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True Number Portability and Advanced Call Screening in a SIP-Based IP Telephony System

Ismail Dalgic, Michael Borella, Rick Dean, Jacek Grabiec, Jerry Mahler, Guido Schuster, an

d Ikhlag Sidhu 3Com Corporation

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Overview

Traditional PSTN (public switched telephone network) features CLASS (custom local area signaling service) PBX (private branch exchange)

PDA Enhanced IP Telephony SIP (session initiation protocol), Etherphone a

nd SIP-EtherPhone System Integration --- Number Portability

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CLASS Features Call blocking

The customer may specify one or more numbers from which he or she does not want to receive calls

Call trace Allows a customer to trigger a trace of the number

of the most recent caller

Call return Returns a call to the most recent caller. If the most

recent caller is busy, the returned call may be queued until it can be completed

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CLASS Features Caller ID

The caller’s number is automatically displayed Caller ID blocking

Allows a caller to block the display of their number in a callee’s caller ID device

Priority ringing Different priority numbers have different rings

Call forwarding A customer may cause calls to their number to be aut

omatically forwarded to another number for a period of time

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PBX Features

PBX is usually used within a medium-to-large-sized business for employee telephony service

Call transfer An established call may be transferred form one

number to another on the same PBX Call forwarding

A PBX number can be programmed to automatically transfer a call to another number when the first number doesn’t answer or is busy

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PBX Features

Camp-on queuing A call to a busy number can be queued, and the

PBX will ring them when the callee answers Conference calling

Two or more parties can be connected to one another by dialing into a conference bridge number

Call parking An established call at one number can be put on

hold and reestablished from another number

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PBX Features

Executive override A privileged individual can break into an

established call and then the call becomes three-way

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PDA Enhanced IP Telephony

True Portable The PDA follows the user wherever he/she goes

Shifting intelligence from the network to

the telephones

Providing personal and location

information to the network by user’s

PDA

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New Application and Services of PDA

The PDA may act as a smart card, providing authentication information for making toll calls

The user may program the system through the PDA. For example, During the business hours the default location to

forward calls could be set to be the user’s office, and during other hours his/her cellular pager

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New Application and Services of PDA

Download voicemail and play it back offline It will be useful if the user could not spend

much time on the phone A traveler at an airport may download his/her

30 min worth of voicemail in a few min just before taking a flight, and may listen to those message during the flight

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Session Initiation Protocol (SIP)

SIP is an application-layer control protocol that can establish, modify and terminate multimedia sessions or calls

Two major architectural elements User agent (UA) : resides at SIP end stations

» User agent client (UAC): issuing INVITE request» User agent server (UAS): accepting the call

Network server: three different types» Redirect server» Proxy server» registrar server

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SIP Network Server

Registrar server Used to record the SIP address (SIP URL) and th

e associated IP address

Redirect server It processes an INVITE message by sending bac

k the SIP address where the callee is reachable Proxy server

Stateful or stateless forking or nonforking

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SIP Network Structure

SIP-based station

SIP-based station

RegistrationRegistrar server

Main SIP Server

Redirect Server (SIP database)

Issuing INTIVE message Proxy server

SIP-basedstation

SIP-basedstation

Connected

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SIP-Etherphone

Etherphone An Etherphone is a telephone that can be plugg

ed into an Ethernet port Support IP using an IP address that is obtained

by Dynamic Host Configuration Protocol ( DHCP)

» If the location is changed, the IP address automatically changed

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SIP-Etherphone

Tow major parts of Etherphone Signaling stack

» Setup phase» Manage phase» Tear down phase

Media engine» Sender: sampling and encoding the voice» Receiver: performing the reverse operations and manage a receiver

buffer to compensate for network jitter

SIP-Etherphone has a serial port through which a PDA can be attached

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The SIP System Architecture

Local Area Network

SIP-based Etherphones at every desk, with PDA interface

Main SIP serverSIP database

SIP-based client

Data network

RouterRouter

office #2203

PDA

office #2209

PDA

(infrared, wireless)

Move to

(infrared, wireless)

PDA

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The connection of SIP network and PSTN

PSTN/SIP gateway The gateway provides a connection between the

LAN and the PSTN The gateway acts as a SIP UA on behalf of the

PSTN phones.

SIP-based LANSIP-based LAN Regular PSTN phoneRegular PSTN phone

Gateway

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True number portability

A caller can reach a particular person rather than a particular phone

A person authenticates himself to the SIP-Etherphone by synchronization their PDA with the SIP-Etherphone

Multiple users can register with one SIP-Etherphone by simply synchronizing one after another

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Conclusions

Advantages Shoppers can make purchases at a store simply by t

apping a few buttons on their PDAs, and the money would be transferred from the PDA to the merchant

Shoppers can also instantaneously receive detailed information on location about the products at the store

Presenters can remotely control computer presentations using their PDAs

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Conclusions

Advanced call screening Making use of the address book and date book

of the PDA to allow the assignment of priorities for meetings and addresses

Blocking unwanted calls Defining the particular behavior for particular

callers

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Conclusions

Such new applications will bring great value by allowing mobile users to save time and money. Furthermore, users are to be more connected at any location and avoid unnecessary disturbance.