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# Tutorial on how to perform a intra-frequency X2 Handover
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**Note: for the moment, openair-cn does not yet support the path switch message required for X2 Ho, so to test you need to use a 3rd party EPC**
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## X2 Handover setup
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The experimentation setup is depicted in Figure below and includes 2 OAI eNBs, 2 USRP B210 equipped with the GPS module (daughter board).
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## Steps
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The experiment methodology/steps are described in the following:
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1. eNBs are synchronized in frequency and frame/subframe timing using GPS
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1. eNB are operating on the same band, frequency, and bandwidth (e.g. band, 2.6GHz, 7 10 MHz)
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The experiment steps are described in the following:
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1. eNBs are synchronized in frequency and subframe timing using GPS (optionally they can also be synced in frame timing)
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1. eNB are operating on the same band, frequency, and bandwidth, see the attached configuration files
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1. Both eNBs are connected to the same EPC that supports the path switch required for X2 HO
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1. UE measures the source/target cell’s signal quality based on the different cell IDs
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1. UE is initially attached to eNB 0 and its mobility is emulated using either real mobility or an attenuator allowing the UE to handover from eNB0 to eNB1 that causes the related X2 HO signalling to be triggered as a consequence of the A3 event
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1. UE is initially attached to eNB 0 and its mobility is emulated using an attenuator (real mobility can also be used) allowing the UE to handover from eNB0 to eNB1 that causes the related X2 HO signalling to be triggered as a consequence of the A3 event
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1. X2 Handover Request is sent from source eNB to target eNB
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1. X2 Handover Request ack is sent back from target eNb to source eNB
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1. UE is connected to eNB1 after the HO process
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In the proposed setup, different possible deployed scenarios can be considered for experimentation, e.g., a) different types of traffic (TCP/UDP) in UL/DL, b) successful/failed HO based on UE’s emulated mobility as well as different OAI network measurements, e.g., packet loss, delay, RSRP/RSRQ etc.
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| ... | ... | @@ -19,9 +24,14 @@ In addition, [octoBoxquadAtten](http://www.octoscope.com/English/Products/Orderi |
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## To Do
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* [Finalize the path switch message at eNB]
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* [Rework oaisim for X2 Handover]
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* [Cleanup the x2-ho branch and merge it back to develop]
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## Additional Materials
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1. [Config files]
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1. [Wireshark traces]
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1. [Master eNB config file sample](/uploads/270cdf095de1b0a8047d7d054e3ff4dd/enb.band7.tm1.x2ho.usrpb210.master.conf) [Slave eNB config file sample](/uploads/5fbf3910435602b19f772090752a1ae7/enb.band7.tm1.x2ho.usrpb210.slave.conf)
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1. [Wireshark Trace (to be updated)](/uploads/33cbdde079a65e6327bf5151164c0dd9/x2_ho_messages.pcap)
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1. [Youtube Video](https://youtu.be/KlwampmhFxw)
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1. [Analyzing X2 Handover in LTE/LTE-A using OpenAirInterface system emulator] (http://www.eurecom.fr/en/publication/4854/download/comsys-publi-4854.pdf)
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