As an ex-switch bitch its not that difficult or impressive these days - 2048 super groups are a basic 2-meg or E1.
SWITCH uses encrypted X25 PACKET SWITCHING.
just log on tinternet and research PDH & SDH (PACKET SWITCHING) - ends up reading like comcen proceedures 18 V'S ZCZC Bla Bla Bla.
speak to your yeoman - if he's switched on he should be able to explain it in Civvy terms or get hold of some one from your unit that has recently got out - i'd send you my old CV but I have not seen it since Oct 1998.
PDH & SDH is being ripped out every where and is no longer supported - company's want Cisco experience (have you any BOWMAN experience?).
Agreed that PDH is on the way out, but not SDH. In fact there's plenty of it out there and will be for ages on the carriers' core. In fact, I'm just putting in an SDH STM-4 metro area network for someone right now.
Cisco is also a very useful skill is you can get some of their qualifications under your belt. If you fancy taking that deeper learn more about their CallManager software - IP Telephony is getting bigger and bigger, so good skills are at a premium right now.