HFC (Cable modem, CATV Internet access)
CATV network (MAN?) upgraded to hybrid fiber-coax, added digital streams for non-symmetrical downstream and upstreams. home: upstream 384 Kbps to 6 Mbps, downstream to 15 Mbps
business: 3 - 30 Mbps
ISP/Internet--CMTS at headend--optical node--coax tree-and-branch backbone--tap--splitter--RG6/RG11 75 Ohm F-type connector--cable modem--PC/LAN
Cable modem connected to router
Cable modem connected to router
DOCSIS says how system works
cable modem as bridge (and router). tunes to downstream channel, demodulates it, extracts only portion of data for it, converts to Ethernet (or USB). upstream: receives Ethernet or USB signal, modulates onto upstream channel, negotiates with headend CMTS to send.
shared medium: headend allocates time slots (TDM) to modems needing to send data.
DHCP from headend. encryption. modem authentication.
peak usage slowdowns reduced by redundant and fiber ?
analog TV channel uses 6 MHz (27 MBps) (inefficiently). several MPEG-2 (6 MBPS) or MPEG-4 (2 MBPS) digital standard channels in one such carrier.
Higher capacity than DSL. Telcos counter with FTTH (fiber to the home/premises)
telcos and cable are competing for the triple play: telephone/voice, television/video, Internet/data
virtual private network: secure tunnel thru Internet. cheaper than leased line. available everywhere. many-to-many connections.
site-to-site (L2L): replacement of private line.
remote access: VPN client on PC (or home router) or IPphone
negotiation: AH, ESP, ESP+AH
encryption: DES, 3DES, AES
authentication: MDS, SHA-1
POTS of PSTN.
cust.premises -- analog local loop -- CO --digital, routed thru exchanges' switches.
RJ11, 2 pair copper twisted pair cable.
designed for voice traffic using analog signaling. 4 KHz bandwidth.
dial-up modem up to 56 Kbps
modem changes digital of computer to analog of local loop.
CCITT, now ITU, series of modem V. protocols.
includes compression and error detection, adjust speed to line conditions.
V.44/V.34 analog both ends. max 34 Kbps
V.90 V.92 you analog, ISP digital. 56 Kbps(download) can't get faster
PPP used for data link layer protocol
PSTN--|--RJ11--external modem -- serial port (w/ UART) as COMn
PSTN--|--RJ11--internal modem (w/ UART) as COMn
COM port = I/O address + IRQ
POTS to be subsumed into Internet??
Modem pool (282 modems)
Modem pool server
Modem pool location map
digitized voice: DS0 64Kbps (8000 Hz sampel rate @ 8 bits sample size)
basic rate interface BRI: two 64 Kbps B channels, one 16
Kbps D channel. 2B+D =128 Kbps
primary rate interface PRI: 23 64 Kbps B channels, one 64 Kbps D channel. 23B+D =1.5 Mbps (==T1, PRI as a repackaged T1)
B channels for data/voice, D channel for control.
reference points (interfaces): R S T U
PSTN--|-- U NT1 S/T -- TE1 (ISDN devices, e.g. phone/fax)
PSTN--|-- U NT1 S/T -- TA -- TE2 (non-ISDN device, e.g. PC)
terminal adapter is "ISDN modem"
NT1 and TA can be card
must be <18,000 ft from CO???
Dial-up service. per minute charges. usually PPP
usually SPID (telphone number) per B channel in BRI.
--authentication (but not usually needed for point-to-point WAN link): CHAP.
--callback to secure telephone number.
--multilink: combine multiple link into one. load-balancing too.
NB. what "they" have:
the WAN traffic crossed two systems: a 10 Gbps circuit from Sunnyvale to Chicago and a 2.49 Gbps transatlantic circuit between Chicago and Geneva. (LANL, SLAC, CERN)
Abilene network of "Internet2": consortium of 220 institutions and corporate partners. 10Gbps backbone. Goal of 100 megabit connectivity between every node by the end of 2006. A private network used for education and research, is not entirely an isolated network, since its members usually provide alternative access to many of their resources through the public Internet. Abilene is not technically part of the Internet since it does not peer with the public Internet networks. Its NOC ishosted at Indiana University. Uses Qwest's optical fiber networks.