User's Manual

Overview 19

Nortel Networks Confidential

The Converged service adds the following capabilities to the end user's

telephony service:

• the ability to manually redirect incoming calls to another party from

the PC

• the ability to set up automated enhanced routing and screening of

incoming calls based on time of day or based on the calling party's

identity

• a call log of all incoming calls

• the ability to send instant messages to the party on the other end of

a call

• the ability to start collaborative applications such as shared

whiteboard, file transfer, and clipboard transfer with the party on the

other end of the call

• the ability to receive a picture ID of the party on the other end of the

call

Network/Address Hiding service

The SIP Application Module uses SIP and the Session Description

Protocol (SDP) to coordinate the establishment of multimedia sessions

for signaling and media, respectively. These protocols embed IP

information in their messaging. While Network Address Translation

(NAT) devices change port and address information in the IP packet

header, most are not currently SIP or SDP aware. IP addresses in these

messages are therefore sent out unchanged through the NAT. If the SIP

Application Module were to forward these messages on unchanged,

sensitive IP information would be given to untrusted clients. In order to

remedy this, the SIP Application Module sanitizes the messages before

forwarding them.

For IP information in the SIP headers, the SIP Application Module

either removes the header (for example, Via headers) or replaces the

IP address with the address of the SIP Application Server (for example,

Contact header). A media portal is necessary in order to replace the IP

information in the SDP headers. The SIP Application Module queries

the Media Portal (using MGCP+) for a new IP and port combination to

replace the IP and port put there by the client. This effectively anchors

the media stream at the Media Portal.

Clients therefore see the SIP Application Module as their signaling

endpoint and the Media Portal as their RTP media endpoint. They have

no knowledge, and therefore no IP information, about the other client

they are in a session with.