Method and apparatus for estimating the call grade of service and offered traffic for voice over internet protocol calls at a PSTN-IP network gateway

1. A method for estimating the grade of service (GoS) and offered traffic for voice over internet protocol (VoIP) calls at a gateway bridging calls between a public switched telephone network and an internet protocol network, the gateway having a dial-control management information base, the method comprising the steps of:

periodically polling a dial-control management information base for dial peer traffic statistics;

storing the polled data;

estimating the carried traffic using the polled data;

estimating the grade of service by utilizing the Erlang-B formula in an inverse manner, operating on the estimated carried traffic obtained in the first estimating step; and

estimating the offered traffic using the estimated values for the carried traffic and the grade of service obtained in the previous estimation steps,

where the dial-control management information base is standardized as per RFC 2128, and where the dial peer traffic statistics obtained in the polling step comprise at least dialCtlPeerConnectTime and dialCtlPeerStatsSuccessCalls as defined in said standard, and

where the carried traffic is estimated using the following equation:

C

=

∑

i

∈

1

⁢

δ

⁡

(

i

)

⁢

(

CT

⁡

(

i

,

b

)

-

CT

⁡

(

i

,

a

)

)

/

(

b

-

a

)

,

where, for each dial peer i, CT(i,b) is the value of dialCtlPeerConnectTime for dial peer i at time b, CT(i,a) is the value of dialCtLPeerConnectTime for dial peer i at time a, and δ(i)=1 if dial-peer i is a dial-peer on the public switched telephone network side of the gateway, δ(i)=0 if the dial-peer is on the internet protocol side of the gateway, and C is the summation over all dial peers, giving the total carried traffic for the gateway.

2. The method of claim 1 , where:

the grade of service seen by the offered traffic in the time interval (a,b) is given by grade of service=Erlang(B, C/(1−G*)), where B is the total number of ISDN B channels on the public switched telephone network side of the gateway, Erlang( ) is the Erlang-B formula, and G* is a solution of the equation G*=Erlang(B, C/(1−G)) subject to the condition that 0<G*<1, and the offered traffic is estimated as Δ=C/(1−G*) in the time interval (a,b).

3. The method of claim 1 where G* is found using numerical methods, and the Erlang-B formula is computed using the following well-known recursion formula:

Erlang(B, Δ)−ΔErlang( B− 1,Δ)/( B +ΔErlang( B −1,Δ)),

with the initial condition set such that Erlang(0,Δ)=1.

4. An apparatus for estimating the grade of service and offered traffic for voice over internet protocol calls at a gateway bridging calls between a public switched telephone network and an internet protocol network, where the gateway has a dial-control management information base, the apparatus comprising:

means for periodically polling the dial control of the management information base for dial peer traffic statistics;

means for storing the polled data;

a first estimating means for estimating the carried traffic using the polled data;

a second estimating means for estimating the grade of service by utilizing the Erlang-B formula in an inverse manner operating on the carried traffic result from the first estimating means;

a third estimating means for estimating the offered traffic using the estimated values for the carried traffic and the grade of service obtained by the first and second estimation means; and

means for numerical calculation for processing numerical data needed by each of the first, second and third estimation means,

where the dial-control management information base is standardized as per the standard described in the Internet Engineering Task Force (IETF) Request for Comment (RFC) 2128,

where the dial peer traffic statistics obtained by the means for polling comprise at least the dialCtlPeerConnectTime and dialCtIPeerStatsSuccessCalls as defined in said standard, and

where the carried traffic is estimated by the first estimating means using the following equation:

C

=

∑

i

∈

1

⁢

δ

⁡

(

i

)

⁢

(

CT

⁡

(

i

,

b

)

-

CT

⁡

(

i

,

a

)

)

/

(

b

-

a

)

,

where CT(i,b) is the value of dialCtlPeerConnectTime for dial peer i at time b, CT(i,a) is the value of dialCtlPeerConnectTime for dial peer i at time a, and δ(i)=1 if dial-peer i is a dial-peer on the PSTN side of the gateway, and δ(i)=0 if the dial-peer is on the IP side of the gateway, and I is the set of all dial peers at the gateway;

the estimate made by the second estimating means of the GoS seen by the offered traffic in the time interval (a,b) is given by solving the equation GoS=Erlang(B, C/(1−G*)), wherein B is the total number of ISDN B channels on the public switched telephone network side of the gateway, Erlang( ) is the Erlang-B formula, and G* is a solution of the equation G*=Erlang(B, C/(1−G*)) subject to the condition that 0<G*<1, wherein said solution G* is generated by the means for numerical calculation; and

the offered traffic is estimated by the third estimating means to be Δ=C/(1−G*) in the time interval (a,b).

5. The apparatus of claim 4 where the nonlinear equation solution G* is found by the means for numerical calculation using numerical methods, and the Erlang-B formula is computed by the means for numerical calculation using the following well known recursion formula:

Erlang( B,Δ )=ΔErlang( B− 1,Δ)/( B +ΔErlang( B− 1,Δ)),

with the initial condition set such that Erlang(0,Δ)=1.

6. Computer executable code stored on one or more computer readable media, the code for estimating the grade of service and offered traffic for voice over internet protocol calls at a gateway bridging calls between a public switched telephone network and an internet protocol network, where said gateway has a dial-control management information base, the code comprising code to cause the performance of the steps of:

periodically polling the dial control of the management information base for dial peer traffic statistics;

storing the polled data;

estimating the carried traffic using the polled data;

estimating the grade of service by utilizing the Erlang-B formula in an inverse manner operating on the estimated carried traffic obtained in the first estimating step, and the number of channels on the public switched telephone network side of the gateway; and

estimating the offered traffic using the estimated values for the carried traffic and the grade of service obtained in the previous estimation steps,

where the carried traffic is estimated using the following equation:

C

=

∑

i

∈

1

⁢

δ

⁡

(

i

)

⁢

(

CT

⁡

(

i

,

b

)

-

CT

⁡

(

i

,

a

)

)

/

(

b

-

a

)

,

where, for each dial peer i, CT(i,b) is the value of dialCtlPeerConnectTime for dial peer i at time b, CT(i,a) is the value of dialCtlPeerConnectTime for dial peer i at time a, and δ(i)=1 if dial-peer i is a dial-peer on the public switched telephone network side of the gateway, δ(i)=0 if the dial-peer is on the internet protocol side of the gateway, and C is the summation over all dial peers, giving the total carried traffic for the gateway.

7. Computer executable code stored on one or more computer readable media, the code for estimating the grade of service and offered traffic for voice over internet protocol calls at a gateway bridging calls between a public switched telephone network and an internet protocol network, where said gateway has a dial-control management information base, the code comprising code to cause the performance of the steps of:

periodically polling the dial control of the management information base for dial peer traffic statistics;

storing the polled data;

estimating the carried traffic using the polled data;

estimating the grade of service by utilizing the Erlang-B formula in an inverse manner operating on the estimated carried traffic obtained in the first estimating step, and the number of channels on the public switched telephone network side of the gateway; and

estimating the offered traffic using the estimated values for the carried traffic and the grade of service obtained in the previous estimation steps,

where the grade of service seen by the offered traffic in the time interval (a,b) is given by grade of service=Erlang(B, C/(1−G*)), where B is the total number of ISDN B channels on the public switched telephone network side of the gateway, Eriang( ) is the Erlang-B formula, and G* is a solution of the equation G*=Erlang(B, C/(1−G*)) subject to the condition that 0<G*<1, and the offered traffic is estimated as Δ=C/(1−G*) in the time interval (a,b).

8. Computer executable code stored on one or more computer readable media, the code for estimating the grade of service and offered traffic for voice over internet protocol calls at a gateway bridging calls between a public switched telephone network and an internet protocol network, where said gateway has a dial-control management information base, the code comprising code to cause the performance of the steps of:

periodically polling the dial control of the management information base for dial peer traffic statistics;

storing the polled data;

estimating the carried traffic using the polled data;

estimating the grade of service by utilizing the Erlang-B formula in an inverse manner operating on the estimated carried traffic obtained in the first estimating step, and the number of channels on the public switched telephone network side of the gateway; and

estimating the offered traffic using the estimated values for the carried traffic and the grade of service obtained in the previous estimation steps,

where G* is found using numerical methods, and the Erlang-B formula is computed using the following recursion formula:

Erlang( B,Δ )=ΔErlang( B− 1,Δ)/( B +ΔErlang( B −1Δ)),

with the initial condition set such that Erlang(0,Δ)=1.