1. Chap 1 Foundation
Broadcasting
Chap 20

2. Introduction Use of broadcasting
to know server address on the local subnet: resource discovery
to minimize network traffic on a LAN
Internet applications
ARP(Address Resolution Protocol)
BOOTP(Bootstrap Protocol)
NTP(Network Time Protocol)
Routing daemons: broadcast routing table

3. Broadcast Addresses Subnet-directed: [subnetid, -1]
Normally routers do not forward these broadcasts
most commonly used today
E.g.) ping
Limited broadcast:
must not forwarded by a router
Some systems do not understand a subnet-directed broadcast address and only interpret as a broadcast
TFTP and BOOTP use this address to know IP address of its diskless workstation on bootstrapping procedure

4. Unicast versus Broadcast

5. dg_cli Function using Broadcasting
Before broadcasting, set SO_BROADCAST socket option
const int on = 1;
setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &on, sizeof(on));
First example dg_cli: Figure 20.5 bcast/dgclibcast1.c
SIFALRM signal이 blocked system call(recvfrom)이외에서 deliver되면 loop을 빠져 나오지 못함
Race Condition: shared data를 여러 process들이 동시에 access할 때 time-dependent error 발생
Case 1: shared data(global variable) among threads
Case 2: dealing with signals  signal handler도 일종의 thread로 봐야
dg_cli with blocked signal: Figure 20.6 bcast/dgclibcast3.c
Still has race condition problem

6. dg_cli Function that broadcasts
bcast/dgclibcast1.c
문제점
SIFALRM signal이 blocked system call(recvfrom)이외에서 deliver되면 loop을 빠져 나오지 못함
Race Condition:
shared data를 여러 process들이 동시에 access할 때 time-dependent error 발생
Case 1: shared data(global variable) among threads
Case 2: dealing with signals  signal handler도 일종의 thread로 봐야

7. Correct Solutions for Avoiding Race Condition
bcast/dgclibcast5.c