COE 799 Lecture 2, Fall 2011

Connection-Oriented Networks – Wissam FAWAZ 1 Chapter 2: SONET/SDH and GFP TOPICS – T1/E1 – SONET/SDH - STS 1, STS -3 frames – SONET devices – Self-healing rings – Generic frame protocol, and Data over SONET Connection-Oriented Networks – Wissam FAWAZ 2 T1/E1 • Time division multiplexing allows a link to be utilized simultaneously by many users M U X D E M U X N input links N output links link 1 2 N 1 2 N Connection-Oriented Networks – Wissam FAWAZ 3 • The transmission is organized into frames. • Each frame contains a fixed number of time slots. • Each time slot is pre-assigned to a specific input link. The duration of a time slot is either a bit or a byte. • If the buffer of an input link has no data, then its associated time slot is transmitted empty. • A time slot dedicated to an input link repeats continuously frame after frame, thus forming a channel or a trunk. Connection-Oriented Networks – Wissam FAWAZ 4 Pulse code modulation • TDM is used in telephony • Voice analog signals are digitized at the end office using Pulse Code Modulation. • A voice signal is sampled 8000 times/sec, or every 125 sec. • A 7-bit or 8-bit number is created every 125 sec. Connection-Oriented Networks – Wissam FAWAZ 5 The Digital Signal (DS) and ITU-T standard • A North American standard that specifies how to multiplex several voice calls onto a single link. • The DS standard is a North American standard and it is not the same as the international hierarchy standardized by ITU-T. • Both standards are independent of the transmission. Connection-Oriented Networks – Wissam FAWAZ 6 T carrier / E carrier • The DS signal is carried over a carrier system known as the T carrier. – T1 carries the DS1 signal, – T2 carries the DS2 signal etc • The ITU-T signal is carried over a carrier system known as the E carrier. • The DS and ITU-T hierarchy is known as the plesiochronous digital hierarchy (PDH). (Plesion means “nearly the same”, and chronos means “time” in Greek). Connection-Oriented Networks – Wissam FAWAZ 7 Digital signal number Voice channels Data Rate (Mbps) DS0 1 0.064 DS1 24 1.544 DS1C 48 3.152 DS2 96 6.312 DS3 672 44.736 DS3C 1344 91.053 DS4 4032 274.176 Table 2.1: The North American Hierarchy Level number Voice channels Data Rate (Mbps) 0 1 0.064 1 30 2.048 2 120 8.448 3 480 34.368 4 1920 139.264 5 7680 565.148 Table 2.2: The international (ITU-T) hierarchy Connection-Oriented Networks – Wissam FAWAZ 8 The DS1 signal • 24 8-bit time slots/frame – Each time slot carries 8 bits/ 125 sec, or the channel carries a 64 Kbps voice. – Every 6th successive time slot (i.e, 6th, 12th, 18th, 24th, etc), the 8 bit is robbed and it is used for signaling. • F bit: Used for synchronization. It transmits the pattern: 10101010… F Time slot 1 Time slot 2 Time slot 3 Time slot 24 . . . Connection-Oriented Networks – Wissam FAWAZ 9 • T1: – Total transmission rate: 24x8+1 = 193 bits per 125 sec, or 1.544 Mbps • E1 – 30 voice time slots plus 2 time slots for synchronization and control – Total transmission rate: 32x8 = 256 bits per 125 sec, or 2.048 Mbps Connection-Oriented Networks – Wissam FAWAZ 10 Fractional T1/E1 • Fractional T1 or E1 allows the use of only a fraction of the T1 or E1 capacity. • For example: if N=2, then only two time slots are used per frame, which corresponds to a channel with total bandwidth of 128 Kbps. Connection-Oriented Networks – Wissam FAWAZ 11 Unchannelized frame signal • The time slot boundaries are ignored by the sending and receiving equipment. • All 192 bits are used to transport data followed by the 193rd framing bit. • This approach permits more flexibility in transmitting at different rates. • This scheme is implemented using proprietary solutions. Connection-Oriented Networks – Wissam FAWAZ 12 The Synchronous Optical NETwork (SONET) • Proposed by Bellcore (Telecordia). – It was designed to multiplex DS-n signals and transmit them optically. • ITU-T adopted the Synchronous Digital Hierarchy (SDH), as the international standard. – It enables the multiplexing of level 3 signals (34.368 Mbps) Connection-Oriented Networks – Wissam FAWAZ 13 STS, STM, OC • The electrical side of the SONET signal is known as the synchronous transport signal (STS) • The electrical side of the SDH is known as the synchronous transport module (STM). • The optical side of a SONET/SDH signal is known as the optical carrier (OC). Connection-Oriented Networks – Wissam FAWAZ 14 The SONET/SDH hierarchy Optical level SONET level (electrical) SDH level (electrical) Data rate (Mbps) Overhead rate (Mbps) Payload rate (Mbps) OC-1 STS-1 - 51.840 1.728 50.112 OC-3 STS-3 STM-1 155.520 5.184 150.336 OC-9 STS-9 STM-3 466.560 15.552 451.008 OC-12 STS-12 STM-4 622.080 20.736 601.344 OC-18 STS-18 STM-6 933.120 31.104 902.016 OC-24 STS-24 STM-8 1244.160 41.472 1202.688 Oc-36 STS-36 STM-12 1866.240 62.208 1804.932 OC-48 STS-48 STM-16 2488.320 82.944 2405.376 OC-96 STS-96 STM-32 4976.640 165.888 4810.752 OC-192 STS-192 STM-64 9953.280 331.776 9621.504 OC-768 STS-768 STM-256 39813.120 1327.104 38486.016 OC-N STS-N STM-N/3 N*51.840 N*1.728 N*50.112 Connection-Oriented Networks – Wissam FAWAZ 15 • SONET/SDH is channelized. – STS-3 consists of 3 STS-1 streams, and each STS- 1 consists of a number of DS-1 and E1 signals. – STS-12 consists of 12 STS-1 streams • Concatenated structures (OC-3c, OC-12c, etc) – The frame of the STS-3 payload is filled with ATM cells or IP packets packed in PPP or HDLC frames. – Concatenated SONET/SDH links are commonly used to interconnect ATM switches and IP routers (Packets over SONET). Connection-Oriented Networks – Wissam FAWAZ 16 The STS-1 frame structure 1 2 3 4 5 6 … 90 1 1 2 3 4 5 6 … 90 2 91 92 93 94 95 96 … 180 3 181 182 183 184 185 186 … 270 4 271 272 273 274 275 276 … 360 5 361 362 363 364 365 366 … 450 6 451 452 453 454 455 456 … 560 7 561 562 563 564 565 566 … 630 8 631 632 636 634 635 636 … 720 9 721 722 723 724 725 726 … 810 Connection-Oriented Networks – Wissam FAWAZ 17 • Main features – The frame is presented in matrix form and it is transmitted row by row. – Each cell in the matrix corresponds to a byte – The first three columns contain overheads – The remaining 87 columns carry the synchronous payload envelope (SPE), which consists of user data, and additional overheads referred to as the payload overhead (POH) Connection-Oriented Networks – Wissam FAWAZ 18 An SPE may straddle between two successive frames Frame i Frame i+1 1 2 3 4 5 6 . . . 90 1 2 3 4 5 6 7 8 9 276 276 275 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 3 4 5 6 7 8 9 Connection-Oriented Networks – Wissam FAWAZ 19 The section, line, and path overheads Section Line STS-1 STS-1 A B regenerator regenerator STS-1 A1 A12 STS-12 . . . STS-1 B1 B12 STS-12 . . . Section Section Section Section Line Line Path Connection-Oriented Networks – Wissam FAWAZ 20 • Section: a single link with a SONET device or a regenerator on either side of it. • Line: A link between two SONET devices, which may include regenerators • The section overhead in the SONET frame is associated with the transport of STS-1 frames over a section, and the line overhead is associated with the transport of SPEs over a line. Connection-Oriented Networks – Wissam FAWAZ 21 The SONET stack Section Line Path Photonic Section Line Path Photonic Section Line Photonic Section Photonic Section Photonic Section Line Photonic Ai A Regenerator Regenerator Bi B Connection-Oriented Networks – Wissam FAWAZ 22 STS-1: Section and line overheads SOH LOH Column 1 2 3 1 A1 A2 J0 2 B1 E1 F1 3 D1 D2 D3 4 H1 H2 H3 5 B2 K1 K2 6 D4 D5 D6 7 D7 D8 D9 8 D10 D11 D12 9 Z1 Z2 E2 Connection-Oriented Networks – Wissam FAWAZ 23 • The following are some of the bytes in the section overhead (SOH) : – A1 and A2: These two bytes are called the framing bytes and they are used for frame alignment. They are populated with the value 1111 0110 0010 1000 or 0xF628, which uniquely identifies the beginning of an STS- frame. – J0: This is called the section trace byte and it is used for to trace the STS-1 frame back to its originating equipment. Connection-Oriented Networks – Wissam FAWAZ 24 – B1: This byte is the bit interleaved parity byte and it is commonly referred to as BIP-8. It is used to perform an even-parity check on the previous STS-1 frame after the frame has been scrambled. The parity is inserted in the BIP-8 field of the current frame before it is scrambled – E1: This byte provides a 64 Kbps channel can be used for voice communications by field engineers. Connection-Oriented Networks – Wissam FAWAZ 25 • The following are some of the bytes in the line overhead (LOH) that have been defined: – H1 and H2: These two bytes are known as the pointer bytes, and they contain a pointer that points to the beginning of the SPE within the STS-1 frame. The pointer gives the offset in bytes between the H1 and H2 bytes and the beginning of the SPE. – B2: This is similar to the B1 byte in the section overhead and it is used to carry the BIP-8 parity check performed on the line overhead section and the payload section. That is, it is performed on the entire STS-1 frame except the section overhead bytes. Connection-Oriented Networks – Wissam FAWAZ 26 The path overhead bytes J1 B3 C2 G1 F2 H4 Z3 Z4 Z5 J1 B3 C2 G1 F2 H4 Z3 Z4 Z5 Location of the POH The POH bytes Connection-Oriented Networks – Wissam FAWAZ 27 • The following are some of the bytes that have been defined: – B3: This byte is similar to B1 used in the section overhead and B2 used in the line overhead. It is used to carry the BIP-8 parity check performed on the payload section. That is, it is performed on the entire STS-1 frame except the section and line overhead bytes. – C2: This byte is known as the path signal label and it indicates the type of user information carried in the SPE, such as, virtual tributaries (VT), asynchronous DS-3, ATM cells, HDLC-over-SONET, and PPP over SONET. Connection-Oriented Networks – Wissam FAWAZ 28 The STS-1 payload • The payload consists of user data and the path overhead. • User data: – Virtual tributaries: sub-rate synchronous data streams, such as DS-0, DS-1, E1, and entire DS-3 frames – ATM cells and IP packets Connection-Oriented Networks – Wissam FAWAZ 29 Virtual tributaries • The STS-1 payload is divided into seven virtual tributary groups (VTG). • Each VTG consists of 108 bytes (12 columns) • Each VTG may carry a number of virtual tributaries, i.e., sub-rate streams. Connection-Oriented Networks – Wissam FAWAZ 30 • The following virtual tributaries have been defined: – VT1.5: This virtual tributary carries one DS-1 signal and it is contained in three columns, that take up 27 bytes. Four VT1.5’s can be transported in a single VTG. – VT2: This virtual tributary carries an E1 signal of 2.048 Mbps. VT2 is contained in four columns, that is it takes up 36 bytes. Three VT2’s can be carried in a single VTG. Connection-Oriented Networks – Wissam FAWAZ 31  VT3: This virtual tributary transports the unchannelized DS-1 signal. A VT3 is contained in 6 columns that takes up 54 bytes. This means that a VTG can carry two VT3s. VT6: This virtual tributary transports a DS-2 signal, which carries 96 voice channels. VT6 is contained in 12 columns, that is it takes up 108 bytes. A VTG can carry exactly one VT2. Connection-Oriented Networks – Wissam FAWAZ 32 ATM cells • Mapped directly onto the SPE. An ATM cells may straddle two SPEs. 10 Cell 1 Cell 2 Cell 2 Cell 3 Cell 14 Cell 15 Cell 15 90 4 1 9 2 8 3 POH Connection-Oriented Networks – Wissam FAWAZ 33 IP packet over SONET • IP packets are first encapsulated in HDLC and the resulting frames are mapped into the SPE payload row by row as in the case above for ATM cels. 10 90 4 1 9 2 8 3 POH 7E 7E 7E 7E 7E 7E Connection-Oriented Networks – Wissam FAWAZ 34 • IP packets can also be encapsulated in PPP instead of HDLC. • A frame may straddle over two adjacent SPEs, as in the case of ATM. • The interframe fill 7E is used to maintain a continuous bit stream Connection-Oriented Networks – Wissam FAWAZ 35 The STS-3 frame structure Overhead section Payload section 1 2 3 4 5 6 7 8 9 10 11 12 270 . . . 1st STS-1 1st STS-1 1st STS-1 1st STS-1 1st STS-1 2nd STS-1 2nd STS-1 2nd STS-1 2nd STS-1 2nd STS-1 3rd STS-1 3rd STS-1 3rd STS-1 3rd STS-1 3rd STS-1 Connection-Oriented Networks – Wissam FAWAZ 36 • The channelized STS-3 frame is constructed by multiplexing byte-wise three channelized STS-1 frames. As a result: – Byte 1, 4, 7, … , 268 of the STS-3 frame contains byte 1, 2, 3, … , 90 of the first STS-1 frame. – Byte 2, 5, 8, …, 269 of the STS-3 frame contains byte 1, 2, 3, … , 90 of the second STS-1 frame – Byte 3, 6, 9, …, 270 of the STS-3 frame contains byte 1, 2, 3, … , 90 of the third STS-1 frame. • This byte-wise multiplexing, causes the columns of the three STS-1 frames to be interleaved in the STS-3 frame Connection-Oriented Networks – Wissam FAWAZ 37 • The first 9 columns of the STS-3 frame contain the overhead part and the remaining columns contain the payload part. • Error checking and some overhead bytes are for the entire STS-3 frame, and they are only meaningful in the overhead bytes of the first STS-1 frame. Connection-Oriented Networks – Wissam FAWAZ 38 SONET/SDH devices • Several different equipment exist: – Terminal multiplexer (TM) – Add/drop multiplexer (ADM) – Digital cross connect (DCS) Connection-Oriented Networks – Wissam FAWAZ 39 • It multiplexes a number of DS-n or E1 signals into a single OC-N signal • It consists of a controller, low-speed interfaces for DS-n or E1 signals, an OC-N interface, and a time slot interchanger (TSI) • It works also as a demultiplexer . . . DS-n OC-N DS-n TM The terminal multiplexer (TM): Connection-Oriented Networks – Wissam FAWAZ 40 • It is a more complex version of the TM • It receives an OC-N signal from which it can demultiplex and terminate (i.e., drop) any number of DS-n or OC-M signals, where M<N, while at the same time it can add new DS-n and OC-M signals into the OC-N signal. . . . DS-n. OC-M OC-N OC-N ADM The add/drop multiplexer (ADM) Connection-Oriented Networks – Wissam FAWAZ 41 SONET rings ADM 1 ADM 2 ADM 3 ADM 4 OC3 OC3 OC3 OC3 • SONET/SDH ADM devices are typically connected to form a SONET/SDH ring. • SONET/SDH rings are self-healing, that is they can automatically recover from link failures. Connection-Oriented Networks – Wissam FAWAZ 42 An example of a connection A B TM 1 TM 2 ADM 1 ADM 2 ADM 3 ADM 4 DS1 OC12 DS1 OC12 OC12 OC12 OC3 OC3 Connection-Oriented Networks – Wissam FAWAZ 43 • A transmits a DS-1 signal to TM 1 • TM 1 transmits an OC-3 signal to ADM 1 • ADM 1 adds the OC-3 signal into the STS- 12 payload and transmits it out to the next ADM. • At ADM 3, the DS-1 signal belonging to A is dropped from the payload and transmitted with other signals to TM 2. • TM 2 in turn, demultiplexes the signals and transmits A’s DS-1 signal to B. Connection-Oriented Networks – Wissam FAWAZ 44 • Connection setup: – Using network management procedures the SONET network is provisioned appropriately. This is an example of a permanent connection. – It remains up for a long time. • The connection is dedicated to user A whether the user transmits or not. Connection-Oriented Networks – Wissam FAWAZ 45 A digital cross connect (DCS) Ring 1 Ring 2 ADM ADM ADM ADM ADM ADM DCS • It is used to interconnect multiple SONET rings • It is connected to multiple incoming and outgoing OC-N interfaces. It can drop and add any number of DSn and/or OC-M signals, and it can switch DSn and/or OC-M signals from an incoming interface to any outgoing one. Connection-Oriented Networks – Wissam FAWAZ 46 SONET rings ADM 1 ADM 2 ADM 3 ADM 4 OC3 OC3 OC3 OC3 • SONET/SDH ADM devices are typically connected to form a SONET/SDH ring. • SONET/SDH rings are self-healing, that is they can automatically recover from link failures. Connection-Oriented Networks – Wissam FAWAZ 47 Self-healing SONET/SDH rings • SONET/SDH rings have been specially architected so that they are available 99.999% of the time (6 minutes per year!) • Causes for ring failures: – Fiber link failure due to accidental cuts, and transmitter/receiver failure – SONET/SDH device failure (rare) Connection-Oriented Networks – Wissam FAWAZ 48 Automatic protection switching (APS) • SONET/SDH rings are self-healing, that is, the ring’s services can be automatically restored following a link failure or degradation in the network signal. • This is done using the automatic protection switching (APS) protocol. The time to restore the services has to be less than 50 msec. Connection-Oriented Networks – Wissam FAWAZ 49 Protection schemes: point-to-point • Schemes for link protection – dedicated 1+1 – 1:1 – Shared 1:N ADM Working Protection ADM Connection-Oriented Networks – Wissam FAWAZ 50 Working/protection fibers • The working and protection fibers have to be diversely routed. That is, the two fibers use separate conduits and different physical routes. • Often, for economic reasons, the two fibers use different conduits, but they use the same physical path. In this case, we say that they are structurally diverse. Connection-Oriented Networks – Wissam FAWAZ 51 Classification of self-healing rings Various ring architectures have been developed based on the following three features: – Number of fibers • 2 or 4 fibers – Direction of transmission • Unidirectional bidirectional – Line or path switching Connection-Oriented Networks – Wissam FAWAZ 52 Number of fibers: 2- or 4-fiber rings Two-fiber ring: fibers 1, 2, 3, and 4 are used to form the working ring (clockwise), and fibers 5, 6, 7, and 8 are used to form the protection ring (counter-clockwise). 1 2 3 4 5 6 7 8 ADM 1 ADM 2 ADM 3 ADM 4 ADM 1 ADM 2 ADM 3 ADM 4 Connection-Oriented Networks – Wissam FAWAZ 53 • In another variation of the two-fiber ring, each set of fibers form a ring which can be both a working and a protection ring. The capacity of each fiber is divided into two equal parts, one for working traffic and the other for protection traffic. 1 2 3 4 5 6 7 8 ADM 1 ADM 2 ADM 3 ADM 4 Connection-Oriented Networks – Wissam FAWAZ 54 • In a four-fiber SONET/SDH ring there are two working rings and two protection rings, one per working ring. ADM 1 ADM 2 ADM 3 ADM 4 Connection-Oriented Networks – Wissam FAWAZ 55 Direction of transmission • Unidirectional ring: – signals are only transmitted in one direction of the ring. • Bidirectional ring: – signals are transmitted in both directions. Connection-Oriented Networks – Wissam FAWAZ 56 Line and path switching  Path switching: Restores the traffic on the paths affected by a link failure (a path is an end-to- end connection between the point where the SPE originates and the point where it terminates.)  Line switching: Restores all the traffic that passes through a failed link. Connection-Oriented Networks – Wissam FAWAZ 57 Based on these three features, we have the following 2-fiber or 4-fiber possible ring architectures: – Unidirectional Line Switched Ring (ULSR) – Bidirectional Line Switched Ring (BLSR) – Unidirectional Path Switched Ring (UPSR) – Bidirectional Path Switched Ring (BPSR) Connection-Oriented Networks – Wissam FAWAZ 58 Of these rings the following three are used: – Two-fiber unidirectional path switched ring (2F-UPSR) – Two-fiber bidirectional line switched ring (2F-BLSR) – Four-fiber bidirectional line switched ring (4F-BLSR) Connection-Oriented Networks – Wissam FAWAZ 59 Two-fiber unidirectional path switched ring (2F-UPSR) ADM 1 ADM 2 ADM 3 ADM 4 5 2 6 4 8 3 7 A Protection ring Working ring 1 B Connection-Oriented Networks – Wissam FAWAZ 60 • Features: – Working ring consists of fibers 1, 2, 3 and 4, and the protection ring of fibers 5, 6, 7, and 8. – Unidirectional transmission means that traffic is transmitted in the same direction. A transmits to B over fiber 1 of the working ring, and B transmits over fibers 2, 3, and 4 of the working ring. – Used as a metro edge ring to interconnect PBXs and access networks to a metro core ring