Medium Access Control (MAC) and Physical Layer (PHY) - CISE

4-June-07 P1901_PRO_016_r0
Open connection
Learn source MAC
address
Last data block
received (empty)
Close connection
Client
MAC_x
PTTP.DATA(N)
Empty
PTTP.RRQ
DST: DS2 Multicast
SRC: MAC_x
Preforwarded to
active ports
PTTP.DATA(1)
DST: MAC_x
SRC: MAC_y
PTTP.ACK(1)
DST: MAC_y
SRC: MAC_x
PTTP.DATA(2)
PTTP.ACK(2)
PTTP.ACK(N)
Figure 153 Usual PTTP operation.
Server
MAC_y
Open connection
Learn source MAC
address
Last block ACK
received
Close connection
Since PTTP protocol operates directly over BPL and Ethernet protocols, it must handle itself lost and duplicated
packets. PTTP implements the stop-and-wait protocol described before. For this purpose, two timers are needed per
each connection: DATA and ACK timers. The DATA timer is in the client, whereas the ACK timer is located in the
server.
If a duplicated DATA or ACK message arrives, it is simply discarded, because its Block Number field will not
match the expected one. If a DATA or ACK message is lost, the ACK timer will expire in the server and this will
retransmit the last DATA message.
There is defined a Maximum Number of Retransmissions, which in case of being exceeded, the connection will be
closed on the server side. Moreover, the connection will be closed on the client side too, because its DATA timer
will expire.
Submission page 364 UPA-OPERA