WAN encapsulation Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern) Announcing the arrival of Valued Associate #679: Cesar Manara Unicorn Meta Zoo #1: Why another podcast?SonicWall tz 215 with three LAN and three WANHow does frame relay and MPLS fit in with BGP and WAN/internet/cloud routing?Can't Ping INTERNET from clients but I CAN from Internal RoutersCisco 1921 private LAN can't access internet on WAN interfaceRunning office WAN via MPLS connected Datacenter's WAN connection. Thoughts?Using an ASE(MPLS) line to route datacenter WAN traffic to officeWhat problem does Frame Relay or ATM solve that Ethernet does not?Lost Ethertype in encrypted MACsec framesWAN/Campus network design - Learning purposesDifference between WAN and VPN(tunnels)

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WAN encapsulation



Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)
Announcing the arrival of Valued Associate #679: Cesar Manara
Unicorn Meta Zoo #1: Why another podcast?SonicWall tz 215 with three LAN and three WANHow does frame relay and MPLS fit in with BGP and WAN/internet/cloud routing?Can't Ping INTERNET from clients but I CAN from Internal RoutersCisco 1921 private LAN can't access internet on WAN interfaceRunning office WAN via MPLS connected Datacenter's WAN connection. Thoughts?Using an ASE(MPLS) line to route datacenter WAN traffic to officeWhat problem does Frame Relay or ATM solve that Ethernet does not?Lost Ethertype in encrypted MACsec framesWAN/Campus network design - Learning purposesDifference between WAN and VPN(tunnels)










3















I am having some trouble understanding why does a WAN link need encapsulation, such as MPLS or frame relay? Is it merely to encrypt the info from one LAN to another LAN across the internet?










share|improve this question
























  • Do you perhaps mean "encode" (put into computer form) not "encrypt" (provide privacy/secrecy) ? Providing secrecy is not normally an L2 function.

    – jonathanjo
    Apr 15 at 17:37












  • Is this the same as asking why not every network node is an IP router? I think so but I'm not sure.

    – immibis
    Apr 15 at 22:42











  • @immibis No, Alexandre is asking about how layer 2 links work. Some nodes not being an IP router is about layer 3 links and whether IP forwarding is taking place.

    – jonathanjo
    Apr 16 at 14:30











  • @immibis it has nothing to do with that, im asking about encapsulation of frame through a wan network

    – Alexandre Amaral Bednell
    Apr 17 at 15:10















3















I am having some trouble understanding why does a WAN link need encapsulation, such as MPLS or frame relay? Is it merely to encrypt the info from one LAN to another LAN across the internet?










share|improve this question
























  • Do you perhaps mean "encode" (put into computer form) not "encrypt" (provide privacy/secrecy) ? Providing secrecy is not normally an L2 function.

    – jonathanjo
    Apr 15 at 17:37












  • Is this the same as asking why not every network node is an IP router? I think so but I'm not sure.

    – immibis
    Apr 15 at 22:42











  • @immibis No, Alexandre is asking about how layer 2 links work. Some nodes not being an IP router is about layer 3 links and whether IP forwarding is taking place.

    – jonathanjo
    Apr 16 at 14:30











  • @immibis it has nothing to do with that, im asking about encapsulation of frame through a wan network

    – Alexandre Amaral Bednell
    Apr 17 at 15:10













3












3








3








I am having some trouble understanding why does a WAN link need encapsulation, such as MPLS or frame relay? Is it merely to encrypt the info from one LAN to another LAN across the internet?










share|improve this question
















I am having some trouble understanding why does a WAN link need encapsulation, such as MPLS or frame relay? Is it merely to encrypt the info from one LAN to another LAN across the internet?







protocol-theory transport-protocol wan






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Apr 15 at 17:15









jonathanjo

12.4k1938




12.4k1938










asked Apr 15 at 14:28









Alexandre Amaral BednellAlexandre Amaral Bednell

1135




1135












  • Do you perhaps mean "encode" (put into computer form) not "encrypt" (provide privacy/secrecy) ? Providing secrecy is not normally an L2 function.

    – jonathanjo
    Apr 15 at 17:37












  • Is this the same as asking why not every network node is an IP router? I think so but I'm not sure.

    – immibis
    Apr 15 at 22:42











  • @immibis No, Alexandre is asking about how layer 2 links work. Some nodes not being an IP router is about layer 3 links and whether IP forwarding is taking place.

    – jonathanjo
    Apr 16 at 14:30











  • @immibis it has nothing to do with that, im asking about encapsulation of frame through a wan network

    – Alexandre Amaral Bednell
    Apr 17 at 15:10

















  • Do you perhaps mean "encode" (put into computer form) not "encrypt" (provide privacy/secrecy) ? Providing secrecy is not normally an L2 function.

    – jonathanjo
    Apr 15 at 17:37












  • Is this the same as asking why not every network node is an IP router? I think so but I'm not sure.

    – immibis
    Apr 15 at 22:42











  • @immibis No, Alexandre is asking about how layer 2 links work. Some nodes not being an IP router is about layer 3 links and whether IP forwarding is taking place.

    – jonathanjo
    Apr 16 at 14:30











  • @immibis it has nothing to do with that, im asking about encapsulation of frame through a wan network

    – Alexandre Amaral Bednell
    Apr 17 at 15:10
















Do you perhaps mean "encode" (put into computer form) not "encrypt" (provide privacy/secrecy) ? Providing secrecy is not normally an L2 function.

– jonathanjo
Apr 15 at 17:37






Do you perhaps mean "encode" (put into computer form) not "encrypt" (provide privacy/secrecy) ? Providing secrecy is not normally an L2 function.

– jonathanjo
Apr 15 at 17:37














Is this the same as asking why not every network node is an IP router? I think so but I'm not sure.

– immibis
Apr 15 at 22:42





Is this the same as asking why not every network node is an IP router? I think so but I'm not sure.

– immibis
Apr 15 at 22:42













@immibis No, Alexandre is asking about how layer 2 links work. Some nodes not being an IP router is about layer 3 links and whether IP forwarding is taking place.

– jonathanjo
Apr 16 at 14:30





@immibis No, Alexandre is asking about how layer 2 links work. Some nodes not being an IP router is about layer 3 links and whether IP forwarding is taking place.

– jonathanjo
Apr 16 at 14:30













@immibis it has nothing to do with that, im asking about encapsulation of frame through a wan network

– Alexandre Amaral Bednell
Apr 17 at 15:10





@immibis it has nothing to do with that, im asking about encapsulation of frame through a wan network

– Alexandre Amaral Bednell
Apr 17 at 15:10










4 Answers
4






active

oldest

votes


















2














The simplest WAN topology is a point-to-point link known as leased line or private wire. No encapsulation is necessary (although, in practice, there is usually a small header and checksum, such as HDLC).



In this scenario, the telco transports your bitstream from end to end, reserving 100% of the contracted bandwith at all points on the network.



Suppose you have a head office and 20 branches in a star of point-to-point links. You will need 20 links and 20 router ports. This is expensive. If you want to create a backup data centre, you multiply the cost by two.



To save money and router ports, the telco can offer you a switched WAN.



At the head office site, you have one high-bandwith link, which encapsulates the data streams to the branches in a protocol such as frame relay or ATM (the first non-proprietary protocol of this type was X.25). Encapsulation is necessary to address the WAN endpoint. One can also give information about priority and congestion. The telco can sell you different levels of garanteed bandwith (less than the circuit capacity), which saves you money. The branches have a similar setup. If necessary, the branches can communicate directly, without passing through head office.



MPLS is a VPN overlay on these layer 2 protocols, which enables the telco to route your packets by IP address, making it much simpler to set up large and complex networks, while still having a secure private network. It is simpler (and therefore cheaper) for the telco to mix private MPLS networks and public internet on their network. They can also provide internet and private MPLS services on the same router at your site.



In all these switched WAN scenarios, adding a backup data centre requires just one extra connection, one router port and the appropriate configuration.



I should also mention Internet VPN. In this case, you are encapsulating and encrypting your data over the public network. Encapsulation allows you to access private IP addresses in the corporate network, encryption is necessary for security. What you do not have (with certain exceptions) is guaranteed bandwidth or high service levels, but it's much cheaper.






share|improve this answer






























    6














    IP packets are encapsulated in a layer 2 protocol, whether they are sent on a LAN or WAN. Frame relay is one such WAN layer 2 protocol. There are others, but most are being rapidly replaced by Ethernet. On LANs, of course, you have Ethernet and Wi-fi.



    MPLS doesn't quite fit into the TCP/IP or OSI model. Some consider it a "layer 2.5" protocol.






    share|improve this answer
































      3














      The term encapsulation is used to describe a process of adding headers and trailers around some data. For example, here is what happens when you send an email using your favourite email program (like Outlook or Thunderbird):



      • The email is sent from the Application layer to the Transport layer.


      • The Transport layer encapsulates the data and adds its own header (with its own information, such as which port will be used) and passes the data to the Internet layer


      • The Internet layer encapsulates the received data and adds its own header, usually with information about the source and destination IP addresses. The Internet layer than passes the data to the Network Access layer


      • The Network Access layer is the only layer that adds both a header and a trailer. The data is then sent through a physical network link.


      Fore more details wiki






      share|improve this answer






























        3














        Layer 2 Encapsulation covers a number of purposes, most notably framing, error detection, compression, addressing, and protocol layering, and these really apply whether the networking is wide area or local area.




        • Framing: We need some way to reliably chunk the data into frames


        • Error detection: If the encapsulation has addressing or length fields, it's normally vastly much more efficient if it can do its own error detection (and perhaps correction), so it can discard frames which have been corrupted. It's good to put this at a low level, because it's much more likely to have knowledge of what kinds of errors are probably and improbable.


        • Compression: it might be that there is a lot of redundant information in the frames, such as for example perhaps all the packets have pretty much the same header, and a low-level compression might be practical.


        • Addressing: Very frequently there are multiple devices on the medium, and we want to be able to select which to disturb with this frame: most notable for broadcast media such as ethernet, and often not present in encapsulation for point-to-point networks.


        • Protocol layering: it's very common that the technology should be capable of being used by several upper protocols, perhaps internet protocol and some other. The encapsulation has some method of saying which upper-layer protocol stack should receive it.

        The simplest encapsulation is SLIP, which just does framing and nothing else: it's for point to point links, so addressing isn't used, and the only upper protocol suppported is IP, so it doesn't even have to say that. Van Jacobson's method of compressing TCP/IP headers is an example of low-level compression.



        One of the most complex is ethernet, which does framing, error checking, broadcast/unicast, local addressing and upper protocol selection.






        share|improve this answer

























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          4 Answers
          4






          active

          oldest

          votes








          4 Answers
          4






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          2














          The simplest WAN topology is a point-to-point link known as leased line or private wire. No encapsulation is necessary (although, in practice, there is usually a small header and checksum, such as HDLC).



          In this scenario, the telco transports your bitstream from end to end, reserving 100% of the contracted bandwith at all points on the network.



          Suppose you have a head office and 20 branches in a star of point-to-point links. You will need 20 links and 20 router ports. This is expensive. If you want to create a backup data centre, you multiply the cost by two.



          To save money and router ports, the telco can offer you a switched WAN.



          At the head office site, you have one high-bandwith link, which encapsulates the data streams to the branches in a protocol such as frame relay or ATM (the first non-proprietary protocol of this type was X.25). Encapsulation is necessary to address the WAN endpoint. One can also give information about priority and congestion. The telco can sell you different levels of garanteed bandwith (less than the circuit capacity), which saves you money. The branches have a similar setup. If necessary, the branches can communicate directly, without passing through head office.



          MPLS is a VPN overlay on these layer 2 protocols, which enables the telco to route your packets by IP address, making it much simpler to set up large and complex networks, while still having a secure private network. It is simpler (and therefore cheaper) for the telco to mix private MPLS networks and public internet on their network. They can also provide internet and private MPLS services on the same router at your site.



          In all these switched WAN scenarios, adding a backup data centre requires just one extra connection, one router port and the appropriate configuration.



          I should also mention Internet VPN. In this case, you are encapsulating and encrypting your data over the public network. Encapsulation allows you to access private IP addresses in the corporate network, encryption is necessary for security. What you do not have (with certain exceptions) is guaranteed bandwidth or high service levels, but it's much cheaper.






          share|improve this answer



























            2














            The simplest WAN topology is a point-to-point link known as leased line or private wire. No encapsulation is necessary (although, in practice, there is usually a small header and checksum, such as HDLC).



            In this scenario, the telco transports your bitstream from end to end, reserving 100% of the contracted bandwith at all points on the network.



            Suppose you have a head office and 20 branches in a star of point-to-point links. You will need 20 links and 20 router ports. This is expensive. If you want to create a backup data centre, you multiply the cost by two.



            To save money and router ports, the telco can offer you a switched WAN.



            At the head office site, you have one high-bandwith link, which encapsulates the data streams to the branches in a protocol such as frame relay or ATM (the first non-proprietary protocol of this type was X.25). Encapsulation is necessary to address the WAN endpoint. One can also give information about priority and congestion. The telco can sell you different levels of garanteed bandwith (less than the circuit capacity), which saves you money. The branches have a similar setup. If necessary, the branches can communicate directly, without passing through head office.



            MPLS is a VPN overlay on these layer 2 protocols, which enables the telco to route your packets by IP address, making it much simpler to set up large and complex networks, while still having a secure private network. It is simpler (and therefore cheaper) for the telco to mix private MPLS networks and public internet on their network. They can also provide internet and private MPLS services on the same router at your site.



            In all these switched WAN scenarios, adding a backup data centre requires just one extra connection, one router port and the appropriate configuration.



            I should also mention Internet VPN. In this case, you are encapsulating and encrypting your data over the public network. Encapsulation allows you to access private IP addresses in the corporate network, encryption is necessary for security. What you do not have (with certain exceptions) is guaranteed bandwidth or high service levels, but it's much cheaper.






            share|improve this answer

























              2












              2








              2







              The simplest WAN topology is a point-to-point link known as leased line or private wire. No encapsulation is necessary (although, in practice, there is usually a small header and checksum, such as HDLC).



              In this scenario, the telco transports your bitstream from end to end, reserving 100% of the contracted bandwith at all points on the network.



              Suppose you have a head office and 20 branches in a star of point-to-point links. You will need 20 links and 20 router ports. This is expensive. If you want to create a backup data centre, you multiply the cost by two.



              To save money and router ports, the telco can offer you a switched WAN.



              At the head office site, you have one high-bandwith link, which encapsulates the data streams to the branches in a protocol such as frame relay or ATM (the first non-proprietary protocol of this type was X.25). Encapsulation is necessary to address the WAN endpoint. One can also give information about priority and congestion. The telco can sell you different levels of garanteed bandwith (less than the circuit capacity), which saves you money. The branches have a similar setup. If necessary, the branches can communicate directly, without passing through head office.



              MPLS is a VPN overlay on these layer 2 protocols, which enables the telco to route your packets by IP address, making it much simpler to set up large and complex networks, while still having a secure private network. It is simpler (and therefore cheaper) for the telco to mix private MPLS networks and public internet on their network. They can also provide internet and private MPLS services on the same router at your site.



              In all these switched WAN scenarios, adding a backup data centre requires just one extra connection, one router port and the appropriate configuration.



              I should also mention Internet VPN. In this case, you are encapsulating and encrypting your data over the public network. Encapsulation allows you to access private IP addresses in the corporate network, encryption is necessary for security. What you do not have (with certain exceptions) is guaranteed bandwidth or high service levels, but it's much cheaper.






              share|improve this answer













              The simplest WAN topology is a point-to-point link known as leased line or private wire. No encapsulation is necessary (although, in practice, there is usually a small header and checksum, such as HDLC).



              In this scenario, the telco transports your bitstream from end to end, reserving 100% of the contracted bandwith at all points on the network.



              Suppose you have a head office and 20 branches in a star of point-to-point links. You will need 20 links and 20 router ports. This is expensive. If you want to create a backup data centre, you multiply the cost by two.



              To save money and router ports, the telco can offer you a switched WAN.



              At the head office site, you have one high-bandwith link, which encapsulates the data streams to the branches in a protocol such as frame relay or ATM (the first non-proprietary protocol of this type was X.25). Encapsulation is necessary to address the WAN endpoint. One can also give information about priority and congestion. The telco can sell you different levels of garanteed bandwith (less than the circuit capacity), which saves you money. The branches have a similar setup. If necessary, the branches can communicate directly, without passing through head office.



              MPLS is a VPN overlay on these layer 2 protocols, which enables the telco to route your packets by IP address, making it much simpler to set up large and complex networks, while still having a secure private network. It is simpler (and therefore cheaper) for the telco to mix private MPLS networks and public internet on their network. They can also provide internet and private MPLS services on the same router at your site.



              In all these switched WAN scenarios, adding a backup data centre requires just one extra connection, one router port and the appropriate configuration.



              I should also mention Internet VPN. In this case, you are encapsulating and encrypting your data over the public network. Encapsulation allows you to access private IP addresses in the corporate network, encryption is necessary for security. What you do not have (with certain exceptions) is guaranteed bandwidth or high service levels, but it's much cheaper.







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Apr 15 at 23:34









              grahamj42grahamj42

              1812




              1812





















                  6














                  IP packets are encapsulated in a layer 2 protocol, whether they are sent on a LAN or WAN. Frame relay is one such WAN layer 2 protocol. There are others, but most are being rapidly replaced by Ethernet. On LANs, of course, you have Ethernet and Wi-fi.



                  MPLS doesn't quite fit into the TCP/IP or OSI model. Some consider it a "layer 2.5" protocol.






                  share|improve this answer





























                    6














                    IP packets are encapsulated in a layer 2 protocol, whether they are sent on a LAN or WAN. Frame relay is one such WAN layer 2 protocol. There are others, but most are being rapidly replaced by Ethernet. On LANs, of course, you have Ethernet and Wi-fi.



                    MPLS doesn't quite fit into the TCP/IP or OSI model. Some consider it a "layer 2.5" protocol.






                    share|improve this answer



























                      6












                      6








                      6







                      IP packets are encapsulated in a layer 2 protocol, whether they are sent on a LAN or WAN. Frame relay is one such WAN layer 2 protocol. There are others, but most are being rapidly replaced by Ethernet. On LANs, of course, you have Ethernet and Wi-fi.



                      MPLS doesn't quite fit into the TCP/IP or OSI model. Some consider it a "layer 2.5" protocol.






                      share|improve this answer















                      IP packets are encapsulated in a layer 2 protocol, whether they are sent on a LAN or WAN. Frame relay is one such WAN layer 2 protocol. There are others, but most are being rapidly replaced by Ethernet. On LANs, of course, you have Ethernet and Wi-fi.



                      MPLS doesn't quite fit into the TCP/IP or OSI model. Some consider it a "layer 2.5" protocol.







                      share|improve this answer














                      share|improve this answer



                      share|improve this answer








                      edited Apr 15 at 16:57

























                      answered Apr 15 at 16:22









                      Ron TrunkRon Trunk

                      40k33781




                      40k33781





















                          3














                          The term encapsulation is used to describe a process of adding headers and trailers around some data. For example, here is what happens when you send an email using your favourite email program (like Outlook or Thunderbird):



                          • The email is sent from the Application layer to the Transport layer.


                          • The Transport layer encapsulates the data and adds its own header (with its own information, such as which port will be used) and passes the data to the Internet layer


                          • The Internet layer encapsulates the received data and adds its own header, usually with information about the source and destination IP addresses. The Internet layer than passes the data to the Network Access layer


                          • The Network Access layer is the only layer that adds both a header and a trailer. The data is then sent through a physical network link.


                          Fore more details wiki






                          share|improve this answer



























                            3














                            The term encapsulation is used to describe a process of adding headers and trailers around some data. For example, here is what happens when you send an email using your favourite email program (like Outlook or Thunderbird):



                            • The email is sent from the Application layer to the Transport layer.


                            • The Transport layer encapsulates the data and adds its own header (with its own information, such as which port will be used) and passes the data to the Internet layer


                            • The Internet layer encapsulates the received data and adds its own header, usually with information about the source and destination IP addresses. The Internet layer than passes the data to the Network Access layer


                            • The Network Access layer is the only layer that adds both a header and a trailer. The data is then sent through a physical network link.


                            Fore more details wiki






                            share|improve this answer

























                              3












                              3








                              3







                              The term encapsulation is used to describe a process of adding headers and trailers around some data. For example, here is what happens when you send an email using your favourite email program (like Outlook or Thunderbird):



                              • The email is sent from the Application layer to the Transport layer.


                              • The Transport layer encapsulates the data and adds its own header (with its own information, such as which port will be used) and passes the data to the Internet layer


                              • The Internet layer encapsulates the received data and adds its own header, usually with information about the source and destination IP addresses. The Internet layer than passes the data to the Network Access layer


                              • The Network Access layer is the only layer that adds both a header and a trailer. The data is then sent through a physical network link.


                              Fore more details wiki






                              share|improve this answer













                              The term encapsulation is used to describe a process of adding headers and trailers around some data. For example, here is what happens when you send an email using your favourite email program (like Outlook or Thunderbird):



                              • The email is sent from the Application layer to the Transport layer.


                              • The Transport layer encapsulates the data and adds its own header (with its own information, such as which port will be used) and passes the data to the Internet layer


                              • The Internet layer encapsulates the received data and adds its own header, usually with information about the source and destination IP addresses. The Internet layer than passes the data to the Network Access layer


                              • The Network Access layer is the only layer that adds both a header and a trailer. The data is then sent through a physical network link.


                              Fore more details wiki







                              share|improve this answer












                              share|improve this answer



                              share|improve this answer










                              answered Apr 15 at 15:51









                              serverAdmin123serverAdmin123

                              3717




                              3717





















                                  3














                                  Layer 2 Encapsulation covers a number of purposes, most notably framing, error detection, compression, addressing, and protocol layering, and these really apply whether the networking is wide area or local area.




                                  • Framing: We need some way to reliably chunk the data into frames


                                  • Error detection: If the encapsulation has addressing or length fields, it's normally vastly much more efficient if it can do its own error detection (and perhaps correction), so it can discard frames which have been corrupted. It's good to put this at a low level, because it's much more likely to have knowledge of what kinds of errors are probably and improbable.


                                  • Compression: it might be that there is a lot of redundant information in the frames, such as for example perhaps all the packets have pretty much the same header, and a low-level compression might be practical.


                                  • Addressing: Very frequently there are multiple devices on the medium, and we want to be able to select which to disturb with this frame: most notable for broadcast media such as ethernet, and often not present in encapsulation for point-to-point networks.


                                  • Protocol layering: it's very common that the technology should be capable of being used by several upper protocols, perhaps internet protocol and some other. The encapsulation has some method of saying which upper-layer protocol stack should receive it.

                                  The simplest encapsulation is SLIP, which just does framing and nothing else: it's for point to point links, so addressing isn't used, and the only upper protocol suppported is IP, so it doesn't even have to say that. Van Jacobson's method of compressing TCP/IP headers is an example of low-level compression.



                                  One of the most complex is ethernet, which does framing, error checking, broadcast/unicast, local addressing and upper protocol selection.






                                  share|improve this answer





























                                    3














                                    Layer 2 Encapsulation covers a number of purposes, most notably framing, error detection, compression, addressing, and protocol layering, and these really apply whether the networking is wide area or local area.




                                    • Framing: We need some way to reliably chunk the data into frames


                                    • Error detection: If the encapsulation has addressing or length fields, it's normally vastly much more efficient if it can do its own error detection (and perhaps correction), so it can discard frames which have been corrupted. It's good to put this at a low level, because it's much more likely to have knowledge of what kinds of errors are probably and improbable.


                                    • Compression: it might be that there is a lot of redundant information in the frames, such as for example perhaps all the packets have pretty much the same header, and a low-level compression might be practical.


                                    • Addressing: Very frequently there are multiple devices on the medium, and we want to be able to select which to disturb with this frame: most notable for broadcast media such as ethernet, and often not present in encapsulation for point-to-point networks.


                                    • Protocol layering: it's very common that the technology should be capable of being used by several upper protocols, perhaps internet protocol and some other. The encapsulation has some method of saying which upper-layer protocol stack should receive it.

                                    The simplest encapsulation is SLIP, which just does framing and nothing else: it's for point to point links, so addressing isn't used, and the only upper protocol suppported is IP, so it doesn't even have to say that. Van Jacobson's method of compressing TCP/IP headers is an example of low-level compression.



                                    One of the most complex is ethernet, which does framing, error checking, broadcast/unicast, local addressing and upper protocol selection.






                                    share|improve this answer



























                                      3












                                      3








                                      3







                                      Layer 2 Encapsulation covers a number of purposes, most notably framing, error detection, compression, addressing, and protocol layering, and these really apply whether the networking is wide area or local area.




                                      • Framing: We need some way to reliably chunk the data into frames


                                      • Error detection: If the encapsulation has addressing or length fields, it's normally vastly much more efficient if it can do its own error detection (and perhaps correction), so it can discard frames which have been corrupted. It's good to put this at a low level, because it's much more likely to have knowledge of what kinds of errors are probably and improbable.


                                      • Compression: it might be that there is a lot of redundant information in the frames, such as for example perhaps all the packets have pretty much the same header, and a low-level compression might be practical.


                                      • Addressing: Very frequently there are multiple devices on the medium, and we want to be able to select which to disturb with this frame: most notable for broadcast media such as ethernet, and often not present in encapsulation for point-to-point networks.


                                      • Protocol layering: it's very common that the technology should be capable of being used by several upper protocols, perhaps internet protocol and some other. The encapsulation has some method of saying which upper-layer protocol stack should receive it.

                                      The simplest encapsulation is SLIP, which just does framing and nothing else: it's for point to point links, so addressing isn't used, and the only upper protocol suppported is IP, so it doesn't even have to say that. Van Jacobson's method of compressing TCP/IP headers is an example of low-level compression.



                                      One of the most complex is ethernet, which does framing, error checking, broadcast/unicast, local addressing and upper protocol selection.






                                      share|improve this answer















                                      Layer 2 Encapsulation covers a number of purposes, most notably framing, error detection, compression, addressing, and protocol layering, and these really apply whether the networking is wide area or local area.




                                      • Framing: We need some way to reliably chunk the data into frames


                                      • Error detection: If the encapsulation has addressing or length fields, it's normally vastly much more efficient if it can do its own error detection (and perhaps correction), so it can discard frames which have been corrupted. It's good to put this at a low level, because it's much more likely to have knowledge of what kinds of errors are probably and improbable.


                                      • Compression: it might be that there is a lot of redundant information in the frames, such as for example perhaps all the packets have pretty much the same header, and a low-level compression might be practical.


                                      • Addressing: Very frequently there are multiple devices on the medium, and we want to be able to select which to disturb with this frame: most notable for broadcast media such as ethernet, and often not present in encapsulation for point-to-point networks.


                                      • Protocol layering: it's very common that the technology should be capable of being used by several upper protocols, perhaps internet protocol and some other. The encapsulation has some method of saying which upper-layer protocol stack should receive it.

                                      The simplest encapsulation is SLIP, which just does framing and nothing else: it's for point to point links, so addressing isn't used, and the only upper protocol suppported is IP, so it doesn't even have to say that. Van Jacobson's method of compressing TCP/IP headers is an example of low-level compression.



                                      One of the most complex is ethernet, which does framing, error checking, broadcast/unicast, local addressing and upper protocol selection.







                                      share|improve this answer














                                      share|improve this answer



                                      share|improve this answer








                                      edited Apr 16 at 11:40

























                                      answered Apr 15 at 17:26









                                      jonathanjojonathanjo

                                      12.4k1938




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