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Comparison of SIP and H.323 - Strengths and Weaknesses
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The table below gives a comparison of the
strengths and weaknesses of the competing
protocols.
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Subject
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SIP
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H.323
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Comments
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Encoding
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Text
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Binary
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Text is easier to decode. Drawback
is that it is a bandwidth hog.
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3G Status
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Yes
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No
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3G vendors have settled on a non-standard
version of SIP
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Call Set Up Delay
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1.5 RTT
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1.5 RTT
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Version 3 of H.323 solves excessive call delay.
However, there is no backward compatibility.
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Protocol Complexity
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Simple HTTP style Protocol
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Highly Complex
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H.323 is a suite of protocols borrowed
from ISDN. Core documentation is 1400
pages
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Extensibility
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Standards-based extensions to perform
new functions
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Extensions are added by using vendor-specific
non-standard elements
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Architecture
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Modular: Does only signaling
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Monolithic:
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H.323 goes beyond basic signaling
capabilities to include conference
control, registration, capability
negotiation, etc.
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Instant Messaging
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Yes
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No
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Loop Detection
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Good
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Imperfect
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Firewall Support
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Inadequate
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Poor
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Addressing Support
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Any URL including E-mail address,
H.323, http, E.164, URLs, ...
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Host, E.164 phone numbers, and
gatekeeper resolved aliases
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Transport Protocol
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UDP and TCP. Mostly UDP.
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UDP and TCP. Mostly TCP.
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TCP makes little sense given
packet integrity checks.
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Internet application integration
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Designed to incorporate Internet style
text-based applications
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Inter-domain Call Routing
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DNS
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Annex G
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Service Standardization
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"Standardize protocols, not
services."
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Standardize everything.
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Supplementary Services
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Poorly defined.
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Rigorously defined.
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H.323 is less likely to result in
interoperability problems among
vendor implementations
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Internet Fit
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High
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Low
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H.323 imposes ISDN architecture
on IP networks. Unnatural fit.
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Scalability
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Excellent
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Poor
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Types of Services
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No obvious limitations
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Only media streams,
including voice.
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SIP is almost perfectly general
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Vendor Interoperability
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Widespread
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Extremely Limited
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H.323 interoperability is virtually
non-existent
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©iLocus Ltd
- Reprinted with permission
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