SIP is a simpler, more open and modular protocol than H.323. It uses TCP and UDP for transport whereas H.323 used only TCP until version 2. SIP allows for call forking by splitting incoming calls to several locations, while forking is not possible in existing H.323 calls. H.323 is better able to support failure of network entities through features like alternate gatekeepers and endpoints, while SIP has no defined procedure for proxy server failures. Overall, SIP is more lightweight and flexible than the more full-featured but complex H.323 protocol.

1. © 2006 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Presentation_ID 1
SIP Vs H.323

2. © 2006 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Presentation_ID 2
SIP H.323
Simple, Open & Horizontal Complex, deterministic & Vertical
SIP Based on TCP & UDP H.323 till version 2 Based on TCP
only
Ability to Fork Calls (Splitting
incoming calls to several locations)
Forking Not Possible in existing call
SIP Has no defined procedure to
support failure of network entities.
If a proxy server fails User Agent(UA)
detects through time expiry & sends
reinvite to another proxy server
leading to time delay.
H.323 has feature to support failure
n/w entities.
e.g. Alternate Gatekeeper,Alternate
Endpoint.

3. © 2006 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Presentation_ID 3
SIP H.323
SIP is a modular protocol because it
covers basic call signaling, user
location, and registration.
H.323 covers almost every service,
such as capability exchange,
conference control, basic signaling,
QoS, registration, service discovery,
and so on.
SIP messages are encoded in ASCII
text format, suitable for humans to
read.
H.323 encodes messages in a
compact binary format that is
complex to understand by user
SIP only understands URL-style
addresses.
Flexible addressing mechanisms,
including URLs and E.164 numbers.
SIP Can cause Interoperability Issue
e.g. Sonus, Nextone doesn't
understand UPDATE instead reinvite
H.323 is designed to avoid conflicts
between vendors.

4. © 2006 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Presentation_ID 4
SIP Does not support load balance
across alternate gatekeepers.
H.323 has ability to load balance EP
across alternate gatekeeper.
SIP Supports IANA registered
codecs
H.323 supports any codec's which
are non ITU-T like e.g. code points
for MPEG & GSM
SIP Has limited support for Video &
no support for data conferencing.
H.323 fully supports video and data
conferencing.