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PoSPacket over SONET/SDHPocket Guide


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This Pocket guide is intended to provide an overview of transporttraffic features and especially the transport below the Internetprotocol (IP) layer, known as Packet over SONET/SDH (PoS).

Towards the end of the 1980s, synchronous digital hierarchy(SDH) and synchronous optical network (SONET) technologywere introduced to overcome the problems with plesiochronousdigital hierarchy (PDH) technology. Both SDH and SONET are timedivision multiplexing (TDM) transmission technologies. The SDH/SONET standard has evolved to 10 G for todays new systems,which are mainly optimized for voice transmission. However,the trend is not only towards higher bit rates like 40 and 80 G,wavelength division multiplexing (WDM) technology is alsoenjoying steady growth. Systems with up to 160 wavelengthchannels are now operating, each transmitting 10 G on one fiber. These trends are driven by market development towards moredata-oriented traffic. IP in particular, continues to grow at an

explosive pace. Leading Internet providers report that bandwidthdoubles approximately every 6 to 9 months on their backbones.

Introduction


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The adoption of Intranets and Extranets for networkedcommerce will bring further changes to the IP-serviceinfrastructure, both through bandwidth demands and feature

requirements. Service providers recognize this unprecedentedexplosion in packet-based traffic and are reevaluating theirnetwork architectures in light of these changes. Resourcefuldesigners combine the benefits of dense wavelength divisionmultiplexing (DWDM), TDM and the reliable SDH/SONETtechnologies. In doing so it is possible to transport data streamsup into the terabit range. The increased IP traffic requires atechnology to transport the IP packets to the physical layer. Thistransport below IP is presented by PoS as one possible route.


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Benefits of Packetover SONET/SDH

Efficient point-to-point IP service at high speeds Future-proof technology IP offers simultaneous handling of voice, video, and data traffic

Utilizes advantages (reliability, scalability, and manageability) of existingSDH/SONET infrastructure

PoS offers significant advantages through efficient bandwidth utilization due toless overhead, see Figure 1

One layer less to manage than with ATM, see Figure 2 Reuse of familiar link-layer protocols

Figure 1. PoS and ATM bandwidthefficiency

Packet size (byte)

64

% E ffi c i e n c y

128 256 512 1024 1518 2048 4352

100

30

40

50

60

70

80

90

110

PoS ATMoS4488


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IPATM

SDH/SONET

DWDM

Figure 2. Possible scenario for IP trafficto the physical layer


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The Application, Presentation, and Session layers (7, 6, and 5) are merged and ifollowing section will be referred to as the Application layer.

The applications can be divided into two groups, one using theTransmission ControlProtocol (TCP) for additional transport, the other utilizingUser Datagram Protocol(UDP) protocol. (The difference between these two protocols will be addressed late


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Table 1 provides an overview of the most commonly used applications to the readerbecause they are regularly used in daily life. Some are mentioned briefly below:

User Application Protocol Request for Comments(RFC)

E-mail Simple Mail Transfer RFC 821 ProtocolSMTPFor copying files File Transfer Protocol RFC 959File transfer FTP

Remote terminal login Telnet RFC 854Exchange of WWW Hyper Text Transfer RFC 1945information ProtocolHTTPFor Simple Network Simple Network RFC 1157Management applications Management ProtocolSNMPIdentification of host Domain Name System RFC 2929, RFC 1591with IP address DNS

This booklet only provides a general overview of the protocols running in theapplication layers.

Table 1. Application protocolsand their use


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Transport Layer

Figure 4. UDP datagram

The Transport layer contains two major protocolsTCP and UDPdistinguishby their reliability and low transport overhead.

User Datagram Protocol (UDP) The User Datagram Protocol is the simpler ofthe two and is typically used when reliability and security are of secondary impotance to the speed and size of the overhead. It is an end-to-end protocol which aport addresses, checksum error control and length information to data from theupper layer. Figure 4 illustrates the UDP header format.

8 bit 8 bit 8 bit 8 bit

Source Port Destination Port

Length Checksum

Payload


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Table 2 provides a brief description of these header fields: Source port Specifies the port address of the application program

which created the messageDestination port Specifies the address of the application program which

will receive the messageLength (16 bit) Specifies the total length of the user datagram in bytesChecksum This is a 16-bit field used in error detection

When paired with theInternet Control Message Protocol (ICMP), UDPcan inform the transmitter when a user datagram has been damaged and discarded.Neither protocol is able to specify which packet has been damaged when repairingan error. UDP can only signal that an error has occurred.

Transmission Control Protocol (TCP) TCP provides full transport layer servicesto applications. It isconnection-oriented, meaning that a connection must beestablished between two peers before either can transmit data. In doing so, TCP

establishes avirtual connection between sender and receiver which remainsactive for the duration of the transmission.

Table 2. Definitions of UDPheader fields


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Figure 5. TCP datagram

Each transmission via TCP starts with a message to the receiver, alerting it thatmore IP packets are on their way. Each transmission is terminated by a terminationmessage. When sending data, TCP divides long data packets into smaller data unit

and packages them into segments. Each segment includes a sequencing number reordering after receipt, as well as an acknowledgment ID number. These segmentare transported across the network inside the IP datagrams. The receiver collectseach datagram as it comes in and re-orders the transmission based on the sequencenumbers. TCP is a reliable protocol, as each data transmission is acknowledged byreceiver with TCP, data is transmitted in both directions. If the sender does not recan acknowledgment within a specified time, it retransmits the data. To provide secdelivery for the TCP an extensive segment header is required (see Figure 5).

8 bit 8 bit 8 bit 8 bit

Source Port Destination Port

Sequence Number

Acknowledgment Number

HLEN Reserved Control Window

Checksum Urgent Pointer

Options Padding

Payload


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Table 3 describes the TCP segment fields.

Source port Defines application program in the source computerDestination port Defines the application program in the

destination computerSequence number The sequence number shows the position of the data

in the original data streamAcknowledgment 32-bit acknowledgment number is used tonumber acknowledge receipt of dataHeader length (HLEN) Indicates the number of 32-bit words in the

TCP headerReserved 6-bit field reserved for future useControl 6-bit field providing control functionsWindow size 16-bit field defines the size of the sliding windowChecksum 16-bit checksum used in error detectionUrgent pointer Valid only when the URG bit in the control field is activeOptions and padding Defines optional fields and are used to convey additional

information to the receiver or for alignment purposes

Table 3. TCP header field definitions


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Comparing UDP and TCP protocols:UDP features TCP features Connectionless protocol Connection-oriented protocol

No error recovery Error detection and recovery Unreliable Reliable Fast speed Slower than UDP Small overhead Large overhead

UDP applications TCP applications Voice HTTP Broadcasting FTP

The History of the Internet Protocol The Internet Protocol (IP) was developedby the Advanced Research Project Agency (ARPA), an arm of the U.S. DepartmDefense and was first tested in 1968/69 with computer-to-computer connectionThe objective was to ensure that the military could maintain communications in

the event of a nuclear war. The protocols and conventions developed by the ARevolved to become TCP/IP. Due to the growth of TCP/IP traffic the ARPANETthe backbone of a network known today as the Internet.

Network Layer Internet Protocol version 4


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Figure 6. The format of anIP datagram

IP is the transmission method used by TCP/IP.IP transport is sent in packets called datagrams, each of which are transportedseparately. The individual packets may travel by different routes, as IP has no track-

ing capabilities or facility for reordering lost datagrams.

Version IHL Type of Service Total Length

Identification Flags Fragment Offset

Time to live Protocol Header Checksum

Source Address

Destination Address Options Padding

Payload

8 bits 8 bits 8 bits 8 bits

An IP datagram is a variable-length packet of up to 65,536 bytes consisting of two

parts; the header (made up of 20 to 60 bytes) and the data (20 to 65,536 bytes). Theheader contains essential information about routing and delivery service of the IPpackets. The structure of the IP header is illustrated in Figure 6. Table 4 provides theIP header field definitions.


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Version This field defines the version number. IPv4 corresponds to bin. 0100.Internet Header This field defines the length of the header in multiplesLength (IHL) of four bytes.Type of Service This field defines how the datagram should be handled (priority of transport, reliability and delay) and contains information on the type of service (ToS).Total Length This field defines the total length of the IP datagram. It is a two-byte field (16 bits) and can define up to 65,536 bytes (this includes the header and the data).Identification This field is used in fragmentation. When packets are moving independently through the network, they are identified by a number in this field.Flag The bits in this field handle fragmentation.Fragmentation This field provides a pointer which shows the offsetOffset of the data in the original datagram.

Table 4. IP header field definitions


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Class A only uses one byte to identify the class type and Net-ID, leaving three bytesavailable for Host-ID numbers. This results in Class A networks accommodatingfar more hosts thanClass B orC networks. At present Classes A and B are full.Addresses are only available in Class C.An overview of how many networks and hosts can be supplied by different types ofclass is shown in Table 5.

Class A 127 possible network IDs 16,777,214 host IDs per network ID

Class B 16,384 possible network IDs

65,534 host IDs per network IDClass C 2,097,152 possible network IDs 254 host IDs per network ID

Class Dis reserved formulticast addresses, meaning that IP datagrams can bedelivered only to a selected group of hosts rather than to an individual.

Class E is reserved for future use. Internet addresses are usually written in decimalform, points separating the bytes (for example, 137.23.145.23).

Table 5. Internet Class addressesand their potential use


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Figure 9. IP addressing in caseof subnetting

Subnetting To circumvent some of the limitations of the addressing conven-tions of IPv4, it is possible to introduce subnet structures. The addressing conve(RFC 950) used results in the following division of the classes (see Figure 9).

The network administrator is able to divide the host address space into groups(subnets) mainly to mirror topological or organizational structures. At a universfor example, the various faculties might be groups under the host name.This procedure simplifies routing in a network and allows a clearer structure of th

network to be seen.Figure 10 illustrates how a subnetting structure might look.

10 Net-ID Subnet ID Host-ID


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Internet Control Message Protocol (ICMP) The Internet Control MessageProtocol (ICMP) is used by hosts and gateways to inform the sender of datagramproblems and to exchange control messages. The ICMP (Recommendation RFC 792)uses IP to deliver these messages. Although IP is an unreliable and connectionless

protocol, ICMP uses IP to inform the sender of undeliverable datagrams. ICMP onlyreports problems, it does not correct errors. The following examples show the mes-sage types that can be sent:

Figure 10. Example of subnetting fora Class-A type IP address

Subnet 1129.69.1.x Subnet 3129.69.3.xSubnet 2129.69.2.x

Host


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Error messages Information messages Destination unreachable Echo request, echo response Redirect packet Time stamp (ping) Time exceeded

If a user types an incorrect HTTP address in the Web browser, it is sent to the Dserver which in turn returns an IP address to be sent to the respective server. If server is down, the user receives the message Destination unreachable.

IP Routing and Switching In the Internet, packets are dynamically routed fromthe source to the destination by a hop-by-hop movement. Routers and switches used to ensure the packet is delivered correctly.Routers are intelligent network elements operating in the Network layer of theOSI model. Routers have access to Network layer addresses and contain softwaenabling them to determine which of several possible paths between addressesis appropriate for a particular transmission. Routers relay packets among multipinterconnected networks and can route packets from one network to any numbedestination networks on an Internet (see Figure 11).


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The IP networks are usually designed in a mesh structure so that if an interruption inthe transmission occurs, an alternative path can be found quickly. The routing processis adynamic procedure which allows the system to forward a packet via its mostefficient path from source to destination address. The decision as to how packets

are routed through a network follows multiple routing algorithms. The description ofthese algorithms would, however, be beyond the scope of this booklet.Switches are layer 2 network elements responsible for establishing temporarystaticconnections between two or more devices linked to the switch, but not to each other.

Figure 11. Possiblerouting scenario Router

Source

Destination

Router

Router

Router

Router

Router


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Figure 12 illustrates a switched network. The communicating devices are labeleB, C, D, and the switches I, II, III, IV. Each switch is connected to multiple linkis used to complete the connections between the communicating peers. As soonthe switches are set, they are static for one specific transmission process and can

then be reconfigured. Figure 13 shows two principal switching methods availab

Figure 12. Switchednetwork

A

III

IVIII

B

C

D


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Circuit switching was designed primarily for voice communication. In a telephoneconversation, for example, once a circuit is established it remains connected for

the duration of the session. Circuit switching is not suitable for data or othernon-conversational transmissions. Non-voice transmissions tend to come in bursts;therefore, in a circuit-switched circuit, the line is often idle and its facilities wasted.In apacket switched network, data is transmitted in discrete units of potentiallyvariable length packets. The maximum length of a packet is established by the net-work and long transmissions are broken into multiple packets. Each packet contains

not only the data but also a header containing the control information. The packetsare sent over the network hop-by-hop and routed through the network according tothe information in the packet header with the address information. WithMessageswitching, a network node receives a message, stores it until the appropriate routeis free, then sends it.

Figure 13. Networkswitching methods Switching methods

Circuit switching Packet switching

Mainly voice traffic Mainly data traffic


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From the Network layer, the IP packets need to be delivered to underlying layerThe actual transmission below the Transport layer is called packet over SONETSDH (PoS). This transmission can be achieved via alternative routes, two of whicillustrated in Figure 14.

The route (black line) described in this booklet is recommended by the InternetEngineering Task Force (IETF) and is illustrated in Figure 15.

Packet overSONET/SDH (PoS)

Figure 14. Alternative routes for transmittingIP packets to the fiber

PPP

HDLC

SDH/SONET

Fiber

ATM

IP


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The IP packets are encapsulated in a Point-to-Point Protocol which in turn is mappedinto a HDLC-like frame. This frame is then mapped into the SONET/SDH frame.

The Point-to-Point Protocol (PPP) provides a standard method for transportingmulti-protocol datagrams, such as IP packets, over point-to-point links. Initially,

PPP was used over plain old telephone service (POTS). However, since the SONET/SDH technology is by definition a point-to-point circuit, PPP/HDLC is well-suited foruse over these lines. PPP is designed to transport packets between two peers acrossa simple link.

Figure 15. Mapping of IP packets intoSONET/SDH frames

Point-to-Point Protocol

Flag Address Control HDLC Payload CRC Flag

H Packet contents

7E FF 03 YY 7E

SONET/SDH

HDLC

PPP

OP

Protocol PPP payload

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OH Payload


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Features of the PPP link: Allows for full-duplex and simultaneous operation No restrictions regarding transmission rates imposed Operates across most data terminating equipment/data circuit-terminating

equipment (DTE/DCE) interfaces (e.g., RS232, RS422, V.35, etc.) Does not require any hardware control signals (e.g., Request to Send, Clear To

Send, etc.)

PPP is intended to provide a common solution for the easy connection of a widevariety of hosts, bridges, and routers. The encapsulation of PPP into HDLC-likeframes allows for the multiplexing of different network-layer protocols, such as

IPX, AppleTalk, and others, simultaneously over the same link.

PPP consists of three main components: A method for encapsulating multi-protocol datagrams (PPP encapsulation) A Link Control Protocol (LCP) for establishing, configuring, and testing of th

link connection

A family of Network Control Protocols (NCPs) for establishing and configuridifferent network layer protocols


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PPP Encapsulation andPPP Emulation

Figure 16. PPP encapsulationaccording to RFC 1661

PPP Encapsulation To allow multi-protocol datagrams to be transmittedacross a link, a method must be used to enable unambiguous decisions to be madebetween the various protocols. The PPP encapsulation of the IP packets is illustratedin Figure 16.

The fields are transmitted from left to right with these names and functions:

Protocol Field Consists of 1 or 2 octets, with values identifying the encapsulated

datagram.Data Field This field is zero or more octets long and it contains the datagram forthe protocol specified in the protocol field. The maximum length, including padding(but not the protocol field) defaults to 1500 octets. This means, for example, that ifan IP datagram with a larger payload were transported it would be fragmented intoseveral packets to fit the size of the data field.Padding Field At the beginning of the transmission this field may be paddedwith an arbitrary number of octets (up to 1500 octets). It is the responsibility of theprotocol to distinguish padding from real information.

Protocol 8/16 bits Payload Padding


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PPP Emulation The PPP Emulation describes: Link Control Protocol Network Control Protocol

The LCP is responsible for correctly establishing, configuring, and testing the Pto-Point Protocol. Before IP datagrams can be transported across a PPP link, eacthe connected PPP interfaces must send out a series of LCP packets.

Figure 17 illustrates the five key LCP steps which are described in this section.

Link Control Protocol (LCP)

Figure 17. Illustration ofLCP procedure

C021 (LCP)

Authenticate

Establish Terminate

Dead Start

NCPNetwork

SONET/SDH

Flag FF03 ProtocolPayload FCS FlagHDLC/PPP

OH Payload


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Step 1: Link Dead Each PPP connection starts and ends in this state. In thisstate there is either no connection to the modem or the connection has been inter-rupted. When an external event (control signal or network administrator) indicatesthat the Physical layer is ready to be used, PPP proceeds to the establishment phase.

Step 2: Link Establishment Before data from an upper layer (e.g., IP) can betransported across a connection, the link is prepared via configuration packets. Thisexchange is completed, and the Open state achieved after a Configure packet hasbeen sent and received. All configuration options are set to default values, unless al-tered. Any non-LCP packets received during the establishment phase are discarded.

Step 3: Authentication This is an optional step, allowing the PPP peers toidentify each other via authentication protocols. These are calledPasswordAuthentication Protocol (PAP) andChallenge Handshake AuthenticationProtocol (CHAP).

ThePassword Authentication Protocol sends a password across the link, tonegotiate the circumstances for operation.


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TheChallenge Handshake Authentication Protocol ensures reliable and secureauthentication because the authenticator and authenticatee share a commonpassword. The authenticator sends the connected peer a challenge in the form ofa random number. The authenticatee uses this random number to derive a secrecode. This code is then transmitted to the authenticator and if the results match, next connection stage can proceed.

Step 4: Network Layer Protocol Configuration This is necessary to configurethe Network Control Protocols (NCP) used on this connection. Each network laprotocol (e.g., IP, Appletalk, etc.) must be separately configured by the appropri

NCP. It is possible with PPP to run several NCPs over one connection.

After an NCP reaches the Opened state, PPP will carry the corresponding netwolayer protocol packets. Any network-layer protocol packets received prior toreaching the corresponding Opened state are discarded. During this phase, linktraffic consists of any possible combination of LCP, NCP, and network-layer propackets.


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Step 5: Link Termination The LCP makes it possible to close a connection atany time. This can be done by a user event, set timer, or missing interface signal.Between step 3 and step 4, link quality monitoring (LQM) can take place andthe data connection tested for transmission quality. TheLink Control Protocolinformation is sent in the form of PPP datagrams, which fall into these threemajor classes: Link configuration packets used to establish and configure a link (RFC 1661) Link termination packets used to terminate a link (RFC 1661) Link maintenance packets used to manage and debug a link (RFC 1661)

A family of Network Control Protocols helps to prepare and configure differentprotocols to run in the various network layers. Figure 18 illustrates and describes anexample of one of these protocols, IPCP.

Network Control Protocol (NCP)


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This protocol enables activation, configuration, and deactivation of the IP protocmodules on both sides of the point-to-point connection. Like the LCP, these funcare achieved by exchanging special data packets; for IPCP, this packet is hex 802(protocol identifier). The exchange of IPCP packets starts after completing step 4the LCP protocols. The NCP then runs through steps equivalent to those of the Lprocedure once the LCP protocol is in the network state (see Figure 18).

Figure 18. Illustration of a commonNCP procedure

8021

Authenticate Network

Establish LCPDead

SONET/SDH

Flag FF03 ProtocolPayload FCS FlagHDLC/PPP

OH Payload

Start


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High-Level Data Link Control(HDLC)

Figure 19. Format of HDLC-like frameaccording to RFC 1662

When the LCP and the NCP protocols are fulfilled the data can be transmitted acrossthe point-to-point connection.

The Point-to-Point Protocol provides a standard method for transporting multi-protocol datagrams over point-to-point links. The PPP packets are encapsulated ina HDLC-like frame which is then mapped into the SONET frame. The format of thisHDLC frame is illustrated in Figure 19.

Flag Sequence Each frame begins and ends with a flag sequence, which is thebinary sequence 01111110 (hex 0x7e). All implementations check for this framesynchronization flag. Only one flag sequence is required between two frames. Twoconsecutive flag sequences constitute an empty frame which is then discarded.

Address Field The address field is a single octet containing the binary sequence11111111 (hex 0xff). Individual station addresses are not assigned.

Flag Address Control Protocol Information FCSFlag

Control Field The control field contains the binary sequence 00000011


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Control Field The control field contains the binary sequence 00000011(hex 0x03). Frames with unrecognized control field values are discarded.

Protocol Field The protocol field is one or two octets, with a value identifyingthe datagram encapsulated within the packets information field.Table 6 shows the identifiers for the most frequently used protocols.

Hex value Protocol used

0021 IPC021 LCP8021 NCP (IPCP)

Information The information field is zero or more octets and contains the datagram for the protocol specified in the protocol field. The Information Field, inclpadding but not including the protocol field, is called the maximum receive unit(MRU) and has a maximum length of 1500 octets.

Padding The Information field may be padded with an arbitrary number ofoctets up to the MRU.

Table 6. Identifiers used in the protocolfield in the HDLC frame


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Frame Check Sequence Field The frame check sequence (FCS) defaults to 16 bitsfor OC-3/STM-1 although other speeds use 32 bits as well. Its use is described in PPPLCP Extensions of RFC 2615.

The FCS field is calculated over all bits of the address, control, protocol, information,and padding fields and is illustrated by the grey fields in Figure 20. Itdoes notinclude the Flag Sequences or the FCS field itself.

PPP uses the FCS for error detection and is commonly available in hardware imple-mentations. The end of the information and padding fields is found by locatingthe closing flag sequence and removing the frame check sequence field. TheHDLCprocess and related recommendations are illustrated in Figure 21.

Figure 20. Fields of the HDLC-like frameused to perform the FCS

Figure 21. How an IP packet is transmittedto and received by the SONET/SDH frame

SONET/SDHFraming

De-Mapping,De-Scrambling

ByteStuffing

FCSGenerationPPP

SONET/SDHFraming

Mapping,De-Scrambling

ByteStuffing

FCSGenerationPPP

Transmit ow

RFC1661 RFC1662 RFC2615 G.707GR.253

Receive ow

Flag Address Control Protocol Information FCSFlag


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Byte stuffing/destuffing The PPP protocolmust not place any restrictions onthe use of certain bit patterns in the network layer packet and must betransparent to any type of data. Because the PPP protocol uses specific patterns, such as thefield 0x7e which indicates the beginning and end of a frame, a method is requireto avoid restrictions. This is achieved throughbyte stuffing where the PPP definesa specialcontrol escape byte, 0x7d. The byte-stuffing procedure also acts for thecontrol field and the control escape byte.

The process of byte stuffing is illustrated in Figure 22 where the Flag 7E is replaby 7D,5E.

Figure 22. Illustration of thebyte-stuffing procedure 03 Flag 7E 59 8A

03 7D 5E 59 8A

before

after


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If the Control Flag 7D is within the payload, it is replaced by 7D,5D.

Scrambling/Descrambling procedure Described in RFC 2615, a data scramblerwith the 1+x43 polynomial is used in this procedure, as shown in Table 7. While theHDLC FCS is calculated, the scrambler operates continuously through the bytes ofthe payload bypassing SONET path overhead bytes and any fixed information. Thistype of scrambling is performed during insertion into the SONET/SDH payload.

ThePath signal label C2, as Table 7 shows, is used so that the SONET/SDH canrecognize the payload content.

Value signal label C2 Scrambler state

0x16 PPP with 1+x43 scrambling0xCF PPP with scrambler off

Table 7. Path signal labelC2 identifier


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With the increase in IP traffic transported across SDH/SONET/DWDM networks, itis necessary to measure the quality parameters with genuine IP traffic. Thus, thepayload is filled with HDLC/PPP/IP packets instead of a traditional pseudorandombit sequence (PRBS). This corresponds to a more realistic representation of the realtraffic to be transmitted on these networks.

The user is provided with information on how many packets were lost in a specifiedperiod (for example, 24 hours), instead of an error rate of 10-14 for instance. This ismore informative than the traditional error rate when sending packets.

Using packets instead of PRBS to fill the payload provides a more realistic trafficprofile. Due to the increased transport data and IP traffic in our networks, thepayload being filled with IP packets will become more widely accepted in the future.

The following applications are suitable for measuring the quality parameters ofindividual network elements (NE) as well as entire SDH/SONET/DWDM networksduring installation.

PoS MeasurementTasks


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Frame errors This error message gives information on the number of HDLCframes lost over a predefined period of time. The customers benefit from receivperformance measurement based on packet rather than byte parameters.

Frame rate This is the rate of frames which are sent over the link and arecalculated from the HDLC frame size and the bandwidth.

Transfer delay The transfer delay is the amount of time it takes for IP packetsto travel a set path through the network.

HDLC bandwidth This corresponds with the user set bandwidth of the link. Theallowable bandwidth depends on the interface used and the container size chose

HDLC utilization This is a percentage measure of how much of the link is actu-ally in use. These parameters are usually measured by the following application Transparency testing Connectivity testing Performance testing


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To guarantee the proper setup of the transmission line, the measuring equipmensends HCLC/PPP/IP frames and receives them again when the transmitter and treceiver are looped back to each other.

The parameters, which can change, are the frame size (in bytes) and the bandwiof the transmission. It is also possible to introduce errors and check the resultingdegradations on the receiver. The result of this measurement provides the following parameters: frame error, frame rate, transfer delay, link bandwidth, and linkutilization.

Usually, this test is performed when a new NE or a new user is connected to thenetwork. It checks whether the NE or user is properly connected to the network if it is able to communicate. A typical test setup is shown in Figure 25.

The test equipment sends out a ping and waits for the response. Thus measurithe round-trip delay of the ping. The ping parameter provides definite informatiabout the NEs connection state. The time delay indicates the health status of thline to and from the NE. The customer benefits by receiving information about tnew NEs connection.

Verify IP Connectivity of NewNetwork Elements

Fi 25 T i l


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This is a test of particular NEs and the entire network under load and checks theinterfaces of NEs.

Figure 26 illustrates a typical arrangement for such a measurement test.

Checking PoS Performance

Figure 25. Typical measurement arrange-ment to check connectivity of NE

pingrequest

ADM withIntegratedIP fabric

Metro area

OC-192

ping response

Router

CO/POPCore backbone

Long haul

DWDM networkl routing

ADMADM

JDSUPoS tester

Fig 26 M t g t


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This test is performed when the customer is connected to the network or whennew connections between NEs are installed. The measuring instrument sends asignal and checks if the NE is connected and can pass the signals through to thenext network element. To perform the PoS performance test, the equipment musbe capable of performing the entire PPP emulation. This measurement delivers tsame parameters as the transparency check.

Figure 26. Measurement arrangementto check performance of PoS NEs

PPPemulation

Router/ intelligentNE

DWDM networkl routing

PPPemulation

Router/ intelligentNE

JDSU

PoS tester

JDSU

PoS tester


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Table 8 shows a summary of the possible applications for PoS systems.

Challenge Solution Parameters

PoS Transparency Is the line be- Send IP traffic Frame error, tween two users and check the frame rate etc. properly set up return traffic. and transparent

for IP traffic?Connectivity Is a NE or Send ping Ping and user properly request and wait delay time.

connected to for answers from the network? NE or user. A full PPP emulation

is required.PoS Performance How does the Perform test Frame error, system behave under load with frame rate, etc. under stress? full PPP emulation.

Summary of applications

Table 8. Summary of possibleapplications for PoS systems

k ll d h h b d d hO tl k


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Future networks will need to cope with the ever-increasing bandwidthrequirements mentioned in the introduction of this booklet.

TDM transmission rates are increasing to 40 G while simultaneously the numbe

channels in DWDM systems are increasing to 128 and more. Total capacity rateapproximately 320 G, 1 T, and higher are therefore quite possible. This challengwill be met by some of the technologies described in the following pages.

When discussing possible future networks the expressionconverging networks is often used.

Outlook

Figure 27. Possible convergence scenario in


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Converging networks lead to a decrease in the number of network elements andpotentially less trouble for network operators. One platform used in this process isthe so called Multi-Service Provision Platform. In addition, techniques like Multi-Protocol Label Switching and Multi-Protocoll Switching will help to establish thistrend. Figure 27 illustrates the possible convergence of functions with various layers.

g gthe telecommunication world

Functions

will merge,variousmigrationscenarios

IP is theUniversalConvergenceLayer

The existingnetwork:reliable, butunaffordable

DWDM is mainlong distance +Metro transmissiontechnology

Multi-Service

transport

Fiber

Opticalnetworking

IP, Service

DWDM

SONET

ATM

Fiber

Si th j it f t l i ti i d t i t d thM lti S i P i i i g


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Since the majority of new telecommunication services are data-oriented, thetransmission on these networks should be data optimized, which can be achiewith Multi-Service Provisioning Platforms (MSPP). These MSPPs enable aggreand switching of data packets by one network element.

MSPPs can switch voice and video as well as different types of data traffic. Thethree main features are necessary to perform the above tasks: Use DWDM technology to increase capacity of fibers Use of SONET/SDH to ensure QoS for time-sensitive applications Use of Layer 2 and Layer 3 data intelligence (switches and routers) thus allow

products to switch and route data traffic

Combining these features into one instrument enables service providers to simptheir networks. Instead of installing a DWDM multiplexer, ADM, and an IP rou just one device can be used. The number of devices and potential problems arereduced as a result.

Multi-Service ProvisioningPlatform (MSPP)

Multi Protocol Label Switching (MPLS) is a high performance method of forwardMulti Protocol Label Switching


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Multi-Protocol Label Switching (MPLS) is a high-performance method of forward-ing packets through a network. It is used by routers at the edge of the network toapply simple labels (or identifiers) to packets. These labels allow routers to switchpackets according to their label with a minimal lookup overhead.

MPLS integrates the performance and traffic management capabilities of Layer 2with the scalability and flexibility of Layer 3.

The label summarizes essential information about routing the packet including: Destination of packet

Precedence of packet QoS information The route for the packet, as chosen by traffic engineering (TE)

At each router throughout the network, only the label of the incomingpacket need be examined in order for it to be sent on to the next router acrossthe network.

Multi-Protocol Label Switchingand Multi-Protocol l Switching

(MPLS and MPlS)

Advantages of this are that only one table lookup list from a fixed length labe


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Advantages of this are that only one table lookup list from a fixed length laberequired and switching and routing functions can be combined. As with a routan optical cross-connect (OXC), can intelligently route a wavelength through OXC. The so called Multi-Protocol l Switching signaling allows an OXC to c

signal to the next OXC. These devices exhibit similar advantages to the MPLreducing the number of elements and potential problems in the network.

With the increasing number of Internet users the pool of available addressesAppendix


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With the increasing number of Internet users, the pool of available addressesdefined by IPv4 is decreasing fast. IP version 6 (IPv6) is addressing this and severalother issues such as:

Quality of Service (QoS). The header is simpler and more flexible than for IPv4 due tothe optional extension header. IPv6 is 128 bits long and consists of 16 bytes (octets).The protocol specifies hexadecimal colon notation. Whereby 128 bits are dividedinto eight sections, each of which are two bytes in length. An example of a principalIPv6 address appears in Figure 28.

FEEA:7648:CD33:9854:7654:FEDC:CE3E:0020

As with IPv4, the IP datagram for IPv6 consists of a mandatory base header followedby the payload. The payload consists of two parts: an optional extension header anddata from an upper layer (see Figure 29).

Appendix

IP version 6 (IPv6)

Figure 28. Possible IP address with IPv6


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Figure 29. IP header for IPv6

Changes in the way IP header options are encoded enable more efficient forwaring, less stringent limits on the length of options, and greater flexibility in introding new options.

A new capability has been added to facilitate the labeling of packets belonging ta particular traffic flow for which the sender must request special handling. Thesimpler header offers faster processing by routers.

Base header Payload

Optional extensionheader Data from upper layer

The following definitions are taken from RFC recommendations.Terminology


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The following definitions are taken from RFC recommendations.

Frame The unit of transmission at the data link layer. A frame may include aheader and/or a trailer, along with some number of units of data.

Packets The basic unit of encapsulation, which is passed across the interfacebetween the network layer and the data link layer. A packet is usually mapped to aframe; the exceptions are when data link layer fragmentation is being performed, orwhen multiple packets are incorporated into a single frame.

Datagram The unit of transmission in the network layer (such as IP). A data-gram may be encapsulated in one or more packets passed to the data link layer.

Peer The other end of the point-to-point link.

Silently discarded The implementation discards the packet without furtherprocessing. The implementation should provide the capability of logging the error,

including the contents of the silently discarded packet, and should record the eventin a statistics counter.

Terminology

AAbbreviations


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ADM add-drop multiplexerARPA Advanced Research Project AgencyATM asynchronous transfer mode

CCHAP Challenge-Handshake Authentication ProtocolCLEC Competitive Local Exchange Carrier

DDCE data communications equipmentDNS Domain Name SystemDTE data terminating equipmentDWDM dense wavelength division multiplexing

FFCS frame check sequence

FTP File Transfer Protocol


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T


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TCP Transfer Control ProtocolTDM Time Division MultiplexingTE traffic engineering

ToS type of service

UUDP User Datagram Protocol

WWDM wavelength division multiplexing


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Notes


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