SDH frames are transmitted from left to right and from top to bottom in a serial code stream, the transmission time of each frame is 125us, and 8000 frames are transmitted per second, and the bytes per frame for STM-l are 8 bits/byte × (9 × 270 × 1) bytes = 19,440 bits, and the transmission rate of STM-l is 19,440 × 8,000 = 155.520 Mbit/s. Similarly, the transmission rate for STM-l is 19,440 × 8000 = 155.520 Mbit/s, and the transmission time for STM-1 is 1.5 seconds. s. Similarly, the transmission rate of

| STM-4 - 622.08Mbit/s

| STM-16 -- 2488.32Mbit/s (2.5G)

| STM-64 - 10Gbit/s

The ITU-T specifies that for any level of STM class, the frame rate is 8000 frames/sec, which means that the frame length or frame period is a constant 125 μs . the E1 signal for PDH is also 8000 frames/sec.

The frame rate is 8000 fps for any STM class, and the constant frame period is one of the characteristics of SDH signals. Think about whether the frame period is constant for the different levels of PDH signaling. The constancy of the frame period gives a regularity to the rate of the STM-N signal. For example, the transmission rate of STM-4 is constant and equal to 4 times the transmission rate of STM-1 signal, and STM-16 is constant and equal to 4 times the rate of STM-4 and 16 times the rate of STM-1. The E2 signal rate in PDH ≠ 4 times the E1 signal rate.This regularity of SDH signals makes it possible to directly split/insert high-speed SDH signals into low-speed SDH signals (or low-speed SDH branch signals), which is especially suitable for large-capacity transmission. That is to say, the low-speed SDH signals are multiplexed in the frame of high-speed SDH signals in the way of byte interpolation in a fixed, regular position. n STM-1 multiplexed to form STM-N, SDH simplifies the multiplexing and multiplexing technology, and can be directly accessed to low-speed tributary without going through high-speed to low-speed step-by-step multiplexing, and the up and down the road is convenient.

Multiplexing of SDH:

The multiplexing of SDH includes two cases: one is the multiplexing of low-order SDH signals into high-order SDH signals; the other is the multiplexing of low-speed tributary signals (e.g., 2Mbit/s, 34Mbit/s, and 140Mbit/s) into SDH signals STM-N.
In the first case, the multiplexing is mainly accomplished by the byte interpolating multiplexing method, and the number of multiplexes is 4-in-1, i.e., 4× STM-1→STM-4, 4×STM-4→STM-16. the frame rate is kept constant (8000 frames/sec) during the multiplexing process, which means that the STM-N signal of the higher level is 4 times the rate of the STM-N signal of the lower level. During byte interpolation multiplexing, the net information load and pointer bytes of each frame are interpolated and multiplexed at their original values, with some trade-off in segment overhead. In the multiplexed STM-N frames, the SOH is not interpolated from all the segment overheads in the lower-order SDH frames, but some of the segment overheads in the lower-order frames are discarded.

The second most used case is the multiplexing of PDH signals into STM-N signals

C-Container, VC-Virtual Container, TU-Tributary Unit, TUG-Tributary Unit Group, AU-Management Unit, AUG-Administration Unit Group VC4 is the one with the 140Mbit/sPDH signal corresponding to the standard virtual container, this process is equivalent to the C4 signal to hit another packet, the overhead of monitoring and management of the channel (POH) into the packet in order to realize the real-time monitoring of the channel signal.

The packetization rate of the virtual container (VC) is also synchronized with the SDH network. Different VCs (e.g., VC12 corresponding to 2 Mbit/s, VC3 corresponding to 34 Mbit/s) are synchronized with each other, whereas the virtual container internally permits the loading of asynchronous net loads from different containers. This information structure of the virtual container maintains its integrity unchanged in SDH network transmission, i.e., it can be viewed as independent units (packets) that can be inserted or removed at any point in the channel very flexibly and conveniently for synchronous multiplexing and cross-connect processing.

That is to say, the smallest unit of SDH is a container, whose size is fixed.SDH is specially designed for voice, and can be applied to fixed-rate services. This means that a fixed container is used to transmit fixed-rate voice services. The bandwidth utilization is higher for fixed rate voice transmission with VC, but SDH is less utilized for non-fixed rate services such as data services. The size of the container is fixed, it can be full for water, but the gap is bigger for stone, and the space utilization rate is smaller.

SDH sampling two-fiber bidirectional multiplexing segment protection ring networking, a great advantage is the use of self-healing hybrid ring network structure.

SDH has the ability to resist a single failure, sampling two-way multiplexing protection ring. A failure in one channel can be transmitted from another protected channel. The current status of the bearer network is shown below.

The self-healing capability of ring networking is a very important feature of SDH.

SDH can only manage channels of a single wavelength, which can be electrically crossed and are ring-organized.

WDM optical division multiplexing, manages multiple wavelengths, optical crossover.

OTN = SDH + WDM (to a certain extent), OTN manages multiple service circuits on multiple wavelengths at the same time, with electrical crossover and optical crossover.

SDH, in addition to the above mentioned inability to adapt to the development of data services, but also can not guarantee the quality of transmission, but also can not monitor the performance, that is to say, can not be network management. the development of IP technology, the dynamic bandwidth requirements, SDH also moved forward to the MSTP - Multi-service Transport Platform.

This section describes the frame structure of SDH, STM-N rates, SDH multiplexing, and the advantages and disadvantages of SDH.

Part III: MSTP

MSTP = SDH + Ethernet (Layer 2 switching) + ATM (signaling)

That is, an Ethernet interface or ATM interface is added to the user side of SDH to realize an IP-based interface. ip over SDH.

The core of MSTP is still SDH, which is improved on SDH.

Key technologies of MSTP:

(1) Protocol Encapsulation

We know that IP is a three-layer protocol, that is, the network layer, and SDH belongs to the physical layer, so IP over SDH requires a two-layer thing to convert between IP and SDH. That is to say, IP packets need to be encapsulated as frames for transmission over SDH.

There are three kinds of protocol encapsulation

PPP/HDLC Point-to-Point Protocol/Advanced Data Link Control

LAPS Link Access Protocol (LAPS) proposed by Wuhan Postal Research Institute (WPRI).

GFP Generalized Framing Procedure (GFP) proposed by ITU-T.

Introducing EOS (Ethernet over SDH) first.

EOS is a method of encapsulating data into Ethernet frames and then mapping them into virtual containers in SDH.

6 6 2 46 ~ 1500 4

Destination MAC Source MAC Length Data FCS

The Ethernet frame length is between 64 ~ 1518 bytes and the maximum length of IP packet is 65535 bytes.

In terms of implementation, it is to map the Ethernet data stream into the SDH channel through some encapsulation, and the channel granule of SDH can be VC12, VC4. Ethernet boards can map Ethernet services, such as 10M, 100M, 1000M, into one or more VCs through encapsulation and transmit them by the SDH system.

For the three protocol encapsulation methods:

PPP/HDLC: A physical connection needs to be established and then a logical connection which is the data link layer connection. Three handshakes are required, so the latency is relatively high and is applicable to 155 Mbps.

LAPS: essentially also a kind of HDLC protocol family, is a kind of simplified PPP-HDLC. it does not have link layer control protocol and network layer control protocol, only specifies the data transmission protocol, so there is no need for the connection establishment process, direct connectivity. Applicable to 2.5G - STM-16

GFP: (1) with low-latency transmission and processing capabilities, suitable for high-speed wide area network applications (such as storage area network SAN); (2) supports service adaptation protocols that can be used for broadband transmission; (3) provides an efficient QOS guarantee mechanism, able to map physical or logical link layer signals into byte-synchronized channels; (4) with client management capabilities, support for the basic client control (5) adopts frame delimitation similar to ATM technology, which reduces the overhead of locating bytes and avoids the impact of transmission content on transmission efficiency; (6) breaks the limitation that the link layer adaptation protocol can only support point-to-point topology, and can realize the support for different topologies.

The most common application of GFP is to directly map Ethernet MAC frames of IEEE802.3 into GFP frames in MSTP devices. This is the protocol that must be selected for all services in the future.

The interface rate of EOS is the same as that of Ethernet, 10Mbps, 100Mbps, 1Gbps, 10Gbps, 40Gbps and 100Gbps.

(2) Cascading Technology

As mentioned above, IP packets can be very large and need to be sliced and diced during encapsulation, and the container is too small relative to the large rate, which leads to the cascading technique, multiplexed into a larger container.VC12, VC3, and VC4, which correspond to 2M, 34M/45M, and 140M/155M, respectively, don't match very well with respect to the Ethernet rate.

There are two cascading techniques

l Adjacent Cascade VC12-5C

This cascading technique, when applied, requires all devices to be supported before it can be used. Cascade five adjacent VC12 virtual containers in the SDH frame. One Vc12 is 2M, and 5 cascaded together is 10M, this cascade needs to be completed in the same frame

l Virtual cascade VC12-5V

The virtual cascade can make five VC12s discontinuous, and it can also cross frames, so it only requires that the equipment at both ends of the transmission supports this cascade.

(3) LCAS link capacity adjustment mechanism

This is a signaling technique in which the network administrator issues LCAS commands to change the number of virtual cascades to adjust the bandwidth.

This part mainly introduces the key technologies of MSTP.

Part IV: ASON-Automatically Switched Optical Network and PTN

A request is issued by the user to flexibly adjust the bandwidth according to the user's requirements.

SDH/MSTP-based ASON Solving <40G transmission

OTN-based ASON Addressing 40G, 100G transmission

ASON = SDH/MSTP + IP Adds a control plane and management plane to the transport plane SDH.

Traditional IP technology TCP/IP is unmanageable and uncontrollable

MPLS: Instead of going through layer 3 to query the routing table for forwarding when it reaches a node like traditional IP, it is directly forwarded by hardware based on layer 2 labeling. Enables better integration of IP and ATM: IP is delivered over the ATM backbone without routers maintaining huge mapping tables.MPLS = ATM + Router Technology

Labeling in MPLS is labeling the electrical domain and extending it to the optical domain labeling, GMPLS, which is the main technology in the ASON control plane.

GMPLS has the following components:

1. signaling protocol

l RSVP-TE Resource reservation based on traffic engineering This is mainly used today

l CR-LDP Label Distribution Protocol based on constrained routing

l PNNI Private Network Network Interface Protocol

2. Routing protocols

l OSPF-TE Open Shortest Path First Protocol This is currently the main one used, supporting traffic engineering.

l IS-IS-TE Intermediate System-Intermediate System

l BGP4 Border Gateway Version 4

3. Link Management Protocol LMP

Work process: the routing protocol selects the route through the link management protocol, and then the signaling protocol establishes the link.

PTN packet transport network = router + SDH

One is PBB-TE/PBT Nortel, one is T-MPLS (MPLS-TP)

ITU-T proposes multiprotocol label switching for T-MPLS transport = MPLS-IP + OAM

But MPLS was first proposed by IEEE, so T-MPLS was renamed to MPLS-TP transport profile

Components of T-MPLS/MPLS-TP:

1. signaling protocol RSVP-TE

2. routing protocol OSPF-TE

3. Link Management Protocol LMP

4. Pseudo-Wire Emulation PWE3 (Pseudo-Wire Emulation Edge to Edge) creates point-to-point virtual circuits in a packet network to carry voice

IP packets of different granularity need congestion control and flow control at the ingress, granularity below 2.5G is achieved by PTN, granularity scheduling above 2.5G needs OTN.SDH network is gradually being marginalized by PTN in metro network, and by OTN, WDM in inter-provincial trunk line.

This section describes the key technologies of ASON and PTN

As mentioned earlier, OTN = SDH + WDM

WDM is a physical layer technology where multiple wavelengths are combined at the transmitter side.