An ASN is an electronic notification of an upcoming delivery sent directly from a supplier to a buyer before shipment. 

ASN stands for "Advance Shipping Notice." It is a notification of an upcoming delivery and is most commonly sent electronically via EDI. The buyer often requests it as part of its trading or EDI requirements. An advanced shipping notice is sent directly before the shipment from a supplier or third-party logistics company to a buyer to improve the efficiency of the goods-receiving process. 

An Advanced Shipping Notice is referred to by various terms depending on the EDI standard used. The GS1 EANCOM standard is called the DESDAV, despatch advice message, whereas the ANSI X12 EDI standard is called the EDI 856 Advance Ship Notice, sometimes called a Ship Notice/Manifest. 

An autonomous system (AS) is an extensive network or group of networks with a single routing policy. Each AS is assigned a unique ASN, which is a number that identifies the AS. The Internet functions as a network of networks, with autonomous systems (ASes) being the major networks that constitute its structure. An autonomous system, defined as a large network or a conglomeration of smaller networks, operates under a unified routing policy. Every computer or device connecting to the Internet must link through an AS.    

Each autonomous system governs a specific set of IP addresses, akin to how a town's post office delivers mail to all addresses within that town. This designated range of IP addresses under the control of a particular AS is referred to as their "IP address space." Generally, a single large organisation operates each autonomous system. These organisations can include Internet service providers (ISPs),  enterprise technology companies, universities, or government organisations.

An AS routing policy defines the IP address space controlled by an autonomous system and includes a list of other autonomous systems to which it connects. This policy is essential for correctly routing packets to their intended networks. Autonomous systems communicate this information to the broader Internet using the Border Gateway Protocol (BGP). 

Not only does an advanced ship notice inform the buyer when the shipment will be delivered, but it also confirms additional information that helps the buyer prepare for the delivery, enabling the receiving costs to be reduced (according to Supply Chain Digest, the cost saving potentially is generally thought to be by about 40%). 

The content of the notice depends on the trading partners' requirements but typically includes: 

Order information – the purchase order number or reference should be included at a minimum 

Delivery details – the delivery date, time and booking reference 

Location information – Global Location Numbers (GLNs) to identify all trading partners involved in the transaction (supplier, buyer and carrier where appropriate), and the delivery address should be included in all ASNs 

Pallet codes – it is essential that the buyer knows how many pallets will be included. 

Physical characteristics – what package will be used, such as pallet type? 

Product details – a description of the products should be included – some companies also include case size, although this is not mandatory. GTINs, which stand for Global Trade Item Number and are the unique number identifying products, should also be included for each product line. 

In many cases, ASNs are provided by the third-party logistics company making the delivery, and some buyers won't accept a shipment without them. Why? Quite simply, due to the improvements they make in warehouses and distribution centres to the receiving process – the ASN gives the buyer an early warning if the supplier cannot fulfil the delivery in full, and they can then plan and make decisions accordingly to ensure there are no disruptions to the supply chain. 

ASNs are often used in conjunction with SSCC which stands for Serial Shipping Container Codes, to further improve the efficiency of the receipt and reconciliation process further. SSCCs are used to identify and track logistics units, which simply refer to items that have been packaged together for storage or transportation, such as outer cases, pallets, or entire shipments. SSCC labels can be scanned and matched against the Advanced Shipping Notice to reconcile what is received against what the buyer was told would be sent.

Sending an Advanced Shipping Notice quickly and easily keeps buyers informed of upcoming deliveries and improves the level of customer service they provide. They can also be used by suppliers as an electronic document trail for each shipment in case of discrepancies. 

Suppliers can also use ASNs for their drop-shipping programs or to inform online marketplaces of expected delivery dates and tracking information.

Network operators require ASNs for many critical reasons. ASNs enable operators to control routing within their networks by providing a unique identifier for each autonomous system (AS). This unique identifier allows operators to manage the flow of data packets through their network infrastructure.  

ASNs facilitate the exchange of routing information through the different Internet Service Providers (ISPs).  ASNs are also linked to specific IP address ranges, allowing the network operator to direct and announce their IP address space. This ensures that data packets are accurately routed to their intended destinations. In summary, ASNs are vital for efficient data routing, interconnection, and IP address management within the global Internet infrastructure.