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IMS

The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is an architectural framework for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched-style network, rather than strictly over an IP packet-switched network. Alternative methods of delivering voice (VoIP) or other multimedia services have become available on smartphones, but they have not become standardized across the industry.[citation needed] IMS is an architectural framework to provide such standardization.

IMS was originally designed by the wireless standards body 3rd Generation Partnership Project (3GPP), as a part of the vision for evolving mobile networks beyond GSM. Its original formulation (3GPP Rel-5) represented an approach for delivering Internet services over GPRS. This vision was later updated by 3GPP, 3GPP2 and ETSI TISPAN by requiring support of networks other than GPRS, such as Wireless LAN, CDMA2000 and fixed lines.

IMS uses IETF protocols wherever possible, e.g., the Session Initiation Protocol (SIP). According to the 3GPP, IMS is not intended to standardize applications, but rather to aid the access of multimedia and voice applications from wireless and wireline terminals, i.e., to create a form of fixed-mobile convergence (FMC).[1] This is done by having a horizontal control layer that isolates the access network from the service layer. From a logical architecture perspective, services need not have their own control functions, as the control layer is a common horizontal layer. However, in implementation this does not necessarily map into greater reduced cost and complexity.

Alternative and overlapping technologies for access and provisioning of services across wired and wireless networks include combinations of Generic Access Network, softswitches and "naked" SIP.

Since it is becoming increasingly easier to access content and contacts using mechanisms outside the control of traditional wireless/fixed operators, the interest of IMS is being challenged.[2]

Examples of global standards based on IMS are MMTel which is the basis for Voice over LTE (VoLTE) and Rich Communication Services (RCS) which is also known as joyn or Advanced Messaging.

History[edit]

  • IMS defined by an industry forum called 3G.IP, formed in 1999. 3G.IP developed the initial IMS architecture, which was brought to the 3rd Generation Partnership Project (3GPP), as part of their standardization work for 3G mobile phone systems in UMTS networks. It first appeared in Release 5 (evolution from 2G to 3G networks), when SIP-based multimedia was added. Support for the older GSM and GPRS networks was also provided.[3]
  • 3GPP2 (a different organization from 3GPP) based their CDMA2000 Multimedia Domain (MMD) on 3GPP IMS, adding support for CDMA2000.
  • 3GPP release 6 added interworking with WLAN, inter-operability between IMS using different IP-connectivity networks, routing group identities, multiple registration and forking, presence, speech recognition and speech-enabled services (Push to talk).
  • 3GPP release 7 added support for fixed networks by working together with TISPAN release R1.1, the function of AGCF (access gateway control function) and PES (PSTN emulation service) are introduced to the wire-line network for the sake of inheritance of services which can be provided in PSTN network. AGCF works as a bridge interconnecting the IMS networks and the Megaco/H.248 networks. Megaco/H.248 networks offers the possibility to connect terminals of the old legacy networks to the new generation of networks based on IP networks. AGCF acts a SIP User agent towards the IMS and performs the role of P-CSCF. SIP User Agent functionality is included in the AGCF, and not on the customer device but in the network itself. Also added voice call continuity between circuit switching and packet switching domain (VCC), fixed broadband connection to the IMS, interworking with non-IMS networks, policy and charging control (PCC), emergency sessions.
  • 3GPP release 8 added support for LTE / SAE, multimedia session continuity, enhanced emergency sessions and IMS centralized services.
  • 3GPP release 9 added support for IMS emergency calls over GPRS and EPS, enhancements to multimedia telephony, IMS media plane security, enhancements to services centralization and continuity.
  • 3GPP release 10 added support for inter device transfer, enhancements to the single radio voice call continuity (SRVCC), enhancements to IMS emergency sessions.
  • 3GPP release 11 added USSD simulation service, network-provided location information for IMS, SMS submit and delivery without MSISDN in IMS, and overload control.

Architecture[edit]

3GPP / TISPAN IMS architectural overview
3GPP / TISPAN IMS architectural overview – HSS in IMS layer (as by standard)

Each of the functions in the diagram is explained below.

The IP multimedia core network subsystem is a collection of different functions, linked by standardized interfaces, which grouped form one IMS administrative network.[4] A function is not a node (hardware box): An implementer is free to combine two functions in one node, or to split a single function into two or more nodes. Each node can also be present multiple times in a single network, for dimensioning, load balancing or organizational issues.

Access network[edit]

The user can connect to IMS in various ways, most of which use the standard IP. IMS terminals (such as mobile phones, personal digital assistants (PDAs) and computers) can register directly on IMS, even when they are roaming in another network or country (the visited network). The only requirement is that they can use IP and run SIP user agents. Fixed access (e.g., Digital Subscriber Line (DSL), cable modems, Ethernet), mobile access (e.g. W-CDMA, CDMA2000, GSM, GPRS) and wireless access (e.g., WLAN, WiMAX) are all supported. Other phone systems like plain old telephone service (POTS—the old analogue telephones), H.323 and non IMS-compatible systems, are supported through gateways.

Core network[edit]

HSS – Home subscriber server:
The home subscriber server (HSS), or user profile server function (UPSF), is a master user database that supports the IMS network entities that actually handle calls. It contains the subscription-related information (subscriber profiles), performs authentication and authorization of the user, and can provide information about the subscriber's location and IP information. It is similar to the GSM home location register (HLR) and Authentication centre (AuC).

A subscriber location function (SLF) is needed to map user addresses when multiple HSSs are used.

User identities:
Various identities may be associated with IMS: IP multimedia private identity (IMPI), IP multimedia public identity (IMPU), globally routable user agent URI (GRUU), wildcarded public user identity. Both IMPI and IMPU are not phone numbers or other series of digits, but uniform resource identifier (URIs), that can be digits (a Tel URI, such as tel:+1-555-123-4567) or alphanumeric identifiers (a SIP URI, such as sip: This email address is being protected from spambots. You need JavaScript enabled to view it. " ).

IP Multimedia Private Identity:
The IP Multimedia Private Identity (IMPI) is a unique permanently allocated global identity assigned by the home network operator, it has the form of an Network Access Identifier(NAI) i.e. user.name@domain, and is used, for example, for Registration, Authorization, Administration, and Accounting purposes. Every IMS user shall have one IMPI.

IP Multimedia Public Identity:
The IP Multimedia Public Identity (IMPU) is used by any user for requesting communications to other users (e.g. this might be included on a business card). Also known as Address of Record (AOR). There can be multiple IMPU per IMPI. The IMPU can also be shared with another phone, so that both can be reached with the same identity (for example, a single phone-number for an entire family).

Globally Routable User Agent URI:
Globally Routable User Agent URI (GRUU) is an identity that identifies a unique combination of IMPU and UE instance. There are two types of GRUU: Public-GRUU (P-GRUU) and Temporary GRUU (T-GRUU).

  • P-GRUU reveal the IMPU and are very long lived.
  • T-GRUU do not reveal the IMPU and are valid until the contact is explicitly de-registered or the current registration expires

Wildcarded Public User Identity:
A wildcarded Public User Identity expresses a set of IMPU grouped together.

The HSS subscriber database contains the IMPU, IMPI, IMSI, MSISDN, subscriber service profiles, service triggers, and other information.

Call Session Control Function (CSCF)[edit]

Several roles of SIP servers or proxies, collectively called Call Session Control Function (CSCF), are used to process SIP signaling packets in the IMS.

  • A Proxy-CSCF (P-CSCF) is a SIP proxy that is the first point of contact for the IMS terminal. It can be located either in the visited network (in full IMS networks) or in the home network (when the visited network is not IMS compliant yet). Some networks may use a Session Border Controller (SBC) for this function. The P-CSCF is at its core a specialized SBC for the User–network interface which not only protects the network, but also the IMS terminal. The use of an additional SBC between the IMS terminal and the P-CSCF is unnecessary and infeasible due to the signaling being encrypted on this leg. The terminal discovers its P-CSCF with either DHCP, or it may be configured (e.g. during initial provisioning or via a 3GPP IMS Management Object (MO)) or in the ISIM or assigned in the PDP Context (in General Packet Radio Service (GPRS)).
    • It is assigned to an IMS terminal before registration, and does not change for the duration of the registration.
    • It sits on the path of all signaling, and can inspect every signal; the IMS terminal must ignore any other unencrypted signaling.
    • It provides subscriber authentication and may establish an IPsec or TLS security association with the IMS terminal. This prevents spoofing attacks and replay attacks and protects the privacy of the subscriber.
    • It inspects the signaling and ensures that the IMS terminals do not misbehave (e.g. change normal signaling routes, disobey home network's routing policy).
    • It can compress and decompress SIP messages using SigComp, which reduces the round-trip over slow radio links.
    • It may include a Policy Decision Function (PDF), which authorizes media plane resources e.g., quality of service (QoS) over the media plane. It is used for policy control, bandwidth management, etc. The PDF can also be a separate function.
    • It also generates charging records.
  • An Interrogating-CSCF (I-CSCF) is another SIP function located at the edge of an administrative domain. Its IP address is published in the Domain Name System (DNS) of the domain (using NAPTR and SRV type of DNS records), so that remote servers can find it, and use it as a forwarding point (e.g., registering) for SIP packets to this domain.
    • it queries the HSS to retrieve the address of the S-CSCF and assign it to a user performing SIP registration
    • it also forwards SIP request or response to the S-CSCF
    • Up to Release 6 it can also be used to hide the internal network from the outside world (encrypting parts of the SIP message), in which case it's called a Topology Hiding Inter-network Gateway (THIG). From Release 7 onwards this "entry point" function is removed from the I-CSCF and is now part of the Interconnection Border Control Function (IBCF). The IBCF is used as gateway to external networks, and provides NAT and firewall functions (pinholing). The IBCF is a session border controller specialized for the network-to-network interface (NNI).
  • A Serving-CSCF (S-CSCF) is the central node of the signaling plane. It is a SIP server, but performs session control too. It is always located in the home network. It uses Diameter Cx and Dx interfaces to the HSS to download user profiles and upload user-to-S-CSCF associations (the user profile is only cached locally for processing reasons and is not changed). All necessary subscriber profile information is loaded from the HSS.
    • it handles SIP registrations, which allows it to bind the user location (e.g., the IP address of the terminal) and the SIP address
    • it sits on the path of all signaling messages of the locally registered users, and can inspect every message
    • it decides to which application server(s) the SIP message will be forwarded, in order to provide their services
    • it provides routing services, typically using Electronic Numbering (ENUM) lookups
    • it enforces the policy of the network operator
    • there can be multiple S-CSCFs in the network for load distribution and high availability reasons. It's the HSS that assigns the S-CSCF to a user, when it's queried by the I-CSCF. There are multiple options for this purpose, including a mandatory/optional capabilities to be matched between subscribers and S-CSCFs.

Application servers[edit]

SIP Application servers (AS) host and execute services, and interface with the S-CSCF using SIP. An example of an application server that is being developed in 3GPP is the Voice call continuity Function (VCC Server). Depending on the actual service, the AS can operate in SIP proxy mode, SIP UA (user agent) mode or SIP B2BUA mode. An AS can be located in the home network or in an external third-party network. If located in the home network, it can query the HSS with the Diameter Sh or Si interfaces (for a SIP-AS).

  • SIP AS: Host and execute IMS specific services
  • IP Multimedia Service Switching Function (IM-SSF): Interfaces SIP to CAP to communicate with CAMEL Application Servers
  • OSA service capability server (OSA SCS) : Interfaces SIP to the OSA framework;
Functional model[edit]

The AS-ILCM (Application Server - Incoming Leg Control Model) and AS-OLCM (Application Server - Outgoing Leg Control Model) store transaction state, and may optionally store session state depending on the specific service being executed. The AS-ILCM interfaces to the S-CSCF (ILCM) for an incoming leg and the AS-OLCM interfaces to the S-CSCF (OLCM) for an outgoing leg. Application Logic provides the service(s) and interacts between the AS-ILCM and AS-OLCM.

Public Service Identity[edit]

Public Service Identities (PSI) are identities that identify services, which are hosted by application servers. As user identities, PSI takes the form of either a SIP or Tel URI. PSIs are stored in the HSS either as a distinct PSI or as a wildcarded PSI:

  • a distinct PSI contains the PSI that is used in routing
  • a wildcarded PSI represents a collection of PSIs.

Media servers[edit]

The Media Resource Function (MRF) provides media related functions such as media manipulation (e.g. voice stream mixing) and playing of tones and announcements.

Each MRF is further divided into a media resource function controller (MRFC) and a media resource function processor (MRFP).

  • The MRFC is a signalling plane node that interprets information coming from an AS and S-CSCF to control the MRFP
  • The MRFP is a media plane node used to mix, source or process media stream s. It can also manage access right to shared resources.

The Media Resource Broker (MRB) is a functional entity that is responsible for both collection of appropriate published MRF information and supplying of appropriate MRF information to consuming entities such as the AS. MRB can be used in two modes:

  • Query mode: AS queries the MRB for media and sets up the call using the response of MRB
  • In-Line Mode: AS sends a SIP INVITE to the MRB. The MRB sets up the call

Breakout gateway[edit]

A Breakout Gateway Control Function (BGCF) is a SIP proxy which processes requests for routing from an S-CSCF when the S-CSCF has determined that the session cannot be routed using DNS or ENUM/DNS. It includes routing functionality based on telephone numbers.

PSTN gateways[edit]

A PSTN/CS gateway interfaces with PSTN circuit switched (CS) networks. For signalling, CS networks use ISDN User Part (ISUP) (or BICC) over Message Transfer Part (MTP), while IMS uses SIP over IP. For media, CS networks use Pulse-code modulation (PCM), while IMS uses Real-time Transport Protocol (RTP).

  • A signalling gateway (SGW) interfaces with the signalling plane of the CS. It transforms lower layer protocols as Stream Control Transmission Protocol (SCTP, an IP protocol) into Message Transfer Part (MTP, an Signalling System 7 (SS7) protocol), to pass ISDN User Part (ISUP) from the MGCF to the CS network.
  • A media gateway controller function (MGCF) is a SIP endpoint that does call control protocol conversion between SIP and ISUP/BICC and interfaces with the SGW over SCTP. It also controls the resources in a Media Gateway (MGW) across an H.248 interface.
  • A media gateway (MGW) interfaces with the media plane of the CS network, by converting between RTP and PCM. It can also transcode when the codecs don't match (e.g., IMS might use AMR, PSTN might use G.711).

Media resources[edit]

Media Resources are those components that operate on the media plane and are under the control of IMS core functions. Specifically, Media Server (MS) and Media gateway (MGW)

NGN interconnection[edit]

There are two types of next-generation networking interconnection:

  • Service-oriented interconnection (SoIx): The physical and logical linking of NGN domains that allows carriers and service providers to offer services over NGN (i.e., IMS and PES) platforms with control, signalling (i.e., session based), which provides defined levels of interoperability. For instance, this is the case of "carrier grade" voice and/or multimedia services over IP interconnection. "Defined levels of interoperability" are dependent upon the service or the QoS or the Security, etc.
  • Connectivity-oriented interconnection (CoIx): The physical and logical linking of carriers and service providers based on simple IP connectivity irrespective of the levels of interoperability. For example, an IP interconnection of this type is not aware of the specific end to end service and, as a consequence, service specific network performance, QoS and security requirements are not necessarily assured. This definition does not exclude that some services may provide a defined level of interoperability. However, only SoIx fully satisfies NGN interoperability requirements.

An NGN interconnection mode can be direct or indirect. Direct interconnection refers to the interconnection between two network domains without any intermediate network domain. Indirect interconnection at one layer refers to the interconnection between two network domains with one or more intermediate network domain(s) acting as transit networks. The intermediate network domain(s) provide(s) transit functionality to the two other network domains. Different interconnection modes may be used for carrying service layer signalling and media traffic.

Charging[edit]

Offline charging is applied to users who pay for their services periodically (e.g., at the end of the month). Online charging, also known as credit-based charging, is used for prepaid services, or real-time credit control of postpaid services. Both may be applied to the same session.

Charging function addresses are addresses distributed to each IMS entities and provide a common location for each entity to send charging information. charging data function (CDF) addresses are used for offline billing and Online Charging Function (OCF) for online billing.

  • Offline Charging : All the SIP network entities (P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS) involved in the session use the Diameter Rf interface to send accounting information to a CDF located in the same domain. The CDF will collect all this information, and build a call detail record (CDR), which is sent to the billing system (BS) of the domain.
    Each session carries an IMS Charging Identifier (ICID) as a unique identifier generated by the first IMS entity involved in a SIP transaction and used for the correlation with CDRs. Inter Operator Identifier (IOI) is a globally unique identifier shared between sending and receiving networks. Each domain has its own charging network. Billing systems in different domains will also exchange information, so that roaming charges can be applied.
  • Online charging : The S-CSCF talks to a IMS gateway function (IMS-GWF) which looks like a regular SIP application server. The IMS-GWF can signal the S-CSCF to terminate the session when the user runs out of credits during a session. The AS and MRFC use the Diameter Ro interface towards an OCF.
    • When immediate event charging (IEC) is used, a number of credit units is immediately deducted from the user's account by the ECF and the MRFC or AS is then authorized to provide the service. The service is not authorized when not enough credit units are available.
    • When event charging with unit reservation (ECUR) is used, the ECF (event charging function) first reserves a number of credit units in the user's account and then authorizes the MRFC or the AS. After the service is over, the number of spent credit units is reported and deducted from the account; the reserved credit units are then cleared.

IMS-based PES architecture[edit]

IMS-based PES (PSTN Emulation System) provides IP networks services to analog devices. IMS-based PES allows non-IMS devices to appear to IMS as normal SIP users. Analog terminal using standard analog interfaces can connect to IMS-based PES in two ways:

  • Via A-MGW (Access Media Gateway) that is linked and controlled by AGCF. AGCF is placed within the Operators network and controls multiple A-MGW. A-MGW and AGCF communicate using H.248.1 (Megaco) over the P1 reference point. POTS phone connect to A-MGW over the z interface. The signalling is converted to H.248 in the A-MGW and passed to AGCF. AGCF interprets the H.248 signal and other inputs from the A-MGW to format H.248 messages into appropriate SIP messages. AGCF presents itself as P-CSCF to the S-CSCF and passes generated SIP messages to S-CSCF or to IP border via IBCF (Interconnection Border Control Function). Service presented to S-CSCF in SIP messages trigger PES AS. AGCF has also certain service independent logic, for example on receipt of off-hook event from A-MGW, the AGCF requests the A-MGW to play dial tone.
  • Via VGW (VoIP-Gateway) or SIP Gateway/Adapter on customer premises. POTS phones via VOIP Gateway connect to P-CSCF directly. Operators mostly use session border controllers between VoIP gateways and P-CSCFs for security and to hide network topology. VoIP gateway link to IMS using SIP over Gm reference point. The conversion from POTS service over the z interface to SIP occurs in the customer premises VoIP gateway. POTS signaling is converted to SIP and passed on to P-CSCF. VGW acts as SIP user agent and appears to P-CSCF as SIP terminal.

Both A-MGW and VGW are unaware of the services. They only relay call control signalling to and from the PSTN terminal. Session control and handling is done by IMS components.

Interfaces description[edit]

TISPAN IMS architecture with interfaces
Interface name IMS entities Description Protocol Technical specification
Cr MRFC, AS Used by MRFC to fetch documents (e.g. scripts, announcement files, and other resources) from an AS. Also used for media control related commands. TCP/SCTP channels
Cx (I-CSCF, S-CSCF), HSS Used to send subscriber data to the S-CSCF; including filter criteria and their priority. Also used to furnish CDF and/or OCF addresses. Diameter TS29.229, TS29.212
Dh AS (SIP AS, OSA, IM-SSF) <-> SLF Used by AS to find the HSS holding the user profile information in a multi-HSS environment. DH_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name. Diameter
Dx (I-CSCF or S-CSCF) <-> SLF Used by I-CSCF or S-CSCF to find a correct HSS in a multi-HSS environment. DX_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name. Diameter TS29.229, TS29.212
Gm UE, P-CSCF Used to exchange messages between SIP user equipment (UE) or Voip gateway and P-CSCF SIP
Go PDF, GGSN Allows operators to control QoS in a user plane and exchange charging correlation information between IMS and GPRS network COPS (Rel5), diameter (Rel6+)
Gq P-CSCF, PDF Used to exchange policy decisions-related information between P-CSCF and PDF Diameter
Gx PCEF, PCRF Used to exchange policy decisions-related information between PCEF and PCRF Diameter TS29.211, TS29.212
Gy PCEF, OCS Used for online flow-based bearer charging. Functionally equivalent to Ro interface Diameter TS23.203, TS32.299
ISC S-CSCF <-> AS Reference point between S-CSCF and AS. Main functions are to :
  • Notify the AS of the registered IMPU, registration state and UE capabilities
  • Supply the AS with information to allow it to execute multiple services
  • Convey charging function addresses
SIP
Ici IBCFs Used to exchange messages between an IBCF and another IBCF belonging to a different IMS network. SIP
Izi TrGWs Used to forward media streams from a TrGW to another TrGW belonging to a different IMS network. RTP
Ma I-CSCF <-> AS Main functions are to:
  • Forward SIP requests which are destined to a public service identity hosted by the AS
  • Originate a session on behalf of a user or public service identity, if the AS has no knowledge of a S-CSCF assigned to that user or public service identity
  • Convey charging function addresses
SIP
Mg MGCF -> I,S-CSCF ISUP signalling to SIP signalling and forwards SIP signalling to I-CSCF SIP
Mi S-CSCF -> BGCF Used to exchange messages between S-CSCF and BGCF SIP
Mj BGCF -> MGCF Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in the same IMS network to send SIP message from BGCF to MGCF SIP
Mk BGCF -> BGCF Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in another IMS network to send SIP message from BGCF to the BGCF in the other network SIP
Mm I-CSCF, S-CSCF, external IP network Used for exchanging messages between IMS and external IP networks SIP
Mn MGCF, IM-MGW Allows control of user-plane resources H.248
Mp MRFC, MRFP Allows an MRFC to control media stream resources provided by an MRFP. H.248
Mr
Mr'
S-CSCF, MRFC
AS, MRFC
Used to exchange information between S-CSCF and MRFC
Used to exchange session controls between AS and MRFC
Application server sends SIP message to MRFC to play tone and announcement. This SIP message contains sufficient information to play tone and announcement or provide information to MRFC, so that it can ask more information from application server through Cr Interface. SIP
Mw P-CSCF, I-CSCF, S-CSCF, AGCF Used to exchange messages between CSCFs. AGCF appears as a P-CSCF to the other CSCFs SIP
Mx BGCF/CSCF, IBCF Used for the interworking with another IMS network, when the BGCF has determined that a breakout should occur in the other IMS network to send SIP message from BGCF to the IBCF in the other network SIP
P1 AGCF, A-MGW Used for call control services by AGCF to control H.248 A-MGW and residential gateways H.248
P2 AGCF, CSCF Reference point between AGCF and CSCF. SIP
Rc MRB, AS Used by the AS to request that media resources be assigned to a call when using MRB in-line mode or in query mode SIP, in query mode (not specified)
Rf P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS Used to exchange offline charging information with CDF Diameter TS32.299
Ro AS, MRFC, S-CSCF Used to exchange online charging information with OCF Diameter TS32.299
Rx P-CSCF, PCRF Used to exchange policy and charging related information between P-CSCF and PCRF

Replacement for the Gq reference point.

Diameter TS29.214
Sh AS (SIP AS, OSA SCS), HSS Used to exchange User Profile information (e.g., user-related data, group lists, user-service-related information or user location information or charging function addresses (used when the AS has not received the third-party REGISTER for a user)) between an AS (SIP AS or OSA SCS) and HSS. Also allow AS to activate/deactivate filter criteria stored in the HSS on a per-subscriber basis Diameter
Si IM-SSF, HSS Transports CAMEL subscription information, including triggers for use by CAMEL-based application services information. MAP
Sr MRFC, AS Used by MRFC to fetch documents (scripts and other resources) from an AS HTTP
Ut UE and SIP AS (SIP AS, OSA SCS, IM-SSF) PES AS and AGCF Facilitates the management of subscriber information related to services and settings HTTP(s), XCAP
z POTS, Analog phones and VoIP gateways Conversion of POTS services to SIP messages

Session handling[edit]

One of the most important features of IMS, that of allowing for a SIP application to be dynamically and differentially (based on the user's profile) triggered, is implemented as a filter-and-redirect signalling mechanism in the S-CSCF.

The S-CSCF might apply filter criteria to determine the need to forward SIP requests to AS. It is important to note that services for the originating party will be applied in the originating network, while the services for the terminating party will be applied in the terminating network, all in the respective S-CSCFs.

Initial filter criteria[edit]

An initial filter criteria (iFC) is an XML-based format used for describing control logic. iFCs represent a provisioned subscription of a user to an application. They are stored in the HSS as part of the IMS Subscription Profile and are downloaded to the S-CSCF upon user registration (for registered users) or on processing demand (for services, acting as unregistered users). iFCs are valid throughout the registration lifetime or until the User Profile is changed.[5]

The iFC is composed of:

  • Priority - determines the order of checking the trigger.
  • Trigger point - logical condition(s) which is verified against initial dialog creating SIP requests or stand-alone SIP requests.
  • Application server URI - specifies the application server to be forwarded to when the trigger point matches.

There are two types of iFCs:

  • Shared - When provisioning, only a reference number (the shared iFC number) is assigned to the subscriber. During registration, only the number is sent to the CSCF, not the entire XML description. The complete XML will have previously been stored on the CSCF.
  • Non-shared - when provisioning, the entire XML description of the iFC is assigned to the subscriber. During registration, the entire XML description is sent to the CSCF.

Security aspects of early IMS and non-3GPP systems[edit]

It is envisaged that security defined in TS 33.203 may not be available for a while especially because of the lack of USIM/ISIM interfaces and prevalence of devices that support IPv4. For this situation, to provide some protection against the most significant threats, 3GPP defines some security mechanisms, which are informally known as "early IMS security," in TR33.978. This mechanism relies on the authentication performed during the network attachment procedures, which binds between the user's profile and its IP address. This mechanism is also weak because the signaling is not protected on the user–network interface.

CableLabs in PacketCable 2.0, which adopted also the IMS architecture but has no USIM/ISIM capabilities in their terminals, published deltas to the 3GPP specifications where the Digest-MD5 is a valid authentication option. Later on, TISPAN also did a similar effort given their fixed networks scopes, although the procedures are different. To compensate for the lack of IPsec capabilities, TLS has been added as an option for securing the Gm interface. Later 3GPP Releases have included the Digest-MD5 method, towards a Common-IMS platform, yet in its own and again different approach. Although all 3 variants of Digest-MD5 authentication have the same functionality and are the same from the IMS terminal's perspective, the implementations on the Cx interface between the S-CSCF and the HSS are different.

See also[edit]

References[edit]

  1. ^ Technical Specification Group Services and System Aspects (2006), IP Multimedia Subsystem (IMS), Stage 2, TS 23.228, 3rd Generation Partnership Project
  2. ^ Alexander Harrowell, Staff Writer (October 2006), A Pointless Multimedia Subsystem?, Mobile Communications International, archived from the original on September 2010
  3. ^ "3GPP Release Descriptions". 3GPP.
  4. ^ 3GPP, 23.228. "3GPP Stage 2 Specifications".
  5. ^ 3GPP, 29.228. "3GPP Stage 2 Specifications".

Books[edit]

  • Camarillo, Gonzalo; García-Martín, Miguel A. (2007). The 3G IP multimedia subsystem (IMS) : Merging the Internet and the Cellular Worlds (2 ed.). Chichester [u.a.]: Wiley. ISBN 0-470-01818-6.
  • Poikselkä, Miikka (2007). The IMS : IP multimedia concepts and services (2 ed.). Chichester [u.a.]: Wiley. ISBN 0-470-01906-9.
  • Syed A. Ahson, Mohammed Ilyas, ed. (2009). IP multimedia subsystem (IMS) handbook. Boca Raton: CRC Press. ISBN 1-4200-6459-2.
  • Wuthnow, Mark; Stafford, Matthew; Shih, Jerry (2010). IMS : A New Model for Blending Applications. Boca Raton: CRC Press. ISBN 1-4200-9285-5.

External links[edit]

Evolved HSPA

HSPA+ sign shown in notification bar on an Android-based smartphone.

Evolved High Speed Packet Access, or HSPA+, or HSPA(Plus), or HSPAP is a technical standard for wireless broadband telecommunication. It is the second phase of HSPA which has been introduced in 3GPP release 7 and being further improved in later 3GPP releases. HSPA+ can achieve data rates of up to 42.2 Mbit/s.[1] It introduces antenna array technologies such as beamforming and multiple-input multiple-output communications (MIMO). Beam forming focuses the transmitted power of an antenna in a beam towards the user’s direction. MIMO uses multiple antennas at the sending and receiving side. Further releases of the standard have introduced dual carrier operation, i.e. the simultaneous use of two 5 MHz carriers. The technology also delivers significant battery life improvements and dramatically quicker wake-from-idle time, delivering a true always-on connection. HSPA+ is an evolution of HSPA that upgrades the existing 3G network and provides a method for telecom operators to migrate towards 4G speeds that are more comparable to the initially available speeds of newer LTE networks without deploying a new radio interface. HSPA+ should not be confused with LTE though, which uses an air interface based on Orthogonal frequency-division multiple access modulation and multiple access.[2]

Advanced HSPA+ is a further evolution of HSPA+ and provides data rates up to 84.4 and 168 Megabits per second (Mbit/s) to the mobile device (downlink) and 22 Mbit/s from the mobile device (uplink) under ideal signal conditions. Technically these are achieved through the use of a multiple-antenna technique known as MIMO (for "multiple-input and multiple-output") and higher order modulation (64QAM) or combining multiple cells into one with a technique known as Dual-Cell HSDPA.

Downlink[edit]

Evolved HSDPA (HSPA+)[edit]

An Evolved HSDPA network can theoretically support up to 28 Mbit/s and 42 Mbit/s with a single 5 MHz carrier for Rel7 (MIMO with 16QAM) and Rel8 (64-QAM + MIMO), in good channel conditions with low correlation between transmit antennas. Although real speeds are far lower. Besides the throughput gain from doubling the number of cells to be used, some diversity and joint scheduling gains can also be achieved.[3] The QoS (Quality of Service) can be particularly improved for end users in poor radio reception where they cannot benefit from the other WCDMA capacity improvements (MIMO and higher order modulations) due to poor radio signal quality. In 3GPP a study item was completed in June 2008. The outcome can be found in technical report 25.825.[4] An alternative method to double the data rates is to double the bandwidth to 10 MHz (i.e. 2×5 MHz) by using DC-HSDPA.

Dual-Carrier HSDPA (DC-HSDPA)[edit]

Dual-Carrier HSDPA, also known as Dual-Cell HSDPA, is part of 3GPP Release 8 specification. It is the natural evolution of HSPA by means of carrier aggregation in the downlink. UMTS licenses are often issued as 5, 10, or 20 MHz paired spectrum allocations. The basic idea of the multicarrier feature is to achieve better resource utilization and spectrum efficiency by means of joint resource allocation and load balancing across the downlink carriers.[5]

New HSDPA User Equipment categories 21-24 have been introduced that support DC-HSDPA. DC-HSDPA can support up to 42.2 Mbit/s, but unlike HSPA, it does not need to rely on MIMO transmission.

The support of MIMO in combination with DC-HSDPA will allow operators deploying Release 7 MIMO to benefit from the DC-HSDPA functionality as defined in Release 8. While in Release 8 DC-HSDPA can only operate on adjacent carriers, Release 9 also allows that the paired cells can operate on two different frequency bands. Later releases allow the use of up to four carriers simultaneously.

From Release 9 onwards it will be possible to use DC-HSDPA in combination with MIMO being used on both carriers. The support of MIMO in combination with DC-HSDPA will allow operators even more capacity improvements within their network. This will allow theoretical speed of up to 84.4 Mbit/s.[6][7]

User Equipment (UE) Categories[edit]

The following table is derived from table 5.1a of the release 11 of 3GPP TS 25.306[8] and shows maximum data rates of different device classes and by what combination of features they are achieved. The per-cell per-stream data rate is limited by the Maximum number of bits of an HS-DSCH transport block received within an HS-DSCH TTI and the Minimum inter-TTI interval. The TTI is 2 ms. So for example Cat 10 can decode 27952 bits/2 ms = 13.976 MBit/s (and not 14.4 MBit/s as often claimed incorrectly). Categories 1-4 and 11 have inter-TTI intervals of 2 or 3, which reduces the maximum data rate by that factor. Dual-Cell and MIMO 2x2 each multiply the maximum data rate by 2, because multiple independent transport blocks are transmitted over different carriers or spatial streams, respectively. The data rates given in the table are rounded to one decimal point.

Notes:
  1. ^ 16-QAM implies QPSK support, 64-QAM implies 16-QAM and QPSK support.
  2. ^ The maximal code rate is not limited. A value close to 1 in this column indicates that the maximum data rate can be achieved only in ideal conditions. The device is therefore connected directly to the transmitter to demonstrate these data rates.
  3. ^ The maximum data rates given in the table are physical layer data rates. Application layer data rate is approximately 85% of that, due to the inclusion of IP headers (overhead information) etc.
  4. ^ Category 19 was specified in Release 7 as "For further use". Not until Release 8 simultaneous use of 64QAM and MIMO were allowed to obtain the specified max. data rate.
  5. ^ Category 20 was specified in Release 7 as "For further use". Not until Release 8 simultaneous use of 64QAM and MIMO were allowed to obtain the specified max. data rate.

Uplink[edit]

Dual-Carrier HSUPA (DC-HSUPA)[edit]

Dual-Carrier HSUPA, also known as Dual-Cell HSUPA, is a wireless broadband standard based on HSPA that is defined in 3GPP UMTS release 9. Dual Cell (DC-)HSUPA is the natural evolution of HSPA by means of carrier aggregation in the uplink.[9] UMTS licenses are often issued as 10 or 15 MHz paired spectrum allocations. The basic idea of the multicarrier feature is to achieve better resource utilization and spectrum efficiency by means of joint resource allocation and load balancing across the uplink carriers.

Similar enhancements as introduced with Dual-Cell HSDPA in the downlink for 3GPP Release 8 were standardized for the uplink in 3GPP Release 9, called Dual-Cell HSUPA. The standardisation of Release 9 was completed in December 2009.[10][11][12]

User Equipment (UE) Categories[edit]

The following table shows uplink speeds for the different categories of Evolved HSUPA.

Multi-carrier HSPA (MC-HSPA)[edit]

The aggregation of more than two carriers has been studied and 3GPP Release 11 is scheduled to include 4-carrier HSPA. The standard was scheduled to be finalised in Q3 2012 and first chipsets supporting MC-HSPA in late 2013. Release 11 specifies 8-carrier HSPA allowed in non-contiguous bands with 4 × 4 MIMO offering peak transfer rates up to 672 Mbit/s.

The 168 Mbit/s and 22 Mbit/s represent theoretical peak speeds. The actual speed for a user will be lower. In general, HSPA+ offers higher bitrates only in very good radio conditions (very close to the cell tower) or if the terminal and network both support either MIMO or Dual-Cell HSDPA, which effectively use two parallel transmit channels with different technical implementations.

The higher 168 Mbit/s speeds are achieved by using multiple carriers with Dual-Cell HSDPA and 4-way MIMO together simultaneously.[13][14]

All-IP architecture[edit]

A flattened all-IP architecture is an option for the network within HSPA+. In this architecture, the base stations connect to the network via IP (often Ethernet providing the transmission), bypassing legacy elements for the user's data connections. This makes the network faster and cheaper to deploy and operate. The legacy architecture is still permitted with the Evolved HSPA and is likely to exist for several years after adoption of the other aspects of HSPA+ (higher order modulation, multiple streams, etc.).

This 'flat architecture' connects the 'user plane' directly from the base station to the GGSN external gateway, using any available link technology supporting TCP/IP. The definition can be found in 3GPP TR25.999. The user's data flow bypasses the Radio Network Controller (RNC) and the SGSN of the previous 3GPP UMTS architecture versions, thus simplifying the architecture, reducing costs and delays. This is nearly identical to the 3GPP Long Term Evolution (LTE) flat architecture as defined in the 3GPP standard Rel-8. The changes allow cost effective modern link layer technologies such as xDSL or Ethernet, and these technologies are no longer tied to the more expensive and rigid requirements of the older standard of SONET/SDH and E1/T1 infrastructure.

There are no changes to the 'control plane'.

Nokia Siemens Networks Internet HSPA (I-HSPA) was the first commercial solution implementing the Evolved HSPA flattened all-IP architecture.[15]

Deployment[edit]

See also[edit]

References[edit]

  1. ^ "HSPA". About Us.
  2. ^ "Ericsson Review #1 2009 - Continued HSPA Evolution of mobile broadband" (PDF). Ericsson.com. 27 January 2009. Retrieved 2014-06-01.
  3. ^ R1-081546, “Initial multi-carrier HSPA performance evaluation”, Ericsson, 3GPP TSG-RAN WG1 #52bis, April, 2008
  4. ^ "3GPP specification: 25.825". 3gpp.org.
  5. ^ "Dual-Cell HSPA and its Future Evolution - Nomor Research". nomor. 2010-10-10. Retrieved 2016-03-30.
  6. ^ "2009-03: Standardisation updates on HSPA Evolution - Nomor Research". nomor. 2010-10-10. Retrieved 2016-03-30.
  7. ^ Dual carrier HSPA: DC-HSPA, DC-HSPDA
  8. ^ 3GPP TS 25.306 v11.0.0 http://www.3gpp.org/ftp/Specs/html-info/25306.htm
  9. ^ Nomor 3GPP Newsletter 2009-03: Standardisation updates on HSPA Evolution
  10. ^ 3GPP releases
  11. ^ Nomor 3GPP Newsletter 2009-03: Standardisation updates on HSPA Evolution, nomor.de
  12. ^ Nomor Research White Paper: Dual-Cell HSDPA and its Evolution
  13. ^ Klas Johansson; Johan Bergman; Dirk Gerstenberger; Mats Blomgren; Anders Wallén (28 January 2009). "Multi-Carrier HSPA Evolution" (PDF). Ericsson.com. Retrieved 2014-06-01.
  14. ^ "White paper Long Term HSPA Evolution Mobile broadband evolution beyond 3GPP Release 10" (PDF). Nokiaslemensnetworks.com. 14 December 2010. Retrieved 2014-06-01.
  15. ^ [1] Archived January 2, 2011, at the Wayback Machine.

External links[edit]

HSUPA

HSPA+ indicator shown in notification shade on an Android smartphone running version 6.0.1 (Marshmallow).

High Speed Packet Access (HSPA)[1] is an amalgamation of two mobile protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing 3G mobile telecommunication networks using the WCDMA protocols. A further improved 3GPP standard, Evolved High Speed Packet Access (also known as HSPA+), was released late in 2008 with subsequent worldwide adoption beginning in 2010. The newer standard allows bit-rates to reach as high as 337 Mbit/s in the downlink and 34 Mbit/s in the uplink. However, these speeds are rarely achieved in practice.[2]

Overview[edit]

The first HSPA specifications supported increased peak data rates of up to 14 Mbit/s in the downlink and 5.76 Mbit/s in the uplink. It also reduced latency and provided up to five times more system capacity in the downlink and up to twice as much system capacity in the uplink compared with original WCDMA protocol.

High Speed Downlink Packet Access (HSDPA)[edit]

High Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third-generation) mobile communications protocol in the High-Speed Packet Access (HSPA) family. HSDPA is also known as 3.5G, 3G+, or Turbo 3G. It allows networks based on the Universal Mobile Telecommunications System (UMTS) to have higher data speeds and capacity. HSDPA was introduced with 3GPP Release 5, which also accompanied an improvement on the uplink providing a new bearer of 384 kbit/s. The previous maximum bearer was 128 kbit/s. HSDPA also decreases latency and therefore the round trip time for applications. Evolved High Speed Packet Access (HSPA+), which was introduced in 3GPP Release 7, further increased data rates by adding 64QAM modulation, MIMO, and Dual-Carrier HSDPA operation. Even higher speeds of up to 337.5 Mbit/s are possible under 3GPP Release 11.[3]

The first phase of HSDPA was specified in the 3GPP release 5. Phase one introduced new basic functions and was aimed to achieve peak data rates of 14.0 Mbit/s with significantly reduced latency. The improvement in speed and latency reduces the cost per bit and enhances support for high-performance packet data applications. HSDPA is based on shared channel transmission, and its key features are shared channel and multi-code transmission, higher-order modulation, short transmission time interval (TTI), fast link adaptation and scheduling, and fast hybrid automatic repeat request (HARQ). Further new features are the High Speed Downlink Shared Channels (HS-DSCH), quadrature phase shift keying, 16-quadrature amplitude modulation, and the High Speed Medium Access protocol (MAC-hs) in base station.

The upgrade to HSDPA is often just a software update for WCDMA networks. In general, voice calls are usually prioritized over data transfer.

User equipment categories[edit]

The following table is derived from table 5.1a of the release 11 of 3GPP TS 25.306[4] and shows maximum data rates of different device classes and by what combination of features they are achieved. The per-cell per-stream data rate is limited by the "maximum number of bits of an HS-DSCH transport block received within an HS-DSCH TTI" and the "minimum inter-TTI interval". The TTI is 2 ms. So, for example, Cat 10 can decode 27952 bits/2 ms = 13.976 MBit/s (and not 14.4 MBit/s as often claimed incorrectly). Categories 1-4 and 11 have inter-TTI intervals of 2 or 3, which reduces the maximum data rate by that factor. Dual-Cell and MIMO 2x2 each multiply the maximum data rate by 2, because multiple independent transport blocks are transmitted over different carriers or spatial streams, respectively. The data rates given in the table are rounded to one decimal point.

Further UE categories were defined from 3GGP Release 7 onwards as Evolved HSPA (HSPA+) and are listed in Evolved HSDPA UE Categories.

Notes[edit]

  1. ^ 16-QAM implies QPSK support, 64-QAM implies 16-QAM and QPSK support.
  2. ^ The maximal code rate is not limited. A value close to 1 in this column indicates that the maximum data rate can be achieved only in ideal conditions. The device is therefore connected directly to the transmitter to demonstrate these data rates.
  3. ^ The maximum data rates given in the table are physical layer data rates. Application layer data rate is approximately 85% of that, due to the inclusion of IP headers (overhead information) etc.

Adoption[edit]

GPRS-speed in a HSDPA plan

As of 28 August 2009, 250 HSDPA networks have commercially launched mobile broadband services in 109 countries. 169 HSDPA networks support 3.6 Mbit/s peak downlink data throughput. A growing number are delivering 21 Mbit/s peak data downlink and 28 Mbit/s.

CDMA2000-EVDO networks had the early lead on performance, and Japanese providers were highly successful benchmarks for it. But lately this seems to be changing in favour of HSDPA as an increasing number of providers worldwide are adopting it.

During 2007, an increasing number of telcos worldwide began selling HSDPA USB modems to provide mobile broadband connections. In addition, the popularity of HSDPA landline replacement boxes grew—providing HSDPA for data via Ethernet and WiFi, and ports for connecting traditional landline telephones. Some are marketed with connection speeds of "up to 7.2 Mbit/s",[5] which is only attained under ideal conditions. As a result, these services can be slower than expected, when in fringe coverage indoors.

High Speed Uplink Packet Access (HSUPA)[edit]

High-Speed Uplink Packet Access (HSUPA) is a 3G mobile telephony protocol in the HSPA family. This technology was the second major step in the UMTS evolution process. It was specified and standardized in 3GPP Release 6 to improve the uplink data rate to 5.76 Mbit/s,[6] extending the capacity, and reducing latency. Together with additional improvements, this creates opportunities for a number of new applications including VoIP, uploading pictures, and sending large e-mail messages.

HSUPA has been superseded by newer technologies further advancing transfer rates. LTE provides up to 300 Mbit/s for downlink and 75 Mbit/s for uplink. Its evolution LTE Advanced supports maximum downlink rates of over 1 Gbit/s.

Technology[edit]

Enhanced Uplink adds a new transport channel to WCDMA, called the Enhanced Dedicated Channel (E-DCH). It also features several improvements similar to those of HSDPA, including multi-code transmission, shorter transmission time interval enabling faster link adaptation, fast scheduling, and fast Hybrid Automatic Repeat Request (HARQ) with incremental redundancy making retransmissions more effective. Similarly to HSDPA, HSUPA uses a "packet scheduler", but it operates on a "request-grant" principle where the user equipment (UE) requests permission to send data and the scheduler decides when and how many UEs will be allowed to do so. A request for transmission contains data about the state of the transmission buffer and the queue at the UE and its available power margin. However, unlike HSDPA, uplink transmissions are not orthogonal to each other.

In addition to this "scheduled" mode of transmission, the standards allows a self-initiated transmission mode from the UEs, denoted "non-scheduled". The non-scheduled mode can, for example, be used for VoIP services for which even the reduced TTI and the Node B based scheduler will be unable to provide the very short delay time and constant bandwidth required.

Each MAC-d flow (i.e., QoS flow) is configured to use either scheduled or non-scheduled modes. The UE adjusts the data rate for scheduled and non-scheduled flows independently. The maximum data rate of each non-scheduled flow is configured at call setup, and typically not changed frequently. The power used by the scheduled flows is controlled dynamically by the Node B through absolute grant (consisting of an actual value) and relative grant (consisting of a single up/down bit) messages.

At the physical layer, HSUPA introduces new channels E-AGCH (Absolute Grant Channel), E-RGCH (Relative Grant Channel), F-DPCH (Fractional-DPCH), E-HICH (E-DCH Hybrid ARQ Indicator Channel), E-DPCCH (E-DCH Dedicated Physical Control Channel), and E-DPDCH (E-DCH Dedicated Physical Data Channel).

E-DPDCH is used to carry the E-DCH Transport Channel; and E-DPCCH is used to carry the control information associated with the E-DCH.

User equipment categories[edit]

The following table shows uplink speeds for the different categories of HSUPA.

Further UE categories were defined from 3GGP Release 7 onwards as Evolved HSPA (HSPA+) and are listed in Evolved HSUPA UE Categories.

Evolved High Speed Packet Access (HSPA+)[edit]

Evolved HSPA (also known as HSPA Evolution, HSPA+) is a wireless broadband standard defined in 3GPP release 7 of the WCDMA specification. It provides extensions to the existing HSPA definitions and is therefore backward-compatible all the way to the original Release 99 WCDMA network releases. Evolved HSPA provides data rates up to 42.2 Mbit/s in the downlink[6] and 22 Mbit/s in the uplink[6] (per 5 MHz carrier) with multiple input, multiple output (2x2 MIMO) technologies and higher order modulation (64 QAM). With Dual Cell technology, these can be doubled.

Since 2011, HSPA+ has been very widely deployed amongst WCDMA operators with nearly 200 commitments.[7]

See also[edit]

References[edit]

  1. ^ Nomor Research: White Paper "Technology of High Speed Packet Access", nomor.de
  2. ^ "Universal Mobile Telecommunications System (UMTS); UE Radio Access capabilities" (PDF). ETSI. January 2014. Retrieved March 4, 2014.
  3. ^ "HSPA". About Us.
  4. ^ 3GPP TS 25.306 v11.0.0 http://www.3gpp.org/ftp/Specs/html-info/25306.htm
  5. ^ "Vodafone UK - Maintenance". vodafone.co.uk.
  6. ^ a b c Sadique, Abubaker. "Introduction to Generation in mobile Communication". Retrieved 3 August 2018.
  7. ^ "DC-HSPA+ brings 42 Mbps to 39 networks". 3GPP. Retrieved 8 July 2017.

Bibliography[edit]

  • Sauter, Martin (2006). Communication Systems for the Mobile Information Society. Chichester: John Wiley. ISBN 0-470-02676-6.
  • Harri Holma and Antti Toskala (2006). HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications. ISBN 0-470-01884-4.
  • Stuhlfauth, Reiner (2012). High Speed Packet Access: Technology and measurement aspects of HSDPA and HSUPA mobile radio systems. Munich. ISBN 978-3-939837-14-5.

External links[edit]

HSPA

HSPA+ indicator shown in notification shade on an Android smartphone running version 6.0.1 (Marshmallow).

High Speed Packet Access (HSPA)[1] is an amalgamation of two mobile protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing 3G mobile telecommunication networks using the WCDMA protocols. A further improved 3GPP standard, Evolved High Speed Packet Access (also known as HSPA+), was released late in 2008 with subsequent worldwide adoption beginning in 2010. The newer standard allows bit-rates to reach as high as 337 Mbit/s in the downlink and 34 Mbit/s in the uplink. However, these speeds are rarely achieved in practice.[2]

Overview[edit]

The first HSPA specifications supported increased peak data rates of up to 14 Mbit/s in the downlink and 5.76 Mbit/s in the uplink. It also reduced latency and provided up to five times more system capacity in the downlink and up to twice as much system capacity in the uplink compared with original WCDMA protocol.

High Speed Downlink Packet Access (HSDPA)[edit]

High Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third-generation) mobile communications protocol in the High-Speed Packet Access (HSPA) family. HSDPA is also known as 3.5G, 3G+, or Turbo 3G. It allows networks based on the Universal Mobile Telecommunications System (UMTS) to have higher data speeds and capacity. HSDPA was introduced with 3GPP Release 5, which also accompanied an improvement on the uplink providing a new bearer of 384 kbit/s. The previous maximum bearer was 128 kbit/s. HSDPA also decreases latency and therefore the round trip time for applications. Evolved High Speed Packet Access (HSPA+), which was introduced in 3GPP Release 7, further increased data rates by adding 64QAM modulation, MIMO, and Dual-Carrier HSDPA operation. Even higher speeds of up to 337.5 Mbit/s are possible under 3GPP Release 11.[3]

The first phase of HSDPA was specified in the 3GPP release 5. Phase one introduced new basic functions and was aimed to achieve peak data rates of 14.0 Mbit/s with significantly reduced latency. The improvement in speed and latency reduces the cost per bit and enhances support for high-performance packet data applications. HSDPA is based on shared channel transmission, and its key features are shared channel and multi-code transmission, higher-order modulation, short transmission time interval (TTI), fast link adaptation and scheduling, and fast hybrid automatic repeat request (HARQ). Further new features are the High Speed Downlink Shared Channels (HS-DSCH), quadrature phase shift keying, 16-quadrature amplitude modulation, and the High Speed Medium Access protocol (MAC-hs) in base station.

The upgrade to HSDPA is often just a software update for WCDMA networks. In general, voice calls are usually prioritized over data transfer.

User equipment categories[edit]

The following table is derived from table 5.1a of the release 11 of 3GPP TS 25.306[4] and shows maximum data rates of different device classes and by what combination of features they are achieved. The per-cell per-stream data rate is limited by the "maximum number of bits of an HS-DSCH transport block received within an HS-DSCH TTI" and the "minimum inter-TTI interval". The TTI is 2 ms. So, for example, Cat 10 can decode 27952 bits/2 ms = 13.976 MBit/s (and not 14.4 MBit/s as often claimed incorrectly). Categories 1-4 and 11 have inter-TTI intervals of 2 or 3, which reduces the maximum data rate by that factor. Dual-Cell and MIMO 2x2 each multiply the maximum data rate by 2, because multiple independent transport blocks are transmitted over different carriers or spatial streams, respectively. The data rates given in the table are rounded to one decimal point.

Further UE categories were defined from 3GGP Release 7 onwards as Evolved HSPA (HSPA+) and are listed in Evolved HSDPA UE Categories.

Notes[edit]

  1. ^ 16-QAM implies QPSK support, 64-QAM implies 16-QAM and QPSK support.
  2. ^ The maximal code rate is not limited. A value close to 1 in this column indicates that the maximum data rate can be achieved only in ideal conditions. The device is therefore connected directly to the transmitter to demonstrate these data rates.
  3. ^ The maximum data rates given in the table are physical layer data rates. Application layer data rate is approximately 85% of that, due to the inclusion of IP headers (overhead information) etc.

Adoption[edit]

GPRS-speed in a HSDPA plan

As of 28 August 2009, 250 HSDPA networks have commercially launched mobile broadband services in 109 countries. 169 HSDPA networks support 3.6 Mbit/s peak downlink data throughput. A growing number are delivering 21 Mbit/s peak data downlink and 28 Mbit/s.

CDMA2000-EVDO networks had the early lead on performance, and Japanese providers were highly successful benchmarks for it. But lately this seems to be changing in favour of HSDPA as an increasing number of providers worldwide are adopting it.

During 2007, an increasing number of telcos worldwide began selling HSDPA USB modems to provide mobile broadband connections. In addition, the popularity of HSDPA landline replacement boxes grew—providing HSDPA for data via Ethernet and WiFi, and ports for connecting traditional landline telephones. Some are marketed with connection speeds of "up to 7.2 Mbit/s",[5] which is only attained under ideal conditions. As a result, these services can be slower than expected, when in fringe coverage indoors.

High Speed Uplink Packet Access (HSUPA)[edit]

High-Speed Uplink Packet Access (HSUPA) is a 3G mobile telephony protocol in the HSPA family. This technology was the second major step in the UMTS evolution process. It was specified and standardized in 3GPP Release 6 to improve the uplink data rate to 5.76 Mbit/s,[6] extending the capacity, and reducing latency. Together with additional improvements, this creates opportunities for a number of new applications including VoIP, uploading pictures, and sending large e-mail messages.

HSUPA has been superseded by newer technologies further advancing transfer rates. LTE provides up to 300 Mbit/s for downlink and 75 Mbit/s for uplink. Its evolution LTE Advanced supports maximum downlink rates of over 1 Gbit/s.

Technology[edit]

Enhanced Uplink adds a new transport channel to WCDMA, called the Enhanced Dedicated Channel (E-DCH). It also features several improvements similar to those of HSDPA, including multi-code transmission, shorter transmission time interval enabling faster link adaptation, fast scheduling, and fast Hybrid Automatic Repeat Request (HARQ) with incremental redundancy making retransmissions more effective. Similarly to HSDPA, HSUPA uses a "packet scheduler", but it operates on a "request-grant" principle where the user equipment (UE) requests permission to send data and the scheduler decides when and how many UEs will be allowed to do so. A request for transmission contains data about the state of the transmission buffer and the queue at the UE and its available power margin. However, unlike HSDPA, uplink transmissions are not orthogonal to each other.

In addition to this "scheduled" mode of transmission, the standards allows a self-initiated transmission mode from the UEs, denoted "non-scheduled". The non-scheduled mode can, for example, be used for VoIP services for which even the reduced TTI and the Node B based scheduler will be unable to provide the very short delay time and constant bandwidth required.

Each MAC-d flow (i.e., QoS flow) is configured to use either scheduled or non-scheduled modes. The UE adjusts the data rate for scheduled and non-scheduled flows independently. The maximum data rate of each non-scheduled flow is configured at call setup, and typically not changed frequently. The power used by the scheduled flows is controlled dynamically by the Node B through absolute grant (consisting of an actual value) and relative grant (consisting of a single up/down bit) messages.

At the physical layer, HSUPA introduces new channels E-AGCH (Absolute Grant Channel), E-RGCH (Relative Grant Channel), F-DPCH (Fractional-DPCH), E-HICH (E-DCH Hybrid ARQ Indicator Channel), E-DPCCH (E-DCH Dedicated Physical Control Channel), and E-DPDCH (E-DCH Dedicated Physical Data Channel).

E-DPDCH is used to carry the E-DCH Transport Channel; and E-DPCCH is used to carry the control information associated with the E-DCH.

User equipment categories[edit]

The following table shows uplink speeds for the different categories of HSUPA.

Further UE categories were defined from 3GGP Release 7 onwards as Evolved HSPA (HSPA+) and are listed in Evolved HSUPA UE Categories.

Evolved High Speed Packet Access (HSPA+)[edit]

Evolved HSPA (also known as HSPA Evolution, HSPA+) is a wireless broadband standard defined in 3GPP release 7 of the WCDMA specification. It provides extensions to the existing HSPA definitions and is therefore backward-compatible all the way to the original Release 99 WCDMA network releases. Evolved HSPA provides data rates up to 42.2 Mbit/s in the downlink[6] and 22 Mbit/s in the uplink[6] (per 5 MHz carrier) with multiple input, multiple output (2x2 MIMO) technologies and higher order modulation (64 QAM). With Dual Cell technology, these can be doubled.

Since 2011, HSPA+ has been very widely deployed amongst WCDMA operators with nearly 200 commitments.[7]

See also[edit]

References[edit]

  1. ^ Nomor Research: White Paper "Technology of High Speed Packet Access", nomor.de
  2. ^ "Universal Mobile Telecommunications System (UMTS); UE Radio Access capabilities" (PDF). ETSI. January 2014. Retrieved March 4, 2014.
  3. ^ "HSPA". About Us.
  4. ^ 3GPP TS 25.306 v11.0.0 http://www.3gpp.org/ftp/Specs/html-info/25306.htm
  5. ^ "Vodafone UK - Maintenance". vodafone.co.uk.
  6. ^ a b c Sadique, Abubaker. "Introduction to Generation in mobile Communication". Retrieved 3 August 2018.
  7. ^ "DC-HSPA+ brings 42 Mbps to 39 networks". 3GPP. Retrieved 8 July 2017.

Bibliography[edit]

  • Sauter, Martin (2006). Communication Systems for the Mobile Information Society. Chichester: John Wiley. ISBN 0-470-02676-6.
  • Harri Holma and Antti Toskala (2006). HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications. ISBN 0-470-01884-4.
  • Stuhlfauth, Reiner (2012). High Speed Packet Access: Technology and measurement aspects of HSDPA and HSUPA mobile radio systems. Munich. ISBN 978-3-939837-14-5.

External links[edit]