Remi, On 25 July 2011 11:59, Rémi Després <[email protected]> wrote: > > Wojciech, > > IPv4-header computations of draft-dec-stateless-4v6-02 are AFAIK too much in > favor of translation (4v6T) vs encapsulation (4V6E). > > The draft has: > +------------------------+--------------------+---------------------+ > | Item | 4V6 Translation | 4V6 Mapped Tunnel | > | | mode | Mode | > +------------------------+-------- ... -------+---------------------+ > | Overhead in relation | a) 0% b) 0% | a) 4.36% b) 1.71% | > | to average payload of | | | > | a) ~550 bytes b) 1400 | | | > | bytes). | | | > | ------------------ | ------------------ | ------------------ | > > An IPv4 packet having a 550 B payload is 570 B long (ignoring possible IPv4 > options): > - 4V6T adds 20 B (3.5 %). > - 4V6E adds 40 B, (7.0 %). > An IPv4 packet having a 1400 B payload is 1420 B long (at least) > - Translation adds 20/1420 = 1,4 % > - Encapsulation adds 40/1420 = 2,8 % > > This gives: > | ------------------ | ------------------ | ------------------ | > | Overhead in relation | a) 3.5% b) 1.4% | a) 7% b) 2.8% | > | to average payload of | | | > | a) ~550 bytes b) 1400 | | | > | bytes). | | | > | ------------------ | ------------------ | ------------------ |
Sure. However, 4V6, as per Figure 1 in the draft is based on IPv6 transport. It thus seemed fair to measure and compare the overhead as relative to IPv6 encapsulation, and not IPv4, since there is no way to send an IPv4-only packet, and the useful data is the Layer4+ payload. Doing it your way you show mixes the basic IPv6 overhead. In any case, subtract the left column from the right and one arrives at the figure at pretty much the figures in the original table. > > In addition, a complete comparison should take in consideration the length of > layer-2 headers, as well as that of the physical preambles if any. This leads > to even less different overhead ratios. With the relative consideration, this actually doesn't matter... And we can choose to ignore the detail of specific radio link protocols that can segment longer packets into many many more. -Woj. _______________________________________________ Softwires mailing list [email protected] https://www.ietf.org/mailman/listinfo/softwires
