Comcast

(CMCSK)

will offer

EarthLink's

(ELNK)

broadband Internet service over its cable system during a technical trial planned for the second quarter in the Philadelphia area.

The trial will be designed to test the companies' services before a possible definitive agreement can be signed. Only certain Comcast customers will be offered the option to use EarthLink's broadband service through a cable connection.

The agreement with EarthLink marks the second time a nonaffiliated company will test high-speed Internet access using Comcast's cable systems. In November, Comcast and

Juno Online

( JWEB) announced plans for a similar trial.

"Based on what we learn from this and other trials, we are eager to move ahead with plans to offer our high-speed Internet customers a choice, which ultimately can benefit our business and that of our ISP partners," Comcast said in a statement.

Shares of Comcast, which is based in Philadelphia, gained $1.75, or 4.4%, to $42 in recent

Nasdaq

trading. EarthLink lost 31 cents, or 2.6%, to $11.81.