Dogs were domesticated so long ago that they traveled with people to the Americas. As far as I know, dogs were also only domesticated in Eurasia - aside from the extinct Fuegian dog - and then spread outwards from there. Dogs even traveled to New Zealand and Polynesia with people, and reached Australia thousands of years ago.
But I feel like I've heard very little about dogs in sub-Saharan Africa, aside from a potentially false memory of groups using hunting dogs in the Congo. Were there domestic dogs in this part of the world, and if so, what were they used for and what were they like?
I asked a friend of mine about this, she is a zoo-archaeologist researching into the history of animal domestication, mainly focusing on dogs. Here is a short summary of what she had to say on OPs question, bearing in mind it's coming solely from an archaeology perspective:
"Yes there are dogs in sub-Saharan Africa (SSA) of course, but we do not know when/how they got there. The archaeology there is not great because the soil conditions are very bad for the preservation of bones. Sites are much harder to find than in other regions. Additionally, the growth rate of vegetation makes things even worse in SSA.
The important thing to know is that all dogs are domesticated from the Eurasian grey wolf and there are no grey wolves in SSA or really even in Africa at all besides Egypt. So all dogs across all of Africa would have been brought there by people.
Which means that even if we don't find the dog bones themselves, if we know about how humans are migrating or trading between Africa and the Middle East etc., then we can try to predict when we'd expect dogs to arrive because we know once people have dogs, they almost always move around with them. "
She also referenced a paper by Greger Larson et al. (2012), Figure 2 shows timings of some of oldest known dog remains across the world, including a rather barren SSA in this respect.
So as u/lubbe did, we might have to turn to historical documentations rather than archaeology in this case, assuming that with the onset of trading to SSA, dogs were brought to SSA and used for mainly the same purposes they were bred for in the first place (speculative here, though).
Archaeological findings could give us insights into the ways in which dogs were domesticated, what they were used for and how they changed through breeding. Since there are barely any bones in the ground, it remains hard to tell from this branch of research.
I'm an Ethiopianist archaeology, but not a zoologist. I had a quick glance through some monographs and found records of domestic dog bones from Aksumite contexts, but these were relatively uncommon and the author, Chester Cain (from Phillipson, ed (2001): Archaeology at Aksum, Ethiopia, 1993-7), doesn't provide much interpretive spin on the finds. The two excavations though covered the period from about 800 BCE - 600 CE and were both core and peripheral residential and working areas of the city of Aksum before and through its rise. The bones were rare, though compared to other remains, specifically cattle. The two contexts had about 7 and 12 dog bones each compared to 200+ and 300+ cattle bones.
The edited volume, Canis Africanis, has an opening paper on the precolonial history of dogs in Africa, but it more or less follows what others have already contributed here: We know they were there, but we don't know much; most of what we know comes from first-hand early colonial accounts, but they don't really tell us much either. There's some interesting details about two different "breeds" of dog being identified in southern Africa, both depicted in San rock art and likely arriving with Bantu-speaking peoples by or before 500 AD. Unfortunately the pdf and reddit are being infuriatingly difficult trying to copy/paste any of the direct quotes. It goes on to speculate that other breeds may have been introduced to the East African coast by Swahili and other Indian Ocean merchants between 900-1400 CE and that they were typically used as vermin control and cargo guards. The author then goes on to speculate, reasonably, that hte introduction of dogs and their utility in pest control and hunting likely had profound impacts on subsistence strategies and other behavioral patterns.
From the Journal of the First Voyage of Vasco da Gama - Page 3 The bay of St Helena (1497) :
The inhabitants of this country are tawny coloured. Their food is confined to the flesh of seals, whales and gazelles and the roots of herbs. They are dressed in skins, and wear sheaths over their virile members. They are armed with poles of olive wood to which a horn, browned in the fire, is attached. Their numerous dogs resemble those of Portugal, and bark like them. The birds of the country, likewise, are the same as in Portugal, and include cormorants, gulls, turtle doves, crested larks, and many others. The climate is healthy and temperate and produces good herbage.