DIAMETER

Diameter Radius

Transportation ProtocolConnection-Oriented Protocols (TCP and SCTP) Connectionless Protocol (UDP)

Agent Support Relay, Proxy, Redirect, Translation Implicit support.

SecurityHop-to-Hop, End-to-End Hop-to-Hop only

Capabilities Negotiation Negotiate supported applications and security level (CER/CEA)Doesn't support

Peer Discovery Static configuration and dynamic lookup Static configuration

Default Port38681812 (Authentication), 1813 (accounting)

Server Initiated Message Supported. for example, re-authentication Message, Session termination Doesn't support

RADIUS has some limitations: Its CHAP authentication is subject to dictionary attacks,and it protects clear-text passwords (PAP) only on a hop-by-hop basis. The EAP support in RADIUS is not described in the generic RFC, but in RFC 2869 "RADIUS Extensions". Diameter base protocol offers support for NAIs, while the NASREQ application (see Sec. 1)for CHAP, EAP and PAP.The Gx Interface application implements the following procedures:On the PGW/GGSN PCEF: Initiate an initial Credit Control Request (CCR-I) for an idle transaction Initiate a Credit Control Update Request (CCR-U) for an active transaction Initiate a Credit Control Terminate Request (CCR-T)for an active transaction Initiate Event Triggers (for a complete list, clickhere); Initiate Indication of IP Connectivity Access Network (IP-CAN) Service Establishment; Initiate Indication of IP-CAN Service Modification; Initiate Indication of IP-CAN Service Termination.On the PCRF: Initiate an Abort Session; Initiate an Reauthorization Request (RAR); Initiate a Termination request from an active transaction; Initiate a rule install for an active transaction; Initiate a rule remove for an active transaction; Initiate an Application Detection and Control (ADC) rule install for an active transaction; Initiate an ADC rule remove for an active transaction; Initiate an event to update Quality of Service (QoS) Information.

During Initial Attach procedure, PGW check for the APN/Charging Characterstics received in Create session request for whether dynamic Policy(configured in PCRF) or Static policy(configured on PGW) should be applied. Depending upon the configuration, PGW forwards the request to PCRF for providing PCC Rule for the UE attach request

Rule name - This is to be used to reference a PCC rule in communication between PCEF and the PCRF . Service data flow filters - shall be used to select the type of traffic that passes through the bearer on which the rule applies.precedence : Determines the precedence of the bearer on which the rule is applied when data is received uplink or downlink for a particular type UDP/TCP etc. QoS parameters - Includes QoS Class Identifier (QCI), also the Allocation and Retention Priority (ARP) and GBR,MBR for uplink and downlik.Charging type - Defines whether online,offline or both or none charging is applied.Call Flow1) PGW sends CCR(Init) to PCRF to get the PCC Rule from PCRF. PCRF has primarily two entities. PDT (Policy Derivation table) and PCT (Policy and Configuration table). In PCT (Policy and Configuration table), PCRF has number of PCC Rules configured. In PDT ((Policy Derivation table), PCRF has the selection criteria based upon which PCRF sends the selected PCC Rules in 2) CCA. Selection criteria- Can be IMSI,APN name, QCI, MBR/GBR etc. means if CCR request contains the given value of IMSI or QCI and so then particular PDT is applied. For Example: In CCR (Init), PCRF receive IMSI 122334455667001. Based upon this IMSI, PCRF has PDT configured in which PCRF applies two PCC Rules let suppose PCC1 and PCC Upon getting successfull PDT matched PCRF sends successfull CCA (Init) to PGW.3) Now, upon getting of successfull CCA (Init) PGW sends CCR (Update) to confirm the PCRF that the Rule is applied successfully on the particular bearer (in this case default bearer) and also inform the ip address of the UE.Then PCRF acknowlege with CCA(Update) success.4) Now PGW has already applied the Rule(Qos,filters,MBR,GBR etc) received from PCRF to the requested bearer, it sends Create Session Response to SGW and then the Default session created successfully. Similar Procedure follows for dedicated bearer also. In dedicated bearer creation/updation/deletion, PGW sends CCR Update to PCRF.PCRF acknowledge the request with CCA UpdateNote: CCR (Init) send by PGW only once for a UE session i.e on default bearer creation

The Rx application IMS/AS and PCRF Initial provisioning of session information Modification of session information AF session termination Subscription to notification of signalling path status IP-CAN session termination Service data flow deactivation IP-CAN type change notification Access network charging information notification The call is initiated from a UE, and arrives at the PCEF. It is forwarded on a CCR Initial to the PCRF using Gx. The PCRF probes the Subscriber Store for relevant data and then returns the CCA initial with the default rules to the PCEF over Gx. The PCEF enforces the default rules, activating content for the UE. At this point the subscriber starts consuming resources. The application function/CSCF sends an AAR message to the PCRF using Rx, which updates the PCRF with application/media information and then the PCRF returns an RAR message to the PCEF. At this point the PCEF enforces the updated rules. The PCEF returns an RAA message over Gx to the PCRF, and then the PCEF sends as many CCR -update messages to the PCRF as necessary. The PCRF returns CCA - update messages in return. For each CCA message events and resource consumption are reported, and the rules are updated. After the call the application function/CSCF sends an STR message to the PCRF using Rx, and the PCRF returns an STA message. The PCEF sends a CCR - termination message to the PCRF, and the PCRF returns a CCA - termination message to disconnect the session. Finally the PCEF sends a deactivate context message to the UE.

QoSQoS to manageBandwidthpacket loss andlatency/jitter..

A bearer has two or four QoS parameters, depending on whether it is a real-time or besteffortservice: QoS Class Indicator (QCI) Allocation and Retention Priority (ARP) Guaranteed Bit Rate (GBR) real-time services only Maximum Bit Rate (MBR) real-time services only

LTE Call flow(Non PCRF)

Generic terms

UE and HSS parameters before attach

CS fall back Vs SRVCCCSFB (Circuit Switched Fallback) is a mechanism where your LTE network moves you to a Legacy network which supports voice call. In case of CSFB, your voice call is never active in LTE. When a voice call needs to be started, the UE initiates ESR(Extended Service Request) and the network moves it to a legacy network through redirection/handover or CCO. The UE then initiates the call control procedures in legacy.

Whereas SRVCC (Single Radio Voice Call continuity) is a process where your active voice call in LTE (may be VOIP), is handed over to the CS domain of the legacy network (MSC), where IMS use STN-SR number (session transfer number) through IMS SCC AS (service call continuity AS). This is useful when you are in an LTE coverage area and have an active voice call over IMS and you move out of the LTE area into a Legacy only network coverage. Instead of the call getting dropped, the same will be handed over to the CS Legacy network if SRVCC is supported.

Default Bearer And Dedicated BearerBearer is just a virtual concept. It defines how the UE data is treated when it travels across the network. Network might treat some data in a special way and treat others normally. Some flow of data might be providedguaranteedbit rate while other may face low transfer.In short, bearer is a set of network parameter that defines data specific treatmente.g. Person A will always getat least256 Kbpsdownload speed on his LTE phone while for person B there is no guaranteed bit rate and might face extremely bad download speed at times

Now let me talk briefly about Dedicated and Default bearer one by one.

Default Bearer in LTEWhen LTE UE attaches to the network for the first time, it will be assigned default bearer which remains as long as UE is attached. Default bearer is best effort service. Each default bearer comes with an IP address.UEcan have additional default bearers as well. Each default bearer will have a separate IP address. QCI 5 to 9 (Non- GBR) can be assigned to default bearer.

Dedicated BearerTo put it simple, dedicated bearers provides dedicated tunnel to one or more specific traffic (i.e. VoIP, video etc). Dedicated bearer acts as an additional bearer on top of default bearer. It does not require separate IP address due to the fact that only additional default bearer needs an IP address and therefore dedicated bearer is always linked to one of the default bearer established previously. Dedicated bearer can be GBR or non-GBR (whereas default bearer can only be non-GBR). For services like VoLTE we need to providebetter user experience and this is where Dedicated bearer would come handy. Dedicated bearer uses Traffic flow templates (TFT) to give special treatment to specific services

ExampleUsually LTE networks with VoLTE implementations has two default and one dedicated bearer

Default bearer 1: Used for signaling messages (sip signaling) related to IMS network. It uses qci 5Dedicated bearer: Used for VoLTE VoIP traffic. It uses qci 1 and is linked to default bearer 1Default bearer 2: Used for all other smartphone traffic (video, chat, email, browser etc)

Why dont we use dedicated bearer for ims signaling as well ?IMS network is separate network from normal internet. And it comes with its own APN. Therefore we need separate default bearer for IMS network. This also helps in separating IMS traffic from normal internet traffic as well

How it is decided to send voip traffic (for example) on dedicated bearer?Both UE and eNB has TFT which has rules for certain services. For example, incase of VoLTE voip traffic, the rule are defined on the basis of protocol number , destination network ip network etc

How is dedicated bearer linked to default bearer?The value of "Linked EPS bearer identity" defined in setup info of dedicated bearer is used to link dedicated bearer to default bearer

Please also visitQuality of Service (QoS) in LTEto get more better understanding on bearers and QoS