NEC UNIVERGE SV9100 Manual page 17

Part 1: VoIP Reference Manual 17
Marking is the first step in this process and is often the only step that the NEC dealer will perform.
Protocol Structure - IP/IPv4 Header (Internet Protocol version 4)
Version - the version of IP currently used.
IP Header Length (IHL) - datagram header length. Points to the beginning of the data. The
minimum value for a correct header is 5.
Type-of-Service - Indicates the quality of service desired by specifying how an upper-layer protocol
would like a current datagram to be handled, and assigns datagrams various levels of importance.
This field is used for the assignment of Precedence, Delay, Throughput and Reliability.
Total Length - Specifies the length, in bytes, of the entire IP packet, including the data and header.
The maximum length could be specified by this field is 65,535 bytes. Typically, hosts are prepared to
accept datagrams up to 576 bytes.
Identification - Contains an integer that identifies the current datagram. This field is assigned by
sender to help receiver to assemble the datagram fragments.
Flags - Consists of a 3-bit field of which the two low-order (least-significant) bits control
fragmentation. The low-order bit specifies whether the packet can be fragmented. The middle bit
specifies whether the packet is the last fragment in a series of fragmented packets. The third or high-
order bit is not used.
Fragment Offset - This 13 bits field indicates the position of the fragment's data relative to the
beginning of the data in the original datagram, which allows the destination IP process to properly
reconstruct the original datagram.
Time-to-Live - It is a counter that gradually decrements down to zero, at which point the datagram
is discarded. This keeps packets from looping endlessly.
Protocol - Indicates which upper-layer protocol receives incoming packets after IP processing is