How does IOS determine the operator of the current network?

How does IOS determine whether the content of the carrier of the current network is transferred to: http://www.iloss.me/2012/07/21/ios?_________ former network operator /#more-1091

There is a retain screen on iOS, So you often need to use high-definition images at some times, and sometimes you need to use normal images.
When the network conditions are good, this is certainly the case. If you are an iPhone user, you can use a mobile card.
If you still use a high-definition image, it is definitely a gray cup.
From the current situation, only mobile GPRS cards are as slow as normal, so we need to weigh the loss of point quality in some occasions.
Exchange speed.
Then we must know that the current network is the Shenma operator. Provide an alternative solution.

- (BOOL)checkChinaMobile{    BOOL ret = NO;    CTTelephonyNetworkInfo *info = [[CTTelephonyNetworkInfo alloc] init];    CTCarrier *carrier = [info subscriberCellularProvider];    if (carrier == nil) {        [info release];        return NO;    }     NSString *code = [carrier mobileNetworkCode];    if (code == nil) {        [info release];        return NO;    }     if ([code isEqualToString:@"00"] || [code isEqualToString:@"02"] || [code isEqualToString:@"07"]) {        ret = YES;    }    [info release];     return ret;}

The Network is a mobile network in three cases: 00-02-07. For details, refer to the following data:
China-CN

MCC	MNC	Brand	Operator	Status	Bands (MHz)	References and notes
460	00	China Mobile	China Mobile	Operational	GSM 900/GSM 1800/TD-SCDMA 1880/TD-SCDMA 2010
460	01	China Unicom	China Unicom	Operational	GSM 900/GSM 1800/UMTS 2100	CDMA network soldChina Telecom, WCDMA inclucial trial started in May 2009 and in full inclucial operation as of October 2009.
460	02	China Mobile	China Mobile	Operational	GSM 900/GSM 1800/TD-SCDMA 1880/TD-SCDMA 2010
460	03	China Telecom	China Telecom	Operational	CDMA 2000 800/CDMA 2000 2100	EV-DO
460	05	China Telecom	China Telecom	Operational
460	06	China Unicom	China Unicom	Operational	GSM 900/GSM 1800/UMTS 2100
460	07	China Mobile	China Mobile	Operational	GSM 900/GSM 1800/TD-SCDMA 1880/TD-SCDMA 010
460	20	China tietong	China tietong	Operational	GSM-R