Packet over SONET

I will try to make my posts according to the CCIE Service Provider Written Exam Checklist v3.0.  This post cover the topics in paragraph 1.1. It took me about 10 hours to check all the references.

Packet over SONET

This post includes following topics:

1. Cisco HDLC(cHDLC) Encapsulation
2. PPP Encapsulation
3. Frame-Relay Encapsulation
4. Maximum Transmission Unit (MTU)
5. Cyclic Redundancy Check (CRC)
6. Keepalive Timer
7. Frame-Relay DLCI on point-to-point sub-interface
8. SONET Controller
9. POS Channel
10. Channelized SONET
11. SONET APS

References:

1. A Brief Overview of SONET Technology
2. Cisco Tech Note: Differences between SDH and SONET
3. Configuring POS Interfaces on Cisco IOS XR 3.9 Software (CRS-1)
4. Configuring POS Interfaces on Cisco IOS XR 3.9 Software (XR12K)
5. Packet-over-SONET Interface Commands on Cisco IOS XR 3.9 Software (XR12000)
6. Configuring Serial Interfaces on Cisco IOS 12.2 SR Software
7. Understanding SONET/ SDH

The default framing type for POS interfaces on Cisco routers is sonet:

Router(config-if)#POs framing [sdh|sonet]

On the Cisco CRS-1 Router, a single POS interface carries data using PPP or Cisco HDLC encapsulation. Frame Relay is not supported on the Cisco CRS-1 Router.

On the Cisco XR 12000 Series Router, a single POS interface carries data using PPP, Cisco HDLC, or Frame Relay encapsulation.

Cisco HDLC (cHDLC) encapsulation

Wikipedia:

Cisco HDLC frames make use of an alternative framing structure to the standard ISO HDLC. One of the primary reasons for the creation of cHDLC was to address the HDLC protocol's inability to provide multi-protocol support. Thus, cHDLC frames contain a field for identifying the network protocol being encapsulated.

Original cHDLC description from Cisco (1990).

Frame structure:

Address

0x0F - Unicast Packets
0x8F - Broadcast Packets

Control

0x00 - Always set to zero

Protocol Codes

0x0200 PUP
0x0600 XNS
0x0800 IP
0x0800 IPv6
0x0804 Chaos
0x4242 DSAP/SSAP for IEEE bridge spanning prot.
0x6003 DECnet phase IV
0x6558 Bridged Ethernet/802.3 packet
0x8019 Apollo domain
0x8035 cisco SLARP (not real reverse ARP!)
0x8038 DEC bridge spanning tree protocol
0x809b Apple EtherTalk
0x80f3 Appletalk ARP
0x8137 Novell IPX
0xFEFE ISO CLNP/ISO ES-IS DSAP/SSAP

Information

Variable length, 0 or more bits, in multiples of 8

FCS

Frame Check Sequence - CRC

Flag

Special bits sequence, indicating beginning or end of the frame 

The cHDLC encapsulation is the default encapsulation type on the Serial and POS links.

IOS Example:

Router(config)# interface serial 1
Router(config-if)# encapsulation hdlc 

IOS XR Example:

RP/0/RP0/CPU0:router(config)# interface POS 0/3/0/1
RP/0/RP0/CPU0:router(config-if)# encapsulation hdlc

PPP Encapsulation

References:

1. Configuring PPP on Cisco IOS XR 3.9 Software (XR12K)
2. Wikipedia: Point-to-Point Protocol
3. Cisco DocWiki: PPP
4. RFC1661: The Point-to-Point Protocol (PPP)
5. RFC2615: PPP over SONET/SDH
6. RFC1662: PPP in HDLC-like Framing

IOS Example:

Router(config)# interface serial 1
Router(config-if)# encapsulation ppp 

IOS XR Example:

RP/0/RP0/CPU0:router(config)# interface POS 0/3/0/1
RP/0/RP0/CPU0:router(config-if)# encapsulation ppp

Network Control Protocols 

PPP provides the following Network Control Protocols (NCPs) for negotiating the properties of data protocols that run on the link:

• IP Control Protocol (IPCP)—negotiates IP properties
• Multiprotocol Label Switching control processor (MPLSCP)—negotiates MPLS properties
• Cisco Discovery Protocol control processor (CDPCP)—negotiates CDP properties
• IPv6CP—negotiates IP Version 6 (IPv6) properties
• Open Systems Interconnection control processor (OSICP)—negotiates OSI properties

Authentication

PPP supports the following authentication protocols, which require a remote device to prove its identity before allowing data traffic to flow over a connection:

• Challenge Handshake Authentication Protocol (CHAP)—CHAP authentication sends a challenge message to the remote device. The remote device encrypts the challenge value with a shared secret and returns the encrypted value and its name to the local router in a response message. The local router attempts to match the remote device's name with an associated secret stored in the local username or remote security server database; it uses the stored secret to encrypt the original challenge and verify that the encrypted values match.
• Microsoft Challenge Handshake Authentication Protocol (MS-CHAP)—MS-CHAP is the Microsoft version of CHAP. Like the standard version of CHAP, MS-CHAP is used for PPP authentication; in this case, authentication occurs between a personal computer using Microsoft Windows NT or Microsoft Windows 95 and a Cisco router or access server acting as a network access server.
• Password Authentication Protocol (PAP)—PAP authentication requires the remote device to send a name and a password, which are checked against a matching entry in the local username database or in the remote security server database.

Use the ppp authentication command in interface configuration mode to enable CHAP, MS-CHAP, and PAP on a POS interface.

Frame-Relay Encapsulation

References:

1. Frame Relay Configuration on Cisco IOS XR 3.9 Software (XR12K).
2. Wikipedia: Frame Relay
3. Cisco DocWiki: Frame Relay

Frame Relay encapsulation is supported on the Cisco XR 12000 Series Router only.

To configure Frame Relay encapsulation on POS interfaces, use the encapsulation frame-relay command.

Frame Relay interfaces support two types of encapsulated frames:

• Cisco (this is the default)
• IETF

Use the encap command in PVC configuration mode to configure Cisco or IETF encapsulation on a PVC. If the encapsulation type is not configured explicitly for a PVC, then that PVC inherits the encapsulation type from the main POS interface.

MTU

The default MTU size is set to 4474 bytes.

The POS MTU range is 64-9216.

CRC

References: 

1. CRC-16 and CRC-32 on Packet Over SONET Interfaces

The default CRC is 32.

Keepalive Timer

Use the keepalive command in interface configuration mode to set the frequency at which LCP sends ECHOREQ packets to its peer. To restore the system to the default keepalive interval of 10 seconds, use the keepalive command with no argument. To disable keepalives, use the keepalive disable command. For both PPP and Cisco HDLC, a keepalive of 0 disables keepalives and is reported in the show running-config command output as keepalive disable.

Frame Relay DLCI on point-to-point subinterface

Reference:

1. IOS: Using Frame Relay Point-to-Point Subinterfaces

On point-to-point subinterfaces, the destination is identified and configured with the frame-relay interface-dlci command beginning in interface configuration mode. When configured on a point-to-point subinterface, the command associates the selected point-to-point subinterface with a DLCI. 

IOS Example:

R4(config)#interface s1/2.403 point-to-point
R4(config-subif)#frame-relay interface-dlci ?
<16-1007> Define a switched or locally terminated DLCI
R4(config-subif)#frame-relay interface-dlci 403 ?
cisco Use CISCO Encapsulation
ietf Use RFC1490/RFC2427 Encapsulation
ppp Use RFC1973 Encapsulation to support PPP over FR
protocol Optional protocol information for remote end<cr>
R4#show frame-relay map
Serial1/2.403 (up): point-to-point dlci, dlci 403(0xC9,0x3090), broadcast status defined, active

R4#

IOS XR Example:

RP/0/0/CPU0:XR12K# configure
RP/0/0/CPU0:XR12K(config)# interface pos 0/3/0/1.20
RP/0/0/CPU0:XR12K(config-subif)#ipv4 address 10.46.8.5/24
RP/0/0/CPU0:XR12K(config-subif)# pvc 20
RP/0/0/CPU0:XR12K(config-fr-vc)# commit

 

SONET Controller

Reference:

1. SONET Controller Commands on Cisco IOS XR 3.9 Software (XR12K)
2. Configuring Clear Channel SONET Controllers on Cisco IOS XR 3.9 Software (XR12K)

IOS XR Example:

configure
controller sonet 0/1/0/0
ais-shut
clock source internal
framing sonet
loopback internal
Loopback is a traffic-effecting operation
overhead s1s0 1
path ais-shut
path delay trigger 0
path overhead j1 line l1
path report pais
path scrambling disable
path threshold b3-tca 6
path uneq-shut
report pais
threshold b2-tca 4
commit

POS channel

Reference:

1. Link Bundling on Cisco 12000 Series Internet Routers

EtherChannel or POS Channel—Cisco proprietary technology that allows the user to configure links to join a bundle, but has no mechanisms to check whether the links in a bundle are compatible. (EtherChannel applies to Ethernet interfaces, and POS Channel applies to POS interfaces.)

IOS XR Example:

RP/0/0/CPU0:Router# config
RP/0/0/CPU0:Router(config)# interface Bundle-POS 5
RP/0/0/CPU0:Router(config-if)# ipv4 address 1.2.3.4/24
RP/0/0/CPU0:Router(config-if)# bundle minimum-active bandwidth 620000
RP/0/0/CPU0:Router(config-if)# bundle minimum-active bandwidth 620000
RP/0/0/CPU0:Router(config-if)# exit
RP/0/0/CPU0:Router(config)# interface POS 0/0/1/0
RP/0/0/CPU0:Router(config-if)# bundle id 5
RP/0/0/CPU0:Router(config-if)# no shutdown
RP/0/0/CPU0:Router(config-if)# exit
RP/0/0/CPU0:Router(config)# interface POS 0/0/1/1
RP/0/0/CPU0:Router(config-if)# bundle id 5
RP/0/0/CPU0:Router(config-if)# no shutdown
RP/0/0/CPU0:Router(config-if)# exit

Channelized SONET

Reference:

1. Configuring Channelized SONET on Cisco IOS XR 3.9 Software (XR12K)

SONET APS

References:

1. SONET Controller Commands on Cisco IOS XR 3.9 Software (XR12K)
2. Configuring Clear Channel SONET Controllers on Cisco IOS XR 3.9 Software (XR12K)
3. A Brief Overview of Packet Over SONET APS
4. IOS 11.1: Automatic Protection Switching of Packet-over-SONET Circuits
5. Single-router APS for the Cisco 12000 Series Router

IOS XR Example:

aps group 1
channel 0 local SONET 0/0/0/1
channel 1 local SONET 0/0/0/2
signalling sonet
commit
show aps
show aps group 3