The Mishnah that begins on today’s daf (=page) discusses the placement of both communal and individual sin-offerings. They are slaughtered on the northern side of the Temple courtyard, where the blood of the sacrifice is collected. That blood is taken by the kohen to the altar where it is placed on each of the four corners of the mizbe’ah. The Mishnah specifies that the kohen is to walk up the ramp and walk along the sovev – the edge surrounding the altar – beginning with the southeastern corner, and continuing to the northeastern corner, the northwestern corner and finally the southwestern corner, placing the blood on each one of the corners in succession.
The outer altar was ten amot (=cubits) high, and at six amot above ground level the top of the altar became thinner, so that there was an amah-wide “step” at the edge of the mizbe’ah. This was the sovev upon which the kohen walked as he placed the blood from the sacrifice on the corners of the altar, as required. Later on in the next perek (=chapter, see daf 62b), the Gemara explains that the ramp upon which the kohen climbed up to the sovev was not the main ramp leading to the altar itself, rather it was a smaller ramp that led to the sovev in the southeast corner where the kohen began his service. {picture of the mizbe’ah on page 155. The sovev is #3}
In contrast to other sacrifices whose blood was usually sprinkled on the lower half of the altar, below a line called the hut ha-sikra, the blood of the sin-offerings was placed only on the upper part of the altar, which was at least five amot (about two-and-a-half meters or eight feet) above the yesod – the foundation – of the mizbe’ah. For this reason it would have been impossible for the kohanim to sprinkle the blood of the sin-offering while standing on the floor; it could only be done while walking along the sovev.