Subject: Re: Why SS7?

From: [email-masked]
Date: Thu, 10 Jun 1999 09:11:59 -0400

Here is a very quick list:

Versus CAS (R1,R2 etc) signaling, SS7 provides the following advantages:
a) Much faster call setup time
b) supports a greater amount of information transfer between switches (such as
calling line id), which enables supplementary services to be supported across
the network.
c) greater installed base - I have heard that the US trunk network is 90-95%
SS7.(dont know the figures for the rest of the world)

but has the following disadvantages
a) more expensive. In the US, to connect into the RBOC STP can be quite
expensive
b) the  SS7 network operators are very cautious when allowing new service
providers to connect to their networks. They require long periods of approval
testing. The SS7 network could be susceptible to implementation bugs that could
bring the whole network down (such as happened to the ATT SS7 network in the
late eighties)

Versus ISDN signaling (PRI, DPNSS etc) SS7 has the following advantages:
a) Scales better, therefore less expensive. A redundant pair of SS7 links can
support the signaling for thousands of trunk circuits. Most PRI implementations
are facility associated (I'm not sure how wide is the support for NFAS and how
may T1s can be grouped together using NFAS)
b) Since PRI is a UNI, it is likely that in most networks, toll switches (Class
4) do not support PRIs, whereas all PSTN switches would support SS7.
c) SS7 supports single stage dialing, whereas most switches force PRI into a
multi-stage dialing pattern.
d) Better routing capabilities. Switches often support more than one trunk route
to reach each destination. When routing to a PRI, the switch thinks it is trying
to reach a subscriber on a PBX. If all the PRI circuits are busy, then it isn't
likely to have an alternate route to get to that subscriber.
e) SS7 has better congestion control procedures than PRI.

Steve Carr
Unisphere Solutions Inc.

Tom Gray <[email-masked]> on 06/10/99 03:40:37 AM

To:   [email-masked], [email-masked]
cc:    (bcc: Steve Carr/Internet/ICN)
Subject:  Why SS7?

I see much written in the IP telephony world about SS7 gateways but I
have seen little written about the basis of this interest. So I will
ask the question.

What is the basis of the interest in SS7 as opposed to any the many
other signaling schemes (R1, R2, No 5, DPNSS ...)?

What advantages does it bring and what are its disadvantages.

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