CBS Sports' lead sideline reporter, Tracy Wolfson, talked to DenverBroncos.com about Sunday's upcoming Broncos-Steelers matchup, what to watch for and how good this Denver defense really is.

How much of a test is the atmosphere at Heinz Field for quarterback Brock Osweiler in his fifth start this season?
"It'll be a huge test. He told us this week [he's] going on the road to an environment he hasn't been in before. [Broncos Head] Coach [Gary] Kubiak said the same thing. The only way to experience it is really to get in there and play, but we know what Heinz Field is like, the environment, the noise, as he said, the waving of the "Terrible Towel". December is their month. That's when they really get at it. It gets cold

there -- not that it doesn't get cold in Denver, but it's just a different atmosphere. This team is playing the best football it has all season long and the fans feed off of that and they come out in full force, especially this time of year, in a game like this — a late game, too, where it starts getting dark and cold and loud and raucous. He'll be in for a little bit of a rude awakening. It's all about keeping composure, and [it's] another challenging test for him and a way for him to grow and learn as a quarterback as well."

What have your impressions of Osweiler been so far?
"To be honest, we haven't really had a chance to see him up close yet as we've been with our other games. But I think composure, the way he's been able to just step in and handle it, take responsibility for mistakes he's made, but also try and go in there and be a leader as well. I think it's a very big challenge, stepping in for a guy like Peyton Manning and I think he's done a tremendous job, and again, know that this is all a learning experience for him. With every game he'll get better, learn new things.

"I think I said coming into this season, even with Peyton Manning at quarterback that this defense was going to lead this team. He knows he just has to go out there and not make mistakes, I think he's trying to do that and I think that will be his biggest challenge yet. He stepped in very nicely against New England. But on the road, against a Steelers team that's playing the best football right now, I think the defense is going to need to do it's job, step up and help him as well and make sure that he gets to stay on the field."

The Broncos need one win to secure a spot in the playoffs and the Steelers are fighting to get a spot down the road as well. Will this game have a playoff feel to it?
"No doubt. We always look to that final game in Week 17 when those games are do-or-die, some are in and some are out, but this is important to both teams — where they're going to place in the playoffs, what seedings they're going to get. Whether the Steelers are going to get in or not -- this has playoff implication written all over it. It's going to have a playoff feel to it. It's two tremendous teams. You have the No. 1 defense, you have the No. 1 offense, you have the cornerbacks versus  their wide receivers and you have [Ben] Roethlisberger out there. I think when you look at this game, and I think Phil Simms said it best: It's a five-star matchup, and that's exactly what it is."

What are some matchups that fans should watch for on Sunday?
"Right away it jumps out at you — the wide receivers of the Steelers versus your cornerbacks of the Denver Broncos. Whether you have Aqib Talib or Chris Harris Jr., and then you have Antonio Brown and Martavis Bryant — I mean, these wide receivers on the Steelers right now, and what Ben can do, staying in the pocket, and he's just so difficult to get down, he just gets the ball out and knows how to utilize it.

"This defense is going to have to be disciplined, but they're up for the challenge. We know what these cornerbacks can do. My biggest concern is the health of the safeties and who you get back. I think they ruled out T.J. Ward and Omar Bolden already. That's the biggest question mark, the safeties and the health of them, but you did get some guys back, so that's huge as well. Those are some big matchups and then you look at the offensive side of the ball for the Broncos and can you establish the run game, and Demaryius Thomas, can he rebound from last week's game? I think they have an advantage there as well. I think those are a few of the matchups I look for so far going into this game."

What challenges will outside linebackers Von Miller and DeMarcus Ware have with Roethlisberger?
"Von and DeMarcus are the best at their craft. But, Roethlisberger, he's so big, he's so strong -- the way he's able to get out of the pocket and scramble when he needs to, the way he's able to get the ball out, the patience that he has, and then he had so many options, the quick passing, getting it into the slot -- they're just going to have to be very vigilant and very patient as well. Pick their spots and then not lose sight of him and just really tackle and grab him and pull him down. I think that's thing about Roethlisberger, being able to actually wrap your arms around him and get him down before he makes that play."

Where does this defense rank in the teams you've seen during the years you've been covering the NFL?
"I'm going to say this year, I think it ranks atop the league and I think it ranks, for us, the best defense we've seen. You can put it up there maybe with those Seattle defenses in the past, obviously  with what they've done and the Legion of Boom. I don't ever like to compare. But I think what they're doing this year is something special, and I said it before we went into the season, actually after Week 1, when we covered you. I felt like this was something special as long as everyone can stay healthy and I think they know it. The confidence – and we saw it last year as well. So it's not like this is coming out of nowhere, but right now, everyone being healthy, being on the same page, playing at the top of their game, whether it's the cornerbacks or the linebackers, or the line, or the safeties. It's just everyone really stepping it up this year and I think we've seen the best defense in the NFL this season."

The Broncos played the undefeated Patriots in Week 12, but with some much on the line and with the Steelers surging, is this going to be the biggest test the defense will face so far this season?
"I would think so, yes. I do. I think this is a really difficult Steelers offense, because of all the weapons that they have and because of the quarterback that they have back there. You mention New England, but they're hobbled. You don't know what you're going to get from them. They keep losing some players. Well, this Steelers team has everyone back now and they're healthy and yeah, they don't have Le'Veon Bell, but they're running the ball still, they're able to throw the ball and you don't know where it's going to go and you have Heath Miller at the tight end position. That's what you look forward to. You look forward to. You look forward to going up against this passing game of the Steelers. He's one of the toughest throwers, Ben Roethlisberger and I think that's a big challenge in itself like we talked about earlier. Just trying to grab him and get him down. But I think this will be the biggest challenge they have. … At this point in the year, certainly this is the biggest challenge."