).

More RRC messages are transported over F1AP until the RRC Connection establishment is complete.

The NR RRC Setup Complete message also transports the initial NAS message and the reception of this message by the gNB-CU CP triggers the setup of a F1AP UE context. The concept of UE context management in F1AP is the same as in NGAP or - when looking back into the E-UTRAN - in S1AP.

The GTP/IP transport tunnel on F1-U is established during F1AP UE Context Setup assisted by E1AP Bearer Context Setup procedure that provides the necessary tunnel endpoint parameters.

In the same manner the NG-U tunnel is established by the NGAP Initial UE Context Setup procedure.

Additional NAS messages (especially for session management) and NR RRC Reconfiguration are exchanged to establish the end-to-end UE connection through the core network. And that's it.

Sunday, 1 March 2020

5G Private and Non-Public Network (NPN)


Private Networks have been around for a while and really took off after 4G was launched. This is due to the fact that the architecture was simplified due to the removal of CS core and also the advancements in silicon, storage, computation, etc. allowed creation of smaller and more efficient equipment that simplified private networks.

While private networks imply an isolated network for selected devices that are allowed to connect on to the network, Non-Public Networks are much broader in scope. Chief among them is the ability of certain devices to be capable of working on Private as well as Public Network or roaming between them.

I recently ran a workshop on 'Introduction to Private 4G & 5G Networks' with a well known Industry analyst Dean Bubley. One of the sections looked at the Network Architecture based on the 3GPP standards. This tutorial is a part of that particular section. Slides and video embedded below. There are also some interesting videos on YouTube that show how and why Private Networks are needed and some use cases. The playlist is embedded in the end.






Playlist of Private Networks Use Cases.



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Wednesday, 12 February 2020

AI your Slice to 5G Perfection


Back in November, The Enhanced Mobile Broadband Group in CW (Cambridge Wireless) held an event on 'Is automation essential in 5G?'. There were some thought provoking presentations and discussions but the one that stood out for me was by Dan Warren from Samsung


The slides are embedded below but I want to highlight these points:
  • Some Network Functions will be per slice whereas others will be multi-slice, the split may not be the same for every slice
  • Two slices that have the same 'per slice vs multi-slice' functional split may be different network hardware topologies
  • Enterprise customers will likely want a 'service' contract that has to be manifested as multiple slices of different types. 
  • Physical infrastructure is common to all slices
The last point is very important as people forget that there is a physical infrastructure that will generally be common across all slices.

Again, when you apply Artificial Intelligence (AI) to optimize the network functions, does it do it individually first and then end-to-end and if this is applied across all slices, each of which may have a different functionality, requirement, etc. How would it work in practice?




As Dan says in his tweet, "It is hard to implement AI to optimise a point solution without potentially degrading the things around it.  Constantly being pushed to a bigger picture view => more data => more complexity"

Let me know what you think.

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Friday, 31 January 2020

Prof. Andy Sutton: Backhauling the 5G Experience - Jan 2020


Prof. Andy Sutton has shared quite a few presentations and talks on this blog. His presentations from the annual 'The IET 5G Seminar' has made it to the top 10 for the last 3 years in a row. His talk from 2019, 2018 & 2017 is available for anyone interested.

The title of this year's conference was '5G 2020 - Unleashed'. The details are available here and the video of all the talks are here. As always, the slides and video is embedded below.

Slides



Video


There are a lot of bands that keep on getting mentioned, especially in relation to backhaul. Here is a summary of these bands that would come handy.



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Wednesday, 4 December 2019

Challenges of 5G Inter-Node Handovers

In all mobile communication networks handovers are the most complex signaling procedures, because multiple network elements (or network functions) are involved. Thus, it is logical that dual connectivity with two different base stations contributing to the radio connection simultaneously are even more complicated. And in EN-DC these two base stations are often covering different footprints using different carrier frequencies.This leads to a situation where we have more options for performing a handover in detail compared with plain LTE handover scenarios before.

The two signaling scenarios presented below illustrate in which different ways a change of the LTE master eNodeB can be performed during an ongoing EN-DC radio connection by using the X2 interface. In a very similar way it is also possible to perform S1 handover from old to new MeNB.

The pros and cons of these options have been discussed already by Martin Sauter in his Wireless Moves blog.

Inter-MeNB Handover without 5G Inter-Site Anchor

Figure 1 shows the easiest way of handing over the signaling connection from one MeNB to another one. Here it is up to the new MeNB to decide if and how the 5G part of the radio connection is continued.

Figure 1: X2 Handoverof EN-DC connection without 5G inter-site anchor

The handover is triggered when the UE sends a RRC Measurement Report (step 1) indicating that a stronger 4G cell than the currently used primary cell was measured. From its neighbor list the current MeNB detects that this better cell belongs to a neighbor eNB.

To provide both, the the Master Cell Group (MCG) and Secondary Cell Group (SCG) parameters to this neighbor eNB the old MeNB queries the SCG configuration parameters from the old SgNB by performing the X2AP SgNB Modification procedure (step 2+3).

Then it sends the X2AP Handover Request message to the target MeNB (step 4) including all information necessary to continue the 5G radio link in case the target MeNB decides to go for this option.

However, what comes back from the target MeNB is a plain LTE handover command (LTE RRC Connection Reconfiguration message [step 6]) embedded in the X2AP Handover Request Acknowledge message (step 5).

Due to this the old MeNB releases all 5G resources and the UE context in the SgNB (steps 7 + 10).

After the UE  successfully connected via radio interface with the target cell in the new MeNB the S1AP Path Switch procedure is executed to re-route the GTP/IP-Tunnels on S1-U (step 8) and releases the X2 UE context in the old MeNB (step 9)

The new MeNB then waits for a new inter-RAT measurement event B1 (step 11) before starting a new SgNB addition procedure (step 12).  Once the SgNB addition is successfully completed including all necessary reconfigurations/modifications on RRC and S1 the payload transmission over 5G resources is continued.

Inter-MeNB Handover with 5G Inter-Site Anchor

Now figure 2 shows what happens when the new MeNB decides to keep the existing UE context in the SgNB while the RRC measurement results and parameters are identical with what was presented above. 
Figure 2: X2 Handoverof EN-DC connection with 5G inter-site anchor

The difference in the call flow starts at step 5 when the new MeNB after receiving the X2AP Handover Request (step 4) starts the X2AP SgNB Addition procedure towards the SgNB (old = new!). The SgNB-UE-X2AP-ID earlier requested in step 2+3 acts as the reference number for the existing context that is going to be continued.

After adding the SgNB UE context successfully the new MeNB sends the X2AP Handover Request Acknowledge message including an UE Context Kept = "true" flag and the Handover Command (step 8).

After the UE successfully connected to the target cell of the new MeNB the S1AP Path Switch procedure is performed and the temporary X2 UE context between old and new MeNB is released (step 10).

The big advantage of handling the handover in this way: The duration of the interruption of the payload transmission over 5G radio resources is minimalized and subscriber experience is significantly better compared to the scenario in figure 1.

Monday, 2 December 2019

Guest Post: Exploring Network Convergence of Mobile, Broadband and Wi-Fi

This is a guest post by Ben Toner, Founder and Director, Numerous Networks


Are multiple networks better than one?

How many articles have you read with a title similar to "Which technology is better, 5G or Wi-Fi6?" If, like me, you regularly use Wi-Fi and cellular (I still use 4G though) then you might find it hard to take sides.

Enter Network Convergence - the concept of bringing multiple networks together to get the best of them all. Imagine, as an end user, not having to decide which network to use but instead feeling satisfied that your data was traversing the best combination of networks at that moment in time.

Imagine a business traveler being connected to Wi-Fi which is slow or busy while trying to take that all important conference call while sitting in an airport. Because you are roaming you want to use that Wi-Fi but you do not want to compromise the video call quality. If your network and device could work together to use just enough cellular data to supplement the slow Wi-Fi so that you stayed within your daily roaming quota but never lost a moment in the video call - then you would probably be very happy with that service. Better still, as you start walking off, if the call transitioned from Wi-Fi to cellular with no dropouts or hangup then you might be delighted!

Earlier I underlined best because that in itself is somewhat complicated.  The example above is easy to desribe but quite hard for to achieve within a framework where all possible scenarios are handled that well, for every user. The common questions which need to be factored into any such choice are:
  • What do I as the end user want? 
  • What performance can each network deliver. 
  • How important is the transfer of content at that time and 
  • How much am I willing to pay for it (how many MB of my data plan am I willing to use?). 

This is one of the challenges that we cannot easily solve today, but technology is being developed to help in that process. The operators and device vendors are working within standardisation to develop technology which can provide such a converged service. However at this time there is still a rules mechanism behind it all which does not really describe how user input and preference is going to be captured.

In the last 10 years I have witnessed many battles within service providers when deciding what "one size fits all" service to offer everyone when deciding how to make service provider Wi-Fi available to their customers; all fuelled by my points above.

A lot of concepts are well designed and somewhat mature but deciding exactly what will be implemented in standards is currently ongoing.

In the following slides and video I introduce this whole concept of Network Convergence. The following content introduces the concept and then takes a detailed look at the ATSSS; technology being defined in 3GPP. I also have highlighted the technologoies you can get hold of today to try out network convergence.

I encourage you all to download the example technologies and try convergence for yourself. I'm eager to hear opinions of what technologies work best for each of you. And better still, what is not being provided which you think should be...

Looking forward to your feedback and answering your questions...





Ben Toner
Founder and Director, Numerous Networks


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Friday, 22 November 2019

5G Call Drops in EN-DC: A Thread for Service Quality?


As explained in the post about EN-DC setup the addition of 5G NR radio resources to an ongoing LTE connection provides additional bandwidth for user plane data transmission. And it seems to be fair to say that at least in social media today 5G speed test results, especially throughput measurements, are treated as the benchmark for EN-DC service performance. Hence, it is also logical that a loss of the physical 5G radio link (5G drop) could have a serious impact on user experience.

I write "could", because as a matter of fact many 5G drops will not be recognized by subscribers using non-realtime services including HTTP streaming.

Due to the dual connectivity of LTE Master eNodeB (MeNB) and Secondary gNodeB (SgNB) the signaling trigger points indicating a 5G drop are also a bit more complex compared to what we know from LTE. Indeed, both network nodes are able to release 5G radio resources abnormally using three different X2AP message flow scenarios as shown in figure 1.

Figure 1: Three Basic Signaling Flows for Abnormal Release of 5G Radio Resources

Which of these individual message flows will be found in the trace data depends on which of the two base stations is the first one that detects a problem on the 5G radio link.

A particular case that is seen quite often in live networks is illustrated in figure 2.

Figure 2: 5G Drop due to SGC Failure in UE



Here the trigger is a LTE RRC SCG Failure Information NR message sent by the UE to the MeNB. Thus, the MeNB requests the release of 5G radio resources, which is acknowledged and executed by the SgNB.

In addition (not show in the figures) also the GTP/IP-Tunnel for user plane transport between S-GW and gNB is released by the MeNB after successful completion of the X2AP SgNB Release procedure.

For the UE the 5G drop is not as serious as a drop of the LTE radio connection would be. It is just a fallback on plain LTE, so to say. And after the switching the GTP/IP-Tunnel back to a downlink endpoint at the eNB 4G payload transmission continues.

The longer the overall duration of the radio connection the higher is the risk that the 5G radio resources are lost during an EN-DC call. One of my favorite cases is a subscriber with a radio connection that last a bit more than two and a half hours - see figure 3.

Figure 3: Location Session Record of a Single Subscriber indicating a total number 340 SgNB Drops over 2:33 Hours

Thanks to the smart algorithms of NETSCOUT's TrueCall geolocation engine there is high confidence that she or he sits in an indoor environment, but is served by an outdoor 5G cell. Thus, the penetration loss of the 5G signal is significant. Due to the higher frequency the path loss has also higher impact on the 5G than on the 4G radio signal. This seems to be the main reason why the 5G radio link drops as often as 340 times, which leads to an overall 5G (SgNB) Drop Rate of 83% for this connection.

However, the impact on the subscriber experience might not be a serious one as a different KPI, the 5G EN-DC Duration Rate indicates. According to the Duration Rate 99.99% of all the time 5G radio resources have been available for the subscriber. This is possible, because as also shown in figure 2 within a relatively short time new 5G radio resources are allocated again to this connection. Even if the subscriber is watching e.g. a Netflix video the buffering of already downloaded data on the end user device should be sufficient to conceal the short interruption of the data transfer over 5G resources.

With rising amount of EN-DC traffic it might be rather problematic for the network to handle the additional signaling load originating from the frequent 5G additions and releases. In extreme cases this may even lead to congestion due to CPU overload in RAN nodes or virtual network functions.

For realtime services like Voice over New Radio (VoNR) the entire situation changes. Here even short interruptions of the user plane radio transmission can be perceived by subscribers so that the above discussed 5G Duration Rate KPI will become insufficient to estimate the service quality. Hence, this will drive the demand for a fully integrated view of 5G RAN and Core KPIs covering both, signaling and application quality.




Thursday, 7 November 2019

Introduction to 5G ATSSS - Access Traffic Steering, Switching and Splitting


Last month we made a short tutorial on 5G and Fixed-Mobile Convergence (FMC). One of the features covered in that was ATSSS. It deserved a bit more detail so we made a short tutorial on this feature.

Access Traffic Steering, Switching and Splitting or ATSSS for short is being standardized as part of 3GPP Rel-16 and allows traffic steering across multiple accesses at a finer granularities than a PDU session.  It is an optional feature both on the UE and the 5GC network. ATSSS introduces the notion of Multi Access PDU session, a PDU session for which the data traffic can be served over one or more concurrent accesses (3GPP access, trusted non-3GPP access and untrusted non-3GPP access). The simplest way to visualize it is as shown below:


The presentation and video is embedded below:







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Tuesday, 22 October 2019

From traditional RAN to Open RAN - O-RAN: Goals and Challenges


My Open RAN tutorial has recently gained popularity with recent announcements from Altiostar, Mavenir, Parallel Wireless, Telefonica and Vodafone. With TIP Summit in few weeks time, I am hoping for a lot more curious people to discover that blog post and video.

Olivier Simon, Director, Radio Innovation, Orange spoke about "O-RAN: Goals and Challenges" at Open Networking Summit Europe 2019. In his presentation, he explained how O-RAN will trigger more intelligence and openness in the RAN domain. He talked about which use cases will require this new architecture and why O-RAN is coming at the right time. Major architectural change are necessary in the next years in order to improve E2E latency and benefit from the flexibility of virtualized network functions. O-RAN will provide the right framework in order to perform this transformation in an open manner and keeping at the same time economies of scale thanks to a global adoption.


The presentation also touches on O-RAN Software Community. The O-RAN Alliance recently partnered with the Linux Foundation to establish the O-RAN-Software Community (O-RAN-SC), to provide that open source software application layer to the RAN. O-RAN-SC will foster development of an open source infrastructure platform for running 5G RAN solutions.

The key aspects of ORAN-SC are:
  • New Open Community focused on RAN Software in collaboration with O-RAN Alliance
  • Set up for collaboration across OPNFV, ONAP, Akraino and other Open Source projects

Here is the video of the conference embedded below:



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Tuesday, 24 September 2019

When does your 5G NSA Device Show 5G Icon?


After I wrote about the 5G Icon Display back in February, I received lots of other useful and related materials, mostly from 3GPP standards delegates. Based on this updated information, I created a presentation and video called 'The 5G Icon Story'. Only recently did I realize that I didn't add it to the blog. So here it is.

And for people who are impatient and directly want to jump to the main point, it's UpperLayerIndication in SIB 2 as can be seen above.

The slides and video is embedded below.





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Sunday, 15 September 2019

Thursday, 12 September 2019

How the Addition of 5G Radio Resources Increases the Complexity of LTE Signaling Procedures


While everybody is excited about the growing number of 5G deployments and speed test results it is easy to forget that a highly reliable LTE core and radio access network is the prerequisite for 5G non-standalone (NSA) data transmission.

Indeed, the 5G radio resources are just added to the ongoing LTE connection to provide higher bandwidth that enables in turn higher throughput. In other words: the current 5G deployments are designed for and limited to the needs of enhanced Mobile Broadband (eMBB) traffic.

To boost the user experience a 4G and a 5G base station cooperate and bundle there joint resources in one radio connection. The whole scenario is known as E-UTRA-NR Dual Connectivity (EN-DC) and as a matter of fact this dual connectivity increases the complexity of the RAN signaling tremendously.

The figure below shows the two base stations involved in the radio connection. On the left side is the Master eNodeB (MeNB) that controls the entire signaling connection. On the right side sits the en-gNB, also called Secondary gNodeB (SgNB). The inconsistency of acronyms originates from 3GPP specs. 3GPP 37.340 "E-UTRA and NR Multi-connectivity" can be seen as an umbrella document that originally coined "MeNB" and "SgNB". However, when standarizing more details these acronyms have been replaced with Master Node (MN) and Secondary Node (SN) and the latter is named "en-gNB" when used in EN-DC scenarios. (Sure this spec has a lot more terms to offer an is a must-read for every acroynm enthusiast.)

However, these naming conventions defined in 3GPP 37.340 have not made it into the protocol specs, especially not into 3GPP 36.423 "X2 Application Part" that names its message set for enabling EN-DC consequently "SgNB ...." - as also shown in the figure.

By the way the SgNB should also not be imagined as a single network element. On the 5G side often a virtual RAN architecture is already deployed. In such a VRAN a gNB central unit (CU) controls several gNB distributed units (DUs) and multiple remote radio heads (RRHs) including the 5G antennas can be connected to each DU.



5G Radio Resource Addition in EN-DC Mode

Before 5G radio resources can be added to the connection a LTE RRC connection and at least a default bearer for the user plane including its GTP/IP-Tunnel between S-GW and eNB must have been successfully established.

The trigger for adding 5G resources to this call is mostly an inter-RAT measurement event B1 (not shown in the figure). However, also blind addition of a 5G cells have been observed in some cases where the 5G cell coverage is expected to overlap exactly the footprint of the LTE master cell. 

All in all, there can be a 1:1 mappig between 4G and 5G cells when antennas are mounted very close to each other and pointing into the same direction. However, it is also possible that several 5G small cells (especially when using FR2 frequency bands) are deployed to cover the footprint of a 4G macro cell. 

The end-to-end signaling that adds 5G resources to the connection starts with the X2AP SgNB Addition Request message (1). It contains information about the active E-RABs of the connection, UE NR capabilities and often the singal strenght of the 5G cell as measured before is included as well. The message triggers allocation of 5G radio resources in the SgNB.

Similar to a X2 handover procedure the X2AP SgNB Addition Request Acknowledge message (2) is used to transport a NR RRC CG-Config message (3) back to the MeNB where it is "translated" into NR RRC Connection Reconfiguration and NR RRC Radio Bearer Config messages that are sent to the UE enclosed in a LTE RRC Connection Reconfiguration message. In these messages beside the Cell Group ID the 5G PCI and the absolute SSB frequency (a synonym for NR ARFCN) are found. Both, 5G PCI and SSB frequency in combination represent the identity of a 5G cell "visible" for the UE on the physical 5G radio interface. 

To keep the figure more simple I have spared the "translation" process in MeNB and show instead as next step the combined LTE/NR RRC Connection Reconfiguration Complete (4) that is send by the UE back to the MeNB to confim activation of the 5G radio link. 

After this the UE and the SgNB are ready to the 5G resources for radio transmission. However, one important component is still missing: a new GTP/IP-Tunnel for transporting the payload from the core network's serving gateway (S-GW) to the SgNB. 

The gNB downlink transport layer address (gNB DL TLA) and its appropriate GTP Tunnel Endpoint Identifier (TEID) have been already to the MeNB in step (2). Indeed, there are some more TLAs and TEIDs found in this X2AP message, especially for data forwarding across the X2 user plane interface (not shown in figure).

The MeNB forwards the gNB DL TLA/TEID to the MME (6) where it is forwarded to the S-GW using GTP-C signaling in case the two core network elements are connected over S11 reference point. The uplink TLA/TEID on the S-GW side remain the same as assigned before during establishement of the E-RAB (not shown in figure). So the new tunnel is now ready to be used (7) and transmission of payload packet starts immediately. 

In step (8) the MME confirms the successful tunnel establishment to the MeNB.

To total duration of the entire procedure from step (1) to (8) sums up to slightly more than 100 ms under lab conditions and typically around 300 ms in the live network. 

This delay does not have a direct impact on user plane latency in the initial 5G setup phase. However, the subscriber experience might be different when it comes to inter-MeNB handover, because there is no direct handover between 5G neighbor cells. 

Changing the MeNB due to subscriber mobility means: release all 5G resources on the source (M)eNB side, perform intra-LTE handover to the target (M)eNB and add new 5G resources after handover is successfully completed. 

Monday, 5 August 2019

An Introduction to Non-Terrestrial Networks (NTN)


I made a short introductory tutorial explaining what is meant by Non-Terrestrial Networks. There is is lot of work on this that is planned for Release-17. Slides and video below.






Related Posts:

Thursday, 7 March 2019

Updated 5G Terminology Presentation (Feb 2019)


I made this video before MWC with the intention to educate the attendees about the various architecture options and 5G terminologies being discussed. As always, happy to get feedback on what can be done better. Slides followed by video below.







Complete list of our training resources are available on 3G4G page here.

Tuesday, 12 February 2019

Prof. Andy Sutton: 5G Radio Access Network Architecture Evolution - Jan 2019


Prof. Andy Sutton delivered his annual IET talk last month which was held the 6th Annual 5G conference. You can watch the videos for that event here (not all have been uploaded at the time of writing this post). His talks have always been very popular on this blog with the last year talk being 2nd most popular while the one in 2017 was the most popular one. Thanks also to IET for hosting this annual event and IET Tv for making this videos available for free.

The slides and video is embedded below but for new starters, before jumping to this, you may want to check out about 5G Network Architecture options in our tutorial here.




As always, this is full of useful information with insight into how BT/EE is thinking about deploying 5G in UK.

Related Posts:

Thursday, 3 January 2019

Nice short articles on 5G in 25th Anniversary Special NTT Docomo Technical Journal

5G has dominated the 3G4G blog for last few years. Top 10 posts for 2018 featured 6 posts on 5G while top 10 posts for 2017 featured 7. In makes sense to start 2019 posting with a 5G post.

A special 25th Anniversary edition of NTT Docomo Technical Journal features some nice short articles on 5G covering RAN, Core, Devices & Use cases. Here is some more details for anyone interested.

Radio Access Network in 5G Era introduces NTT Docomo's view of world regarding 5G, scenarios for the deployment of 5G and also prospects for further development of 5G in the future. The article looks at the main features in 5G RAN that will enable eMBB (Massive MIMO), URLLC (short TTI) and mMTC (eDRX).

Interested readers should also check out:

Core network for Social Infrastructure in 5G Era describes the principal 5G technologies required in the core network to realise new services and applications that will work through collaboration between various industries and businesses. It also introduces initiatives for more advanced operations, required for efficient operation of this increasingly complex network.

This article also goes in detail of the Services Based Architecture (SBA). In case you were wondering what UL CL and SSC above stands for; UpLink CLassifiers (UL CL) is a technology that identifies packets sent by a terminal to a specific IP address and routes them differently (Local Breakout) as can be seen above. It is generally to be used to connect to a MEC server. Session and Service Continuity (SSC) is used to decide if the IP address would be retained when the UE moves to a new area from the old one.

Interested readers should also check out:
Evolution of devices for the 5G Era discusses prospects for the high-speed, high-capacity, low-latency, and many-terminal connectivity features introduced with 5G, as well as advances in the network expected in the future, technologies that will be required for various types of terminal devices and the services, and a vision for devices in 2020 and thereafter.

According to the article, the medium term strategy of R&D division of NTT Docomo has three main themes: 5G, AI and Devices. In simple terms, devices will collect a lot of data which will become big data, 5G will be used to transport this data and the AI will process all the collected Big Data.

NTT Docomo has also redefined the devices as connecting through various technologies including cellular, Wi-Fi, Bluetooth & Fixed communications.

Interested readers should also check out:

The final article on 5G, Views of the Future Pioneered by 5G: A World Converging the Strengths of Partners looks at field trials, partnerships, etc. In fact here the embedded video playlist below shows some of these use cases described in the article



In addition there are other articles too, but in this post I have focused on 5G only.

The 25th Anniversary Special Edition of NTT Docomo Technical Journal is available here.