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Common IMS Discussion

3GPP-3GPP2 Workshop CIMS-080002 Puerto Vallarta, MEXICO, 24th – 25th January 2008 Source: Alcatel-Lucent Title: Common IMS - Discussion Agenda item: 3 Document for: INFORMATION. Common IMS Discussion. Milo Orsic.

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Common IMS Discussion

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  1. 3GPP-3GPP2 Workshop CIMS-080002 Puerto Vallarta, MEXICO, 24th – 25th January 2008 Source: Alcatel-Lucent Title: Common IMS - Discussion Agenda item: 3 Document for: INFORMATION

  2. Common IMSDiscussion Milo Orsic

  3. Common IMS - Layered Architecture SMS PNM Server Application Layer CSI Server Conf. Server Common IMS Layer IMS IP IP Layer Sub-network Access Layer GPRS WiMax cdma2000 SDL Figure 1. • There are two layered models: - There is a Common IMS Layer, and Application Layer on top (Figure 1); - The SIP (IMS) Layer is ”the top” Layer that incorporates all services. cdma2000

  4. Common IMS - Layered Architecture IMS – IP layer interfaces: In layered architecture, a given layer provides services to the layer above it, and obtain services from the layer below it. Hence, the IMS may request services from the IP layer (e.g. QoS) and obtain information from the IP layer (e.g. IP charging information). Models: • The Common IMS uses only the transport capabilities (e.g. UDP, TCP) of the underlying IP layer (socket model). • The Common IMS uses additional services (e.g. QoS, Polices, Charge authorization). Hence, e.g. Tx, Gq interfaces needed. • If the UE is capable to request and obtain IP layer services (which don’t have to be authorized by the IMS layer), and e.g. Operator charges per IP layer services, then there is no need for IMS-IP layer interface in the Common IMS core network (e.g. Tx, Gq). Internal interface in the UE not standardized (i.e. it is internal to the UE stack).

  5. 3GPP/3GPP2 - Historic Perspective Application Servers IMS Rel-5 IMS ???? IP Layer IP IP Sub-network Access Layer cdma2000 GPRS Figure 2. AT the time - the 3GPP2 IP Network and Mobile Stations (MS) supported: The link between the MS and the Access Router (PDSN) was established by using the Point to Point Protocol [RFC 1661] and HDLC-like Framing [RFC 1662]. The PPP transparency was support in accordance with RFC 1662. For IPv4, the Access Router (PDSN) assigned an IPv4 address to the MS during the IPCP phase of PPP according to the PCP [RFC 1332]. cdma2000

  6. 3GPP/3GPP2 - Historic Perspective The Access Router (PDSN) supported the two authentication mechanisms: CHAP [RFC 1994] and PAP [RFC 1334]. The Access Router (PDSN) implemented IPCP configuration options as defined in RFC 1877 for the DNS server address negotiation. The Access Routed (PDSN) negotiated Primary and Secondary DNS server IP addresses with the MS. - For IPv6 the following RFCs were supported: - An IPv6 Aggregatable Global Unicast Address Format [RFC 3587]; - Internet Protocol, Version 6 (IPv6) Specification [RFC 2460]; - Neighbour Discovery for IP Version 6 (IPv6) [RFC 2461]; - IPv6 Stateless Address Autoconfiguration [RFC 2462]; - Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification [RFC 2463]; - IP Version 6 over PPP [RFC 2472]; - IP Version 6 Addressing Architecture [RFC 3513]. cdma2000

  7. 3GPP/3GPP2 - Historic Perspective • The Access Router (PDSN) supported the following header compression algorithms: • Van Jacobson TCP/IP header compression [RFC 1144]. • ROHC, Framework and four profiles: RTP, UDP, ESP, and uncompressed [RFC 3095] with ROHC over PPP [RFC 3241]; • ROHC: A Link Layer Assisted Profile for IP/UDP/RTP [RFC3242]; • IP Header Compression [RFC 2507] with IP Header Compression over PPP [RFC 2509]; For IPv6 - upon negotiation and the establishment of a unique link-local address for both the Access Routed (PDSN) and the MS, the Access Routed (PDSN) immediately transmitted initial unsolicited Router Advertisement (RA) messages on the PPP link using its link-local address as a source address. The Access Routed (PDSN) included a globally unique /64 prefix in the Router Advertisement message to the MS. The MS used this prefix to configure its global IPv6 addresses.

  8. 3GPP/3GPP2 - Historic Perspective • Toward the Network, the Access Routed (PDSN) acted as a RADIUS client in accordance with RFC 2865 when communicating with the Visited RADIUS server (e.g. when exchanging the authentication information). The Visited and Home RADIUS Server followed the guidelines specified in RFCs 2865, 2866, and 3162. • The MS was able to choose an IPv4 only, an IPv6 only, or both IPv4 and IPv6 simultaneously. • For Mobile IPv4 operation the Dynamic Home Agent Assignment was also supported. • For Mobile IPv4 operation the following standards were supported: • RFC 2002-2006; • Reverse Tunnelling [RFC 3024]; • Foreign Agent Challenge/Response [RFC 3012]; • NAI Extension [RFC 2794].

  9. 3GPP/3GPP2 - Differences 3GPP supports link-level mobility (GPRS). Hence, the UE will attach itself in the Visited Network using the SGSN. There is no motivation to place the GGSN in the Visited Network if the P-CSCF is in the Home Network. Therefore, the GGSN and P-CSCF are in the same network. The cdma2000 UE IP-attaches itself to the Visited Network. To support IMS services, there is no need to have the P-CSCF in the Visited Network. To obtain the IMS services the UE doesn’t need the P-CSCF in the Visited Network (same as your corporate NAS and associated IPsec to retrieve your email), i.e. the IMS service may be deployed in spite of not being supported in the Visited Network.

  10. P-CSCF location Visited IMS Network Home IMS Network IP Point of attachment cdma2000 - yes cdma2000 - no Home IP network 3GPP-yes 3GPP-no cdma2000 - yes cdma2000 - yes Visited IP Network 3GPP-no 3GPP-yes 3GPP/3GPP2 - Differences • P-CSCF location Impact: P-CSCF discovery and provisioning (Removable User Identity Module R-UIM) NAT location and traversal [for signaling and media]

  11. 3GPP/3GPP2 - Differences 3GPP supports link-level mobility (GPRS). There is a need for IP flow grouping (e.g. for QoS and charging)specified in RFC-3388 and RFC-3524, and mapping the groups onto the particular links (i.e. “pdp context”). 3GPP2 supports IP level mobility (MoIP), no need for IP flow groupings (e.g. per IP-flow QoS and charging).

  12. 3GPP/3GPP2 - Differences 3GPP Assumptions: - Originally the 3GPP assumed only single IPv6 address (no dual IPv4/IPv6 stack in the UE) used for: - For SIP signaling (hop-by-hop) – OK, since only the entry/exit points (e.g. IBCF, I-CSCF) support dual IP addressing and are advertised in the DNS. - For media (end-to-end). Hence, IPv6/IPv4 address translation needed. - No separation of “media path” from “signaling path”. - UE IP attachment is at GGSN. GGSN and P-CSCF in the same network - no need for NAT insertion between the GGSN and P-CSCF. - IPv6 addressing (no IPv6 address shortage) - no need for NATs. - For Fixed Broadband (NAT at customer premise). NAT traversal for signaling specified (UDP encapsulation of tunneled IPsec).

  13. 3GPP/3GPP2 - Differences 3GPP2 Assumptions: - The cdma2000 MS may have an IPv4 only, an IPv6 only, or both IPv4 and IPv6 simultaneously (dual IPv4/IPv6 stack). - P-CSCF discovery for IPv4 (RFC 3361 and RFC 2131) supported. - There is no need for IPv6/IPv4 address translation for cdma2000 UEs. S-CSCF must be able to handle cdma2000 UEs and 3GPP UEs (may apply to Fixed Broadband UEs). - Separation of “media path” from “signaling path” possible (UE IP-attached in Visited Network, the P-CSCF in the Home Network). - NAT may be needed due to IPv4 address shortage (currently not addressed in 3GPP2). - Impact of MoIP Route Optimization on signaling and media (currently not addressed in 3GPP2).

  14. 3GPP/3GPP2 - Differences Subscription Locator Function (SLF): If the target is a distributed date-base (e.g. HSS, HAAA) identified with a single FQDN, the problem “how to reach the proper server handling the particular subscriber” may be addressed by employing either: - Redirect model (SLF), or - Proxy model. - For IP subscriber identified with a NAI, 3GPP2 used Proxy model. The same mechanism was also used to access the HSS. - Hence, no SLF is used in 3GPP2

  15. 3GPP/3GPP2 - Differences IMS – IP layer interfaces: - Since the UE may may not need or it is capable to request and obtain IP layer services (which don’t have to be authorized by the IMS layer), and e.g. Operator charges per IP layer services, then there is no need for IMS-IP layer interface (e.g. Tx, Gq) in the Common IMS core network. - In 3GPP2 IMS-IP layer interface (e.g. between P-CSCF and PCRF) is optional and the P-Charging-Vector may contain an empty “access network charging info” parameter.

  16. 3GPP/3GPP2 - Differences 3GPP2 P-Charging-Vector syntax: 3GPP2 supports per IP flow charging, hence the syntax of “access network charging info” parameter is different. P-Charging-Vector: icid-value= icid-generated-at= orig-ioi= term-ioi= generic-param (access network charging info)

  17. 3GPP/3GPP2 - Differences ISIM vs. R-UIM/no R-UIM [Removable User Identity Module ] Impact: - R-UIM - Temporary PUID derivation - Home P-CSCF address [FQDN or IP address?] - Authentication procedure (IMS-AKA, SIP Digest, tls)

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