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The interesting question is why did SMS only have 160 characters. I know those 160 bytes are 7 bit characters and that a 8 bit SMS can contain 140 characters, b
by mads 9y ago
The interesting question is why did SMS only have 160 characters. I know those 160 bytes are 7 bit characters and that a 8 bit SMS can contain 140 characters, but why does the control channel limit it to that?
I worked on a WAP browser a long time ago, which would support SMS in PDU mode as a bearer. WDP packets would just be encapsulated in an SMS. I am too old ... :(
- nitwit005 9y agoBecause the technology that came before cell phones was pagers.
- mads 9y agoGood point, but why not 139 bytes or 141 bytes?
- noirknight 9y agoMany years ago I worked on an SMSC. SMS are sent over the same data channels as phone signalling (call setup etc.) using SS7 protocol stack. The SS7 protocol physical layers used fixed size data packets of around 256 bytes, for example on T1 data channels. On top of that you need routing info such as addressing in MTP, TCAP to get the packet to the correct mobile switching center. Then GSM or IS-41 MAP to route to the device. Finally the sms bearer encoding needs some extra bytes for thing like delivery reports and source phone number. This left 160 bytes free.
- uptown 9y agoIn other words, SMS messages could be delivered across the communication channel that the devices were already doing in-order to remain in-contact with towers, essentially allowing providers to charge (SMS used to be an add-on) for something that cost carriers basically nothing in transmission costs. Is that a correct translation?
- julianz 9y agoYup, exactly.