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Femtocell Synchronization Analysis


Rock Xie


3GPP Structure for Femtocell

• The 3GPP TR23.830 report defines the architecture aspects of Home NodeB

(3G UMTS) and Home eNodeB (4G LTE). The HNB represents the femtocell

base station and HNB GW represents the femtocell gateway. The iuh is the

interface specifying the communication between the gateway and base

station.


Femtocell Forum Structure for Femtocell

• The Femtocell Forum also provides a reference model very similar

to 3GPP


The challenges in Femtocell synchronization

The Femtocell network architecture shows that a publ

ic network is used to establish the connectivity betwe

en the femtocell and core network elements, This pre

sents a set of unique challenges:

• Femtocell synchronization security

• Femtocell synchronization connectivity

• Femtocell synchronization network scalability


Security Issue• The security is mandatory since the Gateway and Clock server communicate to

the Femtocells via a public backhaul broadband connection (also known as the

3GPP iuh interface or Femtocell Forum Fa interface).

• The important point worth noting is the large number of Femtocells that might h

ave to be served, as well as the additional bandwidth overhead IPSec represen

ts to the offered load (bandwidth consumption) of synchronization messages.

• The 3GPP has considered some of the security aspects with respect to synchro

nization performance. The [3GPP.33.820] report lists the following:

1. it may be possible to leave some of the messages unprotected, but there mig

ht be security risks. Care should be taken in considering which messages are

protection or not.

2. there may be bandwidth, delay and delay variation problems if all the messa

ges (eg., [IEEE1588]) are to be protected.

3. if delays become excessively long, reliance on internal clock might be import

ant and requires further investigation.


Connectivity Issue

• The Home GW provides Internet sharing for home devices. One of the

challenges is to define the end-to-end connectivity model between the f

emtocell and clock server when a function such as network address tra

nslation (NAT) is present within the Home GW.

• network address translation (NAT) protects the internal home network,

but prevents the direct connection between devices sitting in the home

network and devices that are outside (reachable through the public Inte

rnet). With respect to synchronization, this could limit the ability of a fe

mtocell to communicate directly to a Clock server. Therefore, some me

chanism to handle NAT translation and to guarantee proper flow of syn

chronization messages should be provided.


• The femtocell network could easily extend to millions of devices and th

e offered load of synchronization messages (bandwidth consumption) c

ould become quite large when unicast addressing is used.

• The scalability issue could impact the clock server throughput but more

importantly could increase the difficultly in capacity planning and place

ment of clock servers in the network

• The use of load balancing techniques might be beneficial to help in syn

c capacity planning but might impact performance. The use of multicast

technologies currently being developed might present opportunities to r

educe the bandwidth consumption of synchronization messages and to

considerably increase the number offemtocells a server can support.

Scalability issue


1. The use of IPSec links in public networks could degrade the transport of synch

ronization message and its performance. In order to reduce the impact of secu

rity issue in public networks, it is possible to leave some of the synchronization

messages unprotected. Caution should take place on the use of IPSec and sy

nc performance.

2. Synchronization messages traversing Network Address Translation (NAT) func

tions need to be considered, in order to guarantee proper connectivity between

a Clock Server and Femtocell.

3. Scalability aspects (large number of femtocells), bandwidth consumption and t

he placement of clock servers are important as the network architecture need t

o be developed.

4. If TICTOC intends to develop some form of synchronization profile covering m

obile backhaul for instance, then the aspects of femtocell should be taken into

account.

Conclusion

Thank You

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Download - Femtocell Synchronization A nalysis

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