IPT vs DIA vs dedicated line for China

The three in one minute

IP transit, dedicated internet access (DIA) and a private line are different products. They are not tiers of one pipe, and extra bandwidth on one does not turn it into another.

IP transit buys reachability. You connect to an upstream, receive a BGP session and a routing table, and pay for a committed rate with some burst. The upstream's peering and the congested points between you and the destination decide the rest. DIA buys a business-grade on-ramp: symmetric bandwidth, static addresses, a local loop and a contract that covers the access circuit. It ends at the public internet like any other access service. A private line buys fixed capacity between two named points, handed off as Ethernet (IEPL) or as legacy time-division capacity (IPLC), and it does not connect to the public internet. The IP transit entry covers the base product, and IEPL and IPLC cover the two private-line handoffs.

Ask what sits at the demarcation point. A BGP session and a routing table mean transit. An Ethernet port with a public address and a default route mean access. An Ethernet port that reaches only one distant port means a private line.

Choosing from Latin America

From Latin America the choice follows the traffic. An office that needs email, SaaS and video calls wants DIA or a business internet service with a local loop and a backup path. A content or platform business that serves users in China wants IP transit, because it needs full-table reach and the ability to influence the path through peering and routing policy. A factory, mine or logistics site that exchanges telemetry or bulk files with a Chinese headquarters wants a private line between two named locations.

Most estates use a mix: DIA at the office, transit at the platform edge, private lines for the plant. The route selector turns those answers into a shortlist. The quote should name the handoff and the local loop for each site.

Geography shapes the shortlist. A site far from a carrier hotel may need a longer local loop before international capacity begins. A country with limited terrestrial diversity may need a satellite or microwave backup for the local loop, even when the international path is diverse.

What each option buys

Read a quote by what is being sold. Transit sells a committed rate, a BGP session and a routing table. Ask whether you get the full table or a partial table with a default route, and how many prefixes the upstream will accept from you. DIA sells an access circuit with a committed rate, a handoff type, static addresses and a local loop. Ask whether the loop is included, whether the circuit is symmetric, and what the backup option is. A private line sells fixed capacity between two named demarcation points. Ask for the handoff (E1, STM-N, 1000BASE-LX or 10GBASE-LR), the committed rate, the protection option and the local loop at each end.

All three can run over the same fiber. The difference is what the contract covers at the demarcation point. Transit scales by adding capacity or peers. DIA scales by upgrading the access circuit. Private lines scale in steps set by the port and the transport, and each new site is a new circuit.

Latency and the physics floor

Latency between Latin America and China is set first by distance. Light in fiber travels at about 200,000 km/s, so every 1,000 km of path adds roughly 5 ms one-way, or 10 ms round trip. A great-circle path of 16,000 km therefore has a round-trip floor near 160 ms before any equipment, queuing or detour is counted. Real cable paths are longer than the great circle. No product can go below that floor. A good path avoids unnecessary detours, congestion and extra hops.

Use the fiber latency floor tool to compare city pairs on physics alone, then ask for measured figures for the route you are buying. Do not compare a transit quote with a private-line quote on latency alone: they are measured between different endpoints.

What to check before you buy

Ask where the handoff is, who provides the local loop, and what the demarcation point is. Ask whether the quoted capacity is committed or burstable, and what happens when you exceed it. Ask for the route diversity option and whether the backup path shares a conduit or a physical entry point with the primary. Ask how the provider tests the circuit at turn-up: a throughput and latency test with a written result is more useful than a verbal assurance.

Ask what the escalation path is and who answers at each end. If the traffic crosses into mainland China, ask how the provider scopes the cross-border line approval and ICP filing, and take legal advice on your own obligations; this page is not legal advice. The compliance primer explains the concepts, and China routing explained covers the three parts of a China-bound path.

Common mistakes

Buying transit for interactive traffic and expecting private-line behavior is the first mistake. Buying a private line for general internet access is the second: it is point-to-point capacity, not an on-ramp. Forgetting the local loop is the third, because it can be the slowest part of delivery and the least visible line in the quote. Comparing latency figures measured between different city pairs or with different test methods is the fourth. Assuming that a cross-border circuit removes local filing or data-transfer obligations is the fifth; it does not. Ordering the cheapest handoff and then discovering that the site's router accepts a different interface is the sixth.

Write the handoff, the loop and the test into the order. Keep that list with the contract and the acceptance record.