Subscriber line technology. xdsl. Subscriber line technology. S Verkkopalvelujen tuotanto S Network Service Provisioning

Transcription

1 Lic.Tech. Marko Luoma (1/68) Lic.Tech. Marko Luoma (2/68) Subscriber line technology S Verkkopalvelujen tuotanto S Network Service Provisioning Lecture 3: Subscriber line technologies Subscriber line is the last mile to the customer þ Conventionally only PSTN subscriber lines Twisted pair copper þ One or several pairs to each house þ In urban areas CATV subscriber lines provide same service Hybrid fiber coax network þ Power lines are the last to arrive to the scene Power lines are used to transmit also data traffic þ Conventionally only control messages to fusebox Subscriber lines are the most expensive part of the network þ A lot of physical construction work for each customer Lic.Tech. Marko Luoma (3/68) Lic.Tech. Marko Luoma (4/68) Subscriber line technology xdsl Technology options for broadband data connections are þ XDSL over PSTN subscriber lines þ DOCSIS over CATV lines þ Power line communication (PLC) þ Wireless local loops WLAN / HiperLAN WiMax XDSL is based on the digitalized subscriber line technologies þ IDSL (ISDN Digital Subscriber Line) was the initial invention Also local loop can be digitized with high reliability and low bit error rate þ Both ends of the subscriber line is equipped with modems Information is modulated to frequency range that best serves the communication þ PSTN copper pairs are in general old and contain a lot nonlinearities ý Joints made with variable mechanisms ý irregular twisting of pairs ý Highly variable di-electric properties of insulations ý Optimized for frequency range below 4kHz

2 Lic.Tech. Marko Luoma (5/68) Lic.Tech. Marko Luoma (6/68) xdsl HDSL Non-linearities cause a lot of problems in high data rate communications þ Attenuation þ Crosstalk þ Distortion Magnitude depends on frequency and other usage of copper infrastructure þ Copper pairs do not run individually on the ground ;-) HDSL (High Bit-Rate Digital Subscriber Line) þ First real xdsl-technique þ Baseband operation (2B1Q) Subscriber line cannot be used same time for POTS services þ Symmetric operation Suitable for corporate LAN interconnection PBX subscriber lines þ Part of the time-slots can be left out of usage þ Uses multiple copper pairs Two pairs 1.5Mbps (T1) Three pairs 2Mbps (E1) þ Maximum distance 3-4 km Lic.Tech. Marko Luoma (7/68) Lic.Tech. Marko Luoma (8/68) 2B1Q SDSL Four level baseband transmission þ 2 bits per symbol Used in þ ISDN subscriber line (IDSL) þ HDSL +3 BAUDI SDSL (Single-Line Digital Subscriber Line) þ Single copper pair version of HDSL Uses same modulation (2B1Q) Transmission rates are same as in HDSL þ More popular than HDSL Copper pairs are expensive to rent in urban area þ Maximum distance 3 km

3 Lic.Tech. Marko Luoma (9/68) Lic.Tech. Marko Luoma (10/68) G.SHDSL ADSL G.SHDSL (Symmetric High Bit-Rate Digital Subscriber Line) þ ITU-T Recommendation G T1E1 - HDSL2 ETSI - SDSL þ Transmission rates 192 kbps Mbps þ Coding 16-Level TC-PAM (Trellis Coded Pulse Amplitude Modulation) þ Single copper pair technology þ Information is framed based on various technologies: ATM TDM ADSL (Asymmetric Digital Subscriber Line) þ Most popular xdsl technique þ Asymmetric uplink and downlink þ Three bands Hz POTS kHz Bidirectional data band kHz downlink data band þ Bands are divided into 256 carriers Carriers can be activated and passivated þ Downlink maximum rate 1.5-8Mbps þ Uplink maximum rate 1.5 Mbps þ Maximum distance 3-4 km Lic.Tech. Marko Luoma (11/68) Lic.Tech. Marko Luoma (12/68) CAP/QAM DMT Carrierless AM/PM - Quadrature Amplitude Modulation þ Two dimensional code space Orthogonal components þ Amplitude þ Phase Used in þ ADSL þ VDSL þ DOCSIS Discrete Multitone þ N x CAP/QAM Linecode in divided into N subcomponents þ ADSL -> N = 256 Subcomponents are produced with Fourier transformation (DFT) þ Used in ADSL VDSL

4 Lic.Tech. Marko Luoma (13/68) Lic.Tech. Marko Luoma (14/68) ADSL ATU-R DMT based ADSL system measures the quality of copper pair and adapts symbol rate in each carrier to compensate possible defects þ Crosstalk þ Bit error rate þ Attenuation ADSL Transceiver Unit Remote þ Subscriber network termination Either þ Separate active device (bridge, router) þ NIC in PC Can be equipped with low pass filter to extract voice signal (analog)from data Lic.Tech. Marko Luoma (15/68) Lic.Tech. Marko Luoma (16/68) ATU-C XDSL Framing ADSL Transceiver Unit Central Office þ Core network termination Counterpart for user side mode þ Usually build into larger unit (DSLAM) Several modems Multiplexing unit which concentrates the traffic into high speed backbone link þ ATM 155 ATM 622 XDSL systems are typically build for data transmission Data is transmitted between þ Residential subscriber and ISP (Internet) þ Residential subscriber and corporate network (Intranet) þ Corporate offices (LAN interconnection) In all cases subscriber can be operated as þ Routed Subscriber has its own subnet þ Bridged Several subscribers share one subnet

5 Lic.Tech. Marko Luoma (17/68) Lic.Tech. Marko Luoma (18/68) XDSL Framing RFC2684: Multiprotocol Encapsulation over ATM Adaptation Layer 5 RFC2364: Point to Point Protocol over ATM RFC 2516: A Method for Transmitting Over (oe) Point to Point Protocol over over ATM RFC 2684 RFC 2684: Multiprotocol Encapsulation over ATM Adaptation Layer 5 þ Previous version RFC 1483 (Classical ) PC ATU-R ATU-C DSLAM BRAS PC ATU-R ATU-C DSLAM BRAS RFC2684 RFC2684 Framing Framing ATM ATM ATM ATM ATM ATM ATM ATM Framing LLC/SNAP VCMUX Lic.Tech. Marko Luoma (19/68) Lic.Tech. Marko Luoma (20/68) RFC2684 RFC 2684 Two modes þ VC-multiplexing No framing -> individual ATM PVC can be used only for transmitting one type information Both ends of the connection must share common view of the structure of information Efficient þ LLC-encapsulation IEEE encapsulation is added to information -> contains pointer to data type VC-multiplexing is based on raw ATM AAL5:n CPCS-interface þ Routed protocols are interleaved directly in to CPCS-PDU þ Bridged protocols require destination MAC-address for delivery CPCS-PDU PAD (0-47 octet) CPCS-UU (1 octet) CPI (1 octet) = 0x00 Length (2 octet) PAD =00-00 MAC Destination MAC frame LAN FCS (depends VC:) PAD (0-47 octet) CPCS-UU (1 octet) CPI (1 octet) =0x00 CRC (4 octet) Length (2 octet) CRC (4 octet)

6 Lic.Tech. Marko Luoma (21/68) Lic.Tech. Marko Luoma (22/68) Routed protocols RFC 2684 LLC-encapsulation þ LLC header expresses frame type (protocol) Subnet A Subnet B þ uses LLC/SNAP encapsulation Destination SAP =AA AA-AA-03 -> SNAP Source SAP =AA Frame Type =03 OUI = Ethertype = > Ethertype > v4 AAL5 ATM ATM ATM AAL5 ATM v4 packet PAD (0-47 octet) CPCS-UU (1 octet) CPI (1 octet) =0x00 Length (2 octet) CRC (4 octet) Lic.Tech. Marko Luoma (23/68) Lic.Tech. Marko Luoma (24/68) Bridged protocols RFC 2684 Subnet A bridging uses same LLC/SNAP encapsulation as does Destination SAP =AA Source SAP =AA Frame Type =03 AA-AA-03 -> SNAP OUI =00-80-C2 PID =00-01 / MAC Destination C2 -> Bridging > FCS preserved > FCS not preserved MAC frame LAN FCS (PID=00-01) AAL5 ATM ATM ATM AAL5 ATM PAD (0-47 octet) CPCS-UU (1 octet) CPI (1 octet) =0x00 Length (2 octet) CRC (4 octet)

7 Classical CATV Network Designed for transmission of TV/Radio signals þ Mhz Access network þ Amplifier lines þ Passive tap network at last mile Up to 500 subscribers CATV Core Network -Channel distribution Lic.Tech. Marko Luoma (25/68) Active Passive CATV Access Network -Amplification Lic.Tech. Marko Luoma (26/68) CATV Network with data connections Root amplifier of tap network is changed þ Connection to data network (Internet) þ Modulates the data to high frequency area MHz CATV Core Network -Channel distribution Active Passive CATV Access Network -Amplification Lic.Tech. Marko Luoma (27/68) Lic.Tech. Marko Luoma (28/68) (Euro) DOCSIS CATV Network (Euro) DOCSIS Amplifiers in coax segment are changed to bidirectional þ Uplink Data þ 5 42 Mhz þ Downlink Video and data þ MHz CATV Core Network -Channel distribution Active Passive CATV Access Network -Amplification US þ Frequency ranges Uplink 5 42 MHz Dowlink MHz þ 6 MHz video channels 0.2/1/2 MHz upstream channels QPSK Europe þ Frequency ranges Uplink 5 65 MHz Downlink MHz þ 8 Mhz video channels 1/2 MHz downstream channels QPSK 8 MHz DVB-C channels QAM

8 Lic.Tech. Marko Luoma (29/68) Lic.Tech. Marko Luoma (30/68) (Euro) DOCSIS (Euro) DOCSIS Architecture requires two different components þ Cable modem (CM) User device which modulates and demodulates the information to/from coax network þ interface for end-user Framing is based on framing but within the HFC network separate framing is used for data communication þ Downlink: TDM based MPEG-2 frames þ Uplink: TDMA based minislots þ Cable modem termination system (CMTS) Modem unit on CATV head-end or distribution hub þ Controls the uplink channel usage ý Separate CMTS for each frequency that is used for DOCSIS þ Modulates and demodulates the data to proper frequency TDMA MiniSlot IEEE DOCSIS MAC TDM MPEG 5-65 MHz 8MHz Channels HFC Lic.Tech. Marko Luoma (31/68) Lic.Tech. Marko Luoma (32/68) (Euro) DOCSIS (Euro) DOCSIS Downlink framing based on MPEG-2 þ 204 bytes þ Similar with video Mix and match in single channel þ Header contains info what frame content is PID field 0x1FFE equals to MCNS Data over Cable þ FEC is used to correct possible (probable) errors on transmission Coax networks with multiple amplifiers are prone to bit errors þ Reed Solomon coding Uplink framing is based on timely division of link capacity for different subscribers þ Similar than PDH þ Individual time-slot 6.25 us þ Amount of bytes depends on modulation and coding þ Required amount of time-slots is requested from CMTS to send data þ Length of sync field depends on physical transmission rate þ Data is normal frame Sync (1 byte) Header (3 bytes) Data (184 bytes) FEC (16 bytes) Sync (x bytes) Header (6 bytes) Data ( bytes) FEC (x bytes)

9 Lic.Tech. Marko Luoma (33/68) Lic.Tech. Marko Luoma (34/68) (Euro) DOCSIS (Euro) DOCSIS CMTS controls the resource usage on uplink by allocating certain timeslots for certain CM:s þ Done in granularities of MAP PDU Several time-slots Downlink (per CMTS channel) þ 64-QAM: 38 Mbps þ 256-QAM: 52 Mbps Uplink þ Capacity depends on Version of specification Modulation method Symbol rate (channel size) Previous map Current map For CMTS to map next Time-Slots Current map usage Requests CM A CM B CM C Maintenance þýüûüúùø úöõôúùøù þýüûúùø öõ ì ëêéèêöçù!"ãù# ö ù æåõêùäãâá ø öõùäãü$å ôó%!&'ù # ö ùø öõù äãü$å ôóò ñòò ðñò óïò ðñò ïòò óïò ôñîò óïò îòò ôñîò ñíóò ôñîò ôóòò ñíóò íôñò ñíóò ðñòò íôñò ôòñïò þýüûüúùø þýüûúùø öõ!"ãùäãü$å î%!&'ù äãü$å ôó%!&'ù äãü$å ðñ%!&'ù ä'ü$å óï%!&'ù ä'ü$å ôñî%!&'ù ä'ü$å ôóò ðñò ïîò óïò ò()ó ô(ñî ô()ñ ðñò óïò )óò ôñîò ô()ñ ñ(íó ð(îï óïò ôñîò ô)ñò ñíóò ð(îï í(ôñ *(óî ôñîò ñíóò ðîïò íôñò *(óî ôò(ñï ôí(ðó ñíóò íôñò *óîò ôòñïò ôí(ðó ñò(ïî ðò(*ñ íôñò ôòñïò ôíðóò ñòïîò ðò(*ñ ïò()ó óô(ïï Lic.Tech. Marko Luoma (35/68) Lic.Tech. Marko Luoma (36/68) Power Line Communications PLC Based on fact that majority of houses are connected power grid þ Same cabling system can be used to transmit information other than 50Hz electricity þ Modulation of data information to frequency range that operates in power network Power line twisting þ outdoors is optimized for low frequencies þ Indoors is basically none High frequencies þ Power line operates as antenna ý Regulations to control the emissions Based on three components þ Power line master unit Connects into power line after last transformer Modem unit which handles the transmission on power line þ Assigns turns for communication as in DOCSIS Up to 8 Mbps

10 Lic.Tech. Marko Luoma (37/68) Lic.Tech. Marko Luoma (38/68) PLC PLC Based on three components þ Indoor/Outdoor converter Changes the frequency range which used within the house to one which is used outside the house Modem unit which handles the transmission within the house þ Assigns turns for communication like outdoor master Based on three components þ Indoor modem unit Provides connection to PC and modem services to indoor PLC network Up to 8 Mbps Up to 8 Mbps Lic.Tech. Marko Luoma (39/68) Lic.Tech. Marko Luoma (40/68) PLC Point to Point Protocol () Frequency range 1.6MHz to 30 Mhz þ Several independent carriers (4-8 normally) þ Overall datarate 8Mbps Next generation will bring Mbps (depending on source of estimation) Locally several power companies have tested technology but only few are really offering services based on it RFC 1661: Point-to-Point Protocol (1994) Point-to-Point Protocol () provides common interface for different network protocols on point-to-point manner Three parts: þ Encapsulation, generic encapsulation for all protocols þ Link Control Protocol used to setup, control and tear down of link level point-to-point connections þ Network Control Protocol used to setup, control and tear down of network level point-to-point connections

11 Lic.Tech. Marko Luoma (41/68) Lic.Tech. Marko Luoma (42/68) encapsulation signaling Based on encapsulation of network protocol into þ 1-2 bytes long protocol identifier þ PAD Protocol identifier (1-2 bytes) Network protocol (N bytes) L2 encapsulation depends on used technology þ PSTN þ ISDN þ þ ATM þ FrameRelay PAD (M bytes) Datalink connection open þ LCP sets the layer dependent parameters Authentication þ Authentication is optional feature which must be indicated in opening of datalink connection Network connection open þ Process of opening network layer connection depends on protocol used. NCP sets layer specific parameters Datalink / Network level tear down þ Multiple network level connections can be setup and torn down from individual datalink connection þ Tearing down datalink connection disconnects all network level connections from that particular datalink Lic.Tech. Marko Luoma (43/68) Lic.Tech. Marko Luoma (44/68) LCP parameters LCP parameters Compression þ Protocol-Field-Compression Possibility to compress header protocol field to one byte (50% reduction ;-) þ Address-and-Control-Field-Compression In point-to-point connections after negotiation of full addresses both ends know entities of other end of line þ Replacement with integer ý Good compression ratio ý Modification of headers at both ends -> calculation Maximum Receive Unit þ Expresses maximum size of packet that can be processed within terminal þ Default value 1500 bytes ( MTU) Depending on media rate large MRU can seize the link for a long time þ 1500 bytes in 56 kbps modem line (without framing) lasts 210 ms þ 1500 bytes in 10 Mbps (without framing) lasts 1.2 ms

12 Lic.Tech. Marko Luoma (45/68) Lic.Tech. Marko Luoma (46/68) LCP parameters Authentication Authentication þ Iterative process Both end points declare their set of preferred authentication methods þ Can be done in both directions Neither of parties is trusted NAK Independent methods in both directions NAK 3. Password Authentication Protocol (PAP) þ RFC 1334 þ Uses simple hand-shake Client sends þ User ID þ Password Server acknowledges þ Operation is secured for packet losses by client Sends frequently ID/password combinations for server Weaknesses þ Clear text operation ID and password are not encrypted Can be eyes dropped þ No locking ID / password pairs can be scanned by machine Lic.Tech. Marko Luoma (47/68) Lic.Tech. Marko Luoma (48/68) Authentication Authentication Challenge Handshake Authentication Protocol (CHAP) þ RFC 1994 þ Two way hand-shake Server sends a challenge to client Client responds with hash value of correct answer to the challenge Server checks the answer Hand-shake can be done every N minutes or per transaction þ Reduces the damage from compromised key Secret key which is used in calculation of hash values can be based any technology þ Bank keys Weaknesses þ Secret key has to be in clear text format in server side (or accessible for server in clear text format) CHAP problems þ Challenge is based on knowledge of customer capabilities Customer identity has to be solved first þ PAP þ Subscriber line CHAP problems þ How to deliver correct answers to challenges to customers þ How to secure secret key in case of multiple access points Same key should be available in each access points Access points can not be trusted every time þ Co-located RAS functionalities

13 Lic.Tech. Marko Luoma (49/68) Lic.Tech. Marko Luoma (50/68) Authentication Authentication Extensible Authentication Protocol (EAP) þ RFC 2284 þ Possibility to use several authentication methods þ Delegates the selection process from LCP to separate authentication phase Makes possible to gather additional information from the customer before selection of algorithm Ability to use separate authentication system þ RADIUS þ DIAMETER þ KERBEROS EAP is based on multilevel handshake þ Server sends one or several requests to client First request relates to identity of client Each request contains a field which expresses the nature of request þ Identity þ ID / Password (PAP) þ One time password þ MD5 challenge þ Client answers to requests based on their nature Lic.Tech. Marko Luoma (51/68) Lic.Tech. Marko Luoma (52/68) LCP parameters LCP parameters Quality Protocol þ is designed to work in diverse environments þ Some L2 techniques cause more bit errors and/or packet losses can measure the quality of L2 connection and re parametrize the connection based on the results Both directions on point-to-point connection are independent þ Separate measurement of quality Magic Number þ End-point identifier which is based on randomness Generated from real-time clock, MAC address of NIC or other source which leads with high probability to unique result þ Makes easier to detect malfunctions on link ý echo

14 Lic.Tech. Marko Luoma (53/68) Lic.Tech. Marko Luoma (54/68) over ATM (oa) over ATM (oa) RFC 2364: over AAL5 þ packets are encapsulated into AAL5 frames VC multiplexing LLC/SNAP framing -connection is terminated between ATM end systems þ ATU-R Modem in PC Separate device (router, bridge) þ AAL5 provides to Point-to-point connection which is implemented in bit synchronous manner Control signals þ Connection UP þ Connection DOWN þ At network side termination point is not ATU-C Router which acts as BRAS XDSL DSLAM Lic.Tech. Marko Luoma (55/68) Lic.Tech. Marko Luoma (56/68) over ATM over ATM (oa) VC-multiplexing þ AAL5 frame does not contain information about structure of communication Protocol ID Information Padding LLC encapsulation Destination SAP Source SAP Frame Type (UI) NLPID () Protocol ID Information Padding LLC-header Network Layer Protocol ID Information which is transmitted over connection is either þ frames Bridged service Network layer control protocol -BCP þ packets Routed service Network layer control protocol -CP PAD (0-47 octet) PAD (0-47 octet) CPCS-UU (1 octet) CPI (1 octet) AAL5 -trailer CPCS-UU (1 octet) CPI (1 octet) AAL5 -trailer Length (2 octet) Length (2 octet) CRC (4 octet) CRC (4 octet)

15 - BCP Lic.Tech. Marko Luoma (57/68) Bridged connection Lic.Tech. Marko Luoma (58/68) RFC 2878: Bridging Control Protocol þ Bridge ID if customer device is part of distributed bridge þ MAC support (802.3, 802.4, 802.5) þ Tinygram compression padding for minimum frame length is removed þ MAC-address possibility to advertise own MAC-address to receiver (Access Control) þ IEEE 802 Tag - VLAN tag usage PC ATU-R ATU-C DSLAM ATM ATM ATM BRAS ATM Lic.Tech. Marko Luoma (59/68) Lic.Tech. Marko Luoma (60/68) - BCP - CP encapsulation encapsulation (VLAN support) Bridging 0x00 0x31 0x00 0x31 F 0 Z 0 PAD MAC Type Destination.. F 0 Z 0 PAD MAC Type Destination..... MAC Address Source MAC MAC Address Source MAC Address Length / Type... Address 0x81 0x00 DATA Pri C VLAN ID Length / Type LAN FCS PAD DATA LAN FCS CPCS-UU CPI Length PAD CRC CPCS-UU CPI Length CRC RFC 1332: The Internet Protocol Control Protocol þ address delivery for client þ TCP/ header compression Van Jacobson compression þ 40 bytes -> 2-5 bytes þ Mobile v4 þ DNS (primary, secondary)

16 Routed connection Lic.Tech. Marko Luoma (61/68) over ATM (oa) Lic.Tech. Marko Luoma (62/68) PC ATU-R ATU-C DSLAM ATM ATM ATM BRAS ATM Pros þ ATM connection is truly provisioned for individual clients Capacity is guaranteed Security is guaranteed Cons þ Connection is from provider BRAS to customer xdsl termination point Authentication needs to be set over network layer protocol Client computer can be switched off but network is not aware of it þ LCP session is up if the modem has power on Lic.Tech. Marko Luoma (63/68) Lic.Tech. Marko Luoma (64/68) over (oe) over (oe) RFC 2516: A Method for Transmitting Over (oe) þ packets are framed with headers acts as resource broker in network Two phases þ Discovery stage Where is my BRAS þ Makes possible to build building networks (HPNA) Within building þ Share network þ One (or several) connections to service providers ý Bridged traffic Each client þ Individual agreement with service provider ý Separate account ý Separate bill þ session stage XDSL DSLAM

17 Lic.Tech. Marko Luoma (65/68) Lic.Tech. Marko Luoma (66/68) Framing over (Discovery) PC oe ATU-R Framing ATU-C DSLAM ATM ATM ATM BRAS oe Framing ATM Initiation phase þ Client sends initiation packet into broadcast address (all ones) Point to multipoint þ Packet contains Name of the ISP Name of the service Offer phase þ BRAS devices which deliver service that is requested for answer to the client with unicast point-to-point þ Offer contains Name of the BRAS Name of the service Framing LLC/SNAP VCMUX Lic.Tech. Marko Luoma (67/68) Lic.Tech. Marko Luoma (68/68) over (Discovery) over (Session) Request phase þ Customer chooses one of the BRASes that deliver proper service Point-to-point þ Contains name of the service Session confirmation phase þ BRAS answer to client request Point-to-point þ Contains Name of the service session ID During the session packets are delivered to BRAS with session ID that is generated in discovery phase MRU of the packet cannot exceed 1492 bytes þ 2 bytes protocol ID þ 6 bytes oe header þ 1500 bytes Maximum payload for frame Destination Address Source Address Ether Type Version Type Code Session ID Length Protocol ID Information Padding Checksum header oe header