just finished the Comcast senior SWE loop last week, level maps to what they internally call L5 or Principal I depending on the org. wanted to post the system design piece specifically because that's where I see the least info online.
there were two system design rounds in my onsite. both were 60 minutes, one paneled (two interviewers), one solo interviewer. the panels I got:
Round 1: design a streaming content delivery system. this is Comcast, so they want you to think cable + broadband at scale. they weren't looking for Netflix-level sophistication but they definitely dinged candidates who ignored CDN layer, buffering strategy, and ABR (adaptive bitrate). if you haven't thought about streaming infra, spend an hour on how HLS and DASH work.
Round 2: design a real-time customer service notification pipeline. think: outage detected, 2M subscribers in a region need to know NOW. they cared a lot about fan-out at scale, message deduplication, and fallback channels (push vs SMS vs email). classic pub/sub problem but the interviewer wanted to hear me explicitly call out the tradeoffs between Kafka and SQS rather than just pick one.
format-wise: virtual whiteboard (they used Miro), no pre-built templates. they let me drive but were pretty active with follow-up questions. expect to get challenged when you make any capacity estimate.
scope: they're comfortable with senior candidates who don't know Comcast-specific infra, but they want you to ask the right clarifying questions and show you understand the difference between 10K and 10M concurrent users. they are NOT a leetcode-obsessed shop at this level. nobody mentioned algorithms in either system design session.
one thing that surprised me: both interviewers asked how I'd communicate design decisions to non-engineers. at L5 they're looking for some tech lead sensibility, not pure IC coding.
comp I got was around $185K base + 15% bonus target, remote-eligible. not FAANG money but solid for a stable media/telecom company. i've seen ranges posted elsewhere of $165-210K for this band depending on org and location.