Is "Peering" in networking, always exchanged directly?
Solution 1:
The Wikipedia article on peering has a pretty comprehensive introduction.
do ISPs always exchange traffic directly through Peering?
No, although they may have direct connections with other networks for peering quite often they will use an internet exchange to facilitate peering, allowing an ISP to use a single connection to the IX to (potentially) peer with a large number of other members rather than establishing dedicated links to each of those.
Also an ISP may also still need to buy transit for routes they can't reach (efficiently) by peering for instance.
I heard that peering is an interconnection that charged for no money (free) unlike Transit providers.
There is no such thing as a free lunch... The connection itself will cost money to maintain, to name one.
The public internet exchanges charge a membership fee per 100 Mbit/s or 1/10/100 Gbit/s port.
But the cost associated with peering is a fraction of the price tag for buying transit.
then why most ISPs do not benefit from Peering?
What makes you think they don't?
Solution 2:
You can think of networking interchange as either peering or transit. Peering can be further broken down into settlement free peering and paid peering.
Regional networks are populated by what we call tier 1 network providers. These tier 1 networks can reach the entire internet region through settlement free peering. Other networks in that region or without buy transit from these tier 1 providers.
In the US, for example, tier 1 providers include:
- AT&T
- Verizon
- Sprint (Softbank Broadband)
- Century Link (Qwest)
- Level 3 (with Global Crossing now)
- NTT/Verio
- Cogent (maybe?)
See generally, drpeering.net and peeringdb.com