1、Interworking Internet Telephony and Wireless Telecommunications Networks,Presented By: Matt Vidal,Jonathan Lennox,Kazutaka Murakami,Mehmet Karaul,Thomas F. La Porta,July 1,2003,Bell Labs, Lucent Technologies,lennox kmurakami karaul tlpbell- bell- bell- bell-,2,Introduction,Wireless Mobile Telephony
2、and Internet Telephony are both growing at a rapid pace Mobile: Global System for Mobile communication (GSM) Internet Telephony: Session Initiation Protocol (SIP) What is the best way for calls to be delivered and routed between the two networks? Both SIP and GSM are designed to interface with Publi
3、c Switched Telephone Network (PSTN) PSTN Interface is a bad idea as it can be very inefficient in the mobile realm,3,Introduction (2),Triangular Routing in mobile networks due to PSTN Causes highly inefficient routing of both signaling and media packets,Triangular Routing in Mobile Networks,4,Backgr
4、ound: GSM Mobility and Call Delivery,MSC: Mobile Switching Center Serving MSC routes all mobile calls within its serving area Gateway MSC directs calls from PSTN into mobile access network VLR: Visitor Location Register Stores information about devices in its serving area HLR: Home Location Register
5、 Maintains subscriber information and location GSM device has International Mobile Subscriber Identity (IMSI) HLR gets mobiles location using GSM Mobile Application Part (MAP) Protocol,5,Background: GSM Mobility and Call Delivery (2),GSM call placed from Mobile Station ISDN Number (MSISDN) Sent to g
6、ateway MSC (2 Phases) 1. Gateway MSC obtains temporary Mobile Station Routing Number (MSRN) by contacting subscribers HLR 2. The call is routed to the serving MSC using ISDN User Part Protocol (ISUP) Intra-MSC Handover (Between base stations within one MSCs control) media traffic is simply redirecte
7、d Inter-MSC Handover (To a different serving MSC) old serving MSC is required as an anchor, extending the calls media circuit across the PSTN,6,Background: GSM Mobility and Call Delivery (3),Elements of a GSM Network,7,Background: SIP Mobility and Call Delivery,Simpler than GSM All devices communica
8、te by IP All signaling occurs with SIP GSM / SIP MappingGSM SIPHLR RegistrarGateway MSC Home Proxy ServerServing MSC End System (for REGISTER) MSISDN User Address (in INVITE)IMSI User Address (in REGISTER)MSRN Device Address,8,Background: SIP Mobility and Call Delivery (2),End Systems Contact Regist
9、rars Directly (Not 2 Phases) New SIP device sends SIP REGISTER to its Registrar SIP Address is in the form of UserDomain New call sends SIP INVITE to SIP Address Call is established and media flows directly between the endpoints Handles handovers by reconfiguring the IP Address it is sending to with
10、out having to relay from home address as in mobile IP.,9,Background: SIP Mobility and Call Delivery (3),Elements of a SIP Network,10,Architecture: SIP/GSM Interworking,Three primary issues to consider when interworking Internet Telephony and Wireless Systems 1. How Calls May Be Placed From SIP to GS
11、M 2. How Calls May Be Placed From GSM to SIP 3. How In-Call Mobility (Handovers) Is Handled Issues two and three are easily dealt with The first issue is the most complicated and will be investigated thoroughly,11,SIP/GSM Interworking: Calls From GSM To SIP,Calls from GSM to SIP are functionally sim
12、ilar to calls originating from PSTN to SIP Difference is that they are addressed in telephone form rather than UserDomain form Solution is to perform a lookup (Enum) based on the telephone number Maybe use custom dialing plan prefixes Translate number into UserDomain form Proceed as usual PSTN-to-SI
13、P,12,SIP/GSM Interworking: In-Call Handover,Two Categories 1. Intra-MSC 2. Inter-MSC Intra-MSC needs no special treatment for SIP/GSM Interworking Could optimize by using different IP Addresses to correspond to different base stations under serving MSCs control Inter-MSC affects SIP/GSM Interworking
14、 Remains for future study,13,SIP/GSM Interworking: Mobile-Terminated Calls,Most Complex Aspect of SIP/GSM Interworking Need direct media stream between caller and serving MSC To do so, SIP signaling needs to reach Serving MSC for: IP Address Port Assignment Conventions Media Characteristics Three pr
15、oposals for how SIP devices can determine the MSC at which the GSM device is registered Each has various degrees of complexity, signaling traffic and call setup delay,14,Proposal 1: Modified Registration,Enhance MSCs Registration Behavior Serving MSC registers with Subscribers HLR and with “Home SIP
16、 Registrar” MSC Needs to find SIP Registrar This can be done with an Enum lookup using GSM devices MSISDN number from registration Initial Registration (Dual Registration) 8-10 GSM MAP messages, 6 DNS messages, 4 SIP messages Call Setup (Standard SIP) 1 SIP message, 4 DNS messages,15,Proposal 1: Mod
17、ified Registration (2),Modified Registration Procedure,16,Proposal 1: Modified Registration (3),Advantages Minimal Infrastructure Modifications Requires updates to the serving MSC Requires the addition of an Enum type of Database Call Setup is SIP, one phase lookup Disadvantages With two databases,
18、inconsistency could be a problem GSM HLR is persistent SIP Registrations require refreshing Dual registration requires extra signaling overhead,17,Proposal 2: Modified Call Setup,Adapt GSM Call Setup GSM Registration untouched GSM call setup behaves like SIP SIP Proxy Server determines MSISDN based
19、on SIP Address Queries HLR for MSRN Enum Lookup for serving MSC SIP Address SIP INVITE message sent to serving MSC Initial Registration (Standard GSM) 8-10 GSM MAP messages Call Setup 4 GSM MAP messages, 6 DNS messages, 1 SIP message,18,Proposal 2: Modified Call Setup (2),Modified Call Setup Procedu
20、re,19,Proposal 2: Modified Call Setup (3),Advantages GSM database remains the same No possibility of out-of-sync database like in Modified Call Setup Low registration overhead Same as GSM Disadvantages Three Phase Call Setup! GSM MAP query for the MSRN Enum lookup for SIP device address Call initiat
21、ion SIP and HLR need to be in communication,20,Proposal 3: Modified HLR,GSM HLR in Charge Standard GSM registration HLR determines the SIP device address at the serving MSC HLR performs a Enum lookup to gather the serving MSCs SIP domain (taking advantage of SIP address format) HLR returns SIP Addre
22、ss (mapped from GSM registration, MSISDNhostname.of.serving.MSC) to the SIP Proxy Server Initial Registration 8-10 GSM MAP messages, 2 DNS messages Call Setup 4 DNS messages, 1 SIP message,21,Proposal 3: Modified HLR (2),Modified HLR, Registration Procedure,22,Proposal 3: Modified HLR (3),Modified H
23、LR, Call Setup Procedure,23,Proposal 3: Modified HLR (4),Advantages Very low signaling overhead Nearly matches best registration overhead Has the best call setup overhead Low Call Setup Latency Disadvantages Significant modification of GSM HLR SIP Proxy Server and HLR must be co-located, or have an
24、interface protocol designed,24,Analysis,Two important measures for SIP and GSM Proposals: Signaling Load Setup Delay (to be investigated at a later time) To compare total signaling load, signaling messages were weighted and compared Modified HLR has lowest signaling load (20-30% less) The other two
25、depend on traffic parameters Modified Call Setup best with low incoming call rate and low call/mobility ratio (higher setup time) Modified Registration best with high incoming call rate and high call/mobility ratio (higher registration time),25,Analysis (2),Weighted Signaling Load of all Three Propo
26、sals,26,Implementation,Implemented Modified Call Setup Enhanced Mobile Call Processing (EMCP) of Bell Labs Router for Integrated Mobile Access (RIMA) RIMA composed of Base Station Controller (BSC), PSTN Media Gateway (PSTN-GW), RTP Media Gateway (RTP-GW) and EMCP network BSC: Circuit Voice Formatted
27、 to/from Packet Voice PSTN-GW: RTP/IP Packet Voice Translated to/from Circuit Voice (RIMA PSTN) RTP-GW: RIMA Media Connections to Internet EMCP: Implements RIMAs MSC and VLR Functionality (IP Telephony Signaling Gateway),27,Implementation (2),RIMA-based Network Implementation,28,Implementation (3),E
28、MCP Processing Engine,29,Implementation (4),EMCP Network Architecture,30,Conclusions,Proposed Three Schemes to Directly Interconnect SIP Internet Telephony and GSM Mobile Telephony Systems Modified Registration Modified Call Setup Modified HLR Eliminates Triangular Routing Created by PSTN More Effic
29、ient Media Packet Routing Eliminates Unnecessary Transcodings Due to PSTN Better Voice Quality,31,Conclusions (2),Modified Registration Very Efficient When High Incoming Call Rate And High Call/Mobility Ratio (Higher Registration Overhead) Modified Call Setup Very Efficient When Low Incoming Call Rate And Low Call/Mobility Ratio (Higher Call Setup Overhead) Modified HLR Very Low Signaling Burden(20-30% Less Than Modified Registration / Modified Call Setup) Significant GSM Equipment Modification Development is in progress for a Modified HLR scheme,32,Questions?,
