When you say all sides, there are 4 potential fronts that India could be attacked. These are the China-Indian border, a naval invasion from the Indian Sea (to be more specific the Bay of Bengal), the India-Pakistan border and the India-Myanmar border.
The Chinese-Indian border is the Himalayas. Without applying the largest amount of human effort ever undertaken over a significant period of time (Realistically a dozen or so years if uncontested), it is impossible to transit the 100 of thousands of troops needed, with all associated equipment and supply lines, on a contested front, through these mountains.
Another potential front are a naval invasion from the Indian sea, which China does not have the necessary naval strength to launch an invasion through the Indian naval and air forces. They could raid, but India has more than enough manpower to be able to garrison the coast to deter the amount of forces that China could realistically land.
The India-Pakistan border would be the most likely invasion point, as the infrastructure exists to transport the required Chinese forces into position to be able to launch a potentially effective invasion of India.
*Assumes that Pakistan enters the war with China. Pakistan in steadily drifting into the Chinese sphere of influence, so I can see this happening.
The other wild card is the India-Myanmar border. There are two factors at play,
- The politics of the Myanmar relations. Now, I am not a particularly close study of Myanmar international relations, but they have close relations with China and India, both key economic and strategic partners (but not allies of either). It would seem unlikely that they would voluntarily enter a war on either side, and if China invades, you run into issue 2.
- Myanmar (and to a lesser extent the Indian side of the border)is a mess of mountains, large rivers and other challenges that inhibit any movement significant numbers of forces, which would be made almost impossible under active resistance. While not as bad as the Himalayas, conducting an opposed invasion through Myanmar would rank amongst the greatest military actions in history(think Hannibal crossing the Alps, Alexander the greats invasion of Persia ect). The difficulty of this would have been mitigated somewhat if Myanmar was a nice little bed to development, but unfortunately, they a desperately poor country (153 gdp per capita, plenty more research if you want to look at it), which has lead to a significant lack of development in infrastructure, particularly in the difficult regions i.e connecting the east to west (which is that China would need).
So long story short (I swear this was meant to be a short, quick post) most likely situation, a China/Pakistan VS India war would see ground fighting on only a single front, the India Pakistan border. A worst case scenario would be a two front war, with a perfect natural defensive front in Myanmar.
There would be significant naval battles in the Indian sea as India tries in block China from its middle eastern oil reserves, which China tries to keep them open, and do the same thing.