Subject: Re: SIP and waste of bandwidth in wireless applications

From: "Scott Petrack"<[email-masked]>
Date: Sun, 9 Aug 1998 18:37:54 +0200

From: Scott Petrack@VOCALTEC on 08/09/98 06:37 PM

>Also processing of Text strings requires more processing
>than a bit oriented protocol.

Almost any wireless IP device is going to be able to parse some sort
of HTTP, so it will have text parsing built-in anyway. So if you
insist on having a bit oriented protocol, you will probably need to
add *extra* processing to support it. So it may be that having a
bit oriented protocol for telephony will increase the processing
requirements. (This will be even more true if SIP and HTTP can
actually merge).

Also, I do not know if the particular "bit oriented protocol" in
question, H.323, actually produces shorter messages than SIP.
H.323 messages use Q.931 messages to wrap ASN.1 information elements.
In order to ASN.1 PER to produce short PDUs, the order of the fields
within the messages must be chosen with some care. I have not seen
a direct unbiased comparison of the actual average message length of
"telephony" H.323v2 messages vs. "telephony" SIP messages.

The bottom line is that neither H.323 nor SIP were designed for
bandwidth restricted environments. If we really need to make SIP
messages shorter, we should specify a C/SIP header compression
scheme. I personally think that this is extremely important,
although not at all for the reasons you mention. I'll write a
separate email on this.

>Call setup time in the wireless and landline telephony systems
>is regarded as a required quality of service attribute.

Absolutely, but this is determined by the number of Round Trip Times
(RTTs) needed to set up a call, not by the length of the messages. Both
SIP and H.323v2 "FastStart" get this pretty much right. Although one
could argue the advantages and disadvantages of each, Call setup time
in each case is minimal.

>Are there plans to create a digital call setup protocol?

Uh, SIP is a digital call setup protocol. It uses ASCII which is a
standard for the digital representation of text characters.

Scott

[email-masked] on 08/07/98 07:31:49 PM

To:   [email-masked]
cc:   [email-masked] (bcc: Scott Petrack)
Subject:  SIP and waste of bandwidth in wireless applications

Is seems to me that a Text Based call setup protocol
will waste bandwidth especially in wireless
applications where spectrum must be tightly
managed.
Also processing of Text strings requires more processing
than a bit oriented protocol.
In the SIP Draft dated July 16, 1998 section
1.5.3 it states that "it is believed that the additional
overhead of using a text-based protocol is not significant."
Call setup time in the wireless and landline telephony systems
is regarded as a required quality of service attribute.
Customers will not accept a much increased call setup time
because of the extra processing required to parse strings.
Are there plans to create a digital call setup protocol?
Bruce