Show pagesourceOld revisionsBacklinksBack to top × Table of Contents Datagram Structures OSI Layer 2 Ethernet Wireless LAN ATM cell PPP OSI Layer 3 IP ICMP OSI Layer 4 TCP UDP Datagram Structure Example Datagram Structures Please read Datagram and OSI model. OSI Layer 2 OSI Layer 2 datagrams are called frames. Ethernet IEEE 802.3 IEEE 802.1q: VLANs Wireless LAN Wireless LAN. ATM cell Layer 2 datagrams of the ATM protocol are called cells. ATM cell structure PPP The PPP (Point-to-point protocol) is a somewhat of a partial Layer 2 protocol. It is always used in conjunction with a second Layer 2 protocol, working as a carrier. PPP Header or Field or Tag Field Version Type Code Session-ID Length PPP protocol Payload Bit 4 4 8 16 16 16 x Such PPP frames are encapsulated into the carrier frame: common are Ethernet and ATM. So we talk about PPPoE Frame: TODO (or simply combine the already given information) PPPoA Cell: TODO (or simply combine the already given information) But since ATM protocol is ever present, you only seldom have pure PPPoE over the whole distance from your Modem to the DSLAM. You have ATM as well as Ethernet. And this gives you two possibilities to combine the two protocols. You can either encapsulate or bridge: Encapsulating: PPPoEoA Frame: Point-to-Point_Protocol_over_Ethernet#How_PPPoE_fits_in_the_DSL_Internet_access_architecture Briding: PPPoE-2-PPPoA this means that the Modem, strips the PPPoE header of every frame and replaces it with a PPPoA header. Pure PPPoE: it is being claimed that many VDSL2 connections relinquish the ATM protocols, and use pure PPPoE. OSI Layer 3 Datagrams at OSI Layer 3 are called packets. IP IPv4 Packet IPv6 Packet ICMP ICMPv4 Packet ICMPv6 Packet OSI Layer 4 Some OSI Layer 4 datagrams are referred to as packets. TCP datagrams are called segments. By definition UDP datagrams remain datagrams because they are stateless but are often referred to as packets. TCP TCP UDP UDP Datagram Structure Protocol Header Size in Bytes Total Size in Bytes Ethernet frame 38–42 Size: 84–1542Bytes, Jumbo frame up to 9042 Wireless LAN ?? 23?? IPv4 Packet 20–60 Size: 20– (20-byte header + 0 bytes data) 65.535 IPv6 Packet 40 fixed, Optional Extension Header possible up to 65.535 TCP Segment 20–60 up to 65.535 UDP Packet 4–8 with IPv4 and 6–8 with IPv6 up to 65.535 Example TCP segment in IPv4 packet in Ethernet frame Ethernet Octets Preamble 7 Start of frame delimiter 1 MAC destination 6 MAC source 6 802.1Q tag (opt.) 4 Ethertype or length 2 IPv4 Bits Payload 46 -1500 Version 4 Header Length 4 Differentiated Services Code Point 6 Explicit Congestion Notification 2 Total Length 16 Identification 16 Flags 3 Fragment Offset 13 Time to Live 8 Protocol 8 Header Checksum 16 Source IP Address 32 Destination IP Address 32 Options ( if Header Length > 5 ) ? Payload 1440-1480 Bytes TCP Bits Source Port 16 Destination Port 16 Sequence number 32 Acknowledgment number 32 Data offset 4 Reserved 4 Flag 8 Window Size 16 Checksum 16 Urgent pointer 16 Options (if Data Offset > 5) varies padding 8 Payload Payload CRC 4 Interframe gap 12 This website uses cookies. By using the website, you agree with storing cookies on your computer. Also you acknowledge that you have read and understand our Privacy Policy. If you do not agree leave the website.OKMore information about cookies Last modified: 2018/02/17 12:45by bobafetthotmail