ISDN standards are examined in order to estimate performance criteria that will be required for optical ISLs. To make the estimates, a percentage of the degradation allowed for the end-to-end link is assigned to the ISL and a simplified model of antenna pointing errors are used. Two criteria are found to be sufficient to meet ISDN standards. The first criterion is that the probability of a burst error with a BER greater than 3 x 10-2 must be less than 1.6 x 10-7. The second criterion is that the sum of (a) the average BER (exclusive of burst errors) and (b) 8 x 1O the probability of burst errors (having BERs greater than 8 x 10-3) plus the average BER (exclusive of burst errors) must be less than 6 x 10-8. The impact of these criteria, which depend upon the bandwidth of the tracking subsystem, are examined for several links of differing noise equivalent angles and laser powers. It is concluded that optical ISLs should be able to meet the ISDN standards if noise from the tracking detector is the dominant source of pointing errors.