Packet Guide SONET/SDH

PoSPacket over SONET/SDHPocket Guide

Introduction 4
Benefits of Packet over SONET/SDH 6
OSI Model and Internet Protocol 8
Application Layer 8
Transport Layer 11
User Datagram Protocol (UDP) 11
Transmission Control Protocol (TCP) 12
Network Layer – Internet Protocol version 4 15
History of the Internet Protocol 15
Internet Addressing 19
Subnetting 21
Internet Control Message Protocol (ICMP) 22
IP Routing and Switching 23
Packet over SONET/SDH (PoS) 27
Point-to-Point Protocol 28
PPP Encapsulation and PPP Emulation 30
Link Control Protocol (LCP) 31
Network Control Protocol (NCP) 34
High-Level Data Link Control (HDLC) 36
Mapping into the SONET/SDH frame 41
PoS Measurement Tasks 42
Check for PoS Transparency 44
Verify IP Connectivity of new Network Elements 45
Checking PoS Performance 46
Summary of Applications 48
Outlook 49
Multi-Service Provisioning Platform (MSPP) 51
Multi-Protocol Label Switching and Multi-Protocol l Switching (MPLS and MPlS) 52
Appendix 54
IP version 6 (IPv6) 54
Terminology 56
Abbreviations 57
References 61
Notes 62
Content

4
This Pocket guide is intended to provide an overview of transport
traffic features and especially the transport below the Internet
protocol (IP) layer, known as Packet over SONET/SDH (PoS).
Towards the end of the 1980s, synchronous digital hierarchy
(SDH) and synchronous optical network (SONET) technology
were introduced to overcome the problems with plesiochronous
digital hierarchy (PDH) technology. Both SDH and SONET are time
division multiplexing (TDM) transmission technologies. The SDH/
SONET standard has evolved to 10 G for today’s 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 also
enjoying steady growth. Systems with up to 160 wavelength
channels are now operating, each transmitting 10 G on one fiber.
These trends are driven by market development towards more
data-oriented traffic. IP in particular, continues to grow at an
explosive pace. Leading Internet providers report that bandwidth
doubles approximately every 6 to 9 months on their backbones.
Introduction

5
The adoption of Intranets and Extranets for networked
commerce will bring further changes to the IP-service
infrastructure, both through bandwidth demands and feature
requirements. Service providers recognize this unprecedented
explosion in packet-based traffic and are reevaluating their
network architectures in light of these changes. Resourceful
designers combine the benefits of dense wavelength division
multiplexing (DWDM), TDM and the reliable SDH/SONET
technologies. In doing so it is possible to transport data streams
up into the terabit range. The increased IP traffic requires a
technology to transport the IP packets to the physical layer. This
transport below IP is presented by PoS as one possible route.

6
Benefits of Packet
over 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 existing
SDH/SONET infrastructure
• PoS offers significant advantages through efficient bandwidth utilization due to
less 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 bandwidth
efficiency
Packet size (byte)
64
%Eﬃciency
128 256 512 1024 1518 2048 4352
100
30
40
50
60
70
80
90
110
PoS ATMoS
4488

7
IPATM
SDH/SONET
DWDM
Figure 2. Possible scenario for IP traffic
to the physical layer

8
The Open System Interconnection (OSI) model is used to step through a typical
transmission process leading to the description of the various layer protocols and
finally on to the PoS description. As a result, the correlation between the different
layers becomes clearer.
Figure 3 shows the seven layers of the OSI model. From top to bottom, the OSI
model starts with the Application layer which is directly accessible to the user. The
signal is then transmitted through several layers to the physical layer.
Figure 3. ISO-OSI model
TELNET
FTP
HTTP
SMTP
SNMP
DNS
IP
PPP
HDLC
SONET/SDH
DWDM
TCP UDP
ICMP
Layer 7 Application
Layer 6 Presentation
Layer 5 Session
Layer 4 Transport
Layer 3 Network
Layer 2 Data link
Layer 1 Physical
OSI Model and
Internet Protocol
Application Layer

9
The Application, Presentation, and Session layers (7, 6, and 5) are merged and in the
following section will be referred to as the “Application layer”.
Theapplicationscanbedividedintotwogroups,oneusingtheTransmissionControl
Protocol(TCP)foradditionaltransport,theotherutilizingUserDatagramProtocol
(UDP)protocol.(Thedifferencebetweenthesetwoprotocolswillbeaddressedlater.)

10
Table1providesanoverviewofthemostcommonlyusedapplicationstothereader
becausetheyareregularlyusedindailylife.Somearementionedbrieflybelow:
User Application Protocol Request for Comments
(RFC)
E-mail Simple Mail Transfer RFC 821
Protocol SMTP
For copying files File Transfer Protocol RFC 959
File transfer FTP
Remote terminal login Telnet RFC 854
Exchange of WWW Hyper Text Transfer RFC 1945
information Protocol HTTP
For Simple Network Simple Network RFC 1157
Management applications Management
Protocol SNMP
Identification of host Domain Name System RFC 2929, RFC 1591
with IP address DNS
This booklet only provides a general overview of the protocols running in the
application layers.
Table 1. Application protocols
and their use

11
Transport Layer
Figure 4. UDP datagram
The Transport layer contains two major protocols—TCP and UDP—distinguishable
by their reliability and low transport overhead.
UserDatagramProtocol(UDP) — The User Datagram Protocol is the simpler of
the two and is typically used when reliability and security are of secondary impor-
tance to the speed and size of the overhead. It is an end-to-end protocol which adds
port addresses, checksum error control and length information to data from the
upper layer. Figure 4 illustrates the UDP header format.
8 bit 8 bit 8 bit 8 bit
Source Port Destination Port
Length Checksum
Payload

12
Table 2 provides a brief description of these header fields:
Source port Specifies the port address of the application program
which created the message
Destination port Specifies the address of the application program which
will receive the message
Length (16 bit) Specifies the total length of the user datagram in bytes
Checksum This is a 16-bit field used in error detection
When paired with the Internet Control Message Protocol (ICMP), UDP
can inform the transmitter when a user datagram has been damaged and discarded.
Neither protocol is able to specify which packet has been damaged when repairing
an error. UDP can only signal that an error has occurred.
TransmissionControlProtocol(TCP) — TCP provides full transport layer services
to applications. It is connection-oriented, meaning that a connection must be
established between two peers before either can transmit data. In doing so, TCP
establishes a virtual connection between sender and receiver which remains
active for the duration of the transmission.
Table 2. Definitions of UDP
header fields

13
Figure 5. TCP datagram
EachtransmissionviaTCPstartswithamessagetothereceiver,alertingitthat
moreIPpacketsareontheirway.Eachtransmissionisterminatedbyatermination
message.Whensendingdata,TCPdivideslongdatapacketsintosmallerdataunits
andpackagestheminto“segments”.Eachsegmentincludesasequencingnumberfor
reorderingafterreceipt,aswellasanacknowledgmentIDnumber.Thesesegments
aretransportedacrossthenetworkinsidetheIPdatagrams.Thereceivercollects
eachdatagramasitcomesinandre-ordersthetransmissionbasedonthesequence
numbers.TCPisareliableprotocol,aseachdatatransmissionisacknowledgedbythe
receiverwithTCP,dataistransmittedinbothdirections.Ifthesenderdoesnotreceive
anacknowledgmentwithinaspecifiedtime,itretransmitsthedata.To provide secure
delivery 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

14
Table 3 describes the TCP segment fields.
Source port Defines application program in the source computer
Destination port Defines the application program in the
destination computer
Sequence number The sequence number shows the position of the data
in the original data stream
Acknowledgment 32-bit acknowledgment number is used to
number acknowledge receipt of data
Header length (HLEN) Indicates the number of 32-bit words in the
TCP header
Reserved 6-bit field reserved for future use
Control 6-bit field providing control functions
Window size 16-bit field defines the size of the sliding window
Checksum 16-bit checksum used in error detection
Urgent pointer Valid only when the URG bit in the control field is active
Options 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

15
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
TheHistoryoftheInternetProtocol — The Internet Protocol (IP) was developed
by the Advanced Research Project Agency (ARPA), an arm of the U.S. Department of
Defense and was first tested in 1968/69 with computer-to-computer connections.
The objective was to ensure that the military could maintain communications in
the event of a nuclear war. The protocols and conventions developed by the ARPA
evolved to become TCP/IP. Due to the growth of TCP/IP traffic the ARPANET became
the backbone of a network known today as the Internet.
Network Layer –
Internet Protocol version 4

16
Figure 6. The format of an
IP datagram
IP is the transmission method used by TCP/IP.
IP transport is sent in packets called “datagrams,” each of which are transported
separately. 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). The
header contains essential information about routing and delivery service of the IP
packets. The structure of the IP header is illustrated in Figure 6. Table 4 provides the
IP header field definitions.

17
Version This field defines the version number.
IPv4 corresponds to bin. 0100.
Internet Header This field defines the length of the header in multiples
Length (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 offset
Offset of the data in the original datagram.
Table 4. IP header field definitions

18
Time to Live This field defines the number of hops a packet can travel
before it is discarded. The source host sets this field to
an initial value (max. 256). Each router decrements
this value by “1”. Should this value reach “0” before the
datagram reaches its destination, it is discarded.
Protocol This field defines which upper-layer protocol data are
encapsulated in the packet (for example, TCP, UDP, ICMP,
and others).
Header Checksum Field of 16-bit length, calculates the checksum of the
header only.
Source Address This field contains a four-byte (32-bit) with IPv4 Internet
address and identifies the original source of the packets.
Destination This field contains a four-byte (32-bit) with IPv4 Internet
Address address and identifies the final destination of the packets.
Options This field can carry information which controls the
routing, timing, management, and alignment of the data.
Table 4. IP header field definitions Cont’d

19
Figure 8. Existing Internet
address formats
Figure 7. IP address structure Class
Type Net-ID Host-ID
Internetaddressing — The source and destination address identify the
connection of the host to its network. Each Internet address consists of four bytes
(32 bits) which define three fields: class type, Net-ID, and Host-ID. These fields have
varying lengths depending on the class of the address. The general structure of the
IP address is illustrated in Figure 7.
Currently there are five different classes from A to E, each with different pattern
lengths that cover the needs of different organization types.The Internet classes and
their byte distribution are shown in Figure 8.
Class Octet 1 Octet 2 Octet 3 Octet 4
A 0 Net-ID Host-ID
B 10 Net-ID Host-ID
C 110 Net-ID Host-ID
D 1110 Multicast Address
E 1111 Reserved for Future Use

20
Class A only uses one byte to identify the class type and Net-ID, leaving three bytes
available for Host-ID numbers. This results in Class A networks accommodating
far more hosts than Class B or C 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 of
class 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 ID
Class C • 2,097,152 possible network IDs
• 254 host IDs per network ID
Class D is reserved for multicast addresses, meaning that IP datagrams can be
delivered 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 decimal
form, points separating the bytes (for example, 137.23.145.23).
Table 5. Internet Class addresses
and their potential use

21
Figure 9. IP addressing in case
of subnetting
Subnetting — To circumvent some of the limitations of the addressing conven-
tions of IPv4, it is possible to introduce subnet structures. The addressing convention
(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 university,
for example, the various faculties might be groups under the host name.
Thisproceduresimplifiesroutinginanetworkandallowsaclearerstructureofthe
networktobeseen.
Figure10illustrateshowasubnettingstructuremightlook.
10 Net-ID Subnet ID Host-ID

22
InternetControlMessageProtocol(ICMP) — The Internet Control Message
Protocol (ICMP) is used by hosts and gateways to inform the sender of datagram
problems 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 only
reports problems, it does not correct errors. The following examples show the mes-
sage types that can be sent:
Figure 10. Example of subnetting for
a Class-A type IP address
Subnet 1
129.69.1.x
Subnet 3
129.69.3.x
Subnet 2
129.69.2.x
Host

23
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 DNS
server which in turn returns an IP address to be sent to the respective server. If the
server is down, the user receives the message “Destination unreachable.”
IP Routing and Switching – In the Internet, packets are dynamically routed from
the source to the destination by a hop-by-hop movement. Routers and switches are
used to ensure the packet is delivered correctly.
Routers are “intelligent” network elements operating in the Network layer of the
OSI model. Routers have access to Network layer addresses and contain software
enabling them to determine which of several possible paths between addresses
is appropriate for a particular transmission. Routers relay packets among multiple
interconnected networks and can route packets from one network to any number of
destination networks on an Internet (see Figure 11).

24
TheIPnetworksareusuallydesignedinameshstructuresothatifaninterruptionin
thetransmissionoccurs,analternativepathcanbefoundquickly.Theroutingprocess
isadynamicprocedurewhichallowsthesystemtoforwardapacketviaitsmost
efficientpathfromsourcetodestinationaddress.The“decision”astohowpackets
areroutedthroughanetworkfollowsmultipleroutingalgorithms.Thedescriptionof
thesealgorithmswould,however,bebeyondthescopeofthisbooklet.
Switchesarelayer2networkelementsresponsibleforestablishingtemporarystatic
connectionsbetweentwoormoredeviceslinkedtotheswitch,butnottoeachother.
Figure 11. Possible
routing scenario Router
Source
Destination
Router
Router
Router
Router
Router

25
Figure 12 illustrates a switched network. The communicating devices are labeled A,
B, C, D, and the switches I, II, III, IV. Each switch is connected to multiple links and
is used to complete the connections between the communicating peers. As soon as
the switches are set, they are static for one specific transmission process and can
then be reconfigured. Figure 13 shows two principal switching methods available.
Figure 12. Switched
network
A
I
II
IV
III
B
C
D

26
Circuit switching was designed primarily for voice communication. In a telephone
conversation, for example, once a circuit is established it remains connected for
the duration of the session. Circuit switching is not suitable for data or other
non-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 a packet switched network, data is transmitted in discrete units of potentially
variable 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 packets
are sent over the network hop-by-hop and routed through the network according to
the information in the packet header with the address information. With Message
switching, a network node receives a message, stores it until the appropriate route
is free, then sends it.
Figure 13. Network
switching methods Switching methods
Circuit switching Packet switching
Mainly voice traﬃc Mainly data traﬃc

27
From the Network layer, the IP packets need to be delivered to underlying layers.
The actual transmission below the Transport layer is called packet over SONET/
SDH (PoS).This transmission canbeachievedviaalternativeroutes,twoofwhichare
illustratedinFigure14.
The route (black line) described in this booklet is recommended by the Internet
Engineering Task Force (IETF) and is illustrated in Figure 15.
Packet over
SONET/SDH (PoS)
Figure 14. Alternative routes for transmitting
IP packets to the fiber
PPP
HDLC
SDH/SONET
Fiber
ATM
IP

28
TheIPpacketsareencapsulatedinaPoint-to-PointProtocolwhichinturnismapped
intoaHDLC-likeframe.ThisframeisthenmappedintotheSONET/SDHframe.
The Point-to-Point Protocol (PPP) provides a standard method for transporting
multi-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 for
use over these lines. PPP is designed to transport packets between two peers across
a simple link.
Figure 15. Mapping of IP packets into
SONET/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
16/32
OH Payload

29
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 wide
variety of hosts, bridges, and routers. The encapsulation of PPP into HDLC-like
frames allows for the multiplexing of different network-layer protocols, such as IP,
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 the data
link connection
• A family of Network Control Protocols (NCPs) for establishing and configuring
different network layer protocols

30
PPP Encapsulation and
PPP Emulation
Figure 16. PPP encapsulation
according to RFC 1661
PPP Encapsulation – To allow multi-protocol datagrams to be transmitted
across a link, a method must be used to enable unambiguous decisions to be made
between the various protocols. The PPP encapsulation of the IP packets is illustrated
in Figure 16.
The fields are transmitted from left to right with these names and functions:
ProtocolField — Consists of 1 or 2 octets, with values identifying the encapsulated
datagram.
DataField — This field is zero or more octets long and it contains the datagram for
the 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 if
an IP datagram with a larger payload were transported it would be fragmented into
several packets to fit the size of the data field.
PaddingField — At the beginning of the transmission this field may be padded
with an arbitrary number of octets (up to 1500 octets). It is the responsibility of the
protocol to distinguish padding from real information.
Protocol 8/16 bits Payload Padding

31
PPP Emulation — The PPP Emulation describes:
• Link Control Protocol
• Network Control Protocol
The LCP is responsible for correctly establishing, configuring, and testing the Point-
to-Point Protocol. Before IP datagrams can be transported across a PPP link, each of
the 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 of
LCP procedure
C021 (LCP)
Authenticate
Establish Terminate
Dead Start
NCPNetwork
SONET/SDH
Flag FF03 Protocol Payload FCS FlagHDLC/PPP
OH Payload

32
Step1:LinkDead— Each PPP connection starts and ends in this state. In this
state there is either no connection to the modem or the connection has been inter-
rupted. When an external event (control signal or network administrator) indicates
that the Physical layer is ready to be used, PPP proceeds to the establishment phase.
Step2:LinkEstablishment — Before data from an upper layer (e.g., IP) can be
transported across a connection, the link is prepared via configuration packets. This
exchange is completed, and the Open state achieved after a “Configure” packet has
been 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.
Step3:Authentication — This is an optional step, allowing the PPP peers to
identify each other via authentication protocols. These are called Password
Authentication Protocol (PAP) and Challenge Handshake Authentication
Protocol (CHAP).
The Password Authentication Protocol sends a password across the link, to
negotiate the circumstances for operation.

33
The Challenge Handshake Authentication Protocol ensures reliable and secure
authentication because the authenticator and authenticatee share a common
password. The authenticator sends the connected peer a challenge in the form of
a random number. The authenticatee uses this random number to derive a secret
code. This code is then transmitted to the authenticator and if the results match, the
next connection stage can proceed.
Step 4: Network Layer Protocol Configuration – This is necessary to configure
the Network Control Protocols (NCP) used on this connection. Each network layer
protocol (e.g., IP, Appletalk, etc.) must be separately configured by the appropriate
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 network-
layer protocol packets. Any network-layer protocol packets received prior to
reaching the corresponding Opened state are discarded. During this phase, link
traffic consists of any possible combination of LCP, NCP, and network-layer protocol
packets.

34
Step5:LinkTermination — The LCP makes it possible to close a connection at
any 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 and
the data connection tested for transmission quality. The Link Control Protocol
information is sent in the form of PPP datagrams, which fall into these three
major 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 different
protocols to run in the various network layers. Figure 18 illustrates and describes an
example of one of these protocols, IPCP.
Network Control Protocol (NCP)

35
Thisprotocolenablesactivation,configuration,anddeactivationoftheIPprotocol
modulesonbothsidesofthepoint-to-pointconnection.LiketheLCP,thesefunctions
areachievedbyexchangingspecialdatapackets;forIPCP,thispacketishex8021
(protocolidentifier).TheexchangeofIPCPpacketsstartsaftercompletingstep4of
theLCPprotocols.TheNCPthenrunsthroughstepsequivalenttothoseoftheLCP
procedureoncetheLCPprotocolisinthenetworkstate(seeFigure18).
Figure 18. Illustration of a common
NCP procedure
8021
Authenticate Network
Establish LCPDead
SONET/SDH
Flag FF03 Protocol Payload FCS FlagHDLC/PPP
OH Payload
Start

36
High-Level Data Link Control
(HDLC)
Figure 19. Format of HDLC-like frame
according to RFC 1662
When the LCP and the NCP protocols are fulfilled the data can be transmitted across
the 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 in
a HDLC-like frame which is then mapped into the SONET frame. The format of this
HDLC frame is illustrated in Figure 19.
FlagSequence — Each frame begins and ends with a flag sequence, which is the
binary sequence 01111110 (hex 0x7e). All implementations check for this frame
synchronization flag. Only one flag sequence is required between two frames. Two
consecutive flag sequences constitute an empty frame which is then discarded.
AddressField — The address field is a single octet containing the binary sequence
11111111 (hex 0xff). Individual station addresses are not assigned.
Flag Address Control Protocol Information FCS Flag

37
ControlField — The control field contains the binary sequence 00000011
(hex 0x03). Frames with unrecognized control field values are discarded.
ProtocolField — The protocol field is one or two octets, with a value identifying
the datagram encapsulated within the packet’s information field.
Table 6 shows the identifiers for the most frequently used protocols.
Hex value Protocol used
0021 IP
C021 LCP
8021 NCP (IPCP)
Information — The information field is zero or more octets and contains the data-
gram for the protocol specified in the protocol field. The Information Field, including
padding 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 of
octets up to the MRU.
Table 6. Identifiers used in the protocol
field in the HDLC frame

38
FrameCheckSequenceField—Theframechecksequence(FCS)defaultsto16bits
forOC-3/STM-1althoughotherspeedsuse32bitsaswell.ItsuseisdescribedinPPP
LCPExtensionsofRFC2615.
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. It does not
include 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 locating
the closing flag sequence and removing the frame check sequence field. The HDLC
process and related recommendations areillustrated in Figure 21.
Figure 20. Fields of the HDLC-like frame
used to perform the FCS
Figure 21. How an IP packet is transmitted
to and received by the SONET/SDH frame
SONET/SDH
Framing
De-Mapping,
De-Scrambling
Byte
Stuﬃng
FCS
GenerationPPP
SONET/SDH
Framing
Mapping,
De-Scrambling
Byte
Stuﬃng
FCS
GenerationPPP
Transmit flow
RFC1661 RFC1662 RFC2615 G.707
GR.253
Receive flow
Flag Address Control Protocol Information FCS Flag

39
Bytestuffing/destuffing— The PPP protocol must not place any restrictions on
the use of certain bit patterns in the network layer packet and must be transparent
to any type of data. Because the PPP protocol uses specific patterns, such as the flag
field 0x7e which indicates the beginning and end of a frame, a method is required
to avoid restrictions. This is achieved through byte stuffing where the PPP defines
a special control escape byte, 0x7d. The byte-stuffing procedure also acts for the
control field and the control escape byte.
The process of byte stuffing is illustrated in Figure 22 where the Flag 7E is replaced
by 7D,5E.
Figure 22. Illustration of the
byte-stuffing procedure 03 Flag 7E 59 8A
03 7D 5E 59 8A
before
after

40
If the Control Flag 7D is within the payload, it is replaced by 7D,5D.
Scrambling/Descramblingprocedure — Described in RFC 2615, a data scrambler
with the 1+x43 polynomial is used in this procedure, as shown in Table 7. While the
HDLC FCS is calculated, the scrambler operates continuously through the bytes of
the payload bypassing SONET path overhead bytes and any fixed information. This
type of scrambling is performed during insertion into the SONET/SDH payload.
The Path signal label C2, as Table 7 shows, is used so that the SONET/SDH can
recognize the payload content.
Value signal label C2 Scrambler state
0x16 PPP with 1+x43 scrambling
0xCF PPP with scrambler off
Table 7. Path signal label
C2 identifier

41
Because the frames can be of variable length they are allowed to cross the SONET/
SDH boundaries. The HDLC frames are mapped into the SONET/SDH frame dynami-
cally meaning that when there is no traffic, the SONET/SDH frame is filled with idle
frames 7E, see Figure 23.
Figure 23. Mapping of HDLC/PPP/IP packets
into the SONET/SDH payload
ing
SDH
Pointer
SDH
7E
7E
7E 7
7
H
7
7E
7E
7E
7E
7E
7E
7E7E
7E
7E
7E
7E
7E
7E
7E
7E
7E
7E 7E 7E
7E
7E
7E
7E 7E
7E 7E
7E 7E
7E
7E
7E
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCframing
HDLCfram
7E 7E
7E
7
7
7E
7E
7E 7E
7E 7E 7E 7E
7
7E
7E
7E
POH
The PPP frames are inserted into the SONET/SDH payload sequentially row by row
and sit in the payload envelope as octet streams aligned to octet boundaries.
Mapping into the
SONET/SDH frame

42
With the increase in IP traffic transported across SDH/SONET/DWDM networks, it
is necessary to measure the quality parameters with genuine IP traffic. Thus, the
payload is filled with HDLC/PPP/IP packets instead of a traditional pseudorandom
bit sequence (PRBS). This corresponds to a more realistic representation of the real
traffic to be transmitted on these networks.
The user is provided with information on how many packets were lost in a specified
period (for example, 24 hours), instead of an error rate of 10-14 for instance. This is
more informative than the traditional error rate when sending packets.
Using packets instead of PRBS to fill the payload provides a more realistic traffic
profile. Due to the increased transport data and IP traffic in our networks, the
payload being filled with IP packets will become more widely accepted in the future.
The following applications are suitable for measuring the quality parameters of
individual network elements (NE) as well as entire SDH/SONET/DWDM networks
during installation.
PoS Measurement
Tasks

43
Frameerrors — This error message gives information on the number of HDLC
frames lost over a predefined period of time. The customers benefit from receiving a
performance measurement based on packet rather than byte parameters.
Framerate— This is the rate of frames which are sent over the link and are
calculated from the HDLC frame size and the bandwidth.
Transferdelay — The transfer delay is the amount of time it takes for IP packets
to travel a set path through the network.
HDLCbandwidth— This corresponds with the user set bandwidth of the link. The
allowable bandwidth depends on the interface used and the container size chosen.
HDLCutilization— This is a percentage measure of how much of the link is actu-
ally in use. These parameters are usually measured by the following applications:
• Transparency testing
• Connectivity testing
• Performance testing

44
This measurement is mainly performed by carriers and fiber installers. It is needed
to qualify the line for data transport, thereby guaranteeing that the transmis-
sion between two points (A and B) does not exhibit any errors. A typical setup is
illustrated in Figure 24.
It is also possible to send and receive using the same instrument (see Figure 24,
dotted line) so that a specific line segment can be tested for transparency.
Check for PoS Transparency
Figure 24. Typical setup for a
transparency check
Wavelength
router
JDSU
PoS tester
DWDM network
l routing
JDSU
PoS tester

45
To guarantee the proper setup of the transmission line, the measuring equipment
sends HCLC/PPP/IP frames and receives them again when the transmitter and the
receiver are looped back to each other.
The parameters, which can change, are the frame size (in bytes) and the bandwidth
of the transmission. It is also possible to introduce errors and check the resulting
degradations on the receiver. The result of this measurement provides the follow-
ing parameters: frame error, frame rate, transfer delay, link bandwidth, and link
utilization.
Usually, this test is performed when a new NE or a new user is connected to the
network. It checks whether the NE or user is properly connected to the network and
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 measuring
the round-trip delay of the ping. The ping parameter provides definite information
about the NE’s connection state. The time delay indicates the health status of the
line to and from the NE. The customer benefits by receiving information about the
new NE’s connection.
Verify IP Connectivity of New
Network Elements

46
This is a test of particular NEs and the entire network under load and checks the
interfaces 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
ping
request
ADM with
Integrated
IP fabric
Metro area
OC-192
ping response
Router
CO/POP
Core backbone
Long haul
DWDM network
l routing
ADMADM
JDSU
PoS tester

47
This test is performed when the customer is connected to the network or when
new connections between NEs are installed. The measuringinstrument sends a
signal and checks if the NE is connected and can pass the signals through to the
next network element. To perform the PoS performance test, the equipment must
be capable of performing the entire PPP emulation. This measurement delivers the
same parameters as the transparency check.
Figure 26. Measurement arrangement
to check performance of PoS NEs
PPP
emulation
Router/
intelligent
NE
DWDM network
l routing
PPP
emulation
Router/
intelligent
NE
JDSU
PoS tester
JDSU
PoS tester

48
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 possible
applications for PoS systems

49
Future networks will need to cope with the ever-increasing bandwidth
requirements mentioned in the introduction of this booklet.
TDM transmission rates are increasing to 40 G while simultaneously the number of
channels in DWDM systems are increasing to 128 and more. Total capacity rates of
approximately 320 G, 1 T, and higher are therefore quite possible. This challenge
will be met by some of the technologies described in the following pages.
When discussing possible future networks the expression converging networks
is often used.
Outlook

50
Converging networks lead to a decrease in the number of network elements and
potentially less trouble for network operators. One platform used in this process is
the so called Multi-Service Provision Platform. In addition, techniques like Multi-
Protocol Label Switching and Multi-Protocol l Switching will help to establish this
trend. Figure 27 illustrates the possible convergence of functions with various layers.
Figure 27. Possible convergence scenario in
the telecommunication world
Functions
will merge,
various
migration
scenarios
IP is the
Universal
Convergence
Layer
The existing
network:
reliable, but
unaﬀordable
DWDM is main
long distance +
Metrotransmission
technology
Multi-Service
transport
Fiber
Optical
networking
IP, Service
DWDM
SONET
ATM
Fiber

51
Since the majority of new telecommunication services are data-oriented, the
transmission on these networks should be “data optimized,” which can be achieved
with Multi-Service Provisioning Platforms (MSPP). These MSPPs enable aggregation
and switching of data packets by one network element.
MSPPs can switch voice and video as well as different types of data traffic. These
three 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 allowing
products to switch and route data traffic
Combining these features into one instrument enables service providers to simplify
their networks. Instead of installing a DWDM multiplexer, ADM, and an IP router,
just one device can be used. The number of devices and potential problems are
reduced as a result.
Multi-Service Provisioning
Platform (MSPP)

52
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 to
apply simple labels (or identifiers) to packets. These labels allow routers to switch
packets according to their label with a minimal lookup overhead.
MPLS integrates the performance and traffic management capabilities of Layer 2
with 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 incoming
packet need be examined in order for it to be sent on to the next router across
the network.
Multi-Protocol Label Switching
and Multi-Protocol l Switching
(MPLS and MPlS)

53
Advantages of this are that only one table lookup list from a fixed length label is
required and switching and routing functions can be combined. As with a router,
an optical cross-connect (OXC), can intelligently route a wavelength through an
OXC. The so called Multi-Protocol l Switching signaling allows an OXC to convey a
signal to the next OXC. These devices exhibit similar advantages to the MPLS, by
reducing the number of elements and potential problems in the network.

54
With the increasing number of Internet users, the pool of available addresses
defined by IPv4 is decreasing fast. IP version 6 (IPv6) is addressing this and several
other issues such as:
Quality of Service (QoS). The header is simpler and more flexible than for IPv4 due to
the optional extension header. IPv6 is 128 bits long and consists of 16 bytes (octets).
The protocol specifies hexadecimal colon notation. Whereby 128 bits are divided
into eight sections, each of which are two bytes in length. An example of a principal
IPv6 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 followed
by the payload. The payload consists of two parts: an optional extension header and
data from an upper layer (see Figure 29).
Appendix
IP version 6 (IPv6)
Figure 28. Possible IP address with IPv6

55
Figure 29. IP header for IPv6
Changes in the way IP header options are encoded enable more efficient forward-
ing, less stringent limits on the length of options, and greater flexibility in introduc-
ing new options.
A new capability has been added to facilitate the labeling of packets belonging to
a particular traffic flow for which the sender must request special handling. The
simpler header offers faster processing by routers.
Base header Payload
Optional extension
header
Data from upper layer

56
The following definitions are taken from RFC recommendations.
Frame — The unit of transmission at the data link layer. A frame may include a
header and/or a trailer, along with some number of units of data.
Packets — The basic unit of encapsulation, which is passed across the interface
between the network layer and the data link layer. A packet is usually mapped to a
frame; the exceptions are when data link layer fragmentation is being performed, or
when 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 further
processing. The implementation should provide the capability of logging the error,
including the contents of the silently discarded packet, and should record the event
in a statistics counter.
Terminology

57
A
ADM add-drop multiplexer
ARPA Advanced Research Project Agency
ATM asynchronous transfer mode
C
CHAP Challenge-Handshake Authentication Protocol
CLEC Competitive Local Exchange Carrier
D
DCE data communications equipment
DNS Domain Name System
DTE data terminating equipment
DWDM dense wavelength division multiplexing
F
FCS frame check sequence
FTP File Transfer Protocol
Abbreviations

58
H
HDLC high-level data link control
HTTP Hyper Text Transfer Protocol
I
ICMP Internet Control Message Protocol
IP Internetwork Protocol
L
LCP Link Control Protocol
LQM Link Quality Monitoring
M
MPLS Multi-Protocol Label Switching
MPlS Multi-Protocol l Switching
MSPP Multi-Service Provisioning Platform
N
NCP Network Control Protocol
NE network element

59
O
OSI Open System Interconnection
OXC optical cross-connect
P
PAP Password Authentication Protocol
PDH plesiochronous digital hierarchy
PoS packet over SONET/SDH
PPP Point-to-Point Protocol
R
RFC ‘Request for Comment’ documents, used to develop standards,
procedures and specifications for TCP/IP, under the control of IETF
S
SDH synchronous digital hierarchy
SMTP simple mail transfer protocol
SNMP simple network management protocol
SONET synchronous optical network

60
T
TCP Transfer Control Protocol
TDM Time Division Multiplexing
TE traffic engineering
ToS type of service
U
UDP User Datagram Protocol
W
WDM wavelength division multiplexing

61
RFC 1662 PPP in HDLC-like Framing
RFC 2615 PPP over SONET/SDH
RFC 1661 Point-to-Point Protocol (PPP)
RFC 950 Internet Standard Subnetting Procedure
RFC 821 Simple Mail Transfer Protocol
RFC 959 File Transfer Protocol (FTP)
RFC 854 Telnet Protocol Specification
RFC 1945 Hypertext Transfer Protocol – HTTP/1.0
RFC 1157 Simple Network Management Protocol (SNMP)
RFC 2929 Domain Name System (DNS) IANA Considerations
RFC 1332 PPP Internet Protocol Control Protocol (IPCP)
RFC 1333 PPP Link Quality Monitoring
RFC 2153 PPP Vendor Extensions
RFC 791 Internet Protocol
RFC 792 Internet Control Message Protocol
RFC 793 Transmission Control Protocol
G.707 Network Node Interface for the synchronous digital hierarchy (SDH)
GR.253 SONET Transport system: Common Generic Criteria
References

63
Product specifications and descriptions in this document subject to change without notice.
© 2013 JDS Uniphase Corporation

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