From Tanebaum's Computer Network:

When an application (e.g., a user) process wishes to set up a connection to a remote application process, it must specify which one to connect to. (Con- nectionless transport has the same problem: to whom should each message be sent?) The method normally used is to define transport addresses to which processes can listen for connection requests. In the Internet, these endpoints are called ports. We will use the generic term TSAP (Transport Service Access Point) to mean a specific endpoint in the transport layer.

The analogous endpoints in the network layer (i.e., network layer addresses) are not-surprisingly called NSAPs (Network Service Access Points). IP addresses are examples of NSAPs.

What are endpoints in other layers (the data link layer, physical layer and application layer) called respectively?


  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it.
    – Ron Maupin
    Aug 6 '17 at 23:55

A partial answer: at the data-link layer, it's called a Link Service Access Point (LSAP).

To get the others, you'd have to read the OSI specification, which is 1) expensive to purchase, and 2) irrelevant.

  • Thanks. At data link layer, are endpoints called network interface?
    – Tim
    Oct 8 '15 at 19:31
  • They're called SubNetwork Attachment Points (SNAP)
    – Ron Trunk
    Oct 8 '15 at 19:32
  • (1) Did you say the endpoints are called either LSAP or SNAP? (2) If network interfaces are not endpoints, what are the relation and differences between network interfaces and endpoints?
    – Tim
    Oct 8 '15 at 19:35
  • Sorry for the confusion: LSAP. SNAP is a subset of that.
    – Ron Trunk
    Oct 8 '15 at 19:37
  • Thanks. Did you say data link layer endpoints are called LSAP, while network interfaces are called SNAP? If yes, what are LSAP that are not SNAP?
    – Tim
    Oct 8 '15 at 19:40

Explaination about the Data link layer is frequently related with a software as a driver for a network interface card (NIC). The data link and physical layers are so closely one to the other, because many types of hardware are also associated with the data link layer.

Ex: NICs typically implement a specific data link layer technology, so they are often called Ethernet cards, Token Ring cards, etc.

Then Enpoints on physical and data link layer, is to hard to differetiate, cause the pyshical layer is the medium, electrical or optical signal that travel on some form, to reach some device(where most often, is decoded the signal(link-layer) and the information is passed up to the upper layers.

An application endpoint is the commom application that perform the action, the data request or transmit, ex: an Explorer, FTP_client and so on

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