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Lecture 2. Advanced Networking CSE 8344 Southern Methodist University Fall 2003 Mark E. Allen. Introduction. Miscellaneous notes: Exam dates: (posted on web also). SONET. SONET byte oriented frame format Path, line, and section Multiplexing format Virtual Containers
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Lecture 2 Advanced Networking CSE 8344 Southern Methodist University Fall 2003 Mark E. Allen
Introduction • Miscellaneous notes: • Exam dates: (posted on web also)
SONET • SONET byte oriented frame format • Path, line, and section • Multiplexing format • Virtual Containers • Synchronous payload envelope (SPE) • Pointers • Timing issues • This is what makes SONET synchronous -- the payload can float in the SONET frame. • Overhead • Line, Section, and Path • Performance monitoring
SONET Network LINE SECTION Terminal (LTE) ADM or DCS (LTE) Terminal (LTE) REG REG REG Router (PTE) Router (PTE) PATH
SONET Networking 810 bytes x 8000 frame/sec x 8 bits = 51,840,000 bps OH PAYLOAD OH PAYLOAD OH PAYLOAD STS-1 Synchronous Payload Envelope 9 rows 90 columns (87 columns of payload) 3 columns of transport overhead: Section overhead Line overhead Path overhead
9 Rows 90 Columns BIP-8/BI: Parity Checking Section Trace/Growth STS-1 Frame A1 A2 J1 JO/Z0 B1 E1 F1 B3 D1 D2 D3 C2 87 Columns of Payload STS-1 Synchronous Payload Envelope (STS-1 SPE) H1 H2 H3 G1 B2 K1 K2 F2 D4 D5 D6 H4 D7 D8 D9 Z3 BIP-8/B2: Error Monitoring D10 D11 D12 Z4 S/Z1 E2 Z5 M0/M1 Z2
SONET Overhead • Path overhead – Overhead for entire end-to-end circuit. Path terminating equipment (PTE) terminates this overhead. • Line overhead – Overhead for connection between terminals, cross-connects (DCS), or add-drop mulitplexer (ADM). Line terminating equipment (LTE) terminates this overhead. • Section overhead – Overhead for connection between regenerators. Section terminating equipment (STE) terminates this overhead.
Path overhead • J1 – Used for tracing the circuit • B3 – Bit interleaved parity byte to check for errors • C2 – Path signal label byte to indicate the contents of the SPE • H4 – Virtual tributary (VT) multiframe indicator byte to describe multiframe VT payloads (pointer) • G1 – Path status byte so PTE can detect problems on the path • F2 – Path user channel byte for communications between path elements • Z3,Z4,Z5 – User bytes reserved for future
Line overhead • H1,H2 – pointer to beginning of SPE • H3 – pointer action byte used to hold data when pointer adjustment is made • B2 – byte interleaved parity for line • K1, K2 – used to manage Auto-Protection Switching (APS) • D4 to D12 – Data communication channel (DCC) bytes are 576 kbps • Z1, Z2 – Not defined (Z2 used for FEBE in STS-3) • E2 – express 64 kbps channel between LTE (for STS-1 only)
Section overhead • A1,A2 – Framing bytes • C1 – STS ID set for each STS1 • B1 – Byte interleaved parity for monitoring for errors • E1 – 64 kbps orderwire • F1 – Used by section equipment • D1 to D3 – Data communication channel
SONET multiplexing • To create OC-N signals, SONET streams are BYTE INTERLEAVED. • No bit-stuffing is used because network is synchronous • Pointers are used to account for phase differences in SPE of tributary signals (tribs). • Overhead from all tribs is aligned.
Typical point to point SONET link Atlanta Dallas OC48 W OC192 OC192 OC48 OC48 P OC48 40 mile amplifier spacing
Purpose of switches • Voice networks • Connect dialing party to called party. Required making connections at CO, Tandem, IXC switching nodes • Layer 1 data network • Connection at SONET or optical layer to connect a DS3 or OC3 through the network • Layer 2 data network • Connections via ATM or Ethernet switch to establish a flow, or PVC through which two PCs or routers are connected
Switching systems • Switches vs. Routers • Switches are typically connection oriented, routers are based on datagram routing • Routers use routing lookup tables to send out the packet. • Switches are based on a connection, flow, or circuit that usually traverses several switches from source to destination • Packet switches have queues, circuit switches do not. • Focus on circuit switching for now • Packet switching and routing are an extension of circuit switching. • Optical switching is simpler (conceptually not technically) subset, to be discussed later.
Space switch • Most basic switch, sometimes called crosspoint switch. • Rectangular fabric: any input can connect to any output • Number of crosspoints is N X M • Graded switches • Each input has access to a select group of outputs • Used when crosspoints are expensive or switch would be too big.
Switches (cont) • Square vs. triangular • Square fabrics have two possible ways of making connection • Triangular get rid of extra cross points but require compare • Why multistage switches • For square fabric, N(N-1) switches required • For triangular array, N(N-1)/2 required • This results in too many pieces for a practical sized switch, 5 Billion crosspoints for 100,000 port switch. • Multistage switching is the answer
3 stage switches • Number of cross points in 3 stage switch is: • Nx=2Nk + k (N/n)^2 • Where N is number of inputs • k is number of center stages • n is size of inlet / outlet group • Consider what happens with blocking • There is no center stage that can make a connection to output stage that can switch to the desired output. • Clos showed that if • k = (n-1) + (n-1) + 1 then switch is non-blocking
3 stage switch (cont) • Using this k for number of crosspoints yields (equ 5.2, Bellamy) • Solving for the minimum number of crosspoints yields (equ 5.3)
3-stage (cont, Bellamy) • Note the reduction in required cross points in (Table 5.1) by using a 3 stage Clos switch.
Blocking switches • In reality, Clos switches are “rearrangeably” non blocking. Not strictly non-blocking. • In real-world, connections are continuously being made and torn down. • So we can’t pick the perfect path for each connection beforehand. • Clos switch still requires a fair number of crosspoints.
Switches with blocking • It’s often practical to make a switch that is “blocking” • There is some small probability the switch can’t connect an input to an output • Recall it depends on what other connections have been made (i.e. how “busy” is the switch?) • Many switches aren’t very busy • Considerable cost savings can be enjoyed by reduction in cross points
Analysis of blocking switches • These equations provide probability blocking through a switch fabric • Lee graphs • Jacobaeus • Discrete event simulation software packages are often used in practice when designing switches • Modeling input behavior is a challenge • Call times, relationship between inputs and outputs, etc. • Examples: OPNET
Time Division switching • Time Division Switching allows multiple connections to share cross-points • Results in even fewer cross points than multistage switches • Goes well with Time division multiplexing • Many times, the individual circuits have been TDM’d prior to being connected to the switch
Time slot interchange (TSI) • This is an important function of digital switches. • Memory is used to rearrange data in the time slots • Allows information to arrive at the Space switches at the right time. • Normally used with Space switching to create TST, TSST, etc. matrices that combine both. • The Lucent 4ESS switch uses TSSSST. • 4 internal Switches wrapped in two TSI switches • Can handle from 100,000 to 200,000 calls.
Cross-connects • Digital Cross-connect is a specialized switch fabric • Combines muxing and switching • Used to aggregate (fill) and groom • Typically appear as 3/3, 3/1, 3/1/0, etc. • 3/3 cross connects DS3s • 3/1 cross connects DS1 within DS3s or entire DS3. • 3/1/0 groom to the DS0 level. • Lower granularity of grooming costs more (more crosspoints) • Hierarchy is often used (see figure 5.34)
Big switch example • Example: • SONET cross-connects • 256 OC48 external interfaces • What is total switch capacity? • 256 X 2.5 Gbps = 640 Gbps • IF DS0s were to be groomed, how many possible connections? • 256 X 48 X 28 X 24 = 8.25 Million input channels • Using N(N-1)/2, would be huge!, even Clos is too big • What about STS-1 granularity? • Switches exist to do this (barely!)
Voice network signaling • Signaling function • Supervisory • On hook, Off hook, dial tone, ringing, on-hook, busy signal • Information bearing • Dialed digits, toll charges, etc. • In-channel signaling • In band • Single Frequency (SF), dual tone multifrequency (DTMF), multifrequency (MF) which all operate in voice band • Out of band • DC levels on the loop portion or out of band using FDM • Pulses on phones for dialed digits are out of band
Signaling (cont) • Common channel signaling (CCS) • Here, the signaling information is contained in a separate signaling channel • Channel is carries signaling for several lines • Good for fraud prevention • Simpler to manage signaling between switches • Disadvantages: • Signaling may not propagate through the network to free resources • No automatic testing • Trunks may not all terminate at the same switch (signaling must be forwarded)
Analog interfaces • Subscriber loop interfaces • Battery: 48 volts is supplied to operate the phone • Overvoltage protection: protection from lightning, etc. • Ringing: 20Hz 86 volt rms signal to ring the phone. • Supervision: Detection of on/off hook • Test: Access to testing the loop BORSCHT (Battery, Overvoltage, ….) (Hybrid and Coding are also required at switch end.)
Analog interfaces (cont) • Loop start trunks • Simple connection between switches • Central Office to Private Branch Exchange (PBX) • Problem of “glare” exists • Ground start trunk solve this problem • More elaborate communication between PBX and CO • Direct Inward Dial (DID) trunks • Allow incoming calls to PBX to connect directly to called party (no attendant necessary)
Analog interfaces (cont) • E&M (ear and mouth) trunks • 5 types of E&M interfaces are defined • Type II E&M is a 8 wire interface • TX pair, RX pair, E pair, and M pair • Supervisory signaling happens over the E&M leads • Typically used to connect PBX to CO, PBX to PBX
Digital Networking • Analog loops will exist for some time • Businesses will move to digital phones more quickly • For switching and transport, analog has serious drawbacks • Noise, Ease of multiplexing, switching, • Current approach is to convert to digital at the ingress of the network • Digitization schemes will be discussed later • Time Division Multiplexing is done in digital domain • Digital signals are better to regenerate • Performance monitoring • Ease of encryption (digital can be scrambled easier)
Advantages of Digital • DSP chips have enabled the transition to digital networking • Echo cans now use DSP algorithms (LMS) • Modems • Vocoders / Decoders • Cell phones, Secure phones, Voice over packet, etc. • There are a few drawbacks to digital • Bandwidth management • Network synchronization • Analog interfaces • Multi-access is complicated (drop and insert)
Switched voice architecture From: Digital Telephony Bellamy, chapter 1
The voice network Bandwidth is allocated through the network using a parallel SS7 network.
The SS7 Network • SSP: Service switching point. Originates the messages requesting bandwidth through the network. • STP: Signal transfer points. Packet switches for signaling messages. • SCP: Service control points. Servers that host routing instructions and enhanced services.
