SMEC WHITE PAPER
March 2016
LTE Femto Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE
infrastructure
Presented by
Y.C. Lee
Chief Researcher, SMEC
www.esmec.com | www.newgrid.com
Dr. Harrison Jangwoo Son
Chief Analyst and CEO, Netmanias
www.netmanias.com
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
Table of Contents
1. Introduction
2. HeNB-GW: Benefit and Issues
2.1 Benefits
2.2 Issues X2 Handover Support
3. SMEC HeNB-GW Solution
3.1 SMEC HeNB-GW
3.2 X2 Service Broker
3.3 X2 Service Broker Operation
10
4. Benefits of SMEC HeNB-GW
13
Acronyms
15
Table of Figures
Figure 1-1. Key values provided by femtocell in 4G era
Figure 2-1. Handover options between macro eNB and HeNBs: S1 vs. X2
Figure 2-2. Issues: scalability and uncertainty
Figure 3-1. SMEC HeNB-GW architecture/concept
Figure 3-2. Benefits of X2 broker: scalability and stability
Figure 3-3. SMEC X2 service broker: HeNB ID planning
10
Figure 3-4. SMEC X2 service broker: HeNB1 initiates
TNL address discovery procedure towards an MeNB
10
Figure 3-5. SMEC X2 service broker: X2 setup between HeNB1 and MeNB
11
Figure 3-6. SMEC X2 service broker: Subsequent X2 connection setups
12
Figure 3-7. SMEC X2 service broker: Logical configuration
12
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
1. Introduction
An LTE femtocell* (HeNB) is an ultra-small cellular base station that connects to a mobile operators LTE core
network via broadband Internet. Using this femtocell, a mobile operator can eliminate indoor shadowing
areas, thereby extending LTE service coverage and improving call quality. The mobile operator can benefit
from the femtocell as it allows LTE traffic to be distributed between macro eNB and femtocells at home and
also at indoor and outdoor hotspots in crowded places like coffee shops, restaurants, bus stop, malls, schools,
and so on. This helps the operator to effectively reduce loads at macro cells and in the backhaul, and provide
its users with better QoE.
The beauty of LTE femtocell is that, as all it takes is simply connecting existing broadband Internet to an ultrasmall base station, it gives the advantage of quick deployment. It also minimizes additional costs and burdens
that may be imposed in case of building macro cells, in relation to installation site acquisition, site rental,
power supply, construction of backhaul network, etc. Such benefits make it one of the most cost-effective
ways to expand coverage and capacity in an LTE network.
IMS/Internet
EPC core
IMS/Internet
HeNB-GW
EPC core
Mobile
backhaul
HeNB-GW
Mobile
backhaul
Internet
Macro eNB
Internet
Macro eNB
Fixed broadband
(DSL, Cable, FTTH)
Users fixed broadband
(DSL, Cable, FTTH)
LTE Femto
Handover
LTE Femto
Handover
Residential/SOHO
Hotspot
Coverage and Capacity
Voice continuity
5-bar
Figure 1-1. Key values provided by femtocell in 4G era
* Femtocell and HeNB are interchangeable, and so are Femtocell Gateway and HeNB Gateway in this document.
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
Years ago, mobile operators started building macro LTE networks, and have always been in the quest for
solutions to shadowing areas and high costs of operating multiple networks (2G, 3G and 4G) since then.
Recently, operators are pursuing a strategy to i) provide uninterrupted voice coverage without relying on
legacy networks like 2G or 3G by introducing small cells in shadowing areas and supporting seamless
handover between them and macro cells, and ii) ultimately migrate into an all LTE network through gradual
replacement of legacy networks. That is, many operators are pushing forward with this strategy to minimize
the total OPEX of the entire network by operating only one LTE network instead of multiple mobile networks.
Femtocells are considered the most likely candidate to serve this purpose. Meanwhile, operators without 2G
or 3G, but with LTE macro network, are also active in introducing LTE femtocells in their networks as a costeffective solution to enhance LTE coverage and capacity.
Here, what concerns the operators most is uncertainty that can be caused while these femtocells (HeNB).
Unlike existing macro cells, if deployed in a large scale in tens or hundreds of thousands, these cells can
cause unpredictable, operational risk while interworking with legacy LTE systems (EPC, eNB, etc.).
SMECs Femto GW (HeNB-GW), designed to work as a sponge to absorb such uncertainty and risk, helps to
operate the femto network just as stably as macro networks.
Chapter 2 will look into the benefits and issues of HeNB-GW, and chapter 3 will introduce HeNB-GW solution
of SMEC, specifically X2 broker feature in details. Chapter 4 will summarize the benefits of the SMEC solution.
LTE Femto Network Elements
An LTE Femto access network consists of HeNB, HeNB-GW, HeMS and SeGW as seen below. Their respective
roles in the network are as follows:
EPC
HeMS is a network element
management system for HeNB
access.
HeNB-GW provides femto users
with access to the LTE core
network. It acts as an access
gateway to HeNB and
concentrates connections from
a large number of HeNBs.
S1
HeMS
S1-MME
S1
S-GW
S1-U
Aggregation
HeNB-GW
S1
SeGW
IPsec
SeGW secures the
communication from/to the
HeNBs.
HeNB is a CPE that offers Uu
interface to UE and S1 interface
over IPSec tunnel to HeNB-GW
for accessing LTE core network
in femtocell access network.
MME
Internet
S1
HeNBUu
Uu
S1
S1-MME
S1-U
S1-MME
S1-U
HeNB
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Uu
Uu
Uu
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
2. HeNB-GW: Benefit and Issues
2.1 Benefits
Table 2-1 summarizes issues in connecting HeNBs directly to MME, without HeNB-GW, as compared to the benefits
of deploying HeNB-GW.
Table 2-1. Benefits of deploying HeNB-GW
Without HeNB-GW (HeNB directly connected to MME)
With HeNB-GW (HeNB connected to MME via HeNB-GW)
S1s of MME
MME Load
Per HeNB MME
signaling messages
MME
Paging
Overload control
SCTP heartbeat
MME
...
S1s of
MME
Per HeNB-GW
HeNB-GW
S1-MME
...
HeNBs
...
...
Macro eNB
HeNBs
...
Macro eNB
When HeNBs (LTE femtocells) are directly connected to
MME, MME establishes S1 interfaces (SCTP association)
independently with each HeNB as with macro eNB.
HeNB-GW terminates all SCTP connections between
HeNBs and MME, keeping only a few S1-MME
connections active for interaction with MME.
MME exchanges paging messages, overload control
messages, and SCTP heartbeat with each HeNB through
S1-MME (S1-AP over SCTP). So, tens or hundreds of
thousands of HeNBs in a commercial network means
heavy overload on MME - much heavier than
communicating with macro eNBs, Potentially
undermining stability and reliability of the LTE
network. Even in macro cells, paging accounts for 30%
of MME loads [Alcatel white paper].
MME exchanges paging messages, overload control
messages, and SCTP heartbeat with HeNB-GW instead
of many individual HeNBs, and it helps to keep the load
increase in MME as low as possible no matter how many
HeNBs there are.
Mass deployment of HeNBs results in overloaded MME,
which makes it inevitable to make additional investment
in MME to address the overload issue (e.g. purchasing
additional equipment and license).
HeNB-GW proactively prevents overload at existing MME
by tens of thousands of newly deployed femtocells. It
helps to bring down the costs for additional installation
of MME.
If the number of HeNBs added exceeds the maximum
number of eNBs that can be allowed per MME (i.e.
number of S1 interfaces), installation (or purchase of
additional licenses) of more MMEs becomes inevitable
regardless of the performance of MME.
HeNB-GW terminates all SCTP connections between
HeNBs and MME, keeping just a few S1-MME
connections active for interaction with MME. As a result,
no matter how many additional HeNBs are deployed, the
number of S1 interfaces additionally required at MME is
kept at a minimum.
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
2.2 Issues X2 Handover Support
Mobile operators prefer X2 handover that uses just X2 interface between eNBs to more complicated S1
handover that increases loads at MME. As seen in Figure 2-1(a), the more HeNBs are deployed, the more
hand-in and hand-out activities are performed between macro eNBs and HeNBs (particularly outdoors). This
means even more loads are caused at MME and S-GW by S1 handover, affecting the reliability of the LTE
network. For more reliable, secured operation of the LTE core network, X2 handover without MMEs
intervention is essential in a femto network (Figure 2-1(b)).
MME load
MME load
MME
MME
S1-MME
S1-MME
Macro eNB
S1-MME
Macro eNB
S1-MME
X2
X2
HeNB
(outdoor/open)
HeNB
(outdoor/open)
S1 signaling messages
X2 signaling messages
Handover between macro eNB and HeNB occurs
(a) S1 handover
(b) X2 handover
Figure 2-1. Handover options between macro eNB and HeNBs: S1 vs. X2
Macro eNB
X2
Macro eNB
Potential S1
uncertainty
One X2
connection
between macro
eNB and HeNB
X2
X2 X2 X2
MME
S1
X2
X2 X2
HeNB
eNB
HeNB
(a) X2 interface scalability issue of eNB
(b) Potentially undermining stability
and reliability of the LTE network
Figure 2-2. Issues: scalability and uncertainty
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
But in reality, supporting X2 handover in a femtocell environment is not easy because of possible scalability
and instability issues. If existing macro eNBs establish X2 connections directly with a large number of HeNBs,
scalability can be compromised due to the limit in the number of X2 connections that can be managed (Figure
2-2(a)). For X2 handover, existing MME and eNB must interact directly with HeNBs (S1-MME, X2), and this
process can bring about instability between the two (Figure 2-2(b)). Also, configuring X2 GW requires upgrade
of eNBs and HeNBs all to R-12, consequently aggravating the complexity of the network even further. These
issues have been an obstacle standing in the way of applying X2 handover between macro eNB and HeNB in
the commercial network. The HeNB-GW solution by SMEC is designed to address these issues. We will learn
how in chapter 3.
SMECs HeNB-GW helps to keep the impact of introducing LTE femtocell - even when massively
deployed - in the legacy LTE network low, as low as that of small scale addition of macro eNB. This
ensures the stability of the LTE core network remains unaffected and the additional investment costs
resulting from such deployment are kept to a minimum.
Hey, whats up?
MME
MME
Who?
B!
Hi, its me, eNB!
eNB
NB!
eN
,H
e
m
its
Hi,
SMEC
HeNB-GW
me, H
e
eNB
Hey, whats up?
Hi, it
s
Hi, its
me, He
NB
Hi, its
me, eN
B!
Who?
HeNB
HeNB
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
3. SMEC HeNB-GW Solution
3.1 SMEC HeNB-GW
The Figure 3-1 describes a high level view of LTE network with femtocell and SMEC HeNB-GW. SMEC HeNBGW can provide:
Virtual eNB (eNB ID based HeNB grouping)
X2 service broker (X2 proxy between eNB and HeNB)
S1 and X2 handover between eNB and HeNB
S1 signaling and bearer aggregation with SeGW functionality
EPC Core
MME
S1-MME
Virtual
eNB 1
HeNB-GW
S1-MME
S1-U
S1-MME
Virtual
X2
eNB n
(Closed and Trusted)
S1, X2
HeNB
S1-U
S-GW
S1, X2
HeNB 1
HeNB 256
HeNB Cluster 1
S1, X2
X2
S1-U
Macro
eNB
S1, X2
HeNB 1
HeNB 256
HeNB Cluster n
(Open and Untrusted)
Figure 3-1. SMEC HeNB-GW architecture/concept
SMEC HeNB-GW, technologically based on virtual eNB concept, can group a number of HeNBs for
management by group. Each virtual eNB, capable of aggregating 256 HeNBs, functions as a logical HeNB GW,
providing S1 interface to EPC and HeNBs, and X2 interface to macro eNB and HeNB. From a S1 interface point
of view, MME and S-GW see virtual eNB as one macro eNB, and HeNB sees it as MME and S-GW. Virtual
eNB provides the following functionalities in respect of S1 interfaces:
- Relaying UE-associated S1AP messages between MME and HeNB
- Terminating non-UE associated S1AP procedures towards HeNB and towards MME
- Terminating S1-U interfaces with HeNB and with S-GW
Virtual eNB, as a logical macro eNB, provides X2 interfaces. From X2 interface point of view, the macro eNB
sees virtual eNB as an eNB with 256 cells that offers following functionalities:
- Providing X2 interfaces between macro eNB and HeNBs
- Terminating non-UE associated X2AP messages between eNB and HeNB
- Converting UE-X2AP-ID between eNB and HeNB
- Routing UE-associated X2AP messages between eNB and HeNB
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
3.2 X2 Service Broker
SMEC HeNB-GW features X2 service broker for complexity and stability issues as seen in Figure 2-2. As shown
in Figure 3-2(b), each HeNB establishes X2 connection with virtual eNB (acting as a X2 service broker) at
SMEC HeNB-GW, and macro eNB establishes only one X2 connection with the virtual eNB. This X2 aggregation
function provided by X2 broker drastically reduces the number of X2 connections needed between macro
eNB and HeNBs (256 X2 connections to only one X2 connection). SMEC HeNB-GW makes existing macro eNBs
recognize it as another regular macro eNB, by hiding all the HeNBs behind its back.
Existing MME and eNB must interact directly with HeNBs (S1-MME, X2) for X2 handover, etc., and this can
bring about instability between the two. X2 broker, upon receiving S1 and X2 messages from HeNB, modifies
the messages as if it is eNB itself, and sends them to MME and eNB. This ensures the stability of the LTE core
network and eNB remains unaffected.
As a result, network complexity and unstability anticipated by deployment of HeNB can be significantly
decreased, and kept as low as in existing macro eNB network. LG U+, a South Korean LTE network operator,
has already deployed SMECs HeNB-GW, applying X2 handover between macro eNB and HeNBs in its
commercial network. The company has been able to keep the load level at MME at a minimum and provide
uninterrupted VoLTE service across femto hotspots in macro cells.
Virtual eNB
(X2 broker)
eNB
X2 X2 X2 X2
X2 X2 X2 X2
X2
(a) X2 interface scalability issue of eNB
eNB
X2
(b) X2 aggregation via X2 broker
MME
MME
Potential S1
uncertainty
S1
X2
eNB
X2
S1 Stable as Macro S1
eNB only
network
Virtual eNB
X2
eNB
(X2 broker)
S1
X2
HeNB
HeNB
(c) Potentially undermining stability and
reliability of the LTE network
(d) Protected by virtual eNB (X2 broker)
Figure 3-2. Benefits of X2 broker: scalability and stability
SMEC White Paper LTE Femtocell Gateway with X2 Broker
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
3.3 X2 Service Broker Operation
In order for X2 service broker to work, HeMS allocates HeNB IDs to HeNBs as seen in Figure 3-3. An HeNB ID is
28 bits long, and consists of i) an eNB ID (20 bits long), identical for all HeNBs (up to 256) that belong to the
same virtual eNB, and ii) a cell ID (8 bits long), unique for all the HeNBs (up to 256). This HeNB ID plaNning
scheme lets a macro eNB recognize a virtual eNB as just another macro eNB, and all the HeNBs belonging to it
as its cells.
Virtual eNB
1
HeNB 1
HeNB
...
HeNB 256
...
...
HeNB ID
(28 bits)
eNB ID (20b)
/Cell ID (8b)
Virtual eNB 1
/Cell 256
Virtual eNB 1
/Cell 1
Shared (20b)
Unique per HeNB (8b)
Figure 3-3. SMEC X2 service broker: HeNB ID planning
Detailed call flow for X2 broker operation is as follows:
HeNB1 initiates TNL address discovery procedure towards an MeNB: HeNB1 detects a new cell (cell A of
macro eNB) and decides to setup X2 towards Macro eNB (MeNB). It initiates an TNL address discovery
procedure by sending eNB Configuration Transfer message indicating its own HeNB ID (HeNB1, 28 bits long)
and MeNB ID (20 bits long) as neighbor information to virtual eNB through S1 interface.
The virtual eNB does not have any information on the MeNB's X2 IP address, and it must forward the message
to MME to find the X2 IP address of MeNB. Before forwarding the message, virtual eNB (X2 broker) replaces
the 28-bit HeNB ID with its own ID (virtual eNB, 20 bit long) in the message and forwards it to MME. MME
knows the MeNB and so sends an MME Configuration Transfer message to it (note that virtual eNB does not
disclose 28-bit-long HeNB ID to MME and MeNB).
MME
MME
S1: MME Config. Transfer
S1: eNB Config. Transfer
Virtual eNB(20bits), MeNB(20bits)
S1: MME Config. Transfer
MeNB(20bits), Virtual eNB(20bits)
X2 IP of MeNB
S1: eNB Config. Transfer
MeNB(20bits), Virtual eNB(20bits)
X2 IP of MeNB
Virtual eNB(20bits), MeNB(20bits)
HeNB-GW
Virtual eNB
(X2 broker)
S1: eNB Config. Transfer
HeNB1(28bits), MeNB(20bits)
HeNB 1
(Virtual eNB|Cell1)
Virtual eNB
(X2 broker)
MeNB
Macro Cell
A of MeNB
MeNB
S1: MME Config. Transfer
MeNB(20bits), HeNB1(28bits)
X2 IP of MeNB = Virtual eNB IP
HeNB 1
(Virtual eNB|Cell1)
Figure 3-4. SMEC X2 service broker: HeNB1 initiates TNL address discovery procedure towards an MeNB
SMEC White Paper LTE Femtocell Gateway with X2 Broker
10
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
MeNB returns its X2 IP address, and MME sends it to virtual eNB (now, virtual eNB obtains MeNB's X2 IP
address). Virtual eNB replaces the MeNB's X2 IP address in SeNB Information with its own IP address, and
sends MME Configuration Transfer message to HeNB1. Then, this leads HeNB1 to recognize the virtual eNB IP
address as MeNBs X2 IP address.
X2 setup between HeNB1 and MeNB: HeNB1 starts X2 setup towards MeNB, indicating its HeNB ID (virtual
eNB (20b) + cell 1 (8b)) and MeNB as neighbor information. Since HeNB1 knows virtual eNB's IP address as
MeNBs X2 IP address, this message is actually forwarded to virtual eNB. Virtual eNB starts another X2 setup
procedure to continue the setup of X2-connectivity towards MeNB, indicating its own eNB ID (virtual eNB) and
cell information (cell 1) and MeNB ID as neighbor information. When MeNB and virtual eNB responds, a single
X2 connection is set up between HeNB1 and virtual eNB, and also between virtual eNB and MeNB.
This process lets MeNB add the cell information of HeNB1 (virtual eNB/cell1) to its X2 neighbor list and also
lets HeNB1 add the cell information of MeNB (MeNB/cell A) to its X2 neighbor list.
X2 Setup Request
eNB ID (20b): virtual eNB
Cell ID (8b): Cell 1
Virtual eNB
(X2 broker)
MeNB
X2
Virtual eNB
(X2 broker)
X2 Setup Response
X2 Neighbor List (MeNB)
X2 Setup Response
X2 Setup Request
HeNB ID (28b): virtual eNB | Cell1
Neighbor: MeNB
(to Virtual eNB IP)
MeNB
eNB ID (20b) Cell ID (8b)
IP
Virtual eNB
Cell1
IPVirtual eNB
X2
X2 Neighbor List (HeNB1)
eNB ID (20b) Cell ID (8b)
HeNB 1
(Virtual eNB|Cell1)
HeNB 1
(Virtual eNB|Cell1)
MeNB
Cell A
IP
IPVirtual eNB
Figure 3-5. SMEC X2 service broker: X2 setup between HeNB1 and MeNB
Subsequent X2 connection setups: As X2 connection between virtual eNB and MeNB has already been
setup, any further X2-address request from other HeNBs for X2-connectivity towards MeNB will be responded
by the virtual eNB without forwarding the request via the MME towards the MeNB. Virtual eNB sends its own
IP address in response to other HeNB's X2-address request to the MeNB.
For any further X2 setup request to the MeNB, virtual eNB, through the already-established X2 connection,
sends an X2 message (eNB Configuration Update) containing HeNB2 cell information to inform MeNB of the
updated cell information. Virtual eNB sends X2 Setup Response to HeNB2 if the X2 Configuration Update
between the virtual eNB and MeNB is performed successfully.
SMEC White Paper LTE Femtocell Gateway with X2 Broker
11
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
eNB Config. Update (Cell2)
Virtual eNB
(X2 broker)
Virtual eNB
(X2 broker)
MeNB
X2
MeNB
X2
eNB Config. Update ACK.
S1: eNB Config. Transfer
S1: MME Config. Transfer
HeNB2(28bits), MeNB(20bits) MeNB(20bits), HeNB2(28bits)
X2 IP of MeNB = Virtual eNB IP
X2 Setup Request
(to Virtual eNB IP)
HeNB 2
(Virtual eNB|Cell2)
X2 Setup Response
HeNB 2
(Virtual eNB|Cell2)
Figure 3-6. SMEC X2 service broker: Subsequent X2 connection setups
Once the above process is completed, an X2 connection is set up between each HeNB and virtual eNB (HeNBGW), and also between virtual eNB and macro eNB. Logically, existing macro eNB recognizes HeNB-GW as a
new macro eNB, and all HeNBs belonging to it as cells in the macro eNB as shown in Figure 3-7.
X2 Neighbor List (Macro eNB)
eNB ID (20b)
Virtual eNB
Virtual eNB
Virtual eNB
Virtual eNB
Virtual eNB
(X2 broker)
X2
Cell ID (8b)
Cell1
Cell2
...
Cell 256
EPC
(rel.8)
IPVirtual eNB
MeNB
X2
S1
HeNB 2
X2
Virtual eNB
Macro eNB
(rel.8)
CellA
Cell 1
HeNB 1
S1
Macro Cell A
of MeNB
X2
X2
IP
HeNB 256
Cell 2
Cell 256
CellB
CellC
Virtual eNB|Cell1
Macro eNBs view
Virtual eNB|Cell2
Virtual eNB|Cell256
Figure 3-7. SMEC X2 service broker: Logical configuration
This means, the legacy LTE network (eNB and EPC) will see even a large-scale deployment of HeNBs as a smallscale deployment of additional macro eNBs. This completely eliminates any chance of uncertainty,
complexity, or risk factors that would otherwise be caused by a large-scale deployment of HeNB in the
legacy LTE network. For example, because the 28-bit HeNB IDs are not exposed to MME or eNB, there is no
potential issue in interworking between HeNBs and MME/eNBs, which makes the network architecture even
more stable and reliable.
SMEC White Paper LTE Femtocell Gateway with X2 Broker
12
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
As the X2 service broker feature by SMEC is implemented using S1 interface (eNB n MME) and X2 interface
(eNB n eNB) defined in Rel. 8, no change or modification is needed in the EPC core or eNBs already
deployed in the legacy LTE network. This makes the feature readily applicable to any LTE commercial network
where Rel. 8 or higher is implemented (i.e., in any LTE network).
4. Benefits of SMEC HeNB-GW
SMECs HeNB-GW helps to keep the impact of introducing LTE femtocell - even when massively deployed - in
the legacy LTE network low, as low as that of small scale addition of macro eNB. This ensures the stability of
the LTE core network remains unaffected and the additional investment costs resulting from such
deployment are kept to a minimum.
SMECs HeNB-GW delivers both SeGW feature and aggregation feature (for control plane, S1-MME and user
plane, S1-U) at a single point, proactively preventing overload at existing MME and S-GW, and also easing
potential uncertainty in the legacy LTE network to be caused by tens of thousands of newly deployed
femtocells. Also, it helps to bring down the costs for additional installation of MME resulting from the large
scale deployment of femtocells (e.g. purchasing additional equipment and license).
SMECs HeNB-GW supports S1 and X2 handover between macro eNB and femtocell, which ensures
uninterrupted, reliable call quality, even during switches between the two cells - all just through 4G network
(i.e. just through VoLTE) without 2G or 3G.
SMECs HeNB-GW offers X2 service broker feature that provides X2 handover between macro eNB and
HeNB without having to modify X2 interface used between the macro eNBs.
1) Traditional HeNB-GW can only support S1 handover, and thus heavy overloads are inevitably passed
on to MME during handover. SMEC HeNB GW, however, supports X2 handover where no MME
involvement during handover process is needed, drastically reducing overload at MME.
2) It significantly reduces the number of X2 interfaces needed through aggregation of X2 interfaces
between macro eNB and femtocells, thereby decreasing network complexity to be caused by X2
interface used in small cell environment.
3) The X2 service broker feature by SMEC, implementable through S1 and X2 interfaces defined in 3GPP
Rel. 8., is readily deployable in any LTE system regardless of its release version. Without additional
installation of X2 GW nodes defined in R-12 or upgrade of R-12 X2 GW feature license of MME, eNB
and HeNB, or of LTE network, X2 handover between macro eNB and HeNB can be readily supported.
SMEC White Paper LTE Femtocell Gateway with X2 Broker
13
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
Without HeNB-GW
With HeNB-GW
With SMEC HeNB-GW
MME Load (paging, overload control, etc.)
High
Low
Low
MME Load (abnormal events, etc.)
High
Low
Low
MME Load (eNB ~ HeNB handover)
High1
High1
Low2
S1 Connection Complexity
High
Low
Low
High
High
Low
X2 Connection Complexity
Complex meshed X2 interfaces between
eNBs and HeNBs3
Impact on existing MME for S1/X2
New functions may be required
New functions may be required
No new S1/X2 functions
e.g., managing and routing HeNB ID
(28bits)
e.g., managing and routing HeNB ID
(28bits), TAI-based S1 routing for HeNB
[X2 broker] MME recognizes SMEC's HeNBGW as a macro eNB, and hence MME
manages and routes eNB ID as before.
New functions may be required
New functions may be required
No new S1/X2 functions
e.g., managing and routing HeNB ID
(28bits)
e.g., managing and routing HeNB ID
(28bits)
[X2 broker] Macro eNB recognizes HeNB as
a virtual cell of eNB, and hence macro eNB
manages and routes eNB ID as before.
Impact on existing eNB for S1/X2
Complex meshed X2 interfaces between
eNBs and HeNBs3
[X2 broker] X2 connection aggregation
Impact on existing LTE network
HeNB
HeNB
eNB
!
NB
, He
e
m
its
Hi,
HeNB-GW
Stable as before
eNB
Hi, its me, eNB!
NB!
NB !
me, H
e
!
eNB
H
,
me
its
Hi,
HeNB-GW
MME
me, H
e
eNB
Hi, it
s
X2
Hi, its
me, He
NB!
S1
Potential
uncertainty
Hi, its
me, eN
B!
MME
Hi, it
s
Potential
uncertainty
Hi, its
me, He
NB!
MME
HeNB
1) On the assumption that S1 handover is used. Using X2 GW can reduce overload through X2 handover.
2) On the assumption that X2 handover is used. Supports X2 handover without X2GW.
3) Introduction of X2 GW and upgarde of eNB SW can resolve Meshed X2 issue (Rel.12).
SMEC White Paper LTE Femtocell Gateway with X2 Broker
14
Facilitating instant mass deployment of LTE femtocells in existing LTE infrastructure
Acronyms
3GPP
eNB
EPC
GTP
GW
HeMS
HeNB
HeNB-GW
ID
IMS
ISP
LTE
MeNB
MME
PGW
QoE
RAN
SCTP
SeGW
SeNB
SOHO
S-GW
TNL
UE
VoLTE
X2 AP
X2 GW
3rd Generation Partnership Project
Evolved Node B
Evolved Packet Core
GPRS Tunneling Protocol
Gateway
HeNB Management System
Home eNodeB (Femtocell)
Home eNodeB Gateway (Femto Gateway)
Identifier
IP Multimedia Subsystem
Internet Service Provider
Long Term Evolution
Macro eNB
Mobility Management Entity
Packet Data Network Gateway
Quality of Experience
Radio Access Network
Stream Control Transmission Protocol
Security Gateway
Source eNB
Small Office Home Office
Serving Gateway
Transport Network Layer
User Equipment
Voice over LTE
X2 Application Protocol
X2 Gateway
SMEC White Paper LTE Femtocell Gateway with X2 Broker
15
About SMEC (www.esmec.com | www.newgrid.com)
SMEC has over 20 years of experience developing and deploying
carrier-grade NGN and wireless network solutions. Combining our
technical expertise and along with our fully implemented and
commercially referenced solutions with Global Tier 1 operators, we
offer our global partners and customers competitive solutions.
Its SP series solutions which include LTE HeNB Gateway, ePDG/TWAG
for LTE-WiFi interworking solution and LTE IPsec Security Gateway
enable customers to improve reliability & performance and to
introduce differentiating products and services while monetizing the
mobile network.
Location and Contact Information
1462-7 HCN B/D 5F, Seocho-dong, Seocho-gu, Seoul, South Korea,
137-070
TEL +82-2-581-7384
E-MAIL info@esmec.com
For more information, please visit us at www.newgrid.com
