Evolution of Public Telecom Networks

Slide 1 : Historical Evolution Decrease CAPEX and OPEX Create New Revenue Streams Increase Competitiveness Service Providers Challenges

PSTN Evolution … History : PSTN Evolution … History Voice communication over an analog telephone network

Digital Telephony : Digital Telephony Codec Technique Sampling Stage Analog Audio Source Pulse Code Modulation—Nyquist Theorem Voice Bandwidth = 300 Hz to 3400 Hz

Voice Channel Bandwidth : Voice Channel Bandwidth Output Voltage or Energy Frequency (K-Hertz) 1 2 3 4 .2 Voice Signal Voice Channel Tone Dialing Signals Systems Control Signals

Digitizing Voice: PCM Waveform Encoding : Digitizing Voice: PCM Waveform Encoding Nyquist Theorem: sample at twice the highest frequency Voice frequency range: 300-3400 Hz Sampling frequency = 8000/sec (every 125us) Bit rate: (2 x 4 Khz) x 8 bits per sample = 64,000 bits per second (DS-0) By far the most commonly used method CODEC PCM 64 Kbps = DS-0

Delay : Delay First Bit Transmitted Last Bit Received Network A A Sender Receiver t Network Transit Delay Processing Delay Processing Delay End-to-End Delay

Digital Circuit Switching : Digital Circuit Switching Channels SingleByte Time Division Multiplexing CH0 CH1 CH2 … EngineeredBandwidth Time Capacity WastedBandwidth MSU Tandem RSU RSU MSU Channels are ReservedNo Voice and Data IntegrationHierarchical Design High Network Value but … High Network Cost Used Bandwidth

Data over PSTN : Data over PSTN

Local loop - Analog : Local loop - Analog The information content of an analog signal is conveyed by continuously varying some characteristic such as amplitude, frequency or phase of a voltage or other characteristic of the signal. Computers, motors, lights and other electrical devices generate electrical noise (unwanted electrical signals), which produce undesirable variations on the information content of an analog signal, thus making it error prone. Both voice and data (from modems - sent as sounds) are commonly transmitted as analog information.

Digital Local Loop Technologies : Digital Local Loop Technologies Integrated Services Digital Network (ISDN) Handles voice and data Extends to longer distance Expensive in North America Digital Subscriber Line (DSL) Newer technology Higher speed Several variants exist

2B1Q – 2 Binary 1 Quaternary : 2B1Q – 2 Binary 1 Quaternary The 2B1Q (two binary, one quaternary) line encoding scheme was intended to be used by the ISDN DSL and SDSL applications. 2B1Q is a Block and Linear Code This code is a four-level line code in which two binary bits (2B) represent one quaternary symbol (1Q).

QAM - Quadrature Amplitude Modulation : QAM - Quadrature Amplitude Modulation Combination of Amplitude Modulation (AM) and Phase Shift Keying (PSK). 15 bits requires 32,768 (i.e. 215 ) different combinations of phase shifts and amplitudes Example: 3-bit QAM 8 combinations: 2 amplitude levels with 4 phase shifts Frequency Amplitude

Repeaters : Repeaters Expansion of Baseband signal to greater distances requires the insertion of either a Repeater There are two types of Repeaters to overcome loss and dispersion limitations 2R regeneration, reshaping 3R regeneration, reshaping and retiming Repeaters need to be placed at appropriate distance

Clock Slips : Clock Slips If a bit source generates traffic using a clock of frequency f1 and the recipient expects traffic at a clock rate f2, there is clearly a problem if f1 ≠ f2. If a buffering arrangement is employed, the buffer will either overflow or underflow. This is the notion of a slip. If the transmit clock is high then data is lost; if the receive clock is high then data must be inserted, usually by repeating the last bit.

ISDN Evolution : ISDN Evolution Analog and digital services over the telephone network

ISDN Frame : ISDN Frame

History: ISDN : History: ISDN

ISDN Service Architecture : ISDN Service Architecture ISDN is an access specification to a network ISDN PBX PRA NT1 BRA Common Channel Signalling Network and Database Circuit Switched Services Dedicated Circuit Services Public Packet Network Telco Switch Telco Switch

Packet Switching Concept : Packet Switching Concept Data-link Layer Network Layer Physical Layer Physical Layer Physical Layer Physical Layer Data-link Layer Data-link Layer Data-link Layer Network Layer Network Layer V.C. V.C. HDLC HDLC

The 7 OSI layers : The 7 OSI layers Applications Layer Networks Layer Connectivity Interoperability Internet Sublayer 1 : Physical 2 : Data Link 3 : Network 4 : Transport 5 : Session 6 : Presentation 7 : Application

Virtual Circuits Concept : Virtual Circuits Concept

Private Networks over Public Networks : Private Networks over Public Networks 1 Physical Network == Many Private Networks VPN 1 VPN 4 VPN 3 VPN 2 PHYSICAL LOGICAL The Physical Network Topology R R R R R R R R R R R R R R R R R

Core Network Evolution : Core Network Evolution Connection-oriented Technologies: X.25 - 1970s Frame Relay - 1980s ATM - 1990s X.25 – the oldest of the three Frame Relay still has a fairly large installed base ATM mainly used by Telcos as backbone network. Both X.25 and Frame Relay was designed for Busty Traffic

X.25 Traffic : X.25 Traffic

Frame Relay Traffic: Less Overhead : Frame Relay Traffic: Less Overhead

Frame Relay Frame : Frame Relay Frame

DLCI Inside the Network : DLCI Inside the Network DLCI (Data Link Connections Identifiers) Virtual Circuit

Virtual Circuits: DLCI : Virtual Circuits: DLCI

Virtual Circuits: SVC : Virtual Circuits: SVC

Virtual Circuits: SVC DLCI : Virtual Circuits: SVC DLCI

Frame Relay Switch : Frame Relay Switch

CIR Operation : CIR Operation

Connectivity: ATM vs. Frame Relay : Connectivity: ATM vs. Frame Relay Both ATM cells and Frame Relay frames have address fields used to switch traffic over PVCs. However, ATM allows for “PVCs within PVCs” to aggregate traffic from different sources which are bound for the same destination. Network switches can police these different virtual circuits using “quality of service” parameters.

Permanent Virtual Circuits : Permanent Virtual Circuits There are two “types” of PVCs with ATM VPC (Virtual Path Connection) Address is the VPI (Virtual Path Identifier) Used to simplify switching within the network VCC (Virtual Channel Connection) Address is the VCI (Virtual Channel Identifier) VCCs ride within VPCs Different types of traffic going to the same destination can be assigned different virtual channels within the virtual circuit.

UNI format of the ATM - Cell : Payload (48) VCI VCI:Virtual Channel Identifier 16 bit C L P CLP : Cell Loss Priority 1 bit HEC HEC : Header Error Control 8 bit UNI format of the ATM - Cell

NNI format of the ATM - Cell : Payload (48) VPI VPI:Virtual Path Identifier 12 bit C L P CLP : Cell Loss Priority 1 bit HEC HEC : Header Error Control 8 bit NNI format of the ATM - Cell

ATM Transport : Virtual Connection Types: Virtual Channel Connections (VCC) Virtual Paths Connections (VPC) ATM Transport

VP-only Switching : VP-only Switching

Local Significant VC/VP : Port VP/VC 1 1 2/9 6/4 Port 2 3 VP/VC 4/5 2/9 Each ATM switch may change the VP/VC value. The VP/VC value is unique on each physical interface Local Significant VC/VP

Cell Loss Priority : CLP = 0 (high priority) CLP = 1 (low priority) Cell Loss Priority

Voice, Data, and Video : Voice, Data, and Video ATM has a “built-in” priority system which allows customers to treat one PVC different from another. Delay control on for constant bit-rate applications Ex: Cells transported over PVCs supporting voice will be sent ahead of cells traversing a PVC carrying e-mail ATM can offer Class of Services (CoS) based on the type of traffic handled.

ATM Concepts: Class of Service (CoS) : ATM Concepts: Class of Service (CoS) ABR? CBR? VBR? UBR? Constant Bit Rate (CBR) Variable Bit Rate (VBR) Available Bit Rate (ABR) Unspecified Bit Rate (UBR)

Main Traffic Parameters : The maximum cell rate at which the sender is planning to send cells PCR : (Peak Cell Rate) MCR :(Minimum Cell Rate) The minimum number of cells/sec that the customer considers acceptable MBS :(Maximum Burst Size) Maximum burst size cells) that can be sent at the peak rate Main Traffic Parameters SCR :(Sustained Cell Rate) The minimum number of cells/sec that the customer considers before bursting

QoS Parameters : QoS Parameters Cell Loss Ratio (CLR) Ratio of lost cells to total transmit cells. Cell Transfer Delay (CTD) This is the elapsed time between a cell’s exit at the source and its entry at the destination. Cell Delay Variation (CDV) This is sometimes called cell jitter, is a measure of the inter-cell departure of a given connection with respect to its inter-cell arrival.

CBR ( Constant Bit Rate ) : Bitrate PCR Time Guaranteed CDV ( Cell Delay Variation ) 0 CBR ( Constant Bit Rate ) Above PCR cells discarded Similar to a Dedicated Leased Line PCR, CDV

VBR (Variable Bit Rate) : VBR (Variable Bit Rate) Port Speed SCR PCR 0 Cell Rate Time CLP=1 Discarded * Can Burst Up To PCR but if above PCR is Discarded * Cells Violating SCR more than MBS are Discarded MBS – Maximum Burst Size MBS Discarded

VBR – Real Time and Non Real Time : VBR – Real Time and Non Real Time VBR-nrt Cell Delay Variation (CDV) not specified Very similar to Frame Relay VBR-rt Maximum Cell Delay Variation (CDV) specified Note: CDV is related to Cell Transfer Delay (CTD) and when CTD is fixed CDV = 0 PCR, SCR, MBS PCR, SCR, MBS, CDV

CDV and CTD : 1997/4/30 48 CDV and CTD CTD fixed delay: propagation delay, transmission delay, fixed switch processing delay random delay: queueing(buffering), scheduling delays CDV induced by buffering and scheduling cell transfer delay prob. density fixed delay Peak-to-peak CDV Max. CTD

UBR (Unspecified Bit Rate) : UBR (Unspecified Bit Rate) Port Speed Peak Cell Rate (PCR) 0 Tagged CLP=1 Cell Rate Time Discarded Has No Minimum Guaranteed bandwidth and all Cells Are Tagged Can Transmit Up To PCR and above PCR is Discarded PCR

ABR (Available Bit Rate) and UBR+ : ABR (Available Bit Rate) and UBR+ PCR Port Speed MCR 0 Tagged CLP = 1 Time Cell Rate Discarded MCR is Guaranteed Can burst above MCR up to PCR but cells Between MCR and PCR are Tagged The cells burst above PCR is Discarded Note: ABR has a Rate Feedback congestion control mechanism to reduce the Cell Lost Rate Tagged CLP = 0 PCR, MCR

QoS Terms : QoS Terms Negotiation of QoS parameters during connection establishment Sustainable cell rate (SCR), peak cell rate (PCR), maximum burst size (MBS), cell delay variation (CDV), cell transfer delay (CTD) Connection admission control (CAC) The network has to decide, whether a new connection can be accepted (or not) (at a specific current load)

IP Best Effort Networks : IP Best Effort Networks 1) IP packet is lost 2) IP packet is delayed IP network

Processing and Queuing Delay : Processing and Queuing Delay Processing Delay is the time it takes for a Router to take the packet from an input interface and put it into the output queue of the output interface. Queuing Delay is the time a packets resides in the output queue of a Router. Propagation Delay is the time it takes to transmit a packet. IP IP IP IP bandwidth

Packet Loss : Packet Loss Tail-drops occur when the output queue is full. These are the most common drops which happen when a link is congested. IP IP IP IP IP Tail-drop

Best Effort Connectivity : Best Effort Connectivity This is the fundamental service provided by Internet Service Providers (ISPs) All other IP services depend on connectivity: DNS, email, VPNs, Web Hosting, … IP traffic 135.207.49.8 192.0.2.153

IPv4 Datagram Format : IPv4 Datagram Format ver Total length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier Internet checksum time to live 32 bit source IP address IP protocol version number header length (32 bits) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service “type” of data flgs fragment offset upper layer 32 bit destination IP address Options (if any), plus padding E.g. timestamp, record route taken, specify list of routers to visit.

Classful Addresses : 57 Classful Addresses 0nnnnnnn 10nnnnnn nnnnnnnn nnnnnnnn nnnnnnnn 110nnnnn hhhhhhhh hhhhhhhh hhhhhhhh hhhhhhhh hhhhhhhh hhhhhhhh n = network address bit h = host identifier bit Class A Class C Class B Leads to a rigid, flat, inefficient use of address space …

Classless Inter-Domain Routing : 58 Classless Inter-Domain Routing IP Address : 12.4.0.0 IP Mask: 255.254.0.0 Use two 32 bit numbers to represent a network. Network number = IP address + Mask Usually written as 12.4.0.0/15

IP Fragmentation and Reassembly : IP Fragmentation and Reassembly Network links have MTU (max.transfer size) - largest possible link-level frame. different link types, different MTUs Large IP datagram divided (“fragmented”) within net one datagram becomes several datagrams “reassembled” only at final destination IP header bits used to identify, order related fragments fragmentation: in: one large datagram out: 3 smaller datagrams reassembly

Componentsof an IP Router : Componentsof an IP Router Control Plane Data Plane per-packet processing Switching Forwarding Table Routing Table Routing Protocols

Forwarding Datagrams : Forwarding Datagrams The header contains all the information needed to deliver a datagram to a destination computer Destination address Source address Identifier Other delivery information Routers examine the header of each datagram and forwards the datagram along a path/interface Use routing tables to compute next hop Update routing tables using algorithms based on Routing protocols Link state, distance vector, manually Use forwarding table to forward

Routing vs. Forwarding : 62 Routing vs. Forwarding R R R A B C D R1 R2 R3 R4 R5 E Net Nxt Hop R4 R3 R3 R4 Direct R4 Net Nxt Hop A B C D E default R2 R2 Direct R5 R5 R2 Net Nxt Hop A B C D E default R1 Direct R3 R1 R3 R1 Default to upstream Router A B C D E default Forwarding: Determine next hop Routing: Establish end-to-end paths Forwarding Always works Routing can be badly broken

Forwarding IP Packets : Forwarding IP Packets Destination address in IP datagram is always ultimate destination Router looks up next-hop address and forwards datagram Routing Table entry consist two parameters: Destination Network IP address Next-hop address Next-hop address never appears in IP datagram

IP control process : User Plane Control Plane IP control process ForwardingTable Next Hop + Port OutputQueue Conventional IP forwarding

How Are Forwarding Tables Populated to implement Routing? : 65 How Are Forwarding Tables Populated to implement Routing? Statically Dynamically Routers exchange network reachability information using ROUTING PROTOCOLS. Routers use this to compute best routes Administrator manually configures forwarding table entries In practice a mix of these is used. + More control + Not restricted to destination-based forwarding - Doesn’t scale - Slow to adapt to network failures + Can rapidly adapt to changes in network topology + Can be made to scale well - Complex distributed algorithms - Consume CPU, Bandwidth, Memory - Debugging can be difficult - Current protocols are destination-based