Homework #11 Solutions
cs349 -- Networks


22) The sequence numbers are only 4-bits long, so after 16
    consecutive losses, the sequence numbers will wrap around,
    and the n+16th cell will seem to be the nth.


23) Under AAL3/4

    40 bytes of data gets padded to 44 bytes, and then
    4 bytes of header and 4 bytes of trailer make it 52 bytes.

    It takes two cells to transport: the first one gets
    the first 48 bytes and the second gets the remaining 4
    
    Under AAL5

    The 40 bytes get an 8-byte trailer and then fit perfectly
    into a single 48-byte cell.


28) Cell switching methods almost always use virtual circuit
    routing rather than datagram routing.  Why?

    VCIs are smaller than global addresses, so per-cell overhead
    is smaller, which is more important for (small) cells than
    for (large) variable-length packets.


29) Fastest you can get a packet into memory and back out
    is half the speed of the slower of (I/O Bus, Memory Bus).

    So that's 800/2 = 400 Mbps

    You could handle 400/45 = 8 T3 links running at capacity.


30) 400 Mbps / 100,000 pps = 4000 bits per packet, or 500 bytes.