OPTION PINGS from SAs categorised as "invalid requests" ?

Hi all,

lately I stumbled upon this:

AlphaSBC-1# sh sipd err

11:11:43-159

SIP Errors/Events             ---- Lifetime ----

                       Recent      Total  PerMax

SDP Offer Errors            0          0       0

SDP Answer Errors           0          0       0

Drop Media Errors           0          0       0

Transaction Errors          0          0       0

Application Errors          0          0       0

Media Exp Events            0          8       2

Early Media Exps            0          8       2

Exp Media Drops             0          0       0

Expired Sessions            0          0       0

Multiple OK Drops           0          0       0

Multiple OK Terms           0          0       0

Media Failure Drops         0          0       0

Non-ACK 2xx Drops           0          0       0

Invalid Requests            7     706222      24

Invalid Responses           0          0       0

Invalid Messages            0          0       0

CAC Session Drop            0          0       0

Nsep User Exceeded          0          0       0

after some investigations I realized such invalid requests being sourced by option pings sent from remote Session Agents - some examples taken from sipmsg.log:

Jan  8 11:09:37.128 On [1:781]192.168.2.216:5060 received from 192.168.2.249:5060

OPTIONS sip:192.168.2.216:5060 SIP/2.0