On 12/1/07, Paul D. Amer <amer@xxxxxxxxxxxx> wrote: > First: > I'm teaching a graduate networking class that includes > DCCP as a new experimental protocol. I want to show > students various simple examples. In particular I want to show > which data is delivered (or read by the receiving application) > for different sizes of receive windows, and with/without > loss of DCCP packets. Best I can tell, > the RFC doesn't contain examples. Does anyone know > if any are available elsewhere? > > Second: > After reading the RFC, it's my understanding that > DCCP provides 'in-order, maybe-loss, no duplicate, > controlled/partial data integrity' service. > (TCP provides 'in-order, no-loss, no duplicate, full > data integrity' service.) > > Am I correct that the data delivered to the receiving > application will be in order and never have duplicates, > (albeit with some data missing, and possibly > some bits in error for those data fields not covered > by the checksum)? > > For example, if a sender sends DCCP packets 1,2,3,4,5,6, > the following are valid deliveries to the receiving app: > 1,2,3,4,5,6 > 1,3,4,6 > 1,6 > and the following deliveries may not occur: > 2,1,3,4,5,6 > 1,2,2,2,3,4,5,6 > > If my understanding is correct, it would help > the RFC intro to explicitly discuss that DCCP service provides > in-order and no-duplicates (just like TCP). If > my understanding is incorrect, it would help the > RFC to have an example or two showing how data > is delivered to the receiver out-of-order or > in duplicate. > > > Thanks, > Paul Amer, Professor > Univ of Delaware > > Paul, As I read it order is not guaranteed except on some options/features (RFC4340 6.6.4). Duplicates could occur as well. Some features are reliable but data is not reliable. The way that I explain DCCP is that it is like UDP with sessions and congestion control or TCP without reliability. I also emphasise the pluggable congestion control. This is a gross simplification but helps people understand. Ian -- Web1: http://wand.net.nz/~iam4/ Web2: http://www.jandi.co.nz Blog: http://iansblog.jandi.co.nz
