Isolated E-UTRAN operation for public safety

Updated 24.5.2016

Resiliency and service availability can be enhanced in terrestrial public safety LTE network based on capability called 'Isolated E-UTRAN Operation for Public Safety (IOPS)'. IOPS enables local services in case backhaul connection to centralized macro core is lost. IOPS assumes that local EPC function is co-sited with eNodeB. Local EPC can serve also multiple eNodeBs. Local EPC includes at least HSS, MME, SGW and PGW functions.

The figure below depicts an example of shared RAN, which is serving both PS users and commercial subscribers. There are separate PLMN identities for commercial customers (PLMN 'A')  and PS customers (PLMN 'PPDR') and there are also separate core networks. In normal condition commercial and PS subscribers are attached to their own centralized core networks and all data connectivity and communication services are provided by the centralized core networks. The lower part of figure depicts a transmission failure in backhaul. In that case eNodeBs can activate IOPS mode and offer local services. However IOPS services are available only for PS UEs that have subscription for IOPS mode including access class 11 or 15.

The fall-back procedure is illustrated in the next figure. Public safety UEs are normally attached to centralized EPC and there can be also UEs in active state when the backhaul connection is lost. Any RRC connected UEs are released and the eNodeB establishes S1 connection to local EPC. IOPS mode is indicated by broadcasting an 'IOPS' PLMN ID for which PS UE has a separate USIM application. The IOPS PLMN is marked in system information broadcast as reserved for operator use, which means that access classes 0-9 and 12-14 behave as if the cell status is "barred" (See 36.304).  

Because the minimum functionality of local EPC provides only IP connectivity service, it may be necessary to include also other functions for efficient isolated communication. Mission critical push to talk (MCPTT) is definitely important application for PS users. Also some broadband data applications can be considered for IOPS. For example real time video for situational awareness is typical application enabled by LTE.

IOPS is specified initially in 3GPP release 13 (23.401 Annex K) and it is optional in any public safety LTE network. 

Comments

  1. Hi
    Thanks for you post.
    I have a few questions which I hope you can help clarify.

    1.
    Can I assume that the spectrum assignment for the commercial PLMN 'A' and PLMN 'PPDR' are the same, within the same LTE bands? For example the same 20MHz block in LTE B28? If not the same, wouldn't it be a interference/IMD problem? How is the radio resources/scheduler between the two EPC being coordinated with the eNodeB?

    2. How would the EPC tasks between local and Macro EPC be coordinated? Would both the EPC simultaneously handle EPC tasks (e.g. handover/call flow) or only one at a time? how is this being managed?
    Is it typical for a commercial carrier to have more then 1 EPC being setup? I have heard that for a reasonable size carrier, Singapore for example, only one EPC is required. Not sure for the larger carriers like AT&T in the USA. Comments?

    ReplyDelete
  2. 1. Yes, same carrier can be shared. Either all radio resources are allocated/scheduled according to bearer QoS parameters (QCI, ARP, MBR/GBR) between all subscribers or then eNB vendor has a solution to virtually split the carrier capacity between PLMNs. Alternatively it is also possible that both PLMNs have own carriers (e.g. 2 separate 10 MHz carriers at B28).

    2. Local EPC for IOPS is serving only PPDR subscribers when macro EPC is not reachable. Local EPC is not serving, if macro EPC is available.
    Commercial carriers have typically multiple EPC sites for geo-redundancy (in case of major core network disaster). In very large countries there are multiple EPC sites to keep also e2e latency in reasonable level.

    ReplyDelete
  3. Thanks again for the post. Looking at the specs, it seems that the PLMN PPDR EPC shown in the top figure may not need to exist in that shared network scenario. i.e. the IOPS eNodeB need only start broadcast the IOPS PLMN ID once it detects that the S1 link to macro core is lost

    ReplyDelete
    Replies
    1. The upper figure is showing shared access with separate core networks for commercial and public safety users. So, both macro core networks are active. Local EPC is serving only public safety users in isolated mode. I assume here that backhaul is lost to both core networks.

      Delete
  4. Not sure what authentication/cryptographic protection is used within IOPS - any idea?

    ReplyDelete
    Replies
    1. Standard 3GPP mutual authentication, key generation and air interface ciphering & integrity protection. Standards support SNOW 3G, AES and ZUC ciphering.

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  6. Hi Mika,

    Would it be any difference in IOPS behaviour on commercial network in respect to the type of agreement with PPDR - light MVNO (apn), full MVNO (dedicated core) or RAN sharing ?!
    Tks

    ReplyDelete
    Replies
    1. Standards compliant IOPS requires specific PLMN ID to be used in IOPS mode. In that sense no difference.

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  7. Hi Mika,

    Are you aware if mobility procedures (HO) are applicable in IOPS (i.e. backhaul not available but inter-site connectivity exists...) ?!

    ReplyDelete
    Replies
    1. Yes, HOs are supported between neigboring cells of IOPS eNB or neighboring eNBs, if served by same local EPC.

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